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The transcutaneous Po2 monitoring technique was applied in 20 newborns. The method proved reliable during hypoxemia, normoxemia and hyperoxemia, with a high correlation between Ptco2 and Pao2 in simultaneously obtained arterial samples. Although Ptco2 reliably reflects changes in Pao2, occasional arterial samples are still required for establishing the relationship between Ptco2 and Pao2, especially in patients with impaired circulation. When this relationship has been determined, the therapist may rely on the recorded Ptco2 level for hours, given that the energy supply required to maintain the electrode at a preset temperature level remains constant. A considerable difference between Ptco2 and Pao2 or a change in the energy supply level to the electrode may alert the therapist to check the patient's circulatory status. The Ptco2 technique is now fully developed and can be recommended for use in neonatal intensive care.

The technique for transcutaneous oxygen (TcPO2) monitoring is now routine in neonatal intensive care. The method was presented earlier as a potential tool for fetal surveillance during labor. The current study reports on two techniques generally used for the application of the electrode to the fetus. The application of the electrode by a suction instrument does not influence the TcPO2 level recorded and the use of this technique is very simple. However, the main disadvantage of the suction instrument is that the electrode is easily detached. Application of the electrode by glue is technically a little more difficult but has the advantage of being much more efficient. If the criteria for a reliable recording presented in the study are fulfilled, the technique may be used as an additional parameter to diagnose true fetal hypoxemia.

Continuous transcutaneous oxygen (PtcO2) monitoring is a noninvasive technique for recording changes in central oxygenation. PtcO2 monitoring has been for some years a routine method in neonatal and adult intensive care. The technique is a potential tool in fetal surveillance during labor. Some recently published studies which have been critical of the use of PtcO2 monitoring in the delivery room reveal a lack of thorough understanding of the limitations of the technique. From the author's experience with the technique, it is obvious that, when the PtcO2 electrode is attached according to recommendations and when the monitoring situation fulfills certain criteria, PtcO2 reliably reflects changes in the fetal oxygenation during labor and may be used for the diagnosis of true hypoxemia. PtcO2 monitoring does not replace any other available routine monitoring for fetal surveillance, but when the technique is refined, it may become an additional means of diagnosing fetal jeopardy. As a research parameter, PtcO2 monitoring has already contributed to a more diversified understanding of the process of fetal asphyxia.

At application of the electrode for continuous transcutaneous oxygen monitoring, a superatmospheric pressure may be produced between the skin and the electrode membrane. Such a pressure may change the electrode characteristics resulting in a slower reacting electrode. A superatmospheric pressure may also influence on the subepidermal capillaries and on the oxygen diffusion through the skin. The results in the current in vitro study show that an increase of the pressure between the electrode membrane and the skin results in a slower reacting electrode, only when the pressure also produces an increased diffusion distance from the capillaries to the electrode membrane. Thus, the PtcO2 electrode seems rather rough and different PtcO2 levels recorded among patients or in the same patient at two applications are not produced by the application procedure per se but by physiological differences in the skin at the electrode application site.

Transcutaneous oxygen measurement (PtcO2-measurement) gives by a non-invasive technique continuous information about central PO2. The method has as yet been tested mainly on newborns, and systematic studies of the applicability of the method on adults are still few. The current systematic study reports on consecutive PtcO2 measurements in 15 patients, all with indwelling arterial catheters: 13 of the patients were artificially ventilated; 5 patients had normal body structure and normal skin circulation; 5 patients were obese and had normal skin circulation; and 5 patients were hypothermic with a normal heart frequency or slight bradycardia. The Radiometer equipment TCM1 was used. The electrode surface tempertaure was 45.0 degrees C (within +/- 0.2 degrees C). The oxygen concentration in the inspired air was altered several times for all patients, and arterial samples were drawn at a stable PtcO2 level. On average, seven samples were drawn from each patient. The correlation between PtcO2 and PaO2 was highly significant in 4/5 patients, in both the "obese patient" group and the "normal patient" group. In the "hypothermic patient" group, the correlation between PtcO2 and PaO2 was highly statistically significant in 2/5 patients. The regression line between PtcO2 and PaO2 was calculated for each patient, and a mean regression line was obtained for each group. It was found that the regression line in the "obese patient" group was displaced to the right and parallel to the regression line in the "normal patient" group, while the regression line in the "hypothermic patient" group was less sloping and showed a higher intercept. The PtcO2 monitoring technique reliably reflects changes in the central oxygenation of adult intensive care patients. In some patients with decreased skin circulation, the relationship between PtcO2 and PaO2 seemed to be constant for the same patient, yielding statistically sifnificant correlations. However, the study cannot determine whether this would be true in all clinical situations; the relationship betwee PtcO2 and PaO2 should therefore be checked frequently when measruements are performed in patients with decreased skin circulation. The author's experience with the PtcO2 monitoring method in patients near death has been consistent with the obvious fact that the reliability of the method decreases with decreased skin circulation.

Transcutaneous PO2 (tcPO2) measurement is a non-invasive method which gives continuous information about central PO2. The method has previously been testes primarily on newborns and adults, and reports on the applicability of the method on the fetus during labor are still scanty and restricted to case reports. This paper reports on a systematic study of intrapartum fetal and maternal tcPO2-monitoring. The material is comprised of 19 parturients, the majority being nulliparae. All fetal presentations were vertex. The tcPO2 recordings averaged one hour in duration (Tab. I). FHR was recorded simultaneously. In 12 cases the electrode was affixed with glue, and in 7 cases a suction device was used for fixation. The electrode was attached when the cervix was dilated 4 to 6 cm. The mean tcPO2 was 20 mm Hg in the beginning of the registration, and showed a small decline in level throughout labor reaching 14 mmHg at the end of the registration period (Fig. 5). These values are in good agreement with those found by other authors in previous investigations. In some of the present cases, very low tcPO2 values were recorded. The relevance of these low tcPO2 values is unclear, and it is impossible to determine to what extent these tracings have true physiological relevance versus might be due to technical factors.

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.

The technique of transcutaneous monitoring of oxygen partial pressure (PtcO2), first described in 1969, provided a new clinical possibility for continuous and noninvasive surveillance of changes in the oxygenation of the organism. To obtain optimal arterialization of the skin and thus a relieable recording, the electrodes used have been supplied with microheating elements. The electrode temperature used implies the risk of producing burns; this is especially true when the measurements are performed in patients with decreased skin circulation or in immature children with a thin and vulnerable skin. Thus, a careful choice of the electrode temperature is important in PtcO2 recording; a higher temperature is desirable for obtaining adequate arterialization, whereas a lower temperature is preferred for reducing the risk of burns. The electrode temperatures described for PtcO2 measurements range from 42--45 C. A systematic study with the Radiometer TCM 1 equipment showed that changing the electrode temperature influences the OtcO2 in a systematic way within the temperature range 43.0--45.0 C. The study also showed that simultaneous measurements obtained from two electrodes with different temperatures showed a highly parallel course and a comparable oscillating pattern within this temperature range. The results of the present study suggest that an electrode temperature of 44.5 C may be the most appropriate for this equipment in clinical applications with newborns.

The reliability and physiological significance of continuous non-invasive PO2 recording by means of skin electrodes was studied by comparing simultaneous tracings from different skin areas in a series of 40 newborns with normal labor and birth. A new measuring equipment - the Radiometer prototype unit TPM 1 - was used. In addition, the applicability of the method to the fetus was tested in a primary series of 11 labor cases. Certain technical and physiological factors that can influence the tracings were identified.

The transcutaneous oxygen partial pressure (PtcO2) was monitored in 50 healthy, normally and spontaneously delivered newborns. Measurements were performed during the first to fourth day of life. The electrode temperature was 44.5 degrees C. The mean PtcO2 level recorded during about 45 min was 9.2 kPa (S.D. 1.4) recorded from the minute-to-minute values. The PtcO2 level normally oscillated to a certain extent and the oscillations were closely related to the breathing pattern of the patient. When the patient fell asleep during measurement, the normal oscillating pattern was replaced by a "silent pattern". During crying, the PtcO2 level showed four main reaction aptterns. A decrease in the PtcO2 level could be observed during breast-feeding. One child, recently fed, vomited a small amount of breast milk after a short period of crying and apparently had a laryngospasm, shown by a sudden drop in the PtcO2 level without any other signs of discomfort. The study shows that PtcO2 (and thus also PaO2) very sensitively reacts to changes in activity. This implies that earlier used methods for determination of PaO2 might give values that are not representative for the steady state as the sampling method per se might influence the recorded PO2 value.

Two children aged 1 and 20 months developed alveolar hypoventilation syndrome. They suffered severe apnoeic episodes and periodically required assisted ventilation. Their ventilatory response to carbon dioxide was lower than that of normal children and the transcutaneous oxygen tension during sleep was well below the normal range. Treatment with medroxyprogesterone acetate resulted in an improved response to carbon dioxide, and assisted ventilation was no longer needed. Oxygen and carbon dioxide tensions improved but were still slightly abnormal during sleep. There were no clinical side effects of treatment but one infant had slight pituitary suppression. [ABSTRACT FROM AUTHOR]