Acid-Base Disorders

In the surgical intensive care unit (SICU), both mild and significant acid-base disorders are common and an understanding of their management is key to caring for critically ill and injured patients. Under normal conditions, serum pH is the tightly controlled result of homeostatic buffering mechanisms. Mild, transient aberrations in pH may be physiologic, but if persistent, even subtle pH change may point to underlying pathology. As pH strays outside the normal range, acidemia or alkalemia may become harmful. Often this harm results from taxing attempts at compensation, such as tachypnea in response to metabolic acidosis, or through direct effects, such as systemic or pulmonary vasoregulatory changes, cerebral edema, and arrhythmias. While the intensivist may rush to correct pH, acidosis or alkalosis is ultimately a marker of an underlying disease process, and correcting the pH, while important, is insufficient if the driving pathology is not also identified and corrected. This chapter will review a practical approach to acid-base disorders typically encountered in the SICU, with a focus on diagnosis and initial management strategies.