PH in pleural fluid

Q; 72 years old male is admitted to ICU with fever, right-sided pleuritic chest pain, cough, and low-grade fever. Patient continues to require low-dose pressor in Emergency Room (ER) and is admitted to ICU. On Chest-X-ray (CXR) parapneumonic effusion is suspected due to history, symptoms and presence of infiltrates on CXR. What's the ideal way of drawing pleural PH? - select one

A) into a pediatric venous blood draw tube

B) into an arterial blood gas syringe

Answer: B

In suspected parapneumonic effusion or empyema, pleural fluid for pH should be drawn directly from the pleural space. Ideally, it should be drawn into an arterial blood gas (ABG) syringe. It should be placed immediately on ice and measured in a blood gas analyzer within one hour. It is rather a delicate draw and transport! Mixing pleural fluid with air, lidocaine, or excess heparin can alter the measured pH. Care should be taken particularly for lidocaine, as it can still be present in good amounts in skin, subcutaneous tissue, and underlying structures after local anesthetic application.

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References:

1. Cheng DS, Rodriguez RM, Rogers J, et al. Comparison of pleural fluid pH values obtained using blood gas machine, pH meter, and pH indicator strip. Chest 1998; 114:1368.

2. Bowling M, Lenz P, Chatterjee A, et al. Perception versus reality: the measuring of pleural fluid pH in the United States. Respiration 2012; 83:316.

3. Rahman NM, Mishra EK, Davies HE, et al. Clinically important factors influencing the diagnostic measurement of pleural fluid pH and glucose. Am J Respir Crit Care Med 2008; 178:483.