Inspiratory time and pulmonary function in mechanically ventilated babies with chronic lung disease

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Abstract
To learn if increasing inspiratory time would improve pulmonary function in mechanically ventilated babies with chronic lung disease, we measured lung mechanics and alveolar ventilation at three inspiratory times: 0.4, 0.6, and 0.8 s. Nine babies were studied. Their mean birth weight was 875 g (range, 570–1,100 g), gestational age 27 (24–34) weeks, and age 7 (4–12) weeks. Their mean oxygen requirement was 40% (29–53), ventilator rate 33/min (20–40), and mean airway pressure 8 (5–10) cmH2O. Ventilator rate was kept constant; therefore expiratory time decreased and mean airway pressure and I:E ratio increased at longer inspiratory times. At 0.6 s and 0.8 s, when compared to 0.4 s, significant increases occurred in tidal volume (10.4, 10.1, and 8.4 mL/kg, respectively), dynamic lung compliance (0.68, 0.68, and 0.53 mL/cmH2O/kg, respectively), and alveolar ventilation (6.0, 6.3, and 4.7 mL/kg/breath, respectively). Airway resistance, anatomical dead space to tidal volume ratio, and functional residual capacity were similar at the three inspiratory times. Our findings suggest that an inspiratory time ⩾0.6 s (compared to 0.4 s) increases the effectiveness of mechanical ventilation for babies with chronic lung disease.