The impact of perioperative atelectasis on antibiotic penetration into lung tissue:: an in vivo microdialysis study

Objective: Postoperative pneumonia is a potentially devastating complication associated with high mortality in intensive care unit (ICU)-patients. One of the major predisposing factors is the perioperative occurrence of atelectatic formations in non-dependent lung areas. Perioperative ventilation/perfusion mismatch due to atelectasis may influence antibiotic distribution to lung tissue, hence increasing the risk of postoperative pneumonia. We evaluated whether differences in ventilation/perfusion mismatch can influence antibiotic distribution into lung tissue by means of in vivo microdialysis, comparing patients undergoing coronary artery bypass grafting (CABG) with cardiopulmonary bypass (CPB) (atelectasis model), with patients operated with the off-pump coronary artery bypass grafting (OPCAB)-technique. Patients and methods: We compared five patients operated with CPB (CPB-group) and five patients undergoing CABG with OPCAB-technique (OPCAB-group). Levofloxacin (500 mg) was administered intravenously, after surgery, in the ICU. Time versus concentration profiles of levofloxacin in lung tissue and plasma were measured at regular time-intervals. Results: In the OPCAB-group, the median of the maximum concentration of levofloxacin in lung tissue (4.1 mu g ml(-1) +/- 7, range 3.7-11.8 mu g ml(-1)) was significantly higher compared with the CPB-group (2.5 mu g ml(-1) +/- 0.3, range 2.0-2.9 mu g ml(-1)) (P = 0.046). Median levofloxacin tissue/plasma area under the concentration curve (AUC) ratio in lung tissue was 0.3 +/- 0.2 (range 0.1-0.7) in the CPB-group versus 0.7 +/- 1.6 (range 0.4-0.8) in the OPCAB-group (P = 0.015). Conclusions: Data indicate that postoperative interstitial antibiotic concentration is influenced by perioperative atelectasis formation. Our findings suggest the re-evaluation of clinical dosing schemas of antibiotic therapy in a variety of diseases associated with atelectasis formation.