Colorectal surgery performed prior to 1970 was fraught with postoperative infectious complications which occurred in more than 30–50% of all operations. Diversion of the fecal stream appeared mandatory when operating on an urgent or emergent basis, thereby requiring the performance of multiple, staged operations instead of a single surgery encompassing resection and primary anastomosis as is performed commonly today. Multiple studies conducted in the early 1970s determined that anaerobic colonic microflora were causative agents in postoperative infections in colon and rectal surgery, and these studies initiated the development of effective oral preoperative antibiotic prophylaxis in combination with preoperative mechanical bowel preparation. This dual-tier regimen significantly reduced the incidence of postoperative infectious complications, thus allowing most uncomplicated colon and rectal surgeries to be performed in a single stage without the need for the diversion of the fecal stream and multiple operations. Therefore, a preoperative mechanical and antibacterial bowel regimen serves as the cornerstone of modern elective colorectal surgery, and these regimens now comprise three therapeutic directives. The first step is preoperative mechanical cleansing of the bowel, which is then followed by preoperative oral antibiotic prophylaxis. Finally, perioperative parenteral antibiotics directed against aerobic and anaerobic colonic microflora are utilized.

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Positive end-expiratory pressure (PEEP) is a commonly used adjunct to mechanical ventilation and is known to have deleterious effects on cardiac output (CO). Its effects on regional blood flow are not well known. We evaluated the effect of PEEP on the mesenteric microcirculation and CO. Sprague-Dawley rats were treated with mechanical ventilation and either no PEEP (Control) or increasing levels of PEEP (PEEP). Using in vivo video-microscopy, mesenteric A1 arteriolar optical Doppler velocities and A1 and A3 (the first- and third-order arterioles branching off the feeding mesenteric arcade) intraluminal diameters were measured (n = 6/group). In a separate set of experimental animals, CO was determined by thermodilution technique (n = 5/group). Additionally, after the PEEP group attained a PEEP level of 20-cm H2O PEEP, two boluses of 2 mL 0.9 normal saline (NS) were given intravenously. The Control groups had the same determinations performed over the same time course as the PEEP group but were not exposed to any PEEP. Mesenteric blood flow (MBF) was calculated from vessel diameter and red blood cell velocity. The MBF and CO fell progressively as PEEP was increased from 10- to 15- to 20-cm H2O pressure. MBF was reduced 75% (p < 0.05) and the CO was reduced 31% (p < 0.05) from baseline at 20-cm H2O pressure PEEP. After 4 mL normal saline, the MBF was still 45% below baseline (p < 0.05) while the CO had returned to baseline. In conclusion, both MBF and CO are decreased significantly with increasing PEEP.(ABSTRACT TRUNCATED AT 250 WORDS)

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