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

Abstract

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.

Continuous intravascular blood gas monitoring: development, current techniques, and clinical use of a commercial device

“…The authors concluded that extensive modi®cation of the sensor design would be necessary before the sensor could be used routinely in this area. 17 There are several clinical evaluation studies from the operating theatre and the intensive care unit. Most studies in the operating room are in adults undergoing one lung ventilation for major thoracic surgery (thoracoscopic surgery, lung transplantation), 47 83 85 or major thoracoabdominal surgery (oesophagectomy).…”

Non-Invasive Monitoring of pH and Oxygen Using Miniaturized Electrochemical Sensors in an Animal Model of Acute Hypoxia

“…Different hypoxia-acidosis induction protocols in rabbits have been described, including either metabolic [24,25] or respiratory [11,26,27] induction protocols. Following previous literature, hypoxia-acidosis was successfully achieved combining a reduction of the fraction of inspired oxygen [14,27], breaths per minute [24] and also the inhalatory flux.…”

“…Although different sensors have been already tested in vivo to detect hypoxia and acidosis [11,20,22], most of them are invasive or not compatible to be inserted for long periods of time in fetal tissue without compromising fetal wellbeing.…”

“…Going in this line, previous evidences have demonstrated the feasibility of sensors devices inserted in different tissues, including vascular system [10][11][12][13], brain [14][15][16][17], gastric system [18], subcutaneous or intramuscular [19][20][21][22], to monitor and detect acid-base status. However, most of these sensors are not designed to be used in fetuses during intrauterine period.…”

Miniaturized Electrochemical Sensors to Monitor Fetal Hypoxia and Acidosis in a Pregnant Sheep Model

“…Previous research has demonstrated the usefulness of oxygen and pH sensors to monitor acid-base status continuously in different tissues. Oxygen sensors based on either pulse-oximetry or fiber-optic sensing inserted in fetal tissue during labor in humans or placed endovascularly during endoscopic fetal surgery in sheep have shown promising results in detecting oxygen variations [5][6][7][8]. Similarly, sensors able to monitor the levels of fetal pH have also been described [8][9][10][11].…”