Correlation between NIR spectroscopy and pulse oximetry in the fetus

Near-infrared spectroscopy in the fetus and neonate

Near-infrared spectroscopy allows for real-time, noninvasive measurement of cerebral hemodynamics and oxygenation at the bed-side. This article describes animal and clinical research using near-infrared spectroscopy to study cerebral hemodynamic function in the fetus, neonate, and child.

Brain Cell Function during Hypoxemia in Near-Term Lambs: A Near-Infrared Spectroscopy Study

BACKGROUND

Sufficient O2 supply to the brain is necessary for adequate cerebral energy metabolism, function and growth.

OBJECTIVES

To elucidate the relation between changes in cerebral arterial O2 content and cerebral O2 supply and changes in the oxygenation state of cerebral hemoglobin, and to determine whether concentration changes in oxyhemoglobin (DeltacO2Hb), deoxyhemoglobin (DeltacHHb), and cerebral arterial oxygenation (DeltacHbD; the difference between DeltacO2Hb and DeltacHHb), and cerebral blood volume (DeltaCBV) can be used to assess the decline in brain cell function during hypoxemia in lambs born near term.

METHODS

17 preterm lambs were delivered at a mean gestational age of 133 days. Decreases in cerebral arterial oxygen content were induced by a stepwise reduction in inspired oxygen concentration. Mean values of all continuous variables were calculated over the last 180 s of each hypoxemic level. Cerebral arterial blood gases were analyzed at the end of each level to calculate cerebral arterial O2 content and cerebral O2 supply.

RESULTS

Changes in cerebral arterial O2 content and cerebral O2 supply were positively linearly related with DeltacO2Hb and DeltacHbD, and negatively with DeltacHHb and the concentration changes in total hemoglobin. Electrocortical brain activity remained stable until the cO2Hb and cHbD decreased to >3.0 +/- 0.9 and >8.1 +/- 1.9 (mean +/- SD) micromol/100 g, respectively, and cHHb and CBV increased to >4.3 +/- 1.7 and 1.37 +/- 0.48 ml/100 g, respectively, as compared to baseline.

CONCLUSIONS

Changes in cerebral arterial O2 content and cerebral O2 supply are adequately reflected by changes in the oxygenation state of cerebral hemoglobin. Concentration changes in DeltacO2Hb, DeltacHHb, DeltacHbD and DeltaCBV can be used to assess the decline in brain cell function during hypoxemia in lambs born near term.

Intrapartum Assessment of the Fetus: Historical and Evidence-Based Practice

The principal purpose of intrapartum fetal assessment is to detect hypoxemia-ischemia, which may lead to fetal jeopardy. A quarter century ago, electronic fetal monitoring replaced intermittent auscultation as the primary method of intrapartum fetal assessment in the United States. It seems that electronic fetal monitoring will continue to be the primary mode of intrapartum fetal assessment, with intermittent auscultation used in some centers primarily for low-risk parturients. From this abridged history of intrapartum fetal monitoring, it is recognized that all surveillance methods bear inherent limitations.

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.

Cerebral hemoglobin concentration and oxygen saturation measured by intensity modulated optical spectroscopy in the human fetus during labor

AIMS

To quantify hemoglobin concentration and oxygen saturation in the human fetal brain using intensity modulated optical spectroscopy during labor.

METHODS

A specially designed probe was applied to the fetal scalp in 20 women during uncomplicated labor at term. Optical fibres transmitted near infra-red light to and from an intensity modulated optical spectrometer (IMOS), which detected changes in the optical parameters of the infra-red light source. Using novel off-line analytic techniques, these changes were converted into absolute measurements of oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb). Summing Hb and HbO2 gives total hemoglobin concentration (HbT) and HbO2/HbT x 100% provided measurements of cerebral saturation (SmcO2).

RESULTS

Of 20 fetuses studied, data from 10 fetuses were suitable for analysis. Over three consecutive uterine contractions, the mean (+/- SD) absolute cerebral concentrations of Hb and HbO2 were 30 +/- 18 and 46 +/- 21 mumol/l, respectively. This gave a mean cerebral HbT of 77 +/- 29 mumol/l and a mean SmcO2 of 59 +/- 12%. In the other ten fetuses insufficient light was detected to allow chromophore quantification.

CONCLUSION

These are the first absolute measurements of cerebral Hb and HbO2 in human fetuses during labor. The values of total hemoglobin are similar to those obtained in neonates with hypoxia-ischemia and the measurements of fetal cerebral oxygen saturation are similar to previously published values.

Fetal health surveillance in labour

OBJECTIVE

This guideline defines the standards pertaining to the application and documentation of fetal surveillance in labour that will decrease the incidence of birth asphyxia while maintaining the lowest possible rate of obstetrical intervention. Both high- and low-risk obstetrical populations are considered. It is intended that this guideline could be used by all persons providing intrapartum care in Canada, including nurses, physicians, and midwives.

OPTIONS

Consideration has been given to methods of fetal surveillance currently available in Canada, including intermittent auscultation, electronic fetal monitoring (alone and when paired with vibro-acoustic or scalp stimulation and fetal scalp blood sampling), the "admission strip," computerized heart rate analysis, fetal oxygen saturation monitoring, fetal electrocardiogram analysis, and near-infrared spectroscopy.

OUTCOMES

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

EVIDENCE

A comprehensive review of randomized controlled trials performed from 1995 to date and a search of the literature using Medline and the Cochrane Database of all new studies on fetal surveillance. The level of evidence has been determined using the criteria described by the Canadian Task Force on the Periodic Health Examination.

RECOMMENDATIONS

Part I: Standard Fetal Surveillance in Labour 1. Women in active labour should receive continuous close support from an appropriately trained professional. One-to-one nursing is recommended. (I-A)2. Intermittent auscultation following an established protocol of surveillance and response (Figure 1) is the preferred method of fetal surveillance in healthy pregnancies in the active phase of labour. (I-A). 3. Labour induction requires close monitoring of uterine activity and fetal heart rate. (III-B). 4. In the presence of abnormal fetal heart rate characteristics detected by intermittent auscultation and unresponsive to resuscitative measures, increased surveillance by continuous electronic fetal monitoring or fetal scalp sampling or delivery should be instituted. (I-A). 5. Continuous intrapartum electronic fetal monitoring is recommended: a) for pregnancies where there is an increased risk of perinatal death, cerebral palsy, or neonatal encephalopathy (III-C) b) when oxytocin is being used for augmentation of labour (1-A) c) when oxytocin is being used for induction of labour (III-C). 6. With respect to continuous electronic fetal monitoring, all professionals must be familiar with the paper speed used in each case to avoid misinterpretation. The correct time should be recorded on the electronic fetal monitoring record. (III-C). 7. Electronic fetal monitoring records should be inspected and documented every 15 minutes in the active phase of labour and at least every 5 minutes in the second stage of labour. (III-C). 8. The timing of electronic fetal monitoring patterns should be determined in association with uterine contractions. The contraction frequency, duration, intensity, and resting tone should be assessed and documented. Abdominal palpation, a tocodynamometer, or an intrauterine pressure catheter may be used to facilitate the assessment. (III-C). 9. Practitioners should use standard terminology when describing fetal heart rate characteristics of an electronic fetal monitoring record. (III-C)10. Fetal scalp blood sampling is recommended in association with electronic fetal monitoring patterns that are uninterpretable or non-reassuring, such as sustained minimal or absent variability, uncorrectable late decelerations, increasing fetal tachycardia, and abnormal FHR characteristics on auscultation. (II-3B). 11. The limited knowledge available on the use of labour admission tests warrants further research to establish the usefulness of this screening approach. (III-C)Part II: New Technologies for Fetal Surveillance in Labour. 12. The use of computer-based algorithms alone to interpret fetal heart rate patterns is not recommended as a standard of care at the present time. (III-D). 13. Fetal pulse oximetry as an adjunct to electronic fetal heart monitoring in patients with non-reassuring FHR status is not recommended as a standard of care at the present time. (III-D)14. ST waveform analysis technology is under development but is not recommended as a standard of care at this time. (III-C)15. Near-infrared spectroscopy as an adjunct to electronic fetal monitoring is currently not recommended as there is insufficient evidence to assess its efficacy in fetal surveillance. (III-D)16. Further study of fetal pulse oximetry, ST waveform analysis, and near-infrared technology in clinical research settings is encouraged. (III-B)VALIDATION: This guideline was reviewed by the SOGC Clinical Practice Obstetrics Committee, Maternal Fetal Medicine Committee, and ALARM Committee, as well as by the Canadian Medical Protective Association.

SPONSOR

The Society of Obstetricians and Gynaecologists of Canada.

Intrapartum fetal monitoring: past, present, and future

The concept of intrapartum "monitoring" of the fetal heart rate by auscultation has been extant for almost 200 years and by electronic means for more than 30 years. This article explores historical aspects of fetal monitoring, the advent of electronic fetal monitoring and its controversies, and present and future research opportunities to enhance the reliability, validity, and efficacy of fetal monitoring.

Near-infrared spectroscopy for fetal assessment during labour

BACKGROUND

Over the past four decades, continuous electronic fetal monitoring (EFM) has been increasingly employed to detect fetal acidemia in labor, with a view toward prevention of hypoxic ischemic encephalopathy, permanent neurologic injury, and death. Although very sensitive, this technology has low specificity, and a high false positive rate. This false positive rate has resulted in operative intervention on behalf of many fetuses who were not in fact in danger of neurologic injury or death. Near-infrared spectroscopy has been developed to directly measure fetal cerebral oxygenation, with a view toward identification of those fetuses truly at risk.

OBJECTIVES

To determine the effects of the use of near-infrared spectroscopy (NIRS) to assess fetal condition during labour, on maternal and perinatal outcomes.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group trials register and the Cochrane Controlled Trials Register. Date of last search: November 1999.

SELECTION CRITERIA

Randomized trials comparing near-infrared spectroscopy with continuous EFM alone or continuous EFM and scalp pH.

DATA COLLECTION AND ANALYSIS

Eligibility and trial quality were assessed by one reviewer.

MAIN RESULTS

No randomized trials were identified. Thus no studies were included.

REVIEWER'S CONCLUSIONS

There is currently insufficient evidence to assess the efficacy of fetal surveillance by near-infrared spectroscopy.

Doppler ultrasonographic evidence of intrapartum brain-sparing effect in fetuses with low oxygen saturation according to pulse oximetry

OBJECTIVE

This study was undertaken to verify by means of Doppler ultrasonography and simultaneous fetal pulse oximetry the redistribution of fetal blood flow in favor of the brain during intrapartum hypoxemia.

STUDY DESIGN

During labor 11 term fetuses with abnormal heart rate patterns and arterial oxygen saturation <30% and 14 control term fetuses with normal oxygen saturation were simultaneously monitored by pulse oximetry and Doppler ultrasonography. The results were compared with the Student t test.

RESULTS

The blood flow velocity in the middle cerebral artery was significantly higher in the presence of reduced oxygen saturation, implying lower pulsatility and resistance indices (P <.001). The reduction of blood flow in the umbilical artery was not significant (P =.61).

CONCLUSION

Simultaneous intrapartum pulse oximetry and Doppler ultrasonography proved that reduced arterial oxygen saturation (<30%) is associated with profound changes in fetal hemodynamics and could be tolerated for only a limited period, which should be the subject of further studies.

Fetal pulse oximetry

Within the last ten years several groups adapted pulse oximetry to be used in the fetus. The obvious advantage of this technology is the fact that a biochemical parameter--the arterial oxygen saturation--can be measured continuously during delivery. Nevertheless, the continuous information about the fetal oxygenation during delivery has a couple of obstacles to surmount. It is well known that fetal reflectance pulse oximetry may be influenced by a number of artifacts. In addition, severe physiological considerations should remind us of the limited diagnostic value of saturation monitoring alone in order to predict fetal acidosis. Some recent articles deal with the predictive value of fetal pulse oximetry for fetal compromise. While it appears that the fetal wellbeing is more likely to be in accordance with a normal saturation measured by current pulse oximetry systems, the number of fetuses detected by pulse oximetry suffering from hypoxia seems to be low. Different authors describe a poor sensitivity to predict fetal compromise. One reason therefore may be the reduced precision of the oxysensor in the low saturation range. Therefore, we conclude that the current generation of fetal pulse oximetry sensors is not improving the quality of combined fetal monitoring of fetal heart rate and fetal scalp blood analysis.

Intrapartum reflectance pulse oximetry: effects of sensor location and fixation duration on oxygen saturation readings

OBJECTIVE

To determine the effects of sensor location and suction fixation duration on measurements of intrapartum fetal oxygen saturation (SpO2) with a new reflectance pulse oximetry system.

DESIGN

Fetal SpO2 values (n = 18) were determined in the first stage of labor before and after moving the sensor to another part of the fetal head.

RESULTS

Mean fetal SpO2 values did not differ with sensor location (95% CI: -3.59 to 1.48). The duration of measurement period 1, before moving the sensor, was 104 +/- 44 (range 30-240) min. No time-dependent changes in SpO2 values were seen (r = 0.17).

CONCLUSION

Suction is an effective and noninvasive method of securing the reflectance pulse oximetry sensor to the fetal head in the first stage of labor and does not interfere with reproducible SpO2 values over several hours.