Abstract
Blood pressure changes as a function of the rates of blood withdrawal and infusion were determined during exchange blood transfusion in 2 preterm newborn infants. 10 ml blood withdrawal and infusion completed within 3 minutes resulted in reversible changes in aortic pressure, whereas the same procedure completed within 45 to 60 seconds resulted in a progressive fall in the systolic pressure and in narrowing of the pulse pressure. In one of the cases this was associated with respiratory arrest. An exchange rate of 5 ml/kg per 3 minutes is recommended.