Anesthesia 麻醉
Anesthesia, or anaesthesia, has traditionally meant the condition of having sensation (including the feeling
of pain) blocked. This allows patients to undergo surgery and other procedures without the distress and pain
they would otherwise experience. The word was coined by Oliver Wendell Holmes, Sr. in 1846. Another
definition is a "reversible lack of awareness", whether this is a total lack of awareness (e.g. a general
anaesthestic) or a lack of awareness of a part of a the body such as a spinal anaesthetic or another nerve
block would cause. Anesthesia differs from analgesia in blocking all sensation, not only pain.
Today, the term general anesthesia in its most general form can include:
 Analgesia: blocking the conscious sensation of pain;
 Hypnosis: produces unconsciousness without analgesia;
 Amnesia: preventing memory formation;
 Relaxation: preventing unwanted movement or muscle tone;
 Obtundation of reflexes, preventing exaggerated autonomic reflexes.
Patients undergoing surgery usually undergo preoperative evaluation. It includes gathering history of
previous anesthetics, and any other medical problems, physical examination, ordering required blood work
and consultations prior to surgery.
There are several forms of anesthesia. The following forms refer to states achieved by anesthetics working
on the brain:
 General anesthesia: "Drug-induced loss of consciousness during which patients are not arousable,
even by painful stimulation." Patients undergoing general anesthesia can often neither maintain their
own airway nor breathe on their own. While usually administered with inhalational agents, general
anesthesia can be achieved with intravenous agents, such as propofol.
 Deep sedation/analgesia: "Drug-induced depression of consciousness during which patients cannot
be easily aroused but respond purposefully following repeated or painful stimulation." Patients may
sometimes be unable to maintain their airway and breathe on their own.
 Moderate sedation/analgesia or conscious sedation: "Drug-induced depression of consciousness
during which patients respond purposefully to verbal commands, either alone or accompanied by
light tactile stimulation." In this state, patients can breathe on their own and need no help
maintaining an airway.
 Minimal sedation or anxiolysis]: "Drug-induced state during which patients respond normally to
verbal commands." Though concentration, memory, and coordination may be impaired, patients
need no help breathing or maintaining an airway.
The level of anesthesia achieved ranges on a continuum of depth of consciousness from minimal sedation to
general anesthesia. The depth of consciousness of a patient may change from one minute to the next.
The following refer to the states achieved by anesthetics working outside of the brain:
 Regional anesthesia: Loss of pain sensation, with varying degrees of muscle relaxation, in certain
regions of the body. Administered with local anesthesia to peripheral nerve bundles, such as the
brachial plexus in the neck. Examples include the interscalene block for shoulder surgery, axillary
block for wrist surgery, and femoral nerve block for leg surgery. While traditionally administered as
a single injection, newer techniques involve placement of indwelling catheters for continuous or
intermittent administration of local anesthetics.
o Spinal anesthesia: also known as subarachnoid block. Refers to a Regional block resulting
from a small volume of local anesthetics being injected into the spinal canal. The spinal
canal is covered by the dura mater, through which the spinal needle enters. The spinal canal

contains cerebrospinal fluid and the spinal cord. The sub arachnoid block is usually injected
between the 4th and 5th lumbar vertebrae, because the spinal cord usually stops at the 1st
lumbar vertebra, while the canal continues to the sacral vertebrae. It results in a loss of pain
sensation and muscle strength, usually up to the level of the chest (nipple line or 4th
thoracic dermatome).
o Epidural anesthesia: Regional block resulting from an injection of a large volume of local
anesthetic into the epidural space. The epidural space is a potential space that lies
underneath the ligamenta flava, and outside the dura mater (outside layer of the spinal
canal). This is basically an injection around the spinal canal.
Local anesthesia is similar to regional anesthesia, but exerts its effect on a smaller area of the body.
Anesthetic agents
Local anesthetics
Main article: Local anesthetic
 procaine
 amethocaine
 cocaine
 lidocaine (also known as Lignocaine)
 prilocaine
 bupivacaine
 levobupivacaine
 ropivacaine
 dibucaine
Local anesthetics are agents which prevent transmission of nerve impulses without causing unconsciousness.
They act by binding to fast sodium channels from within (in an open state). Local anesthetics can be either
ester or amide based.
Ester local anesthetics (e.g., procaine, amethocaine, cocaine) are generally unstable in solution and
fast-acting, and allergic reactions are common.
Amide local anesthetics (e.g., lidocaine, prilocaine, bupivicaine, levobupivacaine, ropivacaine and dibucaine)
are generally heat-stable, with a long shelf life (around 2 years). They have a slower onset and longer
half-life than ester anaesthetics, and are usually racemic mixtures, with the exception of levobupivacaine
(which is S(-) -bupivacaine) and ropivacaine (S(-)-ropivacaine). These agents are generally used within
regional and epidural or spinal techniques, due to their longer duration of action, which provides adequate
analgesia for surgery, labor, and symptomatic relief.
Only preservative-free local anesthetic agents may be injected intrathecally.
Adverse effects of local anaesthesia
Adverse effects of local anesthesia are generally referred to as Local Anesthetic Toxicity.
Effects may be localized or systemic.
Examples of systemic effects of local anesthesia:
Local anesthetic drugs are toxic to the heart (where they cause arrhythmia) and brain (where they may cause
unconsciousness and seizures). Arrhythmias may be resistant to defibrillation and other standard treatments,
and may lead to loss of heart function and death.
The first evidence of local anesthetic toxicity involves the nervous system, including agitation, confusion,
dizziness, blurred vision, tinnitus, a metallic taste in the mouth, and nausea that can quickly progress to
seizures and cardiovascular collapse.
Toxicity can occur with any local anesthetic as an individual reaction by that patient. Possible toxicity can be
tested with pre-operative procedures to avoid toxic reactions during surgery.
An example of localized effect of local anesthesia:
Direct infiltration of local anesthetic into skeletal muscle will cause temporary paralysis of the muscle.
Current inhaled general anesthetic agents
Main article: General anaesthesia
 Desflurane
 Enflurane
 Halothane
 Isoflurane
 Nitrous oxide
 Sevoflurane
 Xenon (rarely used)
Volatile agents are specially formulated organic liquids that evaporate readily into vapors, and are given by
inhalation for induction and/or maintenance of general anesthesia. Nitrous oxide and xenon are gases at
room temperature rather than liquids, so they are not considered volatile agents. The ideal anesthetic vapor
or gas should be non-flammable, non-explosive, lipid-soluble, and should possess low blood gas solubility,
have no end organ (heart, liver, kidney) toxicity or side-effects, should not be metabolized, and should be
non-irritant when inhaled by patients.
No anesthetic agent currently in use meets all these requirements. The agents in widespread current use are
isoflurane, desflurane, sevoflurane, and nitrous oxide. Nitrous oxide is a common adjuvant gas, making it
one of the most long-lived drugs still in current use. Because of its low potency, it cannot produce anesthesia
on its own but is frequently combined with other agents. Halothane, an agent introduced in the 1950s, has
been almost completely replaced in modern anesthesia practice by newer agents because of its shortcomings.
Partly because of its side effects, enflurane never gained widespread popularity.
In theory, any inhaled anesthetic agent can be used for induction of general anesthesia. However, most of the
halogenated anesthetics are irritating to the airway, perhaps leading to coughing, laryngospasm and overall
difficult inductions. For this reason, the most frequently used agent for inhalational induction is sevoflurane.
All of the volatile agents can be used alone or in combination with other medications to maintain anesthesia
(nitrous oxide is not potent enough to be used as a sole agent).
Volatile agents are frequently compared in terms of potency, which is inversely proportional to the minimum
alveolar concentration. Potency is directly related to lipid solubility. This is known as the Meyer-Overton
hypothesis. However, certain pharmacokinetic properties of volatile agents have become another point of
comparison. Most important of those properties is known as the blood:gas partition coefficient. This concept
refers to the relative solubility of a given agent in blood. Those agents with a lower blood solubility (i.e., a
lower blood–gas partition coefficient; e.g., desflurane) give the anesthesia provider greater rapidity in
titrating the depth of anesthesia, and permit a more rapid emergence from the anesthetic state upon
discontinuing their administration. In fact, newer volatile agents (e.g., sevoflurane, desflurane) have been
popular not due to their potency (minimum alveolar concentration), but due to their versatility for a faster
emergence from anesthesia, thanks to their lower blood–gas partition coefficient.
Current intravenous anesthetic agents (non-opioid)
While there are many drugs that can be used intravenously to produce anesthesia or sedation, the most
common are:
 Barbiturates
o
Methohexital
o Thiopental (Previously known as Thiopentone in the UK)
 Benzodiazepines
o Diazepam
o Lorazepam
o Midazolam
 Etomidate
 Ketamine
 Propofol
The two barbiturates mentioned above, thiopental and methohexital, are ultra-short-acting, and are used to
induce and maintain anesthesia. However, though they produce unconsciousness, they provide no analgesia
(pain relief) and must be used with other agents. Benzodiazepines can be used for sedation before or after
surgery and can be used to induce and maintain general anesthesia. When benzodiazepines are used to
induce general anesthesia, midazolam is preferred. Benzodiazepines are also used for sedation during
procedures that do not require general anesthesia. Like barbiturates, benzodiazepines have no pain-relieving
properties. Propofol is one of the most commonly used intravenous drugs employed to induce and maintain
general anesthesia. It can also be used for sedation during procedures or in the ICU. Like the other agents
mentioned above, it renders patients unconscious without producing pain relief. Because of its favourable
physiological effects, "etomidate has been primarily used in sick patients".Ketamine is infrequently used in
anesthesia practice because of the unpleasant experiences which sometimes occur upon emergence from
anesthesia, which include "vivid dreaming, extracorporeal experiences, and illusions." However, like
etomidate it is frequently used in emergency settings and with sick patients because it produces fewer
adverse physiological effects. Unlike the intravenous anesthetic drugs previously mentioned, ketamine
produces profound pain relief, even in doses lower than those which induce general anesthesia. Also unlike
the other anesthetic agents in this section, patients who receive ketamine alone appear to be in a cataleptic
state, unlike other states of anesthesia that resemble normal sleep. Ketamine-anesthetized patients have
profound analgesia but keep their eyes open and maintain many reflexes.
Current intravenous opioid analgesic agents
While opioids can produce unconsciousness, they do so unreliably and with significant side effects. So,
while they are rarely used to induce anesthesia, they are frequently used along with other agents such as
intravenous non-opioid anesthetics or inhalational anesthetics. Furthermore, they are used to relieve pain of
patients before, during, or after surgery. The following opioids have short onset and duration of action and
are frequently used during general anesthesia:
 Alfentanil
 Fentanyl
 Remifentanil
 Sufentanil
The following agents have longer onset and duration of action and are frequently used for post-operative
pain relief:
 Buprenorphine
 Butorphanol
 Diamorphine,
 Hydromorphone
 Levorphanol
 Meperidine,

Methadone
 Morphine
 Nalbuphine
 Oxycodone,
 Oxymorphone
 Pentazocine
Current muscle relaxants
Muscle relaxants do not render patients unconscious or relieve pain. Instead, they are sometimes used after a
patient is rendered unconscious (induction of anesthesia) to facilitate intubation or surgery by paralyzing
skeletal muscle.
 Depolarizing muscle relaxants
o Succinylcholine
 Non-depolarizing muscle relaxants
o Short acting
 Mivacurium
 Rapacuronium
o Intermediate acting
 Atracurium
 Cisatracurium
 Rocuronium
 Vecuronium
o Long acting
 Alcuronium
 Doxacurium
 Gallamine
 Metocurine
 Pancuronium
 Pipecuronium
 d-Tubocurarine
Adverse effects of muscle relaxants
 Non Depolarising Muscle Relaxants i.e. Suxamethonium
o Hyperkalaemia - A small rise of 0.5mmol/l occurs normally, this is of little consequence
unless Potassium is already raised such as in Renal Failure
o Hyperkalaemia - Exaggerated potassium release in burn patients (occurs from 24 hours
after injury, lasting for up to 2 years), neuromuscular disease and paralyzed (quadraplegic,
paraplegic) patients. The mechanism is reported to be through upregulation of acetylcholine
receptors in those patient populations with increased efflux of potassium from inside
muscle cells. May cause life threatening arrhymias
o Muscle aches, commoner in young muscular patients who mobilise soon after surgery
o Bradycardia, especially if repeat doses are given
o Malignant hyperthermia, a potentially life threatening condition in susceptible patients
o Suxamethonium Apnoea, a rare genetic condition leading to prolonged duration of
neuromuscular blockade, this can range from 20 minutes to a number of hours. Not
dangerous as long as it is recognised and the patient remains intubated and sedated, there is
the potential for awareness if this does not occur.
o
Anaphylaxis
 Depolarising Muscle Relaxants
o Histamine release e.g. Atracurium & Mivacurium
o Anaphylaxis
Another potentially disturbing complication where neuromuscular blockade is employed is 'anesthesia
awareness'. In this situation, patients paralyzed may awaken during their anesthesia, due to an inappropriate
decrease in the level of drugs providing sedation and/or pain relief. If this fact is missed by the anaesthesia
provider, the patient may be aware of his surroundings, but be incapable of moving or communicating that
fact. Neurological monitors are becoming increasingly available which may help decrease the incidence of
awareness. Most of these monitors use proprietary algorithms monitoring brain activity via evoked potentials.
Despite the widespread marketing of these devices many case reports exist in which awareness under
anesthesia has occurred despite apparently adequate anesthesia as measured by the neurologic monitor.]
Current intravenous reversal agents
 Flumazenil, reverses the effects of benzodiazepines
 Naloxone, reverses the effects of opioids
 Neostigmine, helps reverses the effects of non-depolarizing muscle relaxants
 Sugammadex, new agent that is designed to bind Rocuronium therefore terminating its action
Anesthetic equipment
Main article: Anaesthetic equipment
In modern anesthesia, a wide variety of medical equipment is desirable depending on the necessity for
portable field use, surgical operations or intensive care support. Anesthesia practitioners must possess a
comprehensive and intricate knowledge of the production and use of various medical gases, anaesthetic
agents and vapours, medical breathing circuits and the variety of anaesthetic machines (including
vaporizers, ventilators and pressure gauges) and their corresponding safety features, hazards and limitations
of each piece of equipment, for the safe, clinical competence and practical application for day to day
practice.
Anesthetic monitoring
Patients being treated under general anesthetics must be monitored continuously to ensure the patient's safety.
In the UK the Association of Anaesthetists (AAGBI) have set minimum monitoring guidelines for General
and Regional Anaesthesia. For minor surgery, this generally includes monitoring of heart rate (via ECG or
pulse oximetry), oxygen saturation (via pulse oximetry), non-invasive blood pressure, inspired and expired
gases (for oxygen, carbon dioxide, nitrous oxide, and volatile agents). For moderate to major surgery,
monitoring may also include temperature, urine output, invasive blood measurements (arterial blood pressure,
central venous pressure), pulmonary artery pressure and pulmonary artery occlusion pressure, cerebral
activity (via EEG analysis), neuromuscular function (via peripheral nerve stimulation monitoring), and
cardiac output. In addition, the operating room's environment must be monitored for temperature and
humidity and for buildup of exhaled inhalational anesthetics which might impair the health of operating
room personnel.
General anaesthesia
In modern medical practice, general anaesthesia (AmE: anesthesia) is a state of total unconsciousness
resulting from general anaesthetic drugs. A variety of drugs are given to the patient that have different effects
with the overall aim of ensuring unconsciousness, amnesia and analgesia. The anaesthetist (AmE:
anesthesiologist) selects the optimal technique for any given patient and procedure.
Overview
General anaesthesia is a complex procedure involving:
 Preanaesthetic assessment
 Administration of general anaesthetic drugs
 Cardiorespiratory monitoring
 Analgesia
 Airway management
 Fluid management
 Postoperative pain relief
Preanaesthetic evaluation
Prior to surgery, the anaesthetist interviews the patient to determine the best combination and drugs and
dosages and the degree of how much monitoring is required to ensure a safe and effective procedure.
Pertinent information is the patient's age, weight, medical history, current medications, previous anaesthetics,
and fasting time. Usually, the patients are required to fill out this information on a separate form during the
pre-operative evaluation. Depending on the existing medical conditions reported, the anaesthetist will review
this information with the patient either during his pre-operative evaluation or on the day of his surgery.
Truthful and accurate answering of the questions is important so the anaesthetist can select the proper
anaesthetics. For instance, a heavy drinker or drug user who does not disclose their chemical uses could be
undermedicated, which could then lead to anaesthesia awareness or dangerously high blood pressure.
Commonly used medications such as Viagra can interact with anaesthesia drugs; failure to disclose such
usage can endanger the patient.
An important aspect of this assessment is that of the patient's airway, involving inspection of the mouth
opening and visualisation of the soft tissues of the pharynx. The condition of teeth and location of dental
crowns and caps are checked, neck flexibility and head extension observed. If an endotracheal tube is
indicated and airway management is deemed difficult, then alternative placement methods such as fiberoptic
intubation may be used.
General anaesthesia
Premedication
Anaesthetists may give a pre-medication by injection or by mouth anywhere from a couple of hours to a
couple of minutes before the onset of surgery to induce drowsiness and relaxation.
The most common drugs used for pre-medication are narcotics (opioids such as fentanyl) and sedatives
(most commonly benzodiazepines such as midazolam).
Induction
The general anaesthetic is administered in either the operating theatre itself or a special ante-room.
General anaesthesia can be induced by intravenous (IV) injection, or breathing a volatile anaesthetic through
a facemask (inhalational induction). Onset of anaesthesia is faster with IV injection than with inhalation,
taking about 10-20 seconds to induce total unconsciousness.[citation needed] This has the advantage of avoiding
the excitatory phase of anaesthesia (see below), and thus reduces complications related to induction of
anaesthesia. An inhalational induction may be chosen by the anaesthetist where IV access is difficult to
obtain, where difficulty maintaining the airway is anticipated, or due to patient preference (eg. children).
Commonly used IV induction agents include propofol, sodium thiopental, etomidate, and ketamine. The
most commonly-used agent for inhalational induction is sevoflurane because it causes less irritation than
other inhaled gases.
Maintenance
The duration of action of IV induction agents is generally 5 to 10 minutes,[citation needed] after which time
spontaneous recovery of consciousness will occur. In order to prolong anaesthesia for the required duration
(usually the duration of surgery), anaesthesia must be maintained. Usually this is achieved by allowing the
patient to breathe a carefully controlled mixture of oxygen, nitrous oxide, and a volatile anaesthetic agent.
This is transferred to the patient's brain via the lungs and the bloodstream, and the patient remains
unconscious. Inhaled agents are frequently supplemented by intravenous anesthetics, such as opioids
(usually fentanyl or a fentanyl derivative) and sedative-hypnotics (usually propofol or midazolam). At the
end of surgery the volatile anaethetic is discontinued. Recovery of consciousness occurs when the
concentration of anaesthetic in the brain drops below a certain level (usually within 1 to 30 minutes
depending upon the duration of surgery).
In the 1990s a novel method of maintaining anaesthesia was developed in Glasgow, UK. Called Total
IntraVenous Anaesthesia (TIVA), this involves using a computer controlled syringe driver (pump) to infuse
propofol throughout the duration of surgery, removing the need for a volatile anaesthetic. Purported
advantages include faster recovery from anaesthesia, reduced incidence of post-operative nausea and
vomiting, and absence of a trigger for malignant hyperthermia.
Other medications will occasionally be given to anesthetized patients to treat side effects or prevent
complications. These medications include antihypertensives to treat high blood pressure, drugs like
ephedrine and phenylephrine to treat low blood pressure, drugs like albuterol to treat asthma or
laryngospasm/bronchospasm, and drugs like epinephrine or diphenhydramine to treat allergic reactions.
Sometimes glucocorticoids or antibiotics are given to prevent inflammation and infection, respectively.
Paralysis
The induction of paralysis with a neuromuscular blocker is an integral part of modern anaesthesia. The first
drug used for this purpose was curare, introduced in the 1940s, which has now been superseded by drugs
with fewer side effects and generally shorter duration of action.
Paralysis allows surgery within major body cavities, eg. abdomen and thorax without the need for very deep
anesthesia, and is also used to facilitate endotracheal intubation.
Acetylcholine, the natural neurotransmitter substance at the neuromuscular junction, causes muscles to
contract when it is released from nerve endings. Muscle relaxants work by preventing acetylcholine from
attaching to its receptor.
Paralysis of the muscles of respiration, ie. the diaphragm and intercostal muscles of the chest requires that
some form of artificial respiration be implemented. As the muscles of the larynx are also paralysed, the
airway usually needs to be protected by means of an endotracheal tube.
Monitoring of paralysis is most easily provided by means of a peripheral nerve stimulator. This device
intermittently sends short electrical pulses through the skin over a peripheral nerve while the contraction of a
muscle supplied by that nerve is observed.
The effects of muscle relaxants are commonly reversed at the termination of surgery by anticholinesterase
drugs.
Examples of skeletal muscle relaxants in use today are pancuronium, rocuronium, vecuronium, atracurium,
mivacurium, and succinylcholine.
Airway management
With the loss of consciousness caused by general anaesthesia, there is loss of protective airway reflexes
(such as coughing), loss of airway patency and sometimes loss of a regular breathing pattern due to the effect
of anesthetics, opioids, or muscle relaxants. To maintain an open airway and regulate breathing within
acceptable parameters, some form of "breathing tube" is inserted in the airway after the patient is
unconscious. To enable mechanical ventilation, an endotracheal tube is often used (intubation), although
there are alternative devices such as face masks or laryngeal mask airways.
Monitoring
Monitoring involves the use of several technologies to allow for a controlled induction of, maintenance of
and emergence from general anaesthesia.
1. Continuous Electrocardiography (ECG): The placement of electrodes which monitor heart rate and rhythm.
This may also help the anaesthetist to identify early signs of heart ischemia.
2. Continuous pulse oximetry (SpO2): The placement of this device (usually on one of the fingers) allows for
early detection of a fall in a patient's hemoglobin saturation with oxygen (hypoxemia).
3. Blood Pressure Monitoring (NIBP or IBP): There are two methods of measuring the patient's blood
pressure. The first, and most common, is called non-invasive blood pressure (NIBP) monitoring. This
involves placing a blood pressure cuff around the patient's arm, forearm or leg. A blood pressure machine
takes blood pressure readings at regular, preset intervals throughout the surgery. The second method is called
invasive blood pressure (IBP) monitoring. This method is reserved for patients with significant heart or lung
disease, the critically ill, major surgery such as cardiac or transplant surgery, or when large blood losses are
expected. The invasive blood pressure monitoring technique involves placing a special type of plastic
cannula in the patient's artery - usually at the wrist or in the groin.
4. Agent concentration measurement - Common anaesthetic machines have meters to measure the percent of
inhalational anaesthetic agent used (e.g. sevoflurane, isoflurane, desflurane, halothane etc).
5. Low oxygen alarm - Almost all circuits have a backup alarm in case the oxygen delivery to the patient
becomes compromised. This warns if the fraction of inspired oxygen drops lower than room air (21%) and
allows the anaesthetist to take immediate remedial action.
6. Circuit disconnect alarm - indicates failure of circuit to achieve a given pressure during mechanical
ventilation.
7. Carbon dioxide measurement (capnography)- measures the amount of carbon dioxide expired by the
patient's lungs. It allows the anaesthetist to assess the adequacy of ventilation
8. Temperature measurement to discern hypothermia or fever, and to aid early detection of malignant
hyperthermia.
9. EEG or other system to verify depth of anaesthesia may also be used. This reduces the likelihood that a
patient will be mentally awake, although unable to move because of the paralytic agents. It also reduces the
likelihood of a patient receiving significantly more amnesic drugs than actually necessary to do the job.
Stages of anaesthesia
Stage 1
Stage 1 anaesthesia, also known as the "induction," is the period between the initial administration of the
induction medications and loss of consciousness. During this stage the patient progresses from analgesia
without amnesia to analgesia with amnesia. Patients can carry on a conversation at the time.
Stage 2
Stage 2 anesthesia, also known as the "excitement stage," is the period following loss of consciousness and
marked by excited and delirious activity. During this stage, respirations and heart rate may become irregular.
In addition, there may be uncontrolled movements, vomiting, breath holding, and pupillary dilation. Since
the combination of spastic movements, vomiting, and irregular respirations may lead to airway compromise,
rapidly acting drugs are used to minimize time in this stage and reach stage 3 as fast as possible.
Stage 3
Stage Three: Surgical Anaesthesia. During this stage, the skeletal muscles relax, and the patient's breathing
becomes regular. Eye movements slow, then stop, and surgery can begin.
Stage 4
Stage 4 anaesthesia, also known as "overdose," is the stage where too much medication has been given and
the patient has severe brain stem or medullary depression. This results in a cessation of respiration and
potential cardiovascular collapse. This stage is lethal without cardiovascular and respiratory support.
Postoperative Analgesia
The anaesthesia concludes with a management plan for postoperative pain relief. This may be in the form of
regional analgesia, oral, transdermal or parenteral medication. Minor surgical procedures are amenable to
oral pain relief medications such as paracetamol and NSAIDS such as ibuprofen. Moderate levels of pain
require the addition of mild opiates such as codeine.
Major surgical procedures may require a combination of modalities to confer adequate pain relief. Parenteral
methods include Patient Controlled Analgesia System (PCAS) involving morphine, a strong opiate. Here, the
patient presses a button to activate a pump containing morphine. This administers a preset dose of the drug.
As the pump is programmed not to exceed a safe amount of the drug, the patient cannot self administer a
toxic dose.
Mortality rates
Overall, the mortality rate for general anaesthesia is about five deaths per million anaesthetic administrations.
Death during anaesthesia is most commonly related to surgical factors or pre-existing medical conditions.
These include major haemorrhage, sepsis, and organ failure (eg. heart, lungs, kidneys, liver). Common
causes of death directly related to anaesthesia include:
 aspiration of stomach contents
 suffocation (due to inadequate airway management)
 allergic reactions to anaesthesia (specifically and not limited to anti-nausea agents) and other deadly
genetic predispositions
 human error
 equipment failure
In the US, up until about 1980 anesthesia was a significant risk, with at least one death per 10,000 times
administered. After becoming something of a public scandal, a careful effort was made to understand the
causes and improve the results. It is generally believed that anesthesia is now at least ten times safer than it
was then. However, there is some controversy about this. In the US, the data is not made public (in fact, the
data is not even collected), so the truth is uncertain. The rate for dental anesthesia is reported to be one out of
350,000.
Local anesthesia
Local anesthesia is any technique to render part of the body insensitive to pain without affecting
consciousness. It allows patients to undergo surgical and dental procedures with reduced pain and distress. In
many situations, such as cesarean section, it is safer and therefore superior to general anesthesia. It is also
used for relief of non-surgical pain and to enable diagnosis of the cause of some chronic pain conditions.
Anaesthetists sometimes combine both general and local anesthesia techniques.
The following terms are often used interchangeably:
 Local anesthesia, in a strict sense, is anesthesia of a small part of the body such as a tooth or an area
of skin.
 Regional anesthesia is aimed at anesthetizing a larger part of the body such as a leg or arm.
Conduction anesthesia is a comprehensive term which encompasses a great variety of local and regional
anesthetic techniques.
Techniques
To achieve conduction anesthesia a local anesthetic is injected or applied to a body surface. The local
anesthetic then diffuses into nerves where it inhibits the propagation of signals for pain, muscle contraction,
regulation of blood circulation and other body functions. Relatively high drug doses or concentrations inhibit
all qualities of sensation (pain, touch, temperature etc.) as well as muscle control. Lower doses or
concentrations may selectively inhibit pain sensation with minimal effect on muscle power. Some techniques
of pain therapy, such as walking epidurals for labor pain use this effect, termed differential block.
Anesthesia persists as long as there is a sufficient concentration of local anesthetic at the affected nerves.
Sometimes a vasoconstrictor drug is added to decrease local blood flow, thereby slowing the transport of the
local anesthetic away from the site of injection. Depending on the drug and technique, the anesthetic effect
may persist from less than an hour to several hours. Placement of a catheter for continuous infusion or
repeated injection allows conduction anesthesia to last for days or weeks. This is typically done for purposes
of pain therapy.
Local anesthetics can block almost every nerve between the peripheral nerve endings and the central nervous
system. The most peripheral technique is topical anesthesia to the skin or other body surface. Small and
large peripheral nerves can be anesthetized individually (peripheral nerve block) or in anatomic nerve
bundles (plexus anesthesia). Spinal anesthesia and epidural anesthesia are applied near the spinal cord where
the peripheral nervous system merges into the central nervous system.
Clinical techniques include:
 Surface anesthesia - application of local anesthetic spray, solution or cream to the skin or a mucous
membrane. The effect is short lasting and is limited to the area of contact.
 Infiltration anesthesia - injection of local anesthetic into the tissue to be anesthetized. Surface and
infiltration anesthesia are collectively topical anesthesia.
 Field block - subcutaneous injection of a local anesthetic in an area bordering on the field to be
anesthetized.
 Peripheral nerve block - injection of local anesthetic in the vicinity of a peripheral nerve to
anesthetize that nerve's area of innervation.
 Plexus anesthesia - injection of local anesthetic in the vicinity of a nerve plexus, often inside a
tissue compartment that limits the diffusion of the drug away from the intended site of action. The
anesthetic effect extends to the innervation areas of several or all nerves stemming from the plexus.
 Epidural anesthesia - a local anesthetic is injected into the epidural space where it acts primarily on
the spinal nerve roots. Depending on the site of injection and the volume injected, the anesthetized
area varies from limited areas of the abdomen or chest to large regions of the body.
 Spinal anesthesia - a local anesthetic is injected into the cerebrospinal fluid, usually at the lumbar
spine (in the lower back), where it acts on spinal nerve roots and part of the spinal cord. The
resulting anesthesia usually extends from the legs to the abdomen or chest.
 Intravenous regional anesthesia (Bier's block) - blood circulation of a limb is interrupted using a
tourniquet (a device similar to a blood pressure cuff), then a large volume of local anesthetic is
injected into a peripheral vein. The drug fills the limb's venous system and diffuses into tissues
where peripheral nerves and nerve endings are anesthetized. The anesthetic effect is limited to the
area that is excluded from blood circulation and resolves quickly once circulation is restored.
 Local anesthesia of body cavities (e.g. intrapleural anesthesia, intraarticular anesthesia)
Uses in surgery and dentistry
Virtually every part of the body can be anesthetized using conduction anesthesia. However, only a limited
number of techniques are in common clinical use. Sometimes conduction anesthesia is combined with
general anesthesia or sedation for the patient's comfort and ease of surgery. Typical operations performed
under conduction anesthesia include:
 Dentistry (surface anesthesia, infiltration anesthesia or intraligamentary anesthesia during
restorative operations or extractions, regional nerve blocks during extractions and surgeries.)
 Eye surgery (surface anesthesia with topical anesthetics, retrobulbar block)
 ENT operations, head and neck surgery (infiltration anesthesia, field blocks, peripheral nerve blocks,
plexus anesthesia)
 Shoulder and arm surgery (plexus anesthesia, intravenous regional anesthesia)
 Heart and lung surgery (epidural anesthesia combined with general anesthesia)
 Abdominal surgery (epidural/spinal anesthesia, often combined with general anesthesia)
 Gynecological, obstetrical and urological operations (spinal/epidural anesthesia)
 Bone and joint surgery of the pelvis, hip and leg (spinal/epidural anesthesia, peripheral nerve blocks,
intravenous regional anesthesia)
 Surgery of skin and peripheral blood vessels (topical anesthesia, field blocks, peripheral nerve
blocks, spinal/epidural anesthesia)
 Lip stitching - a local anesthesia can also be injected into the lip when having stitches there, as the
needle goes in it is extremely painful and must be injected in to several different places in the lip for
it to work. Then the pain is over until the stitches are in. You can actually feel the stitch-needle go in
to your lip tissue.
Uses in acute pain
Acute pain may occur due to trauma, surgery, infection, disruption of blood circulation or many other
conditions in which there is tissue injury. In a medical setting it is usually desirable to alleviate pain when its
warning function is no longer needed. Besides improving patient comfort, pain therapy can also reduce
harmful physiological consequences of untreated pain.
Acute pain can often be managed using analgesics. However, conduction anesthesia may be preferable
because of superior pain control and fewer side effects. For purposes of pain therapy, local anesthetic drugs
are often given by repeated injection or continuous infusion through a catheter. Low doses of local anesthetic
drugs can be sufficient so that muscle weakness does not occur and patients may be mobilized.
Some typical uses of conduction anesthesia for acute pain are:
 Labor pain (epidural anesthesia)
 Postoperative pain (peripheral nerve blocks, epidural anesthesia)
 Trauma (peripheral nerve blocks, intravenous regional anesthesia, epidural anesthesia)
Uses in chronic pain
Chronic pain of more than minor intensity is a complex and often serious condition that requires diagnosis
and treatment by an expert in pain medicine. Local anesthetics can be applied repeatedly or continuously for
prolonged periods to relieve chronic pain, usually in combination with medication such as opioids, NSAIDs,
and anticonvulsants.
Miscellaneous uses
Topical anesthesia, in the form of lidocaine/prilocaine (EMLA) is most commonly used to enable relatively
painless venipuncture (blood collection) and placement of intravenous cannulae. It may also be suitable for
other kinds of punctures such as ascites drainage and amniocentesis.
Surface anesthesia also facilitates some endoscopic procedures such as bronchoscopy (visualization of the
lower airways) or cystoscopy (visualization of the inner surface of the bladder).
Adverse Effects
Adverse effects depend on the local anesthetic agent, method, and site of administration and is discussed in
depth in the local anesthetic sub-article.
Overall the effects can be:
1. localized prolonged anesthesia or paresthesia due to infection, hematoma, excessive fluid pressure
in a confined cavity, and severing of nerves & support tissue during injection,
2. systemic reactions such as depressed CNS syndrome, allergic reactions, and cyanosis due to local
anesthetic toxicity.
3. lack of anesthetic effect due to infectious puss such as an abscess.
Intrathecal anesthesia
Intrathecal anesthesia.
•Intrathecal anesthesia result in sympathetic block, sensory analgesia, and motor block (depending on dose,
concentration, or volume of local anesthetic) by local anesthetic is injected into subarachnoid space ( spinal
anesthesia ) or the epidural space ( epidural anesthesia ) and bathes the nerve roots in the subarachnoid
space or epidural space, respectively
Intrathecal block is divided into two classes
• Subarachnoid block (spinal block): Local anesthetic is injected intosubarachnoid space.
• Epidural block: Local anesthetic is injected into the epidural space
Spinal anaesthesia
.
Spinal needles used in spinal anaesthesia
Performance of a spinal anaesthesia
Spinal analgesia, (or commonly called spinal anesthesia or sub-arachnoid block (S.A.B.)) is a form of
regional anaesthesia involving injection of a local anaesthetic into the cerebrospinal fluid (CSF), generally
through a fine needle, usually 3.5 inches long. For extremely obese patients, some anaesthesiologists are
known to prefer spinal needles which are seven inches long. The tip of the spinal needle should, theoretically,
have a short or small bevel. Recently pencil point needles have been made available (Whitakre's).
There are hyperbaric, isobaric and hypobaric solutions of anesthetics to choose for the spinal anesthesia.
Usually, the hyperbaric is chosen, as its spread can be effectively and predictably controlled by the
anaesthesiologist.
Bupivacaine is the local anaesthetic most commonly used, although lignocaine (lidocaine), tetracaine,
procaine, ropivacaine, levobupivicaine and cinchocaine are also available. Sometimes a vasoconstrictor such
as epinephrine is added to the local anesthetic to prolong its duration. Of late, many anaesthesiologists are
preferring to add opioids like fentanyl or buprenorphine, or non-opioids like clonidine, to the local
anaesthetic used in spinal, to give a smoother 'effect' and to provide prolonged pain relief once the action of
the 'spinal' has worn off.
Regardless of the anaesthetic agent (drug) used, the desired effect is to block the transmission of nerve
signals to and from the affected area. Sensory signals from the site are blocked, thereby eliminating pain, and
motor signals to the area eliminate movement. In effect, the result is total numbness of the area and paralysis.
This allows surgical procedures to be performed with little or no sensation whatsoever to the person
undergoing the procedure, and provides a still patient or area for the surgeon to work on.
Some sedation is sometimes provided to help the patient relax and pass the time during the procedure, but
with a successful spinal anaesthetic the surgery can be performed with the patient wide awake. Spinal
anaesthetics are limited to procedures involving most structures below the upper abdomen. To administer a
spinal anaesthetic to higher levels may affect the ability to breathe by paralyzing the intercostal respiratory
muscles, or even the diaphragm in extreme cases (called a "high spinal", or a "total spinal", with which
consciousness is lost), as well as the body's ability to control the heart rate via the cardiac accelerator fibers.
Baricity refers to the density of a substance compared to the density of human cerebral spinal fluid. Baricity
is used in anaesthesia to determine the manner in which a particular drug will spread in the intrathecal space.
Operations
All surgical interventions below the umbilicus, is the general guiding principle:
 Abdominal & vaginal hysterectomies
 Caesarean sections
 Hernia (inguinal or epigastric)
 Piles
 orthopaedic surgeries on the pelvis, femur, tibia and the ankle
 nephrectomy
 cholecystectomies
 trauma surgery on the lower limbs, especially if the patient is full-stomach
 Open tubectomies
 Trans-urethral resection of prostate
Complications
Can be broadly classified as immediate or late (on the table or in the ward):
 Spinal shock.
 Cauda equina injury.
 Cardiac arrest.
 Hypothermia.
 Broken needle.
 Bleeding resulting in hematoma, with or without subsequent neurological sequelae due to
compression of the spinal nerves
 Infection: immediate within six hours of the spinl anaesthetic manifesting as meningism or
meningitis or late, at the site of injection, in the form of pus discharge, due to improper sterilization
of the LP set.
Epidural anesthesia.
An epidural catheter after insertion. The site has been prepared with Tincture of iodine. Depth markings may
be seen along the shaft of the catheter.
The term epidural is often short for epidural anesthesia, a form of regional anesthesia involving injection
of drugs through a catheter placed into the epidural space. The injection can cause both a loss of sensation
(anaesthesia) and a loss of pain (analgesia), by blocking the transmission of signals through nerves in or near
the spinal cord.
The epidural space (or extradural space or peridural space) is a part of the human spine. It is the space
inside the bony spinal canal but outside the membrane called the dura mater (sometimes called the "dura").
In contact with the inner surface of the dura is another membrane called the arachnoid mater ("arachnoid").
The arachnoid encompasses the cerebrospinal fluid that surrounds the spinal cord.
Spinal anaesthesia is a technique whereby a local anaesthetic drug is injected into the cerebrospinal fluid.
This technique has some similarity to epidural anaesthesia, and the two techniques may be easily confused
with each other.
Epidural anesthesia and analgesia
Indications
Injecting medication into the epidural space is primarily performed for analgesia. This may be performed
using a number of different techniques and for a variety of reasons. Additionally, some of the side-effects of
epidural analgesia may be beneficial in some circumstances (e.g. vasodilation may be beneficial if the patient
has peripheral vascular disease). When a catheter is placed into the epidural space (see below) a continuous
infusion can be maintained for several days, if needed. Epidural analgesia may be used:
 For analgesia alone, where surgery is not contemplated. An epidural for pain relief (e.g. in
childbirth) is unlikely to cause loss of muscle power, but is not usually sufficient for surgery.
 As an adjunct to general anaesthesia. The anaesthetist may use epidural analgesia in addition to
general anaesthesia. This may reduce the patient's requirement for opioid analgesics. This is suitable
for a wide variety of surgery, for example gynaecological surgery (e.g. hysterectomy), orthopaedic
surgery (e.g. hip replacement), general surgery (e.g. laparotomy) and vascular surgery (e.g. open
aortic aneurysm repair). See also caudal epidural, below.
 As a sole technique for surgical anaesthesia. Some operations, most frequently Caesarean section,
may be performed using an epidural anaesthetic as the sole technique. Typically the patient would
remain awake during the operation. The dose required for anaesthesia is much higher than that
required for analgesia.
 For post-operative analgesia, in either of the two situations above. Analgesics are given into the
epidural space for a few days after surgery, provided a catheter has been inserted. Through the use of
a patient-controlled analgesia (PCA) infusion pump, a patient may be given the ability to control
post-surgical pain medications administered through the epidural.
 For the treatment of back pain. Injection of analgesics and steroids into the epidural space may
improve some forms of back pain. See below.
 For the treatment of chronic pain or palliation of symptoms in terminal care, usually in the short
or medium term.
The epidural space is more difficult and risky to access as one ascends the spine, so epidural techniques are
most suitable for analgesia for the chest, abdomen, pelvis or legs. They are much less suitable for analgesia
for the neck, or arms and are not possible for the head (since sensory innervation for the head arises directly
from the brain via cranial nerves rather than from the spinal cord via the epidural space.)
Cautions
There are circumstances where the risks of an epidural are higher than normal. These circumstances include:
 Anatomical abnormalities, such as spina bifida, meningomyelocele or scoliosis
 Previous spinal surgery (where scar tissue may hamper the spread of medication, or may cause an
acquired tethered spinal cord)
 Certain problems of the central nervous system, including multiple sclerosis or syringomyelia
 Certain heart-valve problems (such as aortic stenosis, where the vasodilation induced by the
anesthetic may impair blood supply to the thickened heart muscle.)
Contraindications
Circumstances in which epidurals should not be used:
 Lack of consent
 Bleeding disorder (coagulopathy) or anticoagulant medication (e.g. warfarin) - risk of spinal
cord-compressing hematoma
 Infection near the point of insertion
 Infection in the bloodstream which may "seed" via the catheter into the (otherwise relatively
impervious) central nervous system
 Uncorrected hypovolemia (low circulating blood volume)
Anatomy
Main article: Epidural space
Sagittal section of the spinal column. A detailed explanation of the various structures exists within the text
(not drawn to scale).
The diagram at right depicts the various structures of the spinal column. The spinal cord (yellow core) is in
intimate contact with the pia mater (blue). The arachnoid (red) exists superficial to the pia mater, and is
attached to it by many trabeculae, giving it a spider-like appearance. This space (light blue) is filled with
cerebrospinal fluid (CSF) and is called the subarachnoid space. Superficial to the arachnoid is the dura mater
(pink) and although they are unattached, they are kept firmly pressed against one another because of pressure
exerted by the CSF. Superficial to the dura mater is a space (pale green), known as the epidural space, that
exists between it and the internal surfaces of the vertebral bones and their supporting ligamentous structures.
This space is likewise pressed closed by surrounding tissue pressure, so it is called a 'potential' space. The
vertebral bones (taupe) are attached to one another by the interspinous ligaments (teal). Insertion of an
epidural involves threading a needle between the bones, through the ligaments and into the epidural potential
space taking great care to avoid puncturing the layer immediately below containing CSF under pressure.
Technique of insertion
Epidural anaesthesia requires a high level of technical proficiency to avoid serious complications, and should
always be performed by a trained anaesthetist, using a strict aseptic technique to reduce the risk of infection.
Position of the patient
The patient may be in the sitting position or lateral position (lying on the side). The sitting patient is asked to
slouch and bend forward slightly from the waist to increase the curvature of the spine. The lying patient is
asked to draw the knees up to the chin for the same reason.
Insertion site
The anaesthetist palpates the patient's back and identifies a suitable anatomical gap between the bony
spinous processes prior to the procedure. The level of the spine at which the catheter is best placed depends
mainly on the site and type of an intended operation or the anatomical origin of pain. Since innervation of
the chest and abdomen travels under the ribs, the anaesthetist can palpate along the corresponding rib to
determine placement of the catheter tip.
Most commonly, the anaesthetist conducting an epidural places the catheter in the mid-lumbar, or lower back
region of the spine, although occasionally a catheter is placed in the thoracic (chest) or cervical (neck) region.
In adults, the spinal cord terminates at the first lumbar vertebra, below which lies a bundle of nerves known
as the cauda equina ("horse's tail"). Hence, lumbar epidurals carry a very low risk of injuring the spinal cord.
Locating the epidural space
The skin is infiltrated with local anaesthetic such as lidocaine over the identified space. The insertion point is
usually in the midline, although other approaches, such as the paramedian approach, may occasionally be
employed. In the paramedian approach, the needle tip passes along a shelf of vertebral bone called the
lamina until just before reaching the ligamentun flavum and the epidural space. 'Walking' the needle tip off
this lamina allows the clinician to be confident that they are close to the epidural space. This is particularly
important in the thoracic spine, where the spinal cord is larger (than in the lumbar spine) and nearly fills the
spinal canal increasing the risk of dural puncture and cord damage.
A particular type of needle known as a Tuohy needle is almost invariably used. This needle was specially
designed for locating the epidural space safely, and has several specific features for this purpose.
The Tuohy needle is inserted to the interspinous ligament and a loss of resistance to injection technique is
used to identify the epidural space. This technique works because the interspinous ligament is extremely
dense, and injection into it is almost impossible. The anaesthetist attaches a syringe to the Tuohy needle and
advances it slowly.
The syringe may contain air or saline. The principles are the same, but the specifics of the technique are
different due to the greater compressibility of air with respect to saline.
When the tip of the needle enters a space of negative or neutral pressure (such as the epidural space), there
will be a "loss of resistance" and it will be possible to inject through the syringe. There is now a high
likelihood that the tip of the needle has entered the epidural space. A sensation of "pop" or "click" may be
felt as the needle breaches the ligamentum flavum just before entering the epidural space. An innovative
technique for teaching this sensation of 'loss of resistance' using a banana was described by Leighton in
Anesthesiology 70:368-9; 1989 - "A greengrocer's model of the epidural space."
Traditionally anaesthetists have used either air or saline for identifying the epidural space, depending on their
personal preference. However, evidence is accumulating that saline may result in more rapid and satisfactory
quality of analgesia.
In addition to the loss of resistance technique, realtime observation of the advancing needle is becoming
more common. This may be done using a portable ultrasound scanner, or with fluoroscopy (moving X-ray
pictures).
Feeding the catheter
After placement of the tip of the Tuohy needle into the epidural space the catheter is threaded through the
needle. The needle is then withdrawn over the catheter. Generally the catheter is then withdrawn slightly so
that 4-6 cm remains in the epidural space. The catheter has depth markings on it (see photo) so that the
length of catheter in the epidural space can be estimated.
The catheter is a fine plastic tube, down which anaesthetics may be given into the epidural space. Early
catheters had a hole at the end ("end-hole catheters"), but were prone to blockage. More modern catheters
("side-hole catheters") have a blind end but three or more side-holes along the shaft near the tip. This not
only disperses the anaesthetic more widely around the catheter, but lessens the likelihood of blockage.
The catheter is typically secured to the skin with adhesive tape or dressings to prevent it becoming
dislodged.
In some unusual instances, it may not be required to insert a catheter into the epidural space, e.g. for steroid
injections; see below. The anesthesiologist may inject medication into the epidural space through the needle,
then remove the needle.
Anaesthetic drugs
A patient receiving an epidural for pain relief typically receives a combination of local anesthetics and
opioids. This combination works better than either type of drug used alone. Common local anesthetics
include lidocaine, bupivacaine, ropivacaine, and chloroprocaine. Common opioids include morphine,
fentanyl, sufentanil, and pethidine. These are injected in relatively small doses.
Occasionally other agents may be used, such as clonidine or ketamine.
Block height and intensity
Typically, the effects of the epidural are noted below a specific level on the body (dermatome). This level
(the "block height") is chosen by the anaesthetist. The level is usually 3-4 dermatomes higher than the point
of insertion. A very high insertion level may result in sparing of very low dermatomes. For example, a
thoracic epidural may be performed for upper abdominal surgery, but may not have any effect on the
perineum (area around the genitals) or bladder. Nonetheless, giving very large volumes into the epidural
space may spread the block both higher and lower.
The intensity of the block is determined by the concentration of local anaesthetic drugs used. For example,
15ml 0.1% bupivacaine may provide good analgesia for a woman in labour, but would likely be insufficient
for surgery. Conversely, 15ml of 0.5% bupivacaine would provide a more intense block, likely sufficient for
surgery. Since the volume used in each case is the same, the spread of drug, and hence the block height, is
likely to be similar.
Removing the catheter
The catheter is usually removed when the patient is able to take oral pain medications. Catheters can safely
remain in place for several days with little risk of bacterial infection, particularly if the skin is prepared with
a chlorhexidine solution. Subcutaneously tunneled epidural catheters may be left in place for longer periods,
with a low risk of infection or other complications.
Other types of epidural
Combined spinal-epidurals
Main article: Combined spinal and epidural anaesthesia
For some procedures, the anaesthetist may choose to combine the rapid onset and reliable, dense block of a
spinal anaesthetic with the post-operative analgesic effects of an epidural. This is called combined spinal and
epidural anaesthesia (CSE).
The anaesthetist may insert the spinal anaesthetic at one level, and the epidural at an adjacent level.
Alternatively, after locating the epidural space with the Tuohy needle, a spinal needle may be inserted
through the Tuohy needle into the subarachnoid space. The spinal dose is then given, the spinal needle
withdrawn, and the epidural catheter inserted as normal. This method, known as the "needle-through-needle"
technique, may be associated with a slightly higher risk of placing the catheter into the subarachnoid space.
Caudal epidurals
The epidural space may be entered through the sacrococcygeal membrane, using a 22g catheter-over-needle
or regular 21G needle. Injecting a volume of 1 cc/kg of local anaesthetic here provides good analgesia of the
perineum and groin areas. This is typically a single-injection technique and a catheter is not normally placed.
This is known as a caudal epidural or "caudal".
The caudal epidural is an effective and safe analgesic technique in children undergoing groin, pelvic or lower
extremity surgery. It is usually combined with general anaesthesia since children cannot tolerate the injection
awake.
Epidural steroid injections
An epidural injection, or epidural steroid injection, may be used to help reduce the pain caused by a
herniated disc, degenerative disc disease, or spinal stenosis. These spinal disorders often affect the cervical
(neck) and lumbar (lower back) areas of the spine.
The medicine used in the injection is usually a combination of a local anesthetic (e.g. bupivacaine) and a
steroid (e.g. triamcinolone). The technique and risks of the procedure are similar to those for standard
epidural analgesia. The effects of an epidural steroid injection vary, but permanent benefit is unlikely. The
technique is believed to work by reducing the inflammation or swelling, or both, of the nerves in the epidural
space.
Some patients who have some residual pain after the first injection may receive a second or third epidural
steroid injection. Patients who do not receive any relief from the first injection are unlikely to benefit from a
second injection.
Benefits of epidural analgesia after surgery
Epidural analgesia has been demonstrated to have several benefits after surgery. These include:
 Effective analgesia without the need for systemic opioids.
 The incidence of postoperative respiratory problems and chest infections is reduced.
 The incidence of postoperative myocardial infarction ("heart attack") is reduced
 The stress response to surgery is reduced
 Motility of the intestines is improved by blockade of the sympathetic nervous system
 Use of epidural analgesia during surgery reduces blood transfusion requirements.
Despite these benefits, no survival benefit has been proven for high-risk patients.
Potential problems
Side effects
In addition to blocking the nerves which carry pain, local anaesthetic drugs in the epidural space will block
other types of nerves as well, in a dose-dependent manner. Depending on the drug and dose used, the effects
may last only a few minutes or up to several hours. This results in three main effects:
 Loss of other modalities of sensation (including touch, and proprioception)
 Loss of muscle power
 Loss of function of the sympathetic nervous system, which controls blood pressure
Pain nerves are most sensitive to the effects of the epidural. This means that a good epidural can provide
analgesia without affecting muscle power or other types of sensation. The larger the dose used, the more
likely it is that the side-effects will be problematic.
For example, a laboring woman may have an epidural running during labor which is providing good
analgesia without impairing her ability to move around in bed. She requires a Caesarean section, and is given
a large dose of epidural bupivacaine. After a few minutes, she can no longer move her legs, or feel her
abdomen. Her blood pressure is noted to be lower and she is given an intravenous infusion of ephedrine or
phenylephrine to compensate. During the operation, she feels no pain.
Very large doses of epidural anaesthetic can cause paralysis of the intercostal muscles and diaphragm (which
are responsible for breathing), and loss of sympathetic function to the heart itself, causing a profound drop in
heart rate and blood pressure. This requires emergency treatment, and in severe cases may require airway
support. This happens because the epidural is blocking the heart's sympathetic nerves, as well as the phrenic
nerves, which supply the diaphragm.
It is considered safe practice for all patients with epidurals to be confined to bed to prevent the risk of falls.
The loss of the sensation of needing to urinate may require the placement of a urinary catheter for the
duration of the epidural.
Opioid drugs in the epidural space are very safe (as well as effective). However, very large doses may cause
troublesome itch, and rarely, delayed respiratory depression.
Complications of epidural use
These include:
 Block failure (about 1 in 20). Partial failure may still give satisfactory pain relief. However, if pain
relief is inadequate, another epidural may have to be performed.
 Bloody tap (about 1 in 30-50). It is easy to injure an epidural vein with the needle. In patients who
have normal blood clotting, it is extremely rare (e.g. 1 in 100,000) for problems to develop.
However, in a patient who has a coagulopathy, the patient may be at risk of epidural hematoma. If
blood comes back down the needle, the anesthesiologist will normally place the epidural at another
level.
 Accidental dural puncture with headache (common, about 1-3 in 100 insertions[9][10][11]) The
epidural space in the adult lumbar spine is only 3-5mm deep, which means it is comparatively easy
to cross it and accidentally puncture the dura (and arachnoid) with the needle. This may cause
cerebrospinal fluid (CSF) to leak out into the epidural space, which may in turn cause a post dural
puncture headache (PDPH). This can be severe and last several days, and in some rare cases weeks
or months. It is caused by a reduction in CSF pressure and is characterised by postural exacerbation
when the patient raises their head above the lying position. If severe it may be successfully treated
with an epidural blood patch (a small amount of the patient's own blood given into the epidural
space via another epidural needle which clots and seals the leak). Most cases resolve spontaneously
with time.
 Catheter misplaced into a vein (uncommon, less than 1 in 300). Occasionally the catheter may be
misplaced into an epidural vein, which results in all the anaesthetic being injected intravenously,
where it can cause seizures or cardiac arrest in large doses (about 1 in 10,000 insertions). This also
results in block failure.
 High block, as described above (uncommon, less than 1 in 500).
 Catheter misplaced into the subarachnoid space (rare, less than 1 in 1000). If the catheter is
accidentally misplaced into the subarachnoid space (e.g. after an unrecognised accidental dural
puncture), normally cerebrospinal fluid can be freely aspirated from the catheter (which would
usually prompt the anaesthetist to withdraw the catheter and resite it elsewhere). If, however, this is
not recognised, large doses of anaesthetic may be delivered directly into the cerebrospinal fluid.
This may result in a high block, or, more rarely, a total spinal, where anaesthetic is delivered
directly to the brainstem, causing unconsciousness and sometimes seizures.
 Neurological injury lasting less than 1 year (rare, about 1 in 6,700).
 Epidural abscess formation (very rare, about 1 in 145,000). The risk increases greatly with catheters
which are left in place longer than 72 hours.
 Epidural haematoma formation (very rare, about 1 in 168,000).
 Neurological injury lasting longer than 1 year (extremely rare, about 1 in 240,000).
 Paraplegia (extremely rare, less than 1 in 100,000).
 Arachnoiditis (extremely rare, fewer than 1000 cases in the past 50 years)
 Death (extremely rare, less than 1 in 100,000) .
The figures above relate to epidurals in healthy individuals.
There is no evidence to support the concern that epidural analgesia increases the risk of anastomotic
breakdown following bowel surgery
Epidural analgesia in childbirth
Safety and efficacy
Epidural analgesia is a relatively safe method of relieving pain in labor. It provides rapid pain relief in most
cases. It is more effective than nitrous oxide, opioids, TENS, and other common modalities of analgesia in
childbirth.
Prolonged labour and risk of instrumental delivery
Epidural analgesia is associated with longer labor. Some researchers claim that it is correlated with an
increased chance of operational intervention. The clinical research data on this topic is conflicting. For
example, a study in Australia (Roberts, Tracy, Peat, 2000) concluded that having an epidural reduced the
woman's chances of having a vaginal birth, without further interventions (such as episiotomy, forceps,
ventouse or caesarean section) from 71.4% to 37.8%. Conversely, a 2001 study by researchers at the
National Institute of Child Health and Human Development and a 2002 study by researchers at Cornell
University and the University of Ontario demonstrated that epidurals do not increase the likelihood of a
caesarean section. In 2005, a meta-analysis of 21 studies also showed that epidurals do not increase the
likelihood of caesarean section, but they do increase the chance of a forceps or ventouse delivery by 40%
(Anim-Somuah, Cochrane Review, 2005). The COMET Study, published in The Lancet in 2001 (vol358,
No9275 p19-23) showed that a combined spinal epidural in labor may speed up the labor process by a few
minutes, although those women receiving an epidural had a caesarean rate of 28% and only 35% had a
normal birth without instrument assisted delivery.
These differing outcomes may be explained by data that demonstrates that the likelihood of increased
intervention is directly related to the quality of the institution or practitioner providing the care: epidurals
administered at top-rated institutions do not generally result in a clinically significant increase in caesarean
rates, whereas the risk of caesarean delivery at poorly ranked facilities seems to increase with the use of
epidural
An alternative explanation is that women are more likely to request an epidural during a prolonged or
difficult labor, which in turn is more likely lead to an assisted vaginal birth.
Effects on the baby
Some mothers worry that epidural analgesia may harm their newborn. However, although epidural labor
analgesia may be associated with slower progress of labor, it has no adverse effect on perinatal outcome and
perinatal complications.
One study concluded that women whose epidurals contain the drug fentanyl were less likely to fully
breastfeed their infant in the few days after birth and more likely to stop breastfeeding in the first 24 weeks.
However, this study has been criticised for several reasons, one of which is that the original patient records
were not examined in this study, and so many of the epidurals were assumed to contain fentanyl when almost
certainly they would not have. In addition, all patients who used epidurals in labor had also used systemic
pethidine, which would be much more likely to be the cause of any effect on breastfeeding due to the higher
amounts of medication used via that route. If that were the case, then early epidurals which avoided the need
for pethidine may actually improve breastfeeding outcomes, not worsen them.
Anesthesiology 麻醉学
Clinical anaesthesia 临床麻醉
Pain management 疼痛治疗
First-aid and resuscitation 急救复苏
重症治疗
Intensive care
General anaesthesia 全身麻醉
局部麻醉
Local anesthesia
Inhalational anesthesia
吸入麻醉
Intravenous anesthesia
静脉麻醉
Intrathecal block
椎管内阻滞
Subarachnoid block
蛛网膜下腔阻滞
Epidural block
硬脊膜外腔阻滞
Nerve block
神经阻滞
Caudal block
骶管阻滞
Deliberate hypotension
控制性降压
advanced life support ( ALS)
进一步生命支持
麻醉诱导
anesthesia induction
aspiration 误吸
平衡麻醉
balanced anesthesia
基本生命支持
basic life support ( BLS)
臂丛阻滞
brachial plexus block
Cardiopulmonary Cerebral Resuscitation
中心静脉压
central venous pressure (CVP)
颈丛阻滞
cervical nerve block
endotracheal intubation
气管内插管
external chest compression
hypoxemia
低氧血症
hypoxia
缺氧
Intensive Care Unit (ICU)
muscle relaxants
胸外按压
浸润麻醉
infiltration anesthesia
local anesthetic
重症监护治疗室
局麻药
肌松剂
prolonged life support ( PLS)
regional anesthesia
心肺脑复苏
延续生命支持
区域麻醉
total intravenous anesthesia (TIVA)
全凭静脉麻醉