Neonatal metabolism and endocrinology studied by exchange transfusion.

The work reviewed here illustrates how a therapeutic procedure, exchange transfusion of newborn infants, may be used to gather information which is both of practical value to infants treated in this way and also of value in the study of human neonatal physiology. The scientific deductions that can be drawn are weakened by the uncontrolled nature of the subjects available for study but this problem can be mitigated by changing one variable at a time between two groups of clinically similar infants undergoing transfusion and paying attention only to large changes in whatever is measured. In this way it has been possible to show that the glucose of ACD blood stimulates insulin and GH secretion and that the stimulation of insulin secretion is less, and that of GH more, if the transfusion is performed via the umbilical artery rather than via the vein. Arterial transfusions may be more stressful than venous ones since they are associated with greater growth hormone, ACTH and glucocorticoid release. Citrate, the other additive in ACD blood, causes a fall in ionised plasma calcium levels resulting in a stimulation of PTH secretion and mobilisation of calcium and phosphorus. Transfusion with heparinised blood is therefore preferred by some because normoglycaemia is preserved during and for three hours after transfusion, whereas post-transfusion hypoglycaemia may occur after ACD transfusion. However, heparin transfusion causes a marked rise in plasma FFA levels which may interfere with the binding of bilirubin by albumin. In either type of transfusion the side-effects may be minimised by feeding the baby afterwards, as soon as practicable. Thyroid hormones are washed out of the infant during transfusion but normal thyroid balance is restored quickly afterwards. The temperature of the donor blood does have thermal effects on the baby but these are less than might be expected due to the rapid equilibration of donor blood temperature with that of the room. The metabolic consequences of transfusion with cold blood are less than might be anticipated due in part to the glucose infusion that is part of an ACD transfusion.