Scalp blood lactate for intra-partum assessment of fetal metabolic acidosis

Proposed cutoff for fetal scalp blood lactate in intrapartum fetal surveillance based on neonatal outcomes: a large prospective observational study

OBJECTIVE

Determination of lactate in fetal scalp blood (FBS) during labour has been recognised since the 1970s. The internationally accepted cutoff of >4.8 mmol/l indicating fetal acidosis is exclusive for the point-of-care device (POC) LactatePro™, which is no longer in production. The aim of this study was to establish a new cutoff for scalp lactate based on neonatal outcomes with the use of the StatstripLactate^® /StatstripXpress^® Lactate system, the only POC designed for hospital use.

DESIGN

Observational study.

SETTING

January 2016 to March 2020 labouring women with indication for FBS were prospectively included from seven Swedish and one Australian delivery unit.

POPULATION

Inclusion criteria: singleton pregnancy, vertex presentation, ≥35⁺⁰  weeks of gestation.

METHOD

Based on the optimal correlation between FBS lactate and cord pH/lactate, only cases with ≤25 minutes from FBS to delivery were included in the final calculations.

MAIN OUTCOME MEASURES

Metabolic acidosis in cord blood defined as pH <7.05 plus BD_ecf >10 mmol/l and/or lactate >10 mmol/l.

RESULTS

A total of 3334 women were enrolled of whom 799 were delivered within 25 minutes. The areas under the receiver operating characteristics curves (AUC) and corresponding optimal cutoff values were as follows; metabolic acidosis AUC 0.87 (95% CI 0.77-0.97), cutoff 5.7 mmol/l; pH <7.0 AUC 0.83 (95% CI 0.68-0.97), cutoff 4.6 mmol/l; pH <7.05 plus BD_ecf ≥12 mmol/l AUC 0.97 (95% CI 0.92-1), cutoff 5.8 mmol/l; Apgar score <7 at 5 minutes AUC 0.74 (95% CI 0.63-0.86), cutoff 5.2 mmol/l; and pH <7.10 plus composite neonatal outcome AUC 0.76 (95% CI 0.67-0.85), cutoff 4.8 mmol/l.

CONCLUSION

A scalp lactate level <5.2 mmol/l using the StatstripLactate^® /StatstripXpress^® system will safely rule out fetal metabolic acidosis.

TWEETABLE ABSTRACT

Scalp blood lactate <5.2 mmol/l using the StatstripLactate^® /StatstripXpress system has an excellent ability to rule out fetal acidosis.

Calcium and lactate in the fetal-to-neonatal transition

OBJECTIVE

To explore the relationship between calcium and lactate in arterial cord blood of healthy term neonates in response to the stress of labor.

METHODS

This was a prospective cohort study of consecutive, vaginal, term births in a community medical center (April 2029 to February 2020). Calcium and lactate were measured in cord blood gas analysis immediately after delivery.

RESULTS

In the arterial cord blood of 480 neonates, calcium levels were 1.5 (1.4; 1.5) mmol/L and lactate levels were 3.8 (2.9; 4.9) mmol/L. Calcium and lactate showed a statistically significant positive correlation (Pearson's correlation, r = 0.15, p = .001). Calcium levels had a significant positive correlation with PaCO₂ and a significant negative correlation with pH, PaO₂, HCO₃^-, and ABE levels. Multivariable analysis models confirmed that calcium levels were associated with HCO₃^-, gestational age, and birth weight, all accounting for 7% of the variability.

CONCLUSION

In healthy term vaginally delivered neonates, it was found that calcium and lactate were strongly correlated, together pointing to a neonatal response to the stress of labor and delivery. Cord blood calcium regulation may have an ancillary role in defining neonatal adaptation to extrauterine life.

Unusual Circumstances and Additional Procedures for Fetal Evaluation in Labor

This chapter describes several circumstances in which the interpretation of the intrapartum fetal heart rate pattern falls outside the usual frame of reference. This includes a more extensive discussion of causes of tachycardia and bradycardia. Ways in which a fetal dysrhythmia may manifest itself in the context of heart rate monitoring are described. Finally, the chapter reviews technological innovations designed to clarify the fetal status when compromise is suspected from the fetal heart rate pattern.

Fetal lactate levels align with the stage of labour

AIM

To evaluate the association between lactate concentrations in fetal blood samples and the different advanced labour stages.

METHODS

Eighteen-month prospective population-based clinical study of 187 singleton pregnant women in labour who were monitored by fetal blood sampling (FBS) because of non-reassuring intrapartum CTG results at Kuopio University Hospital, Finland. Peripheral lactate concentration and pH were analysed at different stages of labour and in umbilical arterial samples immediately after delivery.

RESULTS

FBS samples (N = 350) were obtained from 5.4 % of all women in labour during the study period, and 48 % had spontaneous delivery, 27 % had vacuum-assisted vaginal delivery, and 25 % had nonelective Caesarean delivery. FBS lactate levels increased 4-11% with every 1-2 cm of cervical dilation and 18 % from early labour to fully dilated cervix. In 42 women with at least two FBSs, lactate levels increased significantly from the early I stage of labour and up to a fully dilated cervix. Lactate values were significantly higher in umbilical arterial samples compared to FBSs. Sensitivity of the highest FBS lactate values for the detection of birth asphyxia were considerably low varying between 42.9-57.1%.

CONCLUSION

FBS lactate levels were related to the stage of labour during vaginal delivery attempt. Wide range of lactate levels during labour complicates its use as a predictor of birth asphyxia.

Maternal arterial blood gas values during delivery: Effect of mode of delivery, maternal characteristics, obstetric interventions and correlation to fetal umbilical cord blood

INTRODUCTION

Obstetricians routinely use biochemical parameters from non-pregnant women to assess the condition of the laboring mother. However, it is well known that pregnancy leads to significant physiological changes in most organ systems. The aim of this study was to determine normal values for maternal arterial blood gases during vaginal deliveries as compared with control values from planned cesarean sections. We also wanted to elucidate the effect of various maternal characteristics, mode of delivery and obstetric interventions on blood gas values.

MATERIAL AND METHODS

We carried out a randomly selected, prospective-observational cohort study of 250 women undergoing vaginal delivery and 58 women undergoing planned cesarean section at the Department of Obstetrics and Gynecology, Skåne University Hospital, Malmö, Sweden.

RESULTS

We found significant differences for gestational age, parity, umbilical venous blood pH, pCO₂ and lactate values between the two study groups (P < .005). Significantly lower pH, pCO₂ , pO₂ and sO₂ were found in mothers delivering vaginally. Higher base deficit, hemoglobin, bilirubin, potassium, glucose and lactate were found in vaginal deliveries than in planned cesarean sections (P < .02). Maternal body mass index (BMI), smoking and hypertension were not significantly correlated to acid base parameters in women with vaginal deliveries. On the other hand, multiple regression showed significant associations for the use of epidural anesthesia on maternal pH (P < .05) and pO₂ (P < .01); and synthetic oxytocin on pCO₂ (P = .08), glucose (P < .00) and lactate (P < .02) levels in maternal arterial blood. Maternal arterial pH, pCO₂ and lactate values correlated significantly to values in venous umbilical cord blood (P < .000).

CONCLUSIONS

Maternal arterial blood gas parameters varied significantly according to mode of delivery, the use of epidural anesthesia and synthetic oxytocin.

Evaluating the value of intrapartum fetal scalp blood sampling to predict adverse neonatal outcomes: A UK multicentre observational study

OBJECTIVE

To evaluate the value of fetal scalp blood sampling (FBS) as an adjunct test to cardiotocography, to predict adverse neonatal outcomes.

STUDY DESIGN

A multicentre service evaluation observational study in forty-four maternity units in the UK. We collected data retrospectively on pregnant women with singleton pregnancy who received FBS in labour using a standardised data collection tool. The primary outcome was prediction of neonatal acidaemia diagnosed as umbilical cord arterial pH < 7.05, the secondary outcomes were the prediction of Apgar scores<7 at 1st and 5th minutes and admission to the neonatal intensive care unit (NICU). We evaluated the correlation between the last FBS blood gas before birth and the umbilical cord blood and adjusted for time intervals. We constructed 2 × 2 tables to calculate the sensitivity, specificity, positive (PPV) and negative predictive value (NPV) and generated receiver operating curves to report on the Area Under the Curve (AUC).

RESULTS

In total, 1422 samples were included in the analysis; pH values showed no correlation (r = 0.001, p = 0.9) in samples obtained within an hour (n = 314), or within half an hour from birth (n = 115) (r=-0.003, p = 0.9). A suboptimal FBS pH value (<7.25) had a poor sensitivity (22%) and PPV (4.9%) to predict neonatal acidaemia with high specificity (87.3%) and NPV (97.4%). Similar performance was noted to predict Apgar scores <7 at 1st (sensitivity 14.5%, specificity 87.5%, PPV 23.4%, NPV 79.6%) and 5th minute (sensitivity 20.3%, specificity 87.4%, PPV 7.6%, NPV 95.6%), and admission to NICU (sensitivity 20.3%, specificity 87.5%, PPV 13.3%, NPV 92.1%). The AUC for FBS pH to predict neonatal acidaemia was 0.59 (95%CI 0.59-0.68, p = 0.3) with similar performance to predict Apgar scores<7 at 1st minute (AUC 0.55, 95%CI 0.51-0.59, p = 0.004), 5th minute (AUC 0.55, 95%CI 0.48-0.62, p = 0.13), and admission to NICU (AUC 0.58, 95%CI 0.52-0.64, p = 0.002). Forty-one neonates had acidaemia (2.8%, 41/1422) at birth. There was no significant correlation in pH values between the FBS and the umbilical cord blood in this subgroup adjusted for sampling time intervals (r = 0.03, p = 0.83).

CONCLUSIONS

As an adjunct tool to cardiotocography, FBS offered limited value to predict neonatal acidaemia, low Apgar Scores and admission to NICU.

Fetal heart rate short term variation during labor in relation to scalp blood lactate concentration

INTRODUCTION

Fetal heart rate short term variation (STV) decreases with severe chronic hypoxia in the antenatal period. However, only limited research has been done on STV during labor. We have tested a novel algorithm for a valid baseline estimation and calculated STV. To explore the value of STV during labor, we compared STV with fetal scalp blood (FBS) lactate concentration, an early marker in the hypoxic process.

MATERIAL AND METHODS

Software was developed which estimates baseline frequency using a novel algorithm and thereby calculates STV according to Dawes and Redman in up to four 30-minute blocks prior to each FBS. Cardiotocography traces from 1070 women in labor who had had FBS performed on 2134 occasions were analyzed.

RESULTS

In acidemic cases (lactate >4.8 mmol/L; Lactate Pro™), median STV 30 minutes prior to FBS was 7.10 milliseconds compared with 6.09 milliseconds in the preacidemic (4.2-4.8 mmol/L) and 5.23 milliseconds in the normal (<4.2 mmol/L) groups (P < .05). There was a positive correlation between lactate and STV (rho = 0.16-0.24; P < .05). Median lactate concentration in cases with STV <3.0 milliseconds (n = 160) was 2.3 mmol/L. When 2 FBS were performed within 60 minutes the change rate of lactate correlated to STV (rho = 0.33; P < .001). Cases with increasing lactate concentration had a median STV of 5.29 milliseconds vs 4.41 milliseconds in those with decreasing lactate (P < .001).

CONCLUSIONS

In the early stages of intrapartum hypoxia, STV increases, contrary to findings regarding chronic hypoxia in the antenatal period. The increase in the adrenergic surge is a likely explanation.

Infant outcome at four years of age after intrapartum sampling of scalp blood lactate for fetal assessment. A cohort study

OBJECTIVE

To correlate the value of lactate in fetal scalp blood at delivery and the outcomes of the offspring at four years of age.

METHODS

Cases where scalp blood lactate was taken within sixty minutes before delivery were identified from the randomized trial "Determination of pH or lactate in fetal scalp blood in management of intrapartum fetal distress". Data were grouped according to the generally accepted cutoffs for normality, pre-acidemia, acidemia and concentrations above mean +2 SD during the second stage. The outcome measures included gross-/fine motor function, vision, hearing, speaking and cognitive disorders, signs of central motor damage and referral to specialized pediatric services.

RESULTS

307 cases were available for final analyse. With normal scalp lactate concentration, the number of children with a diagnosed disorder was lower compared to the pre-acidemic/acidemic groups, although the findings were only significant for fine motor dysfunction (p = 0.036). Elevated lactate values were significantly associated with increased risk for a poorer capacity of attention and understanding of instructions (OR 1.37, 95% CI 1.07-1.74), and for fine motor dysfunction (OR 1.22, 95% CI 1.00-1.49) at the age of four.

CONCLUSION

Higher levels of lactate in fetal scalp blood seems to be associated with increased risk of an aberrant developmental outcome at four years of age in some areas.

Understanding fetal physiology and second line monitoring during labor

Cardiotocography (CTG) is a technique used to monitor intrapartum fetal condition and is one of the most common obstetric procedures. Second line methods of fetal monitoring have been developed in an attempt to reduce unnecessary interventions due to continuous cardiotocography and to better identify fetuses at risk of intrapartum asphyxia. The acid-base balance of the fetus is evaluated by fetal blood scalp samples, the modification of the myocardial oxygenation by the fetal ECG ST-segment analysis (STAN) and the autonomic nervous system by the power spectral analysis of the fetal heart variability. To correctly interpret the features observed on CTG traces or second line methods, it seems important to understand normal physiology during labor and the compensatory mechanisms of the fetus in case of hypoxemia. Therefore, the aim of this review is first to describe fetal physiology during labor and then to explain the modification of the second line monitoring during labor.

Fetal scalp blood lactate during second stage of labor: determination of reference values and impact of obstetrical interventions

OBJECTIVE

To determine the reference interval of fetal scalp blood lactate during second stage of labor.

MATERIAL

Two hundred and fifty-three women in first stage of labor with a reassuring CTG were asked for permission to sample fetal scalp blood during second stage.

RESULTS

In cases with reassuring CTG and five minute Apgar score ≥9, the mean lactate value (±2 SD) was 2.5 mmol/L (lower limit 1.1, higher limit 5.2). The lactate concentration was significantly higher among nulliparous and in cases with use of epidural or oxytocin (p <0.001). There was a moderate positive correlation between scalp lactate values and active pushing time. When parity, epidural, oxytocin and active pushing time were analyzed together, they had equal influence on lactate values (p <0.001). Higher lactate values were associated with intermediate/pathological CTG compared to normal CTG (p <0.001). There was no correlation to gestational age or birthweight (p = 0.72, respectively 0.43).

CONCLUSIONS

The reference interval of fetal scalp lactate during second stage is 1.1-5.2 mmol/L. Parity, use of epidural or oxytocin and the duration of pushing are associated to increased lactate concentration; however, we could not demonstrate any correlation to advancing gestational age or birthweight.

Lactate point-of-care testing for acidosis: Cross-comparison of two devices with routine laboratory results

Objectives

Lactate is a major parameter in medical decision making. During labor, it is an indicator for fetal acidosis and immediate intervention. In the Emergency Department (ED), rapid analysis of lactate/blood gas is crucial for optimal patient care. Our objectives were to cross-compare-for the first time-two point-of-care testing (POCT) lactate devices with routine laboratory results using novel tight precision targets and evaluate different lactate cut-off concentrations to predict metabolic acidosis.

Design and methods

Blood samples from the delivery room (n=66) and from the ED (n=85) were analyzed on two POCT devices, the StatStrip-Lactate (Nova Biomedical) and the iSTAT-1 (CG4+ cassettes, Abbott), and compared to the routine laboratory analyzer (ABL-735, Radiometer). Lactate concentrations were cross-compared between these analyzers.

Results

The StatStrip correlated well with the ABL-735 (R=0.9737) and with the iSTAT-1 (R=0.9774) for lactate in umbilical cord blood. Lactate concentrations in ED samples measured on the iSTAT-1 and ABL-735 showed a correlation coefficient of R=0.9953. Analytical imprecision was excellent for lactate and pH, while for pO₂ and pCO₂ the coefficient of variation was relatively high using the iSTAT-1.

Conclusion

Both POCT devices showed adequate analytical performance to measure lactate. The StatStrip can indicate metabolic acidosis in 1 μl blood and will be implemented at the delivery room.

Newborn outcomes in british columbia after caesarean section for non-reassuring fetal status

OBJECTIVE

To assess the incidence in British Columbia of severe morbidity in neonates delivered by Caesarean section for non-reassuring fetal status, and to examine the accuracy of Apgar score and umbilical cord gas values in predicting severe neonatal morbidity.

METHODS

We assessed rates of hypoxic ischemic encephalopathy, NICU admission, and ventilator days, individually and as a composite outcome with neonatal death, among a total of 8466 term singletons delivered by Caesarean section for non-reassuring fetal status between January 1, 2007, and December 31, 2011. We calculated the predictive accuracy of Apgar scores and umbilical cord blood gas values using the area under the receiver operating characteristic (ROC) curve and the sensitivity and specificity for each outcome.

RESULTS

The incidence of Apgar score at one minute < 4 was 8.0%, and for Apgar score at five minutes < 4 it was 0.6%. The incidence of umbilical cord pH < 7.10 was 6.5%, and for base-excess < -12 it was 2.9%. Apgar score at one minute < 7 had the greatest predictive accuracy for the composite outcome (81% for both sensitivity and specificity). The area under the ROC curve for Apgar score at one minute and at five minutes, umbilical cord pH, and base-excess was 0.87, 0.86, 0.76, and 0.78, respectively.

CONCLUSION

The incidence of abnormal Apgar score and abnormal umbilical cord gas values is very low among neonates in British Columbia delivered by Caesarean section for non-reassuring fetal status. Apgar score at one minute < 7 is a good predictor of severe neonatal morbidity. Electronic fetal monitoring remains a non-specific method for detection of fetal compromise in the intrapartum period.

Cardiotocography patterns and risk of intrapartum fetal acidemia

AIM

To identify cardiotocography (CTG) patterns associated with increased risk of intrapartum fetal acidemia.

METHODS

A prospective observational cohort study of 1070 women with fetal scalp blood sampling (FBS) during labor was conducted at Karolinska University Hospital, Stockholm, Sweden. Women with a nonreassuring CTG pattern underwent FBS, and lactate concentration was measured at the bedside. Lactate concentrations >4.8 mmol/L were defined as fetal acidemia. A senior obstetrician, blinded to the lactate concentration at FBS, visually interpreted the CTG tracings that had prompted FBS.

RESULTS

There were 2134 FBSs performed on 1070 laboring women, constituting 11% of all deliveries at this labor ward. The CTG patterns with the highest frequency of lactacidemia at FBS were late or severe variable decelerations combined with tachycardia (20%-25% at first FBS and 33%-49% at last FBS). With a normal baseline fetal heart rate, normal variability, and absence of serious decelerations, the fetal scalp blood lactate concentration at the first FBS was normal in 97.5% of cases. The group with isolated reduced variability had no increased prevalence of acidemia and median lactate concentration did not differ from the normal group.

CONCLUSION

Isolated reduced variability is in most cases not a sign of hypoxia. If development of hypoxia is ruled out with one FBS, this pattern does not require monitoring with repetitive FBSs throughout labor. Late decelerations and severe variable decelerations increase the risk for intrapartum fetal metabolic acidemia to the same extent. The combination of these decelerations and tachycardia was associated with the highest rate of fetal metabolic acidemia.

Lactate versus pH levels in fetal scalp blood during labor--using the Lactate Scout System

OBJECTIVE

To assess if lactate measured with the Scout Lactate System is a reliable alternative to pH in intrapartum monitoring of the fetus.

METHODS

A prospective study analyzing (1) the correlation between scalp lactate measured by the Scout Lactate System and the Automatic Blood Laboratory (ABL), (2) the correlation between lactate and pH measured in scalp blood and (3) the correlation between fetal scalp lactate and umbilical cord SBE. The sensitivity/specificity and positive/negative predictive values of lactate in predicting low pH were analyzed and expressed as Receiver Operating Curves (ROC).

RESULTS

Lactate measured by the Scout Lactate System and the ABL correlated well (r(2)=0.85). Both lactate and pH were measured in 1009 scalp blood samples. The sensitivity and specificity of lactate ≥ 4.8 mmol/l in predicting a pH <7.20 were 0.63 and 0.85, respectively. The correlation between scalp lactate measured within 15 min prior to delivery and the umbilical cord SBE was low.

CONCLUSION

Monitoring non-reassuring deliveries with scalp lactate instead of pH would have resulted in more (155 instead of 56) instrumental deliveries with no decrease in newborns with severe metabolic acidosis.

Expert review--identification of intra-partum fetal compromise

Whilst most cases of cerebral palsy occur as a consequence of an ante-natal insult, a significant proportion, particularly in the term fetus, are attributable to intra-partum hypoxia. Intra-partum monitoring using continuous fetal heart rate assessment has led to an increased incidence of operative delivery without a concurrent reduction in the incidence of cerebral palsy. Despite this, birth asphyxia remains the strongest and most consistent risk factor for cerebral palsy in term infants. This review evaluates current intra-partum monitoring techniques as well as alternative approaches aimed at better identification of the fetus at risk of compromise in labour.

Validation of a point-of-care (POC) lactate testing device for fetal scalp blood sampling during labor: clinical considerations, practicalities and realities

BACKGROUND

Although fetal blood sampling for pH is well established the use of lactate has not been widely adopted. This study validated the performance and utility of a handheld point-of-care (POC) lactate device in comparison with the lactate and pH values obtained by the ABL 800 blood gas analyzer.

METHODS

The clinical performance and influences on accuracy and decision-making criteria were assessed with freshly taken fetal blood scalp samples (n=57) and umbilical cord samples (n=310). Bland-Altman plot was used for data plotting and analyzing the agreement between the two measurement devices and correlation coefficients (R²) were determined using Passing-Bablok regression analysis.

RESULTS

Sample processing errors were much lower in the testing device (22.8% vs. 0.5%). Following a preclinical assessment and calibration offset alignment (0.5 mmol/L) the test POC device showed good correlation with the reference method for lactate FBS (R²=0.977, p<0.0001, 95% CI 0.9 59-0.988), arterial cord blood (R²=0.976, p<0.0001, 95% CI 0.967-0.983) and venous cord blood (R²=0.977, p<0.0001, 95% CI 0.968-0.984).

CONCLUSIONS

A POC device which allows for a calibration adjustment to be made following preclinical testing can provide results that will correlate closely to an incumbent lactate method such as a blood gas analyzer. The use of a POC lactate device can address the impracticality and reality of pH sample collection and testing failures experienced in day to day clinical practice. For the StatStrip Lactate meter we suggest using a lactate cut-off of 5.1 mmol/L for predicting fetal acidosis (pH<7.20).

Comparing fetal scalp lactate and umbilical cord arterial blood gas values

BACKGROUND

Fetal scalp lactate has been shown to be as effective as scalp pH in predicting fetal outcomes. However, there is limited clinical evidence to demonstrate a strong correlation with fetal acidaemia at birth.

AIMS

To compare the diagnostic accuracy of fetal scalp lactate and umbilical cord arterial blood gas values sampling, as it is used in clinical practice.

METHODS

A retrospective cohort study was performed on 661 term (≥37 weeks) births where a fetal scalp lactate sample was taken during labour. Cases were excluded where either the lactate was taken greater than 1 h prior to delivery, incomplete cord gas analyses were available, or a sentinel hypoxic event occurred prior to delivery. The final data set included 229 microvolume scalp lactate measurements which were compared with neonatal paired cord blood gas values taken at delivery.

RESULTS

A fetal scalp lactate measurement of ≥4.8 mmol/L had a positive predictive value (PPV) of 1% and a negative predictive value (NPV) of 100% in predicting umbilical artery pH ≤7.00, and a PPV of 5% and a NPV of 98% in predicting umbilical artery pH ≤7.10. The sensitivity and specificity for these values were 100%, 23% and 90%, 23%, respectively.

CONCLUSIONS

Fetal scalp lactate microsampling has a strong negative predictive value for fetal acidaemia at birth.

Lactate biosensors: current status and outlook

Many research efforts over the last few decades have been devoted to sensing lactate as an important analytical target in clinical care, sport medicine, and food processing. Therefore, research in designing lactate sensors is no longer in its infancy and now is more directed toward viable sensors for direct applications. In this review, we provide an overview of the most immediate and relevant developments toward this end, and we discuss and assess common transduction approaches. Further, we critically describe the pros and cons of current commercial lactate sensors and envision how future sensing design may benefit from emerging new technologies.

Lactate study using umbilical cord blood: agreement between Lactate Pro hand-held devices with blood gas analyser and evaluation of lactate stability over time

BACKGROUND

Lactate measurements have become increasingly preferred over pH analysis in the evaluation of fetal acidaemia in labour. In a busy labour ward, often the umbilical cord may be sampled late and as a result yield unreliable lactate values.

AIM

To investigate the agreement of hand-held device Lactate Pro with a reference method blood gas analyser and evaluate the stability of umbilical cord lactate values over time.

METHODS

Prospective study carried out at elective caesarean section. Sixteen umbilical cords were double clamped immediately after delivery with paired arterial and venous blood samples collected by an independent researcher, at varying time intervals, and processed by two Lactate Pro devices and a reference method blood gas analyser.

RESULTS

A significant difference of -0.41 to 0.10 mmol/L was found when different groups of Lactate Pro devices were compared with blood gas analyser at lactate values up to 5.70 mmol/L, with average lactate value of 2.45 mmol/L. Over time, there is progressive rise in lactate samples obtained from the umbilical cord.

CONCLUSION

Lactate Pro devices have a significant difference, but when used in clinical practice on cord blood after delivery, this is unlikely to be meaningful. In intrapartum fetal surveillance, a systematic overestimation might lead to unnecessary intervention. It is possible to retrospectively predict the likely level of lactate at birth in delayed cord samples.

Intrapartum fetal asphyxia: study of umbilical cord blood lactate in relation to fetal heart rate patterns

PURPOSES

To correlate between umbilical artery cord blood lactate and acid-base status with intrapartum fetal heart rate monitoring, and to measure the reliability of umbilical cord blood lactate for prediction of early neonatal outcome.

METHODS

Sixty-six participants with intrapartum abnormal fetal heart rate monitoring and 60 participants with normal intrapartum recordings were recruited. The abnormal recordings included late onset, atypical variable and simple variable decelerations. After delivery, the arterial cord blood lactate, pH, actual base excess (ABE), and Apgar score were measured in all participants.

RESULTS

There was significant inverse correlation between cord lactate and pH and ABE in all participants (correlation coefficient = -0.7, p < 0.0001). The cord lactate was significantly higher in the late onset and atypical variable decelerations groups compared to control (p < 0.0001). There was no significant correlation between the Apgar score and blood lactate in all groups; however, the sensitivity and specificity of cord lactate to predict low score at 5 min were higher in comparison to cord pH.

CONCLUSIONS

Umbilical cord blood lactate is a reliable marker for intrapartum fetal asphyxia compared to cord acid-base status with better prediction for newborns with low Apgar score.

Lactate production as a response to intrapartum hypoxia in the growth-restricted fetus

OBJECTIVE

To analyse whether the increase in lactate in response to intrapartum hypoxia differs between small- (SGA), appropriate- (AGA) and large-for-gestational-age (LGA) fetuses.

DESIGN

Observational cohort study.

SETTING

Ten obstetric units in Sweden.

POPULATION

A cohort of 1496 women.

METHODS

A secondary analysis of a randomised controlled trial, in which 1496 women with fetal heart rate abnormalities, indicating fetal scalp blood sampling, were randomised to lactate analyses. After delivery, the neonates were divided according to birthweight for gestational age into SGA, AGA and LGA groups.

MAIN OUTCOME MEASURE

Lactate concentration in fetal scalp blood.

SECONDARY OUTCOME MEASURES

Acid-base balance in cord artery blood and Apgar score <7 at 5 minutes.

RESULTS

Median lactate concentrations in the SGA, AGA and LGA groups were 3.8, 3.0 and 2.2 mmol/l, respectively (SGA versus AGA, P = 0.017; LGA versus AGA, P = 0.009). In the subgroups with scalp lactate >4.8 mmol/l (lactacidaemia), the corresponding median (range) values were 6.2 (4.9-14.6), 5.9 (4.9-15.9) and 5.7 mmol/l (5.0-7.9 mmol/l), respectively (no significant differences between the groups). The proportions of neonates with cord artery pH < 7.00, metabolic acidaemia or Apgar score <7 at 5 minutes were similar in all weight groups.

CONCLUSION

SGA fetuses with fetal heart rate abnormalities have the same ability to produce lactate as a response to intrapartum hypoxia as AGA and LGA fetuses. The risk of a poor outcome associated with high lactate concentration is the same in SGA, AGA and LGA fetuses. Scalp blood lactate analysis is therefore a reliable method for intrapartum fetal surveillance of suspected growth-restricted fetuses scheduled for vaginal delivery at ≥ 34 weeks of gestation.

Comparison of two point-of-care testing (POCT) devices for fetal lactate during labor

BACKGROUND

Point-of-care testing (POCT) of fetal scalp blood lactate is used as an alternative for pH analysis. Lactate measurements have not been standardized and values vary with each device used. The aim of this study was to evaluate the performance of two POCT lactate meters for intrapartum use.

METHODS

Analytical performance of StatStrip Lactate (Nova Biomedical) and Lactate Pro (Arkray) was evaluated using CLSI EP10. Both POCT meters were compared with our lactate reference method (RapidLab 860; Siemens Healthcare Diagnostics) using fetal scalp and neonatal cord blood. Deming regression analysis was performed.

RESULTS

StatStrip Lactate coefficients of variation (CVs) were 5.1%, 5.0% and 2.6% at 0.9, 7.5 and 14.1 mmol/L lactate, respectively. CVs for Lactate Pro were 10.7%, 5.2% and 5.7% at 1.7, 4.1 and 6.4 mmol/L lactate, respectively. Consecutive lactate measurements in 37 fetal scalp and 122 cord blood samples revealed different test characteristics for the two POCT devices. In fetal scalp blood: StatStrip Lactate=1.13*RapidLab-0.39 (R(2)=0.907) and Lactate Pro=0.95*RapidLab-0.03 (R(2)=0.823). In cord artery blood: StatStrip Lactate=1.08*RapidLab-0.09 (R(2)=0.810) and Lactate Pro=0.72*RapidLab+0.59 (R(2)=0.807).

CONCLUSIONS

Overall performance of both Lactate Pro and StatStrip Lactate was good, with StatStrip Lactate having smallest CVs and closest correlation to our reference method. Both StatStrip Lactate and Lactate Pro can be used as a lactate POCT device for obstetric use.