Relative deficiency of arginine vasopressin in children after cardiopulmonary bypass

Objective: To describe changes in plasma arginine vasopressin concentration in children following cardiopulmonary bypass and determine whether, in some patients, plasma arginine vasopressin remains relatively low despite hemodynamic instability. Design: Prospective observational study. Setting: Pediatric intensive care unit at a tertiary care university hospital. Patients: One hundred twenty patients <= 18 yrs of age undergoing open heart surgery requiring cardiopulmonary bypass at Children's Hospital of Michigan between January 2008 and January 2009. Interventions: Blood samples were collected before cardiopulmonary bypass and 4, 24, and 48 hrs after cardiopulmonary bypass for measurement of plasma arginine vasopressin concentration. Measurements and Main Results: Mean plasma arginine vasopressin (pg/mL) for all patients was 21 +/- 63 before cardiopulmonary bypass and 80 +/- 145, 43 +/- 79, and 19 +/- 25 at 4, 24, and 48 hrs, respectively, after cardiopulmonary bypass. Patients with plasma arginine vasopressin below the lower quartile (<9.2 pg/mL) at 4 hrs after cardiopulmonary bypass (n = 29), labeled group A, were examined separately and compared with the rest of the study population, labeled group B. Mean plasma arginine vasopressin was 4.9 +/- 2.6 in group A at 4 hrs after cardiopulmonary bypass, statistically unchanged from its baseline mean plasma arginine vasopressin of 5.0 +/- 10.4 (p = .977). Mean plasma arginine vasopressin in group B was 104 +/- 160 at 4 hrs after cardiopulmonary bypass. Mean plasma arginine vasopressin of group A was also significantly lower as compared with group B before and 24 and 48 hrs after cardiopulmonary bypass. Hemodynamics, inotrope score, and serum sodium did not differ between groups at any time point. Plasma arginine vasopressin was measured immediately before exogenous arginine vasopressin administration in 10 patients; only those (n = 3) with hemodynamic instability and relatively low plasma arginine vasopressin concentration (<9.2 pg/mL) had notable hemodynamic improvement. Conclusions: In some children undergoing open heart surgery, plasma arginine vasopressin concentration is relatively low at baseline and remains low after cardiopulmonary bypass regardless of hemodynamic stability and serum osmolality. These children are likely the optimal candidates for exogenous arginine vasopressin should hemodynamic compromise occur. (Crit Care Med 2010; 38: 2052-2058)