Respiratory Changes and Acid–Base Compensation: Watch the Salt

Imagine you are asked to assess this room air arterial blood gas (ABG): Pao₂ 25 mmHg, Spo₂ 50%, pH 7.53, Paco₂ 13 mmHg, bicarbonate 11 mM, base excess −6.9 mM. Apart from thinking “My goodness!,” or similar thoughts, you will likely diagnosis life- threatening hypoxemia, alkalemia with a mixed picture of respiratory alkalosis and metabolic acidosis, as you look to ensure that the patient is being resuscitated. However, the ABG is the summary results from very fit and fully conscious people, and although this ABG is on “room air,” it was taken on Mount Everest at 8,400 m (27,500 feet) as climbers safely descended from the nearby summit.²  This high-altitude ABG is an extreme example of chronic respiratory alkalosis and associated metabolic (nonrespiratory) compensation. In this issue of Anesthesiology, Zadek et al.³  report a sophisticated individual participant meta-analysis of physiologic...