Fetal pulse oximetry

The original expectation of fetal pulse oximetry (FPO) for the field of obstetrics was predicated on the tremendous positive impact pulse oximetry had upon the fields of anesthesiology, critical care medicine, and many other disciplines of medicine. With the general acceptance that many, if not most, concerning fetal heart rate patterns are not associated with significant fetal hypoxemia and acidemia, the additional physiologic information FPO offers (ie, actual arterial blood oxygenation) was believed and hoped by many to be the reassurance that would allow safe avoidance of unnecessary interventions such as cesarean delivery. To date, FPO has not met that expectation, not because of its inability to measure fetal arterial oxygen saturation, but because of its inability to do so with a reduction in overall cesarean deliveries.     

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.     

Fetal pulse oximetry. Instrumentation and recent clinical experience

Despite the pressing clinical need to improve fetal intrapartum surveillance, fetal oximetry has lagged well behind its application in the neonate because of the difficulty of developing a suitable method to record data from the fetus and testing its accuracy and reproducibility. Acceptable values of oxygen saturation that indicate fetal well-being are much lower than in neonates. The development of fetal pulse oximetry instrumentation is discussed. Recent clinical data acquired using the latest instrumentation are summarized and exciting new clinical applications proposed.     

Fetal monitoring with pulse oximetry

Summary. Continuous fetal monitoring was achieved with a fetal scalp pulse oximetry sensor in 86 labours. The average recorded fetal oxygen saturation in early labour (cervical dilatation < 5 cm) was 68% (SD 13%). At the end of labour (cervical dilatation ≥ 9 cm) the recorded mean oxygen saturation was 58% (SD 17%). The largest range of readings during a single labour was 81%-11% but this drop was associated with cord compression. The average SD during 1 h of normal labour was 10%. A second group of 40 fetuses was monitored during induction of labour before and after elective amniotomy. Oxygen saturation did not appear to change after amniotomy (mean change −0.4%, SD 1.2%) and there was no difference between mean antenatal or early intrapartum readings. We excluded the amniochorionic membranes as a possible source of data corruption by measuring their in vitro absorption spectra and confirming that they do not preferentially absorb light of either 660 or 940 nm wavelength. Non-invasive pulse oximetry can be used to monitor the fetus before and during labour.     

Fetal monitoring with pulse oximetry

Continuous fetal monitoring was achieved with a fetal scalp pulse oximetry sensor in 86 labours. The average recorded fetal oxygen saturation in early labour (cervical dilatation less than 5 cm) was 68% (SD 13%). At the end of labour (cervical dilatation greater than or equal to 9 cm) the recorded mean oxygen saturation was 58% (SD 17%). The largest range of readings during a single labour was 81%-11% but this drop was associated with cord compression. The average SD during 1 h of normal labour was 10%. A second group of 40 fetuses was monitored during induction of labour before and after elective amniotomy. Oxygen saturation did not appear to change after amniotomy (mean change -0.4%, SD 1.2%) and there was no difference between mean antenatal or early intrapartum readings. We excluded the amniochorionic membranes as a possible source of data corruption by measuring their in vitro absorption spectra and confirming that they do not preferentially absorb light of either 660 or 940 nm wavelength. Non-invasive pulse oximetry can be used to monitor the fetus before and during labour.     

Fetal pulse oximetry and neonatal outcome: a study in a developing country.

BACKGROUND: The aim of this cohort, prospective study was to compare the diagnostic value of intrapartum fetal pulse oximetry (FPO) with that of fetal scalp blood gas (FSBG) for an abnormal neonatal outcome in cases with abnormal fetal heart rate (FHR) tracings. METHODS: Fetal oxygen saturation was continuously monitored with Nellcor N-400 FPO during labor. Simultaneous FSBG determinations were obtained. The results were analyzed in relation to umbilical arterial cord blood pH and neonatal outcome. Studied FPO cutoff levels were 30 and 40% hemoglobin saturation and that of FSBG pH was 7.2. RESULTS: During the study, there were 9825 deliveries; 415 had abnormal FHR. Only 150 fulfilled the whole screening panel. When the outcome variable was umbilical arterial pH, the positive predictive values of the three methods (FPO30, FPO40, FSBG) were 57, 61 and 65% and the negative predictive values were 43, 39 and 35% respectively. The sensitivity of FPO30 was highest (75%). Considering abnormal neonatal outcome, again the sensitivity was also highest for FPO30 (89%). The sensitivity of FSBG was 82%. The specificity of the three methods were 53, 49 and 38% respectively. CONCLUSION: The diagnostic value of intrapartum FPO compares favorably with FSBG. FPO seems to be a reliable and less invasive tool and may decrease unnecessary interventions and unnecessary fetal scalp blood sampling in cases of suspected fetal distress. The FPO cutoff of 30% saturation defined by previous studies appears to be appropriate.     

胎儿血氧饱和度监测的临床应用

胎儿脉冲血氧测定(fetal pulse oximetry,FPO)可提高产程中对胎儿健康状况评估的准确性。现有随机对照临床试验结果显示,它可以降低胎心宫缩监护(CTG)提示不确定胎儿情况的剖宫产率,但不会降低总体剖宫产率。     

Fetal pulse oximetry in second stage of labor

OBJECTIVE: To compare the mean values of fetal oxygen saturation with fetal heart rate pattern in the second stage of labor (Melchior classification) MATERIAL AND METHODS: The study included 30 parturients in gestational age 37-41 weeks. Fetal oxygen saturation was recorded and averaged over the last 30 min of the second stage of labor Simultaneously, fetal heart rate and uterine contractions were monitoring. Fetal heart rate patterns were assessed according to Melchior's classification. At birth, the cord acid-base parameter (pH) was calculated. RESULTS: The lowest value of fetal oxygen saturation over the last 30 min of labor was 10%, the highest 60%, and the mean value 39.1 +/- 12.5%. Statistically, significant correlation between the mean value of oxygen saturation over the last 30 min of labor and pH arterial values (n = 25, p = 0.004, r = 0.42) was found. There was no statistically significant correlation between fetal oxygen saturation and pH venous values (n = 24, p. = 0.006, r = 0.49), but trend towards significance could be observed. Statistical analysis revealed that arterial pH was significantly correlated to Melchior's classification. The lowest pH and FSpO2 values coexisted with type 3 and 4 of FHR patterns according to Melchior's classification. CONCLUSIONS: The mean values of fetal oxygen saturation over the last 30 min of labor significantly correlate with arterial pH values. These values correlate with FHR abnormalities according to Melchior's classification. Fetal pulse oximetry seems to be an important, additional method assessing fetal well-being in the second stage of labor.     

Fetal pulse oximetry: duration of desaturation and intrapartum outcome.

OBJECTIVE: To analyze labor outcomes in relation to masked fetal arterial oxyhemoglobin saturation values above or below 30%. METHODS: Consenting gravidas with uncomplicated pregnancies at or beyond 36 weeks' gestation underwent continuous fetal pulse oximetry. Pregnancy outcomes were compared between two groups: women with fetuses with at least one epoch of arterial oxyhemoglobin saturation below 30% (10 seconds or longer) and women with fetuses without such an episode. We also attempted to ascertain whether duration of saturation below 30% correlated with fetal compromise. RESULTS: We measured arterial oxyhemoglobin saturation in 129 fetuses, 69 (53%) of whom had at least one epoch of saturation below 30%. There were no statistically significant differences in labor and delivery outcomes between the high-saturation and low-saturation groups (eg, cesarean delivery: 13 versus 9%, P = .41; umbilical artery [UA] pH less than 7.20: 10 versus 9%, P > .999). However, as duration of fetal arterial oxyhemoglobin saturation below 30% increased from 10 seconds to longer than 9 consecutive minutes, the incidence of fetal compromise (considered present when at least one of the following criteria was met: cesarean delivery for nonreassuring fetal heart rate pattern, UA pH less than 7.20, admission to the special care nursery, or 5-minute Apgar score not more than 3) increased significantly (P = .002). The threshold duration of fetal arterial oxyhemoglobin saturation below 30% associated with increased fetal compromise was 2 minutes. CONCLUSION: Transient fetal arterial oxyhemoglobin saturation values below 30% are common during normal labor and did not predict fetal compromise. Fetal arterial oxyhemoglobin saturation values less than 30% for 2 minutes or longer might be associated with fetal compromise.     

Fetal pulse oximetry: an adjunct to electronic fetal heart rate monitoring

Electronic fetal heart rate monitoring is routinely used as an indirect measure of fetal oxygenation, yet its value continues to be questioned. With a nonreassuring fetal heart rate pattern, the clinician often needs additional information about fetal oxygen status. Fetal pulse oximetry is a new fetal assessment technology. After consideration of the results of a multicenter randomized, controlled, clinical trial on fetal pulse oximetry in the United States, the U.S. Food and Drug Administration approved the technology for clinical use on May 12, 2000. The results of this trial are anticipated to be published in late 2000.     

Fetal pulse oximetry and other monitoring modalities. Future directions

Although in the beginning phase of its use, the application of fetal oximetry in high-risk obstetrics is predicted to increase. Even at its early clinical application, patient data have shown that fetal oximetry has the excellent potential to be used with other fetal monitoring modalities to further characterize the metabolic state of the fetus, especially during labor. Similar to other monitoring modalities, the clinicians also need to be aware of its limitations.     

Fetal pulse oximetry: from the first experimental studies of broad clinical use. An assessment of current status

Pulse oximetry has triggered a revolutionary change in monitoring patients in many branches of medicine. For 4 years fetal sensors with specially calibrated pulse oximeters are tested clinically. Additional examination methods are required for accurate monitoring the fetus intrapartum because of the low specificity of cardiotocographs and also to avoid unnecessary operative deliveries. Research on hand up to now has demonstrated that fetal pulse oximetry is a method easy to learn, easily applicable and well quanitifiable to improve fetal monitoring and the interpretation of the fetal heart rate patterns intrapartum. Prospective intervention studies involving management studies still have to prove the clinical value of this new technology. Only after examining a large number of hypoxic-risk fetuses we can assess whether pulse oximetry in a management can replace invasive fetal blood analysis as a continuous, non-invasive method of monitoring. Various teams try to prove a context between arterial saturation values (SpO2) and biochemical changes of the fetus in connection with a crucial limiting value of 30% by correlating changes of the fetal scalp with the oxygen saturation. Guidelines for the assessment of the SpO2-values are established according to the present level of knowledge and future aspects of the method are examined.     

Fetal pulse oximetry: correlation with intrapartum fetal heart rate patterns and neonatal outcome

AIM: To determine how fetal pulse oximetry behaves in various cardiotocographic (CTG) tracings and correlates with neonatal outcome. PATIENTS AND METHODS: Pregnant women undergoing active labor with singleton pregnancies of 32-42 weeks were enrolled. CTG recordings were reassuring or nonreassuring (namely variable or persisting late decelerations). Pulse oximetry values during labor and changing throughout deceleration and recovery phases, duration and frequency of pulse oximetry recordings <30%, and neonatal outcome were determined. One-way anova, Tukey test, chi(2)-test and multiple logistic regression model were used for statistical analysis where appropriate. RESULTS: A total of 156 pregnant subjects were divided into three groups: reassuring fetal heart rate (FHR) patterns (group 1, n=78 [50%]), late decelerations (group 2, n=16 [10.3%]) and variable decelerations (group 3, n=62 [39.7%]). The initial and final pulse oximetry readings, pulse values in first stage of labor, the duration and the frequency of pulse oximetry recordings <30% were significantly different between groups (P<0.001, P<0.001, P<0.001, P=0.001, P<0.001). Fetal acidosis was significantly more frequent with late decelerations (23.1%, P=0.004). A multiple logistic regression model demonstrated that the initial pulse oximetry value during active labor was the most predictive variable of neonatal well-being (P<0.001). CONCLUSION: Decreased fetal pulse oximetry values, especially prolonged and recurrent recordings <30% are well-correlated with abnormal FHR patterns, indicating an association with fetal compromise and metabolic acidosis. Going through active labor with a lower initial value of FSpO(2) more frequently leads to an altered FHR pattern and subsequent adverse fetal outcome.     

Multicenter study on the clinical value of fetal pulse oximetry: I. Methodologic evaluation

Objective: Our purpose was to evaluate the feasibility of intrapartum fetal pulse oximetry, the distribution of fetal oxygen saturation values, and the relationship with the neonatal outcome in a population with an abnormal fetal heart rate. Study Design: A prospective multicenter observational study was performed from June 1994 to November 1995. Fetal oxygen saturation was continuously recorded with use of a Nellcor N-400 fetal pulse oximeter in case of an abnormal fetal heart rate during labor. Simultaneous readings of fetal oxygen saturation and fetal blood analysis were obtained at inclusion and before birth. Feasibility, adverse effects, distribution of fetal oxygen saturation values, and relationship with neonatal outcome were assessed. Results: One hundred seventy-four patients were included. From 172 attempted sensor placements, the procedure was impossible in three cases and fetal oxygen saturation values were obtained in 164 cases (95.3%). Physicians considered sensor placement an easier task than an attempt at fetal blood analysis (easy in 87.5% vs 78.9% for fetal blood analysis, p = 0.03). The mean reliable signal time (±SD) was 64.7% ± 32% during the first stage. There were no serious adverse effects in the study population. The mean fetal oxygen saturation during the first stage of labor was 42.2% ± 8.0% (10th to 90th percentile range 30% to 53%). Fetal oxygen saturation was significantly correlated with scalp pH (r = 0.29, p = 0.01) but not with neonatal umbilical artery pH or gas values. There was a significant association between low fetal oxygen saturation (<30%) and poor neonatal condition. Conclusion: The feasibility of fetal pulse oximetry is satisfactory in clinical practice. It is easy to use and provides a fair rate of recorded values, even in a population with suspicion of fetal distress. A low fetal oxygen saturation is significantly associated with an abnormal neonatal outcome.