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Peninsula Medical School; University of Plymouth; Plymouth, UK; robert.sneyd{at}pms.ac.uk
To the Editor:
Gurses et al. (1) concluded that bispectral index (BIS) analysis results in an important reduction of propofol requirement and that using BIS analysis may be safer, especially for critically ill elderly patients. However, the patients (28–55 yr, ASA I-II) were neither elderly nor critically ill.
Group I dose: Although scheduled for propofol 2 mg · kg–1 the patients averaging 61.1 kg received propofol 147.4 mg—this equals 2.41 mg · kg–1. Are there errors here? In patients aged 18–50 yr at an infusion rate of 33.3 mg · min–1 the mean induction dose of propofol was 1.36 mg · kg–1 over 145 s (2), thus the Group I dose seems large.
What should be compared with what? Patients titrated to unconsciousness, Group II, required propofol 1.6 mg · kg–1. Thus in Group I, the infusion of 2 (or 2.41?) mg · kg–1would have continued for 1.2 (or possibly 2.43) min after loss of consciousness—clearly an overdose. The BIS monitored Group III should be compared with Group II. Comparisons between Groups I and III are clinically meaningless.
Correct conclusions from the data reported: If we now compare Groups II and III, we can generate statements that accurately reflect the data reported, such as: "When a slow infusion of propofol is titrated to loss of verbal response or to BIS = 50, the time of induction, dose of propofol, bispectral index and hemodynamic changes are similar." Alternatively, we could also state "BIS monitoring does not improve induction of anesthesia if propofol is infused slowly." If we consider the cost, then "The addition of BIS monitoring (cost X dollars) will allow you to stop the propofol infusion 0.6 min earlier and save 11.5 mg of propofol (cost < X dollars), but there will be no benefit in hemodynamics, heart rate, or oxygen saturation." The reader must take his or her pick.
References
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