Aim:

Characterise how changes in chest compression depth and rate affect variations in end-tidal CO₂ (ETCO₂) during manual cardiopulmonary resuscitation (CPR) in out-of-hospital cardiac arrest (OHCA).

Methods:

Retrospective analysis of adult OHCA monitor-defibrillator recordings having concurrent capnogram, compression depth, transthoracic impedance and ECG, and with $⩾$1,000 compressions. Within each patient, during no spontaneous circulation, nearby segments with changes in chest compression depth and rate were identified. Average ETCO₂ within each segment was standardised to compensate for ventilation rate variability. Contributions of relative variations in depth and rate to relative variations in standardised ETCO₂ were characterised using linear and non-linear models. Normalisation between paired segments removed intra and inter-patient variation and made coefficients of the model independent of the scale of measurement and therefore directly comparable.

Results:

A total of 394 pairs of segments from 221 patients were analysed (33% female, median (IQR) age 66 (55–74) years). Chest compression depth and rate were 50.4 (43.2–57.0) mm and 111.1 (106.5–116.1) compressions per minute. ETCO₂ before and after standardization was 32.1 (23.0–41.4) mmHg and 28.5 (19.4–38.7) mmHg. Linear model coefficient of determination was 0.89. Variation in compression depth mainly explained ETCO₂ variation (coefficient 0.95, 95% confidence interval (CI): 0.93–0.98) while changes in compression rate did not (coefficient 0.04, 95% CI: 0.01–0.07). Non-linear trend analysis confirmed the results.

Conclusion:

This study quantified the relative importance of chest compression characteristics in terms of their impact on CO₂ production during CPR. With ventilation rate standardised, variation in chest compression depth explained variations in ETCO₂ better than variation in chest compression rate.

中文翻译：

---

胸外按压对院外心肺复苏期间产生的呼气末二氧化碳水平的贡献。

目标：

描述在院外心脏骤停 (OHCA) 中手动心肺复苏 (CPR) 期间胸外按压深度和频率的变化如何影响呼气末 CO ₂ (ETCO _{2 ) 的变化。}

方法：

成人 OHCA 监护仪-除颤器记录的回顾性分析，包括并发二氧化碳图、按压深度、经胸阻抗和心电图，以及$⩾$1,000 次按压。在每位患者中，在无自主循环期间，确定了胸外按压深度和速率发生变化的附近节段。每个段内的平均 ETCO ₂被标准化以补偿通气率的变化。使用线性和非线性模型表征深度和速率的相对变化对标准化 ETCO _{2相对变化的贡献。}配对段之间的标准化消除了患者内部和患者间的差异，并使模型的系数独立于测量规模，因此可以直接进行比较。

结果：

分析了来自 221 名患者的总共 394 对节段（33% 为女性，中位（IQR）年龄为 66  （55-74）岁）。胸部按压深度和频率为每分钟50.4  (43.2–57.0) 毫米和 111.1  (106.5–116.1)次按压。标准化前后的 ETCO ₂ 分别为 32.1 (23.0–41.4)  mmHg 和 28.5  (19.4–38.7)  mmHg。线性模型决定系数为 0.89。压缩深度的变化主要解释了 ETCO ₂的变化（系数 0.95，95% 置信区间（CI）：0.93-0.98），而压缩率的变化没有（系数 0.04，95% CI：0.01-0.07）。非线性趋势分析证实了结果。

结论：

本研究量化了胸外按压特征在 CPR 期间对 CO _{2产生的影响的相对重要性。}随着通气率标准化，胸部按压深度的变化比胸部按压率的变化更能解释 ETCO _{2的变化。}