Acid and Base Abnormalities

Understanding acid–base physiology is necessary for the management of all critically ill patients. Patients with conditions that predispose them to altered mental status and multi-organ dysfunction will be prone to acid–base disturbances. These disturbances in the patient’s normal physiologic pH are a result of pathology either due to the loss of compensatory mechanisms within the body’s buffer system or the body being overwhelmed by an exogenous insult such as shock. Timely identification and management of these physiologic disturbances will lead to better clinical outcomes for the patient and may even lead to improved neurological outcomes and survival. In this chapter, we will review the basic concepts of acid–base physiology as it relates to critically ill patients and describe how to identify and manage abnormalities. We will also outline a simple step-by-step guide to identifying acid–base abnormalities that can be present in each critically ill patient. Finally, this chapter will include a list of differential diagnoses for respiratory acidosis and alkalosis as well as metabolic acidosis and alkalosis.