Possible role of nitric oxide in postoperative ileus: a comparative study

In the present study, the possible involvement of nitric oxide (NO) in the pathogenesis of postoperative ileus was investigated indirectly by measuring nitrate, a stabile metabolite of NO. Plasma levels and 24-h urinary excretion of nitrate and nitrite were determined in the peri-operative period in three different groups of patients undergoing surgery: group 1 (LT, n=11) underwent a laparotomy, group 2 (LS, n=12) underwent a laparoscopic procedure, whereas group 3 underwent an extra-abdominal procedure (EA, n=9). Duration of postoperative ileus was assessed clinically using first occurrence of flatus and defaecation as the end of the period of ileus. Postoperative ileus lasted significantly longer in the LT group (first flatus after 3.0 [3.0-4.0] days) compared with the LS (1.0 [1.0-2.0] days) and EA (1.0 [1.0-3.0] days) groups. Urinary nitrate excretion increased significantly in the LT and EA groups during the first 24 h after surgery (from 797.0 [214.0-810.0] and 551.5 [438.3-1215.8] to 2079.0 [889.0-4644.0] and 1102.5 [315.3-1238. 0] micromol/24 h, median [IQR]), but normalized before the end of postoperative ileus. Plasma levels of nitrate were unchanged after surgery, whereas CRP levels were significantly increased in all groups (LT > LS=EA). In the first 24 h following surgery, urinary nitrate excretion is increased, suggesting increased endogenous synthesis of NO postoperatively. As no correlation was found between urinary nitrate excretion and duration of postoperative ileus, we conclude that assessment of nitrate has no value in predicting clinical outcome after surgery.