A randomized trial of mechanical bowel preparation versus no bowel preparation with rectal surgery found that the overall and site-specific infectious morbidity rates were significantly higher in no preparation versus the mechanical preparation group. Regarding anastomotic leakage, length of hospital stay, major morbidity and mortality rates, there was no significant difference between the no preparation and mechanical bowel preparation groups. This was the first randomized trial to demonstrate that rectal cancer surgery without mechanical preparation is associated with higher risk of overall and infectious morbidity rates without any significant increase of anastomotic leakage rate. It suggests continuing to perform mechanical preparation before elective rectal resection for cancer (117).
Despite evidence of the infectious complications associated with mechanical preparation or no preparation, many gynecologic surgeons prefer a mechanical preparation to aid with exposure in the pelvic operative field. This may be particularly relevant to the surgeon performing minimally invasive surgery.
Mechanical bowel preparation may be accomplished as presented in (Table 22.10). The traditional use of laxatives and enemas requires at least 12 to 24 hours and causes moderate abdominal distention and crampy pain. Randomized trials comparing traditional mechanical bowel preparation (magnesium citrate and enemas) with oral gut lavage (PEG electrolyte solution, GoLYTELY) found that the use of approximately 4 L of GoLYTELY (administered until the rectal efﬂuent is clear) provides more complete, faster, and more comfortable bowel preparation (118). However, the ingestion of 4 L of ﬂuid is problematic for many patients, so magnesium citrate may be preferable when mechanical preparation is to be used.
An alternative mechanical preparation method is the use of oral sodium phosphate (Phospho-Soda). When evaluated in a randomized trial comparing the 4 L of GoLYTELY with oral sodium phosphate, colonoscopic examination disclosed that both methods were equally effective in colonic cleansing, and more patients preferred the sodium phosphate method (119). Some patients are at higher risk to develop acute phosphate nephropathy, leading to acute renal failure or worsening of chronic renal disease after the use of sodium phosphate. Although the pathophysiology is not fully understood, it may be secondary to substantial ﬂuid shifts and electrolyte changes. It is speculated that potential etiologic factors included inadequate hydration, increased patient age, a history of hypertension, and current use of an angiotensin receptor
Table 22.10 Mechanical Bowel Preparation 4 L of GoLYTELY
OR Fleet Phospho-Soda Saline laxative (3 oz. bottle)a (one bottle of laxative 1 p.m. and another at 7 p.m.) Fleet enemas until no solid stool in p.m. (optional)
Neomycin (oral), 1 g every 4 h for three doses (4, 8, 12 p.m.)
Erythromycin (oral), 1 g every 4 h for three doses or metronidazole 500 mgm every 4 h for three doses aBe aware of acute phosphate nephropathy. Avoid use of phospho-soda in patients with inadequate hydration, increased age, a history of hypertension, current use of an angiotensin receptor blocker, or angiotensin-conversing enzyme (ACE) inhibitors; renal disease or chronic heart failure and those taking nonsteroidal anti-inﬂammatory drugs (NSAIDs) or diuretics.
blocker or angiotension-converting enzyme (ACE) inhibitors. Patients with chronic renal disease or chronic heart failure and those taking NSAIDs or diuretics appear to be at higher risk of acute phosphate nephropathy (120). For these patients, the guidelines recommend an alternative bowel preparation agent, polyethylene glycol, which is not associated with volume shifts and electrolyte abnormalities (121,122).