Relationship Between End-Tidal and Arterial Carbon Dioxide with Laryngeal Mask Airways and Endotracheal Tubes in Children

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Abstract
The laryngeal mask airway (LMA) is a useful tool for securing the airway in adults and children and may be substituted for an endotracheal tube (ETT) in selected patients undergoing general anesthesia. The correlation between end-tidal and arterial carbon dioxide during controlled ventilation via LMA has not been reported in a within-patient design in pediatric patients. After induction of general anesthesia, 22 children had a LMA placed and mechanical ventilation initiated. After reaching steady-state end-tidal carbon dioxide (PETCO2), an arterial blood sample was obtained and the partial pressure of carbon dioxide (PaCO2) was measured. The LMA was then removed, the trachea was intubated, and identical ventilatory variables were resumed. After a stable PETCO2 was reestablished (minimum 5 min), a second PaCO2 was measured and the PETCO2 recorded. The mean PETCO2 and PaCO2 obtained during ventilation via the LMA were 37.7 +/- 3.31 and 41.9 +/- 9.09, respectively. The mean PETCO2 and PaCO2 obtained during ventilation via the ETT were 35.2 +/- 2.86 and 39.2 +/- 5.25, respectively. Analysis of differences between PaCO2 and PETCO2 revealed a bias +/- precision of 4.0 +/- 3.42 and 4.2 +/- 3.66 with ventilation via ETT and LMA, respectively. The root mean square error was 0.85 for the ETT and 0.89 for the LMA. Our results indicate that in infants and children weighing more than 10 kg who are mechanically ventilated via the LMA PETCO2 is as accurate an indicator of PaCO2 as when ventilated via ETT.