The baroresponses of preterm infants during halothane anaesthesia

Anaesthetics depress the baroresponse of adults. If the same is true of infants, they will have difficulty maintaining their cardiac output if they become hypotensive because they are primarily rate dependent for cardiac output. The opportunity to test whether anaesthetics depress the baro-response of neonates arose while anaesthetizing preterm infants for ligation of patent ductus arteriosus. The relationship between heart rate and the systolic blood pressure (baroresponse) was examined in 53 preterm infants (1,065 +/- 205 g) receiving 0.5-1.0 per cent inspired halothane for ligation of patent ductus arteriosus. The arterial pressure was measured by indwelling catheters and strain gauges (43 patients) or a doppler device (10 patients). Heart rate was measured with skin electrodes. The relationship between heart rate and systolic pressure was examined before and after the induction of anaesthesia and before and after ligation of the ductus. Just before ligation of the ductus arteriosus the systolic blood pressure had decreased 33 per cent from awake control values without a change in heart rate. Five minutes after the ductus was ligated the arterial pressure had increased 38 per cent, again without a change in heart rate. The differences between systolic pressures was highly statistically significant in both instances (P less than 0.001). The differences between heart rate were not. These data indicate a lack of baroresponse in these preterm infants during light halothane anesthesia which may alter their ability to maintain cardiac output when hypotensive.