Elective colon and rectal resections have the highest rates of surgical site infection (SSI) of any elective procedure in contemporary surgery. One technique that can be used to prevent SSI is preoperative preparation of the colon. This article examines the efficacy of this procedure as well as providing tips for best practice. The author also outlines some future research topics.

INTRODUCTION
Elective colon and rectal resections have the highest rates of surgical site infection (SSI) of any elective procedure in contemporary surgery. SSI rates for elective colon resection were as high as 80-90% in the 1930s[1] although they improved to approximately 40% by the end of the 1960s.
 
Preoperative systemic antibiotics introduced by Polk and Lopez-Mayor[2] have further reduced SSI rates and performing further placebo-controlled trials to prove this point is considered unnecessary[3].

However, globally there is great variation in the reporting of SSI rates due to different criteria for what constitutes an infection and anomalies in post-discharge follow-up. During the last two decades, there have been three rigorously evaluated patient studies following elective colorectal resection[4-6]. The rate of SSI hovers around 20-25% in studies where systemic antibiotics were appropriately administered and where patients were monitored for 30 days postoperatively[4-6]. Clearly, more needs to be done to prevent the morbidity and cost of SSI following colon surgery.

The aim of mechanical bowel preparation is to remove faecal content from the large bowel, thereby reducing the rate of postoperative infections.  Traditionally, this was performed using enemas in combination with oral laxatives but more recently oral cathartic agents that induce diarrhoea, such as polyethylene glycol and sodium phosphate, have been developed.
 
Preoperative preparation of the colon for the prevention of SSI has attracted a lot of attention. Human stool may contain as many as 10¹² bacteria per gram and purging faecal matter before colonic surgery has always seemed intuitively correct[7]. However, mechanical cleansing alone does not reduce the density of bacteria in the mucosal fluid and it has never been shown to reduce SSI in isolation. This was recognised 70 years ago[8-10] and has been revalidated over the last 10 years by a host of clinical trials and the obligatory meta-analysis[11]. These recently identified failures of mechanical preparation have led to some surgeons abandoning preoperative preparation altogether. Understanding the failure of mechanical preparation led investigators in the late 1930s to pursue possible antimicrobial methods of reducing bacterial concentration.


ORAL ANTIBIOTIC BOWEL PREPARATION
Despite early efforts with sulfa preparations[12] and kanamycin[13], a successful randomised clinical trial was not performed until Washington et al investigated the use of oral neomycin and tetracycline compared to mechanical preparation alone[14]. Clarke et al[15] validated the use of an neomycin and erythromycin base compared to mechanical preparation and a placebo.
 
This latter combination became popular in the US and by the end of the 1990s the oral antibiotic bowel preparation combined with preoperative systemic antibiotics was the most common strategy employed in elective colon surgery[16].
 
Lewis has further validated the merits of the oral antibiotic bowel preparation by conducting a randomised clinical trial of oral neomycin/metronidazole plus systemic antibiotics versus systemic antibiotics alone[17]. These findings were further validated by Lewis with a detailed meta-analysis of 13 total clinical trials demonstrating significance (P <0.0001) in the combination of oral antibiotic bowel preparations allied with systemic antibiotics.

Despite the evidence supporting oral antibiotic bowel preparations, they are not widely used and have not been well received outside of the US and Canada.