Capnodynamic end-expiratory lung volume assessment in anesthetized healthy children

Abstract

Background: Capnodynamic lung function monitoring generates variables that may be useful for pediatric perioperative ventilation.

Aims: Establish normal values for end-expiratory lung volume CO₂ in healthy children undergoing anesthesia and to compare these values to previously published values obtained with alternative end-expiratory lung volume methods. The secondary aim was to investigate the ability of end-expiratory lung volume CO₂ to react to positive end-expiratory pressure-induced changes in end-expiratory lung volume. In addition, normal values for associated volumetric capnography lung function variables were examined.

Methods: Fifteen pediatric patients with healthy lungs (median age 8 months, range 1-36 months) undergoing general anesthesia were examined before start of surgery. Tested variables were recorded at baseline positive end-expiratory pressure 3 cmH₂ O, 1 and 3 min after positive end-expiratory pressure 10 cmH₂ O and 3 min after returning to baseline positive end-expiratory pressure 3 cmH₂ O.

Results: Baseline end-expiratory lung volume CO₂ was 32 mL kg^-1 (95% CI 29-34 mL kg^-1 ) which increased to 39 mL kg^-1 (95% CI 35-43 mL kg^-1 , p < .0001) and 37 mL kg^-1 (95% CI 34-41 mL kg^-1 , p = .0003) 1 and 3 min after positive end-expiratory pressure 10 cmH₂ O, respectively. End-expiratory lung volume CO₂ returned to baseline, 33 mL kg^-1 (95% CI 29-37 mL kg^-1 , p = .72) 3 min after re-establishing positive end-expiratory pressure 3 cmH₂ O. Airway dead space increased from 1.1 mL kg^-1 (95% CI 0.9-1.4 mL kg^-1 ) to 1.4 (95% CI 1.1-1.8 mL kg^-1 , p = .003) and 1.5 (95% CI 1.1-1.8 mL kg^-1 , p < .0001) 1 and 3 min after positive end-expiratory pressure 10 cmH₂ O, respectively, and 1.2 mL kg^-1 (95% CI 0.9-1.4 mL kg^-1 , p = .08) after 3 min of positive end-expiratory pressure 3 cmH₂ O. Additional volumetric capnography and lung function variables showed no major changes in response to positive end-expiratory pressure variations.

Conclusions: Capnodynamic noninvasive and continuous end-expiratory lung volume CO₂ values assessed during anesthesia in children were in close agreement with previously reported end-expiratory lung volume values generated by alternative methods. Furthermore, positive end-expiratory pressure changes resulted in physiologically expected end-expiratory lung volume CO₂ responses in a timely manner, suggesting that it can be used to trend end-expiratory lung volume changes during anesthesia.

Keywords: airway dead space; carbon dioxide; end-expiratory lung volume; pediatrics; volumetric Capnography.