The factor time in fetal heart rate monitoring and the detection of acidosis using the WAS score.

BACKGROUND: Using the naked eye evaluation of fetal heart rate (fhr) patterns remains difficult and is not complete. Computer-aided analysis of the fhr offers the opportunity to analyze fhr patterns completely and to detect all changes due to hypoxia and acidosis. It was the goal of this study to analyze the factor time in fetal monitoring and to evaluate the association between the fhr and the actual pH values in arterial umbilical blood. METHODS: During a period of 11 years the FHR signals (i. e., the R-R interval of the F-ECG) of 646 fetuses were recorded with a CTG and simultaneously by a computer. The computer files were analyzed thereafter, i. e., the results did not influence our clinical management. To enter the study, all fetuses must have been delivered by the vaginal route--in consequence without a significant loss of fhr signals. During forceps and/or vacuum deliveries recordings were continued. If necessary a new electrode was inserted. In this study recordings of fetuses with chorioamnionitis, tracings of malformed neonates and tracings shorter than 30 min were excluded. Thus 484 recordings were left. We used our own computer programs written in MATLAB (USA). 3 parameters were determined electronically: 1) the mean fetal frequency [fhf, (bpm)], 2) the number of turning points (N/min) in the fhr, which we called 'microfluctuation' (micro) and 3) the oscillation amplitude, oamp (bpm). Measurements of the acid-base variables from arterial (UA) and venous (UV) blood were performed using RADIOMETER equipment (ABL500) and trained personnel. However, only the actual pHUA values were used in this study. To detect the influence of hypoxia and acidosis, all 484 cases were separated into 7 groups according to the actual pH(UA) value: 55 fetuses lying in a small non-acidotic "pH-window" (pH(UA)=7.290-7.310, mean=7.300±0.008) were used as 'controls'. RESULTS: In humans fhf, micro and the oamp behave differently during the last 30 min of delivery and with different fetal pHUA values: micro is early (at 0 min) decreased with fetal acidemia and is steadily deceasing (68-40 N/min) during vaginal delivery; the oamp--mainly due to decelerations--is increased from 35 up to 70 bpm during the last 30 min. Hypoxia and acidosis increase the amplitude and duration of decelerations; finally fhf shows only an insignificant reaction to acidemia but is decreased (from 135 to 110 bpm) overall with the course of time. Therefore the 3 characteristics of the fhr might be ranged according to their decreasing sensitivity to acidemia as follows: 1) fetal microfluctuation, 2) oscillation amplitude and 3) mean frequency. The 3 components of the fhr were used to invent and apply a score named the WAS score. This score increases the association between the actual pHUA values and the activity of the fetal heart. The 3 variables of the fhr mentioned above were rated differently; the 3 factors necessary to achieve this were computed electronically using an optimization program. The result is the WAS score: WAS=mean [frq*f(f)(v(j)) * micro*f(m)(v(j))/oamp*f(a)(v(j))](j=1,30). Using the last 30 min of delivery the correlation coefficient r of this score with pH(UA) reaches 0.645, P<< 0.001. The regression is linear in our 484 cases. CONCLUSIONS: Microfluctuation is the most sensible variable of the fetal heart followed by the oscillation amplitude and mean frequency. The WAS score offers the best correlation with the actual pH values measured in arterial umbilical blood.

Fetal heart rate patterns during delivery complicated by hypoxia and acidosis - a computer-aided analysis.

BACKGROUND: Using the naked eye, evaluation of fetal heart-rate (FHR) patterns remains difficult and is not complete. Computer-aided analysis of the FHR offers the opportunity to analyse FHR patterns completely and to detect all changes possibly due to hypoxia and acidosis. It was the goal of this study to make these hypoxic changes of the FHR visible and to compare them directly with normal tracings. METHODS: During a period of 11 years the FHR signals (i. e., R-R intervals of the F-ECG) of 646 fetuses were recorded simultaneously also by a computer. The computer files were analysed thereafter, i. e., the obtained results had no immediate influence on the clinical management itself. To enter the study all fetuses must have been delivered by the vaginal route - in consequence without a significant loss of FHR signals. During forceps or vacuum deliveries recordings were continued. If necessary a new electrode was inserted. Recordings of fetuses with chorioamnionitis, tracings of malformed neonates and tracings shorter than 30 min were also excluded. No additional drugs were given to the mother during the time of recording. Thus 484 recordings were left. In this study only the last 30 min of each record were analysed off-line using our own computer programs written in MATLAB. Only 3 parameters were determined electronically: i) the mean fetal frequency (FRQ, bpm), ii) the number of turning points (N/min, see Fig. 1) in the FHR, which we called 'microfluctuation' (MIC) and iii) the oscillation amplitude of the FHR (OA, bpm, Fig. 1). Routine measurements of the acid-base variables from umbilical arterial (UA) and venous (UV) blood were performed using RADIOMETER equipments (ABL500) and trained personnel. To compare acidotic and non-acidotic FHR tracings, 2 pH groups were chosen: fetuses with a small non-acidotic "pH window" (pHUA=7.290-7.310) and 5 fetuses with severe acidosis, i. e., pHUA values <= 7.103. RESULTS: Using this narrow "pH-window" (7.290-7.310) shows that FRQ, MIC and OA belong together. The 3 variables are strongly associated with each other in a linear manner. All 3 correlation coefficients (r) are highly significant (P<0.001); in this context all 3 regressions seem to be linear. The mean pHUA in this special group amounts to 7.300±0.008 (N=50). In severe fetal acidosis (mean pHUA=7.051±0.060, N=5) MIC and OA are diminished significantly (P << 0.001) whereas the mean frequency is increased (ca.+6 bpm). Microfluctuation (MIC) seems to be the most sensible FHR parameter for the diagnosis of hypoxia and acidosis followed by OA and the fetal frequency niveau. CONCLUSIONS: In non-acidotic fetuses MIC, OA and FRQ belong together and their association can be described by the 3 basic principles presented above. Fetal reaction patterns during hypoxia and severe acidosis differ significantly when compared with tracings of non-acidotic fetuses. Computer-analysis reveals that MIC is the most sensitive FHR variable concerning hypoxia and acidosis followed by OA and the mean FRQ niveau. (Some of the acidotic recordings together with the WAS-score can be observed in full length at www.fhr-monitoring.org.).

Basic principles of the foetal heart rate during delivery without hypoxia and acidosis.

BACKGROUND: Using naked-eye evaluation of foetal heart rate (FHR) patterns remains difficult and is not complete. Computer-aided analysis of the FHR offers the opportunity to analyse the FHR completely and to detect all changes due to hypoxia and acidosis. In order to better understand these changes FHR patterns in non-acidotic foetuses should be studied by first separating FHR into (i) basal FHR (baseline) and (ii) all decelerations. METHODS: The FHR signals (i.e., R-R intervals) of 637 fetuses were recorded by a computer. To enter the study all foetuses must have been delivered by the vaginal route - in consequence without a significant loss of FHR signals. During forceps/vacuum delivery recordings were continued. If necessary a new electrode was inserted. Recordings of foetuses with chorioamnionitis and tracings of malformed neonates and tracings shorter than 30 min were excluded. No drugs were given to the mother during the time of recording. Thus 484 recordings were left. In this study only the last 30 min of each record were analysed using our own programmes written in MATLAB. 3 parameters were determined electronically: (i) the mean frequency (FRQ, bpm), (ii) the number of turning points (N/min), which we called 'microfluctuation' (MIC) and (iii) the oscillation amplitude (OA, bpm) (see Fig. 2). Computer analysis of the FHR offers the opportunity to separate baseline FHR from deceleration patterns using appropriate algorithms rearranging and sequencing all baseline segments (or all decelerations) to a new file. Therefore each of the 2 new files contains only one category of the FHR: baseline segments (with accelerations) only or decelerations only (Fig. 1). 1 min was always taken as the reference time interval. In order to exclude foetal hypoxia and acidosis during the last 30 min, a small pHUA -'window' was chosen (7.290 up to 7.310) using acid-base variables from umbilical arterial (UA) blood measured soon after delivery with RADIOMETER equipment (mainly ABL500) by trained personal. RESULTS: Overall 14,520 min of the 484 foetuses were analysed by measuring in UA blood (X ± SD):pH=7.262 ± 0.065, pCO2 = 53.7 ± 8.8 mmHg, BEEcf,ox=-3.3 ± 2.5 mmol/l and sO2 = 23.9 ± 12.4%. In the whole sample and in non-acidotic (pHUA: 7.29-7.31) foetuses (N=50) there exist 3 fundamental principles which combine the 3 FHR variables under investigation: (I) MIC is strongly associated (r=0.631, P << 0.0001) with mean FRQ (bpm): in ca. 40% of all foetal heart beats a turning of the vector occurs (Fig. 4). (II) MIC is associated also with OA (r = -0.480, P << 0.0001); this regression is non-linear: Smaller band-widths are associated with increased MIC [OA = 0.0027 × MIC2 - 0.56 × MIC + 71 (see Fig. 5)]. (III) In non-acidotic foetuses lowering of the mean frequency niveau is associated with increased OA (overall: r = -0.349, P<< 0.0001); Using baseline segments only: r = -0.283, Nmin=844, P<0.0001. This regression is linear again: OABL = -0.445 × FRQBL + 94.1. Overall a Delta frequency (ΔFRQ) of + 10 bpm leads to a ΔOA of -4.1 bpm. These 3 rules are valid in isolated baseline segments as well as during artificially isolated deceleration patterns. CONCLUSIONS: FHR is a unit and should be analysed by computer-aided technologies as a unit. MIC, OA and FRQ belong together and their interaction can be described in non-acidotic foetuses by the 3 basic principles given above. Standard FHR tracings remain untouched.

The clinical significance of base excess (BEB) and base excess in the extracellular fluid compartment (BEEcf) with and without correction to real oxygen saturation of haemoglobin.

BACKGROUND: Besides actual pH, base excess [ctH (+)(B) (mmol/l)] is of major importance since it is meant to reflect lactate acidosis due to foetal hypoxia; In vivo BE (B) is not independent from pCO (2). Independence is achieved by using the extended extracellular fluid (Ecf) for dilution of haemoglobin (cHb (B)) thus reducing cHb (B) to cHb (B)/3 (in the foetus to cHb (B)/4). Correction of ctH (+)(B) from the normally low foetal oxygen saturation by reoxygenation of Hb increases ctH (+)(B), resulting in 4 different variables: ctH (+)(B,act) (=BE (B)), ctH (+)(Ecf,act) (standard BE), ctH (+)(B,ox.) and ctH (+)(Ecf,ox). 3 questions arise: (i) which variable is most appropriate for perinatal acid-base studies? (ii) are there clinical advantages for using BE when compared with actual pH (UA), and (iii) what are the thresholds of the BE parameters? METHODS: The Apgar 1 min and the WAS score were used thus measuring neonatal vigour and FHR characteristics during the last 30 min of 475 foetuses all delivered by the vaginal route. FHR was evaluated by computation of the WAS index . The WAS index refers to (FHM*W1)*(OZF*W2)*(OZA*W3)(-1) where fhm is mean heart frequency (bpm), ozf denotes the number of turning points (N/min) and oza refers to the oscillation amplitude/min (bpm). The weighting functions W1, W2 and W3 were computed using optimizing software. The WAS score denotes the mean of the WAS indices of the last 30 min of delivery. BE was computed according to the van Slyke/Henderson-Hasselbalch equation using pH and pCO (2) measurements; sO (2) (%) for HbF was determined according to Ruiz et al. . RESULTS: In vivo foetal ctH (+)(B,act) (UA) is closely correlated with pCO (2). UA: r=-0.288, P<10 (-4), N=475: whereas ctH (+)(Ecf,act) (standard BE) becomes independent from pCO (2): r=-0.0068, P=0.881. In UA blood there is no independence of the 2 blood gases pCO (2) and pO (2): both are inversely correlated: r=-0.291, P<<10 (-4). pO (2) shows no correlation with ctH (+)(B,act) (r=-0.074, P=0.105) but correlates well with ctH (+)(Ecf,act): r=-0.1722, P=0.0002. The Apgar score (1 min) is best correlated with pH (UA) (r=0.4078, P<10 (-4)(,) Spearman's rho=0.307, P<10 (-4)). Correction of ctH (+)(B,act) or ctH (+)(Ecf,act) to 100% oxygen saturation always leads to higher coefficients. Using: ctH (+)(B,ox), ctH (+)(B,act), ctH (+)(Ecf,ox) and ctH (+)(Ecf,act): rho=0.2597, 0.2394, 0.1838 and 0.1763, respectively; P all <10 (-4). The same holds true for Apgar 5 min: rho=0.2307, 0.2168, 0.1811 and 0.1771, respectively (P<10 (-4) for all). The WAS score is closely correlated with pH (UA): r=0.656, P<<10 (-4), N=475. The correlation with the 4 variables under investigation: ctH (+)(B,ox), ctH (+)(B,act), ctH (+)(Ecf,ox) and ctH (+)(Ecf,act) leads to r=-0.587, r=-0.565, r=-0.437 and r=-0.427, respectively (P<10 (-4) for all). The threshold of standard BE (ox.)(=ctH (+)(Ecf ox)) in 390 acidotic term infants with still good outcomes is -14.0 mmol/l. CONCLUSIONS: Actual pH (cH (+)) offers the closest correlation with 2 essential clinical parameters: FHF and Apgar scores; the advantages of ctH (+)(B) and ctH (+)(Ecf), are not self-evident; if determination of the metabolic component becomes necessary standard BE, (ctH (+)(Ecf)) should be used with correction to 100% oxygen saturation (ctH (+)(Ecf,ox.)) of haemoglobin (HbF), because this quantity (after pH (UA)) correlates best with clinical indices. However if the 'correction' is omitted the difference seems clinically irrelevant.

[How to define a non-reassuring FHR tracing online]. / Was ist ein "pathologisches" CTG?

BACKGROUND: Sub partu foetal heart-rate (FHR) patterns are difficult to evaluate. Until now we have no numerical criteria to reliably define what is a non-reassuring or even a 'pathological' FHR tracing. Computer-aided FHR analysis using the new WAS score offers the unique opportunity to assess numerical boundaries for these definitions. METHODS: Direct FHR tracings of 475 foetuses, all delivered by the vaginal route, were recorded electronically and the last 30 min of each tracing were used for computation of the WAS score. The WAS score refers to FHR frequency, microfluctuation, and oscillation amplitude per minute. Acid-base and blood-gas analyses were performed in blood of the umbilical artery (UA) and vein (UV) immediately post partum. pH (UA) and the WAS score were correlated (r) and the 4 variables sensitivity, specificity, the false positive rate (FPR) and the false negative rate (FNR) were determined. ROC plots for different threshold pH (UA) values were performed. RESULTS: pH (UA) and the WAS score are normally distributed: mean pH (UA)=7.263+/-0.064 and mean WAS score 2.78+/-0.81, respectively. The correlation coefficient, r amounts to 0.657, P<<10(-4). Using the mean pH (UA) and the mean WAS score leads to a sensitivity and specificity both of 72% with an FPR and FNR both of 28%. Using a WAS score of 1.816 and the threshold pH (UA) of 7.122 sensitivity becomes the first time 100% (FNR=0%) and FPR decreases to 10.7%. These 2 values are chosen to separate a normal (score >1.816) from an abnormal (non-reassuring) CTG (score < or =1.816). According to this definition newborns with a reassuring (normal) FHR tracing (N=417) have a pH (UA)=7.275+/-0.055, pCO (2)=52.3+/-7.9, BE (Ecf,oxy.)=-3.0+/-2.3, sO (2)=24.9+/-12.3 with an acidotic risk (pH (UA) <7.100) of 0% and APGAR 1 min <7=0.96%, respectively. Neonates with an abnormal (non-reassuring) FHR tracing (N=58) present a mean pH (UA)=7.178+/-0.066, pCO (2)=62.6+/-9.6, BE (Ecf,oxy.)=-5.4+/-2.6, sO (2)=18.3+/-12.0 and an acidotic risk of 6.9%. No neonate in this group was severely depressed (APGAR 1 min < or =3). Separation of the true positive (pH (UA) <7.122) from the false positive (pH (UA) > or =7.122) cases yields 10 babies with a mean pH (UA)=7.084+/-0.053, pCO (2)=71.8+/-10.7, BE (Ecf,oxy.)=-8.4+/-2.0, sO (2)=20.2+/-14.5 and an acidotic risk of 44.4%; in this group also not one baby was severely depressed (APGAR 1 min < or =3) but 3 were already moderately affected (<7 after 1 min). No infant scored <7 after 5 min. There must be a lower limit for the definition of a true 'pathological' FHR tracing; this boundary should not be identical with the threshold pH value where hypoxic injuries in term infants usually commence. For FHF this is a WAS score of 0.630 and a threshold pH (UA) of 7.075. CONCLUSION: Using sensitivity, specificity, FPR and FNR of the FHR sub partu, it is possible to discriminate online a normal (reassuring) from an abnormal (non-reassuring) FHR tracing by a simple computer-aided procedure which we call WAS scoring.

Sensitivity, specificity, receiver-operating characteristic (ROC) curves and likelihood ratios for electronic foetal heart rate monitoring using new evaluation techniques.

OBJECTIVE: Hypoxia and acidosis adversely influence many foetal organ functions. We wanted to know how foetal heart rate (FHR) patterns are mirrored by the fetal acid-base status and if they could serve for predicting the actual pH in umbilical artery (UA) blood. For this purpose we condensed the FHR phenomena into one figure which was to be used as a testing variable and to analyse the performance of the new testing procedure. METHODS: The direct FHR signals of 475 foetuses were stored in a computer and analysed offline (MATLAB). All foetuses were delivered by the vaginal route thus without a significant loss of signals. The last 30 min of each recording were used. Acid-base variables and blood gases were determined in cord blood (UA and UV) using RADIOMETER equipments. Three variables of the foetal heart rate (FHR) were computed for each minute: oscillation amplitude [oza (bpm)], microfluctuation [ozm (N/min)] and mean frequency [fhm (bpm)]. These variables were combined to a new index, which we call the WAS index: WAS(T)=FHM(T) x OZF(T)/OZA(T). Using optimisation programmes this index was tailored to actual pH, UA leading to the novel, adapted index: WAS(T)=[FHM(T) x GFHM] x [OZF(T) x GOZF] x [OZA(T) x GOZA]-1,where GFHM, GOZF and GOZA denote three mathematical functions comparable to boundaries in discontinuous scoring-procedures, e. g., the APGAR score. The mean of the WAS index for the last 30 min of delivery is called the WAS score and is used as a discriminator in the testing procedure. WAS score and measured pHUA-values were submitted to correlation and linear regression analysis. Sensitivity, specificity, likelihood ratios, and post-test probabilities were computed including their 95% confidence intervals (CI). A ROC analysis was performed by applying different thresholds for pHUA. RESULTS: pH and WAS score are normally distributed in this sample. The correlation coefficient (r) for pHUA and the WAS score amounts to 0.657, P<<10 (-4). Using ROC plots the area under the curve (AUC) is steadily increased with decreasing pHUA reaching 1.0 for pH 7.0 indicating excellent test accuracy. The AUC for pHUA=7.100 is already 0.963+/-0.066, 95% CI (0.942-0.978), P<0.001. The positive likelihood ratios (+LR) far exceed 10.0 when lowering the threshold for pHUA. Aiming at a sensitivity of 100% the discriminatory power of the test becomes clinically an optimum when using a discriminator of 1.816 and a threshold pH of 7.122: Sensitivity=100%, specificity=89.3%, FNR=0%, FPR(%)=10.7% and AUC=0.958+/-0.049, 95% CI (0.936-0.974), P<0.001. CONCLUSIONS: Computer-aided evaluation of FHR patterns leads to a novel index (WAS score) which predicts foetal acidaemia with a high level of accuracy. Therefore online WAS scoring is proposed as an ancillary test procedure for future evaluation of FHR patterns. The conventional EFM remains untouched.

[A new approach to quantitative electronic foetal heart-rate analysis]. / Ein neuer Weg zur quantitativen elektronischen CTG-Analyse.

BACKGROUND: Recently it was found that a significant correlation exists between the variables of the foetal acid-base balance (ABB) and the parameters of the foetal heart rate (FHR). This dependency can be used for diagnostic purposes. Until now FHR could be evaluated off- and online by computer using scoring procedures, i. e., discontinuous methods, which need considerable computational efforts since FHR must reliably be separated into baseline (BL), decelerations and accelerations. Therefore, the question must arise whether a continuous and less cumbersome evaluation of individual FHR-parameters might lead to even better results? METHODS: The last 30 min of 465 direct recordings of foetuses all delivered by the vaginal route were stored in a computer and analysed offline using our own MATLAB programmes. Five variables were computed for every single minute: The microfluctuation, the oscillation amplitude, the mean frequency, the sum of the absolute differences of time periods and the sum of the absolute differences of frequencies. In this paper the last two variables will be abbreviated 'total sums'. All minutes of a FHR tracing were treated equally i. e. there was no separation anymore between BL and decelerations (accelerations). In order to analyse the physiological intercorrelation of the five variables mentioned above a 'pH window' was chosen between 7.275 and 7.325 [7.275< or =pH, (umbilicalartery (UA)< or =7.325]. Thereafter, the influence of hypoxia and acidosis on the five variables was evaluated. According to the results obtained two of the five variables, the 'total sums', were not further analysed. Using the remaining variables 'frequency', 'oscillation amplitude' and 'microfluctuation' a new index, the WAS index, was created. This index offers the opportunity to evaluate the FHR continuously using 'coding lines' for each of the three parameters. The WAS index was designed according to the FHR characteristics of the awake (Wach), acidotic (Azidotisch) (pH, UA=ca. 7,000) and sleeping (Schlafend) foetus. Using the last 30 WAS indices covering the last 30 min of a single FHR tracing, a WAS score and the corresponding prognostic pH value was computed. These prognostic pH values were compared with the measured pH values of UA blood using again correlation analysis. RESULTS: Without any hypoxia and acidosis (pH, UA window) the five FHR variables are closely correlated with each other. Accepting minutes with decelerations only, the correlation between the 'total sums' and the remaining three parameters vanishes. Accepting hypoxia and acidosis (pH, UA > or =6.960) oscillation amplitude now offers the closest correlation with actual pH, UA (r=-0.440 p<<10 (-4)) followed by microfluctuation (r=0.224, p<0.001) and frequency (r=0.056, P: n. s.). This pattern is obviously due to the retention of all decelerations in the FHR tracings. The 'total sums' show less close correlations with pH, UA and BE(oxy) when compared with microfluctuation and oscillation amplitude (SumPER vs. pH, UA r=-0.125, p<0.001 and SumFRQ vs. pH, UA r=-0.154, p<0.001). All five variables under investigation show a better correlation with pH, UA when compared with BE(oxy) UA. The WAS score computed (mean) for the last 30 min of delivery leads to close correlations (p<<10(-4)) with all variables of the foetal ABB: pH, UA r=0.608; BE(oxy) r=0.535, pCO(2) r=-0.469 and sO(2) r=0.259. The median WAS score amounts to 0.176, the mean to 0.174+/-0.023; it is normally distributed in this sample. CONCLUSIONS: FHR characteristics in different foetal behavioural states offer the opportunity to design a new index, the WAS index, which shows close (p<<10(-4)) correlations with all variables of the foetal ABB. Thus, the pH value in cord blood can be predicted within clinically reasonable limits. The qualitative CTG analysis remains untouched.

Outcome measures in perinatal medicine - pH or BE. The thresholds of these parameters in term infants.

BACKGROUND: Hypoxia and severe foetal acidosis may lead to cerebral injuries and multi-organ failure. Base excess (BE) and actual pH determined in umbilical artery (UA) blood are valid parameters to measure (metabolic) acidosis. Until now there is no consensus worldwide as to which of the two parameters should preferably be used and which thresholds should be applied: the thresholds 7.000, 7.100 and 7.200 are discussed for pH,UA and - 16.0 mmol/l for BE,UA, respectively. The aim of this study was to redefine these thresholds for term infants taking into account the entire spectrum of complications in early neonatal life and to compare the diagnostic power of both variables under investigation. METHODS: 512 foetuses all with a pH,UA < 7.100 were enrolled in this retrospective study. In this paper only term infants (n = 398) without major malformations were analysed. In order to quantify foetal morbidity and mortality an asphyxia complication (AC) score was designed using the Apgar score after 1 min and all possible complications encountered in the neonate until discharge (mainly from the NICU). Routine acid-base (AB) measurements (Radiometer, Copenhagen) were available (UA and UV blood) in nearly all cases. In this context, BE was corrected to 100 % oxygen-saturation (BE (oxy.)) using the (calculated) actual saturation (BE (act.oxy.)) of haemoglobin in each case because sO2 (%) becomes very low in severe acidosis. Oxygen saturation (%) was determined according to Ruiz et al. using haemoglobin F. Matched pairs (pH,UA > 7.10) were defined using the variables (i) gestational age, (ii) birth weight (+/- 100 g), (iii) sex, and (iv) parity. RESULTS: Analysing term infants with a definitely good outcome (n = 389) led to the following AB variables in UA blood: 10 % had a pH < 7.000; the lowest pH was 6.717, the highest pCO2 was 118 mmHg and the lowest BE(oxy.) amounted to - 32.4 mmol / l. 90 % of these neonates had an oxygen saturation that was still > 3.0 %. However, early neonatal morbidity due to hypoxia and acidosis was remarkable; therefore these AB variables could not serve as thresholds. Relying on clinical criteria, no acidotic morbidity was accepted, except for respiration disorders in early neonatal live (C score) together with Apgar scores down to 4 after one minute. This led to an AC score of < or = 8 (n = 378). In this group the lowest pH,UA was 6.890 and BE(oxy.) was - 25.1 mmol / l, respectively. In order to have a "buffer zone" of 10 % in each variable distribution (10 (th) / 90 (th) percentile). the following thresholds could be evaluated in UA blood: pH: 7.000, pCO2: 84 mmHg, sO2: 3.0 % and BE(oxy.) - 20.0 mmol/l. Only 13 (matched) neonates suffered from an AC score > 8 and had all pH values > or = 7.100 (3.3 % overlap). These foetuses seemed to be not at risk concerning injuries and severe complications. In UA blood the actual pH always offers closer correlations with the AC score when compared with the BE (oxy.) value. CONCLUSION: Thresholds in UA blood for pH, pCO2, sO2 and BE(oxy.) in term-infants are: 7.000, 84 mmHg, 3.0 % and - 20 mmol/l, respectively. Delivery of an otherwise healthy baby without getting in touch with these thresholds seems to be safe both for the baby and the obstetrician. In addition, severe neonatal depression (Apgar 1 min: 0 and 1) is usually avoided (0 / 398). BE(oxy.) does not offer a higher diagnostic power when compared with actual pH.

How to determine and use base excess (BE) in perinatal medicine.

BACKGROUND: Foetal hypoxia may lead to multi-organ failure and cerebral injury. Usually this process is accompanied by severe metabolic acidosis. The base excess (BE) determined in umbilical artery (UA) blood is the most appropriate parameter to evaluate metabolic acidosis. The correct determination of BE therefore is of paramount importance both for the jeopardised foetus and the obstetrician in litigation. In blood, BE is dependent on the oxygen saturation [sO2 (%)] of haemoglobin (cHb). Due to the normally low foetal pO2 values in UA blood (median: ca. 18 mmHg) sO2 is low as well; therefore computational correction of BE to - by definition - 100 % oxygen saturation seems to be mandatory. This paper presents an analysis of this complex problem in obstetrics. METHODS: pH, pCO2, pO2 and cHb were measured in UA blood of 6 302 term infants delivered spontaneously using equipments from Radiometer (Copenhagen). BE was computed according to the equation of Siggaard-Andersen actually used in many blood-gas analysers. sO2 (%) was computed for HbF using the algorithm of Ruiz et al. . The numerical correction of BE was achieved with an equation given again by Siggaard-Andersen . APGAR indices after 1 minute were used. RESULTS: Median BE in UA was - 4.6 and the mean was - 4.9 +/- 3.0 mmol / L, respectively. Correction of BE (BEoxy.) to the actual (calculated) oxygen saturation (%) leads (always) to lower values: a median BE (oxy.) in UA of - 7.4 and a mean of - 7.6 +/- 3.2 mmol / L, respectively. There is no correlation between BE and sO2 in UA blood: r = 0.0078, p = 0.532, n = 6 302 (mean oxygen saturation: 27.7 +/- 18.3 % ). The median cHb amounted to 15.2 and the mean to 15.0 +/- 2.6 g %, respectively. The median delta-BE,UA(BE - BEoxy.) amounts to 2.74 mmol / L; the maximum delta-BE reached 5.2 mmol / L in this sample. Correction of BE to 100 % oxygen saturation based on the (calculated) real oxygen saturation (%) leads to significantly (p = 0.0099) higher correlations with the APGAR index (1 min) and pCO2 in UA (p << 10 (-4)) as well. CONCLUSION: Correction of BE in UA, i. e., correction of BE to 100 % oxygen saturation using the (calculated) actual oxygen saturation (%) of the blood sample is mandatory in perinatal medicine. Correction uniformly leads to lower BE values (median: 2.7 mmol / L) and significantly higher correlation coefficients with important clinical variables (e. g., the APGAR index).

[Quantitative Cardiotocography--what does it look like and what can we expect]. / 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.

[Outcome measures in perinatal medicine--pO2 and SO2. With remarks on pulse oximetry]. / Messgrössen in der Perinatalmedizin -- pO(2) und SO(2) -- Mit Anmerkungen zur Pulsoxymetrie.

BACKGROUND: Due to the outstanding pioneer work of Ronald E. Myers (Bethesda, Maryland) using term rhesus monkey fetuses we know for sure that hypoxia is the leading cause for brain damage and death when exposure occurs perinatally. He defined threshold values for oxygen content and time variables leading to death or cerebral injury. Years later pulsoximetry was developed for measuring fetal oxygen saturation (%) continuously. In this context the obstetrician wants to know: 1) what is the diagnostic potential of pO(2) (mmHg), SO(2) (%) and oxygen content (vol%) in umbilical blood? and 2) using these data could we ascertain fetal pulsoximetry which in addition uses the factor time. METHODS: In a sample of 7814 term fetuses, delivered in cephalic presentation by the vaginal route, actual blood gases and the variables of the fetal acid-base balance were determined in umbilical blood using equipments (BMS up to ABL 3) from RADIOMETER, Copenhagen. Measurements were done immediately post-partum by trained medical personal. Fetal oxygen saturation (%) for HbF was computed using the algorithm of Ruiz et al. Oxygen content (vol%) was determined according to Severinghaus using Hb values (g%) in each case. RESULTS: The median pO(2) in blood of the umbilical artery (UA) was 17.9 (mean: 18.8 +/- 8.3) mm Hg and in the umbilical vein (UV) 28.5 (mean: 29.3 +/- 9.2) mmHg, respectively. The median oxygen saturation (%) amounted to 24.8 (UA) and 60.9 (UV) using pO(2), pH and pCO(2) for computation in each case. The oxygen variable pO(2) showed no clinically important correlation neither with actual pH (r = 0.032, P = 0.005) nor with base excess (r = 0.047, P < 10 ( - 4)); the correlation with oxygen saturation (%) however was highly significant both for pH and base excess. Computational evaluation of the BOHR/HALDANE effect reveals that pH values of 6.9 are associated with 10 % oxygen saturation only in UA. P (50) values change dramatically with lowering pH values, i. e., acidosis. Oxygen content (vol %) offers no diagnostic advantages over oxygen saturation. Separation of the whole sample (N = 7814) according to the boundary of 30 % saturation in UA/UV blood leads necessarily to a big difference in saturation (DeltaSO (2)) but to an only very small difference in pH (DeltapH) and base excess (DeltaBE); thus the discriminatory power of SO(2) (%) is weak and clinically insignificant. CONCLUSIONS: For fetal surveillance only oxygen saturation (%) -- not pO(2) and oxygen content -- is a useful variable. Due to the BOHR/HALDANE effect the fetus is able to rapidly mobilize his oxygen reserves and thus to compete with hypoxia; acidosis makes sense in this context. The three oxygen parameters analysed so far offer less diagnostic power than actual pH and base excess.

[Measured quantities in perinatal medicine--the base excess]. / Messgrössen in der Perinatalmedizin -- der Basenexzess.

BACKGROUND: There are convincing data from neonatal studies that the base excess (BE, mmol/L) measured in capillary or cord blood offers special diagnostic and prognostic power in the new-born compromised by hypoxia. For computation of BE the hemoglobin concentration (Hb, %), the oxygen saturation (%) and the distribution of the fetal fluid compartments are necessary. Until now these three factors, which differ in the fetus when compared with adults, have not been taken into account using automatic blood gas equipment. This study therefore attempts to analyse and verify which BE will offer the best fit with the outcome conditions in the newborn. METHODS: Using a cohort of 7701 singletons delivered at term by the vaginal route in whom a blood gas analysis in cord blood together with Hb measurements were available and plausible, three BE values were computed: the ordinary BE (actual BE, according to Radiometer determinations), the BE corrected to the real oxygen saturation (BE,oxy) and the BE in the extracellular fluid compartment of the fetus (BE,ecff) using the algorithms of O. Siggaard-Andersen. Moreover, three different oxygen saturation curves for fetal Hb (HbF) were applied, namely those of Zander et al., Hellegers and Schruefer and Ruiz et al. (Severinghaus). The prognostic potential of the different BE values was analysed using a correlation with the APGAR-score after 1 min, the sum of the APGAR indices after 1 and 5 min, and additionally with the fetal heart frequency (FHF) of the last 30 min ante-partum quantified by a score electronically in a group of 342 fetuses. RESULTS: The median of the actual BE in umbilical artery blood amounted to -4.9 mmol/L. Correction to the real oxygen saturation of the blood sample leads to a median of -7.7 mmol/L. Using three different oxygen saturation curves and thus taking into account HbF reveals little influence on the numerical values of BE. However, application of the true distribution of fetal fluid compartments in the evaluation of BE (BE,ecff) leads to a significant reduction of the numerical value of BE (median = -3.2 mmol/L). Computational correction of BE using the real oxygen saturation (%) in each fetus leads to a important and highly significant increase of the correlation (r and rho) with the APGAR indices. The correlation with the FHF score also increased but failed to reach significance. CONCLUSIONS: Our data show that, in perinatal medicine, a computational correction of BE according to the real oxygen saturation of the blood sample is mandatory. An algorithm for HbF should be used. The BE in the extracellular fluid compartment does not fit to reality. The determination of the Hb concentration in the umbilical blood of each fetus is essential since its variability is higher than expected. In legal controversies the computational origin of BE should be documented and carefully regarded.

[Measured quantities in perinatal medicine--the pCO(2)]. / Messgrössen in der Perinatalmedizin -- das pCO(2).

BACKGROUND: For many years the interest of the obstetrician and neonatologist was focused on the base excess (BE) in umbilical artery (UA) blood. Otherwise, the pCO (2) (mmHg) value which is necessary to compute BE values played only a marginal role in our diagnostic evaluation of the fetus/newborn. This is especially true for pCO (2) values determined in umbilical venous (UV) blood and the feto-matemal interrelations of blood gases and the variables of the acid-base balance (ABB) in the fetus and the mother. In this study we have reevaluated the importance of fetal pCO (2) measurements and analysed the influence of pCO (2) on the actual pH in UA blood, our leading parameter. MATERIAL AND METHODS: The variables of fetal ABB and the actual blood gases measured in UA and UV blood of 7804 neonates, delivered at term without major malformations in vertex presentation by the vaginal route, were used. Several generations of acid-base equipments from RADIO-METER (Copenhagen) were applied (BMS3 - AMS3). In addition arterial acid-base measurements in 101 parturients were performed immediately after delivery for analysis of feto-maternal acid-base dependencies. The software system JMP (SAS, Carolina, USA) and a Think-Pad (IBM) were used for computation. RESULTS: The median pCO (2) in VA blood was 50.5 and in UV blood 36.0 mmHg, respectively. Both distributions are normal. The AV difference amounted to 13.6 mm Hg. The correlation between pCO (2), UA and the actual pH, UA is highly significant (r = -0.720, P << 0.0000). The correlation between pCO (2), UV and the pH, UA is still highly significant (r = -0.560, P<< 0.0000). Analysing only fetuses with an APGAR index of 9 or 10 after 1 min (N = 6304) reveals the important physiological influence of pCO (2), UV on actual pH, UA (r = -0.543, P << 0.0000). Moreover there exists an inverse and also highly significant dependency of pCO (2), UV and pO (2), UV in vigorous infants (P << 0.0000) indicating better fetal oxygenation; this cannot be explained by the weight of the placenta or other feto-placental measures. Taking into account maternal (N = 101) respiration (arterial pH, pCO (2), pO (2)) during the last minutes of delivery leads to convincing evidence (P << 0.000) that pCO (2), UV is determined by maternal pCO (2) and thus by the breathing habits of the future mother (r = 0.514 for pCO (2), UV and arterial pCO (2)). CONCLUSIONS: At the moment of delivery, where we usually determine actual pH and other parameters of the fetal ABB in order to control our obstetrical management, mother and fetus behave functionally as a unit; this fact deeply influences the predictive value of all fetal AB measurements (including BE, UA). This holds true also in fetal pathology. Maternal respiration turns out to be an important co-variable. In legal controversies the feto-maternal associations of blood gases and their implications must be considered carefully.

[Comments on a report by the BQS on obstetric quality indicators]. / Stellungnahme zu einem Gutachten der BQS über geburtshilfliche Qualitätsindikatoren.

When re-evaluating an epidemiologically oriented BQS expertise concerning the quality indicators in obstetrics, we examined three essential methods in obstetrics to verify their scientific evidence and their clinical relevance. In doing so we ascertained that recording the fetal heart rate sub part, analysing fetal blood and determining the blood gas of the umbilical blood are entirely appropriate quality indicators during delivery from a clinical and medical point of view -- although to varying extents. Above all, these three indicators prove to be essentially better evidence-based than described in the BQS expertise. The search for an optimum of evidence-based data in medicine ends in certain fields such as, for example, in obstetrics there where no further randomized studies can be carried out for methodological or ethical reasons. This lack of evidence for the optimum grade I which can clearly be understood from an epidemiological point of view, however, should not lead to an evidence nihilism that fails to accept or admit existing evidence of the weaker grades II and III.

[CTG: microfluctuation]. / 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.

[Quantitative CTG appraisal sub partu with a new CTG score: diagnostic significance of the parameters of the acid-base balance in umbilical blood?]. / Quantitative CTG-Bewertung sub partu mit einem neuen CTG-Score: Wie gut sind die Korrelationen mit den Parametern des fetalen Säure-Basen-Haushaltes im Nabelschnurblut?

BACKGROUND: As a role, the severity of "CTG pathology" in acute or chronic fetal hypoxia could only be registered but not quantified exactly by visual examination. For this reason, the term "CTG pathology" has not been unequivocally defined. The objective of the present study was to describe the dependence of fetal heart rate phenomena on the parameters of the acid-base balance quantitatively and to subject the latter to statistical analysis. METHODS: The last 120 minutes of a total of 411 interference-free cardiotocograms directly registered intra partum (HP, 2 cm/min) were evaluated in terms of the visual appearance of CTG: the frequency level and the fluctuation of every single minute and the deceleration-area sum were considered for 30 CTG minutes per fetus. A new CTG score was conceived which envisages six points for the mean frequency according to specific definitions, three points for the deceleration-area and further six points for the fluctuation (long-term variability). The heart rate data and clinical factors were analyzed off-line using parametric and non-parametric test procedures with special programs (FORTRAN) on an IBM system (6150). Besides the pH values in the umbilical arterial and venous blood, direct measurements of blood gases (pO(2), pCO(2)) were also available in 113 cases, so that the base excess (mmol/l) and the oxygen saturation (%) could be calculated according to known algorithms. RESULTS: For the last 30 minutes ante partum, the CTG score correlates highly significantly (P << 10(-4)) with the actual pH value in the umbilical arterial blood (r = -0.6002). The correlation with the base excess is better (r = 0.642, P << 10(-4)), whereas the correlation with the directly measured pCO (2) is weaker (r = 0.587). Such strict correlations could not be demonstrated for oxygen saturation in the umbilical arterial or umbilical venous blood (r = -0.258, P = 0.0057 and r = -0.308, P = 0.0009). CONCLUSIONS: The good correlations of the variables of the fetal acid-base balance with the CTG phenomena registered with the score can be used for clinical purposes. However, analysis of the CTG with the naked eye is not practically feasible for the obstetricians; it must therefore be done per computer. Quantitative CTG analysis has created the perspective of a promising new method for fetal monitoring sub partu.

[Computer-assisted analysis of intrapartum cardiotocodynagraphs]. / Computerassistierte Analyse von intrapartalen Kardiotokogrammen.

OBJECTIVE: To develop a numerical index by quantifying characteristic cardiotocography parameters in order to determine the intrauterine state of the fetus sub partu with sufficient accuracy to improve the diagnostic potential of cardiotocography. This score is then computerized for offline and online analysis. METHODS: The last 120 minutes of 406 directly recorded intrapartal cardiotocograms (CTG) were evaluated with a magnifying glass on the basis of conventional criteria. The mean basal frequency, the amplitude and the oscillation frequency of each individual baseline minute, the decelerations with depth, duration and type classification as well as the accelerations were determined. The Apgar score and the measurements of blood gases in the umbilical arterial and venous blood served as outcome parameters. The actual pH in the umbilical artery (UA) was the key variable. The newly developed CTG score was converted into a complex programming language after meticulous statistical testing and prepared for offline and online use. RESULTS: A score which is based on the CTG characteristics basal frequency level, baseline fluctuation and total decelerations area was developed on the basis of about 40 000 baseline minutes and more than 8 000 analysed decelerations from 406 fetuses which were all vaginal deliveries with a rate of acidosis (pH,UA < 7.100) of 9.8 % (deliberate selection). This score correlates highly significantly (r = -0.5752) with the actual umbilical arterial pH (p < 0.001). The correlation with the Apgar score (1 min) is r = -0.398, p < 0.001. The positive likelihood ratio (score 9) is 11.0 (95 % confidence interval 7.4-16.5) indicating that the test is very reliable. The score could be prepared for offline analysis of electronically registered CTGs with the assistance of a mathematician, so that the obstetrician's "eye work" can be dispensed with entirely. This program written in "C" also enables online evaluation of fetal heart rate patterns over time and a representation of the output parameters with acoustic and optical warning display options appropriate for the delivery room. CONCLUSIONS: Quantitative registration of fetal heart rate phenomena during delivery can be accomplished successfully by means of a score. The score correlates highly significantly with the actual pH value (UA) and the Apgar score (1 min). It is suitable both for offline and online analysis of intrapartal CTGs, and offers the prospect of quantitative fetal online monitoring.

[Can subpartal fetal acidosis be avoided? Investigations on the complex causes of intrauterine asphyxia]. / In welchem Umfang ist die subpartale fetale Azidose vermeidbar? - Untersuchungen zum Ursachengefüge der intrauterinen Asphyxie.

OBJECTIVE: The extent to which faulty medical treatment and defective apparatus are concomitant causes for the development of subpartal acidosis was investigated in a retrospective study. At the same time, the incidence of acidosis in the Lippe-Detmold Hospital, Department of Gynaecology and Obstetrics, its morbidity and mortality were analysed. METHODS: Data from all case histories of neonates with acidosis (pH in the umbilical artery < 7.100) who were born between 1 st January 1992 and 31 st December 1998 at the Department of Gynecology and Obstetrics at the Lippe-Detmold Hospital were evaluated electronically. Analytical measurements of blood gases (pH, pCO 2 and pO 2 ) in umbilical artery and venous blood were available from all cases. The base excess was corrected by computations according to Siggaard-Andersen and R. Zander for the actual oxygen saturation. The delivery cardiotocograms (CTG) were appraised qualitatively. Equipment defects, mistakes on the part of doctors and/or midwives (including the head of the department) were recorded after critical analysis of each individual case and documented in accordance with a key. The neonatal data were taken from the files of the paediatric division of the hospital (head of the department Dr. K. Wesseler). RESULTS: In seven years under report, 9.876 babies were born, 156 (1.58 %) of whom showed a pH of less than 7.100 in the umbilical arterial blood. The mean actual pH value was 7.047 +/- 0.058, and the oxygen-corrected base excess was - 16.3 +/- 3.2 mmol/l. Correction of the base excess resulted in a numerical lowering by about 2.0 mmol/l. The rate of premature births was 17.4 %. One newborn baby died of hypoxic shock (0.67 %). 94 % of these neonates could be discharged in a healthy condition. 4.6 % still showed symptoms on discharge. Disorders of respiratory adaptation were the most prominent feature in morbidity from acidosis (about 18 %). Only two babies showed neonatal convulsions. Renal, cardiac and haemostaseological complications were rarely observed. Only 5 (3.9 %) of the 128 neonates with available recordings did not show any pathological changes in the CTG. 26.4 % of all acidoses had to be designated as "pure fate". In a further 35 % medical mistakes could not be discerned. Consequently, 61.4 % of the acidoses had to be designated as "unavoidable". In the remaining roughly 40 %, inadequate cardiotocographical knowledge, inattentiveness, defective equipment etc. clearly played a causal role. In the severe cases (pH in the umbilical artery < 7.000), medical mistakes were much more frequent (50 %). CONCLUSIONS: Three-fifths of all subpartal acidoses in this study have a fateful nature, i.e. they cannot be prevented even by optimal professional management in good time. About two-fifths are avoidable if appropriate equipment and trained staff are available around the clock. Use of cardiotocography alone enables the threat of asphyxia to be detected in 97 % of the cases. The short-term prognosis of subpartal acidosis is good provided very low pH values (< 6.900) can be avoided. In perinatological studies, the base excess value should be corrected by computation. "Quality control" worthy of the name should include critical single-case analysis at least in severe acidosis.