Failure of Bacterial Filters to Reduce the Incidence of Pneumonia after Inhalation Anesthesia

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Abstract
There were 520 patients undergoing inhalation anesthesis who were studied to evaluate the efficacy of low resistance 0.22 .mu.m bacterial filters in preventing postoperative pneumonias. Patients undergoing elective thoracic, upper abdominal and lower abdominal surgeries were randomly assigned preoperatively to filtered and nonfiltered anesthesia circuits by a study nurse. A 2nd study nurse, who was unaware of patient assignments, followed each patient for 5 postoperative days to identify possible pulmonary complications. Both groups of patients were similar in age, sex distribution, smoking history, prior pulmonary disease, types and duration of surgery, ASA [American Society of Anesthesiologists] physical status classification, and receipt of intraoperative antibiotics. No differences in rates of postoperative pneumonia were observed between patients assigned to filtered and nonfiltered circuits (16.7% vs. 18.3%, respectively, P = 0.73). No differences were observed when the incidences of other outcome criteria such as postoperative fever, abnormal chest X-ray, sputum production, or abnormal pulmonary physical exam findings were evaluated. Bacterial gas filters apparently do not influence the incidence of postoperative pneumonias. Routine use of these devices for this purpose is seemingly not cost-effective.