Which factor is commonly responsible for sodium and fluid retention in a patient on mechanical ventilation?

Decreased renal perfusion with the release of renin is commonly responsible for sodium and fluid retention in a patient on mechanical ventilation. When a patient is placed on mechanical ventilation, especially in cases of acute respiratory distress syndrome (ARDS), their hemodynamics may be affected. Factors such as hypoxia, fluid shifts, decreased cardiac output, or pressure changes in the thoracic cavity can lead to reduced renal perfusion.

In response to decreased renal perfusion, the kidneys activate the renin-angiotensin-aldosterone system (RAAS). Renin, an enzyme released from the juxtaglomerular cells of the kidney, converts angiotensinogen (from the liver) to angiotensin I. This is subsequently converted to angiotensin II, which has a potent effect on constricting blood vessels and stimulating the adrenal cortex to release aldosterone. Aldosterone promotes sodium and water reabsorption in the kidneys, leading to fluid retention and increased blood volume. Consequently, this response heightens sodium retention, which is crucial for maintaining blood pressure and renal function in the face of perceived low perfusion.

Understanding this mechanism is important in managing patients on mechanical ventilation, as it highlights the need for careful monitoring of fluid balance and kidney function