Quantitative radio-isotope proctography-a new technique for the assessment of rectal evacuation

The aim of this study was to establish a technique for measuring both the efficiency and speed of rectal evacuation and to assess the impact on these parameters of varying the volume of instillate.

Twelve healthy volunteers had 100 ml, 150 ml and 200 ml of isotope-labelled paste inserted into the rectum on three separate occasions and asked to evacuate the paste on a modified commode. Radioactivity within the rectal field was measured at 2-s intervals. The speed of evacuation from both the time at which the command to evacuate was given and the time at which evacuation commenced and efficiency of evacuation were calculated.

The efficiency of evacuation differed little with the changing volumes of instillate (median values 69%, 68% and 67% for 100 ml, 150 ml and 200 ml, respectively). The speed of evacuation increased with increasing volumes of instillate and was significantly faster when comparing the 200-ml group with the 100-ml group (Wilcoxon rank sum test for paired data, P < 0.05). The increase in speed of rectal emptying was, however, due to earlier initiation of evacuation rather than a faster rate of rectal emptying.

The findings suggest that quantitative tests of rectal emptying should use a set volume of instillate to avoid variations in the speed of evacuation and indicate that a larger volume of instillate may be preferable to smaller volumes for the purposes of testing rectal emptying.