Unknown unknowns and pleural effusions

There are plenty of unknowns when it comes to management of pleural effusions on the ICU, which led to a paper with an eye-catching title1.

Mechanically ventilated patients frequently have pleural effusions detected by radiological investigations. Whether to drain them is a common conundrum for intensivists. A systematic review of the literature showed that drainage often improves oxygenation and has a low complication rate2.

While it may have the added advantage of assisting diagnosis and guiding therapy, there is a paucity of literature demonstrating improved patient-orientated outcomes with the routine drainage of pleural effusions in ventilated patients.


1. A pseudo-Rumsfeldian approach to pleural effusions in mechanically ventilated patients.
Crit Care. 2011 Mar 11;15(2):132 Free Full Text

2. Utility and safety of draining pleural effusions in mechanically ventilated patients: a systematic review and meta-analysis.
Crit Care. 2011;15(1):R46 Free Full Text

INTRODUCTION: Pleural effusions are frequently drained in mechanically ventilated patients but the benefits and risks of this procedure are not well established.

METHODS: We performed a literature search of multiple databases (MEDLINE, EMBASE, HEALTHSTAR, CINAHL) up to April 2010 to identify studies reporting clinical or physiological outcomes of mechanically ventilated critically ill patients who underwent drainage of pleural effusions. Studies were adjudicated for inclusion independently and in duplicate. Data on duration of ventilation and other clinical outcomes, oxygenation and lung mechanics, and adverse events were abstracted in duplicate independently.

RESULTS: Nineteen observational studies (N = 1,124) met selection criteria. The mean PaO2:FiO2 ratio improved by 18% (95% confidence interval (CI) 5% to 33%, I2 = 53.7%, five studies including 118 patients) after effusion drainage. Reported complication rates were low for pneumothorax (20 events in 14 studies including 965 patients; pooled mean 3.4%, 95% CI 1.7 to 6.5%, I2 = 52.5%) and hemothorax (4 events in 10 studies including 721 patients; pooled mean 1.6%, 95% CI 0.8 to 3.3%, I2 = 0%). The use of ultrasound guidance (either real-time or for site marking) was not associated with a statistically significant reduction in the risk of pneumothorax (OR = 0.32; 95% CI 0.08 to 1.19). Studies did not report duration of ventilation, length of stay in the intensive care unit or hospital, or mortality.

CONCLUSIONS: Drainage of pleural effusions in mechanically ventilated patients appears to improve oxygenation and is safe. We found no data to either support or refute claims of beneficial effects on clinically important outcomes such as duration of ventilation or length of stay.