Most patients receiving anesthesia care have some care-driven changes in their acid–base status, at least mild respiratory acidosis during general anesthesia with spontaneous ventilation. However, many high-risk patients also have clinically important acid–base changes that anesthesiologists need to interpret and manage, often actual or impending metabolic acidosis and acidemia. These clinical situations can be challenging. Anesthesiologists’ concerns include the nature and clinical importance of acid–base changes, the underlying causes, the likely effects of interventions including fluid therapy and sodium bicarbonate, perioperative risk, and need for postoperative intensive care unit (ICU) admission (refer to examples 1 to 4 in Boxes 1 to 4).

Most anesthesiologists are familiar with the fundamental blood gas machine acid–base measurements of pH and pCO2, and derived bicarbonate concentration, all linked by the Henderson–Hasselbalch equation.2–4  Many will use or be aware of base excess, and some the physicochemical (Stewart) approach.2...

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