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

Abstract

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.

Keywords

capnography - end-tidal carbon dioxide - PaCO₂ - pediatric intensive care unit - arterial blood gas

Introduction

In the pediatric intensive care unit (PICU), to ensure proper patient care and professional credibility, monitoring of CO₂ and O₂ is the recommended “minimum guidelines and levels of care” by American Academy of Pediatrics. Arterial blood gas (ABG) analysis is considered the gold standard in monitoring sick children on a mechanical ventilator. ABG sampling is costly, time-consuming, needs training, invasive with a risk of infection, and provides a snapshot view into the condition of the patient. Pulse oximetry and capnography provide noninvasive and real-time monitoring in PICU. Pulse oximetry provides predictable information about oxygenation. As capnography is dependent on metabolism, perfusion, and ventilation of the patient, it does not provide reliable information on ventilation during hemodynamic instability. Also, in conditions with increased physiological dead space (VD or dead space ventilation), the arterial carbon dioxide (PaCO₂ or partial pressure of CO₂) and end-tidal carbon dioxide (EtCO₂) gradients are increased, and the correlation is affected.[1]

EtCO₂ monitoring is the standard of care during procedures such as intubations and sedations and also used in a variety of clinical situations. However, EtCO₂ may be underused in pediatric settings.[2] There is insufficient data for the use of capnography in PICU as a substitute for repeated ABG sampling in resource-poor settings and parameters affecting noncorrelation of EtCO₂ with PaCO₂._. Hence, this study was designed to assess how reliably EtCO₂ predicts PaCO₂ in critically sick ventilated infants and children in PICU and, to find out the different parameters which may affect the correlation.

Methods

Study Design

This was a prospective study done at PICU of a tertiary care hospital in India. Approval was obtained from the Institutional Ethical Committee. Informed consent was obtained from the parents before enrolling in the study.

Participants

All critically ill children from 1 month to 14 years admitted to PICU and requiring mechanical ventilation were included for the study. Patients diagnosed with or suspected of congenital cyanotic heart disease were excluded from the study as intracardiac shunting is likely to cause an obligatory difference between arterial and EtCO₂.

Data Collection

After obtaining informed written consent from the parents, mechanically ventilated patients were selected from PICU according to inclusion and exclusion criteria. The patients were intubated with appropriate size endotracheal tube and ventilated using Puritan Bennet 840 Ventilator or Maquet (servo-I) ventilator in various modes like synchronized intermittent mandatory ventilation (SIMV) or assist-control modes. Humidifier (Fisher and Paykel M 850/heat and moisture exchanger[HME] filter) was used for all patients whenever available. Uncuffed endotracheal tubes were used in infants and cuffed tubes in older children. Continuous mainstream EtCO₂ monitoring probe, IRMA MAXIMO gas analyzer was attached to the endotracheal tube end for recording the EtCO₂.[3] Capnography and EtCO₂ values were obtained using a multiparameter monitor (Truscope II; 12” Multi-parameter Monitor, Schiller).

Demographic data like age, sex, socioeconomic status were recorded. Anthropometric details were obtained. History and physical findings of each patient were recorded with relevant investigations at the time of admission and progress throughout ICU stay. The disease of the patient, major organ systems involved, indication for ICU admission, and that of mechanical ventilation were noted. The patients were resuscitated by the ICU team and managed as per ICU protocols. Hemodynamic instability was defined as perfusion failure represented by clinical features of circulatory shock and advanced heart failure.[4] In the present study, hemodynamic stability was based on the measurement of vital signs irrespective of the use of vasopressor and ventilatory support. When the baby was hemodynamically stable on the ventilator, ABG was done, and simultaneously EtCO₂ values were noted. The mode of ventilation, humidification used, oxygenation, and ventilator parameters were recorded at each measurement of ABG. Due to the risk of an increase in dead space in infants and young children with the use of HME filter, it was used only in older children and adolescents.[5] A maximum of five ABGs (minimum one ABG) was taken for each patient at an interval of at least 12 hours ensuring stable hemodynamic state. Oxygenation parameters were fractional inspired oxygen concentration (FiO₂), PaO₂, PF ratio, and oxygenation index (OI). PF ratio was calculated using the formula PaO₂/FiO₂, and OI was calculated using the formula (FiO₂ × MAP [mean airway pressure])/PaO₂. Ventilation parameters were respiratory rate (RR), peak inspiratory pressure (PIP), positive end-expiratory pressure (PEEP), tidal volume (Tv), and ventilation index (VI). VI is a calculation used to determine the severity of respiratory illness (acute lung injury and/or respiratory distress syndrome) in critically ill patients. It was calculated in pressure mode of ventilation using the formula [RR × (PIP − PEEP) × PaCO₂]/1,000, whereas RR is the input ventilator respiratory rate.[6]

Laboratory procedures: For ABG analysis, 0.1 mL of arterial blood was collected from radial artery puncture using 1-mL heparinized syringe (flushed with 20 IU/mL heparin solution) and analysis was done within 15 minutes of collection using Instrumentation Laboratory Worldwide (GEM Premier 3000) or Eschweiler Gas analyzer.[7] [8]

Outcomes

The outcome variable was EtCO₂, arterial PaCO₂, PF ratio, OI, and VI.

Statistics

Sample Size

Assuming a confidence level 1 − α(α) of 95%, anticipated population proportions (P) of 50% and absolute precision (d) of 8%, the minimum sample size required was computed to be 150. A total of 223 patients were mechanically ventilated during the study period, 160 patients meeting the inclusion criteria were included for the study during hemodynamically stable condition; 535 pairs of ABG and EtCO₂ were obtained for analysis.

Statistical Methods

Data were analyzed using IBM SPSS statistics 24. Frequency distributions of variables were computed using the frequency procedure (categorical variable) and descriptive statistics (scale variable). Their association with normal (2–5 mm of Hg) and high gradient (> 5 mm of Hg) was computed using Chi-square test of independence (categorical variable), independent sample “t”-test (scale variable), and Mann Whitney test (when standard deviation [SD] > mean for scale variables). Pearson's bivariate correlation between PaCO₂ and EtCO₂ was computed to study the linear correlation. Coefficient of determination was computed applying the linear regression procedure with PaCO₂ as the dependent and EtCO₂ as the independent variable. The cut-off p-value for the test of significance was taken as <0.05.

Results

Out of a total of 646 patients admitted to PICU during the study period, 223 required mechanical ventilation. Three patients with congenital cyanotic heart disease were excluded. A total of 535 recordings of ABG and EtCO₂ were obtained from 160 critically ill ventilated patients during the hemodynamically stable condition, with a maximum of five recordings per individual patient.

Out of 160 patients, 85 (53.1%) were infants below 12 months with a male: female ratio of 1.46:1. The mean (SD) age of the study population was 31.15 ± 40.46 months. Weight for age (Z-score) was < − 2 in 76 (47.5%) children. Pneumonia and meningoencephalitis were leading causes for admission constituting 36 (22.5%) and 32 (20%) children, respectively. Respiratory distress and neurological conditions were the leading causes of ventilation in 89 (55.6%) and 60 (37.5%) children, respectively. Median (IQR [interquartile range]) duration of ventilation was 3 (2,5) days ([Table 1]).

Table 1 Baseline characteristics of ventilated children in PICU (n = 160)

Variable		Value
Sex	Male	95 (59.4%)
	Female	65 (40.6%)
Age (mo)	≤ 1 y	85 (53.1%)
	>1 y	75 (46.9%)
Weight for age (Z-score)	< −2	76 (47.5%)
	−2 to 2	83 (51.9%)
	>2	1 (0.6%)
Duration of ventilation[a] (d)		4.33 (4.89)
Duration of ICU stay[a] (d)		7.02 (9.18)
Indication of ICU admission	Respiratory distress	89 (55.6%)
	Respiratory failure	3 (1.9%)
	Low GCS	60 (37.5%)
	Others	8 (5%)
Etiology	Pneumonia	36 (22.5%)
	Meningoencephalitis	32 (20%)
	Sepsis	19 (11.9%)
	Severe malaria	12 (7.5%)
	CAHD and	24 (15.0%)
	pneumonia	37 (23.1%)
	Others

Abbreviations: CAHD, congenital acyanotic heart disease; GCS, Glasgow coma scale; ICU, intensive care unit; PICU, pediatric intensive care unit.

^a Mean (SD).

[Table 2] shows the EtCO₂ recording of ventilated children in PICU. SIMV (PC or pressure control + PS or pressure support) was the most common mode of ventilation during 327 (61.1%) recordings, and servo-controlled heated wire humidification was used during 357 (66.7%) recordings. EtCO₂ and PaCO₂ differences were normal (2–5 mm of Hg) in 393 (73.4%) pairs in the present study with a mean difference of 6.71 ± 10.14 mm of Hg. EtCO₂ was higher than PaCO₂ in 100 (78.8%) patients with pneumonia.

Table 2 End-tidal carbon dioxide recording of ventilated children in PICU (n = 535)

Variable		Value
Mode of ventilation	SIMV (PC + PS)	327 (61.1)
	SIMV (VC + PS)	193 (36.1)
	Others	15 (2.8)
Humidification	Heated wire (Active)	357 (66.7)
	HME	84 (15.7)
	None	94 (17.6)
End-tidal CO2 [a] (mm Hg)		46.17 (13.87)
End-tidal CO2 [b] (mm Hg)		44 (36,54)
EtCO2 > PaCO2 (n = 482)	Patient with pneumonia	100 (78.8%)
	Patient without pneumonia	382 (93.6%)
EtCO2–PaCO2 difference (mm Hg)	Normal (2–5)	393 (73.5)
	High (>5 mm)	142 (26.5)
EtCO2–PaCO2 difference[a] (mm Hg)		6.71 (10.14)
EtCO2–PaCO2 difference[b] (mm Hg)		4 (2,6)

Abbreviations: HME, heat moisture exchanger; IQR, interquartile range; PC, pressure control; PICU, PICU, pediatric intensive care unit; PS, pressure support; SD, standard deviation; SIMV, synchronized intermittent mandatory ventilation; VC, volume control.

^a Mean (SD).

^b Median (IQR).

[Table 3] shows the factors affecting high PaCO₂–EtCO₂ gradient (>5 mm of Hg). Critically ill children with lower mean weight, prolonged ventilation, pneumonia, high PaCO₂, and high VI have a higher likelihood of having a high gradient. No significant difference was found with age, sex, humidification types, pH, and OI.

Table 3 Factors affecting arterial end-tidal carbon dioxide gradient in ventilated children in PICU

Variables		Normal gradient n = 393	High gradient n = 142	p-Value
Sex	M:F	1.23:1	1.54:1	0.270
Age[b] (mo)		11 (4,42)	8.5 (4,27)	0.162[c]
Duration of ventilation[a] (d)		5.07 ± 4.84	6.26 ± 5.80	0.018
Duration of ICU stay[a] (d)		7.82 ± 9.34	10.09 ± 11.32	0.020
Disease condition	Meningoencephalitis	73 (18.6)	20 (14.1)	0.000
	Pneumonia	73 (18.6)	54 (38)
	CAHD with pneumonia	62 (15.8)	14 (9.9)
	Sepsis	47 (12.0)	20 (14.1)
	Severe malaria	8 (2.0)	1 (0.7)
	Others	130 (33.1)	33 (23.2)
Mode of ventilation	SIMV (PC + PS)	228 (58.0)	99 (69.7)	0.003
	SIMV (VC + PS)	157 (39.9)	36 (25.4)
	Others	8 (2.0)	7 (4.9)
Humidification types	Active	264 (67.2)	93 (65.5)	0.127
	HME	55 (14.0)	29 (20.4)
	None	74 (18.8)	20 (14.1)
Acid base status	pH[a]	7.40 ± 0.09	7.38 ± 0.18	0.386
	HCO3 (meq/L)[a]	24.63 ± 5.64	27.64 ± 8.93	0.000
	TCO2 [a]	27.00 ± 20.83	27.39 ± 18.45	0.844
Oxygenation parameters	PaO2 [a] (mm of Hg)	152.90 ± 77.46	146.36 ± 89.51	0.409
	FiO2 [a] (%)	82.02 ± 19.79	77.01 ± 22.30	0.013
	SpO2 [a] (%)	97.22 ± 2.51	97.77 ± 2.29	0.020
	AaDO2 [a] (mm of Hg)	256.44 ± 157.31	248.7 ± 167.38	0.622
	OI[a]	46.60 ± 28.37	45.48 ± 33.84	0.703
	PF ratio[a]	201.85 ± 133.73	212.10 ± 148.37	0.448
Ventilatory parameters	PaCO2 (mm of Hg)[a]	41.46 ± 10.87	48.57 ± 26.88	0.000
	FiCO2 [a] (%)	3.61 ± 0.73	3.99 ± 1.42	0.000
	Respiratory rate[a]	26.35 ± 5.48	29.79 ± 5.01	0.000
	PIP (n = 235, normal,104 high)[a]	17.48 ± 3.00	16.86 ± 3.77	0.104
	Tv (n = 158 Normal, 38 high)[a]	8.16 ± 1.36	8.38 ± 1.42	0.374
	PEEP	5.48 ± 0.92	5.25 ± 1.16	0.016
	VI (n = 235 normal, 104 high)[a]	15.95 ± 6.32	19.42 ± 15.14	0.003

Abbreviations: AaDO₂, alveolar arterial oxygen gradient; CAHD, congenital acyanotic heart disease; HME, heat and moisture exchanger; IQR, interquartile range; OI, OI, oxygenation index; PC, pressure control; PEEP, positive end expiratory pressure; PF, PaO₂/FiO₂; PICU, pediatric intensive care unit; PIP, peak inspiratory pressure; PS, pressure support; SD, standard deviation; SIMV, synchronized intermittent mandatory ventilation; Tv, tidal volume; SD, standard deviation; VC, volume control; VI, ventilation index.

^a Mean (SD).

^b Median (IQR).

^c Mann-Whitney test.

Note: Bold values represent significant data.

[Table 4] and [Fig. 1] compare the correlation of EtCO₂ with PaCO₂. EtCO₂ had a strong positive correlation with PaCO₂ (r = 0.723, 95%CI [confidence interval] = 0.68–0.76). A subgroup analysis was done with different oxygenation parameters and ventilation parameters to find out any variations in the correlation between EtCO₂ and PaCO₂. Correlation is minimally affected by oxygenation parameters, i.e., PF ratio or OI. At PF ratio <200 and OI >25 we found a strong correlation between EtCO₂ and PaCO₂ (r = 0.697, 95% CI = 0.63–0.74 and r = 0.721, 95% CI = 0.67–0.77, respectively). 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) ([Table 4]; [Figs. 2] and [3]).

Table 4 Correlation between EtCO₂ and PaCO₂ in the study population

No. of pairs	PaCO2 [a]	EtCO2 [a]	Correlation coefficient	95% CI	Coefficient of determination
Total no of Pairs (n = 535)	43.35 (16.95)	46.17 (13.87)	0.723[c]	0.68–0.76	0.522
Children with pneumonia (n = 127)	49.43 (21.78)	50.99 (16.01)	0.449[c]	0.30–0.58	0.202
Children without pneumonia (n = 408)	41.5 (14.7)	44.7 (12.8)	0.867[c]	0.84–0.89	0.867
PF ratio >200 (n = 214)	41.09 (14.81)	44.75 (12.85)	0.770[c]	0.71–0.82	0.593
PF ratio ≤ 200 (n = 321)	44.85 (18.10)	47.12 (14.44)	0.697[c]	0.63–0.74	0.486
OI >25 (n = 405)	44.16 (17.20)	46.58 (13.89)	0.721[c]	0.67–0.77	0.519
OI ≤ 25 (n = 130)	40.83 (15.92)	44.92 (13.80)	0.728[c]	0.63–0.80	0.529
VI >20 (n = 95)	62.61 (17.62)	60.31 (13.90)	0.227[b]	0.03–0.41	0.051
VI ≤ 20 (n = 244)	37.35 (11.28)	42.88 (12.19)	0.742[c]	0.68–0.80	0.550

Abbreviations: CI, confidence interval; OI, oxygenation index; PF, PaO₂/FiO₂; SD, standard deviation; VI, ventilation index.

^a Mean (SD).

^b Significant at 0.05 level.

^c Significant at 0.01 level.

Fig. 1 Bland Altman plot in infants and children (EtCO₂ PaCO₂ pairs 535).

Fig. 2 Correlation of EtCO₂ and PaCO₂ in relation to VI. VI, ventilation index.

Fig. 3 Correlation of EtCO₂ and PaCO₂ in relation to OI. OI, oxygenation index.

Discussion

In the present study, we have evaluated the relationship of EtCO₂ with PaCO₂ in critically sick ventilated infants and children. We found the EtCO₂ had a strong positive correlation with PaCO₂, and it provides a clinically relevant and valid estimation of ventilation in critically sick ventilated children. In patients with high ventilation index (VI > 20) and pneumonia, it showed a correlation coefficient of 0.227 and 0.449, respectively, and R ² is suggestive of only 5 to 20% variation in PaCO₂ that could be explained by EtCO₂.

Bohr equation states that physiological dead space ventilation (VD) is equal to Tv multiplied by PaCO₂ minus partial pressure of expired carbon dioxide (PeCO₂) divided by PaCO₂.[9] As the VD is directly related to the gradient, the weak correlation of EtCO₂ and PaCO₂ in the present study may be explained by the increase in the physiological dead space in critically sick children with a different lung condition which might be driving the gradient between EtCO₂ and PaCO₂.

In a prospective study in children with traumatic brain injury, Yang et al analyzed agreement between arterial carbon dioxide levels with EtCO₂ levels (the agreement was defined as PaCO₂–EtCO₂ gradient between 0 and 5 mm Hg). There was 42% agreement, and on average, PaCO₂ was 2.7 mm Hg (95% limits of agreement, –11.3 to 16.7) higher than EtCO₂. Low PaCO₂–EtCO₂ agreement was seen in patients with acute respiratory distress syndrome (ARDS). However, in the present study, the PaCO₂–EtCO₂ gradient was reported to be normal in 73.4% of children. We found poor correlation coefficient (r = 0.449, 95% CI = 0.30, 0.58) in the children with pneumonia in agreement with the study by Yang et al.[10]

Mehta et al studied the predictive capability of EtCO₂ in sick ventilated infant and children and found PaCO₂ having an excellent correlation with EtCO₂ (n = 96, r = 0.914), similar to our study. They found the PF ratio < 200 adversely affected relationship with a correlation coefficient of 0.83 similar to our result. However, Mehta et al found a good correlation at high VI in contrary to our findings, which might be due to small sample size in their study compared with our study (15 vs. 95 pairs).[11]

Meredith and Monaco and McDonald et al also found a strong positive correlation (n = 1,708, r = 0.716), and (n = 132, r = 0.79) and a negative impact of severe lung disease, similar to our study. However, both the studies had drawn an average of 17 and eight pairs per patient, respectively, whereas we drew up to five pairs per patient to maintain better validity of coefficient of correlation.[12] [13] Previous studies by Hopper et al and McDonald et al also found the influence of VI and PF ratio on the PaCO₂–EtCO₂ relationship similar to our study.[13] [14] Similarly, McDonald et al reported the PaCO₂–EtCO₂ gradient to be higher with increasing duration of mechanical ventilation. However, in contrary to our findings, their study found more percentage of the high gradient (> 10 mm of Hg) in children with PF ratio of < 200 compared with that of > 200 (35 vs. 10%). We found an insignificant difference in PF ratio in both normal and high gradient group.[13]

Sidestream distal EtCO₂ was measured by a microstream capnograph via the extra port of a double-lumen endotracheal tube by Kugelman et al in 27 ventilated neonates with 222 measurements and found a good correlation and agreement between PaCO₂ and mainstream proximal EtCO₂. However, our study using proximal mainstream EtCO₂ excluded neonates. Further studies comparing neonate and older children with proximal and distal EtCO₂ recording are required to validate these results.[15]

Goonasekera et al reported EtCO₂ values to be higher than PaCO₂ in 22.7% of the observation in ventilated children. Similarly, we found EtCO₂ values to be higher than PaCO₂ in 105 (19.6%) children. The PaCO₂–EtCO₂ difference correlated positively with the alveolar-arterial oxygen tension or pressure difference (AaDO₂) difference (ρ = 0.381 p < 0.0001). We have not studied the correlation of PaCO₂–EtCO₂ difference with AaDO₂, but we observed no statistically significant difference in AaDO₂ in both normal and high gradient group (p = 0.622).[16]

McSwain et al monitored mechanically ventilated children using volumetric capnography and compared the EtCO₂–PaCO₂ correlation in different ranges of physiological dead space to tidal volume ratio (Vd/Vt). The correlation coefficient between EtCO₂ and PaCO₂ ranges from 0.78 to 0.95. The EtCO₂–PaCO₂ gradient increased predictably with increasing Vd/Vt. We found a correlation coefficient of 0.723 in our cohort; the low correlation in our study could be due to higher prevalence of severe lung disease (pneumonia and ARDS) with high Vd/Vt.[17]

There are several limitations to our study. The study was conducted at a single center in a limited resource PICU with most children admitted with pneumonia and/or respiratory failure. Studies with different etiologies in multiple centers need to be conducted to validate the results. Only mainstream capnometer was used. However, previous studies comparing both mainstream and sidestream capnometer reveal similar results and can be extrapolated to include both types. Several factors affecting the EtCO₂ and PaCO₂ gradient may be confounding to each other, and a regression analysis could give better results. All efforts have been taken to take the reading at stable hemodynamic state; however, some reading might have been taken in unstable condition confounding the results. Again, capnography, the graphical representation though very useful for an individual patient, it could not be used for analysis and deriving statistical inference.

Conclusion

In hemodynamically stable yet critically ill ventilated children, continuous noninvasive monitoring of ventilation, i.e., EtCO₂ correlates strongly with the gold standard monitoring, i.e., PaCO₂, obviating the need for repeated ABG in resource-poor settings. This emphasizes the practice of EtCO₂ use in PICU. EtCO₂ showed good validity to predict PaCO₂ and not much affected by oxygenation parameters. The correlation was greatly affected by the presence of pneumonia and high ventilation index; hence it is recommended to monitor PaCO₂ invasively in these patients until a good correlation is established.

Conflict of Interest

None.

Acknowledgments

We thank Prof. Leena Das for constantly inspiring us in this work; Dr. Bijaya Bhusan Nanda, Deputy Director, Regional Institute of Planning, Applied Economics and Statistics, Odisha, for providing statistical guidance; Francis Satapathy for his help in drafting the manuscript.

Authors' Contributions

B.K.M. conceived and designed the study, analyzed the data, revised the article, and act as the guarantor of the study. A.K. and D.D.P. collected the data and drafted the paper. A.K. and S.K.S. analyzed the data and revised the article. All the authors approved the final manuscript.

• References

• 1 Riley CM. Continuous capnography in pediatric intensive care. Crit Care Nurs Clin North Am 2017; 29 (02) 251-258
• 2 Selby ST, Abramo T, Hobart-Porter N. An update on end-tidal CO₂ monitoring. Pediatr Emerg Care 2018; 34 (12) 888-892
• 3 IRMA Maximo carbon-dioxide gas analyzer manual. Anon, 2017. Available at: http://www.spectrummedical.com/uploads/documents/IRMA-ISA-brochure-web.pdf . Accessed June 1, 2017
• 4 Weil MH. . Defining Hemodynamic Instability. In: Pinsky MR, Payen D, eds. Functional Hemodynamic Monitoring, 1st ed. Germany: Springer; 2005:9–17
• 5 Kwon MA. The effect of a pediatric heat and moisture exchanger on dead space in healthy pediatric anesthesia. Korean J Anesthesiol 2012; 62 (05) 418-422
• 6 Ventilation index. Available at: http://www-users.med.cornell.edu/~spon/picu/calc/ventindx.htm . Accessed June16, 2018
• 7 Instrumentation Laboratory Worldwide. (GEM Premier 3000) manual. Anon;2017 Available at: http://kr.werfen.com/~/media/werfenmedicalil/doc/critical%20care/gem%203000.pdf . Accessed June 1, 2017
• 8 Eschweiler automated gas analyzer manual Anon; 2017. Available at: http://www.frankshospitalworkshop.com/equipment/documents/automated_analyzer/user_manuals/Eschweiler%20Combi%20line%20-%20User%20manual.pdf . Accessed June 1, 2017
• 9 Siobal MS, Ong H, Valdes J, Tang J. Calculation of physiologic dead space: comparison of ventilator volumetric capnography to measurements by metabolic analyzer and volumetric CO₂ monitor. Respir Care 2013; 58 (07) 1143-1151
• 10 Yang JT, Erickson SL, Killien EY, Mills B, Lele AV, Vavilala MS. Agreement between arterial carbon dioxide levels with end-tidal carbon dioxide levels and associated factors in children hospitalized with traumatic brain injury. JAMA Netw Open 2019; 2 (08) e199448
• 11 Mehta H, Kashyap R, Trivedi S. Correlation of end tidal and arterial carbon dioxide levels in critically Ill neonates and children. Indian J Crit Care Med 2014; 18 (06) 348-353
• 12 Meredith KS, Monaco FJ. Evaluation of a mainstream capnometer and end-tidal carbon dioxide monitoring in mechanically ventilated infants. Pediatr Pulmonol 1990; 9 (04) 254-259
• 13 McDonald MJ, Montgomery VL, Cerrito PB, Parrish CJ, Boland KA, Sullivan JE. Comparison of end-tidal CO₂ and PaCO₂ in children receiving mechanical ventilation. Pediatr Crit Care Med 2002; 3 (03) 244-249
• 14 Hopper AO, Nystrom GA, Deming DD, Brown WR, Peabody JL. Infrared end-tidal CO₂ measurement does not accurately predict arterial CO₂ values or end-tidal to arterial PCO₂ gradients in rabbits with lung injury. Pediatr Pulmonol 1994; 17 (03) 189-196
• 15 Kugelman A, Zeiger-Aginsky D, Bader D, Shoris I, Riskin A. A novel method of distal end-tidal CO₂ capnography in intubated infants: comparison with arterial CO₂ and with proximal mainstream end-tidal CO₂ . Pediatrics 2008; 122 (06) e1219-e1224
• 16 Goonasekera CD, Goodwin A, Wang Y, Goodman J, Deep A. Arterial and end-tidal carbon dioxide difference in pediatric intensive care. Indian J Crit Care Med 2014; 18 (11) 711-715
• 17 McSwain SD, Hamel DS, Smith PB. , et al. End-tidal and arterial carbon dioxide measurements correlate across all levels of physiologic dead space. Respir Care 2010; 55 (03) 288-293

Publication History

Received: 07 April 2020

Accepted: 07 June 2020

Article published online:
20 August 2020