Anaesthesia
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Randomized Controlled Trial Comparative Study Clinical Trial
Comparison of computer-controlled administration of propofol with two manually controlled infusion techniques.
Ninety women were studied in order to compare dose requirements and quality of anaesthesia between target-controlled infusion and two manually controlled infusion schemes for propofol administration: group I received target-controlled infusion for induction (4 micrograms.ml-1 target blood concentration, increased by 2 micrograms.ml-1 after 3 min of consciousness not lost), groups II and III received an induction bolus of propofol at infusion rates of 1200 or 600 ml.h-1, respectively, until loss of consciousness. Anaesthesia was maintained with propofol target-controlled infusion in group 1 or by constant rate infusion in the other two groups. Computer simulations were used to calculate blood and effect-site propofol concentrations. ⋯ There was a lower incidence of apnoea in group I than in groups II and III. There were no significant differences between the groups in other objective parameters of anaesthetic quality studied. Computer simulations showed an "overshoot' in propofol blood and effect-site concentration with manual induction and significantly higher maintenance levels with target-controlled infusion.
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We have sought to define a way in which nitrous oxide can be safely and universally used at minimal to low flows by utilising a circle system with a controlled leak provided by a standard gas analyser sampling line and a fresh gas supply of 50% nitrous oxide in oxygen, entering from a trunk interposed between the ventilator and the circle system. Although preliminary calculations suggested that this arrangement was likely to work, it was found that 13 of 23 patients studied prospectively developed an inspired oxygen fraction below 0.3. We conclude that, although this arrangement provides a new means of introducing nitrous oxide into the circle breathing system, it does not appear inherently safer or more convenient than the conventional route.