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09/14/2011 - lactate due to hyperventilation

posted Sep 28, 2011, 5:56 PM by Chief Resident   [ updated Oct 10, 2011, 10:58 AM by Purnema Madahar ]
Today in Chief of Service, we worked on a confusing acid-base problem that we were not able to conclusively solve.

A elderly gentleman with a history of duodenal carcinoid and intermittent diarrhea that the gastroenterologist thought was not due to the carcinoid (but did not have another diagnosis for) presented with a brief episode of weakness and joint stiffness, resolved by the time he came to the ED. He had not had diarrhea recently. Exam was unremarkable, although he had an unlabored respiratory rate of 24.

His initial ABG and lytes: 7.56/27/60 with a O2 Sat 92%, calculated HCO3 25, lactate 6.6; Na 139, K hemolysed, Cl 92, HCO3 23 which yields a gap of 24

Without treatment, his ABG and lytes 24 hours later (asymptomatic): 7.48/29/99 with a O2 Sat 98%, calculated HCO3 22, lactate 0.6; Na 137, K 3.8, Cl 105, HCO3 21 which yields a gap of 11

Vic Schuster reasoned that this might all be an acute respiratory alkalosis which could give you concomitant lactic acid. Alternatively, the patient might have a triple disturbance with a respiratory alkalosis, a metabolic gap acidosis and a metabolic alkalosis.

Two follow-ups courtesy of Vic Schuster:

1. Of the potential causes of gap metabolic acidoses, salicylates seem most plausible in the history of this patients and should be added on to his recent labs.

2. From the attached paper he sent along, it seems that lactate as a consequence of hyperventilation and alkalemia does not rise to the level we saw in our patient:

'Lactate and pyruvate increased ... and the increases showed an inverse relationship to the decrease in PCO2 and H+ concentration. However, even the maximum changes were relatively small, the mean lactate increasing less than I mmole/liter at PCO2= 20 mm Hg, pH = 7.6 .... In subjects studied over a period of 2 hr, lactate and pyruvate rose to a peak at 45-75 min and then declined.

Suggestions welcome!

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