From the Research
Hypercapnia leads to salt and water retention through various physiological mechanisms, including increased renal bicarbonate reabsorption, activation of the renin-angiotensin-aldosterone system, and stimulation of antidiuretic hormone release, resulting in expanded extracellular fluid volume and edema. When CO2 levels rise, the body compensates by increasing renal bicarbonate reabsorption, which leads to enhanced sodium reabsorption in the kidneys, primarily in the proximal tubule through the sodium-hydrogen exchanger 1. Additionally, hypercapnia activates the renin-angiotensin-aldosterone system (RAAS), with elevated aldosterone levels promoting sodium reabsorption and potassium excretion in the distal tubule 2. The increased sodium retention creates an osmotic gradient that drives water reabsorption, resulting in expanded extracellular fluid volume. Hypercapnia also stimulates antidiuretic hormone (ADH) release, which increases water reabsorption in the collecting ducts 1. These combined mechanisms lead to edema and fluid overload commonly seen in patients with chronic respiratory failure, COPD exacerbations, or mechanical ventilation with inadequate CO2 clearance. Treatment focuses on addressing the underlying cause of hypercapnia through improved ventilation, while diuretics may be needed to manage fluid overload symptoms, as supported by recent studies on chronic non-invasive ventilation for COPD patients 3. In fact, a 2022 study published in the International Journal of Clinical Practice highlights the importance of understanding the pathophysiological mechanisms of hypercapnia to provide targeted therapy and avoid complications 1. Moreover, a 2022 review in the BMJ Medicine emphasizes the potential benefits of non-invasive ventilation in patients with chronic hypercapnic respiratory failure due to COPD, including improved survival and reduced morbidity 4. Therefore, addressing hypercapnia through improved ventilation and targeted therapy is crucial to prevent salt and water retention and its associated complications.