MBP and New Knowledge on Colonic Physiology

MBP is founded on three rules:

1. absolute starvation, especially of fibre;

2. antibiotic prophylaxis;

3. enemas and/or laxative drugs.

One of the last papers on this topic was by Platell and Hall [5], questioning MBP in "Colon and rectum disease" in 1998 [6]. Then many papers in the international literature focused on this argument, especially in the last three years [7-10]. All have stated that MBP is more harmful than useful.

The landmark was a deeper knowledge of the physiology of the colon and its power in finding energy for the body [10]. Really, the viscus is not only able to concentrate water and rescue sodium, but also produces energy for the whole body by producing short-chain fatty acids (SCFA) from the fermentation of food fibres.

The effects of SCFA are concentration dependent. Low doses stimulate motility, while high doses inhibit contractions of the loops [11]. Moreover, SCFA stimulate secretion of gastrointestinal peptides to modulate peristaltic waves [12]. SCFA increase microcirculation of the colon and distal ileum, where the large amount of anaerobes produce SCFA by fermentation [11]. SCFA are mainly produced in the colon and also stimulate mucosal blood flow in the rectum of patients who have undergone Hartmann's procedure [11]. It must be kept in mind that micro-circulatory failure seems to be the main determining factor of anastomosis failure. After production by fermentation, SCFA are readily transported across colonic epithelium [11-13]. So, deprivation of fibre should be detrimental to colonic cells [12].

Fermentation by endogenous bacteria is really the second digestive system of our body. Really, man has two separate digestive systems, one based on digestion by enteric cells of the gut, and another much more complex one based on fermentation by digestion of bacteria. The bacteria are so important that we can call them the "microbe organ". Energy [14] from fermentation produces SCFA and it is more than 8% of the whole daily production of energy of the body.

SCFA are propionic, acetic and butyric acid. Butyric acid is the real fuel of Bifidobacteria and is absorbed at 90% by the colonic cells. These agents could have a protective effect against leakage of anastomosis, enhancing vascularisation and protecting the anastomosis from leakage as failure of microcirculation is caused by this complication [15].

Of extreme interest are the patterns of deprivation colitis found on colon segments without nutrients for many months, such as after dehiscence of colo-colonic anastomosis and performance of ileostomy [16]. The disease is caused by deprivation of nutri ents to the colonic mucosa [10]. So, we have to understand that nutrient delivery should be continuous to improve adequate blood supply and energy production to the mucosal cells [10].

On Burke et al.'s [17] evidence, MBP did not influence the outcome in 2 groups of patients (with and without) submitted to ultra-low anterior rectal resection. In 1998 Platell and Hall [5] performed a metaanalysis of this issue. MBP seems to reduce only wound infection onset. Jansen et al. [8] stated MBP could safely be omitted for right colonic resections, but not antibiotic drugs as prophylaxis of wound infection.

Van Geldere et al. [6] did not find any benefit with the use of MBP on colonic surgery in a trial of 185 patients. Zmora et al. [7] in 380 patients treated by colonic-rectal surgery, found that MBP has to be performed only in the presence of a small (<3 cm) tumour that could not be seen on a perioperative colonscopy. Whilst Zmora and co-workers again, in a last specific review, found no data in support of MBP on colonic sugery [7].

Also, diet restriction is questionable as physiology has shown that faeces are made up of only 5-7% food, while the majority is bacteria, apoptotic enteric cells and mucous. Mucous is the main part of the intestinal barrier and one of the most important weapons against bacterial translocation. It is made up of embedded immunologic cells from lamina propria and mucosal lymphocytes. Therefore, it would be illogical to destroy it by aggressive oral preparation or by enemas.

Slim et al. [1], late in 2004, suggested that MBP using polyethyleneglycol should be omitted before colorectal surgery. Anyway, the presence of hard faeces on left segments of the colon and rectum obstruct surgical procedures.

Kehlet [18] and Basse et al. [19] suggest performing an enema as the surgeon prefers for cleaning the rectum and the colon before resection.

Ljungqvist [20] in 2005 gave up bowel preparation for colon resections, but still use it for rectal resections. In their experience this procedure works fine, without any true benefit for laparoscopic resections for colon or rectum. For the former, this group have patients ready to leave the hospital 2-4 days after rectal surgery and 4-6 days after open surgery using small incisions as best possible. For a right-sided hemi-colectomy the incision is almost the same as in laparoscopic surgery.

Excessively strong enemas could destroy the mucus layer on the rectal and colonic mucosa, and this layer is full of IgA and probiotic bacteria.

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