Transcutaneous carbon dioxide tension in newborn infants: reliability and safety of continuous 24-hour measurement at 42 degrees C

In 58 newborn infants a new iridium oxide sensor was evaluated for transcutaneous carbon dioxide (tcPCO2) monitoring at 42 degrees C with a prolonged fixation time of 24 hours. The correlation of tcPCO2 (y; mm Hg) v PaCO2 (x; mm Hg) for 586 paired values was: y = 4.6 + 1.45x; r = .89; syx = 6.1 mm Hg. The correlation was not influenced by the duration of fixation. The transcutaneous sensor detected hypocapnia (PaCO2 less than 35 mm Hg) in 74% and hypercapnia (PCO2 greater than 45 mm Hg) in 74% of all cases. After 24 hours, calibration shifts were less than 4 mm Hg in 90% of the measuring periods. In 86% of the infants, no skin changes were observed; in 12% of infants, there were transitional skin erythemas and in 2% a blister which disappeared without scarring. In newborn infants with normal BPs, continuous tcPCO2 monitoring at 42 degrees C can be extended for as many as 24 hours without loss of reliability or increased risk for skin burns.     

Skin surface carbon dioxide tension in sick infants

Skin surface PCO2 (PSCO2) was measured at 44 C in 17 sick infants using a Radiometer surface PCO2 electrode. Values obtained for PSCO2 were compared with simultaneous values for arterial PCO2 (PaCO2). PSCO2 was found to be linerarly related to PaCO2 by a regression line with a slope 1.37. PaCO2 could be predicted from PSCO2 to within 6 torr in all instances. The relationship was not affected by the patient's gestational age, postnatal age, weight, or blood pressure. This electrode is a valuable clinical tool in the management of sick infants.     

Cerebral vascular responses to changes in carbon dioxide tension in term and preterm infants with apnea

Carbon dioxide (CO(2)) plays important roles in regulating both respiratory drive and cerebral blood flow. These effects are mediated, in part, by activity of the sympathetic nervous system. We hypothesized that the presence of acute life-threatening events or apnea in term or preterm infants, respectively, would serve as a marker for immaturity of cerebral autonomic innervation and that such infants would display a reduced cerebral vascular response to elevated pCO(2). Therefore, we evaluated the cerebral vascular response during CO(2) challenge tests in groups of term and preterm infants with primary apnea. In term infants (39 +/- 2 weeks gestation) with acute life-threatening events, elevated pCO(2) was accompanied by decreasing pulsatility index and increasing mean anterior cerebral blood flow velocity. However, in preterm infants (29 +/- 2 weeks' gestation) with apnea, pulsatility index and anterior cerebral artery flow velocity did not significantly change in response to CO(2) supplementation. We conclude that preterm, but not term, infants with apnea exhibit impaired vascular responses to hypercarbia.     

Response of cerebral blood volume to changes in arterial carbon dioxide tension in preterm and term infants

The response of cerebral blood volume (CBVR) to a small induced change in arterial carbon dioxide tension was studied by near-infrared spectroscopy in 17 newborn infants born from 26 wk of gestation to term. All 17 infants were undergoing mechanical ventilation but had apparently normal brains. The CBVR per kPa change in arterial carbon dioxide tension within the range 3.9 to 9.6 kPa was calculated from the change in total cerebral Hb concentration ([TCHb]) using the equation: delta CBV = delta [TCHb] x 0.89/[H] where [H] is the large vessel Hb concentration. A least-squares regression line with 95% confidence limits was derived for CBVR against gestational age. A highly significant linear increase in CBVR was found: mean CBVR from the regression increased from 0.07 mL.100 g-1.kPa-1 at 26 wk to 0.51 mL.100 g-1.kPa-1 at 40 wk.     

Cerebral vasoreactivity to arterial carbon dioxide tension in preterm infants: the effect of ibuprofen.

Cerebral vasoreactivity to CO(2), calculated by linear regression of total cerebral hemoglobin, measured by near infrared spectroscopy, and corresponding PaCO(2), in infants <32 weeks' gestation, was found to be unaffected by the administration of ibuprofen, which was given on the first postnatal day as prophylaxis against patent ductus arteriosus.     

Transcutaneous oxygen and carbon dioxide during the first half year of life in premature and normal term infants.

Repetitive polysomnograms were recorded from a total of 33 infants, 19 healthy preterm infants, and 14 term controls between 40 wk postconceptional age and 6 mo of age. These nighttime recordings lasted 2-4 h, except at 52 wk in preterm infants and at 3 mo of age in term infants when an overnight 12-h recording was performed. Minute by minute values of transcutaneous PO2 (PtCO2) and transcutaneous PCO2 (PtcCO2) levels and variability during the awake state, active sleep, and quiet sleep were obtained through computer analyses of the polygraphic data. The results from preterm infants at corrected postconceptional age could not be differentiated from those of control infants. PtCO2 levels rose between 40 wk and 3 mo, and PtcCO2 levels declined. Sleep states modulated only the variability of PtcO2, not the level; in contrast, state modulation was seen in both variability and level of PtcCO2 throughout the age span studied. During sleep the number of transient declines in PtCO2 greater than 2.03 kPa (15 mm Hg) decreased with advancing age. Hypercapnic PtcCO2 values decreased with age as well, but their prevalence in healthy, young infants suggests the need for reevaluation of criteria for hypercapnia based on transcutaneous measurements. The data demonstrate that ventilatory regulation continues to undergo changes between 1 and 3 mo, the age of highest risk for sudden infant death syndrome.     

Increasing arterial carbon dioxide tension: influence on transcutaneous carbon dioxide tension measurements

Despite widespread use of transcutaneous PCO2 (TcPCO2) monitoring, the precise relationship between TcPCO2 and PaCO2 remains unclear. It has been widely assumed that theoretical correction of TcPCO2 (combining temperature correction with a constant metabolic factor of 4 mm Hg) accounts for the elevation of TcPCO2 over PaCO2. To test this assumption, TcPCO2 was measured with a 44 degrees C electrode and compared to PaCO2 in 60 normotensive infants with cardiorespiratory disease during the first four +/- six days of life (mean +/- SD) (range one to 36 days). During hypocapnea, from PaCO2. In contrast, during normocapnea, theoretically corrected TcPCO2 exceeded PaCO2 by 5 +/- 4 mm Hg (P less than .001), and similarly during hypercapnea, theoretically corrected TcPCO2 exceeded PaCO2 by 9 +/- 6 mm Hg (P less than .001). These data suggest that, as PaCO2 increases, there may be an imbalance between tissue CO2 production and removal, resulting in a progressively increasing gradient between TcPCO2 and PaCO2. Clarification of the relationship between TcPCO2 and PaCO2 should enhance the interpretation of TcPCO2 measurements in infants.     

Transcutaneous bilirubin measurement in preterm infants]

Transcutaneous bilirubinometry is an effective screening tool for neonatal jaundice in full-term babies. But its accuracy is not shown yet in preterm infants. METHODOLOGY: We carried out a prospective study in a neonatal intensive care unit. The study included 47 preterm infants. From birth, a transcutaneous bilirubin measurement (BTc) using the BiliCheck was made on the forehead of each newborn every 8 h. Blood sampling for determination of total serum bilirubin (BS) was combined with BTc: 1) if value of BTc was higher than limits values for phototherapy; 2) on the second day of life and 3) 4 hours after cessation of phototherapy. RESULTS: Mean gestational age was 30 week and mean birth weight was 1419 g. We studied 151 pairs of BTc and BS. Mean values obtained by BTc and BS were respectively 160.6+/-50 mumol/L and 190.6+/-61.4 mumol/L. A significant correlation between BTc and BS was found. But the limits of agreement were very wide. The negative predictive value (NPV) of BTc was above 90% in each group of gestational age. DISCUSSION: The need for phototherapy cannot be determined by BTc in preterm infants. But the BTc is reliable when its value is under the limits for phototherapy. CONCLUSION: With a very high incidence of neonatal jaundice (87%) in our cohort, a value of BTc under the limits for phototherapy has a good NPV in preterm infants.     

Transcutaneous oxygen tension during nonnutritive sucking in preterm infants

The effects of nonnutritive sucking on transcutaneous oxygen tension, heart rate, and respiratory rate were studied sequentially in 14 sleeping preterm infants breathing room air. Transcutaneous oxygen tension increased during nonnutritive sucking in infants between 32 and 35 weeks postconceptional age, but not in those between 36 and 39 weeks. This response was not associated with a change in respiratory rate or sleep state, although heart rate tended to increase. These data offer further support for the beneficial effects of nonnutritive sucking in preterm infants.     

Transcutaneous oxygen and carbon dioxide levels and a clinical symptom scale for monitoring the acute asthmatic state in infants and young children

Measurement of transcutaneous PO2 and PCO2 in addition to a clinical symptom grading system was used to monitor the acute asthmatic attack in children under two years of age. tcPO2 was lowered already at signs of mild obstruction and decreased in parallel with clinical deterioration. tcPCO2 was almost unchanged at mild to moderate obstructive symptoms. With clinical deterioration tcPCO2 rose steadily. An increase of the oxygen concentration to 30-40% in the inspired air increased tcPO2, on the average by 70%, but did not change the tcPCO2, level. Continuous recording of tcPO2 and tcPCO2 as well as the clinical grading system are valuable tools when monitoring severely obstructive infants and young children.     

Transcutaneous oxygen and carbon dioxide monitoring in intensive care.

Transcutaneous oxygen (TcPo2) and carbon dioxide (TcPco2) tensions were compared with arterial values in 23 children aged 4 months to 14 years, all requiring some form of respiratory support, but not in shock. Electrodes were placed on the upper chest and were heated to 45 degrees C. For TcPo2 and arterial oxygen (Pao2) a tight linear correlation over the range 6 to 14 kPa was found. Arterial carbon dioxide (Paco2) ranged between 2.63 and 6.8 kPa, and over this range a linear regression adequately described the relation of TcPco2 to Paco2. No effects of age were found for the relation between TcPo2 and Pao2. Over a four hour period, the mean ratio TcPo2/Pao2 rose significantly from 0.96 to 1.04, while the mean ratio of TcPco2/Paco2 fell from 1.65 to 1.62. Five children developed superficial burns which were still present at 48 hours. In children who require respiratory support but are not in shock, TcPo2 and TcPco2 bear a constant and predictable relation to Pao2 and Paco2, and can predict arterial values within clinically acceptable tolerances.     

Impact of volume guarantee ventilation on arterial carbon dioxide tension in newborn infants: a randomised controlled trial

OBJECTIVE: To compare the effects of the two modes of ventilation, synchronous intermittent positive pressure ventilation (SIPPV) and SIPPV with Volume Guarantee (VG), on arterial carbon dioxide tension (PaCO(2)) immediately after neonatal unit admission. STUDY DESIGN: Randomised study of ventilation mode for premature inborn infants admitted to two tertiary neonatal units. After admission, infants were randomised to receive either SIPPV or VG using a Dr?ger Babylog 8000 plus ventilator. In the SIPPV group, peak airway pressure was set clinically. In the VG group, desired tidal volume was set at 4 ml/kg, with the ventilator adjusting peak inspiratory pressure to deliver this volume. The study was completed once the first arterial PaCO(2) was available, with the desirable range defined as 5-7 kPa. RESULTS: PaCO(2) was significantly higher in the VG group (VG: 5.7 kPa, SIPPV: 4.9 kPa; p=0.03). The VG group had fewer out-of-range PaCO(2) values (VG: 42%, SIPPV: 57%) and fewer instances of hypocarbia <5 kPa (VG: 32%, SIPPV: 57%) but neither difference achieved statistical significance. Regression analysis showed PaCO(2) was negatively correlated with gestation (r=-0.41, p=0.01) and also with the mode of ventilation (r=0.32, p<0.05). In the VG group, all infants 23-25 weeks' gestation had out-of-range PaCO(2) values. VG significantly reduced the incidence of out-of-range PaCO(2) and hypocarbia in infants over 25 weeks' gestation (VG: 27%, SIPPV: 61%; p<0.05). CONCLUSION: Using this strategy, VG appears feasible in the initial stabilisation of infants over 25 weeks' gestation, with a halving of the incidence of hypocarbia. In the small number of babies studied below this gestation, VG was not found to be effective.     

Effects of sleep position,sleep state and age on heart rate responses following provoked arousal in term infants

Previous studies have suggested that autonomic dysfunction may be involved in Sudden Infant Death Syndrome (SIDS). The major risk factors for SIDS are the prone sleeping position and maternal smoking. Our aim was to examine the effects of sleeping position and maternal smoking on the postnatal maturation of autonomic function by examining heart rate responses following arousal in healthy term infants. Twenty-four infants (11 born to mothers who smoked during pregnancy and 13 to mother who did not smoke) were studied using daytime polysomnography and multiple measurements of arousal threshold (cm H(2)O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep (AS) and quiet sleep (QS).We demonstrated no difference between smoking and non-smoking groups of infants in any of our measurements, and thus combined data from the groups. Baseline (BHR) was elevated in the prone compared to the supine position in quiet sleep (QS) at 2-3 weeks (p<0.001) and 5-6 months (p<0.001), and in active sleep (AS) at 2-3 and 5-6 months (p<0.05). BHR was significantly elevated in AS compared to QS in the supine position at all ages (p<0.01) and in the prone position at 2-3 (p<0.001) and 5-6 months (p<0.05). Increases in heart rate (deltaHR%) following arousal were significantly greater in the supine compared to the prone position in QS at 2-3 weeks (p<0.05) and in AS at both 2-3 (p<0.01) and 5-6 months (p<0.05). DeltaHR% was significantly greater in AS compared to QS in both supine (p<0.05) and prone (p<0.001) positions at 2-3 weeks and in the supine position at 2-3 months (p<0.001). We conclude that sleep state, sleep position and postnatal age affect the cardiac responses following arousal from sleep in healthy term infants. Impairment of heart rate control in the prone position may be important in understanding the increased risk for SIDS in this position.     

Transcutaneous bilirubinometer: Its use in Chinese term infants and the effect of haematocrit and phototherapy on the TcB index

The application of the transcutaneous bilirubinometer in screening for neonatal jaundice was evaluated in 259 full-term Chinese infants: 202 who had not received any treatment and 57 who were receiving phototherapy. The transcutaneous bilirubin index correlated well with the serum bilirubin level (SB) of the untreated infants and the coefficient of correlation was slightly higher for TcB readings obtained over the mid-sternal area ( r =0.91; P <0.001) than those over the forehead ( r =0.85; P <0.001). Transcutaneous bilirubinometry was unreliable in predicting the SB level in infants receiving phototherapy even if the SB readings were obtained over shaded skin. The haematocrit of the infants, though having a statistically significant effect on the TcB index, contributed only minimally to the regression line and correlation coefficient between the TcB index and SB level.     

Transcutaneous bilirubinometer: its use in Chinese term infants and the effect of haematocrit and phototherapy on the TcB index

The application of the transcutaneous bilirubinometer in screening for neonatal jaundice was evaluated in 259 full-term Chinese infants: 202 who had not received any treatment and 57 who were receiving phototherapy. The transcutaneous bilirubin index correlated well with the serum bilirubin level (SB) of the untreated infants and the coefficient of correlation was slightly higher for TcB readings obtained over the mid-sternal area (r = 0.91; P less than 0.001) than those over the forehead (r = 0.85; P less than 0.001). Transcutaneous bilirubinometry was unreliable in predicting the SB level in infants receiving phototherapy even if the SB readings were obtained over shaded skin. The haematocrit of the infants, though having a statistically significant effect on the TcB index, contributed only minimally to the regression line and correlation coefficient between the TcB index and SB level.