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Florida Heart CPR*
Anesthesia, General
2 hours
GENERAL CONSIDERATIONS
Anesthesia is the process by which a patient is rendered able to undergo surgery.
Surgery was, of course, commonly performed before any means was available to spare
the patient any part of the experience. It takes little imagination to realize that an
unanesthetized person enduring a surgical wound will exhibit several things including
the following:
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Evasive action
Severe pain and emotional distress
Maximum tension in skeletal muscles
Massive increase in sympathetic tone causing sweating, tachycardia, and
hypertension
Vivid and unpleasant memory of the event forever
The goals of anesthesia thus include the following:
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Anesthesia (lack of awareness of surrounding events)
Akinesia (keeping the patient still to allow surgery to take place)
Muscle relaxation (to enable access through muscles to bones and body cavities)
Autonomic control (to prevent dangerous surges in hemodynamics)
General anesthesia
General anesthesia uses drugs given systemically to render the patient unaware of
anything that is being done to or around him or her. It must be safe, not threatening or
unpleasant to the patient, allow adequate surgical access to the operative site, and
cause as little disturbance as possible to internal homeostatic mechanisms. A point
worth noting is that general, as opposed to local or regional anesthesia, may not always
be the best choice.
The optimal technique for any given patient and procedure is selected by the
anesthesiologist based on the following criteria:
Advantages
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Makes no psychological demand of the patient
Allows complete stillness for prolonged periods of time
Facilitates complete control of the airway, breathing, and circulation
Permits surgery to take place in widely separated areas of the body at the same
time
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General Anesthesia
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Can be used in cases of sensitivity to local anesthetic agent
Can be administered without moving the patient from the supine position
Can be adapted easily to procedures of unpredictable duration or extent
Usually can be administered rapidly
Disadvantages
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Requires the involvement of an extra set of healthcare providers
Requires complex and costly machinery
Requires some degree of preoperative patient preparation
Usually associated with some degree of physiological trespass
Carries the risk of major complications including death, myocardial infarction, and
stroke
Associated with less serious complications such as nausea/ vomiting, sore
throat, headache, shivering, and delayed return to normal mental functioning
Associated with malignant hyperthermia, a rare, inherited muscular condition in
which exposure to some (but not all) general anesthetic agents results in acute
and potentially lethal temperature rise, hypercarbia, metabolic acidosis and
hyperkalemia
A given patient’s risk for complications as a direct result of general anesthesia depends
largely on his or her medical co-morbidities but is small.
Anesthetic death rates of 1 per 10,000 generally are quoted, but most anesthesiologists
believe that current advances in anesthesia monitoring such as pulse oximetry and
capnography have made massive contributions to patient safety. Furthermore, it is an
average figure incorporating both elective and emergency patients of all types of
physical conditions. Minor complications occur at predicable rates even in previously
healthy patients.
The incidence of symptoms during the first 24 hours following ambulatory surgery is:
<5% bleeding, vomiting, nausea; fever 5-15%; dizziness, headache, drowsiness,
hoarseness >15%; sore throat (25%); and incisional pain (30%).
PREPARATION FOR GENERAL ANESTHESIA
Safe and efficient anesthesia practice requires certified personnel, appropriate drugs
and equipment, and an optimized patient.
These requirements need to be adapted to the context; no one would criticize a trauma
surgeon attending a patient trapped in the wreckage of a motor vehicle accident for
administering a bolus dose of intravenous (IV) ketamine at the roadside to amputate a
limb and free the victim. Such a general anesthetic, given in an uncontrolled fashion by
an individual with no anesthesia training, would be completely inappropriate for an
elective surgical procedure.
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General Anesthesia
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Minimum requirements
Minimum infrastructure requirements for general anesthesia include a well-lit space of
adequate size, a source of pressurized oxygen (either piped in or from cylinders) an
effective suction device, and equipment to continuously monitor heart rate and rhythm,
blood pressure, oxygen saturation, and temperature.
Additional monitoring requirements exist in certain jurisdictions. Beyond this, some
equipment is needed to deliver the anesthetic agent. This may be as simple as needles
and syringes if the drugs are to be given entirely IV, but in most circumstances this
means the availability of a properly serviced and maintained anesthetic gas delivery
machine.
An array of routine and emergency drugs, including supplies of Dantrolene sodium (the
specific treatment for malignant hyperthermia), airway management equipment, a
cardiac defibrillator, and a recovery room staffed by properly trained individuals
completes the picture.
Preparing the patient
The patient should be adequately prepared. The most efficient method is for the patient
to be reviewed by the person responsible for giving the anesthetic well in advance of the
surgery date.
Persons without concomitant medical problems may need little more than a quick
medical review and the opportunity to discuss anesthetic questions or concerns. Those
with co-morbidity in general should be optimized for the procedure.
Patients with diabetes, coronary artery disease, chronic bronchitis and emphysema, and
other chronic aliments should be stable. The question of whether such a diseased state
is under optimal control is usually a simple matter of good clinical judgment and can be
determined by anyone who asks the appropriate questions. There are a few areas
where anesthesiology review can predict and prevent major adverse events. Foremost
amongst these is a careful examination of the patient's airway anatomy. Identification of
one or more of these anomalies may indicate that management of the patient's airway
might prove difficult under anesthesia.
Airway management
Possible or definite difficulties with airway management include the following:
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Small or receding jaw
Prominent maxillary teeth
Short neck
Limited neck extension
Poor dentition
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General Anesthesia
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Tumors of the face, mouth, neck, or throat
Facial trauma
Interdental fixation
Hard cervical collar
Halo traction
Various scoring systems have been created using orofacial measurements to predict
difficult intubation. The most widely used is the Mallampati score, which identifies
patients in whom the pharynx is not well visualized through the open mouth. High
Mallampati scores predict difficult intubation with good but not perfect accuracy.
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Often, such histories describe factors such as prolonged postoperative vomiting
or slow emergence, which, while important, do not cause undue concern for the
patient at hand.
Of much greater concern is a history of high temperature under anesthesia or
any form of anesthesia complication that resulted in death or the necessity for
intensive care.
It may be necessary to obtain records from other institutions when suspicion of
an adverse event is high but it is deemed necessary to plan a similar anesthetic
technique again.
Other requirements
The necessity to come to the operating room with an empty stomach is well known to
health professionals and the lay public alike.
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While aspiration of food or fluids into the lungs during anesthesia is a serious
complication, do not forget that depriving the patient of fluid is not benign,
particularly in the case of small children, thus strike a reasonable balance
between safe anesthetic care and dehydration.
Most anesthetists would agree that solid food should be avoided for 6 hours and
clear fluids for up to 4 hours prior to the induction of anesthesia.
With a few exceptions, patients should continue to take regularly scheduled medications
up to and including the morning of surgery. There are obvious exceptions, including the
following:
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Discontinue anticoagulants, including aspirin, in good time to avoid increased
surgical bleeding.
Avoid oral hypoglycemics on the day of surgery and manage blood glucose using
IV dextrose and insulin.
Metformin is an oral hypoglycemic agent that is associated with the development
of profound and occasionally irreversible metabolic acidosis under general
anesthesia. Discontinue it 2 weeks prior to the surgery date.
Since monoamine oxidase inhibitors are associated with anesthetic drug
interactions, discontinue them prior to surgery if possible.
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General Anesthesia
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The extent of laboratory testing for the presurgical patient is the subject of ongoing
debate within the anesthesia community. Previous regimens demanding standard
blood-work profiles, ECGs, and chest radiographs on all surgical patients are now
believed to be unnecessarily elaborate by most anesthesia professionals. The most
efficient route is to have the anesthetist order his or her own tests.
THE PROCESS OF ANESTHESIA
Premedication: The first stage of a general anesthetic
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This stage, which is usually conducted in the surgical ward or in a preoperative
holding area, is something of a throwback to the early days of ether and
chloroform anesthesia when drugs such as morphine and scopolamine routinely
were given to make the inhalation of these highly pungent vapors more tolerable.
The goal of this stage of the anesthesia process is to have the patient arrive in
the operating room in a calm, relaxed frame of mind while causing minimal
interference with breathing and cardiovascular status.
For many patients, this step is either unnecessary or impractical because of the
way in which patients are scheduled.
Appropriate drug choices are morphine, lorazepam, diazepam, temazepam, and
others. In anticipation of surgical pain, preemptive analgesics such as
indomethacin or acetaminophen can be used.
Where appropriate facilities are available, an excellent alternative is small doses
of fentanyl and midazolam to be titrated IV by a nurse in the preoperative holding
area.
Drying agents occasionally are used to diminish oral secretions, but this is
perhaps less of an issue than it once was.
The patient is transferred to the operating table and baseline vital signs are
obtained.
Induction: The patient is ready for this stage, usually the most critical part of the
anesthesia process.
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In many ways, induction of general anesthesia is analogous to an airplane taking
off. It is the transformation of a waking patient into an anesthetized one.
This can be achieved by IV injection of induction agents (drugs such as
thiopental and propofol that work rapidly), by the slower inhalation of anesthetic
vapors from a face mask, or a combination of both.
For the most part, contemporary practice dictates that adult patients and most
children be induced with IV drugs; inhaled inductions are reserved for
uncooperative toddlers and special circumstances in adults.
In addition to the induction drug, most patients receive an injection of narcotic
analgesic. A wide range of synthetic and naturally occurring narcotics with
different properties is available. Induction agents and narcotics work
synergistically to put the patient to sleep. In addition, events that are about to
occur, such as endotracheal intubation and incision of the skin, generally raise
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General Anesthesia
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the blood pressure and heart rate. Narcotic helps preempt this undesirable
response.
The next step of the induction process is the securing of the airway. This may be
a simple matter of manually holding the patient's jaw such that his or her natural
breathing is unimpeded by the tongue or may demand the insertion of a
prosthetic airway device such as a laryngeal mask airway or endotracheal tube.
A variety of factors are considered when making this decision. The major issue is
whether the patient requires an endotracheal tube.
Indications for endotracheal intubation under general anesthesia include the
following:
o Potential for airway contamination (full stomach, gastroesophageal [GE]
reflux, gastrointestinal [GI] or pharyngeal bleeding)
o Surgical need for muscle relaxation
o Predictable difficulty with endotracheal intubation or where anesthetist's
access to the airway during the case will be difficult (lateral or prone
position)
o Surgery of the mouth or face
o Prolonged procedure anticipated
Not all surgery requires muscle relaxation. In this context, only the major muscle
groups of the thorax and abdomen are considered.
If surgery is taking place in these areas, then in addition to the induction agent
and narcotic, an intermediate or long-acting muscle relaxant drug is given. This
paralyzes muscles indiscriminately, including the muscles of breathing.
Therefore, the patient's lungs must be ventilated under pressure, necessitating
an endotracheal tube.
Persons who for anatomic reasons are likely to be difficult to intubate are usually
intubated electively at the beginning of the case. This prevents the situation
where attempts are made to manage the airway with a lesser device, only for the
anesthetist to discover that oxygenation and ventilation are inadequate. At that
point during a surgical procedure it can be extraordinarily difficult, if not
impossible, to intubate the patient quickly.
Maintenance phase: At this point, the drugs used to initiate the anesthetic are
beginning to wear off, and the patient must be kept anesthetized using a maintenance
agent.
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For the most part, this refers to the delivery of anesthetic gases (more properly
termed vapors) into the patient's lungs. These may be inhaled as the patient
breathes himself or delivered under pressure by each mechanical breath of a
ventilator.
The maintenance phase is usually the most stable part of the anesthesia.
However, it is important to understand that anesthesia is a continuum of different
depths. A level of anesthesia that is satisfactory for surgery to the skin of an
extremity, for example, would be inadequate for manipulation of the bowel.
Appropriate levels of anesthesia must be chosen both for the planned procedure
and for its various stages. In complex plastic surgery for example, a considerable
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General Anesthesia
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period of time may elapse between the time that the induction of anesthetic is
complete and the skin is incised.
o During the period of skin preparation, urinary catheter insertion, and
marking out incision lines with a pen, the patient should not be receiving
any noxious stimulus. This requires a very light level of anesthesia, which
must be converted rapidly to a deeper level just before the incision is
made.
As the case progresses, the level of anesthesia is altered to give the minimum
amount necessary to ensure adequate anesthetic depth. This is achieved more
through art than science.
o If muscle relaxants have not been used, inadequate anesthesia is easy to
spot. The patient will move, cough, or pupillary obstruct his airway if the
anesthetic is too light for the stimulus being given.
o If muscle relaxants have been used, then clearly the patient is unable to
demonstrate any of these phenomena. In these patients, the
anesthesiologist must rely on careful observation of autonomic
phenomena such as hypertension, tachycardia, sweating, and capillary
dilation to decide that the patient requires a deeper anesthetic.
o This requires experience and judgment. It is from failure to recognize such
signs that tragic and highly publicized cases of awareness under
anesthesia are caused.
o Excessive anesthetic depth, on the other hand, is associated with
decreased heart rate and blood pressure, and, if carried to extremes, can
jeopardize perfusion of vital organs or be fatal. Short of these serious
misadventures, excessive depth results in slower awakening and more
side effects.
As the surgical procedure draws to a close, the patient's emergence from
anesthesia is planned. Experience and close communication with the surgeon
enable the anesthesiologist to predict the time at which the application of
dressings and casts will be complete.
o In advance of that time, anesthetic vapors have been decreased or even
switched off entirely to allow time for them to be excreted by the lungs.
o Excess muscle relaxation is reversed using specific drugs and adequate
long-acting narcotic analgesic to keep the patient comfortable in the
recovery room.
o If a ventilator has been used, the patient is restored to breathing by
himself and as anesthetic drugs dissipate, the patient wakes up.
o Waking up is not synonymous with removal of the endotracheal tube or
other artificial airway device. This is only performed when the patient has
regained sufficient control of his or her airway reflexes.
ANESTHESIA DRUGS IN COMMON USE
There are a number of choices for every aspect of anesthetic care and the way in which
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General Anesthesia
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they are sequenced probably depends more on the personal preference of the person
administering them.
Induction agents
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For 50 years, the most commonly used induction agents were rapidly acting,
water-soluble barbiturates such as thiopental, methohexital, and thiamylal.
These drugs are still commonly in use today, have an enormous record of safety
and reliability, and also are economical.
More recently, propofol, a nonbarbiturate intravenous anesthetic, has displaced
barbiturates in many anesthesia practices.
o The use of propofol is associated with less postoperative nausea and
vomiting and a more rapid, clear-headed recovery.
o In addition to being an excellent induction agent, it can be given by slow IV
infusion instead of vapor to maintain the anesthesia.
o Among its disadvantages are the facts that it often causes pain on
injection, and it is prepared in a lipid emulsion, which if not handled using
meticulous aseptic precautions, can be a medium for rapid bacterial
growth.
Anesthesia also can be induced by inhalation of a vapor. This is a common and useful
technique in uncooperative children and in some special circumstances. Halothane and
Sevoflurane are the most commonly used drugs for this purpose.
Traditional narcotic analgesics
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Morphine, meperidine, and hydromorphone are widely used in anesthesia as well
as in emergency rooms, surgical wards, and obstetric suites.
In addition, anesthesia providers have at their disposal a range of synthetic
narcotics, which in general cause less fluctuation in blood pressure and are
shorter acting. These include fentanyl, sufentanil, alfentanil, and remifentanil.
Remifentanil is the newest drug in this class and has such a short duration of
action that it must be given as a continuous infusion.
Muscle relaxants come in many varieties
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Succinylcholine, a rapid-onset, short-acting depolarizing muscle relaxant, is the
drug of choice when rapid muscle relaxation is needed.
o For decades, anesthetist have used it extensively despite a number of
predictable and unpredictable adverse effects associated with its use.
o The search for a drug that replicates its onset and offsets speed without its
adverse effects is the holy grail of muscle relaxant research.
Other relaxants have durations of action ranging from 15 minutes to more than 2
hours.
Older drugs in this class were often associated with changes in heart rate or
blood pressure, but the newer ones are devoid of these adverse properties.
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Muscle relaxants generally are excreted by the kidney, but some preparations
are broken down by plasma enzymes and can be used safely in partial or
complete renal failure.
Pancuronium is an established drug that is still in widespread use because of its
low cost and familiarity, especially in intensive care units; rocuronium,
mivacurium, and cisatracurium are more likely to be used by contemporary
anesthesiologists.
Anesthetic vapors
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These are highly potent chlorofluorocarbons, which are delivered from precision
vaporizers directly into the patient's inhaled gas stream. They may be mixed with
nitrous oxide, a much weaker but nonetheless useful anesthetic gas.
The prototype of modern anesthetic vapors is halothane. It has an unparalleled
track record of safety and efficacy, although it is associated with rare but
devastating hepatic necrosis to a greater extent than other agents.
In the 1980s, it was displaced by isoflurane and enflurane, agents that were
cleared from the lungs faster and thus were associated with more rapid
anesthetic emergences.
In the late 1990s, 2 new vapors have become very popular, desflurane and
sevoflurane. These drugs are much more maneuverable than their predecessors
and are associated with much more rapid emergence.
There is intense commercial interest in anesthesia drug research, and it seems
inevitable that new and better drug products will be introduced continuously for many
years to come.
REFERENCES
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Nash PG, Cullen BF, Stoelting RK (eds.): Clinical Anesthesia. 2nd ed.
Philadelphia: JB Lippincott 1992.
Chung F: Recovery pattern and home-readiness after ambulatory surgery.
Anesth Analg 1995 May; 80(5): 896-902
Davies JM, Pagenkopf D, Todd K: Comparison of selection of preoperative
laboratory tests: the computer vs the anaesthetist. Canadian Journal of
Anaesthesia 1994; 41: 1156-60
Franks NP, Lieb WR: Molecular and cellular mechanisms of general anaesthesia.
Nature 1994 Feb 17; (6464): 607-14
Stack CG, Rogers P, Linter SP: Monoamine oxidase inhibitors and anaesthesia.
A review. Br J Anaesth 1988 Feb; (2): 222-7
Florida Heart CPR*
General Anesthesia
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Florida Heart CPR*
General Anesthesia Assessment
1. An unanesthetized person enduring a surgical wound will exhibit several things
including the following:
a. Severe pain and emotional distress
b. Maximum tension in skeletal muscles
c. Massive increase in sympathetic tone causing sweating, tachycardia, and
hypertension
d. All of the above
2. The goals of anesthesia include:
a. Akinesia
b. Muscle relaxation
c. Autonomic control
d. All of the above
3. Anesthetic death rates of ____ generally are quoted, but most anesthesiologists
believe that current advances in anesthesia monitoring such as pulse oximetry
and capnography have made massive contributions to patient safety.
a. 1 per 100
b. 1 per 10,000
c. 1 per 500
d. 1 per 5,000
4. Safe and efficient anesthesia practice requires:
a. certified personnel
b. appropriate drugs and equipment
c. optimized patient
d. all of the above
5. Possible or definite difficulties with airway management include the following:
a. Facial trauma
b. Poor detention
c. Hard cervical collar
d. All of the above
6. Most anesthetists would agree that solid food should be avoided for __ hours and
clear fluids for up to __ hours prior to the induction of anesthesia.
a. 6 hours/ 4 hours
b. 12 hours/12 hours
c. 12 hours/ 24 hours
d. 6 hours /10 hours
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General Anesthesia
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7. With a few exceptions, patients should continue to take _____up to and including
the morning of surgery.
a. Vitamins
b. Regularly scheduled medications
c. Aspirin
d. Water
8. In many ways, induction of general anesthesia is analogous to an airplane taking
off. It is the transformation of a waking patient into an anesthetized one.
a. Falling asleep
b. An airplane taking off
c. An airplane landing
d. None of the above
9. At this point, the drugs used to initiate the anesthetic are beginning to wear off,
and the patient must be kept anesthetized using a maintenance agent.
a. Induction
b. Maintenance phase
c. Premedication phase
d. Latent phase
10. Anesthesia also can be induced by_____. This is a common and useful
technique in uncooperative children and in some special circumstances.
Halothane and Sevoflurane are the most commonly used drugs for this purpose.
a. Mouth
b. Inhalation of a vapor
c. IV
d. Injection
Florida Heart CPR*
General Anesthesia