The relationship between umbilical arterial pH, newborn heart rate and ventilation at birth - a prospective observational study.

Abstract

To investigate the relationship between umbilical arterial pH (UA-pH), heart rate (HR) and positive pressure ventilation (PPV) at birth. A prospective cohort study conducted at Stavanger University Hospital, Norway, June 2019-November 2021. Newborns of gestational age ≥28 weeks were eligible for inclusion. UA-pH was routinely obtained at birth and newborn HR captured using dry-electrode ECG. Relationships were evaluated using linear correlation and logistic regression. UA-pH was categorised as <7.00, 7.00-7.09, 7.10-7.19, with reference group 7.20-7.50. Outcome measures were newborn HR and PPV. Among 3662 newborns the median (quartiles) UA-pH was 7.24 (7.19, 7.29). UA-pH <7.00 was identified in 20 (0.5%), 7.00-7.09 in 140 (3.8%), 7.10-7.19 in 833 (23%), and 7.20-7.50 in 2669 (73%) newborns. There was a weak and clinically insignificant linear correlation between UA-pH and first measured HR at 16 (11, 30) s (r = 0.07, p < 0.001), and no linear correlation with HR at one minute (r = -0.03, p = 0.07). Even among newborns with UA-pH <7.00, only 50% were bradycardic with HR values <100 bpm in the first minute (OR 5.0 (1.9, 12.9), p < 0.001). PPV was provided to 117/3662 (3.2%) of newborns. One-third with UA-pH <7.00 received PPV at birth (OR 21.9 (8.0, 55.4), p < 0.001). Apgar scores were strongly associated with UA-pH. There was no linear correlation between UA-pH and HR at one minute. Although HR alone was not a good indicator of acidaemia, low UA-pH is associated with bradycardia and PPV. Apgar scores reflected the degree of birth asphyxia very well. NCT03849781.