The goal of this study is to compare the diagnostic yield in terms of cellular content and biochemical characteristics of pre-aspiration agitated pleural fluid versus that of conventionally aspirated fluid in pleural infection patients. The hypothesis is that the agitated fluid would be more representative and thus may aid the diagnosis of non-infected exudative pleural effusions.

Transudation or exudation are the two mechanisms by which fluid accumulates, where Starling forces' imbalance is responsible for the former and inflammatory increase in capillary permeability accounts for the latter. Despite the history and presentation commonly suggesting the underlying etiology, pleural fluid aspiration and analysis is frequently required for confirmation of the nature and cause of the effusion. Aspirated pleural fluid is routinely subjected to biochemical analysis as well as microbiological and cytological analysis especially when infection or neoplasia is suspected. One drawback however to thoracentesis analysis is the relatively low diagnostic yield in different forms of exudative effusion. Tuberculous pleural effusions have a yield of <10% on acid-fast bacilli smears and overall yield <30% on solid culture. Conventional cytologic analysis from malignant pleural effusions also show a relatively low overall yield of around 51%, though this could be highly variable depending on the primary cancer involved (6% in mesothelioma - 80% in ovarian adenocarcinoma).In addition, it is not uncommon for analysis results to widely vary in the same patient in those with loculated and in malignant pleural effusions. This could be attributed to the compartmentalization in complex septated collections and heterogenous distribution of cellular components throughout the pleural space. The gold standard however in diagnosing unexplained exudative pleural effusions is pleural biopsy which is technically demanding and sometimes associated with longer hospital stay along with the increased incurred costs.

The investigators propose a method for improving the representativeness of pleural fluid samples via pleural agitation prior to aspiration in exudative noninfected pleural effusion. The aim is to test the feasibility and safety of using pleural fluid agitation prior to aspiration and to investigate the potential for an improved diagnostic yield using this novel thoracentesis technique in patients with exudative non-infected pleural effusion. A control group of 10 participants with transudative pleural effusion (based on history, clinical picture, and imaging) will be included to exclude any effect of the agitation procedure on the biochemical profile of the pleural fluid. These will include patients with uncontrolled heart failure, renal or hepatic impairment presenting with classical uncomplicated free pleural effusion.

Inclusion Criteria:

1. Age > 18 years old
2. At least a moderate amount of pleural fluid collection (2 or more intercostal spaces on thoracic ultrasound)

Exclusion Criteria:

1. Minimal - mild pleural fluid deemed unsuitable for aspiration and agitation
2. Hemodynamic instability
3. Pleural infection based on clinical presentation, imaging or laboratory investigations and pleural fluid examination showing glucose < 40 mg/dL or pH <7.2 with lower respiratory infection, positive gram stain or bacterial culture or pus on aspiration

Laboratory personnel responsible for the cytological and biochemical analysis will be blinded to the identity of the paired samples