Plasma vasopressin levels during cardiopulmonary bypass with and without profound haemodilution.

In cardiopulmonary bypass the effect on plasma vasopressin levels of the addition of whole blood to the pump priming solution was measured. Six patients (Group I) had blood added to the lactated Ringer's solution for the prime, and six patients (Group II) had only lactated Ringer's solution. Neither group had significant changes in plasma vasopressin levels until surgical stimulation occurred. Comparable significant elevations occurred during bypass in both groups. Greater decreases in haematocrit and urinary K+ and greater increases in urinary Na+ occurred in Group II. The degree of haemodilution does not appear to effect plasma vasopressin levels but may alter the degree of electrolyte shift.