Comparison of the Expected and Actual Blood Drug Concentrations during Anesthetization with Propofol Delivered by Target Controlled Infusion in a Neurosurgical Setting

Kyoko Nishino, Megumi Kayaba, Naohisa Mori*

Department of Anesthesiology, Research Institute for Brain and Blood Vessels-AKITA, Akita, Japan

Department of Anesthesiology, Iwate Medical University, Iwate, Japan*

We compared the expected and actual blood drug concentrations during neurosurgery managed with propofol delivered by target controlled infusion (TCI).

Methods:

Subjects were 20 neurosurgery patients (9 men, 11 women). TCI (ConGrase; Nagata was developed) was used to maintain and control anesthesia. Blood was collected after a constant concentration had been maintained for one hour or more and when awakened. Expected and actual blood drug concentrations were compared using a total of 47 samples. Blood was immediately centrifuged, plasma was stored at 4 °C and concentrations were measured at a later date using high-performance liquid chromatography.

Results:

Expected and actual blood drug concentrations were 3 µg/ml versus 4.77±1.13 (m±SD) µg/ml (n=21), 3.5 µg/ml versus 5.00±0.64 µg/ml (n=3) and 4 µg/ml versus 7.66±0.66 µg/ml (n=3), respectively. At time of arousal, they were 1.37±0.30 µg/ml and 1.87±0.64 µg/ml (n=20), respectively. In all three patients in whom the expected blood drug concentration was maintained at 3 µg/ml using TCI and in whom blood was collected at two different points in time, the actual blood drug concentration was higher in the second sample collected (1st: 4.69±0.48µg/ml, 2nd: 5.43±0.79 µg/ml).

Conclusion:

A disparity was seen between the expected and actual blood drug concentrations when propofol was administered using TCI. Our findings suggest that the infusion rate gradually decreases when the expected blood drug concentration is maintained at a constant value using TCI, but the actual blood drug concentration may increase during neurosurgery.