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Nervous System IV > General Anesthetics > Flashcards

General Anesthetics Flashcards

1
Q

Minimum Alveolar Concentration (MAC)

A

A measure of anesthetic potency

1.0 MAC is defined as the minimal alveolar concentration of anesthetic which produces insensitivity to painful stimulation in 50% of patients

MAC is inversely proportional to potency (Potency = 1/MAC)

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2
Q

How do volatile anesthetics work?

A

Volatile anesthetics partition into the lipid bilayer of the nerve cell membrane, interacting with hydrophobic pockets in various membrane proteins including:

GABA-A receptor - increases duration of IPSPs
Glycine receptor - potentiates inhibitory Cl- influx
nAChR receptor - decreases CNS excitation
TASK-1 K+ channels - depresses neuronal excitability

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3
Q

Nitrous Oxide - Potency and Uses

A

Low Potency - MAC of 105% means that its impossible to achieve surgical anesthesia with N2O alone

Used as an adjunctive anxiolytic/analgesic in balanced anesthesia

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4
Q

Balanced anesthesia

A

Nitrous oxide + Barbiturate + Opioid

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5
Q

N2O Concentration Effect

A

Because of its high MAC, N2O is administered at high % inspired air (up to 75%); the large volume of N2O taken out of the lung into the blood sucks more gas into the lung by negative partial pressure effect causing faster than expected uptake

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6
Q

N2O Diffusion Hypoxia Effect

A

When anesthetic administration is terminated the large N2O volume leaving the blood expands the lung and dilutes alveolar O2 concentration, causing hypoxia

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7
Q

N2O Second Gas Effect

A

Occurs with concurrent administration of N2O and another gaseous anesthetic; the huge volume uptake of N2O sucks more of both gasses into the lung increasing the rate of uptake of the second agent over its expected value alone

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8
Q

Which hypothetical anesthetic agents are NOT used clinically?

A

Xenon

Diethyl Ether - flammable, excessive respiratory respirations, slow induction and recovery

Chloroform - risk of cardiac arrhythmias and hepatotoxicity

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9
Q

Halothane - Advantages

A

Relatively low blood : gas partition coeffcient leading to efficient induction and recovery

Moderate-high potency

Non-irritant (reduced respiratory secretions)

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10
Q

Halothane - 3 major risks

A
  1. Respiratory / cardiovascular failure
  2. Hepatotoxicity
  3. Malignant Hyperthermia
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11
Q

Halothane-induced hepatotoxicity

A

Occurs in 1/10,000 patients with death secondary to hepatic failure in 50%

Presents as fever, anorexia, nausea, and vomiting developing 2-5 days after anesthesia

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12
Q

Malignant Hyperthermia

A

Occurs in patients with inherited mutations in skeletal muscle RyRs upon administration of Halothane

Presents as rapid onset muscle rigidity and fever

Treated with Dantrolene, which causes muscle relaxation by blocking Ca2+ release from the RyR

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13
Q

Flourinated ether anesthetics - 4 agents

A

Enflurane
Isoflurane
Desflurane
Sevoflurane

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14
Q

Isoflurane

A

Most widely used inhalational anestetic

Potent with rapid induction and recovery; good muscle relaxant

Less risk of hepatotoxicity, renal toxicity, and seizures

Disadvantage: Pungent odor

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15
Q

Enflurane

A

Excellent analgesic with fast induction and recovery; good muscle relaxant

Lower hepatotoxocity than halothane but higher than isoflurane; can trigger seizures

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16
Q

Desflurane

A

Rapid onset and recovery; not hepatotoxic

Not suitable for induction due to pungent odor, irritation, and coughing; contraindicated in patients with risk of malignant hyperthermia

17
Q

Sevoflurane

A

High potency; MAC = 2%
Rapid onset / recovery
Does not cause coughing or airway irritation; therefore suitable for induction

Major disadvantage is renal toxicity

18
Q

Uptake: Phase I

A

Lung factors

Rate of increase in partial pressure of anesthetic gas in alveoli and pulmonary capillary blood is proportional to the rate of ventilation

19
Q

Uptake: Phase II

A

Uptake by blood from alveoli determined by:

  1. Solubility of anesthetic agent in blood - lower solubility causes faster approach to equilibrium
  2. Pulmonary blood flow - increased CO slows the rate of uptake because the blood has less time to equilibrate with the alveoli
20
Q

Anesthetic solubility

A

Determined by the blood:gas partition coefficient

The higher the anesthetic solubility in blood, the slower the approach to equilibrium and the slower the induction of anesthesia

Ex Halothane (more soluble) exhibits a slower induction than N2O (less soluble)

21
Q

Uptake: Phase III

A

Uptake from arterial blood to brain depends on:

  1. Solubility of anesthetic gas in tissue, expressed as the tissue:blood partition coefficient; ~1 for lean tissues (brain) and > 1 for fatty tissues
  2. Tissue blood flow - increased blood flow causes faster uptake of anesthetic within tissue
  3. Partial pressure of anesthetic in blood and tissues - initially high but decreases as concentrations equilibrate
22
Q

Uptake: Phase IV

A

Tissue distribution depends on vascularization and tissue:blood solubility

Vessel-rich group (brain, heart, kidney, etc,) exhibit fast uptake due to good perfusion

Muscle & skin exhibit uptake over 2-4 hours due to relatively less perfusion

Fat exhibits slow uptake due to high lipid solubility of anesthetic agents and low perfusion; fat serves as a huge storage resevoir for anesthetic

23
Q

Stages of general anesthesia

A

Stage I: Analgesia
Stage II: Excitement, delirium
Stage III: Surgical anesthesia
Stage IV: Medullary paralysis

24
Q

Planes of Stage III Anesthesia

A

Plane I: Regular, metronomic respirations
Plane II: Onset of muscular relaxation, fixation of pupils
Plane III: Complete muscular relaxation, depressed intercostal excursion during respiration
Plane IV: Diaphragmatic breathing, dilated pupils

25
Q

Characteristics of Stage IV Anesthesia

A

Respiratory failure
Circulatory Failure
Death within minutes

26
Q

Thiopental

A

Ultra short-acting barbituate; potentiates GABA-A receptor activity, prolonging IPSP duration and depressing CNS excitability

High lipid solubility leads to rapid-on rapid-off effect; good for induction of anesthesia

Major disadvantage is disorientation

27
Q

Ketamine

A

NMDA Glutamate receptor antagonist

Produces dissociative anesthesia characterized by catatonia, amnesia, and analgesia

Major disadvantages are disorientation, hallucination

28
Q

Propofol

A

Non-barbituate; potentiates GABA-A receptor activity

Useful due to rapid onset, faster recovery than thiopental, less post-op nausea

29
Q

Etomidate

A

Nonbarbituate hypnotic; potentiates GABA-A receptor activity but lacks analgesic properties

Useful due to rapid induction and recovery with larger safety margin than thiopental

Disadvantages: Involuntary movement during induction, post-op nausea/vomiting

30
Q

Ondansetron

A

5HT3-type serotonin receptor antagonist

Treats post-op nausea/vomiting

Nervous System IV (10 decks)

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