THE INFLUENCE OF THE MATERNAL POSITION ON THE FETAL TRANSCUTANEOUS OXYGEN PRESSURE (tcPo₂)

Abstract

From the research work of Lemtis (4) and Künzel (3) we know that uterine blood flow (UBF) decreases following vena caval occlusion (VCO) when the mean arterial blood pressure (BP) decreases and/or the venous pressure increases. Fetal heart rate (FHR) will drop when the UBF falls below a certain critical level and this decrease in FHR is associated with a.fall in Po 2 and oxygen Saturation which initially provokes a pressor response in the fetus. Until recently i t has only been possible to consider such pathophysiological questions in animal models, but with the development of the tcPo 2 -technique (1) one is now able to investigate this phenomenon in human labour. MATERIAL AND METHODSIn 43 cases FHR, fetal tcPo 2 , fetal skin blood flpw and maternal uterine activity were continuously monitored and analysed in mothers^ who were \intermittently in supine Position. The observations were all made in the late first and second stage of labour. RESULTS The mean duration of the period spent in supine position was 6 min. In 39 of the 43 cases fetal tcPo 2 was found to decrease when the mother adopted the supine position (91%). During this time uterine activity remained constant and a classical VCO-syndrome followed in only two cases (4.65%). Fetal skin blood flow äs measured by the heating current increased in 60% and remained constant in 40% of cases. FHR showed three different patterns: no change (44%), acceleration (40%) or deceleration (16%). The tcPo 2 level before adoption of the supine position showed no significant difference for these three types of FHR pattern. There was however a significant difference in the initial FHR depending on wether the response was an acceleration or deceleration (130 and 132 bpm) compared with the group where .the FHR (137 bpm) remained constant (2-«0.025; 2-*<0.05). A significant difference was found between the recovery time of tcPo 2 (after returning to the lateral position) of the group with no FHR response and the group which showed an acceleration or decleration (2<f<0.025). In this latter group the recovery period was prolonged (4.21 min.). In all three groups there existed a significant relationship between the initial fetal tcP0 2 and the drop observed during the period in supine position (2*<0.001) (Fig. 1). DISCUSSION It is well known that in the supine position the gravid Uterus may compress the inferior vena cava (IVC) and reduce UBF which will lead to a drop in fetal tcPo 2 . In our study baseline FHR was seen to either increase, decrease or to remain constant. The initial FHR level in the group with an increase or decrease is significantly lower than in the group with no FHR change. In animal experiments Künzel et al. (2) found the response of the FHR to vary with the extent of reduction in UBF. The greatest drop in UBF was always accompanied by a decrease in FHR. In our study no relationship was found between different FHR behaviour and initial fetal tcPo 2 or drop in fetal tcPo 2 with change of maternal position.

Maternal half-sitting position in the second stage of labor

“…Furthermore APGAR scores tended to be better in the* group delivering in halfsitting than supine position in our study. This may come from the fact that a maternal supine position may lead to the development of the vena compression syndrome which in turn can result in a fall of fetal oxygen pressure [9]. Perhaps the variables studied might have differed more if a larger number of mothers had been studied and/or a more erect position employed.…”