An elderly nursing home resident arrives at the emergency

Discussion in 'MRCS Forum' started by Lona., Dec 6, 2007.

  1. Lona.

    Lona. Guest

    An elderly nursing home resident arrives at the emergency room moribund with little helpful history. She is profoundly alkalotic by blood gas measurement, and her urine shows an acid pH. A possible explanation is -
    a- Release of inappropriate antidiuretic hormone
    b- Severe crush injury
    c- Acute tubular necrosis
    d- Gastric outlet obstruction
    e- An eosinophilic pituitary adenoma
  2. Lona.

    Lona. Guest

    Answer: 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 hyperventilation to “bowel off” carbonic acid. On the other hand, we are poorly equipped to deal with metabolic alkalosis. We cannot hold our breath to save acid because 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 order conditions listed would be expected to produce acidosis; consequently, acid urine would not be paradoxical.

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