Visual evoked potentials and changes in serum glycine concentration during transurethral resection of the prostate

Visual evoked potentials were recorded in 10 patients undergoing transurethral prostatectomy under subarachnoid anaesthesia. They were compared with those obtained in a control group (n = 5) having other operative procedures also under spinal anaesthesia. Serum concentrations of glycine, ammonia, glucose and sodium, and osmolality, were determined during the perioperative period. The prostatectomy group demonstrated a significant prolongation of visual evoked potential P2 latency in the postoperative period when compared with preoperative values (P less than 0.01). No significant changes in latency occurred in the control group when measured at similar times. The prostatectomy group demonstrated a significant increase in serum glycine concentration (P less than 0.01); changes in serum ammonia and sodium concentrations and osmolality were not significant. There was no correlation between visual evoked potential latency and changes in serum glycine concentration. Changes in visual evoked potential during transurethral prostatectomy may be the result of an accumulation of a metabolite of glycine.