Osmoregulation of vasopressin secretion is altered in the postacute phase of septic shock.

OBJECTIVE: To determine whether septic shock patients have an abnormal reponse to increasing osmolarity.

DESIGN: Prospective interventional study.

SETTING: Intensive care unit at Raymond Poincaré and Etampes Hospitals.

PATIENTS: Normonatremic patients at > 72 hrs from septic shock onset.

INTERVENTION: Osmotic challenge consisting of infusing 500 mL of hypertonic saline solution (with cumulative amount of sodium not exceeding 24 g) over 120 mins.

MEASUREMENTS AND MAIN RESULTS: Plasma arginine vasopressin levels were measured 15 mins before the test and then four times every 30 mins. A slope of the relation between arginine vasopressin and plasma sodium levels of < 0.5 pg/mEq defined nonresponders. Among the 33 included patients, 17 (52%) were nonresponders. During osmotic challenge, variations throughout the test in plasma sodium levels, blood pressure, and central venous pressure were comparable between the two groups. Arginine vasopressin increased from 4.8 pg/mL [3.3-6.4 pg/mL] to 14.4 pg/mL [11.2-23.3 pg/mL] in responders but only from 2.8 pg/mL [2.3-4.0 pg/mL] to 4.0 pg/mL [3.1-5.3 pg/mL] in nonresponders (p < .0001). Responders had a higher plasma arginine vasopressin levels at baseline and a more severe hematosis alteration. Nonresponders had more frequently bacteremia and liver dysfunction, been referred from the ward and undergone surgery. Critical illness severity, hemodynamic alteration, hydroelectrolytic disturbances, treatment, and outcome did not differ between the two groups.

CONCLUSION: Osmoregulation is dramatically altered in half of patients with prolonged septic shock.