BACKGROUND: Adequate airway management plays an important role in high-quality cardiopulmonary resuscitation (CPR). Airway management is usually performed using an endotracheal tube (ETT) during CPR. However, no study has assessed the effect of ETT size on the flow rate and airway pressure during CPR.METHODS: We measured changes in peak inspiratory flow rate (PIFR), peak airway pressure (Ppeak), and mean airway pressure (Pmean) according to changes in ETT size (intal diameter 6.0, 7.0, and 8.0 mm) and with or without CPR. A tidal volume of 500 mL was supplied at a rate of 10 times per minute using a mechanical ventilator. Chest compressions were maintained at a constant compression depth and speed using a mechanical chest compression device (LUCAS2, mode: active continuous, chest compression rate: 102±2/minute, chest compression depth 2–2.5 inches). RESULTS: The median of several respiratory physiological parameters during CPR was significantly different according to the diameter of each ETT (6.0 vs. 8.0 mm): PIFR (32.1 L/min [30.5–35.3] vs. 28.9 L/min [27.5–30.8], P<0.001), Ppeak (48.84 cmH2O [27.46–52.11] vs. 27.45 cmH2O [22.53–52.57], P<0.001), and Pmean (18.34 cmH2O [14.61–21.66] vs.13.66 cmH2O [8.41–19.24], P<0.001). CONCLUSION: The changes in PIFR, Ppeak, and Pmean were related to the intal diameter of ETT, and these values tended to decrease with an increase in ETT size. Higher airway pressures were measured in the CPR group than in the no CPR group.