Levels of vasopressin in children undergoing cardiopulmonary bypass.

Objectives: It is accepted treatment to give vasopressin to adults in postcardiotomy shock, but such use in children is controversial. Cardiopulmonary bypass is presumed to attenuate the normal endogenous vasopressin response to shock. We hypothesized that levels of vasopressin in children are altered by bypass, and that children having low endogenous levels perioperatively are more likely to develop hypotension, or require vasopressors. Methods: Serial levels of vasopressin were assessed prospectively in children undergoing bypass at a single center. Results: Of 61 eligible patients, we enrolled 39 (63%). Their median age was 5 months. The mean level of vasopressin prior to bypass was 18.6 picograms per millilitre, with an interquartile range from 2.6 to 11.4. Levels of vasopressin peaked during bypass at 87.1, this being highly significant compared to baseline (p < 0.00005), remained high for 12 hours at a mean of 73.5, again significantly different from baseline (p = 0.002), were falling at 24 hours, with a mean of 28.1 (p = 0.04), and had returned to baseline by 48 hours, when the mean was 7.4 (p = 0.3). Age, gender, and the category for surgical risk had no influence on the levels of vasopressin. There was no statistically significant relationship between the measured levels and hypotension or the requirement for vasopressors, although a few persistently hypotensive patients had high levels subsequent to bypass. Higher levels correlated with higher levels of sodium in the serum (r(s) = 0.37, p < 0.00005), higher osmolality (r(s) = 0.37, P < 0.00005), and positive fluid balance (r(s) = 0.23, p < 0.008). Preoperative use of inhibitors of angiotensin converting enzyme, preoperative congestive cardiac failure, and longer periods of bypass predicted higher levels during the first eight postoperative hours. Conclusions: Children do not have deficient endogenous levels of vasopressin following bypass, and lower levels are not associated with hypotension. Any therapeutic efficacy of infusion of vasopressin for pos-tcardiotomy shock in children is likely due to reasons other than physiologic replacement.