Pathophysiology of dialysis hypotension: an update.

Dialysis hypotension occurs because a large volume of blood water and solutes are removed over a short period of time, overwhelming normal compensatory mechanisms, including plasma refilling and reduction of venous capacity, due to reduction of pressure transmission to veins. In some patients, seemingly paradoxical and inappropriate reduction of sympathetic tone may occur, causing reduction of arteriolar resistance, increased transmission of pressure to veins, and corresponding increase in venous capacity. Increased sequestration of blood in veins under conditions of hypovolemia reduces cardiac filling, cardiac output, and, ultimately, blood pressure. Adenosine release due to tissue ischemia may participate in reducing norepinephrine release locally, and activation of the Bezold-Jarisch reflex, perhaps in patients with certain but as yet undefined cardiac pathology, may be responsible for sudden dialysis hypotension. Patients with diastolic dysfunction may be more sensitive to the effects of reduced cardiac filling. The ultimate solution is reducing the ultrafiltration rate by use of longer dialysis sessions, more frequent dialysis, or reduction in salt intake. Increasing dialysis solution sodium chloride levels helps maintain blood volume and refilling but ultimately increases thirst and interdialytic weight gain, with a possible adverse effect on hypertension. Blood volume monitoring with ultrafiltration or dialysis solution sodium feedback loops are promising new strategies. Maintaining tissue oxygenation via an adequate blood hemoglobin level seems to be important. Use of adenosine antagonists remains experimental. Given the importance of sympathetic withdrawal, the use of pharmacologic sympathetic agonists is theoretically an attractive therapeutic strategy.