Jun Wu

Continuous Monitoring of Fetal pH, pO2 and pCO2 Using a Fiberoptic Multiparameter Sensor in Animal Models Reproducing in utero Conditions

Objectives: To evaluate the feasibility and accuracy of continuous fetal monitoring with a multiparameter intravascular sensor (MPIS) in animal models mimicking the fetal metabolic status. Methods: First, the accuracy of the MPIS in hypoxic conditions was tested in adult rabbits (n = 6). The carotid artery (n = 4) or vein (n = 2) was catheterized with a 20-gauge cannula, housing a 500-μm Neotrend® fiberoptic sensor for pCO2, pO2, pH and temperature. Fiberoptic readings were compared with arterial blood-gas (ABG) analyses. Secondly, the feasibility of continuous fetal fiberoptic sensing was tested during experimental fetoscopic surgery in lambs (n = 4). An identical sensor was introduced in a chorionic artery and readings were compared to ABG analyses of fetal blood samples. Results: The overall bias and precision in the first experiment (147 measurement pairs) were –4.2 and 10.9 mm Hg for pO2, +1.6 and 8.2 mm Hg for pCO2 and –0.015 and 0.031 for pH, respectively. In the sheep experiments, continuous readings for all parameters were only available during 50% of the operation time, mainly due to disturbances induced by movement, contact with vessel wall and interference by endoscopic light. 20 sample pairs were obtained resulting in an overall bias and precision of –3.9 and 4.3 mm Hg for pO2, –0.74 and 3.68 mm Hg for pCO2 and –0.0032 and 0.02 for pH. Conclusions: Fiberoptic microsensors are potentially useful for monitoring acid-base status in the low pO2 range present in fetal life.

Biochemical Differentiation of Gestational Compartments in the Midgestational Fetal Rabbit

Objectives: The fetal rabbit at midgestation is increasingly being used as a model in fetal diagnosis and therapy. In this study, we aimed to establish a reliable method for identification of the origin of sampled extra-embryonic fluids based on selected biochemical components. Methods: In 6 pregnant does at 22 days of gestation, 18 gestational sacs were sampled for amniotic, allantoic and exocoelomic fluid. These fluids, as well as matching maternal and fetal blood samples, were assayed for levels of sodium, potassium, chloride, bicarbonate, total protein, alkaline phosphatase, γ-glutamyl transferase and progesterone. Results: Levels of sodium and potassium were, respectively, lower and higher in the allantoic fluid when compared to other extra-embryonic spaces. Amniotic fluid had a significantly lower total protein content and higher level of alkaline phosphatase when compared to the exocoelomic fluid. Significant levels of progesterone could only be detected in maternal blood. Conclusions: In the midgestational rabbit, a combined assay of potassium, alkaline phosphatase and progesterone can determine the gestational cavity of origin of the sampled fluid. The obtained gradients for these markers suggest compartment-specific production and/or inter-cavity transfer mechanisms.