Inappropriate Vasopressin Secretion (SIADH) in Burned Patients

Abstract

To determine if concentration of plasma arginine vasopressin (AVP) is inappropriate for the plasma Na+ concentration in hyponatremic burned patients, 32 plasma samples were obtained from 20 patients with total burn size (TBS) 15-80% of body surface on or after postburn day (PBD) 4 in the morning following all-night recumbency. In the 25 samples (17 patients) with hyponatremia, AVP was elevated, 1.6-14.3 (normal < 0.5) pg/ml. Most patients with normal serum Na+ had normal AVP values. Out of the total, 9 patients (12 samples) without renal failure or sepsis, selected also for hyponatremia and urinary Na .gtoreq. 20 mEq[blood urea nitrogen]/L, were considered separately. BUN[blood urea nitrogen] of 11.7 .+-. 1.8 mg/dl and plasma glucose of 130 .+-. 5.6 mg/dl, Na+ of 130 .+-. 1.1 mEq/L, calculated osmolality of 272 .+-. 1.6 mosm/kg, and cortisol of 20.4 .+-. 1.6 .mu.g/dl were associated with a 24-h fluid intake of 4.3 .+-. 0.26 L and urinary output of 2.7 .+-. 0.33 L, Na+ of 80 .+-. 14 mEq/L, and osmolality of 520 .+-. 73 mosm/kg (mean .+-. SE). In all of the plasma samples, AVP was markedly elevated (6.9 .+-. 1.1 pg/ml). Four hyponatremic burned patients were given a standard water load. Excretion of the water was delayed, and further dilution of the initially hypotonic plasma resulted in a fall of urinary osmolality and plasma AVP. Cutaneous thermal injury can cause resetting of the mechanism linking plasma tonicity and AVP secretion resulting in dilutional hyponatremia. This syndrome occurs in the absence of gross physiologic perturbations such as volume depletion or adrenal insufficiency.