Newborn lambs whose mothers received supplemental oxygen during delivery held significantly higher blood and brain oxygen levels through the first 60 seconds after the umbilical cord was clamped than lambs whose mothers had oxygen reduced, according to a study Nature reported.
Researchers compared seven lambs in the supplementation group (O2Supp) with seven in the oxygen-reduction group (O2Red). Before the maternal oxygen change, fetal pH, PaCO2, PaO2, SaO2, and cerebral tissue oxygenation (SctO2) were not different between groups, and core body temperature stayed similar throughout the study, averaging 37.3 °C in the supplemented group and 37.6 °C in the reduced group.
Supplementation Raised Maternal and Fetal Oxygen Levels
Maternal PaO2 was significantly higher in ewes receiving supplemental oxygen (165.0 ± 29.1 vs. 67.1 ± 6.8 mmHg, p = 0.04), and maternal SaO2 trended higher (96.1 ± 1.2 vs. 74.8 ± 6.7%, p = 0.054). After the maternal oxygen change, supplementation significantly increased fetal PaO2 (p = 0.0002), SaO2 (p = 0.008), and SctO2 (p = 0.001) compared with oxygen reduction. Maternal PaCO2 did not differ between groups (44.3 ± 4.1 vs. 51.3 ± 2.0 mmHg, p = 0.20), and maternal oxygen supplementation did not significantly alter mean, systolic, or diastolic blood pressure.
Cord Clamping Dropped Oxygen Faster in the Low-Oxygen Group
In the 60 seconds between cord clamping and the start of ventilation, SpO2 in supplemented lambs fell from 75.3 ± 2.6% to 40.0 ± 4.6%, while in the reduced group it fell from 53.5 ± 5.1% to 33.7 ± 10.6%. SpO2 was significantly higher in supplemented lambs for the first 30 seconds after clamping, but by 45 seconds the two groups were not different. SctO2, which started higher in supplemented lambs (55.4 ± 3.2% vs. 37.7 ± 3.8%), remained significantly higher throughout the interval before ventilation.
Mean carotid arterial pressure rose significantly in supplemented lambs after clamping, from 52.6 ± 3.0 to 68.2 ± 3.4 mmHg (p = 0.007), while it did not significantly change in the reduced group. Carotid blood flow increased by about 27% in supplemented lambs after clamping (p = 0.003) but was variable and unaltered in the reduced group.
Pulmonary blood flow also diverged: end-diastolic pulmonary blood flow was positive in 5 of the 7 supplemented lambs at the moment of clamping but negative in all 7 reduced-oxygen lambs. Positive end-diastolic flow indicates left-to-right shunting through the ductus arteriosus and low pulmonary vascular resistance. Mean, peak-systolic, and end-diastolic pulmonary blood flow stayed significantly higher in supplemented lambs from clamping until ventilation began.
Ventilation Shifted the Hemodynamic Picture
Once ventilation started, pH, PaO2, and PaCO2 were not different between groups, and ventilator settings — including FiO2, oxygenation index, and peak inflation pressure — did not differ at any point. But SctO2 stayed higher in supplemented lambs after ventilation onset (p = 0.008), significantly so 3 to 5 minutes in. Meanwhile, mean and diastolic carotid arterial pressure rose rapidly in the reduced group and ran significantly higher than the supplemented group during the first 4 to 5 minutes, and carotid artery flow was significantly higher in reduced lambs after ventilation (p = 0.035).
The contrast sharpened against the pre-clamping baseline, when reduced-oxygen lambs already had lower cerebral oxygenation (37.7 ± 3.8%) than supplemented lambs (55.4 ± 3.2%).
Key Findings Clarify Oxygen Effects on Lambs
How much higher was oxygen pressure in mothers receiving supplementation? Maternal PaO2 averaged 165.0 ± 29.1 mmHg with supplementation versus 67.1 ± 6.8 mmHg with reduction, a significant difference (p = 0.04).
What did positive end-diastolic pulmonary blood flow indicate at cord clamping? It indicated left-to-right shunting through the ductus arteriosus and low pulmonary vascular resistance; 5 of 7 supplemented lambs showed it at clamping, versus none of the 7 reduced-oxygen lambs.
How long did the oxygen-saturation advantage last after cord clamping? SpO2 was significantly higher in supplemented lambs for the first 30 seconds after clamping; by 45 seconds, the two groups were not different.
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