Feasibility of simultaneous application of fetal electrocardiography and fetal pulse oximetry

Fetal pulse oximetry measures arterial oxygen saturation during delivery. The fetal electrocardiogram STAN S21 analyzes the repolarisation segment of ECG (ST) waveform, which is altered by the intramyocardial potassium release resulting from metabolic acidemia. This study aimed to evaluate the feasibility of a simultaneous application of pulse oximetry and fetal electrocardiography and to estimate any agreement between both methods indicating fetal compromise.

In an observational trial 35 fetuses were simultaneously monitored by pulse oximetry (OBS-500) and electrocardiography. The evaluation focused on signal output and on the coincidence of desaturation in fetal pulse oximetry and on ST events. Desaturation was defined as a drop of at least 20% of oxygen saturation from base line level occurring within 1 min (steep desaturation) or duration of time (s) with oxygen saturation below the threshold of 30%. Statistical analysis was performed with the Mann-Whitney U-test for continuous variables.

Signal output of the simultaneous application of both sensors was not significantly reduced in the electrocardiogram and in pulse oximetry (8% vs. 12% reduction). In 15 of the 35 fetuses, ST events indicating fetal hypoxia occurred. In these cases, pulse oximetry showed significantly more episodes of desaturation in comparison with fetuses without ST events. Median saturation during the ST events was significantly lower than in the recordings without ST events (60% vs. 74%, p < 0.05). In the umbilical artery these neonates showed significantly lower pH (7.19 vs. 7.33, p < 0.001), significantly higher lactate (5.1 vs. 3.4 mmol/l, p < 0.05) and significantly lower base deficit (-9.4mmol/l vs. -4.0 mmol/l, p < 0.001) levels.

The combination of fetal pulse oximetry and fetal electrocardiography appears feasible and indicates signs of intermittent hypoxia. These findings may encourage the development of technology that combines these different methods of monitoring.