Paradoxical aciduria (the excretion of acid urine in the pre

Paradoxical aciduria (the excretion of acid urine in the presence of metabolic alkalosis) may occur in the presence of

a. Release of inappropriate antidiuretic hormone
b. Severe crush injury
c. Acute tubular necrosis
d. Gastric outlet obstruction
e. An eosinophilic pituitary adenoma 40 Surgery

The answer is d. (Schwartz, 7/e, pp 60–62.)
The body has elaborate mechanisms to compensate for metabolic acidosis. Not only do most body functions work better in an acidotic state, the patient is able to move toward correction of the pH by excreting acid urine and by hyperventilating to “blow off” carbonic acid. On the other hand, we are poorly equipped to deal with metabolic alkalosis. We cannot hold our breath to save acid since the respiratory center overrides our efforts as the PaCO2 rises and the PaO2 falls. The kidney cannot make urine under any circumstance that is very far above normal pH. In the subtraction alkalosis that accompanies gastric outlet obstruction with loss of gastric acid by vomiting or suction, the potassium depletion and volume deficits provoke exchange of sodium for hydrogen ion in the distal tubule with resultant exacerbation of the metabolic alkalosis. All the other conditions listed would be expected to produce acidosis; consequently, acid urine would not be paradoxical.