Is total body weight an appropriate predictor for propofol maintenance dose?

BACKGROUND: Infusion rate of propofol during anaesthesia is usually based on total body weight. In this study, we have determined the relationship between total body weight and plasma propofol levels when the infusion rate was based on total body weight. METHODS: Sixty patients undergoing elective surgery were studied. Anaesthesia was induced with propofol 1 mg x kg(-1), ketamine 1 mg x kg(-1) and fentanyl 2 microg x kg(-1), and maintained with propofol 5 mg x kg(-1) x h(-1), ketamine 0.5-1 mg x kg(1) x h(-1) and fentanyl 5-15 microg x kg(-1). Propofol infusion rate did not change during anaesthesia, and infusion was terminated at the end of surgery. Immediately prior to termination of the propofol infusion, arterial blood (5 ml) was collected to measure plasma level of propofol by a high-performance liquid chromatography equipped with electrochemical detection. RESULTS: There was a significant correlation between plasma propofol and total body weight (r=0.646, P<0.001). Plasma propofol concentration also correlated with infusion rate, corrected to lean body mass (r=0.527, P<0.001). CONCLUSION: During a fixed infusion rate, plasma propofol concentration may be dependent on total body weight.