Reducing perINeal inFILTRation pain with sodium bicArbonaTe buffered lignocainE (INFILTRATE trial)

In 2022, 87% of women giving birth to their first baby suffered a tear to the perineum, most requiring suturing to repair. Perineal suturing frequently involves using injections of local anaesthetic such as lignocaine, which contains an acidic preservative to prolong shelf life. This acidic preservative causes an intense ‘stinging’ sensation when the lignocaine is injected contributing significantly to the discomfort experienced by women during the procedure.

A number of trials have examined the possibility of neutralising the acidic preservative in the lignocaine through the addition of sodium bicarbonate, known as ‘buffering’. This raises the pH of the lignocaine closer to that normally found in human tissue, significantly reducing the associated injection pain, without reducing the anaesthetic effectiveness. Most studies involve small volumes of lignocaine and the use of nerve block techniques. Few studies have explored the use of buffering in suturing of traumatic wounds or need for larger volumes of local anaesthetic. To date, no studies have examined the use of sodium bicarbonate buffering of lignocaine prior to use in perineal suturing. The aim of this trial is to determine the efficacy of sodium bicarbonate buffering of lignocaine to reduce infiltration pain in perineal repair.

This is a randomised placebo-controlled trial. Prior to the injection of local anaesthetic the lignocaine is mixed with either sodium bicarbonate 8.4% (1:10) or the placebo control of sodium chloride 0.9% (normal saline). The addition of normal saline will not neutralise the effect of the acid preservative. The primary outcome for the study is the difference in self-reported pain scores of the injection.

Trial registration