Evaluation of bias in predicted and measured propofol concentrations during target-controlled infusions in obese Japanese patients: an open-label comparative study.

BACKGROUND

Target-controlled infusions (TCIs) of propofol are commonly used for general anaesthesia. The Marsh model pharmacokinetic parameter set incorporated in TCI devices for propofol could increase bias when used in obese patients.

OBJECTIVE

The purpose of this study was to assess the optimal predicted blood concentration (Cp) of 4.0 μg ml of propofol using a correction formula including BMI and to evaluate the influences on propofol concentration in obese patients.

DESIGN

An open-label, comparative study.

SETTING

Sapporo Medical University Hospital, Japan, from October 2011 to December 2013.

PATIENTS

Seventy-five adults scheduled for elective surgery under general anaesthesia with the following exclusion criteria: less than 30 or more than 65 years of age; American Society of Anesthesiologists status 3 to 5; allergy to propofol; the daily use of psychoactive drugs; known or suspected drug or alcohol abuse; and cardiac, hepatic, renal or neurological impairment.

INTERVENTION

Propofol was administered and maintained at a Cp of 4.0 μg ml using a TCI device programmed with the Marsh pharmacokinetic model. Arterial blood samples were collected at 15, 30, 60, 90, 120, 150 and 180 min after the start of the infusion, and the measured propofol concentration (Cm) was determined. After calculation of the adjustment formula using the corrected Cp of 69 patients, we then applied the corrected Cp to five other obese patients.

MAIN OUTCOME MEASURES

The median performance error (MDPE) and median absolute performance error (MDAPE) were calculated to measure bias at each time point.

RESULTS

We analysed 333 samples from the 69 individuals. There was a significant correlation between BMI and Cm, which tended be greater than 4.0 μg ml in obese patients. Our new method improved MDPE and MDAPE from a range of 20 to 40 for both, to ranges of -11.3 to -1.8 and 8.8 to 11.5, respectively.

CONCLUSION

BMI influences blood propofol concentrations, leading to the possibility of overdosage of propofol in obese patients when the Marsh model is used to assess propofol concentration. Our new method using corrected Cp might improve this bias in obese, Japanese patients.