Maternal-fetal argon transfer using skin-surface mass spectrometry during human labor
Spencer JAD., Rolfe P., Johnson P.
Objective: Feasibility study of a potential means to assess placental function by measurement of maternal-fetal inert gas transfer during human labor using skin-surface mass spectrometry. Methods: Skin-surface mass spectrometer probes were attached to the maternal forearm and fetal scalp (after rupture of the membranes) of six women during labor. Measurements of maternal and fetal argon were made before, during, and after the inhalation of 75% argon in oxygen for 2 min. Results: Argon was first measured from the maternal skin after a median time of 44.5 sec (range 33.0-45.8) and the level rose steadily to reach a median peak partial pressure of 94.3 mm Hg (range 68.4-103.7) at a median time of 160 sec (range 138.3-175.0). The maternal level then fell steadily at an exponential rate. Argon was first measured from the fetal scalp after a median interval of 90 sec (range 60.0-123.3) and rose more slowly to a median peak partial pressure of 24.3 mm Hg (range 17.0-38.9) at a median time of 288.5 sec (range 256-390). The median (range) fetal/maternal (F/M) ratio of skin-surface argon peak values was 0.26 (0.22-0.39) and showed good reproducibility within each case. The overall coefficient of variation of mean values from the six women was 9%. Maternal and fetal curves were smooth and showed no influence of uterine contractions while the probes remained in good contact with the skin. Dislodgement of the fetal probe was not a problem in the absence of maternal movement but was likely during the second stage of labor. This was readily apparent from the irregular fetal record which showed alterations with uterine contractions. Conclusions: Continuous assessment of maternal-fetal inert gas transfer, with its potential for investigating placental function during labor, is possible. However, the practical application of this idea awaits development of less expensive and simpler technology, which can then be evaluated in pregnancies complicated by placental dysfunction.