The effect of surgical medicaments on peripheral nerve function

Surgical medicaments are often placed in close proximity to peripheral nerves and maybe responsible for some postoperative sensory disturbances. In this study we investigated the effect of four medicaments - BIPP, (bismuth iodoform paraffin paste), Whiteheadʹs varnish (compound iodoform paint), Surgicel (oxidized regenerated cellulose) and Carnoyʹs solution (ethanol, chloroform and acetic acid) - on peripheral nerve function. The experiments were carried out on the saphenous nerve in anaesthetized adult rats. Electrical stimuli (30 V, 0.1 ms duration) were applied to the saphenous nerve through electrodes placed distally (at the ankle) to evoke a compound action potential (CAP) which was recorded proximally (in the thigh). The CAP was recorded before, and for 2 h after, the application of the medicament to a 1 cm length of nerve between the electrodes. In other animals (n = 4 in each group) recordings were made after the medicament had been placed in a connective tissue pocket immediately overlying the nerve for a 2-week period. BIPP (n = 4) had no immediate or delayed effect on neural function, whereas Whiteheadʹs varnish (n = 4) and Carnoyʹs (n = 4) solution both blocked neural conduction within 2 min of being placed adjacent to the nerve. The effect of Surgicel (n = 8) was more variable; axonal conduction was blocked within 2 h in five of the eight experiments undertaken. After the application of Whiteheadʹs varnish or Surgicel for 2 weeks, the CAPs had regained characteristics which were similar to those of the controls, but after the application of Carnoyʹs solution they remained significantly diminished (P < 0.004). These results suggest that, with the exception of BIPP, the medicaments tested could be responsible for some postoperative sensory disturbances, and the effects of Carnoyʹs solution on neural function may be persistent.