Influence of polyvinyl chloride infusion extension tube on propofol injection pain

BACKGROUND Propofol injection pain is a common and unsolved anaesthesia problem. OBJECTIVES The present study attempted to confirm that the plasticiser di(2-ethylhexyl) phthalate in polyvinyl chloride (PVC) infusion tubes may increase propofol injection pain by increasing the aqueous propofol concentration. DESIGN A randomised controlled study. SETTING University teaching hospital, 1 April to 25 June 2013. PATIENTS One hundred patients scheduled for elective surgery were allocated randomly to the PVC or the control (C) group. The PVC group received a propofol (Diprivan) infusion via a 1-m PVC infusion extension tube, whereas group C received propofol injected directly through the port of the cannula. INTERVENTION After the syringe was loaded with propofol, air was expelled from the tube and the syringe was left standing for 5 min; intravenous propofol 0.5 mg kg was then injected either through the PVC tube or directly into the cannula. MAIN OUTCOME MEASURE A verbal rating scale was used to evaluate the propofol injection pain in both groups. Di(2-ethylhexyl) phthalate and aqueous propofol concentrations were also measured in samples of propofol after simulated injection. To investigate whether the increase in aqueous propofol concentration was caused by leached di(2-ethylhexyl) phthalate, the same amount of di(2-ethylhexyl) phthalate as that measured in the PVC group was added to the samples (group D). RESULTS The incidences of pain in groups PVC and C were 88 and 46%, respectively (P < 0.0001). The di(2-ethylhexyl) phthalate concentration in group PVC (1.01 ± 0.07 μg ml) was greater than that in group C (lower than the detection limit of 0.03 μg ml). No significant difference was found between the aqueous propofol concentrations in groups PVC (25.9 ± 1.8 μg ml) and D (24.4 ± 1.1 μg ml) (P = 0.22), which were significantly higher than that in group C (14.3 ± 1.0 μg ml) (P = 0.079). CONCLUSION Propofol injection pain is increased by contact with PVC infusion tubing as a result of an increase in aqueous propofol concentration caused by di(2-ethylhexyl) phthalate leaching into the lipid emulsion. TRIAL REGISTRATION chictr.org identifier: ChiCTR-TRC-12003170.