Case Study 4: An elderly man was admitted to hospital in an acute confused state. No history was available but the nicotine stains on his fingers indicated he was a heavy smoker. Physical examination revealed he had signs of a right-sided pleural effusion but no other abnormality was detected. He was neither dehydrated nor edematous. A chest x-ray confirmed the presence of the effusion and showed a mass in the right lower zone with an appearance typical of a carcinoma. Chemistry Lab Results Serum Urine Na" 114 mmol/L Na 50 mmol/day K" 3.6 mmol/L Osmolality 1350 mOsmol/kg O 77 mmol/L Co, 22 mmol/L Urea 2.5 mmol/L (2.1-7.1) Glucose 4.0 mmol/L Total protein 48 g/L Osmolality 236 mOsmol/kg Questions: 1. What is the likely cause of the abnormal serum electrolyte results? 2. Calculate the patient's osmolality and osmolal gap, are they normal or abnormal? What does this mean? 3. What might be the cause of the increased urine sodium and osmolality?

Pleural effusion

It is the accumulation of fluid in the pleural space resulting from excess fluid production and decreased absorption.

Causes:

• Congestive heart failure
• Cancer
• Pneumonia
• Pulmonary embolism.

Management

• Thoracentesis.
• Tube thoracostomy (chest tube). 
• Pleural drain.