NEW TECHNIQUES IN FETAL SURGERY

Optimal fetal management during and after fetal surgery has been limited by an inability to reliably monitor the fetal heart rate and temperature, and by a lack of access to the fetal circulation. In order to solve these problems, we used early third trimester fetal sheep to develop: (1) an implantable radiotelemetry device that transmits the fetal electrocardiogram and temperature, and (2) an intraosseous access technique. A miniaturized radiotelemeter was implanted subcutaneously in the axilla of four fetal sheep. Safe implantation of the radiotelemeter was technically feasible and the device reliably recorded the fetal electrocardiogram and temperature both intraoperatively and postoperatively. Although many possible routes for access to the fetal circulation have been tried experimentally and clinically for both resuscitation and blood sampling, none have proven satisfactory. We assessed the use of intraosseous access in fetal sheep (n = 6) for both infusion and blood sampling. Access with an intraosseous needle was obtained in both sheep fetuses and human fetal cadavers. Blood gas values (pH, PCO2, and PO2) obtained from the medullary cavity of fetal sheep accurately reflected peripheral venous values. Resuscitation drugs reached the fetal circulation via the intraosseous route: sodium bicarbonate elevated venous bicarbonate levels from 28.4 ± 1.7 to 31.8 ± 2.1 mEq/dL (P < .05); injected glucose increased venous glucose levels by 520 ± 108 mg/dL (P < .01); and injection of calcium chloride elevated venous calcium levels from 11.8 ± 0.7 to 15.2 ± 2.2 mEq/dL (P < .05). Intraosseous infusion of epinephrine (0.01 mg/kg) had rapid physiological effect, measured as a 30 mm Hg increase in fetal mean blood pressure at 45 seconds after injection (P ≤ .01). Application of the implantable radiotelemeter and intraosseous access techniques may enhance fetal surgery safety by improving fetal monitoring and permitting reliable access to the fetal circulation. © 1992.