Diffusion of Lidocaine Buffered to An Optimal pH Across the Endotracheal Tube Cuff-An in-Vitro Study

Abstract

Diffusion of lidocaine across the endotracheal tube (ETT) cuff helps in smooth emergence of patients from general anaesthesia by preventing ETT-induced cough to occur. Buffering enhances the rate of diffusion from ETT cuff. The aim of this in-vitro study was to determine the optimal pH at which maximum diffusion of lidocaine occurs across the ETT cuff. Fifteen 8.0 mm ID Portex ETT′s were divided into three groups. In each group, the cuffs were filled with 6ml of 2% lidocaine buffered to a pH of 7.4 (Group I), 7.6 (Group II) and 7.8 (Group III). They were then immersed in 20ml distilled water in a water bath set at 38 0 C. The lidocaine diffused was measured using high performance liquid chromatography every half hour interval for up to five hours. There was a significant increase in the onset of diffusion in Group II compared to Groups I and III (P 0.05). At 300 minutes, maximum diffusion occurred in both the Groups I and II, which was significantly higher compared to Group III (P < 0.05). In spite of the above findings, the present study concluded lidocaine buffered to a pH of 7.4 as the optimal pH for the practical reason that solution in Group I was non-precipitating in nature and hence both filling as well as withdrawing the solution from the cuff was easier in this group, unlike that happened in the Groups II and III.

Keywords

• Lidocaine
• Cough.