The reliability of pH-values in fetal blood samples - A study of the second stage.

In 119 cases fetal blood analysis (FBA) was done in the last 15 minutes before birth together with blood sampling from the umbilical artery (UA) immediately after delivery before the first breath. Using the measured pH-values we investigated the relationship between these variables, in particular the degree of influence of considerable caput succedaneum on pH-values in peripheral blood. Our investigation was performed during the time just before delivery, when the disturbance of blood circulation in the presenting fetal part whuld have the highest influence on pH-values measured from peripheral blood samples. We kept in mind especially the critiques of FBA by WULF et al. [21] and ASSALI [2]. As other authors have concluded, we found a high degree of correlation between the pH evaluated by FBA and that determined in the umbilical artery blood. The coefficient of correlation was: pHact r=0.82 pHqu40 r=0.78. The relationship between the corresponding pHvalues in peripheral (FBA) and arterial (UA) blood is given in Fig. 1 a and Fig. 1 b. The correlation of quadrants showed for the actual pH as well for the pHqu40 p less than 0.01. As derived form this, a high degree of correlation between the pH-values can be seen. The mean pH-values were: (see article) 42 of the children had a severe or moderate caput succedaneum. Fig. 2a and 2b show the relationship between central and peripheral pH-values in these cases. Again a good correlation between the pH-values was observed as in the whole collective. The coefficient of correlation was: pHact r=0.78 pHqu40 r=0.79. Caput succedaneum seems to have only minimal influence on the pH of blood obtained from the presenting fetal part. These results lead us to conclude that blood sampling from the presenting fetal part in the second stage provides almost indentical pH-values as in the central fetal blood.     

Transcutaneous carbon dioxide measurements in the fetus during labor

Transcutaneous partial pressure of carbon dioxide (transcutaneous PCO2) was measured in 55 fetuses during labor with a carbon dioxide electrode applied to the fetal scalp by a suction ring. The application procedure was simple and reliable, with reapplication required only 0.6 times per patient. The transcutaneous PCO2 recordings were of good quality and were correlated to carbon dioxide tensions in the umbilical artery (r = 0.60, p less than 0.001) and vein (r = 0.69, p less than 0.001) as well as to capillary PCO2 obtained by fetal scalp blood sampling (r = 0.96, p less than 0.001). If fetal distress occurred, transcutaneous PCO2 was significantly higher than in the uncompromised fetus. Although transcutaneous PCO2 monitoring might be useful for surveillance of the fetus during labor, it must still be reserved for scientific purposes for the time being.     

Reliability of transcutaneous measurement of oxygen and carbon dioxide partial pressure with a combined Po2-Pco2 electrochemical sensor in the fetus during labor

A combined single electrochemical sensor designed to measure synchronously and transcutaneously oxygen partial pressure and carbon dioxide partial pressure (RADIOMETER prototype) was applied onto the scalp in 21 fetuses during labor. The values of tcPo2 respectively tcPco2 were compared with the values of fetal blood analysis (FBA) and blood from the umbilical artery (UA): Comparing the tcPco2 with the values of the FBA we found the values to be very consistent (r = 0.95, p less than 0.001). For the comparison of the tcPco2 with the values of the umbilical artery, the correlation coefficient was lower (r = 0.76, p less than 0.05). The transcutaneous measurement of Po2 as compared with the values of the fetal blood analysis was also quite accurate (r = 0.83, p less than 0.001). Looking at the values of the transcutaneous measurement during the expulsion of the fetus and its comparison with the values of the umbilical artery, it was an interesting finding that values of the transcutaneous estimation of Po2 were much lower in some cases and no statistical correlation was found (p greater than 0.05). We conclude that the combined electrochemical sensor for measuring tcPco2 and tcPo2 is a new additional tool for studying the physiology and pathophysiology of the fetus during labor, but as the accuracy of Po2 and Pco2 in the fetal blood is influenced by the progress of labor, the special characteristic of the transcutaneous measurement has to be taken into account when values are interpreted.     

Glue fixation of the tcPco2 electrode for fetal monitoring

tcPco2 monitoring on the fetal scalp potentially is a beneficial and additional new tool for the surveillance of the unborn child. During a clinical trial we investigated the tcPco2 monitoring using the glue fixation technique. A modified Severingshaus electrode was applied on a prepared area on the fetal scalp by means of an endoscope. The attempt of application was successful in 224 out of 245 cases, while reapplication was only necessary in 8 cases. The accuracy of the tcPco2 measurement using glue fixation was sufficient at both measuring temperatures (39 degrees C and 44 degrees C). The correlation coefficient comparing the data with the tcPco2 of the fetal blood was 0.74 respectively 0.81. The development of a caput succedaneum leads to higher absolute values of the tcPco2. When a caput succedaneum has developed in the measuring area the mean value of the tcPco2 is significantly higher (62.70 mmHg instead of 55.14 mmHg respectively 68.98 mmHg instead of 65.98 mmHg) at 39 degrees C respectively 44 degrees C. No significant influence of different preparation techniques of the measuring site has been found during this investigation. The glue fixation technique leads to a reliable recording of tcPco2 in the fetus during labor, when the electrode is placed in a central and not compressed position on the lower pole of the fetus. The disadvantage is the necessity of extensive training of the personnel and the large number of instruments, factors that will interfere with a more widespread use in clinical routine.     

Outcome of fetuses with lactic acidemia

Umbilical arterial lactate, pH, PO2, PCO2, and base deficit were measured at delivery of 468 live-born infants. The correlation between the 1-minute Apgar score and lactate (r = -0.34) was comparable to that between the 1-minute Apgar score and pH (r = 0.30). The multiple correlation coefficient between the 1-minute Apgar score and all five parameters combined (lactate, pH, PO2, PCO2, and base deficit) was 0.36. This was not significantly higher than the simple correlation coefficient for pH alone (0.30). Similar correlation coefficients were noted for the 5-minute Apgar score. The dividing point between normal and pathologic lactate levels was 3.70 mmol/L. A pH less than 7.20 and a lactate level greater than or equal to 3.70 mmol/L had the same sensitivity, specificity, and positive and negative predictive values for low Apgar scores (less than 7). While pH and lactate are equally correlated with fetal outcome, their combination with each other and with other blood gas parameters does not predict outcome better than either pH or lactate alone.     

Correlation between transcutaneous pCO2 and the corresponding values of fetal blood--a study at a measuring temperature of 39 degrees C

Continuous transcutaneous monitoring of fetal carbon dioxide partial pressure (tcpCO2) may become an important new method for investigating the physiology and pathophysiology of the fetus during labor, as well as an additional tool for fetal surveillance. In order to contribute to the standardization of this newly developed method, we measured tcpCO2 during labor in 105 fetuses. We then compared the transcutaneous pCO2 with the pCO2 of fetal blood gas analysis; the correlation between these two parameters was significant. The relationship between transcutaneous pCO2 and the pH from fetal scalp blood is described, as is the influence of the stage of labor on the correlation between transcutaneous monitoring and blood samples. tcpCO2 during labor appears to be a helpful additional tool, especially in fetuses with pathologic heart rate patterns in whom multiple fetal blood gas analysis would otherwise be necessary.     

Continuous acid-base assessment of the human fetus during labour by tissue pH and transcutaneous carbon dioxide monitoring

Simultaneous monitoring of fetal tissue pH (t-pH) and transcutaneous carbon dioxide (Tc-PCO2) was performed in 30 labours. Both t-pH and Tc-PCO2 at delivery were positively correlated with pH (r = 0.69) and PCO2 (r = 0.68) of the umbilical artery blood. A tissue/transcutaneous standard base excess (t-SBE) was derived from the t-pH and the Tc-PCO2 and calculated for 13 fetuses at delivery; there was a correlation with standard base excess of umbilical artery blood. An analysis of t-pH and Tc-PCO2 changes during the last hour of labour revealed that only infants who were born with decreased pH of the umbilical artery blood had decreasing t-SBE, while all others had a constant t-SBE.     

Arterial PO2, PCO2, and pH versus transcutaneous PO2 and PCO2 and tissue pH in the fetal dog

In the fetal dog, simultaneous recording by transcutaneous PO2 and PCO2 and tissue pH electrodes were compared to corresponding arterial values during hypoxic episodes produced by occlusion of the maternal abdominal aorta. Before occlusion, the differences between the paired values were minimal. Under anoxic conditions, expected changes in the peripheral circulation were observed. However, the transcutaneous PO2 was lower, the transcutaneous PCO2 much higher, and the tissue pH much lower than in blood. Continuous electrodes demonstrate changes resulting from gas and hydrogen ion coming from cells more readily than blood because they are closer to the former. Additionally, carbon dioxide and hydrogen ion are buffered to a greater degree in blood than in cells. Consequently, under conditions of stress and active metabolism, PCO2 is higher while PO2 and pH are lower in cells than in blood. When compared with monitoring of gases and acid-base balance through blood sampling, continuous transcutaneous and intracutaneous monitoring would seem to be more representative of the environment at the cellular level.     

Simultaneous transcutaneous carbon dioxide and transcutaneous oxygen monitoring in neonatal intensive care

Continuous transcutaneous carbon dioxide partial pressure (tc PCO2) and continuous transcutaneous oxygen partial pressure (tc PO2) was monitored simultaneously in 10 consecutive neonatal intensive care patients treated for respiratory problems or immaturity. During measurement the electrode temperature was 44 degrees C while during the resting periods--with the electrodes left in situ--the electrode temperature was 37 degrees C. Measurements were performed for periods up to 31 hours. It was possible to discover changes in central blood gas partial pressures also at the lower electrode temperature. This was especially true for the tc PCO2 recording which was less influenced by the decrease in electrode temperature than the tc PO2 recording. In six patients an increased frequency of apnoea was diagnosed by the transcutaneous blood gas monitoring equipment previous to other clinical signs. A statistically highly significant correlation was found between transcutaneous and arterial blood gas values, the arterial samples obtained from umbilical artery catheters. tc PCO2 and tc PO2 very sensitively reacts to changes in the breathing pattern and to changes in activity of the neonate emphasizing the drawbacks of previous blood gas monitoring techniques. The technique for continuous transcutaneous carbon dioxide monitoring is ready for clinical use and is a valuable additional tool in all neonatal intensive care patients with the risk of alveolar hypoventilation.     

正常晚期妊娠胎儿脐动脉,大脑中动脉及腹主动脉血流速度波形与？…

目的 探讨正常妊娠胎儿血流速度波形与胎儿血气的相关性,方法 应用彩色多普勒超声对４５例正常晚期妊娠初孕妇女于剖宫产术时２４小时内进行胎儿脐动脉（ＵＡ）,大脑中动脉（ＭＣＡ）及腹主动脉（ＡｂＡｏ）的血流速度波形（ＦＶＷｓ）检查,计算搏动指数（ＰＩ）,阻力指数（ＲＩ）及收缩期最大血流速度（Ｓ）与舒张末期血流速度（Ｄ）的比值（Ｓ／Ｄ）,同时对剖宫产分娩的新生称立即进行脐动脉血气ｐＨ,二氧化碳分压（ＰＣＯ     

正常晚期妊娠胎儿脐动脉、大脑中动脉及腹主动脉血流速度波形与胎儿血气相关性探讨

目的探讨正常妊娠胎儿血流速度波形与胎儿血气的相关性。方法应用彩色多普勒超声对４５例正常晚期妊娠初孕妇女于剖宫产术前２４小时内进行胎儿脐动脉（ＵＡ）、大脑中动脉（ＭＣＡ）及腹主动脉（ＡｂＡｏ）的血流速度波形（ＦＶＷｓ）检查，计算搏动指数（ＰＩ）、阻力指数（ＲＩ）及收缩期最大血流速度（Ｓ）与舒张末期血流速度（Ｄ）的比值（Ｓ／Ｄ），同时对剖宫产分娩的新生儿立即进行脐动脉血气ｐＨ、二氧化碳分压（ＰＣＯ２）、氧分压（ＰＯ２）测定。结果ＵＡＲＩ与血ｐＨ、ＰＯ２呈明显负相关（Ｐ＜０．０１，Ｐ＜０．０５），与ＰＣＯ２呈正相关（Ｐ＜０．０５），ＭＣＡＲＩ与血ｐＨ、ＰＯ２呈明显正相关（Ｐ＜０．０１，Ｐ＜０．０５），与ＰＣＯ２呈负相关（Ｐ＜０．０５）。结论产前监测ＵＡ及ＭＣＡ的血流速度波形，可间接了解胎儿血气情况，及时判断胎儿宫内安危的状况。     

Comparative study of application techniques for the tcPCO2 measurement in the fetus

In order to investigate the advantages and shortcomings of two application techniques proposed for the tcPCO2 electrode in the fetus we performed a trial using two electrodes with different modes of fixation synchronously. Comparing the transcutaneously measured values with the values of the fetal blood we found a statistically significant correlation for both techniques (r = 0.83 and 0.80, respectively). The mean values of the tcPCO2 though were significantly higher when the suction fixation was used compared with the glue fixation.     

Contribution of the Bohr effect to the fall in fetal PO2 caused by maternal alkalosis

A decrease in the PO2 of fetal arterial blood is observed in maternal alkalosis caused by hyperventilation in labour or exercise. The contribution of altered blood oxygen affinity to this effect was studied experimentally and by computer simulation of placental gas exchange. Thirteen guinea pigs near term of pregnancy were anesthetized and the right atrium of the fetus was catheterized to enable continuous and simultaneous measurement of PO2 and PCO2 by mass spectrometry. An infusion of base was given through a catheter in the descending aorta of the dam and the effect on fetal respiratory gas tensions observed. The mean change in maternal arterial pH measured in blood taken from a femoral artery was 0.07 +/- 0.04 (mean +/- S. D.). There was an immediate decrease in PO2 in the right atrium of the fetus, but no consistent alteration in PCO2. Two minutes after the start of the infusion, PO2 had fallen by 3.2 +/- 1.6 Torr (p less than 0.001) and PCO2 had risen by 1.7 +/- 1.8 Torr (not significant). The experiments were simulated using a mathematical model of placental gas exchange in the guinea pig. The model was able to predict the change in fetal arterial PO2, given numerical values for the pH, PO2 and PCO2 of fetal and maternal arterial blood prior to infusion of base and for maternal blood during the infusion of base. These values were obtained from the experimental data. Other input variables of the model were maternal and fetal hematocrit and DPG concentration, and the rates of blood flow on the two sides of the placenta.(ABSTRACT TRUNCATED AT 250 WORDS)     

Atrial natriuretic factor, digoxin-like immunoreactive substance, norepinephrine, epinephrine, and plasma renin activity in human fetuses and their alteration by fetal disease

We measured five hormones presumably involved in fetal homeostasis in specimens obtained by cordocentesis for clinical indications from 106 fetuses. Norms for atrial natriuretic factor, digoxin-like immunoreactive substance, plasma renin activity, norepinephrine, and epinephrine were derived from fetuses ultimately shown to be free of detectable abnormality. Atrial natriuretic factor, digoxin-like immunoreactive substance, and plasma renin activity were unrelated to umbilical vessel source or gestational age. Digoxin-like immunoreactive substance was directly related to PCO2 (r = 0.63, p = 0.02). Digoxin-like immunoreactive substance level was elevated in all fetal disease states studied except isoimmunization. The level of atrial natriuretic factor was elevated in fetuses with immune hydrops (NS). Norepinephrine and epinephrine levels were higher in the umbilical artery than in the vein (p = 0.05 and 0.006, respectively). There was a significant correlation between norepinephrine and gestational age in normal fetuses (r = 0.7637, p less than 0.025) and between both catecholamines and many of the respiratory blood gas measurements, with pH and PCO2 being the major determinants. Most disease states were associated with an elevated norepinephrine concentration. There was a negative correlation between plasma renin activity and base deficit (p less than 0.0001). Plasma renin activity was elevated in fetuses with idiopathic growth retardation and nonimmune hydrops (p less than 0.05 for each). In summary, fetal homeostasis as reflected by these five hormones was altered by a variety of disorders. With these baseline values the effects of direct or indirect fetal therapy can begin to be studied.     

Non-invasive continuous fetal transcutaneous pO2 and pCO2 monitoring during labor

Continuous measurements of fetal scalp transcutaneous pO2 (tcpO2) and pCO2 (tcpCO2) monitoring were performed for 49 patients for the purpose of the evaluation of the fetal well-being. The equipment used was transcutaneous pO2/pCO2 monitor Micro Gas 7640 (KONTRON, Switzerland), which was inserted through the vagina and attached to the fetal head with a suction ring. Blood was taken from the umbilical vessels and pO2 and pCO2 values were analyzed. The correlation coefficient between pO2 in the umbilical artery and tcpO2 was 0.78 (p less than 0.01), and that between pCO2 in the umbilical artery and tcPCO2 was 0.79 (p less than 0.01). Relationships between the transcutaneous blood gas analysis and FHR patterns were discussed. Increase of pCO2 and decrease of tcpO2 was observed in the cases of variable deceleration, not observed in the case of early deceleration. FHR patterns don't always indicate fetal condition, for example in the case of fetal arrhythmia, especially fetal bradycardia. But tcpO2 monitoring of the fetus affected fetal arrhythmia during labor aids diagnosis of fetal distress by FHR patterns, especially in the case of fetuses affected by fetal bradycardia.     

The influence of oxygen administration to the mother during labor on the fetal transcutaneously measured carbon-dioxide partial pressure

The aim of this study was to plot the course of the transcutaneously measured PCO2 (tcPCO2) in the fetus during oxygenation of the mother. In our examination 35 parturients with a suspicious or pathologic CTG were given pure oxygen for 10 minutes at a flow speed of 10 l/min. The fetal tcPCO2 was measured with a TCM 3 measuring device from Radiometer. The measuring temperature was 41 degrees C. The fetal tcPCO2 was 67.2 +/- 3.9 mmHg before the O2 application, during the O2 application it was 67.3 +/- 14.1 mmHg and for the period after the O2 application we found an average measurement of 66.7 +/- 13.9 mmHg. Further we investigated whether, depending on the original levels of the fetal tcPCO2 an O2 application to the mother had a measurable effect on the fetal tcPCO2 levels. The average levels of the tcPCO2 in the fetuses with pathological original levels of greater than or equal to 60 mmHg or with normal levels of less than 60 mmHg did not show any significant differences before, during or after the O2 application. Our own results and reports given in the literature about an increase in the fetal O2 partial pressure during maternal oxygenation lead to the conclusion that in cases with fetal hypoxia, the O2 application to the mother--in addition to other measures for intrauterine reanimation or speedy termination of labor--could be of advantage.     

The effect of caput succedaneum on oxygen saturation measurements

Advances in oximetry have allowed the obstetrician to measure oxygen saturation in the fetus with non-invasive transcutaneous techniques. The influence of caput succedaneum formation on the oxygen saturation results obtained with a pulse oximeter was studied in 30 newborn infants. Caput was associated with a reduced oxygen saturation reading (mean reduction of 15%; P less than 0.001). This effect is partly due to a true drop in local tissue oxygenation but is exacerbated by a systematic error intrinsic to the physics of spectrophotometry. If continuous intrapartum oximetry is ever to become a part of routine obstetric monitoring then probes that pass through the cervix beyond the caput of the presenting part will be required if erroneously low readings are to be avoided.     

Influence of maternal hyperoxia or hypercarbia on the hemodynamics of the placenta and fetal brain

Pregnant rabbits were subjected to inhalation of different gases, and the changes in placental blood flow (PBF), fetal heart rate (HR), and fetal cerebral blood flow (CBF) associated with the changes in maternal blood gas levels were studied. The results are given below. In maternal hyperoxia, maternal blood pressure (BP) was not much influenced and PBF remained unchanged or was slightly decreased when the PCO2 level was not varied or when it was lowered. In contrast, not only maternal BP but also PBF was increased when the PCO2 level was elevated. In the absence of a conspicuous increase in PCO2, neither fetal HR nor CBF varied, regardless of PBF. Both maternal BP and PBF were increased in mild to moderate maternal hypoxia (PO2 greater than 40 mmHg) and decreased in severe hypoxia (PO2 less than 30 mmHg). The decreasing trend of fetal HR or CBF was strengthened as maternal hypoxia was intensified. An obvious decrease in either parameter was observed in severe maternal hypoxia (PO2 less than 30 mmHg). Fetal HR and CBF were well maintained. in hypoxic dams with increased PBF as compared with those with unchanged or decreased PBF. The higher the PCO2 level or the lower the pH value, the more was fetal bradycardia that was apt to occur, even in a mildly hypoxic state.     

The effect of caput succedaneum on oxygen saturation measurements

Summary. Advances in oximetry have allowed the obstetrician to measure oxygen saturation in the fetus with non-invasive transcutaneous techniques. The influence of caput succedaneum formation on the oxygen saturation results obtained with a pulse oximeter was studied in 30 newborn infants. Caput was associated with a reduced oxygen saturation reading (mean reduction of 15%; P <0^.001). This effect is partly due to a true drop in local tissue oxygenation but is exacerbated by a systematic error intrinsic to the physics of spectrophotometry. If continuous intrapartum oximetry is ever to become a part of routine obstetric monitoring then probes that pass through the cervix beyond the caput of the presenting part will be required if erroneously low readings are to be avoided.     

Measurement of fetal transcutaneous oxygen tension--problems and potential

In a series of 39 fetuses, continuous intrapartum transcutaneous PO2 recordings were made using a commercially available skin electrode, applied to the shaven fetal scalp. The weak correlation between transcutaneous measurements and umbilical blood PO2 at delivery is believed to be due to scalp ischaemia produced by 'head to cervix' pressure during labour. This 'tonsure' effect presents a major obstacle to the use of surface electrodes for intrapartum blood gas monitoring from the fetal scalp in clinical obstetrics. Modification of the current technique may allow it to be used reliably for research.