Continuous End-Tidal Carbon Dioxide Monitoring during Resuscitation of Asphyxiated Term Lambs

Randomized trial of oxygen weaning strategies following chest compressions during neonatal resuscitation

BACKGROUND

The Neonatal Resuscitation Program (NRP) recommends using 100% O2 during chest compressions and adjusting FiO2 based on SpO2 after return of spontaneous circulation (ROSC). The optimal strategy for adjusting FiO2 is not known.

METHODS

Twenty-five near-term lambs asphyxiated by umbilical cord occlusion to cardiac arrest were resuscitated per NRP. Following ROSC, lambs were randomized to gradual decrease versus abrupt wean to 21% O2 followed by FiO2 titration to achieve NRP SpO2 targets. Carotid blood flow and blood gases were monitored.

RESULTS

Three minutes after ROSC, PaO2 was 229 ± 32 mmHg in gradual wean group compared to 57 ± 13 following abrupt wean to 21% O2 (p < 0.001). PaO2 remained high in the gradual wean group at 10 min after ROSC (110 ± 10 vs. 67 ± 12, p < 0.01) despite similar FiO2 (~0.3) in both groups. Cerebral O2 delivery (C-DO2) was higher above physiological range following ROSC with gradual wean (p < 0.05). Lower blood oxidized/reduced glutathione ratio (suggesting less oxidative stress) was observed with abrupt wean.

CONCLUSION

Weaning FiO2 abruptly to 0.21 with adjustment based on SpO2 prevents surge in PaO2 and C-DO2 and minimizes oxidative stress compared to gradual weaning from 100% O2 following ROSC. Clinical trials with neurodevelopmental outcomes comparing post-ROSC FiO2 weaning strategies are warranted.

IMPACT

In a lamb model of perinatal asphyxial cardiac arrest, abrupt weaning of inspired oxygen to 21% prevents excessive oxygen delivery to the brain and oxidative stress compared to gradual weaning from 100% oxygen following return of spontaneous circulation. Clinical studies assessing neurodevelopmental outcomes comparing abrupt and gradual weaning of inspired oxygen after recovery from neonatal asphyxial arrest are warranted.

Accuracy of a battery-powered portable capnometer in premature infants

Carbon dioxide measurement is useful for confirmation of successful tracheal intubation and ensuring adequate ventilation. There are two types of CO₂ detectors, i.e., single-use-only colorimetric devices and capnometers. Although portable capnometers are widely used for resuscitation, there have been no reports regarding their clinical utility in neonates. The correspondence between end-tidal CO₂ (PetCO₂) level determined using a battery-powered portable capnometer and arterial CO₂ (PaCO₂) was investigated using paired data obtained simultaneously from 26 neonates weighing 1262 ± 589 g at examination on mechanical ventilation. PetCO₂ level and PaCO₂ showed a strong correlation (r = 0.839, P < 0.001), and the correlation equation was: PetCO₂ = 0.8 × PaCO₂ + 1.1. Therefore, PetCO₂ readings obtained with a battery-powered portable capnometer were likely to be underestimated. This became more pronounced with decreasing infant body weight at examination as the net difference in measurements of PaCO₂ and PetCO₂ was significantly positively correlated with infant body weight at examination (r = 0.451, P < 0.001). The observations presented here may be helpful in the use of battery-powered portable capnometers in neonates requiring controlled ventilation with tracheal intubation.

End-tidal capnography monitoring in infants ventilated on the neonatal intensive care unit

OBJECTIVE

To assess whether end-tidal capnography (EtCO₂) monitoring reduced the magnitude of difference in carbon dioxide (CO₂) levels and the number of blood gases in ventilated infants.

STUDY DESIGN

A case-control study of a prospective cohort (n = 36) with capnography monitoring and matched historical controls (n = 36).

RESULT

The infants had a median gestational age of 31.6 weeks. A reduction in the highest CO₂ level on day 1 after birth was observed after the introduction of EtCO₂ monitoring (p = 0.043). There was also a reduction in the magnitude of difference in CO₂ levels on days 1 (p = 0.002) and 4 (p = 0.049) after birth. There was no significant difference in the number of blood gases.

CONCLUSION

Continuous end-tidal capnography monitoring in ventilated infants was associated with a reduction in the degree of the magnitude of difference in CO₂ levels and highest level of CO₂ on the first day after birth.

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.

Chest Compressions for Bradycardia during Neonatal Resuscitation-Do We Have Evidence?

The International Liaison Committee on Resuscitation (ILCOR) recommends the initiation of chest compressions (CC) during neonatal resuscitation after 30 s of effective ventilation if the infant remains bradycardic (defined as a heart rate less than 60 bpm). The CC are performed during bradycardia to optimize organ perfusion, especially to the heart and brain. Among adults and children undergoing cardiopulmonary resuscitation (CPR), CC is indicated only for pulselessness or poor perfusion. Neonates have a healthy heart that attempts to preserve coronary and cerebral perfusion during bradycardia secondary to asphyxia. Ventilation of the lungs is the key step during neonatal resuscitation, improving gas exchange and enhancing cerebral and cardiac blood flow by changes in intrathoracic pressure. Compressing the chest 90 times per minute without synchrony with innate cardiac activity during neonatal bradycardia is not based on evidence and could potentially be harmful. Although there are no studies evaluating outcomes in neonates, a recent pediatric study in a hospital setting showed that when CC were initiated during pulseless bradycardia, a third of the patients went into complete arrest, with poor survival at discharge. Ventilation-only protocols such as helping babies breathe are effective in reducing mortality and stillbirths in low-resource settings. In a situation of complete cardiac arrest, CC reinitiates pulmonary flow and supports gas exchange. However, the benefit/harm of performing asynchronous CC during bradycardia as part of neonatal resuscitation remains unknown.

Oxygenation and Hemodynamics during Chest Compressions in a Lamb Model of Perinatal Asphyxia Induced Cardiac Arrest

The current guidelines recommend the use of 100% O₂ during resuscitation of a neonate requiring chest compressions (CC). Studies comparing 21% and 100% O₂ during CC were conducted in postnatal models and have not shown a difference in incidence or timing of return of spontaneous circulation (ROSC). The objective of this study is to evaluate systemic oxygenation and oxygen delivery to the brain during CC in an ovine model of perinatal asphyxial arrest induced by umbilical cord occlusion. Pulseless cardiac arrest was induced by umbilical cord occlusion in 22 lambs. After 5 min of asystole, lambs were resuscitated with 21% O₂ as per Neonatal Resuscitation Program (NRP) guidelines. At the onset of CC, inspired O₂ was either increased to 100% O₂ (n = 25) or continued at 21% (n = 9). Lambs were ventilated for 30 min post ROSC and FiO₂ was gradually titrated to achieve preductal SpO₂ of 85–95%. All lambs achieved ROSC. During CC, PaO₂ was 21.6 ± 1.6 mm Hg with 21% and 23.9 ± 6.8 mm Hg with 100% O₂ (p = 0.16). Carotid flow was significantly lower during CC (1.2 ± 1.6 mL/kg/min in 21% and 3.2 ± 3.4 mL/kg/min in 100% oxygen) compared to baseline fetal levels (27 ± 9 mL/kg/min). Oxygen delivery to the brain was 0.05 ± 0.06 mL/kg/min in the 21% group and 0.11 ± 0.09 mL/kg/min in the 100% group and was significantly lower than fetal levels (2.1 ± 0.3 mL/kg/min). Immediately after ROSC, lambs ventilated with 100% O₂ had higher PaO₂ and pulmonary flow. It was concluded that carotid blood flow, systemic PaO₂, and oxygen delivery to the brain are very low during chest compressions for cardiac arrest irrespective of 21% or 100% inspired oxygen use during resuscitation.

Effect of various inspired oxygen concentrations on pulmonary and systemic hemodynamics and oxygenation during resuscitation in a transitioning preterm model

BACKGROUND

The Neonatal Resuscitation Program recommends initial resuscitation of preterm infants with low oxygen (O₂) followed by titration to target preductal saturations (SpO₂). We studied the effect of resuscitation with titrated O₂ on gas exchange, pulmonary, and systemic hemodynamics.

METHODOLOGY

Twenty-nine preterm lambs (127 d gestation) were randomized to resuscitation with 21% O₂ (n = 7), 100% O₂ (n = 6), or initiation at 21% and titrated to target SpO₂ (n = 16). Seven healthy term control lambs were ventilated with 21% O₂.

RESULTS

Preductal SpO₂ achieved by titrating O₂ was within the desired range similar to term lambs in 21% O₂. Resuscitation of preterm lambs with 21% and 100% O₂ resulted in SpO₂ below and above the target, respectively. Ventilation of preterm lambs with 100% O₂ and term lambs with 21% O₂ effectively decreased pulmonary vascular resistance (PVR). In contrast, preterm lambs with 21% O₂ and titrated O₂ demonstrated significantly higher PVR than term lambs on 21% O₂.

CONCLUSION(S)

Initial resuscitation with 21% O₂ followed by titration of O₂ led to suboptimal pulmonary vascular transition at birth in preterm lambs. Ventilation with 100% O₂ in preterm lambs caused hyperoxia but reduced PVR similar to term lambs on 21% O₂. Studies evaluating the initiation of resuscitation at a higher O₂ concentration followed by titration based on SpO₂ in preterm neonates are needed.

The Perinatal Asphyxiated Lamb Model: A Model for Newborn Resuscitation

Birth asphyxia accounts for nearly one million deaths worldwide each year, and is one of the primary causes of early neonatal morbidity and mortality. Many aspects of the current neonatal resuscitation guidelines remain controversial given the difficulties in conducting randomized clinical trials owing to the infrequent and often unpredictable need for extensive resuscitation. Most studies on neonatal resuscitation stem from manikin models that fail to truly reflect physiologic changes or piglet models that have cleared their lung fluid and that have completed the transition from fetal to neonatal circulation. The present protocol provides a detailed step-by-step description on how to create a perinatal asphyxiated fetal lamb model. The proposed model has a transitioning circulation and fluid-filled lungs, which mimics human newborns following delivery, and is, therefore, an excellent animal model to study newborn physiology. An important limitation to lamb experiments is the higher associated cost.

Respiratory changes in term infants immediately after birth

INTRODUCTION

Over 5% of infants worldwide receive breathing support immediately after birth. Our goal was to define references ranges for exhaled carbon dioxide (ECO₂), exhaled tidal volume (VTe), and respiratory rate (RR) immediately after birth in spontaneously breathing, healthy infants born at 36 weeks' gestational age or older.

METHODS

This was a single-centre, observational study at the Royal Women's Hospital in Melbourne, Australia, a busy perinatal referral centre. Immediately after the infant's head was delivered, we used a face mask to measure ECO₂, VTe, and RR through the first ten minutes after birth. Respiratory measurements were repeated at one hour.

RESULTS

We analysed 14,731 breaths in 101 spontaneously breathing infants, 51 born via planned caesarean section and 50 born vaginally with a median (IQR) gestational age of 39^1/7 weeks (38^3/7-39^5/7). It took a median of 7 (4-10) breaths until ECO₂ was detected. ECO₂ quickly increased to peak value of 48 mmHg (43-53) at 143 s (76-258) after birth, and decreased to post-transitional values, 31 mmHg (28-24), by 7 min. VTe increased after birth, reaching a plateau of 5.3 ml/kg (2.5-8.4) by 130 s for the remainder of the study period. Maximum VTe was 19 ml/kg (16-22) at 257 s (82-360). RR values increased slightly over time, being higher from minute five to ten as compared to the first two minutes after birth.

CONCLUSIONS

This study provides reference ranges of exhaled carbon dioxide, exhaled tidal volumes, and respiratory rate for the first ten minutes after birth in term infants who transition without resuscitation.

Carbon Dioxide Fluctuations Are Associated with Changes in Cerebral Oxygenation and Electrical Activity in Infants Born Preterm

OBJECTIVES

To evaluate the effects of acute arterial carbon dioxide partial pressure changes on cerebral oxygenation and electrical activity in infants born preterm.

STUDY DESIGN

This retrospective observational study included ventilated infants born preterm with acute fluctuations of continuous end-tidal CO₂ (etCO₂) as a surrogate marker for arterial carbon dioxide partial pressure, during the first 72 hours of life. Regional cerebral oxygen saturation and fractional tissue oxygen extraction were monitored with near-infrared spectroscopy. Brain activity was monitored with 2-channel electroencephalography. Spontaneous activity transients (SATs) rate (SATs/minute) and interval between SATs (in seconds) were calculated. Ten-minute periods were selected for analysis: before, during, and after etCO₂ fluctuations of ≥5  mm Hg.

RESULTS

Thirty-eight patients (mean ± SD gestational age of 29 ± 1.8 weeks) were included, with 60 episodes of etCO₂ increase and 70 episodes of etCO₂ decrease. During etCO₂ increases, brain oxygenation increased (regional cerebral oxygen saturation increased, fractional tissue oxygen extraction decreased; P < .01) and electrical activity decreased (SATs/minute decreased, interval between SATs increased; P < .01). All measures recovered when etCO₂ returned to baseline. During etCO₂ decreases, brain oxygenation decreased (regional cerebral oxygen saturation decreased, fractional tissue oxygen extraction decreased; P < .01) and brain activity increased (SATs/minute increased, P < .05), also with recovery after return of etCO₂ to baseline.

CONCLUSION

An acute increase in etCO₂ is associated with increased cerebral oxygenation and decreased brain activity, whereas an acute decrease is associated with decreased cerebral oxygenation and slightly increased brain activity. Combining continuous CO₂ monitoring with near-infrared spectroscopy may enable the detection of otherwise undetected fluctuations in arterial carbon dioxide partial pressure that may be harmful to the neonatal brain.

Continuous capnography monitoring during resuscitation in a transitional large mammalian model of asphyxial cardiac arrest

BACKGROUND

In neonates requiring chest compression (CC) during resuscitation, neonatal resuscitation program (NRP) recommends against relying on a single feedback device such as end-tidal carbon dioxide (ETCO₂) or saturations (SpO₂) to determine return of spontaneous circulation (ROSC) until more evidence becomes available.

METHODS

We evaluated the role of monitoring ETCO₂ during resuscitation in a lamb model of cardiac arrest induced by umbilical cord occlusion (n = 21). Lambs were resuscitated as per NRP guidelines. Systolic blood pressure (SBP), carotid and pulmonary blood flows along with ETCO₂ and blood gases were continuously monitored. Resuscitation was continued for 20 min or until ROSC (whichever was earlier). Adequate CC was arbitrarily defined as generation of 30 mmHg SBP during resuscitation. ETCO₂ thresholds to predict adequacy of CC and detect ROSC were determined.

RESULTS

Significant relationship between ETCO₂ and adequate CC was noted during resuscitation (AUC-0.735, P < 0.01). At ROSC (n = 12), ETCO₂ rapidly increased to 57 ± 20 mmHg with a threshold of ≥32 mmHg being 100% sensitive and 97% specific to predict ROSC.

CONCLUSION

In a large mammalian model of perinatal asphyxia, continuous ETCO₂ monitoring predicted adequacy of CC and detected ROSC. These findings suggest ETCO₂ in conjunction with other devices may be beneficial during CC and predict ROSC.