Reproducible quantitative relationship between the fall in Bicarbonate and the rise in the P anion gap in metabolic acidosis
Is there a reproducible quantitative relationship between the fall in [HCO 3 − ] and the rise in the P anion gap in all patients with metabolic acidosis?
The relationship between the rise in the P Anion gap and the fall in the concentration of bicarbonate [HCO 3 − ] is used to detect the presence of coexisting metabolic alkalosis in a patient with metabolic acidosis (i.e., the rise in P Anion gap is larger than the fall in [HCO 3 − ]) and/or the presence of both an acid overproduction type and a NaHCO 3 loss type of metabolic acidosis (i.e., the rise in P Anion gap is smaller than the fall in [HCO 3 − ]). It must be recognized, however, that this relationship uses concentration rather than content terms and therefore will underestimate the magnitude of the HCO 3 − deficit if there is significant contraction of the ECF. That is, diminished ECF volume will suggest an underlying alkalosis (i.e., a process that is increasing the content of bicarbonate), when in fact there is none. This carries clinical relevance in bicarbonate-wasting metabolic acidosis, because the provision of bicarbonate-free fluid resuscitation may lead to a rapid, unexpectedly large fall in [HCO 3 − ] and unmask a severe metabolic acidosis, described as follows under specific disorders (e.g., diarrhea;
