General anesthetics

Question 1

Inhalation anesthetics

Answer 1

Maintenance
Nitrous oxide
Halothane (PROTOTYPE)
Sevoflurane
Isoflurane
Desflurane
Continuously inhaled. Requires monitoring, special equipment, and ENDOTRACHEAL intubation
Recovery = exhalation
Narrow therapeutic index (2-4)
ETHER bonds
Mechanism: reversibly interact with hydrophobic sites of specific membrane proteins (signal transduction pathways). evidence: chiral anesthetics.
Targets: GABA-A, glycine receptor activity.
Inhibit glutamate, nicotinic, 5-HT3 receptors.
Voltage gated ion channels (Na+, K+): inhibit AP propagation
GPCRs
Equilibrium: exhaled = inhaled
Uptake affected by: BLOOD SOLUBILITY, ALVEOLAR BLOOD FLOW, PARTIAL PRESSURE

Question 2

Intravenous anesthetics

Answer 2

Induction
Methohexital (barbituate)
Etomidate (non-barb)
Propofol (non-barb)
Ketamine (non-barb) 
Single IV dose
Requires monitoring. No special equipment. 
Rapid onset
Depth/duration not as well controlled 
--metabolism, renal clearance

Question 3

Nitrous Oxide

Answer 3

Inhalation
Higher partial pressure = less soluble. 
Low gamma (partition) 
Faster inducion 
HIGH MAC (needs a lot to do work) 
Low potency. Cannot produce anesthesia by itself.

Question 4

Halothane

Answer 4

Inhalation
Prototype
Low partial pressure = high solubility = bigger blood compartment
MAC = .77

Question 5

Sevoflurane

Answer 5

Inhalation
Induction in kids
MAC = 2.0

Question 6

Isoflurane

Answer 6

Inhalation

MAC = 1.15

Question 7

Desflurane

Answer 7

Inhalation
Lowest partition (gamma)
Fastest induction
High MAC (6.00)

Question 8

Methohexital

Answer 8

Intravenous

Barbituate

Question 9

Etomidate

Answer 9

Intravenous

Non-barbituate

Question 10

Propofol

Answer 10

Intravenous

Non-barbituate

Question 11

Ketamine

Answer 11

Intravenous

Non-barbituate

Question 12

General anesthesia

Answer 12

Reversible CNS depression
Lose response to external stimuli
Permit surgical/noxious procedures

Question 13

Dissociative sedation

Answer 13

Trance-like cataleptic state
Analgesia (ketamine) and amnesia
Retain airway reflexes and CV stability

Question 14

Ideal general anesthetics

Answer 14

Anesthesia
Analgesia/anxiolytic
Amnesia
Muscle relaxation
Inhibit reflex responses to trauma
Rapid
Little/no systemic toxicity 
No anesthetic agents have all of these. Need adjuncts.

Question 15

Stages of anesthesia

Answer 15

1. Conscious, but drowsy. Variable analgesia.
2. Excitement and delirium. Unconscious. Reflex to pain. Irregular respiration. RECOVERY from inhalation anesthesia.
3. Surgical anesthesia
4. Medullary depression. Death.
   Induction –> Maintenance –> Emergence

Question 16

CV effects during anesthesia

Answer 16

Decreased mean arterial pressure
Systemic vasodilation
Myocardial suppression 
Blunted baroreceptor reflex
Reduced sympathetic tone

Question 17

Respiratory effects during anesthesia

Answer 17

Reduced/eliminated ventilatory drive
Assisted ventilation needed
Lost gag/cough reflex
Reduced LES tone (endotracheal intubation)

Question 18

Temperature effects during anesthesia

Answer 18

Hypothermia (<36C)

Question 19

effects during anesthesia (during/after emergence)

Answer 19

N/v (stimulation of chemoreceptor zone) (treat: 5-HT3 antagonists)
return of sympathetic tone (tachy, HTN)
Shivering (tx: meperidine)

Question 20

Partial pressure of inhaled anesthetics

Answer 20

% of total atmospheric pressure
Index of the molecule to leave liquid phase into gaseous phase
More water soluble = lower partial pressure
Increased PP: likes to stay in blood
Ex. High PP: NO. Low PP: halothane.

Question 21

Blood solubility of inhaled anesthetics

Answer 21

Blood:gas partition coefficient
Gamma = [blood] / [gas]
LOW BLOOD SOLUBILITY = MORE RAPID INDUCTION
–counter-intuitive

Question 22

“Second gas” effect

Answer 22

Bulk uptake of an agent can “pull” more agent into lung
Low solubility agents with high partial pressures (ex NO)
Deliver second gas with NO, the second gas will be delivered faster
Only good for first breath

Question 23

Tissue solubility

Answer 23

Lipid content and rate of perfusion

Brain is highly lipophilic. 3x the flow of other tissues

Question 24

Pulmonary ventilation rate

Answer 24

Maintains alveolar tension. Hastens induction.

Important for high blood solubility.

Question 25

Potency of inhalation anesthetics

Answer 25

Minimum concentration required to induce anesthesia.
Minimum Alveolar Concentration (MAC)
1 MAC = partial pressure that prevents movement in 50% of adults in response to pain
NOT RELATED TO INDUCTION RATE
1.3 MAC is ED95 (usual for surgery)
Additive when co administered