Effect of Open-Chest Surgery in the Lateral Position on Blood Propofol Concentration during Target-Controlled Infusion of Propofol

Abstract

Our research hypothesis was that single lung ventilation during thoracic surgery in the lateral position increases the blood concentration of propofol during target-controlled infusion. Thirty adult patients in two tertiary referral hospitals undergoing open-chest surgery were studied. Anaesthesia was induced and maintained with propofol using a Diprifusor (Graseby 3500) computer-controlled pump set to deliver a blood concentration of 4 μg.ml-1. Blood samples were taken with the patient positioned in 1) the supine position 20 minutes after induction (supine); 2) the lateral position just prior to one-lung ventilation (lateral); 3) the lateral position five minutes after commencing one-lung ventilation (OLV5) and 4) the lateral position 20 minutes after commencing one-lung ventilation (OLV20). Propofol concentrations were determined by high performance liquid chromatography. The target-controlled infusion target level was maintained at 4 μg.ml-1 during the study period for all cases. The mean (SD) propofol blood concentration (μg.ml-1) at each stage was 5.5 (1.5) supine, 5.3 (1.1) lateral, 5.3 (1.2) OLV5 and 5.1 (1.2) OLV20. Repeated measures ANOVA showed an F value 1.9, lambda 5.5 and P value 0.15. Post hoc analysis did not identify a significant difference between the sample times. During target-controlled infusion of propofol, mean blood propofol concentrations did not change significantly from those obtained with the patient supine after up to 50 minutes in the lateral position during thoracic surgery, or 20 minutes after commencing one-lung ventilation.