PREDICTIVE VALUE OF MONITORING PARAMETERS IN FETAL SURGERY

Background/Purpose: The choice of monitoring parameters in fetal surge ry has thus far been based on feasibility rather than on predictabilit y. Ideally, monitoring should be noninvasive, have a rapid response ti me and high sensitivity, and be applicable to open and endoscopic tech niques. Herein, the authors studied the response of several parameters to standardized episodes of fetal ischemia and stress. Methods: Eight time-dated fetal lambs (110 days, term, 145 days) were used. Under ge neral anesthesia, a balloon occluder was placed around the umbilical c ord. Pu Ise oximetry (POx + heart rate, HR), electrocardiography (ECG) , direct oximetry (DOx), and blood pressure (BP) were recorded continu ously. After stabilization, the umbilical cord was completely occluded for 5 seconds, then released. False-negative recordings were defined as failure of a parameter to respond to umbilical occlusion; false-pos itive episodes were defined as 10% change in value over less than or e qual to 10 seconds during stabilization (baseline) period. Results: Th e fetuses were monitored for an aggregate of 358 minutes. Baseline DOx was 64% +/- 5%, POx, 66% +/- 16%; HR, 141 +/- 18 beats per minute (bp m); systolic BP (SBP), 51 +/- 3 torr; and diastolic BP (DBP), 38 +/- 2 torr. During umbilical occlusion (n = 15), SEP increased to 56 +/- 3 torr and DBP to 43 +/- 2 torr at 0.5 seconds, then returned to baselin e at 8.0 seconds. A decrease was seen in DOx (start at 3.5s, maximum D elta 9.9 +/- 1.5% at 10.5 seconds) and POx (start at 4.2 seconds, maxi mum Delta 7.3 +/- 2.4% at 20.5 seconds). Heart rate showed <10% decrea se (start at 8.5 seconds, nadir 131 +/- 14 bpm at 19.5 seconds). No EC G changes were noted. Sensitivity was 100% for DOx, POx, and BP, but o nly 14% for HR; specificity was 97% for DOx and 88% for POx; positive predictive value was 58% for DOx and 37% for POx; negative predictive value was 100% for DOx and POx. Conclusions: Direct intravascular oxim etry and blood pressure provide a prompt and reliable response to acut e fetal stress, but are too invasive for routine use. Bradycardia is a n insensitive a nd late sign of feta I distress. Pulse oximetry has a rapid response time (<5 seconds), high sensitivity and negative predic tive value. In addition, its application is noninvasive and has proven to be feasible in open and endoscopic fetal surgical procedures. It t herefore appears to be the monitoring parameter of choice for fetal su rgery. Copyright (C) 1998 by W.B. Saunders Company.