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

BACKGROUND: Supraglottic airway (SGA) devices including the air-Q(®) are being used with increasing frequency for anesthesia in infants and younger pediatric patients. To date, there is minimal research documenting the potentially significant airway deadspace these devices may contribute to the ventilation circuit when compared to an endotracheal tube (ETT). The aim of this study was to evaluate the airway apparatus deadspace associated with an air-Q(®) versus an ETT in young children. METHODS: In a prospective cohort study, 59 patients between 3 months and 6 years of age, weighing between 5 and 20 kg, 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, positive end expiratory pressure, respiratory rate, and end-tidal CO(2) were controlled according to protocol. Airway deadspace was recorded using volumetric capnography every 2 min for 10 min. RESULTS: Groups were similar in demographics. There was a significant difference in weight-adjusted deadspace volume between the air-Q(®) and ETT groups, 4.1 ± 0.8 ml/kg versus 3.0 ± 0.7 ml/kg, respectively (P < 0.001). Weight-adjusted deadspace volume (ml/kg) increased significantly with decreasing weight for both the air-Q(®) and ETT groups. CONCLUSIONS: In healthy children undergoing positive pressure ventilation for elective surgery, the air-Q(®) SGA introduces significantly greater airway deadspace than an ETT. Additionally, airway deadspace, and minute ventilation required to maintain normocarbia, appear to increase with decreasing patient weight irrespective of whether a SGA or ETT is used.