Department of Surgery, SUNY Upstate Medical University, Syracuse, New York.
Department of Surgery, University of Cincinnati, Cincinnati, Ohio.
Respir Care. 2024 Oct 25;69(11):1432-1443. doi: 10.4187/respcare.11745.
Lung volume measurements are important for monitoring functional aeration and recruitment and may help guide adjustments in ventilator settings. The expiratory phase of airway pressure release ventilation (APRV) may provide physiologic information about lung volume based on the expiratory flow-time slope, angle, and time to approach a no-flow state (expiratory time [T]). We hypothesized that expiratory flow would correlate with estimated lung volume (ELV) as measured using a modified nitrogen washout/washin technique in a large-animal lung injury model.
Eight pigs (35.2 ± 1.0 kg) were mechanically ventilated using an Engström Carescape R860 on the APRV mode. All settings were held constant except the expiratory duration, which was adjusted based on the expiratory flow curve. Abdominal pressure was increased to 15 mm Hg in normal and injured lungs to replicate a combination of pulmonary and extrapulmonary lung injury. ELV was estimated using the Carescape FRC INview tool. The expiratory flow-time slope and T were measured from the expiratory flow profile.
Lung elastance increased with induced lung injury from 29.3 ± 7.3 cm HO/L to 39.9 ± 15.1cm HO/L, and chest wall elastance increased with increasing intra-abdominal pressures (IAPs) from 15.3 ± 4.1 cm HO/L to 25.7 ± 10.0 cm HO/L in the normal lung and 15.8 ± 6.0 cm HO/L to 33.0 ± 6.2 cm HO/L in the injured lung ( = .39). ELV decreased from 1.90 ± 0.83 L in the injured lung to 0.67 ± 0.10 L by increasing IAP to 15 mm Hg. This had a significant correlation with a T decrease from 2.3 ± 0.8 s to 1.0 ± 0.1 s in the injured group with increasing insufflation pressures (ρ = 0.95) and with the expiratory flow-time slope, which increased from 0.29 ± 0.06 L/s to 0.63 ± 0.05 L/s (ρ = 0.78).
Changes in ELV over time, and the T and flow-time slope, could be used to demonstrate evolving lung injury during APRV. Using the slope to infer changes in functional lung volume represents a unique, reproducible, real-time, bedside technique that does not interrupt ventilation and may be used for clinical interpretation.
肺容积测量对于监测功能通气和复张非常重要，并且可能有助于指导呼吸机设置的调整。气道压力释放通气（APRV）的呼气阶段可能会根据呼气流量-时间斜率、角度和接近无流量状态的时间（呼气时间 [T]）提供有关肺容积的生理信息。我们假设在大型动物肺损伤模型中，使用改良氮气冲洗/冲洗技术测量时，呼气流量与估计的肺容积（ELV）相关。
8 头猪（35.2 ± 1.0 kg）在 APRV 模式下使用 Engström Carescape R860 进行机械通气。除了呼气时间外，所有设置均保持不变，呼气时间是根据呼气流量曲线进行调整的。正常和受伤的肺中腹部压力增加到 15mmHg，以复制肺和肺外肺损伤的组合。使用 Carescape FRC INview 工具估计 ELV。从呼气流量曲线中测量呼气流量-时间斜率和 T。
肺弹性随着诱导性肺损伤而增加，从 29.3 ± 7.3 cm HO/L 增加到 39.9 ± 15.1cm HO/L，胸壁弹性随着腹腔内压（IAP）的增加而增加，从正常肺中的 15.3 ± 4.1 cm HO/L 增加到 25.7 ± 10.0 cm HO/L，受伤肺中的 15.8 ± 6.0 cm HO/L 增加到 33.0 ± 6.2 cm HO/L（=0.39）。随着 IAP 增加到 15mmHg，受伤肺中的 ELV 从 1.90 ± 0.83L 下降到 0.67 ± 0.10L。这与受伤组中 T 从 2.3 ± 0.8s 下降到 1.0 ± 0.1s 显著相关，随着充气压力的增加（ρ=0.95），与呼气流量-时间斜率相关，该斜率从 0.29 ± 0.06L/s 增加到 0.63 ± 0.05L/s（ρ=0.78）。
ELV 随时间的变化，以及 T 和流量-时间斜率，可以用于在 APRV 期间证明进行性肺损伤。使用斜率推断功能性肺容积的变化代表一种独特、可重复、实时、床边技术，不会中断通气，并且可用于临床解释。
