Change In TcPO2 Research Articles

A combined tc-PO2 and skin blood flow sensor.

A new approach to the determination of energy delivered to the skin during transcutaneous oxygen tension (tc-PO2) measurements was tested. The test was carried out using a tc-PO2 electrode constructed with an active thermal shield in order to provide more sensitive and specific heat transport measurements, and consequently to create the possibility of determining skin blood flow rates. The oxygen measurement properties did not differ from the conventional tc-PO2 electrode. In vivo measurements were performed on 11 adult volunteers. Skin blood flow was determined by a blood flow cessation technique to be 0.124 +/- 0.053 ml . cm-2 . min-1 at the start of the experiments, rising to 0.164 +/- 0.61 ml . cm-2 . min-1. Tc-PO2 changed from 56.2 +/- 9.8 mmHg (7.5 +/- 1.3 kPa) to 68.3 +/- 9.0 mmHg(9.1 +/- 1.2 kPa). It is concluded that a thermally shielded electrode makes it possible to determine the convectional component of the heat loss from the electrode to the skin and consequently to compute a relative measure of skin blood flow rate. The observed change in computed skin blood flow rate was correlated to the observed change in tc-PO2 (P less than 0.1).

Effects of routine care procedures on transcutaneous oxygen in neonates: a quantitative approach.

The changes in transcutaneous oxygen tension (TcPO2) during 123 observations of 10 care procedures were compared with the intrinsic variability of the TcPO2 at the time of the procedures. Standard deviations of the TcPO2 were measured by planimetry from continuous recording in undisturbed infants during a 10-minute control period immediately before each procedure. The decrement of TcPO2 during the procedure and the change in TcPO2 5 minutes after the procedure had ended were measured. A chest x-ray film had the most striking early hypoxic effect, but all the procedures produced early hypoxia in at least one-quarter of the infants. The significant decreases in oxygenation with particular procedures indicate areas in which changes in techniques might be applied to the benefit of the neonate.

Variable heart rate decelerations and transcutaneous Po2 during umbilical cord occlusion in fetal monkeys

In five near-term rhesus monkeys under ketamine anesthesia, fetal heart rate, blood pressure, intrauterine pressure, and transcutaneous oxygen tension (tcPo2) were recorded continuously while the umbilical cord was occluded for 15 or 30 seconds. Fetal heart rate decreased 55 ± 19 bpm, (mean ± SD) and 78 ± 20 bpm, respectively, with 15 and 30 second occlusions, while tcPo2 declined 6.0 ± 1.6 and 11.5 ± 3.3 torr, respectively. Fetal hypertension started promptly with cord occlusion and reached a maximum within 5 to 16 seconds; fetal blood pressure decreased thereafter and, in most instances, fell below the baseline until fetal heart rate began to recover. Fetal heart rate decreased within 1 to 2 seconds of cord occlusion. tcPo2 changes were the same, while heart rate changes were attenuated when the fetus was pretreated with 0.2 mg of atropine. These findings support a rapid and marked initial baroreceptor response, followed by a less marked chemoreceptor response. Thirty seconds following cord occlusion, Pao2 had returned to baseline, white tcPo2 was still 3 to 7 torr below baseline, indicating cutaneous vasoconstriction even though systemic blood pressure was normal. Relative heat output required to maintain the tcPo2 electrode temperature at 44°C did not reflect alterations in skin perfusion during periods of cardiovascular change.

The relationship of fetal heart rate patterns to the fetal transcutaneous Po2

Continuous transcutaneous Po2 (tcPo2) monitoring of the human fetus was performed during 46 labors, 30 of which were complicated by abnormal fetal heart rate (FHR) patterns. FHR variability decreased with increases in the fetal tcPo2, and FHR variability increased with decreases in the fetal tcPo2. Analysis of the tcPo2 and FHR tracings provided an explanation for this apparent discrepancy. While rising fetal tcPo2 values were usually associated with decreased FHR variability, the pattern of late deceleration and decreased variability must still be considered an ominous pattern. The fetal tcPo2 declined during the decleration and rose thereafter, with corresponding decreased FHR variability. Incomplete recovery of the fetal tcPo2 was associated with progressive acidosis. Repetitive and isolated late deceleration patterns showed markedly dissimilar fetal tcPo2 changes, suggesting different mechanisms may be involved in their production. Further studies are required before any definite conclusions can be drawn about the relationship of the FHR and the fetal tcPo2.

1287 EFFECTS OF ROUTINE PROCEDURES ON TRANSCUTANEOUS OXYGEN TENSION (TcPO2) IN NEONATES, A QUANTITATIVE APPROACH

Neonates in the intensive care unit are subjected to many routine procedures, some of which have been qualitatively observed to decrease oxygenation. This study quantitatively compares the changes in tcPO2 during 122 observations of 10 care procedures with the intrinsic variability of the tcPO2 at the time of the procedures. Standard deviations (SD) of tcPO2 were measured by planimetry from continuous recording in undisturbed infants over a 10 minute control period immediately prior to each procedure. The decrement of tcPO2 during the procedure (immediate) and the change of tcPO2 five minutes after completion of the procedure (late) were measured. The Table displays both mean change in tcPO2 (1) in mmHg and the mean change in tcPO2 divided by the mean SD of the control period for each procedure (2).The significant decreases in oxygenation with particular procedures indicate areas in which changes in techniques might be applied to the benefit of the neonate. New techniques for these procedures may be evaluated by the methods used in this study.

261 EFFECT OF INTRALIPID ON RESPIRATORY CALORIMETRY IN PRETERM INFANTS

The purpose of this study was to determine, 1) whether intralipid (IL) infusion in preterm infants leads to decrease in transcutaneous oxygen tension (TcPO2) and apnea, 2) whether change in TcPO2 is due to decreased pulmonary diffusion or increased oxygen utilization. TcPO2, oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory quotient (RQ), respiratory rate, serum triglyceride (TG) & free fatty acid (FFA) were serially measured in 5 preterm AGA infants (B.W. 980-2430 gm) before and during a 4 hr IL infusion with peripheral parenteral alimentation. Total caloric intake ranged from 80-110 Kcal/kg.d. Infants remained in room air at constant environmental temperatures throughout the study. No significant change in skin temperature occurred. Only one infant developed apnea during IL infusion with a simultaneous decrease in TcPO2. One additional infant had a decrease in TcPO2 during IL. A decrease in RQ occurred consistently in all 5 infants and 4/5 infants had an increase in VO2. Concl. 1) Apnea & change in TcPO2 were not consistently observed during IL infusion, 2) RQ values greater than 1.0 suggest the anabolic state of the infants, 3) Preterm infants are capable of adapting to changes in the available nutrients for oxidative metabolism.

In Vivo vs. In Vitro Response Time of Trancutaneous Po2Electrodes A comparison of four devices in newborn infants

Four devices for transcutaneous PO2 (tcPO2) monitoring have been applied simultaneously in 16 infants. Both during a maximal change in PaO2 and during physiological PO2 variations, the in vivo response time of the electrodes did not show the differences observed in vitro. We compared A, a prototype of the electrode by Huck, Lübbers and Huch (25 micrometer Telfon membrane) ; B, the commercial version of A by Hellige--Draeger (25 micrometer Telfon); C, the Radiometer TCM I oxygen monitor (25 micrometer polypropylene); and D, the Roche macrocathode electrode (6 micrometer Mylar), at 44 degree C. In vitro the 50% response times were 2.9 (A), 4.4 (B), 3.7 (C), and 7.4 (D) sec. The rates of tcPO2 changes at the midpoint of the response curves were 3.8(A) 2.0 (B), 3.0 (C), and 1.7 (D) kPa/sec. In vivo during a sudden change from hyperoxemia (FIO2 1.0) to normoxaemia the respective rates were 0.6 (A), 0.8 (B), 1.1 (C), and 1.0(D) kPa/sec. The in vivo 50% response times were 53.3 (A), 51.1 (B), 46.2 (C) and 45.3 (d) kPa/sec. The in vivo 50% response time were 53.3 (A), 51.1 (B), 46.2 (C), and 45.3 (d) kPa/sec. The in vivo 50% resonse time were 53.3 (A), 51.1 (B), 46.2 (C), and 45.3 (D) sec. The lag time between PaO2 and tcPO2 was about one third of this overall response time. The response to more physiological variations of PaO2 (periodic breathing) was not different among the tested electrodes in terms of damping and of delay of the tcPO2 deflections. In a steady state the correlation of tcPO2 44 degree C vs PaO2 was close (r = 0.98) with all devices up to 6.1 kPa (456 torr).

947 USE OF TRANSCUTANEOUS OXYGEN (tcPo2) MONITORING DURING INFANT TRANSPORT

During transport from outlying hospitals, critically ill neonates may be exposed to inappropriate levels of oxygen for prolonged periods. This study was undertaken to determine the feasibility and usefulness of tcPo2 monitoring during transport of infants with respiratory diseases. A standard Roche 5301 oxygen monitor was powered by a portable battery/AC-DC inverter system. The electrode drift was less than 2% for periods up to 120 min. with no interference in recording from ambulance motion. The skin electrode was placed on an infant's thigh immediately after arrival at the referring hospital. Seven infants, gestational age 28-41 weeks, birth weight 820-3490 gm, four of whom required intubation and ventilation, were evaluated. The tcPo2 ranged from 48-98 torr on initial reading at the referring hospital, providing an objective assessment of the infant's oxygenation. With the transcutaneous monitor the F1O2 could be adjusted rapidly to required levels and adequate assisted ventilation established when needed. Unstable infants were identified readily by the large change in tcPo2 with minimal handling. Paired values of tcPo2 & Pao2 were within ±10 torr (range Pao2 42-112) in 70% of measurements. In 3 patients the tcPo2 readings remained in an adequate therapeutic range throughout transport. Two patients had significant lowering (greater than 40 torr) of tcPo2 from various procedures during transport. In summary, we have found tcPo2 monitoring useful during transport of unstable ill infants.

EVIDENCE FOR A TONIC COMPONENT OF THE HERING-BREUER INFLATION REFLEX IN THE TERM NEONATE

Animal studies have shown that an increase in FRC slows respiration, increases expiratory duration and is vagally mediated. To explore whether a similar response occurs in humans, we studied respiratory timing in 10 sleeping, healthy term neonates on days 1, 2 and 3, before and after a change in lung volume accomplished by adding a continuous positive airway pressure(CPAP) of 3 and 6 cm H2O. Using a mask and flowmeter with constant flow to reduce deadspace, we measured inspiratory time(Ti), expiratory time(Te), total respiratory cycle duration (Ttot), and tidal volume. Comparative movements of upper and lower rib cage were recorded via mercury strain gauges and transcutaneous(Tc) PO2, monitored via a skin electrode. Increasing lung volume caused a significant prolongation of Te% (100xTe/Ttot) on all 3 days(mean data in table). As CPAP was raised from 0 to 6. respiratory rate fell from 47 to 42(NS),58 to 42(p<.005) and 50 to 36(p<.005) on days 1, 2, and 3 respectively. CPAP at 6 cm caused a mean increase in FRC of 19±7cc without significant change in tidal volume and there was no change in TcPO2 when compared to the control period. The direction of paradoxical rib cage movement was unaltered by CPAP. These observations suggest that the significant rise in Te% at increased lung volume may be secondary to the stimulation of a tonic inflation reflex.