Bispectral index-guided induction of general anaesthesia.

Editor—We read with great interest the recent article by Petrun and Kamenik regarding the use of a bispectral index (BIS) monitor as a guide to induce anaesthesia using an infusion technique with propofol compared with etomidate. This infusion technique is a plausible concept because of the BIS monitoring. Infusion techniques using propofol were performed many years ago, dating back to 1983–7 when BIS monitors were not in clinical use. Minimally invasive monitors to measure cardiovascular haemodynamic variables, such as the Lidco rapid monitor (Lidco cardiac sensor system, Cambridge, UK) were also not in clinical use. According to the authors, the monitor provides beat-to-beat measurements of cardiac index (CI) by analysing the arterial pressure (AP) tracing. The displayed values are nominal and are derived from a population-based nomogram which may not be absolutely accurate. Therefore, the numbers recorded may be even more negative than expressed in the article. In the article, the authors state that CI was never measured in earlier studies using propofol or etomidate. In fact, the first haemodynamic study was performed in 1985 by Lippmann and colleagues in the USA, using a Swan–Ganz catheter, and studying the effects of a propofol i.v. bolus given over 30–45 s. CI was decreased by 18 (13)%; cardiac work index and stroke work index also decreased by some 35 (16)% over 2–3 min. Petrun and Kamenik feel that intubation would reverse the decreases in AP and heart rate, which occur especially with propofol. Because propofol is so depressant on the heart and vasodilates the peripheral vascular system so strongly, intubation can only modify it minimally. Therefore, patients are always in a compromised position, especially the elderly and the sick.