We derived the predicted effect compartment concentration of thiopental, at loss of the eyelash reflex, following three different injection regimens. Sixty patients were given thiopental for induction of anaesthesia. Twenty patients received multiple small boluses, 20 patients received a single bolus and 20 patients received an infusion. Computer simulation was then used to derive the effect compartment concentration. The median concentration was not significantly different between the three groups. EC50, derived after combining all three groups was 11.3 microg ml(-1). The EC05-EC95 range was 6.9-18.3 microg ml(-1), suggesting wide inter-individual variation.
The effects of 2% and 4% sevoflurane in oxygen and nitrous oxide for induction of anaesthesia in 60 unpremedicated elderly patients was compared to those obtained during an intravenous Thiopentone induction. Intravenous induction induced anaesthesia in 27 +/- 5 seconds, significantly faster than a 2% or 4% sevoflurane induction (109 +/- 36 and 71 +/- 24 seconds respectively). One patient in both the thiopentone and 2% sevoflurane groups, and 2 patients in the 4% sevoflurane group coughed during induction. The postinduction reduction in mean arterial pressure was greatest in the thiopentone group followed by the 4% and the 2% sevoflurane groups. Heart rate changes were minimal in all groups. We conclude that 2% or 4% sevoflurane offered suitable conditions for induction of anaesthesia in the elderly with minimal cardiovascular derangement.
This randomized controlled trial compared Bispectral Index (BIS) values in 40 patients after a modified rapid sequence induction using thiopentone 4 mg/kg or propofol 2 mg/kg with rocuronium 0.6 mg/kg as muscle relaxant. Endotracheal intubation was performed at 60 seconds from induction of anaesthesia and BIS values were recorded for three minutes after induction. At the 120, 150 and 180 second measurements there was a significantly greater proportion of subjects with BIS values < or = 60 ("anaesthetized") in the propofol group compared with the thiopentone group (P values < 0.02, < 0.01 and < 0.01 respectively). All intubations were completed within two minutes. No explicit recall of intubation was detected clinically with either induction agent. The BIS scores we have measured suggest that thiopentone 4 mg/kg is more likely to be associated with lighter planes of anaesthesia and consequent risk of awareness than propofol 2 mg/kg, if intubation is delayed or prolonged.