The influence of thermal environment on pulmonary hemodynamic acclimation to extrauterine life in normal full-term neonates.

Objective: To assess chronological changes of pulmonary blood flow in response to ambient temperature load in normal full-term neonates.

Methods: Group I (n=8) neonates were maintained at 25-26 degrees C for the first 24 h after birth, with Group II (n=7) at 32-33 degrees C. Left pulmonary artery flow volume (Vp) and ductus arteriosus diameter were measured at 2, 4, 6, 12, and 24 h using Doppler ultrasound. Core and peripheral temperatures, as a marker for cold stress, were also evaluated over the same time frame.

Results: For Group I, Vp was steady for the first 6 h after birth before gradually decreasing. In contrast, Vp for Group II significantly decreased from 2-6 h, without later changes. At 6 h after birth in Group II, mean values of both Vp and ductus arteriosus diameter were significantly lower, whereas mean value of peripheral temperature was significantly higher than values in Group I (P<0.05).

Conclusion: Pulmonary blood flow in neonates placed at neutral ambient temperature stabilizes earlier than that of neonates placed at room temperatures. Changes of peripheral flow in response to ambient temperature load may be associated with decreased pulmonary blood flow through a left-to-right ductal shunt.