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AutoPEEP 和总 PEEP 的测量

文章

作者: 临床专家组,Hamilton Medical 哈美顿医疗公司

日期: 14.07.2017

Last change: 30.09.2020

(Originally published 14.07.2017) Previously: select Exp hold, when flow=0 select Exp hold again to deactivate hold maneuver. SW versions updated.

在存在动态肺过度充气的情况下,肺泡内的平均呼气末压力(即实际的总 PEEP (PEEPtot))高于呼吸机施加的 PEEP (PEEPe)。PEEPtot 和 PEEPe 之间的差异对应于内源性 PEEP (PEEPi),也称为 AutoPEEP (1)。

AutoPEEP 和总 PEEP 的测量

AutoPEEP 和 RCexp

AutoPEEP 也可称为空气陷闭、呼吸堆积、动态过度充气、意外 PEEP 或隐匿性 PEEP。

AutoPEEP 是具有长呼气时间常数(RCexp)的机械通气病人的常见现象,例如慢性阻塞性肺病或急性严重哮喘病人。

重要事项:在正常呼吸输送过程中,呼吸机的屏幕上显示的气道压力曲线上看不到由此产生的 AutoPEEP。

(下图 1:来自 Garcia Vicente et al。(García Vicente E, Sandoval Almengor JC, Díaz Caballero LA, Salgado Campo JC. Ventilación mecánica invasiva en EPOC y asma [Invasive mechanical ventilation in COPD and asthma]. Med Intensiva. 2011;35(5):288-298. doi:10.1016/j.medin.2010.11.0042​))

显示 AutoPEEP 和空气陷闭的流量-时间图
图 1:AutoPEEP 和空气陷闭
显示 AutoPEEP 和空气陷闭的流量-时间图
图 1:AutoPEEP 和空气陷闭

AutoPEEP 的影响

AutoPEEP 使病人容易出现呼吸功增加、气压伤、血液动力学不稳定和难以触发呼吸机的情况。未能识别出 AutoPEEP 的血液动力学后果可能导致不适当的液体限制或不必要的升血压治疗。AutoPEEP 可能会影响机械通气撤机。

护理人员应监测通气过程中是否发生 AutoPEEP,并相应地设置其通气控制参数,以避免 AutoPEEP 的负面后果。

测量 AutoPEEP

所有 Hamilton Medical 哈美顿医疗公司呼吸机都具有独特的功能,以逐次呼吸为基础显示 AutoPEEP 作为监测参数。它使用应用于整个呼吸的 LSF 方法计算得出 (Iotti GA, Braschi A, Brunner JX, et al. Respiratory mechanics by least squares fitting in mechanically ventilated patients: applications during paralysis and during pressure support ventilation. Intensive Care Med.1995;21(5):406-413. doi:10.1007/BF017074093​)。但在特殊情况下,例如,当出现严重动态过度充气时,通过 LSF 计算得出的 AutoPEEP 可能会低估实际的 AutoPEEP。在这些情况下,它可以通过执行呼气屏气操作来获得。

用呼气屏气操作测量总 PEEP(见下图 2):

确保显示气道压力波形。

  1. 打开屏气窗口。
  2. 等待,直到气道压力波形图从左侧重新开始。
  3. 等待下一次吸气。
  4. 然后选择呼气屏气。等待 3 至 5 秒,然后再次选择呼气屏气或按下按压式旋钮,禁用屏气操作,并关闭窗口。
  5. 该操作后,“屏气”窗口关闭,并自动激活冷冻功能。
  6. 通过用游标检查压力曲线上流量达到零后的点,测量总 PEEP。
  7. 通过从总 PEEP 中减去外源性 PEEP 计算 AutoPEEP。

计算

AutoPEEP '= 总 PEEP - 外源性 PEEP = 内源性 PEEP
PEEP '= 外源性 PEEP 且已预选
总 PEEP '= 内源性 PEEP + 外源性 PEEP
显示呼气屏气操作的呼吸机屏幕截图
图 2:使用呼气屏气操作测量总 PEEP——总 PEEP 7.6 cmH2O - 外源性 PEEP 5 cmH2O = AutoPEEP 2.6 cmH2O
显示呼气屏气操作的呼吸机屏幕截图
图 2:使用呼气屏气操作测量总 PEEP——总 PEEP 7.6 cmH2O - 外源性 PEEP 5 cmH2O = AutoPEEP 2.6 cmH2O

避免空气陷闭

如果无意中出现 AutoPEEP,护理人员应考虑调整控制参数,通过增加呼气时间来避免空气陷闭。可能需要使用大直径气管内插管、支气管扩张剂、短吸气时间、长呼气时间、低呼吸频率和使用镇静剂,以避免空气陷闭引起的动态过度充气。

Hamilton Medical 哈美顿医疗公司的所有呼吸机都具有智能通气模式—适应性支持通气 (ASV®)。ASV 自动采用肺保护策略,以最大程度减少 AutoPEEP 引起的并发症。

相关设备:HAMILTON-G5/S1 (sw v2.8x and later); HAMILTON-C3 (sw v2.0.x and later), HAMILTON-C6 (sw v1.1.x and later)

见下面的完整引文 (Iotti, G., & Braschi, A. (1999). Measurements of respiratory mechanics during mechanical ventilation.Rhäzüns, Switzerland: Hamilton Medical Scientific Library.1​)。

Measurements of respiratory mechanics during mechanical ventilation

Iotti, G., & Braschi, A. (1999). Measurements of respiratory mechanics during mechanical ventilation. Rhäzüns, Switzerland: Hamilton Medical Scientific Library.

Invasive mechanical ventilation in COPD and asthma.

García Vicente E, Sandoval Almengor JC, Díaz Caballero LA, Salgado Campo JC. Ventilación mecánica invasiva en EPOC y asma [Invasive mechanical ventilation in COPD and asthma]. Med Intensiva. 2011;35(5):288-298. doi:10.1016/j.medin.2010.11.004

COPD and asthmatic patients use a substantial proportion of mechanical ventilation in the ICU, and their overall mortality with ventilatory support can be significant. From the pathophysiological standpoint, they have increased airway resistance, pulmonary hyperinflation, and high pulmonary dead space, leading to increased work of breathing. If ventilatory demand exceeds work output of the respiratory muscles, acute respiratory failure follows. The main goal of mechanical ventilation in this kind of patients is to improve pulmonary gas exchange and to allow for sufficient rest of compromised respiratory muscles to recover from the fatigued state. The current evidence supports the use of noninvasive positive-pressure ventilation for these patients (especially in COPD), but invasive ventilation also is required frequently in patients who have more severe disease. The physician must be cautious to avoid complications related to mechanical ventilation during ventilatory support. One major cause of the morbidity and mortality arising during mechanical ventilation in these patients is excessive dynamic pulmonary hyperinflation (DH) with intrinsic positive end-expiratory pressure (intrinsic PEEP or auto-PEEP). The purpose of this article is to provide a concise update of the most relevant aspects for the optimal ventilatory management in these patients.

Respiratory mechanics by least squares fitting in mechanically ventilated patients: applications during paralysis and during pressure support ventilation.

Iotti GA, Braschi A, Brunner JX, et al. Respiratory mechanics by least squares fitting in mechanically ventilated patients: applications during paralysis and during pressure support ventilation. Intensive Care Med. 1995;21(5):406-413. doi:10.1007/BF01707409



OBJECTIVE

To evaluate a least squares fitting technique for the purpose of measuring total respiratory compliance (Crs) and resistance (Rrs) in patients submitted to partial ventilatory support, without the need for esophageal pressure measurement.

DESIGN

Prospective, randomized study.

SETTING

A general ICU of a University Hospital.

PATIENTS

11 patients in acute respiratory failure, intubated and assisted by pressure support ventilation (PSV).

INTERVENTIONS

Patients were ventilated at 4 different levels of pressure support. At the end of the study, they were paralyzed for diagnostic reasons and submitted to volume controlled ventilation (CMV).

MEASUREMENTS AND RESULTS

A least squares fitting (LSF) method was applied to measure Crs and Rrs at different levels of pressure support as well as in CMV. Crs and Rrs calculated by the LSF method were compared to reference values which were obtained in PSV by measurement of esophageal pressure, and in CMV by the application of the constant flow, end-inspiratory occlusion method. Inspiratory activity was measured by P0.1. In CMV, Crs and Rrs measured by the LSF method are close to quasistatic compliance (-1.5 +/- 1.5 ml/cmH2O) and to the mean value of minimum and maximum end-inspiratory resistance (+0.9 +/- 2.5 cmH2O/(l/s)). Applied during PSV, the LSF method leads to gross underestimation of Rrs (-10.4 +/- 2.3 cmH2O/(l/s)) and overestimation of Crs (+35.2 +/- 33 ml/cmH2O) whenever the set pressure support level is low and the activity of the respiratory muscles is high (P0.1 was 4.6 +/- 3.1 cmH2O). However, satisfactory estimations of Crs and Rrs by the LSF method were obtained at increased pressure support levels, resulting in a mean error of -0.4 +/- 6 ml/cmH2O and -2.8 +/- 1.5 cmH2O/(l/s), respectively. This condition was coincident with a P0.1 of 1.6 +/- 0.7 cmH2O.

CONCLUSION

The LSF method allows non-invasive evaluation of respiratory mechanics during PSV, provided that a near-relaxation condition is obtained by means of an adequately increased pressure support level. The measurement of P0.1 may be helpful for titrating the pressure support in order to obtain the condition of near-relaxation.