Discussion
A principal finding of this study was that GI complications occur with relative infrequency following index adult cardiac surgical procedures, occurring only in 2.4% of our study cohort. These complications tended to occur more commonly in patients who were elderly with an increased comorbidity burden. Other risk-adjusted predictors of developing GI complications included pre-existing impaired renal function, especially those who were dialysis dependent preoperatively, chronic obstructive pulmonary disease, congestive heart failure, use of intra-aortic balloon pumps, and prolonged aortic cross clamp times. Patients who experienced postoperative GI complications had reduced short- and long-term survival, and also experienced higher rates of other concurrent complications including renal failure, multi-system organ failure, and deep sternal wound infections. After propensity-matching patients based on preoperative comorbidities, the occurrence of GI complications was still associated with significantly higher mortality as well as other major complications.
The incidence of GI complications in our cohort was 2.4%, which is comparable to prior series, in which the occurrence of GI complications ranged from 0.5 to 4.5%2–6. Several risk factors such as advanced age, chronic obstructive pulmonary disease, heart failure, and worsening preoperative renal function, were identified to be associated with increased risk for development of GI complications. While these risk-factors typically portend worse prognoses in cardiac surgical patients due to their affiliation with a declining preoperative clinical status, they also serve as surrogates for important physiological events that proceed GI complications as well as concomitant non-GI complications2,3,9,10. For instance, elderly patients and those with chronic obstructive pulmonary disease from smoking may have a higher vascular calcific burden placing them at risk of gastrointestinal ischemia from ischemic events. This may manifest as thrombembolism from a calcified aorta during cross-clamping, or hypoperfusion of abdominal organs during a low flow state in the postoperative period.
Additionally, those requiring intra-aortic balloon counterpulsation had a two-fold increase in the hazard for GI complications. This finding has also been described by Hashemzadeh et al who found several risk factors for GI complications in their series including advanced age (>65 years), preexisting renal disease, intra-aortic balloon pump, and prolonged aortic cross-clamp times3. It is unclear of the etiology of these GI complications result directly from the devices themselves, for instance from thrombus formation on the balloon that is dislodged upon removal or malpositioned balloon pumps leading to intestinal and hepatic ischemia11–15. The use of intra-aortic balloon pump may also represent a surrogate for the critically ill patient with higher likelihood of hemodynamic instability and end-organ malperfusion. We also found increasing aortic cross-clamp time to be correlated with risk of GI complications. Longer case time was also demonstrated by Marsoner and colleagues who found increasing cardiopulmonary pump times to be associated with higher odds of GI complication (OR 1.006, 95% CI 1.001 to 1.011, P=0.026)7. Longer cross-clamp times may subject the patient to longer cardiopulmonary bypass runs, embolic phenomena during bypass, and increased risk of postoperative vasoplegia, all of which may contribute to end-organ malperfusion and/or ischemia. Such events may explain increased propensity for GI complications following longer procedures.
The most common GI complication in our series was Clostridium difficile intestinal infection, but GI bleeding was most prevalent in patients that died within the first postoperative year. In prior series, postoperative GI bleeding has been associated with an 8.8% 30-day mortality, and risk factors included advanced age, congestive heart failure, cerebrovascular disease, and chronic kidney disease. The etiology of the majority of these bleeding events (71%) were from duodenal ulceration16. Unlike other GI complications such as Clostridium difficile infection, acute cholangitis, or prolonged ileus which have the potential for cure with appropriate antibiotic management, surgery, and/or expectant management, GI bleeding may be a recurrent phenomenon outside of the postoperative window and possibly exacerbated by newly-prescribed anticoagulation therapies following cardiac surgery. As such, GI bleeding may confer continual long-term morbidity and mortality after cardiac operations.
Several reports have identified GI complications following cardiac surgery to be linked to reduced short-term survival. In hospital mortality has been reported to be exceedingly high ranging between 34-87%5,17. In our study, we demonstrate a 30-day mortality of 24.8% in those with GI complications. Rates of other events such as renal failure, new dialysis dependency, and multi-system organ failure were more likely to occur concurrently with GI complications. This clustering effect persisted after propensity matching illustrating the profound physiologic insult that GI complications impart to other organ systems, or are a result of processes that also portend increased risk to these other organ systems. These clusters of complications reflect an adverse cascade of physiologic insults that often begin with malperfusion from emboli or hypotension that leads to bacterial translocation, more severe hemodynamic compromise and ultimately worsening malperfusion, Additionally, patients with GI bleeds, intestinal ischemia or severe Clostridium difficile colitis may be intravascularly dry requiring extensive volume resuscitation, which may further compromise patients with reduced ejection fractions and also lead to pulmonary dysfunction. It is well appreciated that as more complications are acquired in an individual patient, the odds of mortality increase exponentially18,19. Furthermore, additional complications increase intensive care and hospital length of stay time, and often require additional medical, and sometimes surgical, resources for management and treatment of these complications. As a result, it is likely that patients experiencing GI and other concurrent complications often pose a significant resource and financial burden to healthcare systems.