Technical and clinical aspects of capnography in neonates

Navigating Pediatric Capnography: A Comprehensive Review of Scope and Limitations

This review comprehensively explores pediatric capnography, a vital tool in contemporary respiratory monitoring. The overview encompasses the foundational principles of capnography, elucidating its real-time measurement of carbon dioxide (CO2) in respiratory gases. The review emphasizes its paramount role in pediatric care and underscores capnography's significance in detecting respiratory abnormalities and guiding timely interventions. The distinctions between mainstream and sidestream capnography, the key to understanding their applications, are meticulously outlined. Addressing the importance of ongoing research and education, the review advocates for a dynamic approach to refine guidelines and optimize capnography utilization in pediatric settings. The conclusion reflects on the scope and limitations of pediatric capnography, acknowledging its transformative impact while advocating for a judicious recognition of constraints. As we navigate the future of pediatric respiratory care, the synergy of research, education, and clinical application emerges as the cornerstone for advancing pediatric capnography to new horizons.

Capnography in newborns under mechanical ventilation and its relationship with the measurement of CO2 in blood samples

INTRODUCTION

Monitoring the partial pressure of CO₂ (PCO₂) in newborns who require ventilation would allow avoiding hypocapnia and hypercapnia. The measurement of end-tidal carbon dioxide (ETCO₂) is an alternative rarely implemented in this population.

OBJECTIVE

To evaluate the relationship between ETCO₂ and PCO₂ in newborns.

METHODS

Cross-sectional study comparing two PCO₂ measurement methods, the conventional one by analysis of blood samples and the one estimated by ETCO₂. The study included hospitalized newborns that required conventional mechanical ventilation. The ETCO₂ was measured with a Tecme GraphNet® neo, a neonatal ventilator with an integrated capnograph, and we obtained the ETCO₂-PCO₂ gradient. We conducted correlation and Bland-Altman plot analyses to estimate the agreement.

RESULTS

A total of 277 samples (ETCO₂ / PCO₂) from 83 newborns were analyzed. The mean values ​​of ETCO₂ and PCO₂ were 41.36mmHg and 42.04mmHg. There was a positive and significant correlation between ETCO₂ and PCO₂ in the overall analysis (r=0.5402; P<.001) and in the analysis of each unit (P<.001). The mean difference was 0.68 mmHg (95% CI, -0.68 to 1.95) and was not significant. We observed a positive systematic error (PCO₂ > ETCO₂) in 2 of the units, and a negative difference in the third (PCO₂ < ETCO₂).

DISCUSSION

The correlation between ETCO and PCO₂ was significant, although the obtained values ​​were not equivalent, with differences ranging from 0.1mmHg and 20mmHg. Likewise, we found systematic errors that differed in sign (positive or negative) between institutions.

Non-invasive carbon dioxide monitoring in neonates: methods, benefits, and pitfalls

Wide fluctuations in partial pressure of carbon dioxide (PaCO₂) can potentially be associated with neurological and lung injury in neonates. Blood gas measurement is the gold standard for assessing gas exchange but is intermittent, invasive, and contributes to iatrogenic blood loss. Non-invasive carbon dioxide (CO₂) monitoring has become ubiquitous in anesthesia and critical care and is being increasingly used in neonates. Two common methods of non-invasive CO₂ monitoring are end-tidal and transcutaneous. A colorimetric CO₂ detector (a modified end-tidal CO₂ detector) is recommended by the International Liaison Committee on Resuscitation (ILCOR) and the American Academy of Pediatrics to confirm endotracheal tube placement. Continuous CO₂ monitoring is helpful in trending PaCO₂ in critically ill neonates on respiratory support and can potentially lead to early detection and minimization of fluctuations in PaCO₂. This review includes a description of the various types of CO₂ monitoring and their applications, benefits, and limitations in neonates.

Continuous Noninvasive Carbon Dioxide Monitoring in Neonates: From Theory to Standard of Care

Ventilatory support may affect the short- and long-term neurologic and respiratory morbidities of preterm infants. Ongoing monitoring of oxygenation and ventilation and control of adequate levels of oxygen, pressures, and volumes can decrease the incidence of such adverse outcomes. Use of pulse oximetry became a standard of care for titrating oxygen delivery, but continuous noninvasive monitoring of carbon dioxide (CO₂) is not routinely used in NICUs. Continuous monitoring of CO₂ level may be crucial because hypocarbia and hypercarbia in extremely preterm infants are associated with lung and brain morbidities, specifically bronchopulmonary dysplasia, intraventricular hemorrhage, and cystic periventricular leukomalacia. It is shown that continuous monitoring of CO₂ levels helps in maintaining stable CO₂ values within an accepted target range. Continuous monitoring of CO₂ levels can be used in the delivery room, during transport, and in infants receiving invasive or noninvasive respiratory support in the NICU. It is logical to hypothesize that this will result in better outcome for extremely preterm infants. In this article, we review the different noninvasive CO₂ monitoring alternatives and devices, their advantages and disadvantages, and the available clinical data supporting or negating their use as a standard of care in NICUs.

A novel method of distal end-tidal CO2 capnography in intubated infants: comparison with arterial CO2 and with proximal mainstream end-tidal CO2

OBJECTIVE

The objective of this study was to evaluate a novel method of distal end-tidal CO2 capnography by comparison with PaCO2 and with the more standard method that measures mainstream proximal end-tidal CO2 in intubated infants.

METHODS

Included in the study were all infants who were ventilated with conventional mechanical ventilation and intubated with a double-lumen endotracheal tube in our NICU during the study period. Data were collected prospectively from 2 capnographs simultaneously and compared with PaCO2. Sidestream distal end-tidal CO2 was measured by a Microstream capnograph via the extra port of a double-lumen endotracheal tube. Mainstream proximal end-tidal CO2 was measured via capnograph connected to the endotracheal tube.

RESULTS

Twenty-seven infants (median [range] birth-weight: 1835 [490-4790] g; gestational age: 32.5 [24.8-40.8] weeks) participated in the study. We used for analysis 222 and 212 measurements of distal end-tidal CO2 and proximal end-tidal CO2, respectively. Distal compared with proximal end-tidal CO2 had a better correlation with PaCO2 and a better agreement with PaCO2. The accuracy of distal end-tidal CO2 decreased, but it remained a useful measure of PaCO2 in the high range of PaCO2 (>or=60 mmHg) or in conditions of severe lung disease. A subanalysis for infants who weighed<1500 g (13 infants, 84 observations) revealed a good correlation and agreement between distal end-tidal CO2 and PaCO2 and poor correlation and agreement for proximal end-tidal CO2.

CONCLUSIONS

Distal end-tidal CO2 measured via a double-lumen endotracheal tube was found to have good correlation and agreement with PaCO2, remained reliable in conditions of severe lung disease, and was more accurate than the standard mainstream proximal end-tidal CO2.

Randomized trial of volume infusion during resuscitation of asphyxiated neonatal piglets

Despite its use, there is little evidence to support volume infusion (VI) during neonatal cardiopulmonary resuscitation (CPR). This study compares 5% albumin (ALB), normal saline (NS), and no VI (SHAM) on development of pulmonary edema and restoration of mean arterial pressure (MAP) during resuscitation of asphyxiated piglets. Mechanically ventilated swine (n=37, age: 8 +/- 4 d, weight: 2.2 +/- 0.7 kg) were progressively asphyxiated until pH <7.0, Paco2 >100 mm Hg, heart rate (HR) <100 bpm, and MAP <20 mm Hg. After 5 min of ventilatory resuscitation, piglets were randomized blindly to ALB, NS, or SHAM infusion. Animals were recovered for 2 h before euthanasia and lung tissue sampled for wet-to-dry weight ratio (W/D) as a marker of pulmonary edema. SHAM MAP was similar to VI during resuscitation. At 2 h post-resuscitation, MAP of SHAM (48 +/- 13 mm Hg) and ALB (43 +/- 19 mm Hg) was higher than NS (29 +/- 10 mm Hg; p=0.003 and 0.023, respectively). After resuscitation, SHAM piglets had less pulmonary edema (W/D: 5.84 +/- 0.12 versus 5.98 +/- 0.19; p=0.03) and better dynamic compliance (Cd) compared with ALB or NS (Cd: 1.43 +/- 0.69 versus 0.97 +/- 0.37 mL/cm H2O, p=0.018). VI during resuscitation did not improve MAP, and acute recovery of MAP was poorer with NS compared with ALB. VI was associated with increased pulmonary edema. In the absence of hypovolemia, VI during neonatal resuscitation is not beneficial.

Capnography rapidly confirmed correct endotracheal tube placement during resuscitation of extremely low birthweight babies (< 1000 g)

During neonatal resuscitation, the routine use of capnography to verify correct placement of the endotracheal tube is not an established international practice. We present four cases that illustrate the successful use of immediate capnography to verify correct tracheal tube placement even in extremely low birthweight (ELBW) prematures (< 1000 g) during resuscitation. Based on this limited experience, we reached institutional consensus among paediatricians and anaesthesiologists that capnography should become standard monitoring during all endotracheal intubations in premature babies.

Current limitations of volumetric capnography in surfactant-depleted small lungs

OBJECTIVE

To investigate the suitability of volumetric capnography for assessing alveolar gas exchange in very small, surfactant-depleted lungs.

DESIGN

Prospective animal trial.

SETTINGS

Animal laboratory in a university setting.

SUBJECTS

Twenty-one ventilated newborn piglets (age <12 hrs; median weight, 890 g; range, 560-1435 g).

INTERVENTIONS

Bronchoalveolar lavage with instillation of 30 mL/kg normal saline. Ventilatory, circulatory, and lung mechanic variables were measured before and 0, 30, and 60 mins after bronchoalveolar lavage.

MEASUREMENTS AND MAIN RESULTS

The alveolar deadspace fraction calculated by the Bohr and the Bohr/Enghoff equations increased three-fold (p<.001) after bronchoalveolar lavage in capnograms with distinct alveolar plateau, whereas in capnograms without alveolar plateau no statistical significant difference was seen. The main problem of capnography in small and especially stiff lungs was the high number of discarded records exclusively caused by a missing alveolar plateau. Rates of discarded records of capnography were 9.5% before lavage and increased (p<.01) to 52.4%, 47.6%,42.8% after bronchoalveolar lavage (0, 30, and 60 mins). With decreasing exhalation time, the number of discarded records increased significantly. No plateau was seen in >75% of recorded files with exhalation times <200 msecs. The effect of bronchoalveolar lavage on all variables measured was quite different, with the highest impact on required ventilatory settings, calculated oxygenation variables, and compliance. The effect of bronchoalveolar lavage on arterio-alveolar CO2 difference, CO2 production, and alveolar deadspace was much lower and statistically significant only in capnograms with alveolar plateau.

CONCLUSIONS

Volumetric capnography is a useful tool to detect impaired alveolar gas exchange in surfactant-depleted small lungs. However, the method failed if there was no alveolar plateau in the volumetric capnogram especially in stiff lungs with short exhalation times.

Accuracy of capnography with a 30 foot nasal cannula for monitoring respiratory rate and end-tidal CO2 in children

We tested the accuracy of a low flow (50 cc/min) sidestream capnography system equipped with an experimental 30-foot nasal cannula to monitor ventilatory status in children. End-tidal CO2 and respiratory rate, both at room air and in the presence of supplemental oxygen, were recorded simultaneously from the experimental 30-foot nasal cannula and the standard, FDA approved, 10-foot nasal cannula. The 30-foot nasal cannula was as accurate as the 10-foot nasal cannula in measuring respiratory rate and end-tidal CO2 in children. When supplemental oxygen was delivered by face-mask, there was no dilutional effect on the respiratory rate or end-tidal CO2 recorded with either the 10-foot or 30-foot nasal cannulas in place.

Accuracy of a new low-flow sidestream capnography technology in newborns: a pilot study

OBJECTIVE

To evaluate the accuracy of a new low-flow sidestream capnography technology and analyze components of the capnogram in mechanically ventilated newborns with and without pulmonary disease.

METHODS

Twenty patients were prospectively identified. Eligible infants were mechanically ventilated and had an indwelling arterial catheter. Two groups were identified: newborns who were receiving mechanical ventilation for pulmonary diseases, and newborns who were receiving postoperative mechanical ventilation for nonpulmonary conditions. End-tidal CO(2) (PetCO(2)) was measured for 1-minute pre- and post-arterial blood sampling, and PetCO(2) and PaCO(2) were compared for each patient. Eight quantitative waveform parameters were also measured on all patients.

RESULTS

Newborns in the pulmonary group (n=13) (persistent pulmonary hypertension of the newborn/meconium aspiration syndrome, respiratory distress syndrome, pneumonia) and newborns in the control group (n=7) were matched for birth weight, gestational age, and postnatal age. PetCO(2)-PaCO2 Gradient values were higher in the pulmonary group (7.4+/-3.3 mm Hg) than controls (3.4+/-2.4 mm Hg). Four waveform parameters (ascending slope, alveolar angle, alpha angle, descending angle) were identified, which independently differentiated patients with pulmonary disease from controls.

CONCLUSIONS

Low-flow capnography with Microstream technology accurately measured alveolar CO(2) in newborns without pulmonary disease, as demonstrated by normal PetCO(2)-PaCO(2) gradients. The measured PetCO(2)-PaCO(2) gradient, as expected, was significantly higher in newborns with pulmonary disease. We also identified four quantitative waveform parameters that may be useful in differentiating between mechanically ventilated newborn patients with and without lung disease.

Capnography in spontaneously breathing preterm and term infants

OBJECTIVE

To investigate sidestream EtCO2 wave patterns as related to prematurity.

DESIGN

The EtCO2 wave pattern was analyzed longitudinally in 20 sequential preterm, 32-37 weeks of gestation and 39 fullterm controls. Infants with a cardiorespiratory disease, neurological deficit or a metabolic disorder were not included in the study. Sidestream EtCO2 was employed. Wave patterns were identified and baseline expiratory/inspiratory length and wave amplitude were measured.

RESULTS

Two predominant (about 75%) wave patterns were identified: (i) (with plateau) significantly more prevalent among infants born at term as compared with preterm infants across their postconceptional ages (PCA) (P=0.005-0.04), (ii) (plateau free) significantly more prevalent among the youngest preterm infants as compared with the fullterm controls. Expiratory length was significantly correlated with respiratory rate (RR) across ages (P=0.01-0.001) whereas inspiratory length was correlated with RR among the two youngest groups of infants only (P=0.002 and 0.004). Wave patterns were not found to be affected by environmental temperatures, blood pressure, body weight, haemoglobin level, aminophylline or O2 supplementation.

CONCLUSION

These findings suggest that EtCO2 wave pattern distribution among preterm infants is distinctly different from that of term controls, regardless of PCA, while inspiration is related to the degree of maturity. Alveolar pathology could probably be missed by sidestream capnography.

Microstream capnograpy technology: a new approach to an old problem

Significant technical limitations inherent in black-body infrared technology used in conventional sidestream and mainstream capnography have hindered the acceptance and growth of capnography as a monitoring tool outside the operating room environment. We describe a new technology (Microstream) for CO2 monitoring, based on molecular correlation spectroscopy, which results in a highly efficient and selective emission of a spectrum of discrete wavelengths exactly matching those for CO2 absorption. The CO2 specific emissions allow for an extremely small sample cell (15 microl), which in turn, permits the use of a very low sample flow rate (50 ml/min) without compromising waveform integrity or end-tidal CO2 accuracy. Design and technology features of the CO2 emission source, sample cell, and breath sampling circuits are described.

Anesthesia for neonatal surgical emergencies

In this review of the anesthetic considerations for the neonate who requires anesthesia for emergency surgery, the authors discuss preoperative, intraoperative, and postoperative management from an anesthetic perspective. Monitoring the cardiorespiratory and metabolic status of neonates during anesthesia is usually difficult because the neonate is not physically accessible. Specific monitoring techniques that provide accurate measurements are discussed. General anesthesia is usually required for the surgery, the airway must be secured and anesthesia managed with a combination of inhalational and intravenous agents. Regional anesthesia and opioids may be included to decrease the intraoperative anesthetic requirements and prevent pain in the postoperative period. The pharmacology of specific anesthetic and adjuvant agents are discussed.

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.

Evaluation of the newborn’s blood gas status

Blood gas measurements and complementary, noninvasive monitoring techniques provide the clinician with information essential to patient assessment, therapeutic decision making, and prognostication. Blood gas measurements are as important for ill newborns as for other critically ill patients, but rapidly changing physiology, difficult access to arterial and mixed venous sampling sites, and small blood volumes present unique challenges. This paper discusses considerations for interpretation of blood gases in the newborn period. Blood gas measurements and noninvasive estimations provide important information about oxygenation. The general goals of oxygen therapy in the neonate are to maintain adequate arterial PaO2 and SaO2, and to minimize cardiac work and the work of breathing. Pulse oximetry and transcutaneous oxygen monitoring are extraordinarily useful techniques of estimating and noninvasively monitoring the neonate’s oxygenation, but each method has limitations. Arterial blood gas determinations of pCO2 provide the most accurate determinations of the adequacy of alveolar ventilation, but capillary, transcutaneous, and end-tidal techniques are also useful. An approach to and examples of acid-base disorders are presented. Three hemoglobin variants relevant to the newborn are considered: fetal hemoglobin, carboxyhemoglobin, and methemoglobin. Blood gases obtained in the immediate perinatal period can help assess perinatal asphyxia, but particular attention must be paid to the sampling site, the time of life, and the possible and proven diagnoses.

Ventilatory support of the neonatal foal

Many sick neonatal foals have respiratory failure secondary to perinatal hypoxia, sepsis, or pneumonia. These foals require ventilatory support to prevent respiratory embarrassment and other complications associated with chronic hypoxia and hypercapnia. This article discusses practical aspects of ventilatory therapy, such as choosing a candidate for mechanical ventilation, choosing the proper ventilatory mode, placing a foal on a ventilator, maintaining a foal on mechanical ventilation, and weaning from mechanical ventilation. This article details some of the techniques that have been developed based on experiences with mechanical ventilation of neonatal foals and encourages other clinicians to consider ventilatory therapy as a feasible option.

Infrared end-tidal CO2 measurement does not accurately predict arterial CO2 values or end-tidal to arterial PCO2 gradients in rabbits with lung injury

End-tidal PCO2 (PETCO2) measurements from two commercially available neonatal infrared capnometers with different sampling systems and a mass spectrometer were compared with arterial PCO2 (PaCO2) to determine whether the former could predict the latter in mechanically ventilated rabbits with and without lung injury. The effects of tidal volume, ventilator frequency and type of lung injury on the gradient between PETCO2 and PaCO2 (delta P(a-ET)CO2) were evaluated. Twenty rabbits were studied: 10 without lung injury, 5 with saline lavage and 5 with lung injury by meconium instillation. Paired measurements of PETCO2 by two infrared capnometers and a mass spectrometer were compared to PaCO2. In the rabbits without lung injury, the values from the infrared capnometers and mass spectrometer correlated strongly with PaCO2 (r > or = 0.91) despite differences in the slopes of the linear regression between PETCO2 and PaCO2 and in delta P(a-ET)CO2 (P < 0.05). Values from the mainstream IR-capnometer more closely approximated the line of identity than the regression between the sidestream IR-capnometer values or the mass spectrometer and PaCO2, but tended to overestimate PaCO2. The delta P(a-ET)CO2 was similar at all tidal volumes and ventilator frequencies, regardless of capnometer type. In the rabbits with induced lung injury, while there was a positive correlation between the slopes of the regression between PETCO2 and PaCO2 for both capnometers (r > or = 0.70), none of the regression slopes approximated the line of identity. The delta P(a-ET)CO2 was greater in rabbits with injured than noninjured lungs (P < 0.05). The delta P(a-ET)CO2 was similar among capnometers regardless of tidal volume, ventilator frequency, or type of lung injury. The 95% confidence interval of plots PaCO2 against PETCO2 was large for rabbits with injured and noninjured lungs.(ABSTRACT TRUNCATED AT 250 WORDS)

Capnometry and the paediatric laryngeal mask airway

The laryngeal mask airway (LMA), an alternative to tracheal intubation in certain situations, has gained popularity in recent years. Initially designed for use in adults it has now become available in suitable sizes for paediatric anaesthesia. The objectives of this study were to identify the preferred site of sampling the end-tidal carbon dioxide (PETCO2) with the LMA and to determine the accuracy of this recording when compared with arterial CO2 (PaCO2). We studied 30 healthy children, age one to five years and weighing between 10 and 25 kg undergoing minor surgery requiring mask anaesthesia. In each case, after induction of anaesthesia, the LMA was inserted under direct vision to eliminate the possibility of epiglottic airway obstruction. The fresh gas flow was provided by a Jackson Rees modification of an Ayre's T-piece and was determined according to the following formula: 3 x (1000 + (100 x body weight)) LPM. Blood pressure, ECG, O2 saturation, temperature and end-tidal gas concentrations were recorded. The measures of peak PETCO2 were taken at pre-determined distances from the elbow connector down the LMA shaft. During the sampling sequence an arterial blood sample was taken for gas analysis. The PaCO2 was 63.5 +/- 9.3 mmHg (mean +/- SD). At any given sampling site, mean PETCO2 values were less than PaCO2 (P < 0.05). However, in eight patients PETCO2 values measured at the distal site were higher than the PaCO2 (negative P(a-ET)CO2 gradients).(ABSTRACT TRUNCATED AT 250 WORDS)