Tc PO2 Research Articles

Effect of tilting on oxygenation in newborn infants.

Transcutaneous (tc) PO2 in newborn infants increased on head up tilting (median increase 0.5 kPa at term, 1.0 kPa preterm). Head down tilting was associated with an equivalent fall in tcPO2. There was no change in tcPCO2. Tilting of infants mechanically ventilated for respiratory distress syndrome or surgery produced no consistent change in PO2.

PHYSIOLOGICAL AND BEHAVIOURAL EFFECTS OF HEELSTICK PROCEDURES ON NEONATES

This study was performed to evaluate possible physiological and behavioural changes in healthy neonates(n.) during heelstick procedures(h.p-).25 n. in room air and without severe perinatal complications (Minde s.<4)undergoing h.p. for bilirubin, glycem., ht., in the first 2 wks of life, were included in the study(G.A. wks 34±3;B.W. g.1935±580;Apgar s. 5m. 8.5±1). Behavioural states(B.S.), transcutaneous oxygen tension(Tc PO2), heart rare(H.R.)and respiratory rate(f.) were monitored 3m before and after h.p. and during h.p. that lasted from 20″ to 240″ x=132″. Data were sampled at 10″ intervals using a timer and an audiotape. Variables were compared between periods before, during and after h.p.(p.t tests).B.S. increased from 2.9±0.9 to 5.6±0.5 during h.p.(p<.001), with behavioural distress lasting after h.p..H.R. increased from 138±14 before h.p. to 168±19 during h.p.(p<.001)and remained elevate after h.p. TcPO2 did not change and f. decreased from 48±10 to 40±10 during h.p.(p<.01)but recovered rapidly after h.p. Our n. react to h.p. with fussing, crying and H.R. increasing; f. decreased briefly without impairing oxygenation.

Transcutaneous measurements of oxygen tension at edges of leg ulcers: preliminary communication.

Using skin-surface sensors, transcutaneous oxygen tension (TcPo2) has been measured at the edges of ulcers and at control sites proximal to wounds on the same legs. TcPo2 at 43 degrees C at the edges of venous ulcers was found to be significantly different (P less than 0.003) from that of arterial and mixed arteriovenous ulcers (P less than 0.05) respectively. TcPo2 on healed skin was higher than at any wound edge. At this temperature TcPo2 was also found to be significantly different (P less than 0.001) on the intact skin of patients with venous disease when compared with measurements at identical sites on healthy controls. In the same group, these TcPo2 values increased with dependency. By contrast, at 37 degrees C TcPo2 was no different between groups (P less than 0.10), nor did it alter with position. This protocol adopted for investigating ulcers enables a quantitative distinction to be made between ulcers of different aetiologies. The differences in TcPo2 between different ulcers and healed skin support the fibrin cuff mechanism which has been suggested as the cause of venous ulceration.

Pulse Oximetry Advantages in Infants With Bronchopulmonary Dysplasia

We studied 12 infants with a clinical and radiologic diagnosis of bronchopulmonary dysplasia who were oxygen dependent and older than 30 days. Simultaneous readings of hemoglobin oxygen saturation (SaO2) determined by two pulse oximeters (Nellcor 100, BTI Biox III) and transcutaneous (tc) PO2 (Sensor Medics, Transend) were correlated with SaO2 (Radiometer, OSM 2 Hemoximeter) and PaO2 (Corning 178) measured on blood from an indwelling arterial catheter. For each infant, the fractional inspiratory oxygen (FiO2) was adjusted to obtain three to five sets of data in the range of 70% to 95% SaO2. Fifty-three data points were generated and pooled for analysis. The slope of the regression line generated for the Nellcor 100 was .86; for the BTI Biox III, it was .91; and for the Sensor Medics Transend, it was .55, resulting in average errors of +2.5%, +1.0%, and -29%, respectively, when comparing corresponding transcutaneous and arterial values. When SaO2 was equal to or less than 95%, no infants were hyperoxic. These data confirm reports by others that tcPO2 values do not accurately represent PaO2 values in older infants with bronchopulmonary dysplasia. Pulse oximeters do not require user calibration, and their sensor is unheated so they will not cause skin burns. We conclude that pulse oximetry offers major advantages over tcPO2 measurements in the management of infants with bronchopulmonary dysplasia.

1356 THE EFFECT OF PHENOBARBITAL (PB) ON CEREBRAL BLOOD FLOW VELOCITY (CBFV) FOLLOWING ENDOTRACHEAL UZ3U SUCTION (ETS)

ETS produces a transient fall in PaO2 and a rise in mean arterial blood pressure (MABP). PB may decrease the neonatal response of CBFV as a result of ETS. 7 infants, mean birthweight 819g and mean gestational age of 27 wks, were studied in the first 20 hrs of life. Area under the velocity curve (AVC), peak systolic velocity (PSV), and end diastolic velocity (EDV) were measured with a doppler velocimeter before (C) and after (S) ETS at 3 time periods: prior to PB (baseline: 0), 2 hrs after and 4 hrs after an i.v. dose of 20 mg PB/kg. Heart rate, mean arterial blood pressure (MABP) and transcutaneous PO2(Tc PO2) were measured simultaneously with the doppler determinations. There were no changes at any time with PSV (values: 7.4 cm/sec) and EDV (values: 2.1 cm/sec). As shown above, ETS produced a significant rise in MABP and a fall in TcPO2. Four hours following PB treatment, the percent change in ΔAVC associated with ETS was reduced. We speculate that PB may modulate the response of ΔAVC to ETS.

THE IMPROVED OXYGENATION OF PRETERM INFANTS DURING NON-NUTRITIVE SUCKING DEPENDS ON POSTCONCEPTIONAL AGE

Non-nutritive sucking (NNS) has been reported to stabilize transcutaneous (tc) PO2 in preterm infants during both gavage feeding and assisted ventilation. To evaluate the effect of NNS in the resting preterm infant, we measured TcPO2, heart rate (HR) and resp. rate in 14 healthy, sleeping infants (G.A. at birth 26-33 wk, B.Wt 710-1450g). Each study was begun in active sleep, and comprised 15 min. of data collection divided into 3 equal periods: preNNS, NNS and postNNS. Sucking was recorded with a pacifier adapted to measure sucking pressure, and respiration was detected with a nasal thermistor. Subjects were studied at two weekly intervals until discharge and divided into 4 groups based on postconceptional age.During NNS, TcPO2 increased 2.3±0.9 mmHg at 32-33 wk (p<.01) and 4.0±1.5 mmHg at 34-35 wk (p<.05). In contrast, TcPO2 did not increase during NNS at either 36-37 or 38-39 wk. HR increased during NNS in all 4 groups although this was only significant at 34-35 wk (p<.01) and 36-37 wk (p<.02), while resp. rate never changed. Time spent in active sleep during the 5 min. epochs did not differ between the 3 periods and ranged from 61% to 96%. Thus the increase in TcPO2 during NNS is dependent on the infant's postconceptional age and does not appear to be due to a change in resp. rate or sleep state. These data suggest that providing an opportunity for NNS may be a beneficial intervention in the care of healthy preterm infants between 32 and 35 wk postconceptional age.

Scalp blood flow measured by the xenon clearance technique and transcutaneous PO2 in the fetal lamb.

Scalp blood flow and transcutaneous (tc) PO2 were measured in four fetal lambs at 130-135 days of gestation. Scalp blood flow was measured by the xenon clearance technique using a technetium source to correct for changes in distance from the detector. The effect of circular pressure, the so-called "tonsure effect" on scalp flow and tcPO2, was evaluated by pressing a ring on the scalp. A circular pressure between 20-30 mmHg markedly reduced local scalp blood flow and was sufficient to reduce tcPO2 to zero. We found evidence of significant recirculation of xenon in the fetal circulation indicating right-left shunting. This study showed that the tonsure effect seriously affected scalp blood flow and tcPO2 in the fetus.

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.

1634 CHANGING PATTERN OF CHEST WALL MOVEMENTS IN RESPIRATORY DISTRESS SYNDROME (RDS)

To determine the influence of RDS on chest wall (CW) movements 6 infants (B.W. 1.7±.3Kg,G.A. 32±2 wks) with mild RDS requiring O2 for ≥3 days and 8 infants (B.W. 1.7±.5Kg, G.A. 33±2 wks) without cardiopulmonary disease were studied for 60 min on days 1,3 and 7. We determined CW movements by strain gauges over upper (URC), lower (LRC) ribcage and abdomen, airflow by nasal thermistor, transcutaneous(Tc) PO2 and PCO2 and behavioral state through out each study. Asynchronous (Asyn) CW movement was defined as inward ribcage motion during inspiration. Total duration of apneic episodes ≥5 sec was calculated/hour. Asyn URC movements and apneic time increased abruptly by day 7 in infants with RDS and gradually in the non-RDS group. LRC was largely Asyn in both gps. TcPO2, TcPCO2 and behavioral state did not differ between groups or over time. These data suggest that RDS enhances respiratory drive and intercostal muscle activity with a resultant decrease in Asyn URC movements and apnea. The comparable blood gases of the two groups suggest that nonchemical factors are responsible for the increased respiratory drive in infants with RDS.

1695 VULNERABILITY OF PRETERM INFANTS TO NASAL OBSTRUCTION

This study was designed to determine cardiopulmonary responses to nasal obstruction in different sleep states. 8 healthy preterm infants (wt 1.8±.1Kg) were studied at a corrected G.A. of 35±2 wks by multiple 10 sec occlusions during active (AS) and quiet (QS) sleep, via nasal prongs fitted with a thermistor to measure airflow. Heart rate (HR), mouth airflow, transcutaneous PO2 (Tc PO2), chest wall movements, respiratory frequency (f) and sleep state were continuously monitored. Nasal occlusion was invariably accompanied by a fall in TcPO2, which was greater during AS than QS (8±2 vs 5±3 mmHg, p<.01). In contrast, HR fell with only 54% of occlusions, more in AS than QS (35±15 vs 21±7/min, p<.05). During obstruction the frequency of respiratory efforts decreased from 45±10 to 35±7/min (p<.001) compared to preocclusion levels, while mouth airflow was only sporadic and did not influence the fall in TcPO2 or HR. In the initial 5 sec following occlusion, f returned to preocclusion levels. During the subsequent 5 sec, f decreased from 47±10 to 35±13/min (p<.03) in AS and from 41±9 to 31±16/min (p<.03) in QS, as compared to preocclusion levels. Furtheremore, in the 20 sec following occlusion (vs preocclusion) the duration of respiratory pauses ≥2 sec increased in both AS and QS (p<.01). We conclude that 1) preterm infants are more vulnerable to nasal obstruction in AS with a greater fall in PO2 and HR, 2) airway obstruction may enhance susceptibility to the subsequent development of central apnea, and 3) since obstruction may not be accompanied by a fall in HR, routine cardio-respiratory monitoring may fail to detect many episodes.

Measurement of Heated Skin O2Diffusion Conductance and Po2Sensor Induced O2Gradient

A large cathode heated transcutaneous PO2 electrode was used to measure the resistance of skin to diffusion of O2 from the capillary bed to the surface. With a non-O2-consuming tcPO2 electrode, one would read ideal tcPO2, Pi, which approximates PaO2 between 50 and 100 mmHg due to approximate cancellation of the rise by heating and the fall by skin O2 consumption. When a large cathode tcPO2 electrode is used, its O2 consumption causes a PO2 gradient across skin resistance, Rs, which depends on electrode membrane resistance RM (with Mylar), or RT (with Telfon). Surface PO2 will fall below Pi, and assuming no change in capillary PO2: PT/Pi = RT/(RT + Rs) and PM/Pi = RM/(RM + Rs) (1) 12 micrometer Telfon is 50 times as permeable to O2 as 6 micrometer Myler. When an electrode, covered alternately with these two membranes, was mounted on the same skin site in six subjects, the mean observed PT/PM was about 0.3. Substituting in equation (1) yields RT/Rs = 0.4, Rm/Rs = 20, and PM/Pi = 0.95. Using the known O2 permeability of Teflon, we computed skin O2 conductance to be 6.6 pmol O2/(cm2 .s .kPa), or 15 nl O2/(cm2 .s .atm). This method thus provides a way of determining ideal tc PO2 and stirring effect, phi, of other electrodes and various membranes.

1238 SKIN METABOLISM AND BLOOD FLOW MEASUREMENT: ROLE IN TCPo2 ANALYSIS

The effect of heating by a tc Po2 electrode on skin metabolism and blood flow, and on the relationship of Pao2 to tcPo2 was determined in 3 normal adults. While breathing O2, skin metabolism was measured as O2 solubility × ΔtcPo2/Δt (torr/min), at 37° and 45° after arterial cuff occlusion. Using this, skin blood flow and diffusion gradients for O2 and heat between capillaries and surface were measured by solution of simultaneous equations for tcPo2 vs Pao2 from 6 steady state correlations at 2 temperatures (43°,45°) and 3 Po2s (75,150,600), using the changes of O2 dissociation and solubility thereby induced. Heating efficiency, (Tc-37)/(Te-37) averaged .84 (c=capillary,e=electrode). (c-e)Do2 was 28±3 torr at 44° Te. Skin O2 consumption and blood flow were .0043±.0001 ml O2 and .75±.10ml blood per gm per min. From these parameters, tcPo2 was computed for O<Pao2<700 defining a sigmoid relationship. At Te=44°, tcPo2 nears O at Pao2=20, approximates Pao2 when 60<Pao2<130, and parallels Pao2, (about 50 torr lower) when Po2>300. TcPo2 was most dependent on blood flow at high O2. The data yield algorithms for “correcting” tcPo2 measurements to obtain Pao2. Skin metabolism increases 7%/°C, while blood flow (after 30 min. heating at 45°C) fell only 1.2%/°C with brief reduction of Te to 43°C. Skin blood flow, independently determined from tcPo2 washin time constant after release of occlusion while breathing O2, averaged about 33% higher than above, possibly due to post-ischemic hyperemia, and uncertainty regarding skin O2 solubility. Similar analysis will be done in children.

Transcutaneous, noninvasive PO2 monitoring in adults during exercise and hypoxemia.

A new, commercially available, transcutaneous (tc) PO2 monitor was tested in adult females and in laboratory animals to assess its applicability in measuring arterial oxygen tension during physiological stress. Observed values on dogs correlated well with direct measurements of arterial PO2 and with previous data obtained from measurements of arterial blood during exercise and hypoxemia. In our female subjects the unit responded rapidly to changes in inspired ambient oxygen and electrical stability was excellent during maximal exercise tests. Transcutaneous PO2 decreased to an average of 87.8 Torr during maximum exercise breathing 20.9% O2, and to 32 Torr while breathing 12.6% O2 at maximum work. Two distinct patterns of response to tc PO2 were observed during hypoxic and normoxic exercise. The technique appears to have substantial future application both in clinical and physiological investigation involving adult subjects.

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.

Transcutaneous Po2 Monitoring in Routine Management of Infants and Children With Cardiorespiratory Problems

Results are reported concerning the clinical application of the transcutaneous PO2 method (tc PO2 method) according to Huch et al. for monitoring arterial PO2. Thirty long-term continuous tc PO2 recordings were made in 22 ventilated children and infants with cardiorespiratory problems in four different pediatric intensive care units (Zürich, Göttingen, Kassel, and Mainz). These recordings were compared with 132 arterial PO2 determinations made during the same period of time. There was a linear relationship and a close correspondence between arterial PO2 and tc PO2 (r = .94). The continuous recordings have shown that the variability of PO2 is much greater than assumed so far by single blood gas analysis. This fact restricts greatly the value of single samples. Continuous tc PO2 monitoring has proved to be a great help in optimal respirator setting.

Additional Comments on Tc Po2, by Dr. Rooth

Since the publication of my article1, further data on tc Po2 have become available. There is some risk that a too low tc Po2 value may be recorded in seriously sick infants unless the temperature of the electrode is kept at 43 C. Even at this temperature the Huchs have seen no blisters at the site of measurements in the 500 cases they studied. In one premature infant with hemorrhagic tendency after exchange transfusion we saw a blister on the day after a four-hour recording had been performed.

Is Transcutaneous Po2, Reliable for Arterial Oxygen Monitoring in Newborn Infants?

The necessity of frequent Po2 controls in newborns exposed to high oxygen concentrations entails the use of indwelling arterial catheters. Any method of bypassing the complications of arterial catheters would be a great advantage for the newborn. Recently, electrodes were engineered allowing transcutaneous Po2 (tc Po2) measurements. tested two of them, the oxygen monitor 5300 Roche and the oxygen electrode of Huch et al. Good correlation between tc Po2, and Po2, has been reported in both in the newborn.