Continuous measurement of blood gas tensions in the fetal guinea pig by mass spectrometry

Contribution of the BOHR effect to the fall in fetal Po2caused by maternal alkalosis

“…Oxygen and carbon dioxide tensions in the right atrium of the fetus were measured continuously and simultaneously by mass spectrometry [11]. The blood gas catheter [18] was a flexible, stainless steel tube (O. D. 0.8 mm) connected to the high vacuum chamber of the mass spectrometer (MICROMASS SX 200, VG GAS ANALYSIS, Middlewich, England).…”

“…The pH in the umbilical artery was set at 7.27, which was the value measured in blood obtained by cardiac puncture [5]. The blood flow rates on the fetal and maternal sides of the placenta have been measured under closely similar experimental conditions [4,11] and were assigned values of 7.5 ml/min and 7.3 ml/min, respectively. The fetal DPG value was set to 1.73mM [2].…”

“…The present study is a theoretical and experimental analysis of the contribution of the BOHR effect to the reduction in fetal Ρθ2 caused by maternal alkalosis. We measured respiratory gas tensions in fetal guinea pigs by mass spectrometry [11] during a step change in the pH of maternal blood achieved by infusing an isotonic solution of sodium hydroxide in the descending aorta. The measured response of fetal Ρθ2 was then compared with that predicted by a computer model of placental gas exchange in the guinea pig, given the initial conditions and the extent of the change in maternal arterial pH.…”

Acid-base status of pregnant guineapigs during neuroleptanalgesia with diazepam and fentanyl-fluanisone

“…The poor condition of the fetuses can be assumed to reflect an inadequate supply of oxygen. In subsequent work, with diazepam and pentobarbitone as the anaesthetic agents, fetal acid-base status was measured and shown to be similar to Gr0nlund, 1982). The latter regimen is preferable to neuroleptanalgesia for acute experiments of longer duration, provided that the dam is allowed to breathe oxygen-enriched air.…”

“…A catheter was placed in a femoral artery to enable measurement of blood pressure and the withdrawal of 0'7 ml samples of arterial blood. Details of the other surgical procedures, including those required for the measurement of maternal placental blood flow, are given elsewhere (Gr0nlund & Carter, 1982). Fluid replacement was given by the s.c. injection of isotonic saline solution (c. 4 ml/h).…”