28 March 2009

Respiratory vs metabolic acidosis

The symptoms of respiratory and metabolic acidosis are pretty similar. In both you see generalized weakness, fatigue, nausea, vomiting and CNS depression (1). How does a blood test distinguish from the two?

Respiratory acidosis differs from metabolic acidosis because it is a result of impaired pulmonary function causing a build-up of CO2 that lowers pH instead of one that is mainly caused by increased acid metabolic products (1). A blood test can indicate between the two by measuring pH, bicarbonate (HCO3-) and carbon dioxide (PCO2) (1).

If the test reveals acidic extracellular fluid (ECF) but normal CO2 indicating adequate respiratory function or low PCO2 indicating active ventilation response, then pH disruption has a metabolic source (1). An elevated PCO2 indicates inability to clear CO2 and the drop in pH is a result of carbonic acid formed (1).

Now if for any reason you accidentally swallow antifreeze, methanol or high doses of aspirin, you should know it can potentially cause either acidosis. To correct acidosis you use sodium bicarbonate (1). The same as baking soda.

Reference List

1. Nowak TJ, Handford AG. Pathophysiology: Concepts and Applications for Health Professionals. New York: McGraw-Hill, 2004.

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