Rates of infection secondary to CABG surgery varied widely across a 33-hospital consortium engaged in an adult cardiac-surgery quality initiative in Michigan. The variation was less pronounced but still substantial after adjustment for comorbidities and other patient-related factors.
Isolated pneumonia was overwhelmingly the most common CABG-related infection, seen in about 3% of the total population at all centers. The overall rate of any infection averaged 5.1%, but infection rates for each center ranged from 0.9% to 19.1%, a span of 18.2 percentage points.
Predicted risk after adjustment for comorbidities and other patient-related factors averaged 4.9% over all patients, but center-by-center ranged from 3.9% to 6.7%. That means there’s still a 2.8-point spread in their predicted CABG-related infection risks that can’t be explained away by variation in patient mix at the different surgical centers, according to Dr Donald S Likosky (University of Michigan, Ann Arbor).
Perhaps it resulted from unknown, unmeasured confounders that affected predicted infection rates, he said. “But the effect of that confounding would have to be very large, implausibly large, to account for the [18.2-point spread across centers] in the observed rates.”
Rather, the variation in predicted infection rates was related to differences in “something about the way we take care of patients,” according to Likosky, “because it’s not a function of the different types of patients that we see.” He is senior author on the study, which was published July 1, 2014 in Circulation: Cardiovascular Quality and Outcomes with lead author Dr Terry Shih (University of Michigan).
Covariates in deriving the predicted infection rates included age, body-mass index, cardiovascular disease, smoking status, ejection fraction, dyslipidemia, hypertension, chronic lung disease, immunosuppressive therapy, peripheral arterial disease, diabetes, congestive heart failure, NYHA class, cardiogenic shock, and anticoagulant usage.
Four of the 33 Michigan centers were outliers with respect to observed infection rates and accounted for most of their variation; without them, observed rates ranged only from 0.9% to 6.9%. Likosky said he wasn’t at liberty to reveal those four centers’ distinguishing characteristics. Those could potentially explain their outlier status.
Importantly, the four centers’ predicted rates didn’t differ greatly from those of the other 29 centers, suggesting that their contribution to the wide range in observed rates wasn’t the result of patient factors. “Institutional or surgeon-level factors” that may instead account for it are under further study by Likosky’s group.
Shih et al looked at 20 896 patients who underwent isolated CABG surgery at the 33 participating centers over a 3.5-year period starting in 2009. Of the 1071 patients (5.1%) who developed the “healthcare-acquired infections” tracked in the analysis, 3.1% had isolated pneumonia and 0.6% had multiple infections. Isolated sepsis or septicemia, deep sternal-wound infection, and infections of the harvest/cannulation and thoracotomy sites were seen at rates of less than 1% each. Patients with endocarditis had been excluded.
“We hypothesize that efforts to reduce this variation should focus on developing and supporting multidisciplinary clinical-care teams across traditional silos of care,” the group writes. Clearly, they note, pneumonia and, to a lesser extent, multiple infections, drove the variable rates of CABG-related infections at the 33 centers.
“Traditional approaches to improving cardiac surgery have focused on modifying surgical practices in the operating room. Such strategies have included the wide-scale adoption of minimally invasive approaches for harvesting the saphenous vein. Nonetheless, our current data suggest that this conceptual model may yield only modest gains.” Their data, in fact, suggest that the infection rate associated with conduit harvesting was only 0.5%.