Aim: To determine the accuracy of delayed arterial gas sampling (1) from the umbilical cord and (2) from the placental surface at room temperature.
Methods: Term deliveries were classified a priori into three groups: normal vaginal deliveries, elective caesarean sections and high risk deliveries. The cord was double clamped and paired arterial samples were taken from the cord and the placenta at 0, 30, 60 and 90 minutes.
Results: 90 placentas were sampled with 30 cases per group. At time 0 the mean cord pH 7.207 (plusmn0.08) was significantly lower than the placenta pH 7.240 (plusmn0.08). The cord pH dropped significantly: by 0.050 (95% CI 0.036 to 0.063) at 30 minutes, 0.087 (95% CI 0.069 to 0.105) at 60 minutes, and 0.112 (95% CI 0.086 to 0.138) at 90 minutes. The placenta pH fell at twice the rate of the cord pH over 90 minutes. At time 0 the mean cord base excess -7.0mmol/L (plusmn4.1) was significantly lower than the placenta base excess - 6.3mmol/L (plusmn3.6). The cord base excess fell at 30 minutes by 4.1mmol/L (95% CI 3.4 to 4.7), at 60 minutes by 7.1mmol/L (95% CI 6.1 to 8.0), and at 90 minutes by 9.0mmol/L (95% CI 7.9 to 10.0). The pH and base excess rate of fall was similar for each of the three delivery groups despite differing starting values.
Conclusion: Arterial blood gases should be taken as soon as possible after delivery from the umbilical cord. However, when this is not possible, the arterial pH and base excess from a delayed sample from a clamped cord at room temperature can be used to estimate the values at birth.
- blood gas analysis
- umbilical cord
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