如何设置呼气触发灵敏度（ETS）

文章

作者: 临床专家组，Hamilton Medical 哈美顿医疗公司

日期: 22.02.2018

最佳的人机同步至关重要，因为不同步会导致呼吸功增加和病人不适。

人机同步的两个主要设置

不同步也与更高的死亡率和长时间机械通气有关 (Blanch L, Villagra A, Sales B, et al.Asynchronies during mechanical ventilation are associated with mortality.Intensive Care Med. 2015;41(4):633-641. doi:10.1007/s00134-015-3692-61, Tassaux D, Gainnier M, Battisti A, Jolliet P. Impact of expiratory trigger setting on delayed cycling and inspiratory muscle workload. Am J Respir Crit Care Med. 2005;172(10):1283-1289. doi:10.1164/rccm.200407-880OC2, Thille AW, Rodriguez P, Cabello B, Lellouche F, Brochard L. Patient-ventilator asynchrony during assisted mechanical ventilation. Intensive Care Med.2006;32(10):1515-1522. doi:10.1007/s00134-006-0301-83)。由于漏气和患者状况的变化，在无创通气 (NIV) 过程中实现最佳的人机同步尤其具有挑战性。

当尝试将呼吸机与病人的活动同步时，有两个主要设置需要考虑：吸气触发和呼气触发。这决定了呼吸机何时开始或结束自主呼吸。在 Hamilton Medical 哈美顿医疗公司呼吸机上，呼气触发设置为呼气触发灵敏度 (ETS)。此值表示吸气峰流量的百分比，达到此百分比后呼吸机从吸气阶段切换到呼气阶段。在 Hamilton Medical 哈美顿医疗公司呼吸机上，ETS 可设置为 5% 和 80% 之间的任何值。通常，增加 ETS 设置导致吸气时间缩短，而降低 ETS 则导致吸气时间延长。

在其他设备上，此流量周期机制称为 ‘ESENS’、‘End Inspiration’、‘Flow Cycle’ 等。

呼吸终止的另一个标准是最大吸气时间。如果漏气严重且未达到设定周期，则使用该设置，提供后备通气，从而可以终止吸气。达到所设的最大吸气时间时，呼吸机会切换到呼气阶段。

典型的 ETS 设置

接受无创通气的肺力学正常病人的典型 ETS 设置为 25%，这是 Hamilton Medical 哈美顿医疗公司呼吸机的默认 ETS 设置（见图 1）。对于呼吸道阻塞病人（如慢性阻塞性肺部疾病 (COPD)），应将 ETS 设置得更高，以增加呼气时间，从而避免空气陷闭和内源性 PEEP。

导致呼气不同步的错误 ETS 设置可从导致双重触发的延迟或过早切换中识别出来。

显示最大流量和 ETS 设置为 25% 的流量波形截图 — 图 1：默认 ETS 设置为 25%

延迟切换

延迟切换可以从主动呼气努力引起的压力曲线中的吸气末峰值，以及吸气流量向基线的斜率变化中识别出来（见图 2）。通常在 COPD 病人中描述这种情况。吸气流量的减少较小，可能是由动态过度充气和气道阻力导致的。

在延迟切换的情况下，以 10% 的增量增加 ETS 以缩短吸气时间 (TI)，并根据病人状况调整最大吸气时间。

双重触发

除了吸气时间短外，双重触发也是过早切换的一个征象（见图 3）。在过早切换期间，吸气肌肉继续收缩，导致呼吸机预计会再次用力。这导致双重触发，伴随更高的潮气量输送、呼吸堆积和更高的呼吸功。一种可能的解决方案是尝试将自然吸气时间与呼吸机吸气时间相匹配。压力支持不足也可能导致双重触发。

在双重触发的情况下，以 10% 的增量减少 ETS 以延长 TI，根据病人状况调整最大吸气时间，或增加支持压力以达到所需的潮气量。

使用 IntelliSync+ 调整触发

HAMILTON-C6 和 HAMILTON-G5/S1 呼吸机使用 IntelliSync+ 提供自动调整选项（HAMILTON-S1 上的标准功能A）（并非所有市场均提供所有呼吸机B）。呼吸机监测病人发出的传感器信号，使用一组算法连续分析波形，然后实时动态调整设置，以应对不断变化的病人或系统状况。IntelliSync+ 可以设置为自动调整吸气或呼气触发，或两者。

脚注

A. HAMILTON-S1 标准功能
B. 并非所有市场均提供所有呼吸机

参考文献

1. Blanch L, Villagra A, Sales B, et al. Asynchronies during mechanical ventilation are associated with mortality. Intensive Care Med. 2015;41(4):633-641. doi:10.1007/s00134-015-3692-6
2. Tassaux D, Gainnier M, Battisti A, Jolliet P. Impact of expiratory trigger setting on delayed cycling and inspiratory muscle workload. Am J Respir Crit Care Med. 2005;172(10):1283-1289. doi:10.1164/rccm.200407-880OC
3. Thille AW, Rodriguez P, Cabello B, Lellouche F, Brochard L. Patient-ventilator asynchrony during assisted mechanical ventilation. Intensive Care Med. 2006;32(10):1515-1522. doi:10.1007/s00134-006-0301-8

Asynchronies during mechanical ventilation are associated with mortality.

Blanch L, Villagra A, Sales B, et al. Asynchronies during mechanical ventilation are associated with mortality. Intensive Care Med. 2015;41(4):633-641. doi:10.1007/s00134-015-3692-6

Link to article

PURPOSE

This study aimed to assess the prevalence and time course of asynchronies during mechanical ventilation (MV).

METHODS

Prospective, noninterventional observational study of 50 patients admitted to intensive care unit (ICU) beds equipped with Better Care™ software throughout MV. The software distinguished ventilatory modes and detected ineffective inspiratory efforts during expiration (IEE), double-triggering, aborted inspirations, and short and prolonged cycling to compute the asynchrony index (AI) for each hour. We analyzed 7,027 h of MV comprising 8,731,981 breaths.

RESULTS

Asynchronies were detected in all patients and in all ventilator modes. The median AI was 3.41 % [IQR 1.95-5.77]; the most common asynchrony overall and in each mode was IEE [2.38 % (IQR 1.36-3.61)]. Asynchronies were less frequent from 12 pm to 6 am [1.69 % (IQR 0.47-4.78)]. In the hours where more than 90 % of breaths were machine-triggered, the median AI decreased, but asynchronies were still present. When we compared patients with AI > 10 vs AI ≤ 10 %, we found similar reintubation and tracheostomy rates but higher ICU and hospital mortality and a trend toward longer duration of MV in patients with an AI above the cutoff.

CONCLUSIONS

Asynchronies are common throughout MV, occurring in all MV modes, and more frequently during the daytime. Further studies should determine whether asynchronies are a marker for or a cause of mortality.

Impact of expiratory trigger setting on delayed cycling and inspiratory muscle workload.

Tassaux D, Gainnier M, Battisti A, Jolliet P. Impact of expiratory trigger setting on delayed cycling and inspiratory muscle workload. Am J Respir Crit Care Med. 2005;172(10):1283-1289. doi:10.1164/rccm.200407-880OC

Link to article

RATIONALE

During pressure-support ventilation, the ventilator cycles into expiration when inspiratory flow decreases to a given percentage of peak inspiratory flow ("expiratory trigger"). In obstructive disease, the slower rise and decrease of inspiratory flow entails delayed cycling, an increase in intrinsic positive end-expiratory pressure, and nontriggering breaths.

OBJECTIVES

We hypothesized that setting expiratory trigger at a higher than usual percentage of peak inspiratory flow would attenuate the adverse effects of delayed cycling.

METHODS

Ten intubated patients with obstructive disease undergoing pressure support were studied at expiratory trigger settings of 10, 25, 50, and 70% of peak inspiratory flow.

MEASUREMENTS

Continuous recording of diaphragmatic EMG activity with surface electrodes, and esophageal and gastric pressures with a dual-balloon nasogastric tube.

MAIN RESULTS

Compared with expiratory trigger 10, expiratory trigger 70 reduced the magnitude of delayed cycling (0.25 +/- 0.18 vs. 1.26 +/- 0.72 s, p < 0.05), intrinsic positive end-expiratory pressure (4.8 +/- 1.9 vs. 6.5 +/- 2.2 cm H(2)O, p < 0.05), nontriggering breaths (2 +/- 3 vs. 9 +/- 5 breaths/min, p < 0.05), and triggering pressure-time product (0.9 +/- 0.8 vs. 2.1 +/- 0.7 cm H2O . s, p < 0.05).

CONCLUSIONS

Setting expiratory trigger at a higher percentage of peak inspiratory flow in patients with obstructive disease during pressure support improves patient-ventilator synchrony and reduces inspiratory muscle effort. Further studies should explore whether these effects can influence patient outcome.

Patient-ventilator asynchrony during assisted mechanical ventilation.

Thille AW, Rodriguez P, Cabello B, Lellouche F, Brochard L. Patient-ventilator asynchrony during assisted mechanical ventilation. Intensive Care Med. 2006;32(10):1515-1522. doi:10.1007/s00134-006-0301-8

Link to article

OBJECTIVE

The incidence, pathophysiology, and consequences of patient-ventilator asynchrony are poorly known. We assessed the incidence of patient-ventilator asynchrony during assisted mechanical ventilation and we identified associated factors.

METHODS

Sixty-two consecutive patients requiring mechanical ventilation for more than 24 h were included prospectively as soon as they triggered all ventilator breaths: assist-control ventilation (ACV) in 11 and pressure-support ventilation (PSV) in 51.

MEASUREMENTS

Gross asynchrony detected visually on 30-min recordings of flow and airway pressure was quantified using an asynchrony index.

RESULTS

Fifteen patients (24%) had an asynchrony index greater than 10% of respiratory efforts. Ineffective triggering and double-triggering were the two main asynchrony patterns. Asynchrony existed during both ACV and PSV, with a median number of episodes per patient of 72 (range 13-215) vs. 16 (4-47) in 30 min, respectively (p=0.04). Double-triggering was more common during ACV than during PSV, but no difference was found for ineffective triggering. Ineffective triggering was associated with a less sensitive inspiratory trigger, higher level of pressure support (15 cmH(2)O, IQR 12-16, vs. 17.5, IQR 16-20), higher tidal volume, and higher pH. A high incidence of asynchrony was also associated with a longer duration of mechanical ventilation (7.5 days, IQR 3-20, vs. 25.5, IQR 9.5-42.5).

CONCLUSIONS

One-fourth of patients exhibit a high incidence of asynchrony during assisted ventilation. Such a high incidence is associated with a prolonged duration of mechanical ventilation. Patients with frequent ineffective triggering may receive excessive levels of ventilatory support.