In Reply.—We would like to thank Dr Lou and his colleagues for their comments. We agree that if autoregulation is lost, the risk for germinal matrix hemorrhage increases. One major point from previous studies by Lou et al1 was the age of the premature infant at the time of study and the association of asphyxia. Their patient population was studied in the very early hours of life, while our population was studied through the first several days of life.
Despite the variability of mean arterial pressures in our study, only when there was an elevation of carbon dioxide tension or acidosis associated with hypoxia were we able to demonstrate an alteration of the pulsatility index of sufficient magnitude to be considered significant. As we noted in the study, too few instances of hypoxia were observed without acidosis to make valid judgments as to the effect of hypoxia alone