BACKGROUND: In volume-controlled ventilation, the use of inspiratory pause increases the inspiratory time and thus increases mean airway pressure and improves ventilation But under the same I : E ratio, the effects of in spiratory pause on mean airway pressure and gas exchange are not certain. Moreover, the effects may be different according to the resistance of respiratory system. So we studied the effects of inspiratory pause on airway pressure and gas exchange under the same I : E ratio in volume-controlled ventilation. METHODS: Airway pressure and arterial blood gases were evaluated in 12 patients under volume-controlled mechanical ventilation with and without inspiratory pause time 5%. The I : E ratio of 1 : 3, FiO2, tidal volume, respiratory rate, and PEEP were kept constant. RESULTS: PaCO2 with inspiratory pause was lower than without inspiratory pause (38.6 +/- 7.4 mmHg vs.41.0 +/- 7.7 mmHg. p < 0.01). p(A-a)O2 was not different between ventilation with and without inspiratory pause (185.3 +/- 86.5mm Hg vs. 184.9 +/- 84.9mmHg vs. p=0.766). Mean airway pressure with inspiratory pause was higher than without inspiratory pause (9.7 +/- 4.0 cmH2O vs. 8.8 +/- 4.0 cm H2O, p < 0.01). The resistance of respiratory system inversely correlated with the pressure difference between plateau pressure with pause and peak inspiratory pressure without pause (r=-0.777, p < 0.01), but positively correlated with the pressure difference between peak inspiratory pressure with pause and peak inspiratory pressure without pause (r=0.811, p < 0.01). Thus the amount of increase in mean airway pressure with pause positively correlated with the resistance of respiratory system (r=0.681, p < 0.05). However, the change of mean airway pressure did not correlated with the change of PaCO2. CONCLUSION: In volume-controlled ventilation under the same I : E ratio of 1 : 3, inspiratory pause time of 5% increases mean airway pressure and improves ventilation. Although the higher resistance of respiratory system, the more Increased mean airway pressure, tile increase in mean airway pressure did not correlated with the change in PaCO2.