Critical Care Medicine-Renal, Electrolyte and Acid Base Disorders>>>>>Calcium, Phosphate, and Magnesium
Question 7#

A 45-year-old male with past medical history of COPD is admitted for acute hypoxemic respiratory failure secondary to influenza H1N1. He is intubated for 7 days. On hospital day 7, his P/F ratio has improved to 220 and the patient’s chest x-ray looks improved. He fails spontaneous breathing trial for two consecutive days secondary to low tidal volumes. He has poor cough reflex and was given 5 days of steroids for his acute illness. 

Which electrolyte is most likely to be deficient in this patient?

A. Serum phosphorus
B. Serum free cortisol
C. Serum calcium
D. Serum potassium

Correct Answer is A

Comment:

Correct Answer: A

Low serum phosphorus has been strongly associated with diaphragmatic weakness. Since the duration of steroid therapy was short, the probability of steroid induced myopathy is low.

Reference:

1. Aubier M, Murciano D, Lecocguic Y, et al. Effect of hypophosphatemia on diaphragmatic contractility in patients with acute respiratory failure. N Engl J Med. 1985;313(7):420-424.