Pharm Independent Study: Anesthetics
January 10, 2019
Lecturer: Dr. Clarkson
Notetaker: Abby Solomon (asolomon1@tulane.edu)
Feedback: https://goo.gl/forms/nv1Fz4j6aFqHo0I02
Introduction: Welcome back to Pharm after a long hiatus. This noteset will cover both the 9:45 and
11:00 AM independent studies about anesthesia, which are actually the same powerpoint just posted in
2 separate lecture spots. So yes this noteset is 12 pages long but it’s really 2 lectures, and the
questions/cases start on page 9. There are also some yummy high yield summary chart at the end!
Local Anesthetic Objectives:
1. Describe the mechanism by which local anesthetics produce their effects on neuronal tissue
2. Describe the nomenclature by which local anesthetics are classified & be able to categorize
different local anesthetics
3. Explain how the duration of local anesthesia can be prolonged by coadministration of a local
anesthetic with epinephrine.
4. Describe the CNS and cardiovascular side effects that can be expected when a local anesthetic is
inadvertently injected i.v.
General Anesthetic Objectives:
1. List the main inhalational and intravenous (parenteral) anesthetic agents & describe their major
sites of action.
2. Describe the relationship of the blood:gas partition coefficient of an inhalational anesthetic with
its speed of onset of anesthesia & its recovery time.
3. Explain the concept of minimum alveolar concentration (MAC).
4. Identify the major toxicities associated with nitrous oxide & the halogenated anesthetics
5. Describe the risk factors & treatment for malignant hyperthermia.
6. Describe how the effects of NMJ blockers can be rapidly reversed during the post-op period.
7. Explain the drugs used to prevent or treat nausea & vomiting following the delivery of
anesthesia (including ondansetron, and ketorolac).
8. Justify why so many different categories of drugs typically need to be used during surgeries
involving general anesthesia (anti-anxiety, analgesics, induction agent, NMJ blockers,
maintenance agents, anti-emetics, drugs to reverse NMJ blockers, drugs to reverse the effects of
benzodiazepines).
Drug List:
• Local Anesthetics:
o Amides: lidocaine, bupivacaine, mepivacaine, ropivacaine
o Esters: cocaine, procaine, 2-chloroprocaine, tetracaine
• General Anesthetics:
o Inhaled anesthetics: halothane, isoflurane, desflurane, sevoflurane, nitrous oxide
o Intravenous anesthetics: diazepam, midazolam, morphine sulfate, fentanyl, etomidate,
propofol, ketamine
o Skeletal muscle relaxants: succinylcholine, mivacurium, pancuronium, rocuronium.
Reversal of blockade: neostigmine, glycopyrrolate.
o Rx for malignant hypertherimia: dantrolene.
o Prevention of nausea: ondansetron, ketorolac
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Pharm Independent Study: Anesthetics
January 10, 2019
Types of Anesthesia
• Local Anesthesia: loss of sensory perception over a small area of the body
• Regional Anesthesia: loss of sensation over a specific region of the body
• General Anesthesia: loss of sensory perception of the entire body
Local Anesthesia
• Reversibly blocks conduction along nerve fibers
• Produces sensory loss without loss of consciousness
• Local anesthetics come in 2 categories: amides and esters, with different durations of action
o Amides: Each name has an “i” before “caine”
▪ Medium Action: lidocaine (Xylocaine)
▪ Long Action: bupivacaine, ropivacaine
o Esters:
▪ Short action: procaine (Novicaine)
▪ Long action: tetracaine
▪ Surface action: benzocaine, cocaine
• All local anesthetics are tertiary amines, except benzocaine
• Mechanism of action: local anesthetics reversibly block Na channels in neurons
o Hydrophobicity of local anesthetics increases its potency and duration of action because
the drug can more easily cross the lipid bilayer
o Inflammation causes extracellular acidosis, which causes a decreased local anesthetic
effect because of decreased nerve sheath penetration
• Epinephrine can be combined with local anesthetics to:
o Decrease systemic toxicity
o Prolong local anesthesia by up to 50%
o Decrease local bleeding (this improves visualization of the surgical field)
o Detect whether an injection was “intravascular”
o DO NOT use vasoconstrictors in the extremities, where there is limited circulation,
because this will lead to hypoxia
• Metabolism of local anesthetics
o Esters are hydrolyzed by plasma and liver pseudocholinesterases
▪ One metabolite created from this hydrolyzation is PABA, which rarely can cause
allergic reactions
o Amides are metabolized by the liver, so if a patient has liver disease or reduced hepatic
blood flow, there is an increased chance of toxicity
• Local Anesthetic Toxicity
o Symptoms listed from least (warning sign)→most serious (lawsuit)
▪ Numbness of tongue and mouth
▪ Behavioral and sensory disturbances (ears ringing, metallic taste, tingling
sensation)
▪ Tonic-clonic seizures
▪ Depression/loss of consciousness
▪ Respiratory failure, arrhythmias, CV collapse
o Treatment:
▪ ABCs: airway, breathing, circulation
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Pharm Independent Study: Anesthetics
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Rx Seizures: diazepam IV, oxygen, Na Bicarb to prevent metabolic acidosis
Rx CV toxicity/arrhythmias: lipid emulsions
• Lipids are injected and they bind to lipid-soluble anesthetics in the
aqueous phase. This reduces the amount of circulating anesthetic.
Note: bupivacaine is more cardiotoxic than lidocaine
▪
▪
o
General Anesthesia
• Definition: loss of response to and perception of ALL external stimuli
• Components:
o Unconsciousness
o Analgesia (although this effect depends on the dose)
o Attenuation of autonomic responses to painful stimuli
o Amnesia
o Immobility (neuromuscular relaxation)
• Phases of general anesthesia
o Induction: putting the patient to sleep
o Maintenance: keeping the patient asleep
o Emergence: waking the patient up
• Classic Stages of general anesthesia
o These stages are seen mainly with ether. Not all stages are observed with modern
general anesthetics.
o Stage 1: Analgesia (decreased awareness of pain, amnesia)
o Stage 2: Disinhibition (delirium and excitation, enhanced reflexed, retching,
incontinence, irregular respiration)
o Stage 3: Surgical Anesthesia (unconscious, no pain reflexes, regular respiration, BP is
maintained)
o Stage 4: Medullary Depression (respiratory and cardiovascular depression require
ventilation and pharmacologic support)
• Types of general anesthetics
o Inhalational:
▪ Gas: Nitrous oxide
▪ Volatile liquids: halothane, sevoflurane, isoflurane, desflurane
o Parenteral: Propofol, Etomidate, Ketamine
o Adjunct drugs:
▪ Benzodiazepines: valium, midazolam
▪ Opioids: morphine, fentanyl
▪ Skeletal muscle relaxants: succinylcholine, pancuronium
▪ Antiemetics: odansetron
• Mechanism of Action
o Enhanced GABA effect on GABAA receptors (increased inhibition)
▪ Inhaled anesthetics, barbiturates, benzodiazepines, etomidate, Propofol
o Inhibit NMDA (glutamate) receptors (decrease excitation)
▪ Nitrous oxide, ketamine, and high dose barbiturates
o Other mechanisms that are specific to certain drugs
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▪
▪
▪
▪
January 10, 2019
Block nicotinic receptors
Activate K channels (hyperpolarize Vm)
Inhibit synaptic proteins→decrease neurotransmitter release
Enhance glycine effect on glycine R’s (immobility)
This image shows how different CNS depressants interact with GABAA receptors at different sites.
Probably low yield though
•
Parenteral Anesthetics (intravenous)
o Given BEFORE major surgical procedures begin:
▪ Benzodiazepines (midazolam) reduce anxiety
▪ Opioids (morphine and fentanyl) reduce pain responses
▪ Propofol induces general anesthesia (IV)
• Most popular choice, especially for adults
• Produces anesthesia as rapidly as IV barbiturates, but recovery is more
rapid than with barbiturates
• Recovery is not delayed after prolonged infusion, due to more rapid
clearance. Patients are able to ambulate sooner, and patients feel
better post-op compared to other IV anesthetics. This means the
patient can be more rapidly discharged from the recovery room!
• Antiemetic effects help patients with increased risk of nausea
• Can cause serious hypotension, more so than barbiturates
• Commonly used also as a component of “balanced anesthesia” for
maintenance of anesthesia following induction of anesthesia
▪ 2 Alternatives to Propofol:
• Etomidate
o Good for patients with hemodynamic instability
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Rapid induction (1 min), short duration of action (3-5
min)→used as a supplement with NO for short surgical
procedures
o Hypnotic, but NOT analgesic
o Little change on CV and respiration (BP, HR, and CO)
▪ Used in patients with limited cardiac or respiratory
reserve (coronary artery disease, cardiomyopathy)
o Can cause post-op nausea and vomiting
o Can decrease cortisol production with long term infusion
• Ketamine
o Mechanism: NMDA antagonist
o A “dissociative anesthetic” that produces a cataleptic state
▪ Intense analgesia, amnesia, eyes open, involuntary limb
movement, unresponsive to commands or pain
o Increased BP, HR, CO
▪ Opposite effect of other general anesthetics
o Good for patients with shock: hypovolemia, hemorrhage, sepsis
o Good for patients at risk of bronchospasms
o Used in children and young adults for short procedures
o Side effects: nystagmus, pupillary dilation, salivation,
hallucinations, vivid dreams
▪ Risk of psychomimetic reactions (if you were alive in
2009 you’ve already seen this video, but search “David
After Dentist” on YouTube to see psychomimetic
reactions)
Benzodiazepines
▪ Midazolam (or diazepam, lorazepam)
• Used to produce anxiolysis, amnesia, and sedation prior to induction of
general anesthesia with another agent
• Sedative doses achieved within 2 minutes
• Short duration of action (30 min)
• Effects are reversed with flumazenil
o Increased risk of seizures, so it is not used for routine
procedures
o Only used in emergency/overdose situations
Opioids (morphine, fentanyl, remifentanil)
▪ General anesthetics do not produce effective analgesia (except for ketamine), so
opioids are added as adjunct
• Given before surgery to minimize hemodynamic changes produced by
painful stimuli
• This reduces the amount of general anesthetic required
▪ Therapeutic doses will inhibit respiration (increased CO2 in blood)
• High doses of opioids causes chest wall rigidity and post-op respiratory
depression
o
o
o
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Opioids are used for post-op analgesia
Remifentanil is an ester opioid metabolized by plasma esterases
• Very potent but with a short half life (3-10 min)
Clinical Correlation: Colonoscopy
o Colonoscopies are a common procedure that requires some level of sedation, analgesia,
and amnesia, but may not require induction with traditional anesthetics
o This procedure does not require an anesthesiologist, which makes it a much less
expensive procedure
▪ Patients with heart disease, sleep apnea, or pulmonary disease are considered
high risk and need an anesthesiologist to be present
o Patients are usually sedated with a benzodiazepine (midazolam or diazepam) and an
opioid (fentanyl or meperidine)
▪ Propofol is becoming increasingly popular for colonoscopies, but it can cause
respiratory depression, so medical team must be prepared to manage this
Inhaled Anesthetics: halothane, isoflurane, desflurane, sevoflurane, nitrous oxide
o Easily vaporized liquid halogenated hydrocarbons, administered as gases
o 1st choice for induction in children
o Used for maintenance of anesthesia
o Concentration is measures as partial pressure or “tension” in inspired air
o Speed of Induction depends on:
▪ Solubility: less soluble GAs equilibrate more quickly with blood and into tissues
(brain)
• Halothane works slower because it is more soluble. Equilibration may
take hours to achieve, meaning longer time and $$ spent in the OR
• Nitrous oxide works faster because it is less soluble
▪ Ventilation rate
• Hyperventilation increases the speed of induction, especially for general
anesthetics with a slow onset
▪ Inspired gas partial pressure (AKA concentration of GA)
• Increased partial pressure of inhaled gas→greater speed of induction
• Fine adjustments in the partial pressure are made by the
anesthesiologist as you go through different stages of surgery
o Minimum Alveolar Concentration (MAC)
▪ The minimum alveolar anesthetic concentration required to eliminate the
response to a painful stimulus in 50% of patients. It is a “population average”
measure of GA potency
▪ When several general anesthetics are mixed, their MAC values are additive
▪ General anesthetics have steep dose-response curves (AKA a narrow
therapeutic window)
▪ General anesthetics have a small therapeutic index (dose that produces toxic
effect (LD50) divided by dose that gives therapeutic effect (MAC))
▪
▪
•
•
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Conditions that change MAC
• Pregnancy decreases MAC (elevated progesterone)
• Elderly people have a decreased MAC (less brain activity)
• Chronic alcoholics have an increased MAC (cross tolerance)
• Acute alcohol poisoning patients have decreased MAC (additive—EtOH
also binds GABA receptor)
Nitrous Oxide
▪ MAC >100%, meaning it is an incomplete anesthetic, and will not be able to
produce adequate analgesia alone. This is why nitrous oxide is commonly used
with other anesthetics to achieve the therapeutic goal.
▪ Good analgesic, no metabolism, with rapid onset and recovery
▪ Elimination of Nitrous oxide:
• Abruptly removing outflow of high concentrations of nitrous oxide can
cause diffusion hypoxia
• Large volume of nitrous oxide can displace O2 in the lungs, which is a
potential problem in compromised patients
• Treat this by giving pure O2 following anesthesia with nitrous oxide
Desflurane
▪ Most rapid onset of action and recovery of the halogenated general anesthetics
▪ Widely used for outpatient surgery
▪ Irritating to the airway in awake patients: causes coughing, salivation, and
bronchospasm
• NOT used as an induction agent—used for MAINTENANCE of anesthesia
Sevoflurane
▪ Most frequently used inhaled agent for induction of general anesthesia
▪ Very low blood:gas partition coefficient with rapid onset of action and recovery
▪ Widely used for outpatient surgery
▪ Not irritating to the airway
▪
o
o
o
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Useful induction agent, especially in children
• Children hate needles, so these inhaled agents are better for them.
Adults typically already have an IV line in place, and parenteral agents
are easy to administer.
o Isoflurane
▪ Medium rate of onset and recovery
▪ Pungent (not used for induction)
▪ Used for MAINTENANCE of GA
o Halothane
▪ First halogenated inhalational anesthetic
▪ Not pungent (used for induction with children, fewer side effects seen in
children)
▪ Medium rate of onset and recovery
▪ Use has declined, although it is inexpensive
▪ Sensitizes the heart to epinephrine-induced arrhythmias
▪ Induces hepatitis in 1/10,000 patients
General Anesthetic Toxicity
o Malignant Hyperthermia occurs when halogenated GA + succinylcholine is used
▪ Reverse this hyperthermia with dantrolene IMMEDIATELY
• Dantrolene interferes with the release of calcium from the sarcoplasmic
reticulum through the SR calcium channel complex
• Malignant hyperthermia is fatal in >50% of cases without dantrolene
• Given by IV at onset of symptoms, when there is an unexpected rise in
CO2 levels
• Also give supportive measures and 100% Oxygen
o Halothane undergoes 40% hepatic metabolism, so postoperative hepatitis can occur
o Halothane can sensitize the heart to Epinephrine and cause arrhythmias
o Nitrous Oxide can cause megaloblastic anemia after prolonged exposure, because it
decreases methionine synthase activity→Vit B12 deficiency
o General anesthetics affect the chemoreceptor trigger zone and brainstem vomiting
center→causes nausea and vomiting
▪ Treat with:
• Odansetron (5HT3 antagonist) prevents nausea and vomiting
• Avoid nitrous oxide
• Use Propofol for induction because it doesn’t cause nausea and
vomiting
• Use ketorolac (NSAID) instead of an opioid for pain
• Droperidol, metaclopromide, dexamethasone
Skeletal Muscle Relaxers/NMJ Blockers: succinylcholine, pancuronium
o Used to:
▪ relax skeletal muscle
▪ facilitate intubation (needed to maintain airway and prevent aspiration)
▪ ensure immobility
o Reversed by quaternary drugs: neostigmine and glycopyrrolate during post op period
▪
•
•
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WOW, congrats for making it this far, that was dense. Next we have cases, questions, and summary
chart at the end. I even typed out explanations for all of them. Let’s do this!
Case 1
EM is a 24-year-old graduate student in organic chemistry. While working in the lab one
morning, he spills a beaker of hydrofluoric acid (HF) in the fume hood. Some of the acid falls on the
fingertips of his left hand. Thinking quickly, he rinses his hand with water and a magnesium sulfate
solution (to chelate toxic fluoride ions). About 10 minutes after the accident the pain is still significant
and he telephones 911 and is transported to the Emergency Department.
The resident notes that the HF has penetrated the nail beds of the affected fingers, and that EM
is in severe pain. She commends him on his timely and appropriate actions, and decides on treatment
with calcium gluconate (another fluoride chelator) to neutralize the remaining HF, in conjunction with a
digital nerve block to reduce the pain. Lidocaine without epinephrine is injected into the fingers,
followed by application of calcium gluconate. By the time his wounds are dressed and covered with
plastic wrap, he cannot feel any sensation in his fingers. Over the next two weeks heals spontaneously
and the pain, now well controlled with ibuprofen, abates. He is able to plunge back into lab work, but his
brush with serious injury affects him in an unforeseen way: he begins to contemplate applying to
medical school.
Q1: What is lidocaine’s mechanism of action? To which broader subclass of local anesthetics does it
belong?
A: Reversibly block Na channels in neurons. It is an amide.
Q2: Why is epinephrine sometimes administered with lidocaine, and why was it not co-administered
in this case?
A: Epinephrine is administered with lidocaine because it prolongs the lidocaine’s action, decreases
systemic toxicity, and decreases local bleeding during surgery. However, epinephrine should NOT be
administered with lidocaine if you are dealing with the extremities, because there is limited circulation,
and will cause hypoxia.
Case 2
Matthew is a 7-year old, 20 kg boy who has been undergoing multidrug chemotherapy for aggressive
osteosarcoma of his right femur. The time has now come for a surgical resection.
8:00 PM (night before the operation): Dr. Snow, the anesthesiologist, provides reassurance and revisits
the importance of fasting after midnight to prevent aspiration of gastric contents while under general
anesthesia.
6:30 AM: Matthew clings to his mother and appears anxious, cachectic, and in some pain. His vital signs
are stable with an elevated pulse of 120 and a blood pressure of 110/75. An oral dose of midazolam is
given to relieve anxiety and to allow Matthew to separate from his parents.
7:00 AM: Dr. Snow injects a small amount of lidocaine subcutaneously before inserting an intravenous
catheter (which he carefully conceals from Matthew until the last possible moment). Through the
catheter, Dr. Snow delivers an infusion of morphine sulfate for analgesia.
7:30 AM: Dr. Snow rapidly induces anesthesia with an intravenous bolus of 60 mg (3 mg/kg) of
thiopental. Within 45 seconds Matthew is in a deep anesthetic state. The doctor adds a dose of
intravenous succinylcholine to facilitate endotracheal intubation, and Matthew is placed on artificial
respiration.
*NOTE: thiopental is no longer available. It was used for surgery but was also used as 1 of 3 drugs for
lethal injections. It is not made in USA and cannot be imported.
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7:32 AM: A mixture of inhaled general anesthetics consisting of 2% isoflurane, 50% nitrous oxide, and
48% oxygen is provided through the ventilator to maintain the anesthetic state.
7:50 AM: Matthew shows no response, either through movement or increased sympathetic tone (e.g.
increased heart rate, increased blood pressure), to the first surgical incision.
8:20 AM: Dr. Snow notices with a start that Matthew’s pulse has fallen from 55 and his blood pressure
to 85/45. Berating himself for forgetting to turn down the inspired partial pressure of the anesthetic as
its mixed venous partial pressure increased, Dr. Snow reduces the inspired isoflurane level to 0.8% while
keeping the nitrous oxide level at 50%. Within 14 minutes, Matthew’s pulse and blood pressure
rebound.
12:35 PM: After a long surgery, Dr. Snow stops the isoflurane and nitrous oxide and turns on pure
oxygen for a few minutes.
12:45 PM: In less than 10 minutes, Matthew is breathing spontaneously and is able to respond to
questions, although he is still somewhat groggy. Matthew’s parents are relieved to find him awake and
cheerful after more than 5 hours of anesthesia.
Q1: Why is it necessary to reduce the inspired partial pressure of isoflurane some minutes into the
procedure (as Dr. Snow initially neglected to do)?
If the partial pressure of inhaled anesthetics is too high, it will cause respiratory depression with
decreased cardiac output and blood pressure.
Q2: What are the advantages of using a mixture of two anesthetics (in this example, nitrous oxide and
isoflurane) instead of just one or the other?
Nitrous oxide’s MAC>100% indicates that it alone cannot produce sufficient analgesia. Since MAC values
are additive, nitrous oxide can be mixed with isoflurane to achieve full analgesic effect.
Q3. Why did Dr. Snow give pure oxygen for a few minutes following the cessation of anesthetic
administration?
Following the withdrawl of nitrous oxide, diffusion hypoxia occurs, which can be prevented by
administering pure oxygen immediately after cessation of anesthesia.
Questions
Question 1: A patient has a documented severe allergic reaction to procaine. Which of the following is
also a member of the same class, and so would be the most likely to provoke an allergic or anaphylatic
reaction if given to this patient?
A. Bupivacaine
B. Lidocaine
C. Mepivacaine
D. Prilocaine
E. Tetracaine
Answer: E, Tetracaine. We are looking for an ester, because those sometimes cause allergic reactions,
and the rest of the choices are amides.
Question 2: A patient who is going to have an uncomfortable colonoscopy is pretreated with i.v.
midazolam & fentanyl. Both drugs cause generalized CNS depression & desired sedation. Which of the
following is the main effect for which midazolam was used as supplement?
A. Causes analgesia to supplement sedation by fentanyl
B. Causes amnesia of short duration and anxiety relief
C. Counteracts the fentanyl-induced increase in heart rate
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Pharm Independent Study: Anesthetics
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D. Prevent fentanyl-induced increase in BP
E. Prevents fentanyl-induced ventilatory depression
Answer: B, axiety relief. Medazolam is a benzodiazepine that is given to reduce anxiety before surgery.
Question 3: A young woman is taken to the Tulane ED by some of her friends. It seems they were at a
bar in the FQ & someone slipped something into her beer, the first and only one she consumed that
night. She is now unresponsive & has little recall of what happened between the time she finished her
drink & now. Someone overheard another bar patron talking about “roofies”. Being knowledgable about
your pharmacology, you suspect her drink was spiked with rohypnol (flunitrazepam). Assuming your
guess is correct, which of the following drugs would most likely reverse rohypnol’s effects?
A. Diazepam
B. Flumazenil
C. Ketamine
D. Naloxone
E. Naltrexone
Answer: B, flumenazil. Flumenazil is the drug used to reverse benzodiazepine toxicity.
Flunitrazepam/rohypnol/roofies is a benzodiazepine. This wasn’t on our drug list but its certainly worth
knowing.
Question 4: A 55 yr old man undergoes open heart surgery. He receives several drugs for preanesthesia
care, intubation, interoperative skeletal muscle paralysis & a mixture of inhaled anesthetics to produce a
balanced anesthesia. Toward the end of the procedure he develops hyperthermia, hypertension,
hyperkalemia, tachycardia, muscle rigidity & metabolic acidosis. Which of the following drugs is most
likely to have participated in this reaction?
A. Fentanyl
B. Halothane
C. Ketamine
D. Midazolam
E. Propofol
Answer: B, halothane. Malignant hyperthermia and CV toxicity occurs when halothane is used with
succinylcholine. It can be reversed using dantrolene.
•
•
•
SUPER HIGH YIELD SUMMARY OF THIS WHOLE LECTURE
For adults: use Propofol to induce general anesthesia
o Advantages: rapid onset, rapid recovery. Disadvantage: hypotension.
o Propofol is preferred over inhaled anesthetics that have a pungent odor and cause
nausea/vomiting
For patients with hemodynamic instability:
o Use Etomidate to induce general anesthesia (little change in BP, HR, CO)
o Use Ketamine to induce general anesthesia (increases BP, HR, CO)
▪ Causes profound analgesia and amnesia, with reflexes intact
For children: inhalation is preferred because of fear of needles
o Disadvantage: takes longer to induce anesthesia with inhalation
o Use Sevoflurane +/- nitrous oxide to achieve loss of consciousness within 1 minute with
7-8% by face mask (not pungent)
o Pungent anesthetics: isoflurane, desflurane
o Halothane side effects: epinephrine-induced arrhythmias, hepatotoxicity, myocardial
depression, slow onset and slow recovery
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Finally, here is a summary chart of what I think is most important!
Local Anesthetics: reversibly block Na channels
Amides: can cause liver toxicity
Lidocaine
Medium action
Bupivacaine
Long action
Esters: PABA metabolite causes allergic reactions
Procaine
Short action
Tetracaine
Long action
Benzocaine, Cocaine
Surface action
General Anesthetics: enhanced GABA inhibitory effect, inhibits NMDA receptors
Inhalational: best for children
Nitrous oxide
Works quickly because it is less soluble
Incomplete analgesic: requires an additional drug
Removal causes diffusion hypoxia, so give O2 after cessation
Causes megaloblastic anemia
Desflurane
Irritates airway, so not used for induction
Used for maintenance of anesthesia
Halothane
Works slowly because it is more soluble
Used for induction of anesthesia in children
Causes epinephrine-induced arrhythmias
Rarely causes hepatitis
Sevoflurane
Rapid onset of action and recovery
Not irritating to airway
Used to induce anesthesia in children
Isoflurane
Pungent, used for maintenance of anesthesia
Parenteral (IV)
Propofol
Most popular choice for adults: rapid recovery, antiemetic
Disadvantage: hypotension
Etomidate
Used as a supplement for short procedures
Little change in BP, HR, CO; causes nausea/vomiting
Ketamine
Used for patients in shock: increases BP, HR, CO
“David After Dentist” psychomimetic reactions
Adjunct Drugs
Benzodiazepines
Used to reduce anxiety before an operation
(Midazolam)
Reverse toxicity with flumazenil
Opioids (morphine,
Inhibits respiration
fentanyl)
Very addictive
Skeletal Muscle Relaxers
Ensures immobility and facilitates intubation
(succinylcholine,
Reverse toxicity with neostigmine and glycopyrrolate
pancuronium)
Other Drugs
Dantrolene
Reverses malignant hyperthermia causes by an inhaled anesthetic +
succinylcholine
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