Effects of decreased respiratory frequency on ventilator-induced lung injury

To determine if decreased respiratory frequency (ventilatory rate) improves indices of lung damage, 17 sets of isolated, perfused rabbit lungs were ve ntilated with a peak static airway pressure of 30 cm H2O. All lungs were ra ndomized to one of three frequency/peak pulmonary artery pressure combinati ons: F20P35 (n = 6): ventilatory frequency, 20 breaths/min, and peak pulmon ary artery pressure, 35 mm Hg; F3P35 (n = 6), ventilatory frequency, 3 brea ths/min, and peak pulmonary artery pressure of 35 mm Hg; or F20P20 (n = 5), ventilatory frequency, 20 breaths/min, and peak pulmonary artery pressure, 20 mm Hg. Mean airway pressure and tidal volume were matched between group s. Mean pulmonary artery pressure and vascular flow were matched between gr oups F20P35 and F3P35. The F20P35 group showed at least a 4.5-fold greater mean weight gain and a 3-fold greater mean incidence of perivascular hemorr hage than did the comparison groups, all p less than or equal to 0.05. F20P 35 lungs also displayed more alveolar hemorrhage than did F20P20 lungs (p l ess than or equal to 0.05). We conclude that decreasing respiratory frequen cy can improve these indices of lung damage, and that limitation of peak pu lmonary artery pressure and flow may diminish lung damage for a given venti latory pattern.