Anesthetics 1 Flashcards
General Anesthetics
• General Anesthetics: Reversible state of loss of
sensation and consciousness
• Inhalational Anesthetics: Gases or volatile liquid
General Anesthetics: Halogenated
Halothane Isoflurane Enflurane Sevoflurane Desflurane
General Anesthetics: Non-Halogenated
Nitrous oxide
General Anesthesia, “the ideal”
• Amnesia • Analgesia • Produce state of consciousness or unresponsiveness • Block sensory and autonomic reflexes • Skeletal muscle relaxation (not respiratory muscles) • Rapid induction and emergence • Wide window of safety • “Balanced Anesthesia”
Pharmacokinetics-Inhalational Anesthetics
• Potency expressed as minimum alveolar
concentration (MAC)
• MAC: inspired concentration of anesthetic
required to produce anesthesia in ½ of subjects.
– Equivalent to ED50
– Expressed as % of inhaled gas
MAC
inspired concentration of anesthetic
required to produce anesthesia in ½ of subjects.
– Equivalent to ED50
– Expressed as % of inhaled gas
Not affected by: Type of noxious stimulus Sex Height Weight Duration of exposure
MAC affected by: Age Health status Drug interactions Red hair
MAC: Affected by:
Affected by: – Age: MAC is for a 35-40 year old • ↑ infancy/childhood; • ↓ old age – Health Status: • ↑ hyperthyroidism; • ↓ hypothyroidism – Drug Interactions: • ↓ Sedatives; • ↑ Amphetamines – Red Hair ↑
Rate of induction
Condition
↑Concentration of anesthetic in inspiredgas
mixture: Increase
↑Alveolar ventilation: Increase
↑Solubility of anesthetic in blood (blood:gas partition coefficient): Decrease
↑Cardiac output: Decrease
Cardiac output = decrease
A higher cardiac output removes more volatile
anesthetic from the alveoli and lowers therefore the
alveolar partial pressure of the gas. The agent might
be faster distributed within the body but the partial
pressure in the arterial blood is lower. It will take
longer for the gas to reach an equilibrium between
the alveoli and the brain. Therefore, a high cardiac
output prolongs induction time.
Pharmacokinetics-Inhalational
Anesthetics
Concentration of agent is directly proportional to Partial
Pressure
Anesthetic Induction occurs faster with agents which are less soluble in blood
MAC and Lipid Solubility
• A linear relationship exists between lipid
solubility and MAC.
Mechanism of Action
• Meyer-Overton Theory: Anesthetic dissolves in the membrane
and “affects” the function of membrane proteins – no specific
receptor, no specific antagonist
• Agents may interact with hydrophobic regions of proteins
embedded in lipid bilayer of neuronal membranes
• Anesthetics may impede the breakdown of GABA
• Potentiation of GABA-increased Cl- influx
• Increase K+ efflux; Reduce Na+, Ca2+ influx
Halothane
• Potent anesthetic
• Weak analgesic
• Blood:gas partition coefficient (2.3)
• Usually coadministered with nitrous oxide, opioids,
local anesthetics
• Has a pleasant odor
• Do not repeat at intervals less than 2-3 weeks
Halothane: Cardiovascular
effects
Sensitizes heart to catecholamines → Increased risk of arrhythmias Vagomimetic → bradycardia ↓ Blood pressure → hypotension • Myocardium depressed • Cardiac output ↓ • Depression of baroreceptor reflex
Halothane: Respiratory
effects
Breathing is rapid/shallow
Responsiveness to CO2 ↓
Ventilation needs to be controlled
Halothane: Metabolism
Metabolism may cause liberation of hydrocarbons, bromide
ion which can result in hypersensitivity reactions and
hepatitis (less hepatotoxic in children)
Halothane + succinylcholine
– increased risk of malignant hyperthermia
– sustained contraction of skeletal muscles;
dramatic increase in O2 consumption;
• ↑ body temperature
• effects due to the inability of the sarcoplasmic
reticulum to sequester Ca2+
• Treatment: dantrolene
Enflurane
- Less potent than halothane
- Rapid induction/recovery
- Pleasant odor
Enflurane: Cardiovascular
effects, resp
Cardiovascular effects Less sensitization of heart to catecholamines ↓ blood pressure; then recovers ↓ myocardial contractility Reduced tendency for
Respiratory
effects
Respiratory depression in dose-dependent manner
Enflurane: Muscular
effects
Greater potentiation of muscle relaxants Depolarizing • succinycholine Enhances effects of non-depolarizing neuromuscular blockers • Block ACh effects at NMJ • D-tubocurarine, atracurium, vecuronium
Enflurane: CNS effects, Metabolism
CNS effects CNS excitation → Seizures
Metabolism Metabolized, producing Fl-
; renal excretion
Isoflurane
- Smooth/rapid induction and recovery
- Pungent odor
- Structural isomer of enflurane
Isoflurane: Cardiovascular
effects
Does not induce arrhythmias
Does not sensitize heart to catecholamines
Dose dependent ↓ blood pressure
Does not ↓ cardiac output
Isoflurane: Respiratory
effects
Dose dependent ↓ respiration
