Anesthesia Fast Facts

Anesthesia Notes for Surgery Rotations

Mallampati Classification

Evaluation of the oropharynx is accomplished by asking the patient to open his mouth and stick out his tongue (but not by vocalizing).

Class I: Entire uvula and tonsillar pillars visible

Class II: Tip of uvula and pillars hidden by tongue

Class III: Only soft palate visible

Class IV: Only hard palate visible

ASA Physical Status Classification

ASA-I: Healthy patient with no systemic disease

ASA-II: Mild systemic disease, no functional limitations

ASA-III: Moderate to severe systemic disease, some functional limitations

ASA-IV: Severe systemic disease, incapacitating, and a constant threat to life

ASA-V: Moribund patient, not expected to survive > 24 hours without surgery

ASA-VI: Brain-dead patient undergoing organ harvest

E: Added when the case is emergent

Commonly Used Medications

1. Volatile Anesthetics

a. Halothane

i. Positives

1. Cheap

2. Nonirritating so can be used for inhalation induction

ii. Negatives

1. Long time to onset/offset

2. Significant Myocardial Depression

3. Sensitizes myocardium to catecholamines

4. Association with Hepatitis

b. Isoflurane

i. Positives

1. Cheap

2. Excellent renal, hepatic, coronary, and cerebral blood flow preservation

ii. Negatives

1. Long time to onset/offset

2. Irritating so cannot be used for inhalation induction

c. Sevoflurane

i. Positives

1. Nonirritating so can be used for inhalation induction

2. Extremely rapid onset/offset

ii. Negatives

1. Expensive

2. Due to risk of “Compound A” exposure must be used at flows >2 liters/minute

3. Theoretical potential for renal toxicity from inorganic fluoride metabolites

d. Desflurane

i. Positives

1. Extremely rapid onset/offset

ii. Negatives

1. Expensive

2. Stimulates catecholamine release

3. Possibly increases postoperative nausea and vomiting

4. Requires special active-temperature controlled vaporizer due to high vapor pressure

5. Irritating so cannot be used for inhalation induction

2. Nitrous Oxide

a. Positives:

i. Decreases volatile anesthetic requirement

ii. Dirt cheap

iii. Less myocardial depression than volatile agents

b. Negatives

i. Diffuses freely into gas filled spaces (bowel, pneumothorax, middle ear, gas bubbles used during retinal surgery)

ii. Decreases FiO2

iii. Increases pulmonary vascular resistance

iv. Combustible like oxygen

3. IV Anesthetics – All have very rapid onset (<1 minute) and short duration (5-8 minutes)

a. Thiopental

i. Positives

1. Excellent brain protection

2. Stops seizures

3. Cheap

ii. Negatives

1. Myocardial depression

2. Vasodilation

3. Histamine release

4. Can precipitate porphyria in susceptible patients

b. Propofol

i. Positives

1. Prevents nausea/vomiting

2. Quick recovery if used as solo anesthetic agent

ii. Negatives

1. Pain on injection

2. Expensive

3. Supports bacterial growth

4. Myocardial depression (the most of the four)

5. Vasodilation

c. Etomidate

i. Positives

1. Least myocardial effect of IV anesthetics

ii. Negatives

1. Pain on injection

2. Adrenal suppression (? significance if used only for induction)

3. Myoclonus

4. Nausea/Vomiting

d. Ketamine

i. Positives:

1. Works IV, PO, PR, IM – good choice in uncooperative patient without IV

2. Stimulation of SNS  good for hypovolemic trauma patients

3. Often preserves airway reflexes

ii. Negatives

1. Dissociative anesthesia with postop dysphoria and hallucinations

2. Increases ICP/IOP and CMRO2

3. Stimulation of SNS  bad for patients with compromised cardiac function

4. increases airway secretions

4. Local Anesthetics

a. Esters

i. Metabolized by plasma esterases

1. one metabolite is PABA, which can cause allergic reactions.

a. Patients with “allergy to novacaine” usually do well with amides for this reason.

ii. All have only one “i” in their name, eg. Procaine, Tetracaine

b. Amides

i. Metabolized by hepatic enzymes

ii. All have at least two “i”s in their name, eg. Lidocaine, Bupivacaine

c. With or without epinephrine

i. Use of local anesthetics with epinephrine cautioned in areas of the body with a terminal blood supply that could be impaired by

vasoconstriction

1. Fingers, toes, penis, nose, and ears

5. Opioids

a. Morphine

i. long acting

ii. histamine release

iii. renally excreted active metabolite with opiate properties therefore beware in renal failure

b. Dilaudid

i. long acting

ii. no active metabolites

iii. no histamine release

iv. same onset/duration as morphine

c. Demerol

i. Euphoria

ii. stimulates catecholamine release, so beware in patients using MAOI’s

iii. renally excreted active metabolite associated with seizure activity

1. beware in renal failure

d. Fentanyl/Alfentanil/Sufentanil

i. low doses produce brief effect, but larger doses are long acting

ii. increased incidence of chest wall rigidity vs. other opiates

iii. no active metabolites

e. Remifentanil

i. almost instantaneous onset/offset of action due to metabolism by plasma esterases

ii. must be given as continuous infusion

iii. significant incidence of chest wall rigidity and nausea/vomiting

6. Muscle Relaxants

a. Depolarizing

i. Succinylcholine

1. inhibits the postjunctional receptor and passively diffuses off the membrane, while circulating drug is metabolized by plasma

esterases.

2. Associated with increased ICP/IOP

3. muscle fasciculations and postop muscle aches

4. triggers Malignant Hyperthermia

5. increases serum potassium especially in patients with burns, crush injury, spinal cord injury, muscular dystrophy or disuse

syndromes

6. Rapid and short acting.

b. Nondepolarizing

i. Many different kinds, all ending in “onium” or “urium”

ii. Each has different site of metabolism, onset, and duration making choice depend on specific patient and case

iii. Examples

1. Pancuronium

a. Slow onset

b. long duration

c. tachycardia due to vagolytic effect

2. Cisatracurium

a. Slow onset

b. intermediate duration

c. Hoffman (nonenzymatic) elimination so attractive choice in liver/renal disease

3. Rocuronium

a. Fastest onset of nondepolarizers making it useful for rapid sequence induction

b. intermediate duration

7. Reversal Agents/Anticholinergics

a. Reversal Agents

i. all are acetylcholinesterase inhibitors

1. allow more acetylcholine to be available to overcome the neuromuscular blocker effect at the nicotinic receptor

2. also causing muscarinic stimulation

ii. Examples

1. Neostigmine

a. shares duration of action with glycopyrrolate (see below)

2. Edrophonium

a. shares duration of action with atropine (see below)

3. Physostigmine

a. crosses the BBB

b. useful for atropine overdose

b. Anticholinergics

i. given with reversal agents to block the muscarinic effects of cholinergic stimulation

ii. excellent for treating bradycardia and excess secretions

iii. Examples

1. Atropine

a. used in conjunction with edrophonium

b. crosses the BBB causing drowsiness

i. maybe bad at end of surgery for reversal

c. some use as premed for all children since they tend to become bradycardic with intubation and produce copious drool

2. Glycopyrrolate

a. used in conjunction with neostigmine

b. does not cross the BBB

Malignant Hyperthermia

1. Subclinical myopathy in which general anesthesia triggers an uncontrollable contraction of skeletal muscle that leads to a life-threatening hypercatabolic state and increase in body temperature.

2. The disease is primarily autosomal dominant

a. Some cases <10% are due to a spontaneous mutation

3. Mutations in receptors (especially ryanodine receptor type 1) predispose to volatile anesthetic agents or succinylcholine causing an accumulation of intracellular calcium in skeletal muscle that leads to its overactivation and hypermetabolism.

4. In the acute setting, diagnosis is based mainly on clinical presentation and end-tidal capnography, which reveals an increase in end-tidal CO2

a. Tachycardia

b. Tachypnea

c. Cyanosis

d. Rigidity

5. Immediate treatment measures involve stopping the triggering agent and administration of dantrolene.

a. Hyperventilate the patient

b. 100% FiO2

c. Get them off the OR table ASAP!!!