Pleural Effusions in the Medical ICU

Abstract & Commentary

Synopsis: When pleural effusions were deliberately sought by radiograph and ultrasound, most patients in the medical ICU had them; in the absence of clinical infection they generally did not require specific management.

Source: Mattison LE, et al. Chest 1997;111:1018-1023.

Mattison et al prospectively studied 100 consecutive medical ICU admissions using standard chest X-rays and bedside ultrasound in order to determine the prevalence of pleural effusions in this population. Of the patients, 41 were found to have effusions on admission to the ICU, and an additional 21 patients developed effusions during their MICU stay. Most of the effusions were small. Diagnostic thoracenteses were attempted in 14 of the 100 patients and were successful in 11.

Patients with effusions were older (mean, 54 vs 4.7 years, P = 0.04), had higher APACHE II scores (mean, 17.2 vs 12.0, P = 0.01), and had longer stays in the ICU (mean, 9.8 vs 4.6, P = 0.0002) than patients who did not develop effusions. Mortality rates were the same, and no adverse outcomes were thought to be related to pleural effusion.

Using standardized criteria, the cause of the effusion was noninfectious in 51 of 62 patients (82%), with heart failure the leading etiology (22/62, 35%), followed by atelectasis in 14 of 62 (23%). Unilateral effusions were due to atelectasis more often than to another cause, while bilateral effusions were most often due to heart failure. Of the eight patients with effusions associated with infection, seven had uncomplicated parapneumonic effusions and one had bilateral empyemas.


This study, from a group of investigators at the Medical University of South Carolina that has done a number of studies on pleural effusions in the ICU, demonstrates that if effusions are prospectively and deliberately sought they can be demonstrated in the majority of medical ICU patients. Such a finding would be cause for alarm if it were also demonstrated that a substantial number of the effusions required specific management, since their prevalence appears to be much higher than most clinicians appreciate. However, it is reassuring to note that the great majority of the effusions were simply observed and had no detectable adverse effect on the patients’ clinical course.

Most of the effusions were judged to be noninfectious and acute, and thus either not associated with a specific problem in the pleural space or benign and self-limited. Thus, this study does not change the dogma that "the sun should never set on an untapped parapneumonic pleural effusion." That remains the best advice because of the crucial importance of early diagnosis of pleural empyema. Fortunately, as shown by this prospective study in a general medical ICU population, most patients with effusions do not have clinical infection as a likely etiology, and the majority do not require thoracentesis.