End-tidal PCO₂ monitoring via nasal cannulae in pediatric patients: Accuracy and sources of error

Abstract

Objective. To assess the correlation and accuracy of end-tidal PCO₂ (PetCO₂) sampled via nasal cannulae in pediatric patients by comparison to the criterion standard PaCO₂, and to identify sources of error during PetCO₂ monitoring via nasal cannulae.Methods. PetCO₂ was monitored continuously by sampling end-tidal gas through nasal cannulae that had been designed and manufactured for this purpose in spontaneously breathing children undergoing conscious or deep sedation during either cardiac catheterization (n = 43) or critical care (n = 54). When both the capnographic wave form and the PetCO₂ value had been stable for at least 10 minutes, the PetCO₂ value was recorded while blood was drawn from an indwelling arterial line for PaCO₂ measurement. The effects of age, weight, respiratory rate, oxygen delivery system, airway obstruction, mouth breathing, and cyanotic heart disease were evaluated by linear regression analysis and calculation of absolute bias (PaCO₂-PetCO₂).Results. Mouth breathing, airway obstruction, oxygen delivery through the ipsilateral nasal cannula, and cyanotic heart disease adversely affected accuracy. In patients without those factors, PetCO₂ correlated well with PaCO₂ (R² = 0.994), and absolute bias was 3.0 ± 1.8 mmHg.Conclusions. Several factors — some controllable and all recognizable — affect the accuracy of PetCO₂ monitored via nasal cannulae in pediatric patients. When these factors are not present, PetCO₂ correlates well with PaCO₂ and appears to be a useful monitor of ventilatory status during conscious or deep sedation.