Critical Care Department, University Hospital of Wales, Heath Park, Cardiff, CF14 4XW, UK.
University College London, Gower Street, London, WC1E 6BT, UK.
Crit Care. 2022 Dec 21;26(1):396. doi: 10.1186/s13054-022-04282-9.
The relationship between indices of mechanical ventilation and pulmonary artery pressures remains ill-defined in ARDS. As our understanding of mechanical ventilation has progressed, there is now a greater appreciation of the impact of high driving pressures and mechanical power in perpetuating lung injury. However, the relationship between the newer derived indices of mechanical ventilation and pulmonary artery pressure is unclear. We performed a post hoc analysis of the Fluid and Catheters Treatment Trial (FACTT) trial to investigate the associations between mechanical ventilation indices in ARDS patients and the prevalence of pulmonary hypertension. This may help elucidate future clinical targets for more, right ventricular protective, mechanical ventilation strategies.
We performed a post hoc analysis of the FACTT database to identify ARDS patients who had a pulmonary artery catheter (PAC) inserted and pulmonary artery pressure readings recorded. We excluded any patient with a PAC inserted who was spontaneously breathing, as driving pressure and mechanical power are not validated in this cohort. Three independent analyses were performed: a univariate analysis, to assess for associations between mPAP and mechanical ventilation parameters using Pearson correlation coefficients, a multivariate analysis, to assess for independent associations with mPAP using a multiple regression model according to Akaike's information criteria and finally an analysis for nonlinearity, using the best-fitting model according to the Bayesian information criterion (BIC) from linear, quadratic, fractional polynomial and restricted cubic spline models.
All the ventilation parameters demonstrated a significant correlation with mPAP, except tidal volume (once adjusted for respiratory rate) in the univariate analysis. The multivariate analysis demonstrated that the blood pH level, P/F ratio, PaCO level, mean airway pressure and the mechanical power indexed to compliance were independently associated with mPAP. In the final nonlinear analysis, associations did not differ from linearity except for 4 variables for which the fractional polynomial was the best-fitting model. These were mechanical power (p = 0.01 compared to the linear model), respiratory rate (p = 0.04), peak pressure (p = 0.03) and mean airway pressure (p = 0.01). Two nonlinear variables associated with mPAP were assessed in more detail, respiratory rate and mechanical power. Inflexion points at a respiratory rate of 16.8 cycles per minute and a mechanical power of 8.8 J/min were demonstrated.
The associations identified between mPAP and mechanical ventilation variables in this analysis would suggest that classical ARDS lung protective strategies, including low tidal volume ventilation and permissive hypercapnia, may negatively impact the management of the subset of ARDS patients with associated right ventricular dysfunction or ACP. Additionally, respiratory rates above 17 cycles per minute show an incremental increase in mPAP. Therefore, increases in tidal volume (within the limitation of driving pressure < 18 cmH20) may represent a more right ventricular protective way to control CO2 and pH.
ARDS 中机械通气指数与肺动脉压之间的关系仍未明确。随着我们对机械通气理解的深入，现在越来越认识到高驱动压和机械功率对肺损伤的持续影响。然而，新型机械通气衍生指数与肺动脉压之间的关系尚不清楚。我们对 Fluid and Catheters Treatment Trial（FACTT）试验进行了事后分析，以研究 ARDS 患者的机械通气指数与肺动脉高压患病率之间的关系。这可能有助于阐明未来更有利于右心室保护的机械通气策略的临床目标。
我们对 FACTT 数据库进行了事后分析，以确定插入肺动脉导管（PAC）并记录肺动脉压读数的 ARDS 患者。我们排除了任何自主呼吸的 PAC 插入患者，因为在该队列中未验证驱动压和机械功率。进行了三项独立分析：单变量分析，使用 Pearson 相关系数评估 mPAP 与机械通气参数之间的关联；多变量分析，根据赤池信息量准则（Akaike's information criteria）使用多元回归模型评估与 mPAP 的独立关联；最后根据线性、二次、分数多项式和限制立方样条模型的贝叶斯信息准则（Bayesian information criterion，BIC）进行非线性分析，选择最佳拟合模型。
所有通气参数与 mPAP 均呈显著相关性，除单变量分析中潮气量（调整呼吸频率后）外。多变量分析表明，血液 pH 值、P/F 比、PaCO 水平、平均气道压和顺应性指数的机械功率与 mPAP 独立相关。在最终的非线性分析中，除了 4 个变量（分数多项式是最佳拟合模型）外，与线性关系没有差异。这些变量是机械功率（与线性模型相比，p=0.01）、呼吸频率（p=0.04）、峰压（p=0.03）和平均气道压（p=0.01）。与 mPAP 相关的两个非线性变量进行了更详细的评估，即呼吸频率和机械功率。在 16.8 次/分钟的呼吸频率和 8.8 J/min 的机械功率处显示出拐点。
本分析中 mPAP 与机械通气变量之间的关联表明，包括低潮气量通气和允许性高碳酸血症在内的经典 ARDS 肺保护性策略可能会对伴有右心室功能障碍或 ACP 的 ARDS 患者亚组的管理产生负面影响。此外，呼吸频率超过 17 次/分钟会导致 mPAP 呈递增性增加。因此，在不超过 18 cmH20 的驱动压限制内增加潮气量可能代表一种更有利于右心室保护的控制 CO2 和 pH 的方式。
