Suction fixation of the tcPco2 electrode for fetal monitoring

The fixation ring for suction fixation is made of a soft plastic material and is measuring 24.5 mm in diameter and 5.8 mm in height. The electrode is mounted into the center of the ring and kept in position by the elasticity of the material. A polyethylene catheter is glued into the ring connecting it to the vacuum pump (-20 kPa). The soft plastic material will be deformed by heating, and sterilization should be performed by gamma radiation or by fluid aldehydes. The electrode mounted in the suction ring is attached to the fetal head during vaginal examination without amnioscopy or the use of application tools. The suction fixation technique was evaluated in relation to the glue fixation technique by simultaneous measurements with two electrodes. In adult monitoring no differences in stabilization times and Pco2 values were found. In fetal monitoring a little difference (0.3 kPa) in mean values was found at a cervical dilatation of less than 8 cm, but no difference was found at a cervical dilatation of more than 8 cm. Calibration may be performed by either two-point or one-point calibration. One-point calibration is usually sufficient, but the sensitivity of the electrode should be checked regularly. Electrode sterilization by fluid aldehydes following the calibration does not influence electrode drift. A close correlation was found between the transcutaneous carbon dioxide tension just before delivery and the Pco2 of umbilical artery blood (r = 0.77, n = 64). Stabilization time was short (2.1 min.) and the electrode drift usually low (mean -0.14 kPa or 2.7%) independent of the duration of the monitoring.(ABSTRACT TRUNCATED AT 250 WORDS)