A model incorporating 17 easily obtainable preoperative variables may help clinicians estimate patients’ risk of developing pneumonia after undergoing coronary artery bypass graft surgery, according to a report published in Annals of Thoracic Surgery.
“This model may be used to inform clinician-patient decision making and to identify opportunities for mitigating a patient’s risk,” said Raymond J. Strobel, a medical student at the University of Michigan, Ann Arbor, and his associates.
American Heart Association
Postoperative pneumonia is the most common hospital-acquired infection following CABG, and it raises mortality risk fourfold and increases length of stay threefold. But reliable estimation of patient risk of post-CABG pneumonia has been difficult because of its low relative incidence – roughly 3% – and because most studies of the disorder are nearly a decade out of date.
To devise a predictive model using current data, Mr. Strobel and his associates assessed numerous potential risk factors and outcomes for 16,084 consecutive patients undergoing CABG at all 33 cardiac centers across Michigan during a 3-year period. They identified 531 cases of post-CABG pneumonia (3.3%) in this cohort.
The investigators performed a univariate analysis to test the associations between pneumonia and numerous factors related to patient demographics, medical history, comorbid diseases, laboratory values, cardiac anatomy, cardiac function, pulmonary function, the CABG procedure, and the institution where the procedure was performed. Variables that were found to be significantly associated with pneumonia (though usually with small absolute magnitudes) were then assessed in a multivariate analysis, which was further refined to create the final model.
The final model includes 17 factors that clearly raise the risk of post-CABG pneumonia. These include an elevated leukocyte count; a decreased hematocrit; older patient age; comorbidities such as peripheral vascular disease, diabetes, and liver disease; markers of pulmonary impairment such as cigarette smoking, the need for home oxygen therapy, and chronic lung disease; markers of cardiac dysfunction such as a recent history of arrhythmia and decreased ejection fraction; and emergency or urgent rather than elective operative status.
“This model performs well and demonstrates robustness across important clinical subgroups and centers,” the investigators said (Ann Thorac Surg. 2016 Jun 1; doi: 10.1016/j.athoracsur.2016.03.074).
In particular, this study identified preoperative leukocytosis to be a significant predictor of post-CABG pneumonia across several subgroups of patients. “We speculate that patients presenting with an elevated white blood cell count before surgery may be mounting an immune response against a pathogen and that the insult of CABG significantly increases their odds of postoperative pneumonia. ... It may be prudent to delay surgery until the source of leukocytosis is satisfactorily investigated, if not identified and treated, or the leukocytosis has otherwise resolved,” Mr. Strobel and his associates noted.