Intrapartum fetal pulse oximetry. Part 2: Clinical application

No. 197b-Fetal Health Surveillance: Intrapartum Consensus Guideline

OBJECTIVE

This guideline provides new recommendations pertaining to the application and documentation of fetal surveillance in the intrapartum period that will decrease the incidence of birth asphyxia while maintaining the lowest possible rate of obstetrical intervention. Pregnancies with and without risk factors for adverse perinatal outcomes are considered. This guideline presents an alternative classification system for antenatal fetal non-stress testing and intrapartum electronic fetal surveillance to what has been used previously. This guideline is intended for use by all health professionals who provide intrapartum care in Canada.

OPTIONS

Consideration has been given to all methods of fetal surveillance currently available in Canada.

OUTCOMES

Short- and long-term outcomes that may indicate the presence of birth asphyxia were considered. The associated rates of operative and other labour interventions were also considered.

EVIDENCE

A comprehensive review of randomized controlled trials published between January 1996 and March 2007 was undertaken, and MEDLINE and the Cochrane Database were used to search the literature for all new studies on fetal surveillance antepartum. The level of evidence has been determined using the criteria and classifications of the Canadian Task Force on Preventive Health Care (Table 1).

SPONSOR

This consensus guideline was jointly developed by the Society of Obstetricians and Gynaecologists of Canada and the British Columbia Perinatal Health Program (formerly the British Columbia Reproductive Care Program or BCRCP) and was partly supported by an unrestricted educational grant from the British Columbia Perinatal Health Program. RECOMMENDATION 1: LABOUR SUPPORT DURING ACTIVE LABOUR: RECOMMENDATION 2: PROFESSIONAL ONE-TO ONE CARE AND INTRAPARTUM FETAL SURVEILLANCE: RECOMMENDATION 3: INTERMITTENT AUSCULTATION IN LABOUR: RECOMMENDATION 4: ADMISSION FETAL HEART TEST: RECOMMENDATION 5: INTRAPARTUM FETAL SURVEILLANCE FOR WOMEN WITH RISK FACTORS FOR ADVERSE PERINATAL OUTCOME: When a normal tracing is identified, it may be appropriate to interrupt the electronic fetal monitoring tracing for up to 30 minutes to facilitate periods of ambulation, bathing, or position change, providing that (1) the maternal-fetal condition is stable and (2) if oxytocin is being administered, the infusion rate is not increased (III-B). RECOMMENDATION 6: DIGITAL FETAL SCALP STIMULATION: RECOMMENDATION 7: FETAL SCALP BLOOD SAMPLING: RECOMMENDATION 8: UMBILICAL CORD BLOOD GASES: RECOMMENDATION 9: FETAL PULSE OXIMETRY: RECOMMENDATION 10: ST WAVEFORM ANALYSIS: RECOMMENDATION 11: INTRAPARTUM FETAL SCALP LACTATE TESTING.

Fetal anesthesia and pain management for intrauterine therapy

Anesthesia provision for fetal intervention differs from most other anesthetic situations insofar as anesthesiologists must care for 2 or more patients-each with potentially conflicting requirements. The first is the mother who can readily indicate discomforts, can be monitored directly, and to whom drugs may be administered directly and easily. For the fetus (or fetuses), nociception must be assumed or inferred indirectly, monitoring is limited at best, and drug administration is complicated and often indirect. Fetal and maternal hemodynamic stability must be assured; and a plan to resuscitate the fetus, should problems occur during the procedure, must be developed.

Effectiveness of pulse oximetry versus fetal electrocardiography for the intrapartum evaluation of nonreassuring fetal heart rate

OBJECTIVES

To compare the effectiveness of pulse oximetry and fetal electrocardiography in the management of labor with nonreassuring fetal heart rate (NRFHR).

STUDY DESIGN

This randomized experimental study consisted of two arms. In group 1 we used pulse oximetry and in group 2 we used STAN® technology. The participants in each group were 90 pregnant women with a full-term singleton fetus in cephalic presentation and cardiotocographic tracings compatible with NRFHR. We compared the following variables: rate of cesarean delivery, indications for operative delivery due to NRFHR, and repercussions on the newborn's acid-base status.

RESULTS

The two groups differed significantly in the mode of delivery, with a cesarean delivery rate of 47.6% in group 1 vs. 30% in group 2 (p=0.032). The groups did not differ in the indications for ending labor due to NRFHR (62% vs. 61%, NS). In terms of neonatal outcomes, the 1-min Apgar score was 6 or lower in 17.8% of the group 1 neonates vs. 4.44% of the group 2 neonates (p<0.001). The groups also differed significantly in umbilical cord vein pH (7.23 vs. 7.27) and pCO₂ (57.27 vs. 46.86) at birth.

CONCLUSIONS

Fetal electrocardiography with the STAN® 21 system was more effective in detecting good fetal status and thus in identifying cases in which labor could proceed safely. Intrapartum surveillance with the STAN® 21 system reduced the rate of emergency cesarean delivery.

Predictive value of pulse oximetry for the development of fetal acidosis

AIMS

To determine the predictive value of fetal pulse oximetry (FPO) for the development of fetal acidosis in cases of non-reassuring fetal heart rate (FHR).

METHODS

In a prospective observational study, pulse oximetry monitoring was examined in cases of non-reassuring FHR during singleton cephalic delivery at 36-42 weeks' gestation. The study examined whether fetal arterial oxygen saturation (FSpO(2)) values <30% for at least 10 min during the last 60 min before delivery increase the risk of fetal acidosis. The predictive reliability of this algorithm and the correlation to fetal acidosis [umbilical artery pH (UApH) <7.15] were analyzed.

RESULTS

We included 101 patients with non-reassuring FHR during delivery. The incidence of fetal acidosis was significantly higher when FSpO(2) values <30% were recorded for at least 10 min (P=0.0). An UApH <7.15 was reliably excluded with a negative predictive value of 98.7% and detected with a sensitivity of 92.9%.

CONCLUSIONS

A low pulse oximetry oxygen saturation <30% for at least 10 min correlates highly with fetal acidosis in cases of non-reassuring FHR. FPO reliably excludes moderate to advanced acidosis and can reduce the frequency of fetal blood analysis (FBA) in cases of non-reassuring cardiotocography (CTG).

Fetal pulse oximetry during labor: theory, clinical use and the future

Fetal pulse oximetry (FPO) has evolved through various phases of technical development and calibration. Clinical studies have addressed the issue of determining threshold action values and how well the technology is accepted by childbearing women and their caregivers. This article considers a variety of situations and factors that commonly occur during labor and that may influence fetal oximetry values. These include uterine contractions, supplemental oxygen and intravenous fluids administered to the mother, maternal position and epidural analgesia. The five randomized, controlled trials that compared the use of FPO in addition to fetal heart-rate monitoring with fetal heart-rate monitoring alone, have been systematically reviewed and subjected to meta-analysis where appropriate. Current clinical practice guidelines do not support the routine use of FPO; however, the recent emergence of robust multiwavelength oximeters may, in the future, offer further clinical applications for FPO.

[Fetal pulse oximetry: clinical practice]

OBJECTIVE

To assess in current practice the application of our protocol of using fetal pulse oximetry during labor, to evaluate whether fetal scalp blood sampling can be reduced and to determinate reliability of fetal pulse oximetry on the prediction of poor neonatal outcomes.

STUDY DESIGN

Prospective observational unicenter cohort including 449 patients during two years. All pregnancies were singleton, greater than or equal to 37 weeks' gestation, cephalic presentation, and had non reassuring fetal heart rate. The poor neonatal outcome was defined by one of the followings: arterial umbilical cord pH<or=7.15, umbilical cord base deficit greater than or equal to 12 mmol/l, 5 min Apgar score less than or equal to 7, transfer in neonatal intensive care unit, secondary respiratory distress and death.

RESULTS

The use of fetal pulse oximetry was concordant with our protocol in more than 80% of cases. The frequency of fetal scalp blood sampling was significantly reduced from 9.9 to 8.6% after the introduction of our protocol. With a 30% threshold, diagnostical values of fetal oximetry for a poor neonatal outcome were 9.1% for sensitivity, 93.1% for specificity, 79.4% for negative predictive value and 25.9% for positive predictive value. With a 40% threshold, the diagnostic values were 74, 51.6, 88.2 and 28.9% respectively.

CONCLUSION

The strict application of our protocol allow a less aggressive management of labor with a significant decrease in fetal scalp blood sampling. This study shows that with a 40% threshold, fetal pulse oximetry could be considered as a reliable tool for the management of labor with no increase of poor neonatal outcomes. On the other hand, the threshold which could determine whether an abnormal fetal heart rate needs immediate intervention still remains unclear.

Intrapartum oximetry of the fetus

Fetal monitoring during labor aims to identify fetal problems which, if uncorrected, may result in morbidity or death. A nonreassuring or abnormal fetal heart rate trace by cardiotocography (CTG) does not necessarily equate with fetal hypoxia and/or acidosis. However, in the absence of more objective data, the use of CTG often results in variable, but inappropriately high, operative delivery rates (forceps, vacuum, or cesarean delivery) for nonreassuring fetal status in many hospitals. The addition of fetal pulse oximetry (FPO) has the potential to improve the assessment of fetal well-being during labor. In this review we consider several aspects of FPO. Several factors, such as sensor to skin contact, uterine contractions, fetal hair, and caput succedaneum, influence the performance and use of FPO. Issues such as clinicians' perspectives of FPO sensor placement, maternal perspectives of FPO during labor, and an economic analysis have all favored FPO. Several randomized controlled trials (RCTs) of FPO reported a reduction in cesarean delivery for nonreassuring fetal status when FPO was added to conventional CTG monitoring, with no difference in overall cesarean delivery rates. One large RCT reported no difference in mode of birth for any indication. Several issues relevant to the future of FPO have been addressed by these RCTs, the major issue being that it makes no difference to cesarean rates. It may be argued that FPO has a valid clinical use in monitoring the fetus with congenital heart block. Additionally, in situations of nonreassuring fetal status and dystocia, FPO may provide the necessary reassurance until adequate resources for cesarean delivery are available.

Transabdominal fetal pulse oximetry with near-infrared spectroscopy

OBJECTIVE

The purpose of this study was to determine the feasibility of noninvasive fetal pulse oximetry in the human fetus with transabdominal continuous-wave near-infrared spectroscopy.

STUDY DESIGN

The instrument has 3 wavelength light-emitting diodes (735, 805, and 850 nm) as light sources and a photomultiplier tube as a detector. This instrument was used in 6 pregnant women (>36 weeks of gestation). First, a fetal heart rate was obtained with a fetal heart rate monitor. Then, the depth of fetal tissue (head) from the maternal abdomen was determined by ultrasound examination; the distance between the optodes (light source and the detector) was set to be approximately twice the depth of the fetus (7-11 cm). The data analysis was based on the modified Beer-Lambert law and the use of optical densities at 735 and 850 nm to obtain the concentration changes of the oxyhemoglobin and deoxyhemoglobin. The saturation was expressed as the percent of oxygen saturation equal to 100 x oxyhemoglobin/(oxyhemoglobin + deoxyhemoglobin). We recorded the spectroscopy data and the fetal heart rate for approximately 3 to 10 minutes in each patient.

RESULTS

The mean oxygen saturation values of each of the 6 individual fetuses ranged from 50% to 74% (overall mean saturation, 61% +/- 14.8% [SD]).

CONCLUSION

This preliminary data indicate that transabdominal fetal pulse oximetry is feasible for human patient application. The measured values were similar to those that are obtained with transvaginal pulse oximetry. Future studies should correlate transabdominally obtained measurements with those measurements that are obtained by transvaginal fetal pulse oximetry.

Fetal pulse oximetry: a critical appraisal

Despite 40 years of cumulative clinical experience, and a number of randomized clinical trials, electronic fetal heart rate monitoring is perceived by many obstetrical caregivers as a suboptimal method of intrapartum fetal assessment. Fetal pulse oximetry emerged 15 years ago as a promising new technology intended to improve assessment of fetal condition during labor. A large amount of physiologic data and one large randomized clinical trial have brought this technology into clinical practice. We know that fetal acidemia is rare when the arterial oxygen saturation is >30% but fetal pulse oximetry as currently understood and applied does not reduce the overall cesarean rate. Thus, many clinicians remain unconvinced of the benefit of this technology and its utilization has stalled in the US and Europe. We need to further understand if there is a way to use fetal pulse oximetry in the setting of labor dystocia and a non-reassuring fetal heart rate pattern. Although hypoxemia is an accepted mechanism of fetal brain injury, other potential mechanisms should be explored. Current controversies and fertile areas of research are presented.

Trauma in pregnancy

The anatomic and physiologic changes make treatment of the pregnant trauma patient complex. The fetus is the challenge, because, in pregnancy, trauma has little effect on maternal morbidity and mortality. Aggressive resuscitation of the mother, in general, is the best management for the fetus, because fetal outcome is directly related to maternal outcome. Recent literature has attempted, with little success, to identify factors that may predict poor fetal outcomes. Cardiotocographic monitoring should be initiated as soon as possible in the emergency department to evaluate fetal well-being. Other key points include: Maternal blood pressure and respiratory rate return to baseline as pregnancy approaches term. Initial fetal health may be the best indicator of maternal health. Inferior vena cava compression in the supine patient may cause significant hypotension. Maternal acidosis may be predictive of fetal outcome. Kleihauer-Betke testing is not necessary in the emergency department. Early ultrasonographic evaluation can identify free intraperitoneal fluid and assess fetal health. Necessary radiographs should not be withheld at any period of gestation. Radiation beyond 20 weeks' gestation is safe. Patients with viable gestations require at least 4 hours of CTM monitoring after even minor trauma.

Intrapartum cardiotocography and fetal pulse oximetry in assessing fetal hypoxia

OBJECTIVES

A retrospective analysis of short-term variability (STV), a cardiotocography (CTG) parameter, in relation to fetal blood saturation values (FSpO(2)) obtained by fetal pulse oximetry.

METHODS

The study included 26 healthy pregnant women monitored continuously during delivery with both cardiotocography and fetal pulse oximetry.

RESULTS

Lower FSpO(2) values were observed in the group showing STV levels <or=6.0 ms in the 1st stage of labor (44.7+/-3.46% vs. 49.2+/-1.8%), but this result was not statistically significant. In the 2nd stage of labor, FSpO(2) values in the group with STV levels <or=6.0 ms were significantly lower than those with STV levels >6.0 ms (34.4+/-2.9% vs. 43+/-7.2%; P<0.001). A positive correlation was found between STV levels <or=6.0 ms and mean FSpO(2) values in the 2nd stage of labor.

CONCLUSIONS

1. A significant relationship was observed between short-term variability in the cardiotocographic records and fetal blood saturation levels in the 2nd stage of labor. 2. Fetal pulse oximetry can be valuable in assessing fetal wellbeing, especially when CTG records are abnormal.