Acid–Base Disorders in Critically Ill Patients

Abstract

Acid–base disorders are extremely common in patients admitted to the critical care units because of multiorgan dysfunction. Sepsis, septic shock, toxin ingestion, diabetic ketoacidosis, removal of vomitus by nasogastric suction, massive transfusion with citrated blood, and renal as well as respiratory failure are some of the important causes for acid–base disorders. Hyperchloremic metabolic acidosis is frequently seen due to fluid resuscitation with normal saline or fluids that contain high Cl⁻. Among acid–base disorders, some reports suggested metabolic acidosis as the predominant disorder in critically ill patients. For example, an observational cohort study reported that 64% had acute metabolic acidosis. Other studies showed metabolic alkalosis to be the most common acid–base disorder in critically ill patients. Therefore, it is difficult to predict which acid–base disorder predominates in critically ill patients. It should be noted that any acid–base disorder is associated with high morbidity and mortality in critically ill patients. Lindner et al. (Intensive Care Med 39:399–405, 2013) described an acid–base disorder called hypernatremic alkalosis in critically ill patients. Their study included 51patients who developed hypernatremia (serum Na⁺ level > 149 mEq/L) after admission to intensive care units (ICUs). Based on an increase in base excess, hypernatremia was accompanied by an increase in serum HCO₃ ⁻ level and pH. The authors suggest that hypernatremic alkalosis should be part of the differential diagnosis of metabolic acid–base disorders. In this chapter, we will discuss the pathophysiology and management of only four primary acid–base disorders (metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis) in critically ill patients.