Context and Definition

A pleural effusion is an abnormal collection of fluid within the pleural space.

The annual incidence of pleural effusion in the developed world has been estimated at 320 per 100,000 population per year [1]. In the USA approximately 1.5 million people are diagnosed with a pleural effusion each year [2]. There are no reliable figures for the UK, however there are estimated to be 50,000 new cases of pleural effusions due to malignancy alone each year. [3]

Little data relating specifically to the frequency of pleural effusions presenting to ED exists. Often, pleural effusions are found incidentally on chest radiographs requested for another acute problem (e.g. heart failure, pneumonia) or a chronic condition already known to the patient (e.g. malignant effusion).

Mortality and morbidity for patients with pleural effusion is related more to the underlying cause than the size of the effusion. However, pleural effusions are not entirely innocuous. Patients with pneumonia have a poorer outcome if it is associated with a para-pneumonic effusion [4] and patients with a malignant pleural effusion (particularly those associated with carcinoma of the lung or gut) have a mean survival time of only a few months [5].

Mortality and morbidity is also related to the biochemical make-up of the pleural fluid (e.g. protein content, pH, cell content). This is because it reflects the underlying cause of the effusion (e.g. transudate in heart failure; exudate in pneumonia or malignancy).