DOC_ACADEMIA: ANAESTHESIA STUDENT

 It is the ratio of the amount of anaesthetic agents present in the blood compared to gas when two phases are of equal volume and pressure and in equilibrium at 37 degrees Celsius.  ⇒ Also called as Ostwald coefficient of blood gas.  ⇒ It expresses the solubility of the agent in blood.  ⇒ The higher the blood/gas partition coefficient, the more the agent is soluble. It will take longer to raise the agent's partial pressure in the blood.  Anaesthesia is related to the partial pressure of the anaesthetic agent at the effect site.  ↑ B/G partition coefficient:  ↑ Duration Onset time  of anaesthesia  ↑ Duration of Offset time of anaesthesia  ↓ B/G partition coefficient:  ↓ Duration of Onset time ↓ Duration of Offset time  The blood gas partition coefficient of the volatile agents: Halothane: 2.4  Isoflurane: 1.4 Sevoflurane: 0.6  Desflurane: 0.4  Halothane is present in the blood 2.4 times more than that present in t...

Due to the preferable pharmacodynamics, Sevoflurane is the most favoured drug for the induction and maintenance of anaesthesia. Its low blood-gas partition coefficient helps to rapid alteration of the level of anaesthesia.  CVS effects:  → Mild ↓ cardiac contractility (dose-dependent, equal to isoflurane) → Mild ↓ SVR (dose-dependent, equal to Halothane) → Mild ↓ BP (dose-dependent, most least compared to others) → Minimal effect on HR → May cause prolongation of the QT interval  → Not associated with coronary steal  → Doesn't sensitize the myocardium  → No effect on splanchnic blood flow  Respiratory effects: → Non-irritant  → Dose-dependent Tidal volume depression (less than Isoflurane, equal to Halothane)  → ↑ RR (equal to Isoflurane, more than Halothane)  → ↓ MV causing ↑ PaCO2 → Depression of hypoxic and hypercapnic ventilatory drive  → Inhibition of hypoxic pulmonary vasoconstriction  → Bronchial smooth muscle r...