Natalini Giuseppe, Tuzzo Daniele, Rosano Antonio, Testa Marco, Grazioli Michele, Pennestrì Vincenzo, Amodeo Guido, Berruto Francesco, Fiorillo Marialinda, Peratoner Alberto, Tinnirello Andrea, Filippini Matteo, Marsilia Paolo F, Minelli Cosetta, Bernardini Achille
Department of Anesthesia and Intensive Care, Fondazione Poliambulanza Hospital, Brescia, Italy.
Department of Anesthesia and Intensive Care, Spedali Civili Hospital, Brescia, Italy.
Ann Intensive Care. 2016 Dec;6(1):53. doi: 10.1186/s13613-016-0158-0. Epub 2016 Jun 16.
In some patients with auto-positive end-expiratory pressure (auto-PEEP), application of PEEP lower than auto-PEEP maintains a constant total PEEP, therefore reducing the inspiratory threshold load without detrimental cardiovascular or respiratory effects. We refer to these patients as "complete PEEP-absorbers." Conversely, adverse effects of PEEP application could occur in patients with auto-PEEP when the total PEEP rises as a consequence. From a pathophysiological perspective, all subjects with flow limitation are expected to be "complete PEEP-absorbers," whereas PEEP should increase total PEEP in all other patients. This study aimed to empirically assess the extent to which flow limitation alone explains a "complete PEEP-absorber" behavior (i.e., absence of further hyperinflation with PEEP), and to identify other factors associated with it.
One hundred patients with auto-PEEP of at least 5 cmH2O at zero end-expiratory pressure (ZEEP) during controlled mechanical ventilation were enrolled. Total PEEP (i.e., end-expiratory plateau pressure) was measured both at ZEEP and after applied PEEP equal to 80 % of auto-PEEP measured at ZEEP. All measurements were repeated three times, and the average value was used for analysis.
Forty-seven percent of the patients suffered from chronic pulmonary disease and 52 % from acute pulmonary disease; 61 % showed flow limitation at ZEEP, assessed by manual compression of the abdomen. The mean total PEEP was 7 ± 2 cmH2O at ZEEP and 9 ± 2 cmH2O after the application of PEEP (p < 0.001). Thirty-three percent of the patients were "complete PEEP-absorbers." Multiple logistic regression was used to predict the behavior of "complete PEEP-absorber." The best model included a respiratory rate lower than 20 breaths/min and the presence of flow limitation. The predictive ability of the model was excellent, with an overoptimism-corrected area under the receiver operating characteristics curve of 0.89 (95 % CI 0.80-0.97).
Expiratory flow limitation was associated with both high and complete "PEEP-absorber" behavior, but setting a relatively high respiratory rate on the ventilator can prevent from observing complete "PEEP-absorption." Therefore, the effect of PEEP application in patients with auto-PEEP can be accurately predicted at the bedside by measuring the respiratory rate and observing the flow-volume loop during manual compression of the abdomen.
在一些存在内源性呼气末正压（auto-PEEP）的患者中，应用低于auto-PEEP的呼气末正压（PEEP）可维持恒定的总PEEP，从而降低吸气阈值负荷，且无有害的心血管或呼吸效应。我们将这些患者称为“完全PEEP吸收者”。相反，当总PEEP因此升高时，在存在auto-PEEP的患者中应用PEEP可能会产生不良反应。从病理生理学角度来看，所有存在气流受限的受试者预计都是“完全PEEP吸收者”，而在所有其他患者中PEEP应会增加总PEEP。本研究旨在实证评估仅气流受限能在多大程度上解释“完全PEEP吸收者”行为（即应用PEEP后无进一步的肺过度充气），并识别与之相关的其他因素。
纳入100例在控制机械通气期间呼气末压力为零时auto-PEEP至少为5 cmH₂O的患者。在呼气末压力为零时（ZEEP）以及应用等于在ZEEP时测得的auto-PEEP的80%的PEEP后，均测量总PEEP（即呼气末平台压）。所有测量均重复三次，并使用平均值进行分析。
47%的患者患有慢性肺部疾病，52%患有急性肺部疾病；通过手动按压腹部评估，61%的患者在ZEEP时存在气流受限。在ZEEP时平均总PEEP为7±2 cmH₂O，应用PEEP后为9±2 cmH₂O（p<0.001）。33%的患者为“完全PEEP吸收者”。采用多因素逻辑回归来预测“完全PEEP吸收者”的行为。最佳模型包括呼吸频率低于20次/分钟以及存在气流受限。该模型的预测能力极佳，在经乐观偏差校正后的受试者工作特征曲线下面积为0.89（95%CI 0.80 - 0.97）。
呼气气流受限与高度和完全的“PEEP吸收者”行为均相关，但在呼吸机上设置相对较高的呼吸频率可防止观察到完全的“PEEP吸收”。因此，通过测量呼吸频率并在手动按压腹部时观察流量 - 容积环，可在床边准确预测auto-PEEP患者应用PEEP的效果。
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