The incision is placed over the suspected site of the lesion. If the location of the small bowel obstruction is not known, a lower midline incision is often used, since the lower ileum is most frequently involved. The incision is made preferably above or below an old abdominal scar, if present, because the site of the obstruction will most likely be near this point, especially if the scar was tender before operation. A culture of the peritoneal fluid is taken, the amount, color, and consistency being noted. Bloody fluid indicates vascular obstruction. The dilated loops of intestine are retracted or removed carefully from the peritoneal cavity to a warm, moist surface and covered with gauze packs soaked in warm saline solution. When strangulation is present, the surgeon must determine the viability of the involved intestine by taking into consideration these factors: (1) a cadaveric odor; (2) the presence of bloody fluid indicating venous thrombosis; (3) failure of peristalsis to progress over the involved intestine; (4) loss of the normal luster and color of the serosal coat; and, most important of all, (5) absence of arterial pulsation. What may at first appear to be nonviable intestine requiring resection will often return to viability when the cause of the obstruction has been relieved and when the bowel has been packed for a time in warm, moist gauze. There is also a prompt change in the color of viable bowel when 100% oxygen is inhaled. Infiltration of the mesentery with 1% procaine hydrochloride solution may also overcome vascular spasm and bring about arterial pulsations in questionable cases. The intra-arterial injection of fluorescein followed by ultraviolet lamp illumination may be used to evaluate the regional perfusion. A hand-held Doppler ultrasound device in a sterile cover may also be useful in verifying the arterial supply.
In the presence of tumor, the mesentery should be explored for metastatic nodes. If there is any doubt as to the site of the obstruction, the surgeon should not hesitate to eviscerate the patient until the offending lesion is adequately exposed and to pass the bowel between the fingers, section by section, from the ligament of Treitz to the cecum. The surgeon must be certain no secondary lesion or distal cause of obstruction exists.