Disorders of Fluid, Electrolytes, and Acid Base Balance

Disorders of fluid, electrolytes, and acid-base balance are very common in critically ill patients. In all cases, the delicate balance of patients’ physiology and homeostatic processes is disrupted. This imbalance appears particularly severe in critical illness and requires prompt identification and timely resolution before irreversible processes are triggered. In the specific field of fluid balance, the difference between inputs and outputs should be carefully controlled in the context of critical illness since the narrow spectrum between hypoperfusion and organ congestion should be avoided. Currently, a restrictive approach can be recommended in the intensive care unit along with careful hemodynamic goal-directed fluid resuscitation, especially in the phase of blood pressure stabilization. Electrolyte disorders involve sodium, potassium, calcium, phosphorus, and magnesium. In all cases, both hypo- and hyperconcentration of these elements can occur and are addressed in the text. Finally, acid-base disorders imply acidosis and alkalosis, both metabolic and respiratory. Critically ill patients may encounter specific causes and challenging interpretations of their acid-base balance, and the text will thoroughly review these aspects.