A comparison of the breathing apparatus deadspace associated with a supraglottic airway and endotracheal tube using volumetric capnography in young children.

Background: Supraglottic airway devices including the air-Q® are being used with increasing frequency for elective anesthetics in infants and younger pediatric patients. To date, there is minimal research documenting the potentially significant airway dead space these devices may contribute to the ventilation circuit when compared to an endotracheal tube (ETT).

Methods: In a prospective cohort study, 59 pediatric patients between the ages of 3 months and 6 years, weighing between 5 and 20 kg, and scheduled for outpatient urologic or general surgery procedures were recruited. An air-Q® or ETT was inserted at the discretion of the attending anesthesiologist, and tidal volume, respiratory rate, and end-tidal CO2 were controlled according to protocol. Ventilatory parameters including airway dead space were recorded or calculated using volumetric capnography every two minutes for 10 minutes.

Results: Groups were similar in demographics. There was a significant difference in weight-adjusted dead space volume between the air-Q® and ETT groups, 4.1 ± 0.8 mL/kg versus 3.0 ± 0.7 mL/kg, respectively (p<0.0001). Weight-adjusted dead space volume (in mL/kg) increased significantly with decreasing weight for both the air-Q® and ETT groups.

Conclusion: In healthy children undergoing positive pressure ventilation for elective surgery, the air-Q® supraglottic airway introduces significantly greater airway dead space than an endotracheal tube. Additionally, airway dead space, and minute ventilation required to maintain normocarbia, appear to increase with decreasing patient weight irrespective of whether a supraglottic airway or endotracheal tube is used.