Comparison of arterial CO2 estimation by end-tidal and transcutaneous CO2 measurements in intubated children and variability with subject related factors

Accuracy and Interpretation of Transcutaneous Carbon Dioxide Monitoring in Critically Ill Children

OBJECTIVES

Transcutaneous carbon dioxide (Tc co2 ) monitoring can noninvasively assess ventilation by estimating carbon dioxide ( CO2 ) levels in the blood. We aimed to evaluate the accuracy of Tc co2 monitoring in critically ill children by comparing it to the partial pressure of arterial carbon dioxide (Pa co2 ). In addition, we sought to determine the variation between Tc co2 and Pa co2 acceptable to clinicians to modify patient care and to determine which patient-level factors may affect the accuracy of Tc co2 measurements.

DESIGN

Retrospective observational cohort study.

SETTING

Single, quaternary care PICU from July 1, 2012, to August 1, 2020.

PATIENTS

Included participants were admitted to the PICU and received noninvasive ventilation support (i.e., continuous or bilevel positive airway pressure), conventional mechanical ventilation, or high-frequency oscillatory or percussive ventilation with Tc co2 measurements obtained within 15 minutes of Pa co2 measurement.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Three thousand four hundred seven paired arterial blood gas and Tc co2 measurements were obtained from 264 patients. Bland-Altman analysis revealed a bias of -4.4 mm Hg (95% CI, -27 to 18.3 mm Hg) for Tc co2 levels against Pa co2 levels on the first measurement pair for each patient, which fell within the acceptable range of ±5 mm Hg stated by surveyed clinicians, albeit with wide limits of agreement. The sensitivity and specificity of Tc co2 to diagnose hypercarbia were 93% and 71%, respectively. Vasoactive-Infusion Score (VIS), age, and self-identified Black/African American race confounded the relationship between Tc co2 with Pa co2 but percent fluid overload, weight-for-age, probe location, and severity of illness were not significantly associated with Tc co2 accuracy.

CONCLUSIONS

Tc co2 monitoring may be a useful adjunct to monitor ventilation in children with respiratory failure, but providers must be aware of the limitations to its accuracy.

Alveolar target ventilation and dead space in children under anaesthesia: The proventiped cohort study

INTRODUCTION

Ventilator settings in children under anaesthesia remain difficult because of the changes in the physiology and the high dead space.

OBJECTIVE

To determine the alveolar minute-volume to sustain normocapnia in children under mechanical ventilation.

DESIGN

A prospective observational study.

SETTINGS

This study was performed between May and October 2019 in a tertiary care children's hospital.

PATIENTS

Children between 2 months and 12 years, weighing between 5 and 40 kg, admitted for general anaesthesia.

INTERVENTION

Volumetric capnography was used to estimate the alveolar and dead space volume (Vd).

MAIN OUTCOME MEASURES

Total and alveolar minute ventilation in (ml kg -1  min -1 ) over 100 breaths.

RESULTS

Sixty patients were included comprising 20 per group: 5 to 10 kg (group 1), 10 to 20 kg (group 2), 20 to 40 kg (group 3). Seven patients were excluded for aberrant capnographic curves. After normalisation to weight, the median [IQR] tidal volume per kilogram was similar between the three groups: 6.5 ml kg -1 [6.0 to 7.5 ml kg -1 ], 6.4  ml kg -1 [5.7 to 7.3  ml kg -1 ], 6.4  ml kg -1 [5.3 to 6.8  ml kg -1 ]; P  = 0.3. Total Vd (in ml kg -1 ) was negatively correlated to weight ( r  = -0.62, 95% confidence interval -0.41 to -0.76, P  < 0.001). The total normalised minute ventilation (ml kg -1  min -1 ) to obtain normocapnia was higher in group 1 than in group 2 and in group 3; 203  ml kg -1  min -1 [175 to 219 ml kg -1  min -1 ], 150  ml kg -1  min -1 [139 to 181  ml kg -1  min -1 ] and 128  ml kg -1  min -1 [107 to 157  ml kg -1  min -1 ]; P  < 0.001 (mean ± SD), but (mean ± SD) alveolar minute ventilation was similar between the three groups; 68 ± 21  ml kg -1  min -1 .

CONCLUSION

Total dead space volume (including apparatus dead space) represents a major component of tidal volume in children less than 30 kg, when using large heat and moisture exchanger filters. The total minute ventilation necessary to achieve normocapnia decreased with increasing weight, while the alveolar minute ventilation remained constant.

TRIAL REGISTRATION

ClinicalTrials.gov, identifier: NCT03901599.

Efficacy of high-flow nasal oxygenation compared with laryngeal mask airway in children undergoing ambulatory oral surgery under deep sedation: A randomized controlled non-inferiority trial

BACKGROUND

High-flow nasal oxygenation (HFNO) has been suggested as an alternative oxygenation method during procedural sedation. This randomized, non-inferiority trial evaluated the safety and efficacy of HFNO compared with laryngeal mask airway (LMA) in pediatric ambulatory oral surgery under deep sedation.

METHODS

In total, 120 children aged 2-7 years (weight: 10-30 kg) were equally assigned into two groups, namely, HFNO with propofol total intravenous anesthesia infusion (HFNO-IV) or LMA with propofol total intravenous anesthesia infusion (LMA-IV). The primary objective was to monitor carbon dioxide (CO2) accumulation during perioperative surgery. Secondary objectives included monitoring transcutaneous oxygen saturation, grade exposure to the surgical field, perioperative adverse events, or other events. The predefined non-inferiority margin was 7 mmHg. During the COVID-19 pandemic, a novel WeChat applet was implemented to gather follow-up data after discharge.

RESULTS

Non-inferiority could be declared for HFNO relative to LMA (mean difference in transcutaneous CO2 (TcCO2) = -1.4 mmHg, 95% CI: -2.9, 0.1 mmHg; P > 0.05). The pre-surgical TcCO2 of the HFNO-IV group (45.4 ± 4.5 mmHg) was similar to that of the LMA-IV group (44.0 ± 3.5 mmHg), within the clinically acceptable normal range. All the children maintained SpO2 levels of >97%. The surgical field exposure score of the HFNO group was significantly better than that of the LMA group. There was no significant difference between the two groups regarding risk or adverse events.

CONCLUSION

HFNO was not inferior to LMA for maintaining oxygenation and ventilation in patients undergoing pediatric ambulatory oral surgery under deep sedation under strict isolation from the oral cavity to the upper airway.

Transient End-Tidal Carbon Dioxide Elevation During Pediatric Upper Endoscopy With Carbon Dioxide Insufflation: Is It True Hypercapnia?

BACKGROUND

Endoscopic insufflation, long performed using air, is being replaced by carbon dioxide (CO2) at many pediatric centers, despite limited published data on its use in children. We have previously demonstrated that CO2 use during esophagogastroduodenoscopy (EGD) in non-intubated children is associated with transient elevations of end-tidal CO2 (EtCO2). This observation raised concerns about possible CO2 inhalation and systemic absorption. Here, we investigate this concern by concurrently measuring both EtCO2 and transcutaneous CO2 (tCO2) during upper endoscopic procedures in children.

AIM

To determine if elevations in EtCO2 levels seen in non-intubated children undergoing CO2 insufflation during EGD are associated with elevated systemic CO2 levels.

METHODS

Double-blinded, prospective, randomized clinical trial. Children were randomized 1:1 to receive either CO2 or air for endoscopic insufflation. EtCO2 was sampled with a CO2-sampling nasal cannula and tCO2 was monitored using the Radiometer transcutaneous monitoring device.

RESULTS

Fifty nine patients were enrolled; 30 patients in the CO2 insufflation group and 29 in the air group. All patients underwent a procedure involving an EGD. Transient elevations in EtCO2 (defined as >60 mmHg) were observed only in the CO2 insufflation group. This contrasted with the similar elevations of tCO2 between the CO2 and air insufflation groups. None of these events were of clinically significant magnitude or duration.

CONCLUSION

This study demonstrates that the observed transient elevations in EtCO2 seen during EGD in non-intubated children receiving CO2 insufflation are most likely measurements of eructated CO2 without evidence of excessive systemic absorption of CO2.

End-Tidal Carbon Dioxide Pressure Measurement after Prolonged Inspiratory Time Gives a Good Estimation of the Arterial Carbon Dioxide Pressure in Mechanically Ventilated Patients

Background: End-tidal carbon dioxide pressure (PetCO₂) is unreliable for monitoring PaCO₂ in several conditions because of the unpredictable value of the PaCO₂–PetCO₂ gradient. We hypothesised that increasing both the end-inspiratory pause and the expiratory time would reduce this gradient in patients ventilated for COVID-19 with Acute Respiratory Distress Syndrome and in patients anaesthetised for surgery. Methods: On the occasion of an arterial blood gas sample, an extension in inspiratory pause was carried out either by recruitment manoeuvre or by extending the end-inspiratory pause to 10 s. The end-expired PCO₂ was measured (expiratory time: 4 s) after this manoeuvre (PACO₂) in comparison with the PetCO₂ measured by the monitor. We analysed 67 Δ(a-et)CO₂, Δ(a-A)CO₂ pairs for 7 patients in the COVID group and for 27 patients in the anaesthesia group. Results are expressed as mean ± standard deviation. Results: Prolongation of the inspiratory pause significantly reduced PaCO₂–PetCO₂ gradients from 11 ± 5.7 and 5.7 ± 3.4 mm Hg (p < 0.001) to PaCO₂–PACO₂ gradients of −1.2 ± 3.3 (p = 0.043) and −1.9 ± 3.3 mm Hg (p < 0.003) in the COVID and anaesthesia groups, respectively. In the COVID group, PACO₂ showed the lowest dispersion (−7 to +6 mm Hg) and better correlation with PaCO₂ (R² = 0.92). The PACO₂ had a sensitivity of 0.81 and a specificity of 0.93 for identifying hypercapnic patients (PaCO₂ > 50 mm Hg). Conclusions: Measuring end-tidal PCO₂ after prolonged inspiratory time reduced the PaCO₂–PetCO₂ gradient to the point of obtaining values close to PaCO₂. This measure identified hypercapnic patients in both intensive care and during anaesthesia.