General Anesthetics

Question 1

Components of Anesthetic State

Answer 1

Amnesia
Unconsciousness
Analgesia
Immobility in response to noxious stimuli

Question 2

Define MAC

Answer 2

Minimal alveolar concentration –> Measured by concentration of anesthetic in the end-tidal expired air (correlates well with concentration at the site of action – brain)

Question 3

Molecular Targets of Anesthetics

Answer 3

GABA(A) receptors
NMDA receptors
Other membrane associate proteins

Question 4

Stages of General Anesthesia

Answer 4

1. Pre-medicatoin
2. Induction
3. Maintenance

Question 5

Parenterally administered Anesthetic
Barbiturate
Activates GABA(A) receptors; used to induce anesthesia; 1/2 life = 12 hours (hangover)

Answer 5

Sodium Thiopental

Question 6

SE of Sodium Thiopental

Answer 6

CNS depression (decrease O2 demand, decrease BF, decrease intracranial P); CV vasodilator; Respiratory depression

Question 7

Most commonly used anesthetic in the US; GABA(A) mechanism; Used to induce and maintain anesthesia; anti-emetic; Half-life in body: 3.5 hrs (less hangover)

Answer 7

Propofol

Question 8

SE of Propofol

Answer 8

Pain on injection; Can cause initial excitation on induction; CNS effects; CV Effects more severe reduction in BP than thiopental and depression of myocardial contractility; Respiratory: more depression than Thiopental

Question 9

Used to induce anesthesia in patients at risk for hypotension

Answer 9

Etomidate

Question 10

SE of Etomidate

Answer 10

Pain on injection, myoclonus; N/V; Suppression of adrenocortical response to stress – only used to induce anesthesia in patients with hemodynamic problems

Also CNS SE; CV: less than thiopental; Respiratory: less than thiopental

Question 11

Produces dissociative anesthesia; NMDA receptor antagonist; No effect on respiration

Answer 11

Ketamine

Question 12

SE of Ketamine

Answer 12

Nystagmus, salivation, lacrimation, increase muscle tone and spontaneous movement;
Increased intracranial pressure d/t increased cerebral blood flow;
Emergence delirium; Hypertension (sympathomimentic)

Question 13

What populations is Ketamine useful for?

Answer 13

Patients with bronchospasm; Children undergoing short, painful procedures

Question 14

Short acting benzodiazepine; GABA(A) activator; Used for conscious sedation, anxiolysis, amnesia during short procedures; Used preoperatively to decrease anxiety

Answer 14

Midazolam

Question 15

How does Midazolam differ from Sodium Thiopental?

Answer 15

Slower induction and longer duration; Metabolized by hydroxylation to active metabolite

Question 16

SE of Midazolam

Answer 16

Respiratory depression and arrest (IV); Use with caution in patients with NM disease, Parkinson’s, Bipolar; CV effects similar to Thiopental

Question 17

What does it mean if a anesthetic has a low blood:gas PC?

Answer 17

1. Need high amounts in inspired air
2. Induction is quick (equilibrium is reached quickly)
3. Recovery will be quick (drug moves out of blood into gas readily)

Question 18

What does it mean if a anesthetic has a high blood:gas PC?

Answer 18

1. Need less in inspired air

2. Induction and recovery are slow (equilibria is reached slowly)

Question 19

What does it mean if an anesthetic has a high fat:blood PC?

Answer 19

Half-life will be long (hang over) d/t slow release into blood; enough gets into brain to make the patient feel sleepy

Question 20

What are some factors that affect induction with a gaseous anesthetic?

Answer 20

1. Anesthetic concentration in the inspired air
2. Pulmonary Ventilation
3. Pulmonary BF
4. Arteriovenous concentration gradient

Question 21

When is anesthesia achieved with gaseous anesthetics?

Answer 21

Anesthesia is achieved when the brain partial pressure is equal to MAC

Question 22

How does elimination of the gas occur?

Answer 22

Reverse of induction: gas moves from blood into inspired air
Rate of elimination is dependent upon the blood:gas partition coefficient (lowest eliminated fastest)
Gas needs to get into the blood to be eliminated

Question 23

Moderate blood:gas PC; Excreted unchanged in expired air

Answer 23

Isoflurane

Question 24

What is Isoflurane used for?

Answer 24

Can be used to induce and maintain; but mostly for maintenance

Question 25

SE of Isoflurane

Answer 25

Airway irritant, coughing, decreases tidal volume and increases respiratory rate; CV: myocardial depression, decreases BP, arrythmias, cerebral vessel vasodilation

Question 26

Very low solubility in blood; induction and recovery are rapid; Excreted unchanged in expired air

Answer 26

Desflurane

Question 27

What are the clinical uses of Desflurane?

Answer 27

Outpatient surgeries/maintenance; Skeletal muscle relaxation

Question 28

SE of Desflurane

Answer 28

CV; Respiratory: worse irritant, can produce bronchospasm

Question 29

Very low blood: gas partition coefficient; 5% of administered does is metabolized to fluoride ion in the liver; Degraded to compound A by absorbents

Answer 29

Sevoflurane

Question 30

What are the clinical uses of Sevoflurane?

Answer 30

Very popular; Inpatient and outpatient, can be used to induce and maintain in children and adults; NOT a respiratory irritant

Question 31

Very insoluble in blood, rapidly equilibrates; Uptake from air results in increased concentration of other anesthetics; Useful for induction

Answer 31

Nitrous Oxide

Question 32

Why do you patients need to breathe 100% O2 during emergence when given N2O?

Answer 32

N2O can dilute oxygen

Question 33

What are some clinical uses of N2O?

Answer 33

Weak anesthetic; Good for sedation and analgesia; Used together with other inhaled anesthetics to reduce dose needed

Question 34

What is N2O CI for?

Answer 34

Pneumothorax