15. General anaesthetics: Inhalational anaesthetics Flashcards
Inhalational anaesthetics chemically are…
Halogenated volatile liquids (Except nitrous oxide)
- Non-flammable, non-explosive
Summarise the effect of inhalational general anaesthetics
- ↓Cerebral vascular resistance
- ↑ Perfusion of brain
- Ligand-gated ion channels activated
- ↑ Cl- conductance, hyperpolarize & inhibit neuronal membrane activity
- Inhibit ligand-gated Na+ channels
Inhalational GAs: Potency
- The ↓ the MAC, the ↑ the potency
- MAC ↓ with age, pregnancy, hypothermia, hypotension
- MAC depends on patient’s weight
Define: MAC
Minimum alveolar conc.
- Minimum alveolar conc. at steady state that results in immobility in 50% of patients
The lower the MAC…
The more potent the agent
MAC ↓ with…
- Age
- Pregnancy
- Hypothermia
- Hypotension
MAC is dependent on the patient’s…
Weight
Solubility of inhalational GAs
The rate at which partial pressure of an inhalational anaesthetic reaches equilibrium between various tissues & inspired air
- Depends primarily on drug solubility
Relative solubility of an inhalational anaesthetic in blood relative to air is defined by its…
Blood-gas partition coefficient
↑ anaesthetic conc in inspired air will…
↑ rate of induction
↑ Rate of depth of ventilation will…
↑ partial pressure more rapidly for anesthetics with intermediate or high blood solubility
↑ Pulmonary blood flow will… the rate of rise in partial pressure
Decrease
The less soluble an anaesthetic…
The more rapid its elimination
For soluble anaesthetics, the larger the exposure…
The longer the time to recovery
Nitrous oxide
Good analgesic & sedative properties
- Often used in combination with other inhalational anaesthetics
- Post-operative nausea & vomiting
- Anaemia
- Leukopenia
