Accuracy of intrapartum fetal blood gas analysis by scalp sampling: A retrospective cohort study

Fetal blood gas analysis (FBGA) using scalp blood is commonly used to identify serious fetal distress. However, there is a lack of data regarding its accuracy and reliability. The aim of this study was to determine the positive predictive value (PPV) and negative predictive value (NPV) of FBGA for predicting postpartum acidosis in case of nonreassuring fetal heart rate tracings (NRFHRT). To this end, we conducted a retrospective cohort study of singleton term deliveries with NRFHRT according to Fédération Internationale de Gynécologie et d'Obstétrique and Fisher cardiotocography scores undergoing FBGA in a university hospital. The PPV and NPV of FBGA regarding neonatal acidosis (defined as a pH value ≤ 7.15 in arterial or venous umbilical cord blood) and Apgar scores indicating neonatal depression (defined as a 5-min Apgar score ≤5) were evaluated. Multivariate analysis was used to determine the influence of cardiotocography variations and the time delay between FBGA and delivery on the accuracy of FBGA. We analyzed 343 deliveries with NRFHRT. In 32 (9%) of these cases, fetal acidosis was confirmed by a postpartum umbilical cord blood pH value ≤ 7.15. In 308/343 (90%) cases, FBGA identified NRFHRT as false positive (as confirmed by nonacidotic postpartum pH values) and thus avoided unnecessary interventions such as operative delivery. The overall test accuracy of FBGA was 91%. FBGA accurately predicted postpartum cord blood pH values with a margin of ±0.2 in 319/343 (93%) cases. On the other hand, the false negative rate of FBGA was 8% (29/343). The PPV and NPV of FBGA for predicting postpartum acidosis were 50% and 91%, respectively. The sensitivity was 9% and the specificity was 99%. In a multivariate logistic regression analysis, maternal body mass index (odds ratio [OR] 1.1; 95% confidence interval [CI] 1.01-1.17; P = .029) and cardiotocography variations (OR 0.80; 95% CI 0.66-0.98; P = .029) independently affected the predictive value of FBGA. The PPV of FBGA regarding neonatal depression according to Apgar scores was low with only 17%. We conclude that FBGA may be used in clinical practice to rule out, but not to rule in, neonatal acidosis in parturients with NRFHRT. It can avoid unnecessary interventions such as cesarean section or operative vaginal delivery in up to 90% of cases, but cannot reliably detect fetal acidosis.

Fetal sheep left ventricle is more sensitive than right ventricle to progressively worsening hypoxemia and acidemia

OBJECTIVE

In a sheep model we tested the hypothesis that the fetal left ventricle is less tolerant to worsening acidemia than the right ventricle.

STUDY DESIGN

At 106-124/145 days of gestation, 12 fetuses were instrumented. After a 4-day recovery, placental vascular resistance was increased by fetal angiotensin (AT) II infusion. After a 2h ATII infusion, to further deteriorate fetal oxygenation, maternal hypoxemia was induced. Fetal cardiac function and hemodynamics were assessed by tissue Doppler imaging (TDI) and pulsed Doppler imaging. Ultrasonography was performed at baseline, at 1 and 2h after the beginning of ATII infusion and during the ATII+hypoxemia phase.

RESULTS

Fetal pH and pO₂ decreased significantly and progressively during the experiment. Left ventricular TDI-derived isovolumic relaxation velocity (IVRV) was lower during ATII 2h and ATII+hypoxemia phases than at baseline. The IVRV deceleration was significantly less during the ATII+hypoxemia phase than at baseline. Right ventricular IVRV was significantly lower during the ATII+hypoxemia phase than at baseline. IVRV deceleration did not change. Only left ventricular IVRV deceleration correlated with fetal pO₂ (R=0.36, p<0.05). Fetal right and left ventricular cardiac outputs, as well as umbilical artery, aortic isthmus and ductus venosus pulsatility indices remained unchanged during the experiment.

CONCLUSION

Our results show that signs of cardiac dysfunction develop earlier in the left ventricle than in the right ventricle. The fetal left ventricle seems to be more sensitive to progressively worsening hypoxemia and acidemia than the right ventricle.

Monitoring fetal electrocortical activity during labour for predicting worsening acidemia: a prospective study in the ovine fetus near term

Background

Severe fetal acidemia during labour with arterial pH below 7.00 is associated with increased risk of hypoxic-ischemic brain injury. Electronic fetal heart rate (FHR) monitoring, the mainstay of intrapartum surveillance, has poor specificity for detecting fetal acidemia. We studied brain electrical activity measured with electrocorticogram (ECOG) in the near term ovine fetus subjected to repetitive umbilical cord occlusions (UCO) inducing FHR decelerations, as might be seen in human labour, to delineate the time-course for ECOG changes with worsening acidemia and thereby assess the potential clinical utility of fetal ECOG.

Methodology/Principal Findings

Ten chronically catheterized fetal sheep were studied through a series of mild, moderate and severe UCO until the arterial pH was below 7.00. At a pH of 7.24±0.04, 52±13 min prior to the pH dropping <7.00, spectral edge frequency (SEF) increased to 23±2 Hz from 3±1 Hz during each FHR deceleration (p<0.001) and was correlated to decreases in FHR and in fetal arterial blood pressure during each FHR deceleration (p<0.001).

Conclusions/Significance

The UCO-related changes in ECOG occurred in advance of the pH decreasing below 7.00. These ECOG changes may be a protective mechanism suppressing non-essential energy needs when oxygen supply to the fetal brain is decreased acutely. By detecting such “adaptive brain shutdown,” the need for delivery in high risk pregnant patients may be more accurately predicted than with FHR monitoring alone. Therefore, monitoring fetal electroencephalogram (EEG, the human equivalent of ECOG) during human labour may be a useful adjunct to FHR monitoring.

Predictors of outcome at 2 years of age after early intrauterine growth restriction

OBJECTIVE

To examine the relative importance of antenatal and perinatal variables on short- and long-term outcome of preterm growth restricted fetuses with umbilical artery (UA) Doppler abnormalities.

METHODS

This was a cohort study of 180 neonates with birth weight < 10(th) percentile, gestational age at delivery < 34 weeks and abnormal Doppler ultrasound examination of the UA. Various antenatal and perinatal variables were studied in relation to short- and long-term outcome.

RESULTS

Neonatal and overall mortality (up to 2 years of age) were predicted by low gestational age at delivery. Neonatal mortality was additionally predicted by absent or reversed UA end-diastolic flow, while the presence of severe neonatal complications and placental villitis were additional predictors of both infant (between 28 days and 1 year of postnatal life) and overall mortality. Placental villitis was found to be the only predictor of necrotizing enterocolitis. Low gestational age at delivery, male sex, abnormal cardiotocography, absent or reversed UA end-diastolic flow and the HELLP syndrome predicted respiratory distress syndrome. Abnormal neurodevelopmental outcome at 2 years was predicted by low birth weight (< 2.3(rd) percentile), fetal acidosis (UA pH < 7.00), and placental villitis.

CONCLUSION

Less advanced gestation at delivery remains an important predictor of short-term outcome in growth-restricted fetuses. In addition, the presence of placental villitis may aid neonatologists in the early identification of infants at increased risk of necrotizing enterocolitis, death and abnormal neurodevelopment at 2 years of age. Abnormal neurodevelopment was related to low weight and acidosis at birth, indicating that the severity of malnutrition and fetal acidosis affect long-term outcome.

Linear and nonlinear fetal heart rate analysis of normal and acidemic fetuses in the minutes preceding delivery

Linear and nonlinear fetal heart rate (FHR) indices, namely mean FHR, interval index (II), very low, low and high frequencies, approximate (ApEn) and sample entropy (SampEn), were computed, immediately before delivery, in the initial and final FHR tracing segments, from 48 normal, 10 mildly acidemic and 10 moderate-to-severely acidemic fetuses. Progression of labor was associated with a significant increase in linear frequency domain indices whereas nonlinear indices were significantly decreased. Moderate-to-severe fetal acidemia was associated with a significant decrease in nonlinear indices. The best discrimination between moderate-to-severe acidemic fetuses and the remaining cases was obtained combining II and ApEn(2,0.15), with a specificity of 71% and a sensitivity of 80%. These findings support the hypothesis of increased autonomic nervous system activity in the final minutes of labor and of decreased central nervous system activity, both in the final minutes of labor and in moderate-to-severe acidemic fetuses.

Quantitative Kardiotokographie - wie sieht sie aus und was dürfen wir von ihr erwarten?

BACKGROUND

[corrected] Cardiotocography (CTG) seems to be a non-reliable, expensive but nevertheless practical method for fetal surveillance. Moreover, its diagnostic value is dependent on a long-standing experience of the obstetrician (midwife). It is difficult to define exact diagnostic criteria since nearly all CTG phenomena are lacking precise qualification by the naked eye. Therefore, the idea must be born in mind to analyze fetal heart frequency (FHF) by computer, first off-line then on-line, in order to evaluate its true diagnostic power objectively.

METHODS

The FHF of 583 deliveries terminated by the vaginal route were registered prospectively using a PC and an RS422 interface. In 443 cases acid-base measurements (ABL 500, RADIOMETER, Copenhagen) in blood of the umbilical artery (UA) and vein (UV) were available and plausible. In this study only the last 30 min ante-partum were analyzed. The program for FHF analysis was written in MATLAB (The Mathworks Inc., USA). A CTG score was developed using three components of FHF: basal FHF, the deceleration area of all dips, and the micro-fluctuation (MF) of the basal fetal heart rate (FHR). MF denotes the true number of "turning-points" per minute of basal FHR. For each component a maximum of 6 scoring points could be assigned according to empirical cut-off values. These cut-off values were determined using correlation analysis with acid-base parameters in UA blood, especially the actual pH. The accordance between score and pH values was further demonstrated by assignment of 0.036 pH-units to each of the 19 (18 + zero) scoring points, thus covering a pH range between 6.700 and 7.350 (UA). A resulting variable, delta pH (pH measured, UA-pH assigned) was studied and used for further analysis. In order to define criteria for fetal mortality in utero only cases with pH, UA between 7.250 and 7.350 were accepted.

RESULTS

Median basal FHF under normal conditions amounted to 138 bpm (mean: 137 +/- 14.9) in 4180 minutes of 372 fetuses. 120 bpm equals the 13.4(th) and 160 bpm the 94.6(th) centile of the distribution. Given fetal normacidity (UA) MF is 58/minute and the mean MF 57.9 +/- 13.4, respectively, with a 10 (th) centile of 41/minute. MF and basal FHF are correlated significantly (r = 0.410, P << 10(-4)). The declaration-area per fetus is significantly correlated with actual pH (UA), r = -0.473, P << 10(-4). the score itself is highly significantly correlated with actual pH (UA) (r = -0.559, P << 10(-4)) and the other parameters of fetal acid-base balance. Nevertheless, prediction variability for pH, especially in score = 1, 2 and zero (minimal CTG pathology) is still present: 80% of all predicted pH values lie in between -0.092 and + 0.071. It is strongly suggested that this score-related predictive pH variability is caused by maternal breathing habits during the last 30 minutes of delivery.

CONCLUSION

Adequate quantification of only three variables of FHR using a score leads to fairly good correlations with parameters of the fetal acid-base balance. Thus actual pH (UA) can be predicted in reasonable clinical limits. Still present variability in prediction of pH seems to be, in part, of maternal origin. The maternal influence could be eliminated by continuous (transcutaneous) monitoring of maternal pCO(2). Along these lines the quantitative electronic monitoring of FHR will be realized and instrumented (off-line and on-line) by nexus/gmt, Frankfurt, a.M., Germany.

Computerized cardiotocography in the management of intrauterine growth restriction associated with Doppler velocimetry alterations

OBJECTIVE

To verify the reliability of computerized cardiotocography (cCTG) in the prediction of the oxygen metabolism status of fetuses with growth restriction and Doppler velocimetry alterations.

METHODS

From 24 third-trimester cesarean section performed because of intrauterine growth restriction (IUGR) and Doppler velocimetry alterations, there were 11 cases of fetal heart rate alterations (Dawes-Redman criteria were not satisfied) and 13 cases of reactive cCTG. Fetal lung maturity was detected by amniocentesis and blood samples for umbilical blood gas analysis (UBGA) were collected before the first neonatal breath from the umbilical artery in a double-clamped segment of the cord.

RESULTS

Umbilical cord gas analysis showed arterial cord blood pH to be 7.20 or less in 11 newborns (45.8%), 7.10 or less in 6 (25%), and 7.00 or less in 3 (12.5%). Linear regression analysis showed short-term variation (STV) in the fetal heart rate to be significantly correlated with umbilical artery pH (r = 0.49; P = 0.01) and pCO2 (r = -0.50; P = 0.01). There were no significant correlations between cCTG and the other UBGA parameters considered. Receiver operator curves permitted to calculate the STV values at which pathological neonatal UBGA values can be expected (pH < 7.00 and pCO2 > 80 mmHg). A short-term variation less than 4.5 ms was found to predict acidemia with a sensitivity of 100% and a specificity of 70% (positive predictive value, 33%; negative predictive value, 100%), and hypercarbia with a sensitivity of 100% and a specificity of 77.8% (positive predictive value, 55.6%; negative predictive value, 100%).

CONCLUSION

In view of the results of this study, 4.5 ms for STV may be a threshold below which timing of delivery should be decided in cases of fetal growth restriction.

Die Zuverlässigkeit der fetalen Pulsoxymetrie bei der Detektion einer fetalen Azidose

Fetal pulse oximetry is a continuous method to exclude the lack of oxygen in cases of non-reassuring fetal heart rate. This study aims at the evaluation of the predictive value of this method concerning the development of fetal acidosis. 136 fetuses with non-reassuring heart rate were monitored by fetal pulse oximetry. In all cases fetal blood pH and base excess were determined repeatedly by fetal blood analysis (FBA). The pH value and base excess in the umbilical artery and scalp blood as well as the changes of pH and base excess were correlated to the duration of low, medium and high fetal oxygen saturation (FSpO (2)). Sensitivity, specificity, positive and negative predictive values were calculated for the assumption that "FSpO (2) < or = 30 % for at least 10 or 15 minutes" predicts a pH or base excess in the umbilical artery and in FBA of < 7.1/7.15/7.2 or < or = -4/8/12 mmol/L and a decline of pH (base excess) by more than 0.05 (0.1) pH units (4 mmol/L). A highly significant negative correlation was found between umbilical artery and FBA pH and base excess as well as the change of both and the duration of low oxygen saturation. Additionally the change of FBA pH depends on the duration of medium FSpO (2). A pH below 7.15 in FBA as well as base excess < or = -12 mmol/L were safely detected by a cut-off of "FSpO (2) < or = 30 % for at least 10 minutes" and pH < 7.1 and base excess < or = -12 mmol/l in FBA in 100 % and 75 %, respectively. A decline of pH by more than 0.1 pH units and of base excess by more than 4 mmol/L were excluded by a negative predictive value of 98 %. In conclusion, medium and progressive acidosis can be reliably excluded by fetal pulse oximetry.

Severe Variable Decelerations and Fetal Pulse Oximetry during the Second Stage of Labor

OBJECTIVES

The aim of the study was to investigate the usefulness of fetal pulse oximetry in cases of severe variable decelerations in the second stage of labor.

METHODS

It is a prospective study including 58 patients. Thirty-eight patients (group A) had a normal uncomplicated labor and 20 patients (group B) developed severe variable decelerations during the second stage of labor. All patients were primiparous with normal pregnancies and had electronic fetal monitoring of labor in conjunction with fetal pulse oximetry. An estimation of fetal pH and base deficit was performed at delivery in all patients.

RESULTS

There was no statistically significant difference in relation to maternal age and gestational age between the two groups. Group A patients did not delivered neonates with metabolic acidosis. Six out of 20 (group B) patients delivered neonates with a pH <7.10 despite a fetal pulse oximetry reading of >30%.

CONCLUSIONS

It appears that fetal pulse oximetry is not capable of detecting pre-acidotic or acidotic fetuses during the second stage of labor in patients with severe variable decelerations and the management of such patients should be supported by fetal scalp pH when indicated or otherwise the obstetrician should expedite delivery either with assisted operative delivery or cesarean section. Fetal heart rate monitoring was introduced into clinical practice over 30 years ago. It continues to be the predominant method of intrapartum fetal surveillance despite worries about its accuracy and efficacy.

CTG: Mikrofluktuation

OBJECTIVE

Microfluctuation (MF) of fetal heart rate (FHR) is regarded as the most sensitive parameter for diagnosing the condition of the fetus. The MF can only be crudely quantified with the naked eye. Therefore the following questions arise: 1) How can MF be exactly measured numerically? 2) What interrelationships are there between the MF determined electronically, the basal FHR, the oscillation amplitude (OA) of the FHR and the beat-to-beat variability (beat-to-beat var.) 3) What are the effects of hypoxia and acidosis on these index parameters?

METHODS

387 intrapartal FHR tracings were registered directly (F-ECG) with the cardiotocograph (HP instruments) via an RS422 interface and stored on diskette. The data were processed further with a computer program we developed ourselves (MATLAB, the MathWorks Inc., USA). The parameters of the fetal acid-base balance were measured in the blood of the umbilical artery (UA) and umbilical vein (UV) with instruments from Radiometer, Copenhagen (ABL 500, ABL 5) and stored off-line with a selection of clinical data and processed further on a laptop (HP, Omnibook XE 3). The fluctuation of the basal FHR was determined on the basis of the following four parameters: the number of high and low points (extrema) per minute (EXT),the mean beat-to-beat variability per minute and the OA (bpm). In order to correlate the MF of the basal FHR with the parameters of the fetal acid-base balance, only the last 30 CTG minutes ante-partum of each tracing were included. All decelerations and optionally in addition all accelerations were electronically deleted from the FHR curve.

RESULTS

Basic statistical values and the distribution of the four index parameters in 5486 minutes of basal FHR were studied: the median of EXT is at 59 and the mean value at 58.9 +/- 13.9 extrema/min. The distribution is normal. The median frequency amounts to 138 bpm, the median OA to 22.2 bpm and the median beat-to-beat variability to 161.7 bpm, respectively. The mean pH value in UA blood was 7.262 +/- 0.064. The acidotic risk (pH, UA < 7.100) reached 1.3 %. There were no pH values below 7.0. With increasing basal FHR, EXT increases highly significantly (r = 0.468, P << 0.0000). EXT decreases highly significantly (r = -0.432, P << 0.0000) with increasing OA. The mean basal frequency shows the best correlation with the base excess in UA blood (r = -0.263, P << 0.0000). Beat-to-beat variability and EXT alone correlate poorly with the actual, pH and BE values (UA). Multiplication of the index parameters leads to an increase of the correlation coefficients when compared with their single values.

CONCLUSION

With increasing hypoxia and acidosis the four index parameters do show a complex pattern which is characterized by tachycardia, increase of EXT and opening of the OA. A loss of EXT and a reduction of OA seems to be the result of already severe acidosis (pH, UA < 7.000). Using the four parameters of basal FHR alone, there is no possibility to evaluate fetal jeopardization. Numerical combination (e. g., multiplication) of some index parameters ameliorates their prognostic power and should be used in future online scoring procedures.

The prediction of fetal acidosis by means of intrapartum fetal pulse oximetry

OBJECTIVES

The study's objectives were to verify a threshold value for fetal arterial oxygen saturation as the critical boundary for fetal compromise during labor and to investigate a method of predicting acidosis caused by hypoxemia.

STUDY DESIGN

In a multicenter study involving 3 German obstetric centers, a total of 400 deliveries were monitored by fetal pulse oximetry (Nellcor-Puritan-Bennett Model N-400 Oxygen Saturation Monitor and FS-14 Sensor; Nellcor, Inc, Pleasanton, Calif). The durations of low (</=30%), medium (31%-60%), and high (>60%) fetal arterial oxygen saturations during the measurement were compared between neonates with a pH <7.15 versus >/=7.15 and a base excess <-12 mmol/L versus >-12 mmol/L in the umbilical artery post partum and in neonates with an Apgar score <7 versus >/=7 by Mann-Whitney U test. In 121 of the pulse oximetry measurements the durations of low, medium, and high fetal arterial oxygen saturations were measured from one fetal scalp blood sampling to the next and correlated with the change of scalp blood pH between samplings. Multiple regression analysis was performed to estimate the expected change of pH between 2 fetal scalp blood samplings, and receiver operating characteristic analysis was done to define a minimum duration of low fetal arterial oxygen saturation values to exclude or predict a significant decline of pH.

RESULTS

Neonates with a 1-minute Apgar score <7 differed from those with 1-minute Apgar score >/=7 significantly in the duration of low fetal arterial oxygen saturation but not in the durations of medium and high fetal arterial oxygen saturations. The duration of low fetal arterial oxygen saturation had been significantly longer in children with pH <7.15 or base excess <-12 mmol/L in the umbilical artery compared with those with a pH >/=7.15 or base excess >/=-12 mmol/L. The duration of high fetal arterial oxygen saturation was significantly shorter for children with a pH <7.15 or base excess <12 mmol/L than for those with a pH >/=7.15 or base excess >/=12 mmol/L. There was no difference in the groups with respect to the duration of medium fetal arterial oxygen saturation values. The duration of low fetal arterial oxygen saturation proved to be the best predictor of a decline of scalp pH between 2 fetal scalp blood samples. The pH declined significantly with a longer duration of low fetal arterial oxygen saturation (0.02 per 10 minutes). No decrease of pH by more than 0.05 was observed unless fetal arterial oxygen saturation had remained at </=30% for >/=10 minutes.

CONCLUSION

An arterial oxygen saturation of 30% was confirmed as the critical boundary for fetal compromise during labor. The development of acidosis seems to be predictable by the duration of hypoxemia, as indicated by fetal arterial oxygen saturation </=30%.

Cerebral oxygen delivery is reduced during the acidaemia associated with prolonged hypoxaemia in the immature ovine fetus

Our aim was to determine the effects of 12 h of hypoxaemia on cerebral blood flow (CBF) and cerebral O2 delivery in ovine fetuses at 0.6 gestation. During fetal hypoxaemia, induced by reduced uterine blood flow, fetal SaO2 and PaO2 were reduced (p < 0.01) from control values of 77.0 +/- 1.6% and 27.3 +/- 1.0 mm Hg, respectively, to 28.4 +/- 3.4% and 15.6 +/- 0.6 mm Hg; fetal pHa decreased from control values of 7.37 +/- 0.01 to 7.20 +/- 0.02 at 3 h, but returned to control values before 12 h. CBF (ml/min/100 g) was 2.0- to 2.6-fold higher (p < 0.01) than control values during hypoxaemia, but only 1.7-fold higher (p < 0.01) at 3 h when pHa was lowest. Cerebral O2 delivery (ml/min/100 g) was lower (p < 0.01) than control values of 3.15 +/- 0.29 at 1.5h (2.09 +/- 0.36) and 3h (1.84 +/- 0.22) of hypoxaemia and higher 1 h after hypoxaemia had ceased (3.81 +/- 0.22, p < 0.01). We conclude that the ovine fetus at 0.6 gestation is unable to sustain increased CBF and hence maintain cerebral O2 delivery during the first 6 h of hypoxaemia, a time which coincides with acidaemia; in contrast, at 6 and 12 h of hypoxaemia, when pHa was normal, cerebral O2 delivery was similar to control values. Reduced cerebral O2 delivery during the early, acidaemic, stages of hypoxaemia may lead to impaired neural development.

Vasopressin and catecholamine responses to 24-hour, steady-state hypoxemia in fetal goats

The purpose of the present study was to determine the effect of prolonged hypoxemia without acidemia on fetal stress hormones. Twenty-four-hour hypoxemia was conducted in nine chronically catheterized pregnant goats to determine fetal plasma concentrations of arginine vasopressin (AVP), epinephrine (E), and norepinephrine (NE). Nine experiments were performed. Six resulted in nonacidemic, steady-state hypoxemia, and three incidentally resulted in hypoxemia with progressive acidemia. In steady-state hypoxemia, fetal PO2 decreased significantly from 28.1 +/- 2.4 Torr to 18.8 +/- 2.5 Torr, fetal PCO2 also decreased significantly by about 5 Torr, and pH values did not change significantly. Fetal plasma concentrations of AVP, E, and NE were significantly increased at 1 h of hypoxemia. As hypoxemia continued, AVP returned to control level by 24 h, while E and NE remained elevated throughout the hypoxemic period. In the three experiments with progressive acidemia, AVP, E, and NE increased further as fetal acidosis progressed. We conclude that fetal AVP acts as a shorter-term stress hormone than E and NE in steady-state hypoxemia. This adaptive response is present without progressive acidosis. We also conclude that accompanying acidemia is a more potent stimulus for AVP, E, and NE than isolated hypoxemia during longer-term studies.

Carbon dioxide pneumoamnios causes acidosis in fetal lamb

Recently developed techniques of video-endoscopic surgery may offer new hope for the future of fetal surgery. To allow this approach, the amniotic cavity has to be temporarily enlarged, either by carbon dioxide (CO2) insufflation or by amnioinfusion. In 6 anesthetized ewes, CO2 insufflation of the amniotic cavity produced severe fetal hypercapnia (from 57.6 +/- 1.6 to 87.0 +/- 7.0 torr) and acidosis (from 7.22 +/- 0.03 to 7.11 +/- 0.08) despite normal maternal CO2 pressure and pH. CO2 pneumoamnios does not therefore appear to be an ideal working medium. Fetal endoscopic surgery through amnioinfusion of physiologic fluid may be a safer alternative.

Acidemia stimulates ACTH, vasopressin, and heart rate responses in fetal sheep

Adrenocorticotropic hormone (ACTH), arginine vasopressin (AVP), and renin responses to hemorrhage are highly correlated to the hemorrhage-induced decreases in arterial pH. The present study was designed to test the responses of these three systems to acute fetal acidemia, produced by intravenous infusion of H+. HCl was infused into chronically catheterized fetal sheep at rates of 0.02 (n = 5), 0.10 (n = 6), and 0.50 (n = 5) meq/min. Infusions at rates of 0.10 and 0.50 meq/min significantly decreased fetal arterial pH and increased arterial PCO2. Fetal heart rate and plasma concentrations of ACTH, cortisol, and AVP were significantly increased during infusion of HCl at 0.5 meq/min. Neither fetal plasma renin activity nor fetal arterial blood pressure was significantly altered by any of the infusions. The results of these experiments suggest that fetal ACTH, AVP, and heart rate are stimulated by decreases in arterial pH and/or increases in arterial PCO2. We speculate that these responses are chemoreceptor mediated, although we cannot distinguish the apparent relative roles of peripheral and central chemoreceptors on the basis of the present study.

Effect of acidosis and hypoxia on intestinal blood flow of sheep fetus

In sheep fetuses 110-130 days of age acidosis (blood pH 6.95; produced by infusion with 1.1 M lactic acid) significantly lowered blood flow (ml/min/100g) to the full thickness wall of the jejunum from 135 +/- 11 to 93 +/- 14 and in the full thickness wall of the ileum from 122 +/- 13 to 95 +/- 11. The decrease was mainly due to the decline in blood flow to mucosa of the segment, where flow decreased from 182 +/- 20 to 83 +/- 14 in the jejunum and from 130 +/- 10 to 107 +/- 9 in the ileum. Fetal hypoxemia (PaO2 of 14.9 mm Hg; induced by allowing ewes to breath 11.1% O2 and 88.9% nitrogen) reduced blood flow only to the jejunal mucosa from 142 +/- 14 to 99 +/- 16. The reduction in blood flow to the full thickness wall of the jejunum and the ileum did not change significantly from the control period, when PaO2 was 25 mm Hg.

Maternal halothane anesthesis reduces cerebral blood flow in the acidotic sheep fetus

Cerebrovascular autoregulation is lost during fetal asphyxia as cerebral vessels undergo compensatory vasodilation. In such a situation, maternal anesthetics, which decrease fetal arterial blood pressure and cardiac output, may further aggravate cerebral hypoxia. To examine this possibility, we prepared six pregnant ewes in such a manner as to be able to measure fetal regional cerebral blood flow in utero during acidosis produced by partial umbilical cord compression both before and after 15 minutes of halothane anesthesia given to the mother. Umbilical cord compression in the absence of anesthesia caused fetal metabolic and respiratory acidosis as evidenced by a decrease in arterial pH from 7.34 to 7.05; fetal arterial oxygen saturation simultaneously decreased from 29 to 17%. Halothane anesthesia administered to the mother of the acidotic fetus caused further aggravation of fetal acidosis (arterial pH 6.85) and oxygen desaturation (10%) and the fetus became markedly hypotensive. Blood flow to four cerebral areas increased 27 to 69% above control levels in the fetus during acidosis in the absence of maternal anesthesia but decreased to levels 30 to 42% below acidosis values when maternal anesthesia was combined with fetal acidosis. These data suggest that potent cardiovascular depressant anesthetics administered to the mother in the presence of fetal acidosis could decrease fetal cerebral oxygen delivery by interfering with fetal cardiovascular compensation during acidosis and reducing fetal cerebral blood flow.

Development of ammonia and glucose productions from glutamine in foetal rat kidney; effects of metabolic acidosis

Ammoniagenesis and gluconeogenesis have been studied in foetal rat kidneys during the five last days of gestation by measuring in vitro NH3 and glucose productions from glutamine and by assaying activities of soluble phosphoenolpyruvate carboxykinase(PEPCK) and glucose 6-phosphatase (G6Pase). These studies were carried out in normal (mean blood pH: 7.30) and acidotic (pH: 7.12) foetuses. In normal foetuses, NH3 production by kidney cortex slices remains constant throughout the studied period of development, at a level 10-fold lower than the maternal one. On day 20 of gestation, a low glucose production (20-fold lower than the maternal one) appears for the first time. This may be related to an increase of PEPCK and G6Pase activities which occurs between day 19 and 20. In 20 days old foetuses, NH4Cl induced acidosis stimulates NH3 production but has no effect on PEPCK activity and glucose production. A response of gluconeogenesis to acidosis is observed one day later (day 21).