Volatiles & IV anaesthetic drugs

Question 1

Isoflurane

Answer 1

Consists of 2 stereoisomers.
Has similar BP & SVP as Halothane (BP: 48.5 v 50.2; SVP 31.9 v 32.5).
Associated with cerebral steal- where vasodilatation of healthy vessels diverts blood flow away from critically perfused areas supplied by non compliant vessels , which cannot dilate further.
Coronary steal (not believed to be clinically significant).

Question 2

Speed of onset of IV anaesthetic agent depends on

Answer 2

1) Protein binding & lipid solubility (how easy it would be to cross BBB)
2) Blood flow to brain- reduced blood flow results in reduced delivery of blood to brain e.g. carotid stenosis. However if CBF is reduced due to low cardiac output then initial blood concentration are higher than normal after iv administration and anaesthetic effect may be delayed but enhanced.
3) extracellur pH & pKa of drug
4) speed of injection

Question 3

Speed of onset of gaseous induction agent depends on

Answer 3

Rx factors: blo-gas solubility; concentration; use of N2O.

Patient factors: Cardiac output; minute volume.