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Ann Thorac Surg 1995;59:1210-1213
© 1995 The Society of Thoracic Surgeons

Postoperative Abdominal Complications in Cardiopulmonary Bypass Patients: A Case-Controlled Study

Mark J. Ott, MD, Timothy G. Buchman, MD, PhD, William A. Baumgartner, MD

Department of Surgery, The Johns Hopkins Medical Institutions, Baltimore, Maryland

Accepted for publication February 9, 1995.


   Abstract
Top
 Footnotes
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 
Intraabdominal complications (IAC) after cardiopulmonary bypass often are difficult to diagnose and are associated with high mortality (13% to 67%). From 1984 to 1991 we retrospectively analyzed 53 patients undergoing cardiopulmonary bypass for coronary artery bypass grafting, valve reconstruction, or arch reconstruction who experienced 55 episodes of IAC and compared them with matched control patients (matched for operation, age, and sex). The overall incidence of IAC was 0.65%. Univariate analysis identified the following preoperative variables as significantly (p < 0.05) increasing the risk of IAC: history of congestive heart failure, chronic renal failure, and more than three medical problems. A history of congestive heart failure was the most powerful predictor by multivariate analysis (p = 0.045). Early post–cardiopulmonary bypass complications were increased significantly in IAC patients. These included acute renal failure (p < 0.0001), cerebrovascular accidents (p < 0.03), and lower extremity ischemia (p < 0.05). Twenty-eight of 38 laparotomies performed were diagnostic. However, analysis of 58 combined clinical, radiologic, and laboratory tests failed to identify which predicted the diagnostic utility of a laparotomy. Fifteen of the 53 IAC patients (28%) survived: 8 patients had had a therapeutic laparotomy, 1 patient underwent a nondiagnostic laparotomy, and 6 patients were managed nonoperatively. Multivariate analysis identified ventilator dependence (p = 0.004) and acute renal failure with creatinine level greater than 1.9 mg/dL (p = 0.011) as the most powerful predictors of mortality regardless of intervention. These data suggest a profile of cardiac surgical patients at risk for IAC as well as those patients who are most likely to benefit from timely intervention.


   Introduction
Top
 Footnotes
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 
Twelve separate retrospective studies [1–12] since 1980 have documented high mortality (13% to 67%) associated with cardiopulmonary bypass–induced intraabdominal complications (IAC). Fortunately the frequency of IAC in these studies was low (0.41% to 2.0%). However, due to the large number of cardiac surgical procedures being performed each year, most major cardiac surgical centers can expect to see on average one IAC per month. These complications are difficult to diagnose, thereby delaying therapy [4–7, 11] and augmenting mortality. We retrospectively evaluated an 8-year period in a case-controlled fashion to determine preoperatively which patients were at highest risk of development of IAC. We also wanted to determine early clinical and laboratory indicators of postoperative patients in whom IAC developed and which of these patients were likely to benefit from surgical exploration. Finally, we wanted to identify a profile of patients who, despite maximal medical and surgical therapy, have irreversible abdominal catastrophes.


   Patients and Methods
Top
 Footnotes
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 Acknowledgments
 References
 
All adult nontransplant patients who underwent operation involving cardiopulmonary bypass from 1984 through 1991 were eligible for inclusion in the study. Intraabdominal complications were defined as any postoperative event involving the gastrointestinal tract or abdominal cavity requiring medical or surgical intervention. Purposefully excluded from this study were patients with isolated upper gastrointestinal bleeding. Also excluded from our series were patients with isolated hyperamylasemia not requiring surgical intervention. Both of these patient groups were excluded based on the fact that they are diagnosed rapidly and easily and have a low morbidity and mortality in our series and that of others [12]. The focus of this study was on the recognition of IAC that carried a high mortality.

Candidates for inclusion in the study were identified by review of the minutes of the monthly morbidity and mortality conferences. The monthly morbidity and mortality conference minutes contain a complete list of complications of all types including autopsy findings when performed, and have been used previously to identify other patient populations (eg, pulmonary embolism, mediastinitis) for analysis. Once identified, charts were reviewed extensively to include the following data: age, sex, race, past medical problems requiring regular medical care or medication, previous cardiac surgical procedure(s), type of operation, and date of operation. Cardiopulmonary bypass data included body surface area; cardiopulmonary bypass time; cross-clamp time; lowest, highest and mean flow rate and arterial pressure; pulsatile versus nonpulsatile flow; and need for intraaortic balloon pump support either before or after cardiopulmonary bypass. Chronic renal failure was defined as a creatinine value of more than 1.9 mg/dL.

Also included in the analysis was the postoperative time to onset of abdominal abnormalities and the following clinical, radiologic, and laboratory parameters at the time of recognition of the abdominal abnormality: presence and location of abdominal tenderness or guarding; presence of bowel sounds; distention; alteration in mental status; temperature; heart rhythm and rate; blood pressure; cardiac index; systemic vascular resistance; central venous pressure; pulmonary capillary wedge pressure; type of inotropic support; blood in the gastric aspirate and on rectal examination; presence of a new cerebral deficit; acute lower extremity ischemia; ventricular tachycardia/fibrillation; number of returns to the operating room for postoperative complications; radiologic, nuclear medicine, and endoscopic findings; ventilator dependence; arterial blood gases; hematologic, electrolytic, and chemical profiles; lactate level; microbiologic data; number of days after CPB to exploratory laparotomy; the general surgeon's preoperative diagnosis; laparotomy findings; autopsy results when available; presence of multiple organ dysfunction [13]; survival after exploratory laparotomy; and final abdominal diagnosis and outcome. Postoperative acute renal failure was defined as a creatinine level of more than 1.9 mg/dL or worsening of preexisting renal failure of more than 1.5 mg/dL.

For statistical comparison appropriate case controls without IAC then were selected at random from the general cardiopulmonary bypass population and matched for similar operation, sex, age, race, date, and urgency of operation (Table 1Go).


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  		Table 1. . Preoperative Factors
 
In a univariate analysis, patients with IAC were compared with their matched case controls without IAC by means of an odds ratio analysis with 95% confidence intervals followed by {chi}2 analysis and Fisher's exact test (two-tailed). Multivariate analysis was performed using multiple logistic regression analysis according to the SAS program (Cary, NC). A p value of less than 0.05 was considered significant.


   Results
Top
 Footnotes
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 Acknowledgments
 References
 
During the 8-year study, 8,448 adult nontransplant surgical patients underwent cardiopulmonary bypass at The Johns Hopkins Hospital. A total of 55 IAC occurred in 53 patients (Table 2Go) during this time period (frequency = 0.65%). Thirty-eight of the 53 patients with an IAC died yielding a 72% mortality rate compared with no deaths in the case control group (p < 0.001). The overall mortality for adult nontransplant cardiac surgery patients during that same period was 5.3%.


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  		Table 2. . Abdominal Complications
 
Preoperative Variables Predictive of Intraabdominal Complications
Through case controlled analysis we identified the following preoperative variables as significant predictors of an IAC (Table 3Go). By univariate analysis, preexisting chronic renal failure increased the likelihood of IAC by 4.37 times (95% confidence interval, 1.14 to 16.6). If patients had more than three preoperative medical problems they were 4.98 times more likely to have an IAC (95% confidence interval, 2.1 to 11.7). Patients with a history of congestive heart failure had a 2.93-fold increased risk of IAC (95% confidence interval, 1.24 to 6.9). However, analysis of all variables by multivariate logistic regression demonstrated the history of congestive heart failure to be the most significant predictor of increased risk of IAC (p = 0.045). Interestingly, a preoperative history of atrial fibrillation, peripheral vascular disease, hypertension, and diabetes mellitus, each of which were analyzed separately, did not have a significant predictive value for IAC.


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  		Table 3. . Preoperative Predictors of Intraabdominal Complications
 
Postoperative Variables Predictive of Intraabdominal Complications
Analysis of early postoperative variables demonstrated IAC to be associated with acute renal failure, cerebrovascular accidents, and lower extremity ischemia (Table 4Go). The development of acute renal failure in the postoperative period correlated with a 40-fold increase in IAC (95% confidence interval, 5.1 to 310). Although the development of either cerebral insufficiency (n = 6) or lower extremity ischemia (n = 5) also achieved statistical significance (p < 0.025 and p < 0.05, respectively), the absence of these events in the control group was associated with statistical uncertainty and thus weakened the predictive value of these latter two complications.


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  		Table 4. . Postoperative Complications Predictive of Intraabdominal Complications
 
Surgical Intervention
Thirty-eight laparotomies were performed on 53 patients experiencing 55 episodes of IAC (see Table 2Go). Of these 38 laparotomies, 28 were diagnostic, with the surgeon documenting definitive pathology that accounted for the patient's deterioration. Ten procedures were nondiagnostic although the surgeon had a high suspicion of IAC before laparotomy.

Of the 28 diagnostic laparotomies, 8 were also therapeutic, leading to survival. One of the patients with nondiagnostic laparotomy survived and the other 9 died of multiple organ dysfunction.

Of the 17 patients with IAC that were managed nonoperatively, 6 survived. Analysis of 58 separate clinical, laboratory, and radiologic variables in the 38 patients undergoing laparotomy failed to identify any single variable or set of variables predictive of the need for a laparotomy in a particular patient.

Postoperative Variables Predictive of Mortality
By multivariate logistic regression analysis the following variables were predictive of mortality regardless of medical or surgical intervention (Table 5Go). Among the 15 patients who survived, only 1 (7%) was ventilator dependent at the time of onset of IAC. Thirty-one of 38 patients (82%) who were ventilator dependent died, resulting in a 63-fold (95% confidence interval, 7.7 to 639) increase in mortality for ventilator-dependent patients.


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  		Table 5. . Postoperative Predictors of Mortality
 
Renal failure after cardiopulmonary bypass was also a significant predictor of mortality among patients experiencing IAC. Renal failure developed in only 3 of the 15 survivors compared with 32 of 38 nonsurvivors (84%) (p = 0.011), leading to a 25-fold (95% confidence interval, 4.6 to 99) increase in mortality in patients with renal failure. Other postoperative univariate variables predictive of mortality included decreased or altered mental status and an alkaline phosphatase level greater than 120 U/L (see Table 5Go).


   Comment
Top
 Footnotes
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
Acknowledgments
 References
 
Intraabdominal complications after cardiopulmonary bypass, although infrequent, are associated with a high mortality. Survival depends on timely diagnosis and intervention, which requires a high level of awareness by cardiac surgeons and critical care personnel. Ideally, preoperative awareness of patients at high risk might prevent these IAC or result in earlier intervention. Patients with chronic renal failure, multiple medical problems, and, most importantly, a history of congestive heart failure should be considered at higher risk for IAC.

Our study did not look specifically at intraoperative methods to monitor or alter this risk. However, other studies have looked at measurements of effective hepatic blood flow [14], small intestinal transport and permeability using uptake of various sugars from the gut [15], and continuous pH measurements of the stomach [16] as methods of assessing intraabdominal compromise during cardiopulmonary bypass. Each of these methods appears to be able to document impaired perfusion of intraabdominal organs. The application of such specialized monitoring methods to reduce morbidity and mortality in these high-risk patients is unclear. At present, identification of high-risk patients and either exclusion from operation or heightened awareness postoperatively would appear to be the most effective operative strategy.

Diagnosis of patients with IAC has been vexing in prior series [1–12] and in our own series as documented by the time from onset of abdominal abnormalities to institution of definitive therapy being an average of 3.4 days (range, 0.17 to 21 days). The second aim of this study was to identify early clinical and laboratory indicators of patients in whom IAC developed in the postoperative period and determine which patients might benefit from surgical exploration. The development of early complications such as acute renal failure, lower extremity ischemia, or a cerebrovascular accident all correlated with the occurrence of IAC and should increase the clinician's suspicion of incipient IAC. These three complications together with preoperative congestive heart failure are consistent with low cardiac output syndrome as the cause of IAC. However, a persistent episode of low cardiac output was not documented in our patients experiencing IAC. Similarly, review of the combined 58 clinical, radiologic, and laboratory values failed to identify any test or finding predictive of a patient with a specific pathology.

Surgical exploration, however, was beneficial. Twenty-eight of the 38 laparotomies performed revealed pathology that accounted for the patient's deterioration. Eight of these laparotomies led to life-saving surgical intervention. There was 1 survivor among the 10 patients who had a nondiagnostic laparotomy. At the same time there were 17 patients with episodes of IAC that were managed nonoperatively, of which 6 patients ultimately survived. Thus even though one cannot predict the therapeutic value of laparotomy, the number of patients surviving ultimately was doubled in our series by expeditious surgical exploration. We acknowledge that there is a selective bias regarding the decision to operate.

Outcome was analyzed to determine which patients had IAC at the time of diagnosis that led to irreversible deterioration and death. Multivariate analysis showed that patients who were ventilator dependent had a 65-fold increased risk of dying (82% mortality). Likewise patients with acute renal failure had a 25-fold increased risk of dying (84% mortality). Mortality resulted regardless of medical or surgical intervention. Ventilator dependence and acute renal failure were clear predictors of mortality.

In summary, this study identified a preoperative profile of patients at risk for IAC during and after cardiopulmonary bypass. Patients at high risk included those with a preoperative history of chronic renal failure, multiple medical problems, and most importantly a history of CHF. Patients who match this profile should be informed of their increased risk and be monitored closely in the postoperative period.

Acute renal failure, lower extremity ischemia, and a cerebrovascular accident in the early postoperative period all were associated with the simultaneous occurrence of IAC. We failed to identify any indicators that were predictive of the need for surgical intervention. However, half of the surviving patient group had undergone surgical intervention, and we would recommend the continued use of early surgical exploration in patients in whom the diagnosis or management is obscure. Patients with acute renal failure or ventilator dependence at the time of recognition of IAC are unlikely to survive despite maximal medical and surgical intervention.


   Acknowledgments
Top
 Footnotes
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
References
 
This study was supported in part by research career development award GM00581 to Dr Buchanan.


   Footnotes
Top
 Footnotes
Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 
Address reprint requests to Dr Baumgartner, The Johns Hopkins Hospital, 600 N Wolfe St, Blalock 618, Baltimore, MD 21287-4618.


   References
Top
 Footnotes
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 

  1. Egleston CV, Gorey TF, Wood AE, McGovern EM. Gastrointestinal complications after cardiac surgery. Ann R Coll Surg 1993;75:52–6.
  2. Huddy SPJ, Joyce WP, Pepper JR. Gastrointestinal complications in 4473 patients who underwent cardiopulmonary bypass surgery. Br J Surg 1991;78:293–6.[Medline]
  3. Ohri SK, Desai JB, Gaer JAR, et al. Intraabdominal complications after cardiopulmonary bypass. Ann Thorac Surg 1991;52:826–31.[Abstract]
  4. Widera R, Lindenau KF, Prehl J, Grossman M. Abdominal complications after cardiac surgery with cardiopulmonary bypass. Zent Bl Chir 1990;115:885–91.
  5. Krasna MJ, Flancbaum L, Trooskin SZ, et al. Gastrointestinal complications after cardiac surgery. Surgery 1988;104: 773–80.[Medline]
  6. Leitman IM, Paull DE, Barie PS, Isom OW, Shires GT. Intra-abdominal complications of cardiopulmonary bypass operations. Surg Gynecol Obstet 1987;165:251–4.[Medline]
  7. Welling RE, Rath R, Albers JE, Glaser RS. Gastrointestinal complications after cardiac surgery. Arch Surg 1986;121:1178–80.[Abstract]
  8. Moneta GL, Misbach GA, Ivey TD. Hypoperfusion as a possible factor in the development of gastrointestinal complications after cardiac surgery. Am J Surg 1985;149:648–50.[Medline]
  9. Pison CW, Alberty RE. General surgical complications after cardiopulmonary bypass surgery. Am J Surg 1983;146:133–7.[Medline]
  10. Hanks JB, Curtis SE, Hanks BB, Andersen DK, Cox JL, Jones RS. Gastrointestinal complications after cardiopulmonary bypass. Surgery 1982;92:394–400.[Medline]
  11. Wallwork J, Davidson KG. The acute abdomen following cardiopulmonary bypass surgery. Br J Surg 1980;67:410–2.[Medline]
  12. Christenson JT, Schmuziger M, Maurice J, Simonet F, Velebit V. Gastrointestinal complications after coronary artery bypass grafting. J Thorac Cardiovasc Surg 1994;108:899–906.[Abstract/Free Full Text]
  13. Fry DE, Pearlstein L, Fulton RL, Polk HC. Multiple system organ failure: the role of uncontrolled infection. Arch Surg 1980;115:136–40.[Abstract]
  14. Hampton WW, Townsend MC, Schirmer WJ, Haybron DM, Fry DE. Effective hepatic blood flow during cardiopulmonary bypass. Arch Surg 1989;124:458–9.[Abstract]
  15. Ohri SK, Bjarnason I, Pathi V, et al. Cardiopulmonary bypass impairs small intestinal transport and increases gut permeability. Ann Thorac Surg 1993;55:1080–6.[Abstract]
  16. Fiddian-Green RG, Baker S. Predictive value of the stomach wall pH for complications after cardiac operations: comparison with other monitoring. Crit Care Med 1987;15:153–6.[Medline]



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