Simultaneous tissue pH and transcutaneous carbon dioxide monitoring in critically ill neonates

Recent Technologies for Transcutaneous Oxygen and Carbon Dioxide Monitoring

The measurement of partial pressures of oxygen (O2) and carbon dioxide (CO2) is fundamental for evaluating a patient's conditions in clinical practice. There are many ways to retrieve O2/CO2 partial pressures and concentrations. Arterial blood gas (ABG) analysis is the gold standard technique for such a purpose, but it is invasive, intermittent, and potentially painful. Among all the alternative methods for gas monitoring, non-invasive transcutaneous O2 and CO2 monitoring has been emerging since the 1970s, being able to overcome the main drawbacks of ABG analysis. Clark and Severinghaus electrodes enabled the breakthrough for transcutaneous O2 and CO2 monitoring, respectively, and in the last twenty years, many innovations have been introduced as alternatives to overcome their limitations. This review reports the most recent solutions for transcutaneous O2 and CO2 monitoring, with a particular consideration for wearable measurement systems. Luminescence-based electronic paramagnetic resonance and photoacoustic sensors are investigated. Optical sensors appear to be the most promising, giving fast and accurate measurements without the need for frequent calibrations and being suitable for integration into wearable measurement systems.

Transcutaneous CO2 Monitoring in Extremely Low Birth Weight Premature Infants

Extremely low birth weight (ELBW) premature infants are particularly susceptible to hypocarbia and hypercarbia, which are associated with brain and lung morbidities. Transcutaneous CO2 (TcCO2) monitoring allows for continuous non-invasive CO2 monitoring during invasive and non-invasive ventilation and is becoming more popular in the NICU. We aimed to evaluate the correlation and agreement between CO2 levels measured by a TcCO2 monitor and blood gas CO2 (bgCO2) among ELBW infants. This was a prospective observational multicenter study. All infants < 1000 g admitted to the participating NICUs during the study period were monitored by a TcCO2 monitor, if available. For each bgCO2 measured, a simultaneous TcCO2 measurement was documented. In total, 1828 pairs of TcCO2-bgCO2 values of 94 infants were collected, with a median (IQR) gestational age of 26.4 (26.0, 28.3) weeks and birth weight of 800 (702, 900) g. A moderate correlation (Pearson: r = 0.64) and good agreement (bias (95% limits of agreement)):(2.9 [-11.8, 17.6] mmHg) were found between the TcCO2 and bgCO2 values in the 25-70 mmHg TcCO2 range. The correlation between the TcCO2 and bgCO2 trends was moderate. CO2 measurements by TcCO2 are in good agreement (bias < 5 mmHg) with bgCO2 among premature infants < 1000 g during the first week of life, regardless of day of life, ventilation mode (invasive/non-invasive), and sampling method (arterial/capillary/venous). However, wide limits of agreement and moderate correlation dictate the use of TcCO2 as a complementary tool to blood gas sampling, to assess CO2 levels and trends in individual patients.

Transcutaneous PCO2 Monitoring in Newborn Infants During General Anesthesia Is Technically Feasible

Published ahead of print July 26, 2016.

BACKGROUND:

Transcutaneous (TC) measurement of Pco₂ (TC Pco₂) is a well-established method to monitor assisted ventilation in neonatal intensive care, but its use in the operating room is limited, and the data regarding its performance during general anesthesia of the newborn are lacking. The aim of this study is to evaluate the performance of continuous TC Pco₂ monitoring during general anesthesia in newborn infants.

METHODS:

Infants (n = 25) with a gestational age of 23 to 41 weeks and a birth weight of 548 to 4114 g were prospectively enrolled. During general anesthesia and surgery, TC Pco₂ was measured continuously and recorded at 1-minute intervals. Five-minute mean values were compared with simultaneously obtained blood gas (BG) analyses of Pco₂. Only the first paired TC and BG samples were used in this analysis. We defined precision as 2.1 times the standard deviation of the difference of the 2 samples. P < .01 was considered statistically significant.

RESULTS:

We obtained samples from 25 infants. The difference between TC and BG was 0.3 ± 0.7 kPa (mean ± standard deviation) giving a precision of 1.47 kPa. Nineteen of twenty-five (76%) sample pairs displayed a difference of <1 kPa (99% confidence interval, 48%–92%, P = .016). The difference in paired samples was similar for different gestational and postnatal ages and did not appear to be affected by electrocautery.

CONCLUSIONS:

In this small study, we did not demonstrate that TC CO₂ monitoring was accurate at P < .01. This partly reflects the small size of the study, resulting in wide 99% confidence bounds.

Transcutaneous Oxygen and Carbon Dioxide Measurement in Peripheral Vascular Disease

Combined transcutaneous oxygen tension (tcPO2) and transcutaneous carbon dioxide tension (tcPCo2) measurements were carried out at both the subclavicular and metatarsal level in 29 controls and 100 patients with peripheral arterial obstructive disease (PAOD) (intermittent claudication: n = 40, critical limb ischemia: n = 60). Interindividual variation coefficients of arterial and subclavicular tcPCO2 (n = 94 subjects) were superimposable, while tcPo2 variability was twice the arterial value. Furthermore, arterial tensions were better predicted by tcPCO2 than by tcPO2 measurement. In the 75 limbs with an ABI < 0.9 of patients with intermittent claudication, tcPCO2 did not differ significantly from controls (n = 58 limbs), but it was elevated in those with critical limb ischemia (n = 74 limbs), although control and pathological values overlapped widely even in this latter group. At variance with tcPCO2, tcPQ2 was lower in intermittent claudication than in controls, and undetectable in most of the symptomatic limbs with critical ischemia, irrespective of concomitant diabetes. In the overall sample (n = 255 limbs), tcPCO2 did not show significant changes for tcPo2 values ranging from 80 to 10 mmHg, and it increased markedly in several—but not all—patients whose tcPo2 values were below that limit.

To evaluate further the biological significance of an increase in tissue tcPCO2, another sample of 24 subjects underwent acute forearm ischemia for a period of thirteen minutes, a maneuver that increased tcPCO2 markedly, indicating that this parameter is indeed a correlate of drastic reductions in limb perfusion. Thus, tcPCO2 is methodologically less variable than tcPo2 and more predictive of arterial values. However, the wide overlap with control values restrains its use as an isolated diagnostic tool to substantiate PAOD, even in the most advanced stages of disease. Marked elevations in tCPCO2 can be found in patients with critical limb ischemia, although normal values may coexist with low or negligible tcPO2 levels for reasons to be clarified. Further work is needed to establish the extent to which tcPcO2 determination may complement tcPO2 to differentiate extreme from less severe degrees of critical limb ischemia.

Agreement of Mixed Venous Carbon Dioxide Tension (PvCO2) and Transcutaneous Carbon Dioxide (PtCO2) Measurements in Ventilated Infants

Background:

Noninvasive transcutaneous carbon dioxide monitoring has been shown to be accurate in infants and children, limited data are available to show the usefulness and limitations of partial transcutaneous carbon dioxide tension (PtCO₂) value.

Objectives:

The current study prospectively determines the effectiveness and accuracy of PtCO₂ measurements in newborns.

Materials and Methods:

Venous blood gas sampling and monitoring of the PtCO₂ level (TCM TOSCA, Radiometer) were done simultaneously. All measurements are performed on mechanically ventilated infants. Partial venous carbon dioxide tension (PvCO₂) values divided into three groups according to hypocapnia (Group 1: < 4.68 kPa), normocapnia (Group 2: 4.68–7.33 kPa), hypercapnia (Group 3: > 7.33 kPa) and then PvCO₂ and PtCO₂ data within each group were compared separately.

Results:

A total of 168 measurements of each PvCO₂ and PtCO₂ data were compared in three separated groups simultaneously (13 in Group 1, 118 in Group 2, and 37 in Group 3). A bias of more than ± 0.7 kPa was considered unacceptable. PtCO₂ was related to PvCO₂ with acceptable results between the two measurements in hypocapnia (mean difference 0.20 ± 0.19 kPa) and normocapnia (0.002 ± 0.30 kPa) groups. On the other hand in hypercapnia group PtCO₂ values were statistically significant (P < 0.001) and lower than PvCO₂ data (mean difference 0.81 ± 1.19 kPa)

Conclusions:

PtCO₂ measurements have generally good agreement with PvCO₂ in hypocapnic and normocapnic intubated infants but there are some limitations especially with high level of CO₂ tension. Monitoring of PtCO₂ is generally a useful non-invasive indicator of PvCO₂ in hypocapnic and normocapnic infants.

Review of respiratory management of extremely premature neonates during transport

INTRODUCTION

The objective was to evaluate the respiratory management of neonates of 23 to 26 weeks' gestation transported after birth outside a tertiary center. Another objective was to collect data regarding survival, intraventricular hemorrhage (IVH), and chronic lung disease.

METHODS

This was a retrospective study of transports from a statewide dedicated neonatal and pediatric transport service over a 3-year period. Data were collected from the local databases. Neonates with and without transcutaneous carbon dioxide (TcCO2) monitoring were compared. Outcomes were compared with the inborn group from the same period.

RESULTS

A total of 43 mechanically ventilated neonates were included. Significant hypocarbia and/or hypercarbia were seen in 49%. Hyperoxia was noted in 46.5%. Despite the moderate correlation between PCO2 and TcCO2 readings, no clinical benefit was seen with TcCO2 monitoring. Survival was 65.1%. Rates of IVH were 60% for any IVH and 27.5% for severe IVH. IVH was more common in the study cohort.

CONCLUSIONS

Neonates born at 23 to 26 weeks' gestation outside tertiary centers have high rates of mortality and morbidity. The avoidance of hypocarbia, hypercarbia, and hyperoxia is challenging in the transport environment. Transcutaneous monitoring is an imperfect tool for following PCO2 levels.

Sidestream microstream end tidal carbon dioxide measurements and blood gas correlations in neonatal intensive care unit

OBJECTIVE

The study was designed to assess the use of newer sidestream microstream end tidal carbon dioxide (ETCO(2) ) device in predicting blood carbon dioxide (PCO(2) ) measurements in very low birth weight (VLBW = birth weight <1,500 g) and non-VLBW NICU neonates.

STUDY DESIGN

Sidestream microstream ETCO(2) detectors were allowed time to calibrate and reach steady state prior to blood gas measurements. Blood CO(2) (PCO(2) ) and simultaneous ETCO(2) were recorded. Ratio of dead space to tidal volume (VD/VT) was calculated using modified Bohr's equation. Correlation coefficient, estimates of difference, standard deviation, and 95% limits of agreement between ETCO(2) and PCO(2) concentrations were calculated.

RESULTS

Two hundred eighty-six paired samples were collected from 48 ventilated NICU patients. Average PCO(2) and ETCO(2) were 58.4 and 50.6 with a correlation of 0.76. Subgroup analysis showed a correlation of 0.73 in 204 paired blood from 34 VLBW infants and 0.82 in 82 paired samples from non-VLBW infants. Estimates of difference ± standard deviation between PCO(2) and ETCO(2) concentrations in these three groups, respectively (ALL, VLBW, and non-VLBW) were 7.84 ± 9.96, 8.2 ± 10.16, and 6.95 ± 9.45. The correlation coefficient significantly improved in the VLBW group to 0.86 with dead space to tidal volume ratio (VD/VT) <30% (0.86 vs. 0.42; P < 0.001).

CONCLUSION

ETCO(2) measurements using sidestream microstream technology in VLBW demonstrated that the correlation of ETCO(2) and PCO(2) was moderate, but the agreement was less than adequate (bias > 5 mmHg in all groups). The results improved with lower VD/VT, suggesting that sidestream capnography is more reliable in conditions of less severe lung disease.

Noninvasive capnometry for end-tidal carbon dioxide monitoring via nasal cannula in nonintubated neonates

BACKGROUND

Arterial blood gas analysis is the gold standard for assessing the adequacy of ventilation. However, arterial blood sampling may be associated with serious complications in neonates. The aim of the study was to utilize the side-stream capnometry measurement of end-tidal carbon dioxide (PetCO₂) via nasal cannula circuits and to verify the reliability of PetCO₂ in reflecting the arterial blood carbon dioxide(PaCO₂) level in nonintubated neonates.

METHODS

A retrospective medical record review analysis was performed in nonintubated neonates admitted to the neonatal ward in a medical center. Simultaneous arterial PaCO₂ and PetCO₂ levels were evaluated. PaCO₂ and PetCO₂ levels were compared by paired t test and were correlated using Pearson's correlation. The PetCO₂ bias was defined as the difference between PaCO₂ and PetCO₂, and was assessed by Bland-Altman plot analysis.

RESULTS

A total of 34 neonates were recruited, and data of 54 pairs of PaCO₂ and PetCO₂ levels were available for comparison. The average (mean ± SD) gestational age was 32.5 ± 4.2 weeks, and the average birth weight was 1881 ± 1077 g. There was a good correlation between PetCO₂ and PaCO₂ levels among all paired samples (r = 0.809, p < 0.001). When the data were divided into those with respiratory disease (n = 34) and those without (n = 20), significant correlation between PetCO₂ and PaCO₂ levels were both noted in the former group (r = 0.823, p < 0.001) and the latter group (r = 0.770, p < 0.001). The overall average mean value of PetCO₂ was lower than that of PaCO₂ (39.4 ± 8.8 mmHg vs. 41.3 ± 9.2 mmHg, p = 0.014). The difference between PetCO₂ and PaCO₂ levels was significant only among those with respiratory disease (38.8 ± 9.8 mmHg vs. 41.2 ± 10.3 mmHg, p = 0.027), but not among those without (40.5 ± 7.0 mmHg vs. 41.6 ± 7.2 mmHg, p = 0.289).

CONCLUSIONS

End-tidal CO₂ measurement by side-stream capnometry through nasal cannula could provide an accurate and noninvasive estimate of PaCO₂ levels in nonintubated neonates.

Detection of carbon dioxide thresholds using low-flow sidestream capnography in ventilated preterm infants

BACKGROUND

Monitoring CO2 levels in preterm infants receiving mechanical ventilation is designed to avoid the harmful consequences of hypocapnia or hypercapnia. Capnography is of questionable accuracy for monitoring PCO2 in preterm infants.

OBJECTIVES

To determine the accuracy of sidestream capnography in ventilated preterm infants by comparing end-tidal carbon dioxide (EtCO2) values to mixed venous carbon dioxide pressure (PvCO2) and to transcutaneous carbon dioxide pressure (TcPCO2).

METHODS

Simultaneous recordings of EtCO2, TcPCO2 and PvCO2 in 37 ventilated preterm infants. The PvCO2-EtCO2 gradient was calculated. The Bland-Altman technique and the intra-class correlation coefficient (ICC) were used to assess agreement between methods. The area under the curve (AUC) was calculated.

RESULTS

Ninety-nine EtCO2/PvCO2 pairs were studied from 37 preterm infants with a mean gestational age of 27.7 +/- 1.9 weeks and a mean birth weight of 1,003 +/- 331 g. The mean PvCO2-EtCO2 gradient was 11.2 +/- 8.0 mmHg, and the ICC was 0.28. The mean PvCO2-TcPCO2 gradient was 0 +/- 7.8 mmHg, and the ICC was 0.78. AUCs for EtCO2 and TcPCO2 were similar in detecting high or low PvCO2.

CONCLUSION

Despite an insufficient correlation between EtCO2 and PvCO2, capnography was able to detect low and high CO2 warning levels with a similar efficacy to that of TcPCO2, and may therefore be of clinical interest.

Are carbon dioxide detectors useful in neonates?

Maintenance of neonatal normocarbia may prevent chronic lung disease and periventricular leucomalacia, but this requires frequent arterial sampling, which has risks. Alternative methods for measuring CO2 are therefore desirable. These include end tidal CO2, capillary sampling, and transcutaneous measurements. CO2 detectors have also proved effective and rapid indicators of endotracheal intubation. However, this method relies on the presence of exhaled CO2, which may be reduced in certain situations, such as cardiopulmonary arrest. Colorimetric CO2 detectors are therefore valuable adjuncts for airway management, especially during resuscitation, but Pa(CO2) is still the best measure of CO2 in neonatal practice.

Agreement of carbon dioxide levels measured by arterial, transcutaneous and end tidal methods in preterm infants < or = 28 weeks gestation

OBJECTIVE

To assess the agreement of transcutaneous carbon dioxide (TcPCO(2)) and end tidal carbon dioxide (PetCO(2)) with arterial carbon dioxide (PaCO(2)) values in infants < 28 weeks gestational age.

STUDY DESIGN

In all, 27 ventilated preterm infants were prospectively studied. PaCO(2) was compared with TcPCO(2) and PetCO(2) measured at three similar time points within first 24 hours after birth.

RESULTS

The Intraclass correlation coefficients for TcPCO(2) and PaCO(2) were 0.45, 0.73 and 0.53; and for PetCO(2) and PaCO(2) were 0.61, 0.56 and 0.57 at 4, 12 and 24 hours after birth, respectively.

CONCLUSION

A moderate agreement with a wide variation in individual values was observed between noninvasive methods and PaCO(2) in preterm infants in the first 24 hours. Noninvasive monitoring methods cannot be substituted for PaCO(2) analyses in preterm infants during this critical period.

Mainstream end-tidal carbon dioxide monitoring in the neonatal intensive care unit

BACKGROUND

Continuous noninvasive monitoring of arterial carbon dioxide (CO2) in neonatal intensive care unit (NICU) patients would help clinicians avoid complications of hypocarbia and hypercarbia. End-tidal CO2 monitoring has not been used in this population to date, but recent technical advances and the introduction of surfactant therapy, which improves ventilation-perfusion matching, might improve the clinical utility of end-tidal monitoring.

OBJECTIVE

To determine the accuracy and precision of end-tidal CO2 monitoring in NICU patients.

DESIGN

Nonrandomized recording of simultaneous end-tidal and arterial CO2 pairs.

SETTING

Two university NICUs.

PATIENTS

Forty-five newborn infants receiving mechanical ventilation who had indwelling arterial access, and a predefined subsample of infants who were <1000 g birth weight, <8 days of age, and who received surfactant therapy (extremely low birth weight -ELBW- <8).

OUTCOME MEASURES

The correlation coefficient, degree of bias, and 95% confidence interval were determined for both the overall population and the ELBW <8 subgroup. Those factors which significantly influenced the bias were identified. The ability of the end-tidal monitor to alert the clinician to instances of hypocarbia or hypercarbia was determined.

RESULTS

There were 411 end-tidal/arterial pairs analyzed from 45 patients. The correlation coefficient was 0.833 and the bias was -6. 9 mm Hg (95% confidence interval, +/-11.5 mm Hg). The results did not differ markedly in the ELBW <8 infants. Measures of the degree of lung disease, the ventilation index and the oxygenation index, had small influences on the degree of bias. This type of capnometry identified 91% of the instances when the arterial CO2 pressure was between 34 and 54 mm Hg using an end-tidal range of 29 to 45 mm Hg. End-tidal values outside this range had a 63% accuracy in predicting hypocarbia or hypercarbia.

CONCLUSION

End-tidal CO2 monitoring in NICU patients is as accurate as capillary or transcutaneous monitoring but less precise than the latter. It may be useful for trending or for screening patients for abnormal arterial CO2 values.

Fetal transcutaneous PCO2 measurements during labour

The departments of Obstetrics and Gynaecology of the Universities of Bonn and Copenhagen and the Free University of Amsterdam cooperated in the European Community Concerted Action Project 'New methods for Perinatal Surveillance'. In 95 patients fetal transcutaneous PCO2 (tcPCO2) recording (measuring temperature 41 degrees C) during labour was evaluated regarding its clinical applicability. During the first stage of labour fetal tcPCO2 was rather stable at a level of 7.3 +/- 1.4 kPa. In the second stage there were marked differences between the three subpopulations. In the first stage of labour the correlation between tcPCO2 and PCO2 in fetal blood samples was 0.38 (P = 0.02) and in the second stage -0.20 (P = 0.36). The correlation of fetal tcPCO2 with umbilical artery PCO2 was 0.30 (P = 0.01) and with pH -0.30 (P = 0.01). Using a fetal tcPCO2 level of 8.0 kPa as a cut-off point to predict an umbilical artery pH less then 7.20, sensitivity was 88%, specificity 65%, positive predictive value 29% and negative predictive value 97%. The likelihood ratio of a positive test was 2.47 and of a negative test 0.13. It is concluded that fetal tcPCO2 possibly can be an additional tool to exclude fetal acidosis. In case of values above 8.0 kPa further evaluation of the fetal acid-base balance is indicated.

Factors influencing transcutaneous oxygen and carbon dioxide measurements in adult intensive care patients

Transcutaneous PO2 (PtcO2) is suggested to reflect tissue oxygenation in intensive care patients, whereas transcutaneous PCO2 (PtcCO2) is advocated as a noninvasive method for assessing PaCO2. In 24 critically ill adult patients (mean Apache II score 14.2, SD 4.7) we investigated the impact of variables that are commonly thought to determine PtcO2 and PtcCO2 measurements. A linear correlation was found between PtcO2 and PaO2 (r = 0.6; p less than or equal to 0.0001) and between PtcO2 and mean arterial blood pressure (MAP; r = 0.42; p less than or equal to 0.003). Cardiac index (CI) correlated with tc-index (PtcO2/PaO2; r = 0.31; p less than or equal to 0.03). There was no relationship between PtcO2 and hemoglobin concentration (Hb) and the position of the oxygen dissociation curve (ODC). Stepwise multiple regression analysis demonstrated a significant influence of PaO2 and MAP on PtcO2. The contribution of CI, Hb and the ODC was not significant. Only 40% of the variability of a single PtcO2 measurement could be explained by PaO2 and MAP. A significant linear correlation was demonstrated between PtcCO2 and PaCO2 (r = 0.76; p less than or equal to 0.0001) but not between PtcCO2 and CI, MAP and arterial base excess (BEa). Stepwise multiple regression analysis revealed an influence of PaCO2 and of CI on PtcCO2; 66% of the variability of a single PtcCO2-value could be explained by PaCO2 and CI. Our data demonstrate that transcutaneous derived gas tensions result from complex interaction between hemodynamic, respiratory and local factors, which can hardly be defined in ICU-patients.

Transcutaneous CO2 monitoring in adults with sleep-related breathing disorders

The accuracy of transcutaneous CO2 monitoring (PtcCO2) was studied in 22 subjects suspected of having sleep-related breathing disorders, by comparison with arterial CO2 measurements (PaCO2). At rest 40 simultaneous sets of PaCO2 and PtcCO2 were obtained. The mean PaCO2 (+/-SD) was 5.3 +/- 0.9 kPa and PtcCO2 was 5.7 +/- 1.0 kPa (r = 0.79). The ventilatory response to CO2 was evaluated by a CO2 rebreathing method, and simultaneous measurements of PaCO2, PtcCO2 and end-tidal PCO2 (PETCO2) were made every min. Both PaCO2 and PETCO2 increased more during the first min of CO2 rebreathing than PtcCO2 (p less than 0.001). Between 1 to 5 min after the start of rebreathing there were no significant differences between the three methods. During sleep there was an increase in PtcCO2 (by 0.1-0.3 kPa) with each apneic event, the magnitude of the increase depending on the length and distribution of these events. With repeated long apneas there was a cumulative increase in PtcCO2, especially during REM sleep. Continuous PtcCO2 monitoring proved useful in monitoring and diagnosing sleep-related breathing disorders.

Transcutaneous monitors during one-lung ventilation: Are they reliable?

During one-lung ventilation, levels of oxygen and carbon dioxide in the blood are commonly assessed by intermittent blood gas sampling. Transcutaneous PO2 (tcPO2) and transcutaneous PCO2 (tcPCO2) have been reported to accurately reflect arterial PO2 (PaO2) and arterial PCO2 (PaCO2) in hemodynamically stable patients. Transcutaneous monitors appear to be ideal for detecting trends toward hypoxia and hypercarbia, conditions that may not be evident when using intermittent blood gas sampling, while pulse oximetry, since it reflects saturation, may not detect hypoxia until it has already occurred. Thirty: one patients undergoing one-lung ventilation were monitored using both transcutaneous electrodes applied to the upper arm (group 1) or chest (group 2) and arterial blood gas sampling. Arterial blood gases were sampled while tcPO2 and tcPCO2 values were being recorded. Regression, correlation, and covariance analyses were performed. Correlation coefficients of PaO2 to tcPO2 varied from .05 to .99 for each patient. The slopes of individual regression lines varied from 0.03 to 1.16. Correlation coefficients of PaCO2 to tcPCO2 varied from .01 to .99, while the slopes of individual regression lines ranged from 0.02 to 5.89. Covariance analyses revealed considerable variation in PaO2 to tcPO2 and PaCO2 to tcPCO2 in individual patients even under stable hemodynamic conditions. Analysis of covariance also demonstrated that in group 2 the slopes comparing arterial and transcutaneous values were significantly different for PaO2 <100 mmHg and PaO2 >200 mmHg. In group 1, for PaO2 <100 mmHg, there was no difference in slopes but y-intercepts were significantly different (P < .05). However, transcutaneous indices were significantly different in both groups for PaO2 <100 mmHg and PaO2 >200 mmHg. It is concluded that transcutaneous monitoring is useful to indicate trends in arterial values in some patients, but blood gas analysis is still necessary to verify the reliability of such monitoring.

Rapid assessment of ventilation by measurement of carbon dioxide elimination during high-frequency ventilation of kittens

Monitoring of the effectiveness of ventilation is a significant problem during high-frequency ventilation (HFV). The time necessary to achieve equilibrium of the arterial tension of carbon dioxide (Paco2) following step changes in ventilation is appreciable, because of large body stores of CO2. Waiting for Paco2 to reach equilibrium is not only time-consuming but a potentially dangerous means of monitoring ventilator adjustments during HFV. Five kittens of mean +/- SD 1,082 +/- 383 gm weight were studied during HFV, both with normal lungs and lungs injured by saline lavage-induced surfactant depletion. The transcutaneous tension of carbon dioxide (Ptcco2) was monitored continuously to determine the time required to achieve equilibrium of Paco2 following a step change in ventilation. The rate of pulmonary CO2 elimination (VECO2) was measured immediately before and immediately after (less than 12 sec) step changes in ventilation and was used to predict the change in Paco2 achieved once equilibrium was reestablished. With normal lungs, equilibration time following step changes in ventilation was found to be approximately 20 minutes. After step decreases in ventilation of the injured lung, achieving equilibrium state took significantly longer, approximately 30 minutes. The Paco2 predicted was significantly related to the change in Paco2 achieved at equilibrium for both normal and injured lung studies. We concluded that direct monitoring of VECO2 during HFV may be a useful clinical monitoring technique, allowing rapid and accurate assessment of the efficiency of ventilation following step changes in ventilation and potentially assisting in optimizing ventilator settings.

Transcutaneous oxygen and carbon dioxide monitoring in sick neonates using a combined sensor

Using a combined O2-CO2 sensor, we evaluated the effect of cathode size and membrane thickness and incorporation of correction factor upon transcutaneous O2-CO2 readings. The present studies were carried out in three phases in newborns less than a week of age. The data from these studies indicate that a combined O2-CO2 sensor with a smaller cathode, Teflon membrane and with a built-in correction factor can accurately reflect arterial O2 and CO2 tension and can replace the present two heated sensors.

Correlation between transcutaneous pCO2 and the corresponding values of fetal blood--a study at a measuring temperature of 39 degrees C

Continuous transcutaneous monitoring of fetal carbon dioxide partial pressure (tcpCO2) may become an important new method for investigating the physiology and pathophysiology of the fetus during labor, as well as an additional tool for fetal surveillance. In order to contribute to the standardization of this newly developed method, we measured tcpCO2 during labor in 105 fetuses. We then compared the transcutaneous pCO2 with the pCO2 of fetal blood gas analysis; the correlation between these two parameters was significant. The relationship between transcutaneous pCO2 and the pH from fetal scalp blood is described, as is the influence of the stage of labor on the correlation between transcutaneous monitoring and blood samples. tcpCO2 during labor appears to be a helpful additional tool, especially in fetuses with pathologic heart rate patterns in whom multiple fetal blood gas analysis would otherwise be necessary.