Bowel Preparation - Yes or No

 Ian Botterill

Powerpoint File

Dogma (n.) : - a doctrine or code of beliefs accepted as authorative

- a doctrinal notion asserted without regard to evidence or truth; an arbitary dictum

History

Mechanical bowel preparation (bowel prep) has been enshrined in colorectal surgical practice since the late 19th century. The perceived value of bowel prep became established following observational studies and authoritative texts that stated that reduction of faecal loading in the colon appeared to reduce rates of wound infection and anastomotic leakage. Bowel prep initially took the form of several days of in-patient purgatives coupled with frequent enemas. This was rounded off by a period of intensive colonic irrigation.

This searching peri-operative care package was first challenged in the early 1970’s. However, stronger quicker acting osmotic laxatives were being developed and concerns relating to prolonged pre-operative stay were to be quelled by these newer agents. Nevertheless, such laxatives were quickly recognised to carry significant side-effects (profound hypovolaemia, hyponatremia, hypokalemia, hypocalcaemia).

‘Heresy’

In 1987 Irving reported a consecutive series of elective and emergency patients in whom bowel prep was omitted. No anastomotic leaks were described. The report effectively questioned the validity of routine bowel prep. The paper was strongly criticised by the then editor of the BJS.

The ‘evidence’

Over the ensuing years there have been several randomised trials of varying quality. The debate regarding bowel prep prompted a Cochrane review (2005). The Cochrane review has included 9 randomised studies in which oral bowel prep or enema were compared to no bowel cleansing. A meta-analysis has been performed on the nine studies. There were clear deficiencies in the collated papers (7/9 studies did not have clear randomisation processes, 7/9 did not mention blinding, 0/9 used an intention to treat analysis, 4/9 did not describe the diagnostic methods to determine primary and secondary outcomes, 7/9 studies were underpowered, 0/9 included patients who had undergone prior chemotherapy or radiotherapy). The Cochrane analysis reported that the primary outcome measure (overall anastomotic leak rate in all patients) was 6.2% with bowel prep and 3.2% without bowel prep (p0.003). Stratification into anterior resection and colonic surgery showed no significant difference in terms of anastomotic leaks. None of the other secondary outcomes (mortality, peritonitis, reoperation, wound infection etc) showed any statistically significant difference.

The Cochrane reviewers concluded that bowel prep has not been shown to be beneficial and might in fact predispose to anastomotic leakage. As such they recommended that mechanical bowel prep should be omitted. However in their implications for future research they stated that further more rigorously conducted trials of bowel preparation v. no bowel prep were required. These two statements from the Cochrane Database therefore appear to be contradictory.

Other considerations

Other factors to consider include:

1 Radiotherapy and chemoradiotherapy are now in widespread usage for rectal malignancy. Such treatments can lead to increased anastomotic leak rate and as such it is commonplace to consider a defunctioning stoma. However, there is little merit in a defunctioning stoma if a column of residual stool remains between stoma and anastomosis (should bowel prep have been avoided). Given that the decision to defunction a colorectal or colo-anal anastomosis may only be made after actual anastomosis (eg incomplete donut) it is my practice to carry out bowel prep on patients for rectal or distal sigmoid surgery.

2 Laparoscopic surgery inherently limits tactile feedback. As such tumour localisation can be difficult. If diagnosis has involved colonoscopy then there is a strong case for routinely tattooing the tumour to aid location. If the tumour cannot be located laparoscopically, then the only realistic option may be conversion, since on table colonoscopy will be impossible in the absence of bowel prep, and would in any event, cause excessive colonic dilation which would seriously hamper further dissection.

3 There seems little merit in bowel preparation for the following: right hemicolectomy, subtotal colectomy, total colectomy, panproctocolectomy (with or without ileal pouch), Hartmann’s procedure, left hemicolectomy, APER, abdominal rectopexy. Additionally, Kehlet has reported a series of anal sphincter repairs managed according to accelerated recovery principles without pre-operative oral bowel prep.

4 An incompletely prepared colon can be less easy to deal with than an unprepared colon due to the risks of faecal spillage (peritoneal soiling, wound infection etc).

Summary

The evidence is not sufficiently clear to dismiss bowel prep for all colorectal operations. The Cochrane conclusions certainly seem contradictory. Due to the limited quality data available, the use of bowel prep should probably be tailored to the individual operation pending more robust evidence.