Agreement Between Arterial Carbon Dioxide Levels With End-Tidal Carbon Dioxide Levels and Associated Factors in Children Hospitalized With Traumatic Brain Injury
Authors: Jen-Ting Yang, Scott L. Erickson, Elizabeth Y. Killien, Brianna Mills, Abhijit V. Lele, Monica S. Vavilala
Journal: JAMA Network Open (2019)

<h3>Importance</h3> Alterations in the partial pressure of carbon dioxide, arterial (Paco<sub>2</sub>) can affect cerebral perfusion after traumatic brain injury. End-tidal carbon dioxide (EtCO<sub>2</sub>) monitoring is a noninvasive tool used to estimate Paco<sub>2</sub>values. <h3>Objective</h3> To examine the agreement between Paco<sub>2</sub>and EtCO<sub>2</sub>and associated factors in children with traumatic brain injury. <h3>Design, Setting, and Participants</h3> A secondary analysis was conducted using data from a prospective cohort study of 137 patients younger than 18 years with traumatic brain injury who were admitted to the pediatric intensive care unit of a level I trauma center between May 1, 2011, and July 31, 2017. Analysis was performed from December 17, 2018, to January 10, 2019. <h3>Main Outcomes and Measures</h3> The closest EtCO<sub>2</sub>value obtained within 30 minutes of a Paco<sub>2</sub>value and the closest systolic blood pressure value obtained within 60 minutes prior to a Paco<sub>2</sub>value during the first 24 hours after admission were recorded. The main outcome of Paco<sub>2</sub>-EtCO<sub>2</sub>agreement was defined as Paco<sub>2</sub>between 0 and 5 mm Hg greater than the paired EtCO<sub>2</sub>value, and it was determined using Bland-Altman analysis, Passing and Bablok regression, and the Pearson correlation coefficient. Multivariable regression models determined which factors were associated with agreement. <h3>Results</h3> The analysis included 137 patients (34 girls and 103 boys; mean [SD] age, 10.0 [6.3] years) and 445 paired Paco<sub>2</sub>-EtCO<sub>2</sub>data points. On average, Paco<sub>2</sub>was 2.7 mm Hg (95% limits of agreement, –11.3 to 16.7) higher than EtCO<sub>2</sub>. Overall, 187 of all Paco<sub>2</sub>-EtCO<sub>2</sub>pairs (42.0%) agreed. There was larger variation in the Paco<sub>2</sub>-EtCO<sub>2</sub>difference during the first 8 hours compared with 9 to 24 hours after admission to the pediatric intensive care unit. Development of pediatric acute respiratory distress syndrome within 24 hours of admission was associated with a lower likelihood of Paco<sub>2</sub>-EtCO<sub>2</sub>agreement (adjusted odds ratio, 0.20; 95% CI, 0.08-0.51) compared with no development of pediatric acute respiratory distress syndrome. A diagnosis of pediatric acute respiratory distress syndrome 1 to 7 days after admission was associated with a larger first-day Paco<sub>2</sub>-EtCO<sub>2</sub>difference compared with those who never developed pediatric acute respiratory distress syndrome (mean [SD] difference, 4.48 [3.70] vs 0.46 [5.50] mm Hg). <h3>Conclusions and Relevance</h3> In this study of pediatric traumatic brain injury, Paco<sub>2</sub>-EtCO<sub>2</sub>agreement was low, especially among patients with pediatric acute respiratory distress syndrome. Low Paco<sub>2</sub>-EtCO<sub>2</sub>agreement early in hospitalization may be associated with future development of pediatric acute respiratory distress syndrome. Data on EtCO<sub>2</sub>should not be substituted for data on Paco<sub>2</sub>during the first 24 hours.