Foetal scalp mass spectrometer blood-gas transducer.

A number of authors have described the design of transducers to be used with mass spectrometers for the skin-surface measurement of gases in newborn infants and adults. We have also previously considered the feasibility of designing a transducer for attachment to the foetal scalp during labour. This paper describes the problems which have been encountered in producing a practical transducer design for foetal scalp use. The major problem has been that of achieving adequate signal-to-noise ratio for the low oxygen levels encountered in the human foetus. A mathematical model is described, and results of the use of the model in optimising critical transducer design parameters are presented. Typical recordings obtained during labour are shown for O2, CO2 and N2O.