Rectal Evacuation and Antegrade Colonic Luminal Transport by Sacral Anterior Root Stimulation in Pigs

PURPOSE: Electrical sacral anterior root stimulation with a selective anodal block may relieve difficulties with bowel evacuation by selective colorectal activation and anal sphincter suppression. This study compares rectal evacuation induced by anodal block with that induced by unselective stimulation. METHODS: The sacral anterior roots were stimulated with cuff electrodes in seven chloralose-anesthetized minipigs. Anodal block and unselective stimulation were applied in random order and compared by anorectal manometry and by the obtained colorectal evacuation. Evacuation was quantified scintigraphically after retrograde radioactive paste installation. RESULTS: Unselective stimulation evoked sphincter activation which obstructed rectal evacuation during the 30-second stimulation period, after which poststimulation evacuation occurred (mean, 13%; P < 0.05). Anodal block reduced the anal canal pressure by median 83% compared with unselective stimulation. With unrestrained evacuation, a different evacuation pattern (mean, 18%; P < 0.05) occurred within the first ten seconds of the stimulation period and evacuated volume was higher (P = 0.08). Colonic evacuation reached a mean of 17% with unselective stimulation and 11% with anodal block. CONCLUSION: Anodal block and unselective sacral root stimulation induce rectal evacuation and colonic luminal transport in pigs. However, anodal block may improve stimulation-induced defecation by enabling a near-physiologic defecation pattern.