Effect of hyperosmolality on vasopressin secretion in intradialytic hypotension: a mechanistic study.

BACKGROUND: Administration of a small volume of hypertonic solution has been used as an effective treatment for patients with intradialytic hypotension. Hypertonic solutions have been considered to act as plasma volume expanders. This clinical study examines whether arginine vasopressin (AVP) is involved in this mechanism of blood pressure control. STUDY
DESIGN: Nonrandomized trial. SETTING & PARTICIPANTS: 42 patients on long-term hemodialysis therapy at a single hospital. INTERVENTION: Effects of intravenous infusions of 20 mL of 10% saline, 20 mL of 50% glucose, 200 mL of 0.9% saline, or physiological doses of AVP were examined during intradialytic hypotension. OUTCOMES & MEASUREMENTS: Changes in plasma AVP levels, osmolality, plasma volume, and blood pressure were analyzed.
RESULTS: Hypertonic saline infusion increased plasma osmolality (mean, 292.7 to 302.3 mOsm/kg H(2)O; P < 0.001), plasma AVP levels (3.9 to 7.8 pg/mL; P = 0.03), and mean arterial pressure (66.6 to 71.8 mm Hg; P = 0.01). The increase in plasma volume (2.3%; P = 0.03) was too small to increase blood pressure because of volume alone. Hypertonic glucose infusion yielded similar results. Isotonic saline infusion increased blood pressure with an abrupt increase in plasma volume (12.7%; P < 0.001). AVP infusion increased blood pressure and plasma AVP to levels similar to those induced by the hypertonic solutions. LIMITATIONS: There are limitations in accurately measuring changes in plasma volume during hemodialysis.
CONCLUSIONS: Results strongly suggest that the osmotic stimulation of AVP secretion by hypertonic solutions has an important role in increasing blood pressure in patients with intradialytic hypotension. Manipulating plasma AVP appropriately may help correct and prevent intradialytic hypotension.