Objectives: To determine whether respiratory system mechanics measurements could detect lung injury in oxygen toxic rabbits before clinical deterioration. To determine whether respiratory system mechanics measurements, casing a power analysis, leave the statistical power to detect significant reductions in hyperoxic lung injury due to an intervention when compared with traditional post mortem measurements of lung injury, extravascular lung water, and bronchoalveolar lavage protein concentration. Design: Prospective, con trolled study, Setting: Institutional animal laboratories. Subjects: Adult New Zealand white rabbits. Interventions: Spontaneously breathing adult New Zealand white rabbits were exposed continuously to either >95% oxygen or room air. Measurements and Main Results: We measured arterial pH, blood gas tensions, and respiratory system mechanics in rabbits twice, both before exposure to >95% oxygen, and after the rabbits developed symptoms of mild lung dysfunction. After the second set of respiratory system mechanics measurements, we measured extravascular lung water and bronchoalveolar lavage protein concentration in the hyperoxia-exposed rabbits and compared the values with those values obtained in animals that breathed room air only. Our hyperoxia-exposed rabbits developed symptoms of mild respiratory impairment at 69 +/- 2 hrs. In these hyperoxia-exposed rabbits, measurements of static compliance, quasi-static compliance and resistance all changed significantly (p < .05) when compared with baseline measurements, Functional residual capacity and arterial blood gas values did not change significantly. Furthermore, assuming that an intervention reduced hyperoxic lung injury by a given amount, we performed a power analysis and found that the measurement of static compliance had at least equivalent power to detect a reduction in lung injury from an intervention when compared with measurement of extravascular lung water and bronchoalveolar lavage protein concentration. Conclusions: Measurements of respiratory system mechanics can detect lung injury in hyperoxic rabbits before the onset of severe clinical deterioration or death. Furthermore, measurement of static compliance of the respiratory system is likely to be a powerful tool to detect a reduction in lung injury produced by an intervention.
