Metabolic Alkalosis Is Caused by the Excessive Elimination of Hydrogen Ions or by the Intake of Base, Such as BicarbonatefWhich Increases Blood pH

The most common cause of metabolic alkalosis is vomiting, during which H⁺-rich gastric contents are lost from the body. In ruminants, torsion and dilation of the abomasum cause metabolic alkalosis because H’ ions are trapped in the aboma­sum.

The loss of H^t from the body frees buffer, and thus the plasma [HCO₃^-] and total buffer base increase. The [HCO₃^- /0.03 ∙ Pco₂] ratio, pH, and base excess all increase (see Figure 52-5). The increase in pH reduces the drive to ventilate; alveolar ventilation decreases, and so Pco₂ increases. This adjusts the [HC0₃70.03 ∙ Pco₂] ratio toward normal, and thus the pH decreases toward normal (see Figure 52-5).