Interactive Cardiovascular and Thoracic Surgery 3:475-478(2004)
© 2004 European Association of Cardio-Thoracic Surgery
Institutional report - Cardiac general |
Gut ischaemia following cardiac surgery
S. Hasana,*,
C. Ratnatungaa,
C.T. Lewisb and
R. Pillaia
a Department of Cardiothoracic Surgery, John Radcliffe Hospital, Oxford OX3 9DU, UK
b Derriford Hospital, Plymouth, UK
* Corresponding author. Tel.: +44-1869-349844; fax: +44-1865-220244
faizashafqat{at}hotmail.com
Received January 7, 2004;
received in revised form April 8, 2004;
accepted April 9, 2004
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Abstract
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Gut ischaemia following cardiac surgery carries a high mortality and is usually due to non-occlusive mesenteric ischaemia. We reviewed 4464 patients undergoing cardiac surgery over a 5-year period. Sixteen of them developed gut ischaemia post-operatively, 13 of whom were discovered at laparotomies while the remaining 3 were post-mortem diagnoses. Eleven patients were found to have extensive ischaemia and all 11 died irrespective of the treatment and the delay in diagnosis. In five patients ischaemia was localized, involving the caecum in three and terminal ileum in two. They all underwent local resections and survived. The differences in the groups were analysed and the average time between onset of symptoms and laparotomies was longer in the localized ischaemia group compared to the extensive ishaemia group. Our experience illustrates the continuing difficulty in diagnosis of mesenteric ischaemia before gut infarction has occurred. We conclude that different pathologies might be involved in post-cardiac surgery gut ischaemia and although early diagnosis and treatment is considered to be crucial, early laparotomies do not necessarily equate to survival in cases of extensive ischaemia. There is a need to evaluate aggressive strategies for early diagnosis if prognosis is to be improved in these cases.
Key Words: Cardiac surgery; Gut ischaemia; Complications
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1. Introduction
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Major intra-abdominal complications following cardiac surgery are uncommon with an incidence varying from 0.4 to 2% [1–4]. They carry a very high mortality and figures of 13–67% have been reported [1–12]. Gut ischaemia has the highest reported mortality of all the intra-abdominal complications [1–4].
The vast majority of the cases of gut ischaemia are due to non-occlusive mesenteric ischaemia. The condition is difficult to diagnose and this contributes to the catastrophic end result. Early diagnosis is thought to be of critical importance as the only chance of cure is with early surgery. We retro and prospectively studied all cases of gut ischaemia to identify means of improving survival in these patients.
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2. Patients and methods
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We retrospectively and prospectively studied 4464 patients undergoing cardiac operations at Derriford Hospital Plymouth and John Radcliffe Hospital Oxford between November 1997 and July 2003. Sixteen patients developed gut ischaemia in this group. Thirteen of these were diagnosed at laparotomies while three cases were discovered at post-mortem. Twenty-six patients underwent laparotomies during the study period in which four were negative and other abdominal pathologies were discovered in nine patients. Abdominal complications that settled on medical management were not included.
We reviewed the sixteen patients with gut ischaemia in detail. Data was obtained on patient characteristics and details of the mode and timing of presentation, the relevant investigations and treatment received were recorded. The following information regarding the cardiac operation was found: type of operation, degree of urgency, method of myocardial protection, bypass time and cross-clamp time. Intensive care notes were reviewed to find out time to extubation and length of stay in the intensive care unit. A note was made of inotrope requirements, intra-aortic balloon pump support, perioperative arrhythmias and any prolonged periods of hypotension. The 16 patients were divided into two groups on the extent of gut ischaemia present. All those with localized ischaemia survived with resections and all those with extensive ischaemia died. The differences in the two groups were analysed statistically.
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3. Statistical analysis
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The differences in the two groups of patients of patients were analysed for significance using the  -test for continuous data and the  -method for categorical data.
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4. Results
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Out of 4464 patients reviewed, 16 patients developed gut ischaemia (0.3%). The mean age of the group was 73.9 years with a male to female ratio of 3:1. Eleven out of them were coronary revascularizations (69%) and 5 were valve replacements. Thirteen patients were diagnosed at laparotomies while 3 were discovered at post-mortem examinations. There were 4 negative laparotomies performed for suspected bowel ischaemia during this period. Eleven of the 16 patients with ischaemia died and only 5 survived, giving an overall mortality of 68.7%. All patients with localized ischaemia survived and all those with extensive ischaemia died. They were divided into two groups for comparison.
Five patients had localized ischaemia that was involving the caecum in 3 cases and a small segment of distal ileum in the remaining 2. They were all treated with local resections and they all survived. The other 11 patients had extensive ischaemia and 3 of them were discovered at post-mortem examinations. Resection was only possible in 4 of these cases and even that did not make any difference to the outcome and they all died. The details of the two groups are given in Table 1. The mean age and male to female ratio of the groups was not statistically different but there was a significant difference in their pre-operative left ventricular function, post-operative incidence of arrhythmias and inotrope use. Seven of the patients in the extensive ischaemia group were in a low cardiac output state on inotropes. The details of the procedures performed and the myocardial protection used are given in Table 1 and the bypass and ischaemic times were similar. Three of the extensive ischaemia group were done off-pump. Moderate hypothermia was used in all cardiopulmonary bypass cases ranging from 32 to 34 °C on surgeons' preference. Three of the localized and 2 of the extensive ischaemia group patients presented with pain and signs of peritonitis, while 2 of the localized and 3 of the extensive group presented with signs of pseudo-obstruction. Six patients in the generalized group had a non-specific presentation as signs were masked probably because of them being sedated and ventilated. The mean interval between onset of symptoms and laparotomy was 45.6 h in the localized as compared to 22.2 h in the extensive group, which was not a statistically significant difference.
Various investigations were carried out in these patients. Abdominal X-rays were performed in all cases and showed non-specific features of ileus/pseudo-obstruction in patients who presented with distension. CT scan of the abdomen was performed only in 4 patients, as it was either thought to be not necessary, as in patients with clear signs or not logistically possible, as in case of unstable patients. Three of the scans were reported as normal and one showed gas in the caecal wall in a patient with localized caecal necrosis. Abdominal ultrasound was performed in 2 patients and showed dilated bowel loops. Arterial blood gases showed metabolic acidosis in 1 of the 5 localized and 9 of the extensive gut ischaemia cases. This means that even in two of the cases with extensive ischaemia metabolic acidosis was absent and the serum lactate level was normal. The white blood cell count was elevated in most patients and serum amylase was found to be elevated in two.
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5. Discussion
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Intra-abdominal complications after cardiac surgery carry a high mortality but by far the most dangerous of them is gut ischaemia, which constitutes about 0.3% of all intra-abdominal complications. Majority of these are due to non-occlusive mesenteric ischaemia [5,6], and other causes like superior mesenteric artery thrombosis and embolism are rare. The prognosis of gut ischaemia remains dismal and our mortality of 68.7% is in line with most series [7].
Early diagnosis is paramount in patients with bowel ischaemia as this offers the only chance of cure [7]. This can only be achieved by maintaining a high index of suspicion and a low threshold for exploration. The diagnosis is usually clinical as there is no non-invasive investigation that is diagnostic [8]. Diagnosis is often delayed as signs either appear late or are masked [9]. Even pain is a late feature in these cases and by that time the process may be irreversible. Mesenteric angiography is the only test that can be diagnostic but it is not routinely performed as it is invasive, requires special expertise and is difficult to do in unstable patients. In our experience all patients with clear signs of intestinal ischaemia died. Thus by the time clear signs develop, ischaemia has usually progressed to infarction. Unexplained metabolic acidosis is considered an important early indication for intervention in these cases [7], but in our experience it can be absent and the serum lactate can be normal even in cases of extensive ischaemia. It is important that if there is any doubt a diagnostic laparotomy should be carried out. We exercised a policy of early intervention in these cases, which is apparent from the 4 negative laparotomies in our series. Even though a low threshold for exploration was maintained the diagnosis was missed in 3 patients, who were sedated and ventilated and they were discovered at post-mortem. It is disappointing that in spite of our interventions all our cases with global type of bowel necrosis died. This is in keeping with the experience of other authors. This suggests that a more aggressive approach needs to be adopted and some have advocated mesenteric angiography in all suspected cases [8].
There is still a debate about the exact aetiology of non-occlusive mesenteric ischaemia. It is related to hypoperfusion [10] and certainly gut is one of the first organs to undergo ischaemia in haemodynamic stress. Vasculitis of the mesenteric vessels has also been suggested [9]. The presence of pre-existing atherosclerosis in the mesenteric arteries is thought to be a contributory factor. Pseudo-obstruction and distension is thought to aggravate mucosal ischaemia and lead to necrosis. Most authors have found an association of ischaemic bowel with prolonged hypotension, ventilator dependence, congestive cardiac failure, chronic renal failure, low cardiac output state, intra-aortic balloon pump dependency, cerebro-vascular events and lower limb ischaemia [7,10–12]. Our experience is in keeping with others as most of our extensive ischaemia cases occurred in patients with impaired ventricular function who were in a low output state. Three of our cases occurred in patients that were done off-pump and thus we feel that cardiopulmonary bypass may not necessarily be the cause. It has also been suggested by others that off-pump cases are just as susceptible to mucosal hypoxia as on-pump cases [13].
At the same time a third of our cases were different as they presented out of the blue in patients doing well after surgery and they developed localized gut ischaemia, which seemed a different pathology. There were no marked differences in these groups when compared with respect to age, sex, surgical technique, myocardial protection used, bypass and cross-clamp times. There were significant differences with respect to pre-operative left ventricular function, incidence of post-operative arrhythmias and post-operative inotrope and intra-aortic balloon pump usage. All the patients with ischaemia localized to the caecum or terminal ileum survived and those with extensive ischaemia died. These two groups may represent two separate pathologies or early and late stages of the same pathological process. Certainly some authors have claimed a better survival for cases operated within 6 h of onset of symptoms [7]. In our experience this difference in outcome and degree of intestinal ischaemia cannot be accounted for by a delay in diagnosis as, if anything, the mean length of time from presentation with abdominal symptoms and surgical intervention was longer in the localized ischaemia group. Histopathological examination of all the resected specimens did not give any clues to the aetiology and just showed trans-mural necrosis in both groups.
There were three distinct modes of presentation of this complication in our experience. First there was the non-specific presentation in cases of low output syndrome and multi-organ failure. Here a central role of the impaired gut barrier function has been described in driving the systemic inflammatory syndrome and multi-organ failure. Gut ischaemia in these cases is a terminal event as it causes a viscous circle that is usually fatal. This condition remains difficult to treat and will continue to carry a poor prognosis. The second presentation is with acute onset pain and tenderness. This needs to be treated promptly with surgery, preferably within 6 h of onset as this offers the best chance of cure. The third and last presentation is the one with abdominal distension and pseudo-obstruction. This ileus and pseudo-obstruction points to a low cardiac output and is reflective of ischaemia. This needs to be managed aggressively to prevent the viscous circle that leads to systemic inflammatory response and multi-organ failure. Gastro-intestinal integrity in these cases is a predictor of outcome. It has been proposed that if these cases do not settle on conservative therapy for 3 days they should have mesenteric angiography and if non-occlusive mesenteric ischaemia is shown, treatment with local papaverine infusions has been recommended with good results [8]. Early operations and colonic decompression in the form of caecostomies and colostomies for pseudo-obstruction with massive distension have also been recommended. Further work needs to be done in this field.
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6. Conclusion
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We conclude that different pathologies may be involved in post-cardiac surgery gut ischaemia. Diagnosis is difficult and early laparotomies are paramount but unfortunately do not necessarily effect survival in cases of extensive ischaemia, if the diagnosis is made on clinical grounds. There is a need to adopt an aggressive approach to diagnosis in suspected cases of non-occlusive mesenteric ischaemia and the role of mesenteric angiography needs to be evaluated. More work is needed in this field as early diagnosis and prevention of progression from ischaemia to necrosis appears to be the only hope and for this a greater understanding of the disease process is required.
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Appendix A
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ICVTS on-line discussion
Author: Dr. Hitoshi Hirose, Juntendo Univesity Hospital, Department of Cardiovascular Surgery, Hongo, Bukyo-ku, Tokyo
Date: 18-May-2004
Message: I agree with the author's idea. Ischemic bowel is difficult to diagnose, especially in a patient who is intubated and sedated. However, in a patient with septic condition early after surgery, ischemic bowel should always be considered. The initial sign of the ischemic bowel is just abdominal pain. Physical examination or abdominal x-rays may not help for diagnosis. Fever, peritoneal signs, and elevated white cell count may be late signs of ischemic bowel, suggesting the patient may have been developing bowel necrosis. The diagnosis is essentially dependent on the physician's high index of suspicions, and laparotomy is necessary for definitive diagnosis and treatment. As the author pointed out clearly in this paper, delay of the diagnosis results in a mortality.
doi:10.1016/j.icvts.2004.04.003
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Abstract
1. Introduction