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ANESTHETIC PHARMACOLOGY

The Effect of Mixing Lidocaine with Propofol on the Dose of Propofol Required for Induction of Anesthesia

Li-Hoon Tan, Mmed (Anaesthesiology)^*, and Nian-Chih Hwang, FFARCSI FAMS

Department of Anaesthesia and Surgical Intensive Care, *Changi General Hospital, and Singapore General Hospital, Singapore, Singapore

Address correspondence and reprint requests to Dr. Li-Hoon Tan, Department of Anaesthesia and Surgical Intensive Care, Changi General Hospital, 2 Simei St. 3, Singapore 529889, Singapore. Address e-mail to Li_Hoon_Tan{at}cgh.com.sg

Lidocaine is used to reduce pain associated with propofol injection, either mixed with propofol or preceding it as a separate injection. The addition of lidocaine to propofol causes destabilization of the emulsion and reduces anesthetic potency in rats and humans. We conducted a randomized double-blinded study on 67 patients to assess the effect of mixing lidocaine with propofol on the dose of propofol required for the induction of anesthesia. Patients in Group S (n = 32) received IV lidocaine 0.2 mg/kg followed by an infusion of propofol whereas those in Group M (n = 35) received IV normal saline (placebo) followed by an infusion of a freshly prepared mixture of propofol 1%/lidocaine 1% in 10:1 volume ratio. The infusion was stopped when the subjects lost consciousness, as detected by the syringe-drop method. There was no statistically significant difference between the two groups in the mean (95% confidence interval) doses of propofol required for loss of consciousness: 2.0 (1.8–2.2) mg/kg for Group S versus 1.9 (1.7–2.0) mg/kg for Group M (P = 0.206). Mixing 20 mg of lidocaine with 200 mg of propofol is unlikely to affect the dose of propofol required for the induction of anesthesia.

IMPLICATIONS: Adding lidocaine to propofol destabilizes the propofol emulsion. A randomized double-blinded trial found no statistically significant difference in the doses of propofol required for the induction of anesthesia whether administered as a freshly prepared propofol 1%/lidocaine 1% 10:1 mixture or as a separate injection after a dose of lidocaine.

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