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.