Influence of polyvinyl chloride infusion extension tube on propofol injection pain: A randomised controlled study

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(−1) 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(−1)) was greater than that in group C (lower than the detection limit of 0.03 μg ml(−1)). No significant difference was found between the aqueous propofol concentrations in groups PVC (25.9 ± 1.8 μg ml(−1)) and D (24.4 ± 1.1 μg ml(−1)) (P = 0.22), which were significantly higher than that in group C (14.3 ± 1.0 μg ml(−1)) (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.