Postoperative lymphopenia: An independent risk factor for postoperative pneumonia after lung cancer surgery, results of a case-control study

Postoperative lymphopenia has been proposed as a risk factor for postoperative infections but has never been identified as such in a multivariate analysis. Postoperative pneumonia (POP) is one of the most common complications after lung cancer surgery and is associated with a worse outcome. We aimed to evaluate the association between postoperative lymphopenia and POP after lung cancer surgery. Patients admitted for lung cancer surgery (lobectomy, bilobectomy, or pneumonectomy) aged ≥ 18 years and with no history of an immunosuppressive state were eligible for inclusion. Lymphocyte counts were determined in blood drawn on the day before surgery and at postoperative days 1, 3 and 7. POP diagnosis was based on clinical, biological and radiological data. A logistic regression model adjusted on currently described risk factors for POP was used to explain the onset of this condition. Two hundred patients were included, of whom 43 (21.5%) developed POP. Preoperative lymphocyte count was 1.8±0.6x10(9) cells/L and 2.0±0.7x10(9) cells/L in patients with and without POP, respectively (P = .091). In both groups, the lymphocyte count nadir occurred at postoperative day 1. In multivariate analysis, lymphopenia at postoperative day 1 was significantly associated with increased risk of POP (odds ratio: 2.63, 95% CI [1.03-5.40]). POP rate at postoperative day 7 was higher in patients presenting low lymphocyte counts (≤1.19x10(9) cells/L) at postoperative day 1 (P = .003). Our study showed that lymphopenia following lung cancer surgery was maximal at postoperative day 1 and was associated with POP.