CAUSES OF FEVER AND PULMONARY DENSITIES IN PATIENTS WITH CLINICAL MANIFESTATIONS OF VENTILATOR-ASSOCIATED PNEUMONIA

Background: Ventilator-associated pneumonia, a leading cause of sepsis in patients with acute respiratory failure, is difficult to distingui sh clinically from other processes affecting patients receiving mechan ical ventilation. We conducted a prospective study of patients with su spected ventilator-associated pneumonia to identify the causes of feve r and densities on chest radiographs and to evaluate the diagnostic yi eld and efficiency of tests used alone and in combination. Methods: Th e 50 patients entered into the study underwent a systematic diagnostic protocol designed to identify all potential causes of fever and pulmo nary densities. Diagnoses responsible for fever were established by st rict diagnostic criteria for 45 of the 50 patients. The prevalence of specific conditions and diagnostic yield of individual tests were used to formulate a simplified diagnostic protocol. Results: The diagnosti c protocol identified 78 causes of fever (median 2 per patient). Infec tions were the leading causes of fever and pulmonary densities. Of the 45 patients with fever, 37 had one or more infections identified (67 sources). Most infections (84 percent) were one of four types: pneumon ia, sinusitis, catheter-related infection, or urinary tract infection. Ventilator-asseciated pneumonia occurred in only 42 percent. All but nine infections (87 percent) were directly or indirectly related to in sertion of a catheter or a tube. Concomitant infections were frequent (62 percent), particularly in patients with sinusitis (100 percent), c atheter-related infections (93 percent), and pneumonia (74 percent). O f concomitant infections, 60 percent were caused by a different pathog en. Noninfectious causes of fever were more common in the 22 patients with adult respiratory distress syndrome. Histologically proved pulmon ary fibroproliferation was the only cause of fever in 25 percent of pa tients with adult respiratory distress syndrome. Radiographic densitie s were caused by an infection in only 20 patients (19 pneumonia, 1 emp yema). In more than 50 percent of the 25 patients without adult respir atory distress syndrome, congestive heart failure, and atelectasis wer e the sole causes of pulmonary densities, and fever always originated from an extrapulmonary site of infection. Used in combination, broncho scopy with protected sampling, computed tomographic scan of the sinuse s, and cultures of maxillary sinus aspirate, central intravenous or ar terial lines, urine, and blood identified 58 of the 78 sources of feve r (74 percent). Conclusions: The observations in this study document t he complex nature of acute respiratory failure and fever and underscor e the need for accuracy in diagnosis. The frequent occurrence of multi ple infectious and noninfectious processes justifies a systematic sear ch for source of fever, using a comprehensive diagnostic protocol. A s implified diagnostic protocol was devised based on the diagnostic valu e of individual tests.