Correlation of end tidal and arterial carbon dioxide levels in critically Ill neonates and children

Factors affecting the arterial to end-tidal carbon dioxide gradient in ventilated neonates

Objective. To determine factors which influenced the relationship between blood carbon dioxide (pCO₂) and end-tidal carbon dioxide (EtCO₂) values in ventilated, newborn infants. Furthermore, to assess whether pCO₂levels could be predicted from continuous EtCO₂monitoring.Approach. An observational study of routinely monitored newborn infants requiring mechanical ventilation in the first 28 d after birth was undertaken. Infants received standard clinical care. Daily pCO₂and EtCO₂levels were recorded and the difference (gradient: ∆P-EtCO₂) between the pairs were calculated. Ventilatory settings corresponding to the time of each blood gas assessment were noted. End-tidal capnography monitoring was performed using the Microstream sidestream Filterline H set capnograph.Main results. A total of 4697 blood gas results from one hundred and fifty infants were analysed. The infants had a median gestational age of 33.3 (range 22.3-42.0) weeks and birth weight of 1880 (395-5520) grams. Overall, there was moderate correlation between pCO₂and EtCO₂levels (r= 0.65,p< 0.001). The ∆P-EtCO₂for infants born less than 32 weeks of gestation was significantly higher (1.4 kPa) compared to infants born at greater than 32 weeks of gestation (0.8 kPa) (p< 0.001). In infants born at less than 32 completed weeks of gestation, pCO₂levels were independently associated with EtCO₂, day after birth, birthweight and fraction of inspired oxygen (FiO₂) (modelr² = 0.52,p< 0.001).Significance. The results of end-tidal capnography monitoring have the potential to predict blood carbon dioxide values within the neonatal population.

Correlation of End-Tidal Carbon Dioxide with Arterial Carbon Dioxide in Mechanically Ventilated Neonates: A Scoping Review

Monitoring CO2 levels in intubated neonates is highly relevant in the face of complications associated with altered CO2 levels. Thus, this review aims to present the scientific evidence in the literature regarding the correlation between arterial carbon dioxide measured by non-invasive methods in newborns submitted to invasive mechanical ventilation. The search was carried out from January 2020 to January 2021, in the Scopus, Medline, The Cochrane Library, Web of Science, CINAHL and Embase databases. Also, a manual search of the references of included studies was performed. The main descriptors used were: "capnography," "premature infant," "blood gas analysis," and "mechanical ventilation." As a result, 221 articles were identified, and 18 were included in this review. A total of 789 newborns were evaluated, with gestational age between 22.8 and 42.2 weeks and birth weight between 332 and 4790 g. Capnometry was the most widely used non-invasive method. In general, the correlation and agreement between the methods evaluated in the studies were strong/high. The birth weight did not influence the results. The gestational age of fewer than 37 weeks implied, in its majority, a moderate correlation and agreement. Therefore, we can conclude that there was a predominance of a strong correlation between arterial blood gases and non-invasive methods, although there are variations found in the literature. Even so, the results were promising and may provide valuable data for future studies, which are necessary to consolidate non-invasive methods as a reliable and viable alternative to arterial blood gasometry.

Capnography in Pediatric Critical Care Unit and Correlation of End-Tidal and Arterial Carbon Dioxide in Ventilated Children

Recording of end-tidal carbon dioxide (EtCO2) noninvasively reflects a real-time estimation of arterial carbon dioxide (PaCO2 [partial pressure of CO2]). However, as the EtCO2 is dependent on metabolism, perfusion, and ventilation, predicting PaCO2 from EtCO2 is not linear. The objective of the study was to find out the predictability of PaCO2 from EtCO2 in PICU and to evaluate the factors affecting the correlation of EtCO2 and PaCO2 in critically ill ventilated children. The design involved was prospective observational study. The setting discussed over here is that of pediatric intensive care unit (PICU) of tertiary care hospital. A total of 160 children between 1 month and 14 years received mechanical ventilation. EtCO2, PaCO2, PaO2/FiO2 (PF) ratio, oxygenation index (OI), and ventilation index (VI) are the factors involved in main outcome measures. A total of 535 pairs of EtCO2 and PaCO2 were recorded in 160 ventilated children during the stable hemodynamic state. Mean age and weight (Z-score) of patients were 31.15 ± 40.46 months and −2.10 ± 1.58, respectively. EtCO2 and PaCO2 differences were normal (2–5 mm of Hg) in 393 (73.5%) pairs. High gradient (>5 mm of Hg) was mostly found with children with pneumonia, prolonged ventilation, and pressure mode of ventilation (p < 0.05). EtCO2 had a strong positive correlation with PaCO2 (r = 0.723, 95% confidence interval [CI] = 0.68 and 0.76) and not significantly affected by PF ratio or OI. However, presence of pneumonia and high ventilation index (VI > 20) adversely affected the relationship with poor correlation coefficient (r = 0.449, 95% CI = 0.30, 0.58 and r = 0.227, 95% CI = 0.03, 0.41, respectively). EtCO2 reading showed good validity to predict PaCO2 and not affected by oxygenation parameters. The correlation was affected by the presence of pneumonia and high ventilation index; hence it is recommended to monitor PaCO2 invasively in these patients till a good correlation is established.

Relationship Between Pulmonary-to-Systemic-Blood-Flow Ratio (Qp:Qs) Based on Cardiac Catheterization and Indices Derived from Simultaneously Measured End Tidal CO2 (EtCO2) in Children with Complex Congenital Heart Disease

CO₂ removal by the lungs depends upon ventilation and pulmonary blood flow, with end tidal CO₂ (EtCO₂) as surrogate for it. We studied indices based on EtCO₂ measured routinely during anesthesia for cardiac catheterization, along with simultaneously calculated Qp:Qs (pulmonary-to-systemic-blood-flow ratio) in children with complex congenital heart disease to assess the relationship between these measures. A retrospective, single-center, correlational cohort study was conducted at a tertiary-care, free-standing children's hospital. All included subjects had Qp:Qs calculated as well as EtCO₂ and PaCO₂ documented during a single cardiac catheterization. Children with stage-1 single ventricle or complex biventricular repair with highly variable Qp:Qs were defined as Group 1, and Group 2 comprised those with stage 2 or 3 repairs with less variable Qp:Qs. Exclusion criteria were uncuffed artificial airway, EtCO₂ > PaCO₂, and abnormally high Qp:Qs. EtCO₂ indices were defined as EtCO₂:PaCO₂ (alveolar functional fraction) and EtCO₂ gap (PaCO₂-EtCO₂). Correlation coefficients were obtained between Qp:Qs and EtCO₂ indices in both groups. A total of 29 patients in Group 1 and 24 in Group 2 underwent final analysis. Even with highly variable Qp:Qs, Group 1 showed a strong correlation between Qp:Qs and EtCO₂:PaCO₂ (r = 0.83, p < 0.0001). A similarly strong correlation was maintained in Group 2 (r = 0.79, p < 0.0001) and in both groups combined (r = 0.86, p < 0.0001). A very strong negative correlation was present between Qp:Qs and EtCO₂ gap (r = - 0.77, p < 0.0001). EtCO₂:PaCO₂ has a very strong correlation with Qp:Qs simultaneously calculated during catheterization. It can be an additional parameter to estimate Qp:Qs in critical management of children with congenital heart disease. Our results also provide a basis for future prospective studies to assess dynamic changes in EtCO₂-based indices and Qp:Qs.

Effect of corrective or palliative procedures on arterial to end-tidal carbon dioxide pressure difference in pediatric cardiac surgery

BACKGROUND

The normal small difference (3-5 mmHg) between arterial (partial pressure of carbon dioxide [PaCO₂]) and end-tidal carbon dioxide pressure (ETPCO₂) increases in children with congenital heart disease. The present study was conducted to evaluate the effect of corrective or palliative cardiac surgery on this difference (known as DPCO2).

PATIENTS AND METHODS

In a prospective study, 200 children (aged <12 years old) candidate for corrective or palliative cardiac surgery were studied. Using arterial blood gas measurement and simultaneous capnography, DPCO₂ was calculated at various intra- and postoperative periods. DPCO₂ values were compared within and between corrective or palliative procedures.

RESULTS

Corrective and palliative procedures were carried out on 154 and 46 patients, respectively. Initial DPCO₂ was higher than normal values in corrective or palliative procedures (15.50 ± 13.1 and 10.75 ± 9.1 mmHg, respectively). DPCO₂ was higher in patients who underwent palliative procedure, except early after procedure. The procedure did not have any effect on the final DPCO₂ in palliative group. Although DPCO₂ decrease was significant in the corrective group, it did not return to normal values. Operation time was longer, and the need to inotropic support was higher in corrective procedures; however, longer periods of ventilatory support were needed in the palliative group. Complication rate and Intensive Care Unit stay time were the same in two operation types.

CONCLUSIONS

DPCO₂ did not change after palliative cardiac procedures. DPCO₂ decreased after corrective procedures; however, it did not return to normal values at early postoperative period. Thus, DPCO₂ may not have any clinical value in monitoring the quality of corrective or palliative procedures.

Validity of sidestream endtidal carbon dioxide measurement in critically ill, mechanically ventilated children

INTRODUCTION

Capnography is used to monitor the endtidal carbon dioxide tension (EtCO2) in exhaled gas. Sidestream capnography has great potential to monitor mechanically ventilated pediatric patients, given the continuous sampling from the endotracheal tube into a gas sensor. However, hemodynamic and respiratory impairments may reduce reliability and validity of sidestream capnography to monitor arterial carbon dioxide tension (PaCO2) in critically ill, mechanically ventilated children.

METHODS

In 47 mechanically ventilated pediatric patients (aged 0-14 years, median age 17.2 months), a total of 341 consecutive measurements of PaCO2, EtCO2, respiratory and hemodynamic parameters were performed, and capnogram shape was determined. Validity was assessed with the Bland-Altman limit of agreement (loa), mixed models were used to adjust for variation between patients, and potential confounders were considered with multivariable analyses.

RESULTS

EtCO2 (mean 4.50 ± 0.96 kPa) underestimated PaCO2 (mean 5.37 ± 0.87) considerably, resulting in a loa of 0.87 kPa [95% confidence interval (95% CI) -1.03;2.77] and 42.2% percentage error. The association improved significantly b = 0.54 [95 %CI = 0.45;0.64, P < 0.001] when corrected for individual differences. The association between EtCO2 and PaCO2 was not influenced by any of the potential confounders.

CONCLUSIONS

Sidestream capnography in mechanically ventilated infants and children seems moderately reliable and valid when corrected for individual differences. Therefore, it could only be used with caution for trend estimation in the individual patient.