Inhalational anesthetics

Question 1

Nitrous oxide characteristics

Answer 1

Fast acting, non irritating

Analgesic, but not Muscle relaxing

Minimal/no CNS or Respiratory depression

Not irritating, and very cheap.
Lowers the MAC of other inhalation anesthetics, used as an adjunct for induction and maintenance.

Question 2

Nitrous oxide kinetics

Answer 2

Very fast acting, Partition coefficient 0.47.
Very high MAC 105%

No metabolism excreted unchanged

Question 3

Nitrous oxide SEs

Answer 3

Diffusional hypoxia - MAC is so high that it can lower alveolar oxygen and cause hypoxia

Increased pressure of abdomen, thorax, inner ear (from diffuse into these cavities and high MAC)

Spontaneous Aboriton

Question 4

Halothane kinetics

What is unique about halothanes structure

Answer 4

MAC 0.8%

Part coeff 2.3

Halothane is NOT an ether, like all the rest of the inhalational anesthetics ending in ‘-ane’

Question 5

Halothane uses and Pros

Answer 5

Cheap, potent, widely used outside US

Causes muscle rlaxation
Non-irritating

Question 6

Halothane SEs and Cons

Answer 6

Cumulative hepatotoxicity
DELAYED from between 2 days and 1 month after surgery
-Potential severe acute necrotic hepatitis

Simultaneous Cardiac suppression AND sensitization to catecholamines
–Can cause arrythmias

Increases cerebral flow and intracranial pressure

Malignant hyperthermia.

Question 7

Isofluorane Kinetics

Answer 7

MAC 1.4

pc: 1.4

Question 8

What is the partition coefficent equation

Answer 8

Blood concentration / Gas concentration

at equal partial pressures.

Question 9

Isofluorane uses and pros

Answer 9

Only for maintenance, causes airway irritation

Cheap, still widely used.

Lowers ICP much less than the other agents.

Question 10

Isofulorance cons

Answer 10

Airway irritation

Minor cardiac suppression and sensitization, but still has potential for arrythmias

Minor resp suppression

Minor increase in ICP

Question 11

Enflurane kinetics

uses

Answer 11

MAC 1.7
Part 1.8

Non irritating and faster than halothane.

Used for rapid induction.

Question 12

Enflurane SEs

Answer 12

Kidney toxicity

Can cause seizures

Cardiac and Respiratory depression

Maligfnant hypertension

Coronary steal syn.

Question 13

Methoxyfluorane kinetics and uses

Answer 13

MAC 0.16
Part. 12%

Slow but potent. Used for maintenance

Question 14

Methoxyfluorane SEs

Answer 14

Just kidney toxicity.

Question 15

Sevoflurane kinetics

Answer 15

MAC 2.0

Part 0.69

Question 16

Sevoflurane pros and uses

Answer 16

No liver damage
No kidney damage
No respiratory irritation AND faster induction that halothane or enfluorane

Is now the most widely used inhalational agent.

Question 17

Cons

Answer 17

Cardiac depression, decreases MAP and CO

Potential for nephrotoxic fluoride metabolite if low carrier gas flow is used.
Need to have flow rate high enough to exhale the metabolite before toxicity builds up.

Question 18

Which agents can cause malignant hyperthermia

Answer 18

Halothane
Enflurane
Succinylcholine

Question 19

Symptoms of malignant hyperthermia

Answer 19

Fever
Muscle rigidity
Tachycardia

Can lead to Rhabdomyolysis

• Muscle ATP depletion and cell death
• Hyperkalemia
• Myoglobeniemia
• Elevated Creatinine
• Potential kidney damage

Question 20

Mechanism of the inhalational anesthetics

Answer 20

Exact mechanism unclear: Increases neuronal threshold for firing
Sedation by actions on the thalamus
Amnesia by actions in the hippocampus

Lipid theory - older “Overton-Meyer theory”; drug must be lipophilic to have effect + lipophilicity is directly correlated to effect; modifies neuronal cell membrane → non-specific interactions causing receptor/ion channel function changes

Protein theory - specific interaction of anesthetics with certain ion channels/Rs; stimulate GABAA/K+ channels and inhibit NMDA/nAChR

Potentiation of glycine and GABA signaling,
particularly increased GABA-A receptor activity.

Question 21

What is the MAC

Answer 21

MAC: “minimal alveolar concentration”;
% of drug in the gas that is needed to produce surgical anesthesia in 50% of patients; inversely proportional to potency (1/MAC)

Question 22

What are the stages of anesthesia/narcosis

Answer 22

Analgesia - loss of pain sensation + eventually consciousness

Excitation - cortical neurons sensitive to anesthetics → cortical neurons inhibited → subcortical neurons disinhibited; patient may wake up and run away

Tolerance / Surgical Anesthesia - ↓ pain response and immobility; 4 subphases, phase 2 best for surgery

Asphyxia

Question 23

Types of Anesthesia:

Answer 23

“Balanced Anesthesia” - uses mostly IV drugs to induce anesthesia + accelerate the excitation phase with inhaled anesthetics to maintain anesthesia
Total Inhalation Anesthesia - mostly used in children
Total IV Anesthesia (TIVA) - usually used in smaller interventions