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Two hundred eighty-two umbilical artery catheters with oxygen electrodes on their tips were passed into the aortas of 268 newborn infants with severe respiratory illnesses between 1974-1977; 254 (90%) of the electrodes recorded PaO2 satisfactorily for a mean of 66 hours; 212 (75%) electrodes were still functioning well when removed, because they were no longer clinically needed, after a mean of 87 hours. The 27 electrodes that failed to record PaO2 on insertion, 42 that failed later, and 25 that temporarily malfunctioned were examined after removal from the infants. A structural cause was found which accounted for the failure or malfunction of 43 electrodes. Problems with the remaining 51 electrodes were thought often to have been due to clotting over the tip of the electrode. The main complication of catheterization was temporary impairment of the circulation to the legs in 69 (26%) infants. Autopsies were done on 69 (85%) of the infants who died; 22 (32%) infants were found to have thrombi in an iliac artery, which spread in ten (15%) of the aorta. It was concluded that the intravascular electrode usually functioned satisfactorily and that the incidence of complications was no higher than that reported with ordinary umbilical artery catheters. Improvements in the performance of the catheter-tip electrode would be expected if structural causes for failure were eliminated and if means to reduce the incidence of clot formation around the catheter and electrode could be found. It is believed that intravascular electrodes cannot be replaced by skin electrodes for the initial management of severe respiratory illnesses.

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Transcutaneous PO2 simultaneously recorded by Drager and Radiometer electrodes on the abdominal skin was compared for six-hour periods with aortic PaO2 recorded by a Searle intravascular oxygen electrode. Ten newborn infants with serious respiratory illnesses, six of whom needed mechanical ventilation, were studied. The skin electrodes were heated to 44 degrees C and calibrated first in vitro, and then in vivo against the infant's PaO2. The results showed that 1) after in vivo calibration both skin electrodes gave an accurate estimate of PaO2 for six hours without resiting of the electrodes; 2) the Radiometer electrode gave as satisfactory an estimate of PaO2 after in vitro as after in vivo calibration; 3) the Drager electrode gave a significantly less accurate estimate of PaO2 after in vitro than after in vivo calibration; 4) no evidence suggesting that peripheral vasoconstriction interfered with the accuracy of estimation of PaO2 by the skin electrodes was found.

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Transcutaneous oxygen tension (tcPO2), measured by two skin electrodes of different design, and arterial oxygen tension (PaO2), measured by an intravascular oxygen electrode, were continuously recorded for periods of six hours in 15 newborn infants with serious respiratory illnesses. Ten of the infants needed mechanical ventilation and three needed continuous positive airway pressure. One skin electrode had three microcathodes surrounded by a heated ring-shaped anode, and the other had a large heated cathode. The temperature of both electrodes was set at 44 degrees C and they were calibrated in vitro. The tcPO2 recorded by the electrode with the microcathodes was found to estimate PaO2 reasonably accurately for the whole six-hour duration of the study. The tcPO2 recorded by the electrode with the large cathode gave a similar estimate of PaO2 for three hours, but then tcPO2 often fell relative to PaO2. This fall was probably caused by skin changes at the electrode site. For a variety of reasons, our results suggest that measurement of tcPO2 is unlikely to replace continuous intravascular measurement of PaO2 in infants with severe respiratory illnesses.

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Transcutaneous oxygen tension (tcPO2) measured by two skin electrodes of different design, and arterial oxygen tension (PaO2) measured by an intravascular oxygen electrode, were continuously compared for periods of 6--27 h in 45 newborn infants with respiratory illnesses. One skin electrode (Dräger) had three microcathodes surrounded by a heated ring-shaped anode and the other (Roche) a large heated cathode. The electrodes were calibrated in vitro; 44 degrees C was found to be a suitable electrode temperature for the estimation of Pao2. tcPo2 recorded by the electrode with the microcathodes estimated Pao2 reasonably accurately for 6 h without the necessity for re-siting. tcPao2 recorded by the electrode with the large cathode gave a similar estimate of Pao2 for 3 h, but then tcPao2 often fell relative to Pao2. This fall was probably caused by skin changes at the electrode site. Poor skin perfusion causing underestimation of Pao2 by tcPo2 could not be identified by a number of methods tried.

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An oxygen electrode mounted in the tip of an umbilical artery catheter was used in 36 newborn infants with severe respiratory illnesses, 28 of whom survived. Thirty-seven electrodes were used. The median age at insertion was 4 hours (range, 30 minutes to 122 hours). Three electrodes failed to work and they were removed or replaced, and two could not be properly evaluated. Thirty-two electrodes functioned satisfactorily for 10 to 190 hours (mean, 75 hours) after a one-point calibration against blood sampled through the catheter. Twenty-two did not need recalibrating before they were removed after 10 to 190 hours (mean, 88 hours. Four of the remaining ten electrodes were recalibrated once after 33 to 97 hours and then functioned until removed 15 to 55 hours later. The other six electrodes failed after 32 to 105 hours (mean, 49 hours). Complications were few. A total of 356 arterial blood samples, obtained after the initial calibration and before any recalibration was necessary, gave a correlation coefficient of 0.93 (P less than .0001) against an independent system for measuring arterial oxygen tension (Pao2) (Radiometer Type E.5046 oxygen electrode). We conclude that the catheter-tip electrode is a safe and reliable instrument for continuously recording Pao2 in newborn infants which much simplifies the management of serious respiratory illnesses.

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The measurement of arterial oxygen tension (PaO2) has for some time now been regarded as an essential part of the management of newborn babies receiving oxygen therapy. A system for monitoring arterial oxygen tension by means of a catheter-tip transducer is described. Comparisons of the transducer output with PO2 obtained by blood sample analysis are discussed. Up to the present time the PaO2 of more than sixty sick newborn babies have been monitored using these transducers in the Neonatal Unit at University College Hospital. The results obtained with these transducers in the first eighteen babies are reported in detail and demonstrate the possibility of continuous, reliable measurement of PaO2 under routine clinical conditions.

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