The effects of mechanical pressure and local stasis on transcutaneous monitoring of fetal oxygen tension.

A methodological study of the influence of local stasis and mechanical pressure on the continuous transcutaneous oxygen tension electrode (tcPO2 electrode) during intrapartum monitoring is presented. No effect of mechanical pressure up to 7.3 kPa (55 mm Hg) on the electrode membrane was found. Reduced blood flow in the capillaries of the tissue beneath the electrode caused by stasis or pressure effect resulted, below a certain threshold value, in tcPO2 decrease. The results emphasize that an attempt to differentiate between a methodologically caused decrease and a decrease due to impaired oxygenation must be made when evaluating the absolute fetal arterial oxygen tension from fetal tcPO2. The consistently observed decrease in relative local perfusion ('flow') may be a help in this respect.