Continuous Telemetric In Utero Tracheal Pressure Measurements in Fetal Lambs

The study aim to develop a method that allows continuous monitoring and logging of fetal intratracheal and amniotic pressure in unrestrained pregnant animals. Advantage of this innovative telemetric approach is continuous measurements without externalized catheters, which permit more natural unrestrained ewe movement and reduce stress. The device provides continuous data logging on an internal memory, and on-demand wireless access through real time measurements.

Continuous telemetric measurement of intratracheal pressure during fetal tracheal occlusion may help researchers understand the optimal method, degree, and duration of occlusion for antenatal treatment of congenital diaphragmatic hernia. Telemetric pressure measurements could provide insight into the function of multiple organ and fluid filled compartments in the body, including the cerebrospinal fluid, heart, pleural cavity, diaphragm, bladder, uterus, and intestinal tract. To begin prepare the ewe at 80 days of gestation for surgery, and cover the prepped abdomen with a sterile drape or plastic wrap.

Using surgical scissors, create a window in the drape. Then make a five to seven centimeter incision through the ewe's abdomen with cautery cutting, avoiding blood vessels. Locate the fetal head and thorax via palpation.

Now exteriorize the fetal head and forelimbs. Use Babcock uterine clamps to seal the uterine incision edges, and wrap the sterile plastic tightly around the fetal abdomen, preventing amniotic fluid loss. Then using a 60 milliliter sterile syringe, bathe the exposed fetal skin with warm Hartmann's Solution.

To perform a left osterolateral thoracotomy, use electrocautery to make a two to four centimeter skin incision in the ninth intercostal space adjacent to the cranial border of the 10th rib. Then use Mosquito Hemostats to dissect subcutaneous tissue, intercostal muscles, and pleural membrane exposing the diaphragm. Elevate the diaphragm using two small Mosquito Hemostats, creating space for a one centimeter hernia site.

Now using small angled scissors, incise a one centimeter section between the hemostats and release the hemostats from the diaphragm. Employ Atraumatic Potts Forceps to maneuver the stomach through the diaphragmatic hole. Then use a single tie of absorbable 5.0 polydioxanone monofilament to secure the ninth and 10th ribs while avoiding lung damage.

Afterward, close the thoracotomy incision with a mattress suture. Return the fetus to the amniotic sac and replenish the lost amniotic fluid using warm Hartmann's Solution with intraamniotic piperacillin and tazobactam. Then align the surfaces of the chorioamnion and the adjacent uterine walls and employ a 2.0 polyglactin 910 absorbable braided suture in an inverted mattress pattern to suture the uterus and amniotic sac.

Close the ewe's linea alba subcutaneous tissue and skin. After exteriorizing the fetal head as demonstrated earlier, keep the fetal head and neck enveloped in a sterile plastic drape to preserve temperature and fluid. For an unoccluded trachea, intubate the fetal lamb with a 5 French Suction catheter, 14 centimeter deep at the corner of the mouth.

Then connect the catheter to a silicone tubing using appropriate connectors. In case of an occluded trachea, intubate the fetal lamb with a 3.0 micro cuff endotracheal tube without a connector to a depth of 14 centimeters at the corner of the mouth. Then connect the external end of the catheter to 30 centimeter long silicone tubing using a 3.18 millimeter connector.

Use a connector to attach the opposite end of the silicone tubing to the pressure measurement device. Afterwards, secure the catheter at the lamb's mouth and neck and affix the pressure measurement device to the lamb's chest. Pressure measurements taken during the 18 days of gestation indicated that an occluded fetal trachea resulted in higher transrespiratory pressure as compared to an unoccluded trachea.

The most important thing to remember is that the fetal skin during that first procedure is extremely delicate and friable. Therefore, the skin should be kept moist throughout the procedure. Telemetry can also be used for other physiological signals, including palpitations, temperature, pulse rate, movement, respiration, and metabolic variables.

Hence telemetry monitoring of her broad utility for remote and stress-free functional assessments. The telemetry technique allowed us to use transrespiratory pressure as a measure of the efficacy of fetal tracheal occlusion using hydrogel versus balloon to occlude the trachea.