A therapeutic intervention was performed culminating in further drainage and
considerable clinical improvement. A CT scan selleck inhibitor of the chest was performed (Fig. 3, Fig. 4 and Fig. 5) and the patient discharged home with early follow-up (Fig. 6). What diagnosis is suggested by the pleural fluid analysis? The analysis is in keeping with an exudative, complicated parapneumonic effusion. Classically, a pleural fluid protein >30 g/l suggests an exudative cause and <30 g/l a transudative cause. However, it has been known since 1976 that the reliability of absolute values is poor.1 Hence, the application of Light’s criteria is recommended in the interpretation of pleural fluid results.2 Pleural fluid is an exudate if one or more of the following criteria are met: 1. Pleural fluid protein divided by serum protein is >0.5. Light’s criteria are nearly 100 percent sensitive at identifying exudates, but approximately 20 percent of patients with pleural effusion caused by heart failure may fulfil the criteria for an exudative effusion after receiving diuretics.3 An empyema is defined as pus in the pleural cavity. In this case the fluid was straw coloured but the clinical suspicion of pleural space infection was high. Therefore pH analysis was undertaken. Pleural fluid
acidosis is a marker of increased metabolic activity due to an increase in lactic acid and carbon dioxide production.4 Increased consumption of glucose occurs also such that the pleural fluid glucose concentration is low.5 Pleural fluid acidosis can also be associated with malignancy and see more connective tissue disease and should therefore be interpreted with the contemporary clinical picture. More importantly, a meta-analysis of studies examining pleural pH and the need for chest tube drainage or surgery in patients with parapneumonic effusions found
MTMR9 that a pH < 7.2 was the most specific discriminator of complicated pleural infection and of the need for immediate chest drainage.6 The current British Society Guidelines7 support this and indicate that if pH measurement is not possible, a pleural fluid glucose level <3.4 mmol/l may be used as an alternative marker to indicate a need for chest drain insertion, with the caveat that in certain other conditions like rheumatoid arthritis, the glucose level may be low too. What is the patho-physiology of this type of effusion? A progressive process occurs as a simple exudate transitions through a fibrino-purulent stage culminating in an organising stage with scar tissue formation. The normal volume of pleural fluid in humans is less than 1 ml and it forms a thin film between parietal and visceral pleura. In the early inflammatory phase, pro-inflammatory cytokines cause increased vascular permeability leading to fluid shift into the pleural space. This fluid is free flowing and has no bacteria within it. With ongoing damage to the endothelium, bacterial invasion can occur.