Prolonged saltatory fetal heart rate pattern leading to newborn metabolic acidosis

PURPOSE

The saltatory pattern, characterized by wide and rapid oscillations of the fetal heart rate (FHR), remains a controversial entity. The authors sought to evaluate whether it could be associated with an adverse fetal outcome.

MATERIAL AND METHODS

The authors report a case series of four saltatory patterns occurring in the last 30 minutes before birth in association with cord artery metabolic acidosis, obtained from three large databases of internally acquired FHR tracings. The distinctive characteristics of this pattern were evaluated with the aid of a computer system.

RESULTS

All cases were recorded in uneventful pregnancies, with normal birthweight singletons, born vaginally at term. The saltatory pattern lasted between 23 and 44 minutes, exhibited a mean oscillatory amplitude of 45.9 to 80.0 beats per minute (bpm) and a frequency between four and eight cycles per minute.

CONCLUSIONS

A saltatory pattern exceeding 20 minutes can be associated with the occurrence of fetal metabolic acidosis.

Change in heart rate variability in relation to a significant ST-event associates with newborn metabolic acidosis

OBJECTIVE

To find whether low-to-high frequency (LF/HF) ratio of fetal heart rate (FHR) variability changes in relation to a significant ST-event during delivery, and if the change is predictive of metabolic acidosis of the newborn.

DESIGN

A case-control study.

SETTING

Data from a multicentre project.

SUBJECTS

Acidotic and control fetuses with abnormal cardiotocography together with a ST-event in fetal electrocardiogram (ECG).

METHODS

We studied intrapartum FHR variability with spectral analysis from 34 fetuses with a significant ST-event in the fetal ECG. LF/HF ratio of FHR variability was measured within a period of 1 hour before and 1 hour after a significant ST-event. Sensitivity and specificity of the change in LF/HF ratio of FHR variability in prediction of metabolic acidosis (pH < or = 7.05 and base deficit value > 12.0 mmol/l) of the newborn were described by means of the receiver operating characteristic curve.

MAIN OUTCOME MEASURES

Change in LF/HF ratio of FHR in relation to a significant ST-event.

RESULTS

We found that a relative change in LF/HF ratio greater than 30% in relation to a significant ST-event predicted cord arterial metabolic acidosis with a sensitivity of 89% (95% CI 68-100%) and specificity of 80% (95% CI 64-96%).

CONCLUSIONS

Relative changes in LF/HF ratio of FHR variability in relation to a significant ST-event are more pronounced in fetuses born with metabolic acidosis.

STAN, a clinical audit: the outcome of 2 years of regular use in the city of Varberg, Sweden

OBJECTIVE

To monitor and analyze (audit) the introduction of the STAN methodology in a district hospital.

DESIGN

Retrospective study covering the total population of deliveries at term during 2004 and 2005.

MATERIAL AND METHODS

1,875 out of 3,193 term pregnancies (59%) were monitored using the STAN fetal heart monitor (Neoventa Medical, Moelndal, Sweden) and the associated clinical guidelines. Cord metabolic acidosis, neonatal outcome, and rates of operative deliveries for fetal distress were recorded.

RESULTS

The overall cesarean section rate was significantly reduced in the STAN group. Emergency (crash) cesarean sections were significantly reduced from 1.51% to 0.27% in the cardiotocography- and STAN-monitored groups, respectively (OR 0.18, 95% CI 0.07-0.49). When cesarean section was performed only because of non-reassuring cardiotocography, cord acid base was significantly higher, 7.26 versus 7.19 (p<0.01), as compared to when STAN guidelines were followed. Total population rates for operative deliveries for fetal distress and cesarean section rates were 6.7% and 3.5% respectively. The corresponding metabolic acidosis rate was 0.5%.

CONCLUSION

High STAN usage in a busy labor ward setting provided an outcome equaling that noted previously in a larger academic unit, demonstrating the safe implementation of the STAN methodology in a nonacademic unit.

Electrocardiographic changes following umbilical cord occlusion in the midgestation fetal sheep

BACKGROUND

Clinical studies show that analysis of the fetal electrocardiographic (FECG) ST waveform at term gives important information on the myocardial response to intrapartum asphyxia. However, it is not known whether the preterm fetus responds in a similar fashion. The objective of the present study was to evaluate the FECGST response to umbilical cord occlusion in the preterm fetal sheep.

METHODS

Fetal sheep at midgestation were subjected to 25 min umbilical cord occlusion (n = 7) and compared to controls (n = 5). Changes in the FECGST waveform were recorded together with arterial blood pressure, heart rate, and acid base status during the occlusion and for 3 days afterward.

RESULTS

Umbilical cord occlusion resulted in immediate bradycardia (control: 187 +/- 7 bpm versus occlusion: 102 +/- 7 bpm), hypertension (control: 43.2 +/- 1.1 mmHg versus occlusion: 59.8 +/- 2.2 mmHg), and an initial increase in the T/QRS ratio (control: 0.10 +/- 0.02 versus occlusion: 0.60 +/- 0.10, P < 0.001), followed by hypotension (21.7 +/- 1.2 mmHg), normalization of the T/QRS ratio, and in some cases the development of negative T waves toward the end of the occlusion.

CONCLUSIONS

These studies show that the midgestation fetal sheep has the capacity to react to umbilical cord occlusion with a significant increase in the amplitude of the ST waveform together with an augmentation of blood pressure, which then subsides as the occlusion continues. The appearance of negative ST segment appears to signify significant cardiac dysfunction. The characteristic progression of ST-waveform changes in response to umbilical cord occlusion in midgestation fetal sheep, suggests that monitoring the ST waveform may contribute clinically important information also in the preterm individual.

ST analysis of the fetal electrocardiogram during labor: Nordic observational multicenter study

OBJECTIVE

To assess the diagnostic power of cardiotocography (CTG) plus the ST interval of the electrocardiogram (ECG) clinical guidelines with combined fetal heart rate and ST waveform analysis of the fetal ECG recorded during labor, to identify an adverse labor outcome (neonatal neurological symptoms and/or metabolic acidosis).

STUDY DESIGN

An observational, multicenter study was undertaken in 12 Nordic labor wards. A total of 573 women in labor were monitored using a prototype of the STAN S 21 recorder with fetal ECG data and computerized ST analysis.

RESULTS

Fifteen cases of intrapartum fetal hypoxia identified from neurological neonatal symptoms and/or cord artery pH < 7.05 with base deficit in extracellular fluid > 12.0 mmol/l were recorded. All these cases were identified by CTG + ST clinical guidelines. Five developed neonatal symptoms and had ECG abnormalities during the first stage of labor and, of the remaining ten, eight showed ST changes during active pushing in the second stage. Another eight cases had acidemia only and normal neonatal outcome. Seven of these displayed CTG + ST abnormalities. The high sensitivity of CTG + ST to predict fetal acidosis was associated with a marked increase in positive predictive values compared with conventional CTG.

CONCLUSION

The STAN clinical guidelines identify fetuses at risk of intrapartum asphyxia.

Fetal electrocardiogram waveform analysis in labour

The fetal electrocardiogram recorded during labour has so far been used for heart rate recording only. Extensive experimental, bioengineering and clinical research for more than 25 years on changes in the morphology of the electrocardiogram have provided more detailed information on fetal reactions to the stress and strain of labour. ST waveform analysis has been shown to provide new parameters that have the ability to monitor intrapartum hypoxia, thereby not only reducing the risk of the baby being born with hypoxia, but also significantly reducing the number of operative interventions.

Reduction of fine airborne particulates (PM3) in a small city centre office, by altering electrostatic forces

A two stage intervention study was carried out to establish the degree to which a newly developed, electrostatic air cleaning (EAC) system can improve indoor air quality (IAQ) by reducing the number of airborne fine particles. The IAQ and how employees in a city centre office (49 m2) perceived it, was monitored from May until November 1998. The number of fine particles, PM3 (0.3-3.0 microm); number of coarse particles, PM7 (3.0-7.0 microm); number of small positive and negative air ions; relative humidity and temperature were recorded in and out of doors. To assess the employees' perception of any changes in their work environment, a questionnaire was completed. Number of particles, relative humidity and temperature were also recorded in a nearby office, equipped with an identical air processor, where no interventions were made. The results from the first intervention (Stage 1), comparing number of airborne particles outdoors to indoors, gave a 19% reduction for PM3 and a 67% reduction for PM7 (P < 0.001). The reduction in PM3 was inconsistent and not statistically significant (P = 0.3). The reduction in PM7 from outdoors and the removal of PM7 created indoors was achieved by optimizing the existing air moving equipment. The results from the second intervention (Stage 2--with EAC units installed) comparing indoor to outdoor values, gave a further reduction in PM3 of 21% (P < 0.001) and a further 3% reduction for PM7 (P > 0.05). Therefore, at the end of Stage 2, the total reductions in particles from outdoors to indoors were 40% for PM3 and 70% for PM7 (P < 0.001). The Stage 2 results strongly suggest that electrostatic forces, created by the EAC unit(s) improved the removal of PM3, with no further significant improvement in the reduction of PM7. The questionnaire indicated an improvement in the IAQ, as perceived by the employees. The results suggest that the EAC system is effective in reducing PM3 and thereby improving IAQ in an urban office.

European Community multi-Center Trial "Fetal ECG Analysis During Labor": ST plus CTG analysis

This report form part of the European Community Multi-Center Trial "Fetal ECG Analysis during Labor". Aim of this prospective trial was to identify changes in the fetal ECG waveform with cases of verified fetal hypoxia. In this paper we also report on the use of a newly developed automatic system for identification of ST waveform changes (ST Log). All ECG were recorded with the STAN recorder (Neoventa Medical AB, Gothenburg, Sweden). The ECG information was not displayed during labor in order not to influence the clinical management. This report includes data from 320 cases and include six cases of fetal intrapartum hypoxia. Twenty seven cases showed changes in ST waveform. All five cases with the most marked ST change (a rise in T/QRS of > 0.10 units and lasting more then 10 minutes) had signs of ongoing intrapartum hypoxia. Six out of six cases with evidence of intrapartum asphyxia, showed ST changes. On the basis of our multi-center trial it appears that the combined analysis of CTG and ST waveform changes provides an accurate way to identify adverse events during labor. The work is continuing with a new STAN recorder developed by Neoventa Medical in Göteborg and currently being tested in a Swedish randomized, controlled multi-center trial.

Would removing indoor air particulates in children's environments reduce rate of absenteeism--a hypothesis

To conduct a controlled trial to test the ability of a newly developed electrostatic air cleaning technology (EAC) to improve Indoor Air Quality (IAQ) as defined by levels of airborne particles and to investigate the potential to reduce non-attendance rates due to illness among children in two Swedish day care centres. The EAC technology was shown to significantly reduce the indoor particulate load for very fine particles caused by outdoor air pollution by 78% and to reduce the number of fine particles produced indoors by 45%. To test the hypothesis, non-attendance was followed in two centres during 3 years. The EAC technology was in operation during year 2. Non-attendance rates among children in the larger day-care centre decreased by 55%, equalling those levels noted in family-based day care. It is speculated that the air cleaning effect may be due to alterations in electrostatic forces operating within the room enabling fine particulate matter to more easily become and stay airborne. The EAC technology is cost-efficient and might be a way forward to improve IAQ.

European Community Multicentre Trial "Fetal ECG Analysis During Labour": the P-R interval

The aim of the European Community Multicentre Trial on Fetal ECG Analysis During Labour was to collect a clinical database of electrocardiograms on which the different patterns of ST waveform and time interval changes, so far identified, could be studied. The aim of this paper was to study the PR-RR relationship and the P wave patterns during normal labour. One thousand three hundred fifty accelerations and 350 decelerations were analysed in 618 labours, all with normal fetal outcome. All ECGs were recorded with the STAN recorder and linked to a PC system for data acquisition and analysis. A positive relationship between P-R and R-R intervals was identified in all reactive fetal heart rate traces. A P-R shortening was identified also with all decelerations of more than 40 bpm from the baseline, resulting in a negative PR-RR relationship. Experimental works have described a P-R shortening concurrent with the maximal R-R lengthening during acutely induced hypoxemia in fetal lambs. In our study normal cord acid-base status indicated that the majority of bradycardia episodes recorded were not related to acute hypoxemia: PR-RR relationship changes seem therefore to indicate an intact physiological fetal heart adaptive response to rapid change in the environment of either hypoxemic or haemodynamic origin. A negative PR-RR relationship by itself seems to be nothing more than an indicator of decelerations during labour and seems unable to discriminate between decelerations of different origin. Finally the P wave was no longer detectable during decelerations of more than 800 msec: in this situation the P-R interval can not be reliably measured.

The fetal electrocardiogram: ST waveform analysis during labour

Intrapartum fetal surveillance is still under debate, despite 30 years of clinical experience and numerous clinical trials. Waveform analysis of the fetal electrocardiogram has emerged not as an alternative to cardiotochography but as a support tool to allow more accurate interpretation of intrapartum events. During hypoxia, the healthy fetus is utilizing a series of defense mechanisms. Among these, the increase in sympathetic activity, with an increase in circulating adrenaline, activates the myocardium with an increase in workload (the product of cardiac output, myocardium contractility and blood pressure). If there is an imbalance between myocardial oxygen supply and consumption, determined by the workload, then anaerobic metabolism, with a breakdown of myocardial glycogen stores starts and high T waves emerges. ST depression with negative T waves has recently been observed during hypoxia experiments in experimentally growth retarded guinea pigs whilst their normally grown littermates showed ST elevation. These findings have stimulated the development of a dedicated fetal ECG monitor - STAN - incorporating both standard CTG and ST waveform analysis. The STAN concept has now been taken through the process of recognized validation including several prospective studies and a large randomized trial in Plymouth of 2400 high risk, term deliveries. The T/QRS ratio is only one parameter to be used - equally important is to identify the occurrence of ST depression with biphasic negative T waves and to interrelate the CTG and the ST waveform as outlined in the clinical guidelines (table I). This table contains the clinical experience gained over many years and has formed the basis for the first randomized controlled trial comparing ST waveform + CTG with CTG only. Obviously, when the T/QRS ratio is used as the only component of such a scheme, confusion emerges. The analysis should also contain cases with significant intrapartum hypoxia. Recent findings indicate that only when cord artery pH falls below 7.0 and when there is substantial metabolic acidemia is there a significant risk of intrapartum asphyxia. Metabolic acidemia should be estimated from base deficit in the extracellular fluid and the combination of cord artery and vein data should allow for a more accurate assessment of intrapartum events, including the assessment of the duration of hypoxia. The Plymouth trial has tested the hypothesis that the combination of ST wave form and CTG analysis compared with CTG analysis only would reduce operative interventions for fetal distress without placing the fetus at a risk.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in the PR, RR intervals and ST waveform of the fetal lamb electrocardiogram with acute hypoxemia

The PR and RR intervals and T wave amplitude of the fetal lamb electrocardiogram were studied during acute hypoxemia produced by reduction of the maternal placental blood flow. Five chronically-instrumented fetal lambs (124 to 143 days of gestation) were subjected to acute hypoxemia (observations = 13) through complete occlusion of the maternal aorta for 60 s. The fetuses responded to the occlusion with a fall in oxygen tension (2.18 +/- 0.12 kPa to 1.11 +/- 0.14 kPa, SEM, P < 0.001) and oxygen saturation (48 +/- 4% to 19 +/- 4%, P < 0.001). Modest changes of pH (7.37 +/- 0.05 to 7.35 +/- 0.01, p), carbon dioxide tension (5.79 +/- 0.15 kPa to 6.17 +/- 0.14 kPa, P < 0.001) and plasma lactate concentration (2.1 +/- 0.6 mmol/l to 2.2 +/- 0.6 mmol/l, ns) occurred. The PR interval showed a triphasic pattern following occlusion. Initially, and simultaneously with the onset of the RR interval lengthening, a prolongation of the PR interval occurred (P < 0.01) with a peak value after 41 +/- 3 s after occlusion. Following this transient prolongation, the PR interval shortened concurrently with a maximum lengthening of the RR interval (P < 0.001) 2 +/- 3 s after the end of the occlusion. A maximum PR shortening (P < 0.001) occurred 27 +/- 5 s after occlusion followed by a prolongation of the PR interval (P < 0.001) with a peak value 203 +/- 21 s after release of the occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

ECG waveform, short term heart rate variability and plasma catecholamine concentrations in response to hypoxia in intrauterine growth retarded guinea-pig fetuses

After unilateral uterine artery ligation in midpregnancy twelve guinea-pig does were anesthetized at 63 days of gestation. The ST waveform of the fetal electrocardiogram and the short term heart rate variability were studied during normoxia and in response to acute hypoxia in growth retarded fetuses (n = 12, mean +/- SEM, 58.5 +/- 3.9 g) and their normal sized littermates (n = 12, 94.3 +/- 3.5 g). Hypoxia was induced by letting the doe breathe a low-oxygen gas mixture. After 10 min of hypoxia fetal blood was sampled by decapitation and blood gases, acid-base status and catecholamine concentrations were analyzed. The does responded to decrease in inspired oxygen concentration with changes in oxygen tension (13.8 +/- 0.8 to 4.3 +/- 0.2 kPa) and oxygen saturation (99.9 +/- 0.1% to 70.5 +/- 1.8%). Fetal blood gases and plasma catecholamine concentrations did not differ between the groups. In the growth retarded group standard bicarbonate was significantly lower compared to controls. The T/QRS ratio (the quotient between T wave height and QRS peak to peak amplitude) was normal and similar in both groups prior to the hypoxic period. In response to hypoxia T/QRS ratio increased in the normal sized group and T/QRS was correlated to carbon dioxide tension, oxygen saturation, pH, lactate, standard bicarbonate concentration, standard base excess and plasma noradrenaline concentration, respectively. The growth retarded fetuses presented a completely different pattern where 7 out of 12 fetuses showed a biphasic ST waveform during hypoxia with depression and downward sloping of the ST segment and negative T wave.(ABSTRACT TRUNCATED AT 250 WORDS)

Diameters of the common carotid artery and aorta change in different directions during acute asphyxia in the fetal lamb

The aim of this experimental ultrasound study on six fetal lambs was to evaluate how blood flow variables and vessel diameters of the descending aorta and the common carotid artery change during fetal asphyxia in the acute preparation. When acute asphyxia was induced by obstructing the maternal aortic blood flow all fetuses reacted with significant decrease in the aortic diameter and blood flow. In the common carotid artery vessel diameter and the blood flow increased significantly. The results support the theory of a brain sparing effect during fetal distress with significant changes of blood vessel diameters occurring in opposite directions in the aorta and the common carotid artery, thereby contributing to the centralisation of circulation.

How to assess fetal metabolic acidosis from cord samples

The degree of metabolic acidosis at birth has been calculated in cord artery and vein samples from 21 term fetuses with cord artery pH less than 7.20. The aim of the study was to compare base deficit values calculated from either Siggaard-Andersen alignment nomogram (BD blood) or the Acid-Base chart (BD extra cellular fluid, BDecf). BDblood was found to be consistently higher in the cord artery as compared with BDecf, 13.2 +/- 3.5 and 9.9 +/- 2.9 mmol/l (Mean +/- SD), respectively. A significant correlation was found between cord artery PCO2 and BDblood whereas BDecf appeared unaffected by PCO2. In cases with cord entanglement BDecf a-v differences were increased to 3.4 +/- 2.3 mmol/l as compared with the small a-v difference noted in acidotic cases without cord entanglement, 1.1 +/- 1.25 mmol/l. It is speculated that with acutely emerging, intermittent asphyxia due to cord compression, a cord artery and vein difference in metabolic acidosis may exist and where the vein captures the basal level and the artery the acute changes. It is concluded that BDecf in both cord artery and vein add valuable information on the mechanisms behind metabolic acidosis.

ECG wave form, short term heart rate variability and plasma catecholamine concentrations in intrauterine growth-retarded guinea-pig fetuses

Electrocardiogram waveform, short term heart rate variability and catecholamine concentrations were studied with maternally-induced anesthesia in eleven growth-retarded guinea-pig fetuses and their normal-sized littermates at 63 days of gestation. Intrauterine growth retardation was induced by unilateral uterine artery ligation performed between day 32 and 35. In the growth-retarded group fetal weight was reduced by 45%. Blood gases, acid-base status and oxygen content were similar in the two groups. The growth-retarded guinea-pig fetuses were hypoglycemic and demonstrated a rise in hemoglobin concentration. The T/QRS ratio (T wave amplitude/QRS amplitude) was similar in both groups. The short-term heart rate variability was significantly reduced in the growth-retarded group. Plasma catecholamine concentrations were increased in growth-retarded fetuses but differed only significantly for noradrenaline compared to controls. We suggest that similar T/QRS ratio in both groups of fetuses indicates that aerobic myocardial metabolism is maintained among growth-retarded fetuses. The mechanism behind the reduced variability is unclear.

Fetal ECG waveform analysis should improve fetal surveillance in labour

Fetal heart rate (FHR) and fetal electrocardiogram (ECG) recordings were obtained from a scalp electrode with maternal thigh as reference and used for ST waveform analysis in 201 patients in labour. Nearly 45% had suspicious or abnormal FHR traces whilst only 27% had T/QRS ratio greater than 0.25 (mean +/- 2 SD). A normal T/QRS ratio identified 99.3% of fetuses with normal buffering capacity in cord artery blood. Of 13 infants with a cord artery blood pH less than 7.15, standard bicarbonate was less than 15.0 mmol/l in five who had an average T/QRS ratio less than 0.25 throughout labour. Of the eight with respiratory acidosis, five had an increase in T/QRS ratio greater than 0.25 for longer than 20 minutes prior to delivery, in two the ratio increased during the last few minutes and one had no change (pH 7.14). Persistent elevation of T/QRS in the first stage of labour identified those with decrease in buffer capacity in cord arterial blood (sensitivity of 94.1%). Acute hypoxia was recognized by the rapid rise in T/QRS. The specificity of T/QRS to identify fetuses at risk increased by combining the ST waveform analysis with FHR changes.

STAN--the Gothenburg model for fetal surveillance during labour by ST analysis of the fetal electrocardiogram

Waveform analysis of the fetal ECG for fetal surveillance is regaining widespread interest. This paper presents our present knowledge on ST waveform analysis during human labour. A unipolar scalp lead with the maternal thigh as reference makes it possible to identify the T wave and at the same time decrease signal noise. The development of an ECG analyser (STAN) has enabled us to collect 201 ECG recordings during labour on which ST analysis could be undertaken. The data indicate that waveform analysis of the fetal ECG improves fetal surveillance during labour.

Microprocessor based waveform analysis of the fetal electrocardiogram during labor

An increase in T wave amplitude of the fetal ECG (FECG) has experimentally been correlated to elevated catecholamine levels and myocardial glycogenolysis. The FECG changes have also been described during human delivery. The present aim was to investigate whether these ECG changes could be reproduced in an easily handled real time microprocessor system, and to correlate them to biochemical and clinical data. During 40 deliveries the FECG signal was transferred to a microcomputer system for real time averaging of the FECG. There was a high capacity of the system to reproduce the ST waveform changes though the averaging procedure reduced the QRS magnitude by 10%. With a normal umbilical artery pH (greater than or equal to 7.25) the highest T/QRS ratios recorded during each delivery was 0.26 +/- 0.19 (mean +/- S.D.). With lowered pH (less than 7.25) the T/QRS increased to 0.33 +/- 0.10 (P less than 0.02). A similar difference between the two groups was seen when the T/QRS ratios from the last hour before birth were compared; 0.13 +/- 0.08 and 0.18 +/- 0.05, respectively (P less than 0.01). Changes in the ST waveform with T/QRS greater than or equal to 0.30, ST segment alterations, or negative T waves appeared during 40% of the deliveries, however, 30% were short standing changes (less than 30 min). Intermediate CTG changes during at least 30 min occurred in 41% and the pattern was classified as abnormal in 18%. Using the scalp electrode as signal source, the ECG analysis could add further information to the routine CTG recording on the fetal condition during delivery.

Electrocardiographic waveform changes and catecholamine responses during acute hypoxia in the immature and mature fetal lamb

The aim of the present study was to investigate the changes in electrocardiographic waveform and the release of catecholamines in the fetal lamb during nonacidemic fetal hypoxia. Chronically instrumented fetal lambs were subjected to reproducible hypoxia by reduction of the maternal placental blood flow. This was achieved by complete obstruction of the maternal aorta for 60 seconds. The fetuses were divided into an immature (119 to 126 days, n = 10) and a mature group (129 to 141 days, n = 6). Both groups of fetuses had a marked fall in oxygen tension (from 2.43 +/- 0.12 to 1.46 +/- 0.12 and 2.22 +/- 0.15 to 1.11 +/- 0.17 kilopascals [kPa] in the immature and mature groups, respectively) and in oxygen saturation (from 48% +/- 3% to 17% +/- 2% and 49% +/- 3% to 15% +/- 3%, respectively), but only modest changes occurred in pH and carbon dioxide tension. Basal fetal catecholamine concentrations did not differ between the groups but increased more significantly in the mature group with acute hypoxia. An increase in the T wave amplitude of the fetal electrocardiogram occurred in both groups during the latter part of occlusion with peak values shortly after removal of the occlusion. A linear correlation was found between the plasma epinephrine concentration and the T/QRS ratio in the mature group. Fetuses in both groups showed a marked bradycardia of similar magnitude during the occlusion but differed during the early phase of heart rate recovery by a slower acceleration of heart rate in the mature group. In connection with this marked bradycardia, the mature group showed a significant rise in mean arterial blood pressure at end of the occlusion. We suggest that fetal maturity has a significant influence no only on the release of catecholamines during nonacidemic hypoxia but also on the cardiovascular reaction pattern and changes in the ST waveform.

Fetal ECG during labour: a presentation of a microprocessor system

Changes in the ST waveform of the fetal ECG have been detected in 47 term deliveries with vertex presentations using a specially developed microprocessor-based system for on-line recording of T wave amplitude. The T wave was quantified by the T/QRS ratio. The recording included one scalp electrode for exploration and a maternal skin electrode as reference. Signal quality allowed optimal ST waveform assessment in 89% of the cases. The degree of perinatal asphyxia was judged from cord artery acid-base status and the neonatal outcome. In completely normal fetuses at term the mean T/QRS ratio was 0.148 with a standard deviation of 0.048. With this basic information we can proceed in the investigation of the T/QRS ratio as a means for fetal surveillance.

Fetal ECG during labour: a suggested standard

Recording the fetal ECG as a means of fetal monitoring during labour has been investigated by many researchers. Different signal processing methods have been used, making comparisons difficult so that agreement on several topics has not been reached. We suggest the basis of a standard method of recording and processing the signal which we believe will be acceptable to the research and clinical communities.

Acute blockade of beta 1-receptors in the asphyxiated sheep fetus

The effects of acute beta 1-blockade on fetal cardiovascular reactions during asphyxia were evaluated in 11 exteriorized sheep fetuses. Gestational age was 110-142 days. Asphyxia was induced either by ventilating the mother with low oxygen gas mixture or by mechanical reduction of placental blood flow. During asphyxia all fetuses reacted to metoprolol injection with a decrease in heart rate, myocardial contractility, cardiac output and arterial blood pressure. Five experiments resulted in irreversible fetal cardiovascular collapse. Isoprenaline was given to the fetuses during hypoxia to test the ability to further increase heart rate and activate myocardial beta-adrenoceptors. In those experiments with fetal cardiovascular demise after metoprolol, the isoprenaline injection did not result in a significant tachycardia. The surviving fetuses could increase their heart rate as a sign of a capacity to further increase the sympatho-adrenergic drive.

Postasphyxial cerebral survival in newborn sheep after treatment with oxygen free radical scavengers and a calcium antagonist

Acute, severe intrapartum asphyxia was mimicked by tying the umbilical cord in the exteriorized fetal sheep. After a standard time period cardiopulmonary resuscitation was instituted. In the treatment group (n = 14) the lambs were given a composition of scavengers of oxygen-derived free radicals and a calcium channel blocker. The control group of lambs (n = 12) was given placebo. The trial was blind and randomized. Hemodynamic and neurophysiological variables were measured from 30 min before asphyxia to 2 h postresuscitation. Mean arterial blood pressure, sagittal sinus venous pressure, heart rate, and cardiac output did not differ between the two groups although dramatic changes took place during asphyxia and resuscitation. Cerebral blood flow measured by 133-Xe washout method increased in both groups immediately after resuscitation. The treated animals retained an augmented cerebral blood flow during the 2 h postresuscitation while the control animals lost the increase of cerebral blood flow. The treated lambs recovered their somatosensory evoked potentials partially or completely in eight of 14 cases while the same figures for the control lambs were one of 12 cases. Immediately after resuscitation the cerebral reactions recovered to some extent in both groups but during the following 2 h the cerebral cortical function deteriorated in the control group but improved in the treated lambs. It is concluded that part of the brain damage in connection with acute, severe asphyxia may be inflicted by oxygen-derived free radicals released during the reoxygenation phase after resuscitation and that oxygen-derived free radical scavengers and calcium channel blockers may find a place in cardiopulmonary resuscitation.

Fetal cerebral, cardiovascular and metabolic reactions to intermittent occlusion of ovine maternal placental blood flow

In 10 mature, acutely exteriorized fetal sheep cardiovascular, cerebral and metabolic reactions were followed during intermittent occlusions of maternal placenta blood flow. The response was analysed from blood pressure, heart rate, myocardial contractility, combined cardiac output, ST waveform analysis of the fetal ECG, and from the evoked EEG response. The metabolic response was judged from blood gases, pH, lactate and circulating catecholamines. Basal values were within the range seen in the 'chronic' fetal lamb preparation. During moderate asphyxia, achieved by 10 1 min occlusions separated by 2 min periods of free maternal aorta blood flow, cardiovascular performance was increased with a substantial catecholamine surge but minor effects on cerebral and metabolic functions. During the marked asphyxia, achieved by five 2 min occlusions, marked metabolic changes occurred together with abolition of cerebral function. Forty-five minutes after asphyxia, 9/10 of the fetuses had regained cerebral, metabolic and cardiovascular functions.

Alterations in the fetal electrocardiogram as a sign of fetal asphyxia--experimental data with a clinical implementation

Although considerable progress occurred with the introduction of electronic fetal monitoring it is now clear that the fetal heart rate alone does not provide optimal information about the fetus. Thus, a question arises whether additional information could be gained by further analyzing the fetal ECG as this is likely to be the parameter presently most easily accessible during labor. For the past 10 years work by our group in Göteborg has been focused on the evaluation of ST waveform changes in the fetal ECG as a method for fetal surveillance. Fetal hypoxemia results in a reproducible pattern of changes with the progressive increase in T wave amplitude as the main response. The ratio between the amplitude of the T wave and QRS complex, the so called T/QRS ratio, quantifies this T wave alteration. Considerable information has been gained, using this parameter, by conducting experiments on the fetal lamb and guinea-pig. The closest relationship was found between the rate of breakdown of myocardial glycogen and the increase in T wave amplitude. This utilization of myocardial glycogen during hypoxia is stimulated by beta-adrenoreceptors. The data also indicate a close link between the adrenaline surge and the appearance of high T waves in the fetal ECG. Relating T wave changes to other biochemical parameters shows a relationship during marked asphyxia with the appearance of a metabolic acidosis which is a result of an increase in blood lactate concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Maternal treatment with a cardioselective beta-blocking agent--consequences for the ovine fetus during intermittent asphyxia

To evaluate the effect of chronic beta 1-adrenoceptor blockade on physiological adaptation to asphyxia a study was done on exteriorized sheep fetuses of 127-142 days gestational age. Eleven pregnant ewes were infused with metoprolol for 5 days prior to experiment. Another 10 ewes were infused with saline and served as controls. Asphyxia was induced by intermittent complete obstruction of maternal placental blood flow. Fetal electro-cardiogram, heart rate, cardiac output, myocardial contractility and cerebral blood flow were measured together with blood pH, lactate and hypoxanthine. Neurophysiological responses were evaluated by changes in somatosensory evoked electroencephalogram. The beta 1-blocked fetuses showed less responsiveness in myocardial contractility and heart rate during reoxygenation. This curtailed reaction resulted in accelerated lactic acidosis, increased break-down of intracellular energy rich substances and impaired cerebral function. Nine of the ten controls survived the experiment and 8 of them regained their somatosensory evoked EEG potentials, whereas 7 of the 11 beta-blocked fetuses survived and only 3 regained original somatosensory evoked EEG potentials. It is concluded that beta 1-adrenoceptor blockade impairs the adaptive responses to asphyxia in the ovine fetus and decreases its ability to survive severe asphyxia.

ST waveform changes of the fetal electrocardiogram during labour--a clinical study

Waveform changes in the fetal electrocardiogram (ECG) are under reassessment as a means of fetal surveillance. The purpose of the study was to identify ST waveform changes from the fetal scalp lead during labour and to compare any change with conventional signs of fetal distress. Two scalp electrodes provided a sufficiently stable signal from which ST waveform changes could be identified and measured as the T/QRS ratio. No infant was clinically hypoxic. Only 26% of the 46 patients studied had a continuously normal CTG whereas 67% had no ST waveform abnormalities. A relation was found between the two variables as the mean T/QRS ratio increased from 0.20 (SD 0.11) during epochs of normal CTG to 0.27 (SD 0.17) with CTG changes. A linear correlation (r = 0.58, P less than 0.01) was found between the T/QRS ratio before birth and the cord plasma lactate values.

Cardiovascular effects of enflurane and asphyxia during long-term beta 1-adrenoceptor blockade

The haemodynamic effects of enflurane (1.7% and 3.4% expiratory concentrations) were investigated in sheep (n = 6) pretreated with an infusion of metoprolol (0.2 mg X kg-1 X h-1 for 5 days) and in control animals (n = 6). Chloralose was used as basal anaesthetic. A 90 s apnoea period was included in the experiment to evaluate further the possible side-effects of long-term metoprolol treatment in combination with enflurane anaesthesia. MAC 1.0 for enflurane in the sheep was found at 1.45% end-tidal concentration by separate measurements. Before enflurane administration, the only significant differences between the two groups of animals were a lower systemic vascular resistance and a higher stroke volume during metoprolol treatment. Enflurane abolished these discrepancies in a dose-dependent fashion and similar cardiovascular depression was observed in both groups of animals at 3.4% expiratory concentration of enflurane. Metoprolol did not significantly affect the hypertensive response to apnoea during chloralose anaesthesia alone. At enflurane 1.7% expiratory concentration the apnoea response was small and only the metoprolol-treated animals showed a significant increase in left ventricular end-diastolic pressure. We conclude that 5 days of pretreatment with metoprolol in the sheep model does not significantly impair cardiovascular performance during enflurane anaesthesia.

The relationship between circulating catecholamines and ST waveform in the fetal lamb electrocardiogram during hypoxia

Previous studies from this laboratory have shown that changes in the ST waveform in the fetal electrocardiogram are a sign of fetal asphyxia. In the present study, seven chronically instrumented fetal lambs between 117 and 143 days' gestation were studied during 16 one-hour periods of maternally induced hypoxia. The aim was to test the hypothesis of a relationship between the concentration of circulating catecholamines and T-wave amplitude. The response to hypoxia was aged-dependent. Fetuses below 126 days of gestation did not react with electrocardiographic changes and output of epinephrine unless acidosis occurred. In more mature fetuses, hypoxia per se would induce a surge of epinephrine and changes in the ST waveform. Overall there was a strong correlation between the T/QRS ratio and the level of circulating epinephrine. During normoxia, epinephrine was undetectable (less than 0.1 nmol/L) in most fetuses; norepinephrine showed an increase at term. The analysis showed one fetus with chronic changes in the ST waveform (T/QRS ratio greater than 0.30) related to a marked increase in the plasma level of epinephrine in spite of normal blood gas values. These findings complement previous results in the acute and chronically instrumented fetal lamb and suggest that changes in the ST waveform expressed as T/QRS ratio identify a change to anaerobic myocardial metabolism mediated by beta-adrenergic stimulation.

Maternal beta-adrenoceptor blockade reduces fetal tolerance to asphyxia. A study in pregnant sheep

Maternal and fetal beta 1-adrenoceptor blockade was induced in sheep by infusing i.v. 11 pregnant ewes with metoprolol in doses producing maternal plasma concentrations of metoprolol comparable to those obtained in clinical use. Ten other ewes and their fetuses served as controls. Under acute anaesthesia the fetus was exteriorized and subjected to two levels of controlled asphyxia by intermittent, complete obstruction of the maternal placental blood flow. Fetal haemodynamic reactions were assessed by measuring fetal heart rate, cardiac contractility, cardiac output and cerebral blood flow. The metabolic reactions were evaluated from blood gases, pH, lactate and hypoxanthine concentrations, while the electrophysiological status of the brain was evaluated from the somatosensory evoked EEG potentials (SEP). Already during the period of moderate asphyxia the beta-blocked fetuses demonstrated a blunted haemodynamic response, in comparison with the control fetuses, resulting in an accelerating lactic acidosis, signs of a breakdown of intra-cellular energy-rich phosphates and an impaired cerebral function. During the period of severe asphyxia, both groups of fetuses exhibited signs of extensive cerebral deterioration. During the ensuing recovery phase, 80% of the control fetuses regained their brain function, as assessed by SEP, whereas this was true for only 30% of the beta 1-blocked fetuses. It is concluded that the ovine fetus relies heavily on greatly increased sympatho-adrenal activity to adapt itself to asphyxia and that blockade of the fetal beta 1-adrenoreceptors by maternal medication is a hazard to the potentially asphyctic fetus.

Contribution of heart muscle, liver, skeletal muscle and placenta to the asphyxial hypoxanthine elevation in the acutely exteriorised fetal lamb

The metabolic response to different degrees of hypoxia was studied in 14 lamb fetuses. We have previously found a substantial rise in the fetal arterial plasma hypoxanthine (HX) level, in parallel with alterations of other hypoxia indices during induced asphyxia. Measurements of the arterio-venous (A-V) difference in the HX level across the CNS demonstrated a late efflux of this substance from the fetal brain, with a high resistance to asphyxia. In this study, the effluxes of HX, lactate, and in some cases glucose, from the myocardium, liver, hindleg (skeletal muscle) and placenta were investigated in acutely exteriorised sheep fetuses with graded asphyxia. The main findings were as follows: (a) myocardium: a release of HX early during asphyxia, the magnitude of which paralelled the amount of mechanical work performed by the heart; a significant lactate influx into the heart during normoxia and recovery period; (b) liver: hepatic HX release even during normoxia, increasing to substantial amounts in connection with increasing asphyxia; (c) hindleg: release of HX only during the recovery period; lactate efflux during all periods apart from severe asphyxia, when an influx was seen for both substances; (d) placenta: production of lactate during normoxia, and an efficient clearance of both lactate and HX from the fetal plasma in combination with their concentration increasing during asphyxia. It is concluded that the myocardium and liver are the main contributors to the elevated HX level during fetal asphyxia among the fetal organs investigated, while skeletal muscle releases HX mostly during the period of reoxygenation.

Changes in the ST waveform of the fetal lamb electrocardiogram with hypoxemia

The ST waveform of the fetal electrocardiogram (ECG) was examined in 10 chronically instrumented fetal lambs from 115 days to term. Averaged ST waveforms were plotted at 5-minute intervals in six fetuses for 2 to 22 days. No diurnal or other rhythms were seen. To correct for changes in signal gain the amplitude of the T wave was measured relative to the amplitude of the QRS complex. The T/QRS ratio was normally less than 0.30. Persistently elevated ST waveforms with a T/QRS range 0.32 to 0.65 preceded fetal death by some days in three fetuses and were associated with anemia and/or hypotension in a further three. In these animals hypoxia produced a further rise in the ST waveform (mean T/QRS, from 0.48 to 0.81) and all died during labor. In lambs with a normal ST waveform there were differences in the response to hypoxia over 1 hour for a similar fall in PO2. In eight experiments the ST segment and T wave increased (mean T/QRS, from 0.17 to 0.59) and promptly reverted to normal with normoxia. There was a significant rise in mean arterial blood pressure, plasma lactate, and glucose and a fall in pH. In four experiments there was little change (mean T/QRS, from 0.19 to 0.25), with a small rise in plasma lactate suggesting that these lambs were able to maintain aerobic myocardial metabolism. Overall there was a strong correlation of the T/QRS ratio to the rate of rise of lactate. These findings complement previous results in the acute fetal lamb preparation and suggest that ST waveform elevation expressed as the T/QRS ratio identifies a change to anerobic myocardial metabolism.

Intestinal colonization and antibody response

Rapid bacterial colonization of the gastrointestinal tract takes place immediately after birth. Only a few of the Escherichia coli strains colonizing the gut of healthy full-term neonates expressed MS pili. On the other hand, most E. coli strains isolated carried MR pili resembling the P-fimbriae which are a known virulence factor for pyelonephritogenic E. coli. The presence of serum antibodies against pili and K antigens of E. coli after vaccination did not influence the capacity of E. coli to colonize and persist in the intestine of experimental animals.

Changes in hypoxanthine and lactate during and after hypoxia in the fetal sheep with chronically-implanted vascular catheters

The effect of intra-uterine hypoxia on the hypoxanthine and lactate concentration in fetal sheep with catheters chronically implanted was investigated. Experiments were conducted on five fetuses. Sixty-four blood samples from nine hypoxic and recovery periods were analysed. A significant increase of hypoxanthine and lactate occurred in parallel with the fall of arterial oxygen saturation (SaO2) and arterial oxygen pressure (PaO2) during the first 20 min of hypoxia. The elevations in plasma hypoxanthine and lactate were significantly greater during more severe hypoxia than mild hypoxia, as judged from the amount of low oxygen gas mixture given to the ewe (7 or 9%). There were no difference in PaO2 and only minor difference in SaO2 between the two groups. The increase in lactate over 20 min was the same throughout the one-hour period of hypoxia, while the increase of hypoxanthine was less pronounced at the end of the period. This might be due to the fact that hypoxanthine was cleared from fetal plasma at a fairly rapid rate, half of the excess concentration being eliminated after 25 +/- 21 min compared to 85 +/- 47 min for lactate in six experiments post hypoxia. Linear regression analysis revealed a highly significant correlation between hypoxanthine and SaO2, pH and lactate (P less than 0.001). These three variables explained 77% of the variance of hypoxanthine, when calculated by multiple regression analysis.

Myocardial metabolism in relation to electrocardiographic changes and cardiac function during graded hypoxia in the fetal lamb

Previous studies from this laboratory have demonstrated early and progressive alterations in the ST-T period of the fetal and neonatal electrocardiogram in relation to asphyxia. The aims of the present study were to investigate the metabolic background of these hypoxic ECG changes by means of serial myocardial biopsies in fetal lambs, relating these changes to the hypoxic depletion of glycogen, ATP and creatine phosphate stores in the heart and to the altered myocardial performance as measured by heart rate, mean arterial blood pressure, combined cardiac output and max. dP/dt. The experiments were performed on 21 fetal lambs, acutely exteriorized and subjected to graded hypoxia. During hypoxia there was a significant relationship between the degree of changes in the ST-T period according to a scoring system and the depletion of myocardial glycogen and ATP, a highly significant correlation between the rate of myocardial glycogenolysis and the rate of increase in T wave amplitude, and a parallelism between the amount of glycogen available and fetal cardiovascular function. The myocardium was capable of regenerating its glycogen stores under conditions of adequate oxygenation and in the absence of acidosis and hypoglycaemia.

Alterations in the electrocardiogram of the fetal lamb as a sign of fetal asphyxia. A comparison between the scalp lead and the precordial lead

Progressive changes in the ST-T period of the fetal electrocardiogram (FECG) were studied in 18 lamb fetuses, acutely exteriorized and subjected to graded hypoxia. The aim of the study was to compare the bipolar precordial lead (CR-lead) with the unipolar scalp lead, and to correlate the alterations in the FECG to blood-gas and acid-base status. The scalp lead gave less information regarding fetal condition and was more difficult to interpret than the precordial lead. This might be one factor in the controversy regarding the significance of alterations in the FECG during asphyxia and labor, since the scalp lead is used mainly in clinical situations. Our previous results demonstrating progressive changes in the ST-T period of the FECG during hypoxia in experimental animals and showing the same ECG changes in newborn human infants immediately after birth, were registered with the bipolar precordial lead. It is possible that a bipolar scalp lead might give more information regarding the fetal condition than the unipolar scalp lead mainly used in clinical practice.

ECG-changes in the fetal lamb during asphyxia in relation to beta-adrenoceptor stimulation and blockade

Progressive changes in the S-T interval of the fetal electrocardiogram (FECG) were studied in 14 lamb fetuses, acutely exteriorized and subjected to graded hypoxia. The aims of the study were to investigate whether beta-adrenoceptor stimulation and hypoxia exerted additive or potentiating effects on the FECG and several cardiovascular parameters and whether the hypoxic changes of the FECG could be blocked by beta-adrenoceptor blocking agents. The FECG changes were studied in order to correlate them with cardiovascular function, as measured by heart rate, mean arterial pressure, end diastolic pressure, maximum dP/dt and combined cardiac output, estimated by the thermodilution method, as well as with blood gases, acid base status, blood lactate and glucose. Injections of small doses (0.02 to 0.4 microg kg-1 min-1) of isoprenaline induced the same pattern of changes in the FECG as we have previously recorded during hypoxia. By increasing the isoprenaline dose an increase in the duration of the FECG changes and amplitude of the T-wave changes was obtained. Propranolol was found to completely abolish the FECG changes induced by isoprenaline, as well as by mild hypoxia. During severe hypoxia the FECG changes could not be abolished by propranolol. Our previous findings indicated that the hypoxic changes could be regarded as a sign of myocardial glycolysis. Thus, the present finding that even small doses of isoprenaline given to the fetus, initiates the same pattern of FECG changes corroborate this hypothesis.

Neonatal electrocardiographic changes in relation to cardiotocographic changes

Electrocardiograms (ECG) were made immediately after delivery in 28 infants with normal cardiotocographic patterns in labour and in 29 with abnormal patterns. Changes in the S-T segment and T-wave were quantified in a scoring system. High and peaked T-waves (high T/QRS-ratios) were significantly more common in the group with abnormal cardiotocographic patterns. The infants with ECG-changes also had significantly lower Apgar scores and more neonatal complications. The immediate postpartum ECG seems to be a useful indication of the accumulated hypoxic stress to which the child has been subjected in labour.