The effect of oxygen content during an initial sustained inflation on heart rate in asphyxiated near-term lambs.
OBJECTIVE
At birth, an initial sustained inflation (SI) uniformly aerates the lungs, increases arterial oxygenation and rapidly improves circulatory recovery in asphyxiated newborns. We hypothesised that lung aeration, in the absence of an increase in arterial oxygenation, can increase heart rate (HR) in asphyxiated near-term lambs.


METHODS
Lambs were delivered and instrumented at 139±2 days of gestation. Asphyxia was induced by umbilical cord clamping and then delaying the onset of ventilation until mean carotid arterial pressures (CAPs) had decreased <20 mm Hg. Lambs then received a single 30-s SI using nitrogen (N2; n=6), 5% oxygen (O2; n=6), 21% O2 (n=6) or 100% O2 (n=6) followed by ventilation in air for 30 min.


METHODS
HR, CAP and pulmonary blood flow (PBF) were continuously recorded.


RESULTS
HR and PBF increased more quickly in lambs resuscitated with 100% and 21% O2 than with 5% O2 or N2. HR and PBF recovery in the 5% O2 group was delayed relative to all other oxygen SI groups. HR in 5%, 21% and 100% O2 groups reached 100 bpm before the SI was complete. HR and PBF in the N2 group did not increase until 10 s after the SI was completed and ventilation was initiated with air. CAP tended to increase quicker in all O2 groups than in N2 group.


CONCLUSIONS
Oxygen content during an SI is important for circulatory recovery in asphyxiated lambs. This increase in HR is likely driven by the increase in PBF and venous return to the heart.
The Ritchie Centre, Monash Institute of Medical Research, Monash University, Clayton, Australia.
K S
KS
Sobotka
The Ritchie Centre, Monash Institute of Medical Research, Monash University, Clayton, Australia.
T
T
Ong
The Ritchie Centre, Monash Institute of Medical Research, Monash University, Clayton, Australia Department of Obstetrics and Gynaecology, Monash University, Clayton, Australia.
G R
GR
Polglase
The Ritchie Centre, Monash Institute of Medical Research, Monash University, Clayton, Australia.
K J
KJ
Crossley
The Ritchie Centre, Monash Institute of Medical Research, Monash University, Clayton, Australia Department of Obstetrics and Gynaecology, Monash University, Clayton, Australia.
T J M
TJ
Moss
The Ritchie Centre, Monash Institute of Medical Research, Monash University, Clayton, Australia Department of Obstetrics and Gynaecology, Monash University, Clayton, Australia.
S B
SB
Hooper
D000818:Animals; D000831:Animals, Newborn; D001238:Asphyxia Neonatorum / Q000097:blood / Q000503:physiopathology / Q000628:therapy; D001784:Blood Gas Analysis; D001794:Blood Pressure; D004195:Disease Models, Animal; D006339:Heart Rate; D006801:Humans; D007231:Infant, Newborn; D007327:Insufflation / Q000379:methods*; D008168:Lung / Q000098:blood supply / Q000503:physiopathology; D010100:Oxygen / Q000627:therapeutic use*; D020127:Recovery of Function / Q000502:physiology; D012129:Respiratory Function Tests / Q000379:methods; D012756:Sheep; D034561:Sheep, Domestic
D010100:Oxygen
Animal Research; Neonatology; Resuscitation