Sigmoid capnometry in abdominal aortic aneurysm surgery

EDITOR: It was with great interest that I read the paper by Lebuffe and colleagues [1]. My colleagues and I have monitored patients operated for aortoiliac disease with sigmoid colon saline tonometry since 1992 [2]. Initially, we monitored all patients, but since only 0.9% of patients undergoing elective surgery suffer clinically relevant intestinal ischaemia [3], since 1994 we have monitored only high-risk patients: all operated on for a ruptured abdominal aortic aneurysm or with other risk factors [4]. We published a 5 yr prospective study [5] in which we concluded that the method was diagnostic for colon ischaemia and that it could distinguish mucosal from transmural gangrene. Such a distinction is not possible with any other diagnostic method [6]. We reported no mortality after elective surgery, and a 25% mortality rate after operation for a ruptured abdominal aortic aneurysm. This, in combination with the fact that no patient died from colon ischaemia, suggested that pHi monitoring of the sigmoid colon may improve survival among these patients. Lebuffe and colleagues wrote: 'the first saline method to determine PrCO2 did not allow easy gut perfusion monitoring and, therefore, its routine use was limited'. Though we used the saline method with success, I agree that the idea of continuous and on-line measurements is more practical and less time-consuming. In 1999, we therefore started to use the air-automated sigmoid capnometer (Tonocap®), i.e. the same device used by Lebuffe and colleagues. Considering that the supplier (Datex-Ohmeda, Helsinki, Finland) ceased production of the saline sigmoid colon tonometry balloon-catheter, we had no choice. Commercially, the new capnometer was more interesting, at least to the supplier. However, we soon realized that the capnometer could only measure PCO2 to the upper limit of 15 kPa. This measuring interval is quite sufficient for gastric monitoring, but when patients develop severe sigmoid colon ischaemia the regional PCO2 can reach levels >30 kPa. One of the main advantages of the diagnostic method, to distinguish between benign mucosal ischaemia and bowel gangrene requiring relaparotomy, was lost. Even though the old surgical wisdom 'it is better to look and see than to wait and see' is relevant in many situations, reoperation of a patient recovering from a ruptured abdominal aortic aneurysm is not without risk. We have developed a 'home made' device to convert the air tonometry to a conventional saline tonometry, when PCO2 levels >14 kPa are registered. Lebuffe and colleagues report that among eight patients operated on electively, three suffered severe and four mild ischaemic colitis. One patient died. Previous studies [7,8] relating to routine colonoscopy after elective aortic surgery reported a frequency of mucosal ischaemia in approximately 5-9%, and the frequency of severe ischaemia is approximately 1% [3]. How can Lebuffe and colleagues explain their frequencies of 88 and 38%, respectively? And how did they act when the Tonocap® registered values close to 15 kPa? In my opinion, the new promising method of air-automated sigmoid capnometry needs to be evaluated among patients operated on for a ruptured abdominal aortic aneurysm. In this situation, we found the frequency of clinically relevant colonic ischaemia to be 7%, and 22% of the deaths were associated with this devastating complication [3]. M. Björck Department of Surgery; University Hospital; Uppsala, Sweden