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.     

Umbilical cord pH, PCO2, and bicarbonate following uncomplicated term vaginal deliveries

Normal values for umbilical arterial and venous pH, PCO2, PO2, and bicarbonate must be known before these parameters can be used for assistance in clinical decisions. We evaluated the cord blood from 146 infants born after uncomplicated labor and vaginal deliveries at 37 to 42 weeks' gestation. All infants had a normal baseline fetal heart rate and normal beat-to-beat variability for at least 10 minutes preceding expulsion. The cord blood of infants born to women with pregnancy complications such as diabetes mellitus, preeclampsia, twins, meconium-stained amniotic fluid, or fetal growth retardation was not included. Mean umbilical arterial values +/- 1 SD for the parameters studied were: pH, 7.28 +/- 0.05; PCO2, 49.2 +/- 8.4 mm Hg; PO2, 18.0 +/- 6.2 mm Hg; bicarbonate, 22.3 +/- 2.5 mEq/L. Umbilical venous values were: pH, 7.35 +/- 0.05; PCO2, 38.2 +/- 5.6 mm Hg; PO2, 29.2 +/- 5.9 mm Hg; bicarbonate, 20.4 +/- 4.1 mEq/L.     

The influence of sampling site and time upon umbilical cord blood acid-base status and PO2 in the newborn infant

Measurement of umbilical cord blood acid-base status is routinely carried out in many obstetric centers. Umbilical cord blood pH, PO2, PCO2 and SBE (standard base excess) may change between clamping of the cord and analysis due to diffusion and metabolism. It was the aim of this study to evaluate these changes separately in artery and vein blood during storage in the clamped umbilical cord. The umbilical cords from 11 normal term deliveries were clamped immediately after delivery and kept at room temperature. Samples of artery and vein blood were drawned separately 1, 5, 10, 15 and 30 minutes post partum and pH, PO2 and PCO2 were measured and SBE calculated. As demonstrated in table I, the vein blood pH and PO2 values were higher and PCO2 values lower than in the artery blood. The changes over time are given in figure 1 with the 1 min values as points of reference. Changes within the first 15 minutes were modest. A significant fall in vein pH, vein SBE and artery PO2 and a significant rise in artery PCO2 was found. Greater variation in the changes over time was found in artery than in vein blood, being most evident for the 30 min values. Although significant changes in the umbilical cord acid-base values and PO2 do occur when the blood is stored in the clamped cord, we find these changes to be minor and we conclude that sampling can be postponed for up to 15 minutes after delivery.     

Evaluation of respiratory gases and acid-base gradients in human fetal fluids and uteroplacental tissue between 7 and 16 weeks' gestation

OBJECTIVE: Our purpose was to evaluate the changes in intrauterine gases and acid-base gradients inside the human fetoplacental unit at 7 to 16 weeks' gestation. STUDY DESIGN: Respiratory gases and acid-base values were recorded by means of a multiparameter sensor and samples from inside the exocoelomic or amniotic cavity, placental tissue, decidua, and fetal blood of 30 early pregnancies. RESULTS: Before 11 weeks' gestation, placental PO(2) was 2.5 times lower than decidual PO(2). The PO(2) increased independently at both sites during gestation, but a PO(2) gradient of 13.3 mm Hg persisted during the fourth month. At 13 to 16 weeks, PO(2), oxygen saturation, and oxygen content gradients were observed between the fetal blood and the placenta and between the placenta and underlying decidual tissue. There was no fetoplacental gradient for pH and PCO(2) between 7 and 16 weeks, but fetal blood pH values were much lower and fetal PCO(2) values were much higher than those reported in older fetuses. CONCLUSIONS: Early human placental tissue develops in a physiologically low-oxygen environment compared with uterine tissue. This may be necessary to allow specific placental metabolic activities and to protect both placental and fetal tissues against toxic oxygen metabolites.     

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.     

Umbilical cord pH and PCO2: effect of interval from delivery to determination

Determinations of umbilical blood pH and PCO2 can be useful for correlating intrapartum fetal heart rate patterns, intrapartum samples of scalp blood, and Apgar scores, for the retrospective evaluation of the management of a particular labor. Occasionally, such data can indicate and clarify needed resuscitative measures and intensive neonatal observation. Cumbersome techniques have been described for the handling of specimens of cord blood to ensure an accurate determination. This study was performed to determine the effect on cord blood pH and PCO2 of room temperature and time from delivery. One hundred five cord venous or arterial determinations had a linear pH decrease versus time at room temperature. The regression slope was -3.66 X 10(-4) per minute with a standard deviation of 1.37 X 10(-2). The PCO2 showed only a slight increase with time at room temperature, although the scatter was high, with a standard deviation of 3.8 torr. The conclusion is that samples of cord blood drawn for determination of pH and PCO2 can be kept at room temperature in plastic syringes for up to 30 minutes without significant alteration in these values, i.e., pH decrease no greater than 0.04 unit (p less than 0.05).     

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)     

Fetal scalp blood sampling and transcutaneous PO2

Continuous transcutaneous PO2 monitoring has yielded some interesting information about the relationships of fetal oxygenation and the fetal heart rate. Notwithstanding the factors that may adversely affect the results obtained by this technique, further insights regarding fetal oxygenation may be gained. Ultimately, the clinical application of this instrument in high-risk situations is possible, yielding more information about the fetus during labor. Fetal scalp blood sampling, performed meticulously, will provide accurate blood pH values and should be employed when a differentiation between fetal stress and distress must be made. Other means of obtaining information about fetal acid-base balance are being developed and may become important tools in selected instances.     

Umbilical blood gas analysis: I. Effect of storage of samples on outcome

The pH and blood gas values of umbilical blood samples must be determined as soon as possible after birth to avoid changes in pH, oxygen pressure (PO2) and carbon dioxide pressure (PCO2). Since a continuous around-the-clock laboratory service is not available in every hospital, a method of reducing these changes is desirable. Determination of pH and blood gas values at different time intervals while the samples were stored on ice showed that pH decreased by a mean of 0.003 unit/hr, whereas PCO2 and PO2 increased. A method of reducing glycolysis in blood cells must be found to make postponement of analysis acceptable.     

The influence of the progress of labor on the reliability of the transcutaneous PCO2 of the fetus

Transcutaneous PCO2 measurements were performed on 105 fetuses during labor. A modified Severinghaus electrode was calibrated with 5% and 10% carbon-dioxide gas at 33 and 66torr. This corresponds to a drop in the PCO2 levels measured transcutaneously of about 13% and to an adjustment to the blood gas level. The levels measured transcutaneously were compared with data compiled from the fetal blood analysis and values of blood gas analysis from the umbilical artery immediately after delivery. The object of the study was to find out to what extent the progress of labor influences the conformity between the PCO2 levels measured transcutaneously and measured in blood. Comparing the data of the transcutaneous measurement (pb PCO2) with the pb PCO2 of the peripheral blood (pb PCO2) in cases without a caput succedaneum, we found a correlation coefficient of r = 0.79 and a slope of 1.1. On the other hand with the development of a caput succedaneum the correlation coefficient was lowered to r = 0.72 and the slope to 0.85. An influence of the propulsion of the fetal head in the birth canal on the accuracy of the transcutaneous measurement was also obvious. When the position of the fetal head was either above or in the interspinal plane, the correlation coefficient amounted to r = 0.85. With the progression below the interspinal plane, the correlation coefficient was clearly lowered. While our results show a good overall conformity between PCO2 levels measured transcutaneously and those from peripheral blood, our analysis shows also to what extent the conformity can be influenced both by the existence of a caput succedaneum and by the propulsion of the presenting part.     

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 relationship of transcutaneous PO2 and laser Doppler measurements in a human model of local arterial insufficiency

Transcutaneous PO2 and laser Doppler measurements were made over areas of unheated and heated skin of the feet of normal volunteers. Stepwise elevation of the foot above the level of the heart systematically reduced the local arterial pressure and, thus, the local arteriovenous gradient in these areas. Results indicated that transcutaneous PO2 and laser Doppler measurements reflect changes in local arteriovenous gradient when made over areas of warmed skin, but not unwarmed skin. Comparison of skin surface and subcutaneous temperatures obtained with two heater types revealed the importance of heater configuration. Results confirm a previously hypothesized nonlinear relationship between transcutaneous PO2 and local cutaneous blood flow and indicate that a transcutaneous PO2 reading of zero may be obtained in the presence of significant local cutaneous blood flow.     

A practical approach to umbilical artery pH and blood gas determinations.

The use of the Apgar score as a means of identifying birth asphyxia has been challenged. Routine umbilical cord blood pH has been recommended as a more objective measure of the condition of the newborn. The purposes of this study were to evaluate a simplified and selective method of umbilical artery pH blood sampling and to determine the effect of delay in sampling upon umbilical artery pH, carbon dioxide pressure (PCO2), and oxygen pressure (PO2). Umbilical arterial blood of 25 patients was sampled from clamped umbilical cord segments every 15 minutes for 1 hour after delivery. The clamped umbilical cord segments were left at room temperature with no special care given. The blood samples were collected in non-heparinized and non-iced plastic syringes and processed promptly after sampling. During the 60 minutes after delivery, there were no statistically significant changes in pH, PCO2, or PO2 of umbilical arterial blood. Our results indicate that umbilical arterial blood may be obtained simply and reliably from clamped umbilical cord segments for pH and gas determinations for up to an hour after delivery.     

Fetal carbon dioxide tension during human labour

Fetal carbon dioxide tension during labour is elevated in both metabolic and respiratory acidosis, but intermittent fetal blood analyses often fail to detect PCO2 changes during acute complications. Transcutaneous carbon dioxide monitoring is continuous and the possibility of diagnosing PCO2 changes is therefore better. The theoretical background for transcutaneous measurements and methods for clinical monitoring are described. Close correlations with capillary and arterial blood values have been found, and the atraumatic principle with a simple electrode application indicates a promising new method for acid-base assessment during human labour.     

Blood gases, pH, and lactate in appropriate- and small-for-gestational-age fetuses

The pH, PO2, PCO2, and lactate concentration were measured in umbilical blood samples obtained by cordocentesis from 208 appropriate-for-gestational-age and 196 small-for-gestational-age fetuses at 18 to 38 weeks' gestation. In the appropriate-to-gestational-age fetuses umbilical venous (n = 173) and arterial (n = 35) PO2 and pH decreased, and umbilical venous and arterial PCO2 increased with advancing gestation. Blood lactate concentration did not change. Compared with the appropriate-for-gestational-age fetuses, the small-for-gestational-age fetuses were hypoxemic, hypercapnic, hyperlacticemic, and acidotic. There was mixed respiratory and metabolic acidosis, and the decrease in pH was significantly correlated with both hypercapnia and hyperlacticemia. In the umbilical artery (n = 53) there was a significant linear correlation between the degree of hypoxemia and the degrees of hypercapnia or acidosis. In the umbilical vein (n = 143), the correlations between the degree of hypoxemia and the degrees of hypercapnia, hyperlacticemia, or acidosis were exponential.     

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.     

Do postsuctioning transcutaneous PO2 values change when a neonate's movements are restrained?

The purpose of this research was to examine the effects of containment (restraint of an infant's movements) on premature infants' postsuctioning transcutaneous PO2 values. The hypothesis was that premature infants receiving containment would have significantly different postsuctioning transcutaneous PO2 levels than infants receiving no containment. Premature infants with respiratory disease require suctioning to remove excess secretions from their lungs. Research studies document a variety of infant responses to suctioning; hypoxia, hypoxemia, increased blood pressure, bradycardia, increased intracranial pressure, and increased cerebral blood flow velocity. Most studies have examined only a few isolated variables and the magnitude and duration of hypoxemia in response to suctioning. Our sample comprised 24 infants less than 72 hours of age, who had respiratory distress syndrome and had been born at between 24 and 33 weeks' gestational age. The setting was a neonatal intensive care unit of a large county hospital. The same nurse performed the suctioning and containment procedures in all subjects. Student's t-tests and analysis of variance were carried out to determine the effect of the technique.     

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

Summary. Simultaneous monitoring of fetal tissue pH (t-pH) and transcutaneous carbon dioxide (Tc- P co₂) was performed in 30 labours. Both t-pH and Te- P co_-2 at delivery were positively correlated with pH ( r = 0·69) and P co₂( 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- P co₂ and calculated for 13 fetuses a t delivery; there was a correlation with standard base excess of umbilical artery blood. An analysis of t-pH and Tc- P co₂ 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.     

Continuous variability of fetal PO2 in the chronically catheterized fetal sheep.

A method of continuous monitoring of fetal intravascular PO2 at various sites in the circulation in the chronically catheterized fetal sheep for up to 41 days (mean 11.1 days) has been compared with values obtained in blood samples measured extracorporeally in a standard blood gas analyzer. A double-blind comparison of the two methods showed that there was no bias between the two methods and correlation was 0.94. The stability of the electrodes was superior to that of a conventional blood gas analyzer. In every animal there was continuous variability of fetal vascular PO2. In the period from 105 to 126 days' gestation we noted the presence of slow increases in basal uterine tone that we have called "contractures". The frequency of these contractures was very regular at approximately one per hour. The frequency of these contracutres was very regular at approximately one per hour. There is a statistically significant related fall in fetal vascular PO2 in relation to these contractures. Well-coordinated uterine contractions during labor also produced a fall in fetal vascular PO2 that was related to the uterine activity.     

Continuous measurement of tissue pH in the human fetal scalp.

A method for continuous measurement of scalp tissue pH is described. The tissue pH probe was found to be robust and values for tissue pH were close to those for scalp blood pH. Combining the pH and fetal heart fate (FHR) electrodes in the one mechanical assembly facilitated application to the fetal scalp in early labour but the combined assembly electrode was found to have some disadvantages and manufacture of a separate tissue PH electrode is recommended. Continuous monitoring of scalp tissue pH enables closer study of the physiological basis of changes in fetal acid base status and should prove useful to the obstetrician in management of high risk pregnancies during labour.