A nurse is caring for a client who is on a mechanical ventilator. Blood gas results indicate a pH of 7.50 and a PCO2 of 30 mm Hg. The nurse has determined that the client is experiencing respiratory alkalosis. Which laboratory value would most likely be noted in this condition?
A. Sodium level of 145 mEq/L
B. Potassium level of 3.0 mEq/L
C. Magnesium level of 2.0 mg/L
D. Phosphorus level of 4.0 mg/dl
Correct Answer: B. Potassium level of 3.0 mEq/L
Clinical manifestations of respiratory alkalosis include headache, tachypnea, paresthesias, tetany, vertigo, convulsions, hypokalemia, and hypocalcemia. Since the primary cause of all respiratory alkalosis etiologies is hyperventilation, many patients present complaints of shortness of breath. The exact history and physical exam findings are highly variable as there are many pathologies that induce the pH disturbance. Options 1, 3, and 4 identify normal laboratory values. Option 2 identifies the presence of hypokalemia.
Option A: In hypoxic patients, it is important to calculate the A-a gradient to determine the etiology and further diagnosis. If the A-a gradient is wide, be suspicious of pulmonary embolism and appropriately work up the patient.
Option C: Serum electrolytes should be measured with particular attention to sodium, potassium, and calcium levels as aberrations in these may lead to further complications. Magnesium and phosphate are also essential to measure.
Option D: Physical exam findings may be just as varied depending on etiology to include fever, tachycardia, tachypnea, diaphoresis, hyper or hypotension, altered mental status, productive or non-productive cough, wheezing, rales, crackles, cardiac murmur or arrhythmia, jugular venous distension, meningeal signs, focal neurological loss, Trousseau sign, Chvostek sign, jaundice, melena, hematochezia, hepatosplenomegaly, or there may be no definitive signs at all.
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