Discussion
In this analysis, KPTx was associated with a 3.5-fold higher occurrence of any complication following CABG, and even higher after emergency CABG (OR 3.707, p<0.01). Previous literature has shown that transplant patients undergoing cardiac procedures may experience higher complication rates compared to the general population7,19,20. Each transplant group in this study carried a significantly higher Elixhauser comorbidity index score (calculated by preexisting comorbidities) compared to Non-Tx, which may reflect an increased baseline risk. However, it has also been demonstrated that transplant recipients have comparable mortality and long-term survival to non-transplanted individuals3,20,21. It remains critical to investigate surgical complications and risk factors in this unique population to establish preventative measures and comprehensive management protocols.
Emergency surgeries in transplant patients have been associated with worse surgical outcomes3,6,22,23. Non-elective surgery has been identified as a risk factor for major postoperative morbidity and mortality, including decline in renal function3,6. Emergency abdominal surgery in solid organ transplant is associated with up to 32.7% morbidity and 17.5% mortality22, findings significantly higher than the general population. This association is likely explained by greater case complexity, greater incidence of complication, or immunosuppressive regimens that predispose to certain issues, such as infections5,23.
Compared to the non-transplant population, KPTx had the highest complication following CABG (78.3% vs. 47.8%). Cardiovascular issues occurred evenly among all groups regardless of transplant status. However, rates of respiratory complications were significantly higher among transplant patients, with the highest in KPTx (8.0%). After excluding renal dysfunction, John et al. demonstrated that most transplant recipients required ventilatory support after cardiac surgery (11.4%)3. Pulmonary morbidity after cardiac surgery is common regardless of transplant status, including pleural effusions, pneumonia, and atelectasis. Transplant recipients may be at increased risk for pulmonary issues due to chronic immunosuppression, as well as changes in pulmonary compliance from pre-transplant fluid overload of ESRD24.
The incidence of SIRS was increased in all transplant recipients, with significantly higher rates in PTx (8.0%). Following cardiac surgery, rates of major infection in the transplant population may be as high as 19%20. Transplant recipients face a unique post-operative infection burden due to lifelong immunosuppression. These regimens downregulate inflammatory mediators, impair T-cell activation, and interfere with critical phases of wound healing25. Sirolimus may predispose to wound complications, including deep infections, cellulitis, and fascial dehiscence26. Likewise, chronic corticosteroid use is associated with a 2 to 5-fold increase in wound complications rates when compared to those not taking steroids27. However, we were unable to evaluate the risk in specific treatment regimens as the NIS database does not provide this detail.
Acute renal failure was a significant complication in all transplant groups following CABG. PTx had the highest risk of acute renal failure (40.7%), followed by KTx (35.7%), and KPTx (26.7%). Cardiopulmonary bypass itself may pose a risk of kidney injury due to hypoperfusion or inflammatory reactions inherent to the bypass mechanism28. Postoperative kidney dysfunction appears to be significantly more common in transplant patients after cardiac surgery3. Elevated preoperative serum creatinine (SCr >2 mg/dL) confers a higher risk and predisposes to postoperative kidney failure3,6. Transplant recipients may be at even greater risk from the nephrotoxic maintenance immunosuppressive regimens which lower baseline GFR. Off-pump surgery (beating heart surgery) has demonstrated fewer postoperative kidney complications and may show promise in transplant patients28. Larger studies are needed to evaluate whether this approach should be preferred.
Transplant recipients required more blood products than their Non-Tx counterparts, which may have further impacted their risk of complication. Perioperative red blood cell (RBC) transfusion increases the risk of AKI after cardiac surgery 29,30. This may be the result of impaired oxygen handling by transfused RBCs, or faster breakdown causing more iron release and oxidative stress29,30. Additionally, blood transfusions pose a unique risk in the transplanted population. RBC transfusions increase HLA sensitization and antibody response which can increase the risk of future graft failure31. Sensitization can occur after a single transfusion, and nearly one-third of patients have already received a transfusion before being added to the transplant list31. Overly aggressive blood transfusions may increase the risk of perioperative AKI, future graft rejection, and render subsequent re-transplantation more difficult from the presence of reactive antibodies.
Rates of perioperative mortality in transplant patients have ranged from 1.4% to as high as 15.7%3,32. While there was no in-hospital mortality to analyze PTx and KPTx, the rate of KTx mortality in this report (3.9%) was similar to that of other reviews33. Three- and five-year survival rates in kidney transplants after CABG ranged from 70% and 66%, respectively6,34, to as high as 85% for 5-year survival35. Importantly, although KPTx carried the greatest rate of complication, this did not influence in-hospital mortality. However, the data is unable to show how long-term survival is affected as a result.
We identified greater total hospital charge and LOS in transplant recipients on the univariate analysis. PTx had greatest median total charge overall ($276,012) and longer LOS following CABG (14 days in PTx vs. 8 days in Non-Tx). However, in the adjusted outcomes, LOS and total hospital charge were not increased in transplant recipients, despite being more likely to suffer a complication. Further analysis of pancreas transplant recipient surgical costs is needed to reconcile these conflicting results.
Our findings demonstrated increased risk in both non-transplant and transplant centers. It is unclear whether transplant centers provide superior care. Most surgeons believe care is better at transplant centers and recommend acute surgery be performed at these facilities36. However, in transplant recipients undergoing abdominal surgeries, DiBrito et al. found no statistically significant difference in complication rates at transplant centers vs. non-transplant centers37,38. Although we found increased in-hospital mortality in KTx at transplant centers, this was likely skewed by a greater proportion of deaths at these centers, as the overall mortality rate was 3.9% (or 106 out of 2678 patients).