How to set expiratory trigger sensitivity (ETS)

Article

Author: Clinical Experts Group, Hamilton Medical

Date of first publication: 22.02.2018

Optimal patient-ventilator synchrony is of prime importance, as asynchronies lead to increased work of breathing and patient discomfort.

How to set expiratory trigger sensitivity (ETS)

Two main settings for synchronizing patient and ventilator

Asynchronies are also associated with higher mortality and prolonged mechanical ventilation (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). Achieving optimal patient-ventilator synchrony is particularly challenging during noninvasive ventilation (NIV), due to variations in leaks and patient conditions.

When trying to synchronize the ventilator with the patient’s activity, there are two main settings to be considered: the inspiratory and the expiratory trigger. These dictate when the ventilator starts or ends a spontaneous breath. On Hamilton Medical ventilators, the setting for the expiratory trigger is the expiratory trigger sensitivity (ETS). This value represents the percent of peak inspiratory flow at which the ventilator cycles from inspiration to exhalation. On Hamilton Medical ventilators, ETS can be set to anywhere between 5% and 80%. In general, increasing the ETS setting results in a shorter inspiratory time, while decreasing it results in a longer inspiratory time.

On other devices, this flow cycle mechanism is called ‘ESENS’, ‘End Inspiration’, ‘Flow Cycle’, etc.

Another criterion for breath termination is TI max. This setting is used if gas leakage is significant and the set cycle is not reached, providing a back-up so that inspiration can be terminated. The ventilator switches over to exhalation when the set TI max is reached.

Typical ETS setting

A typical ETS setting in a patient with normal lung mechanics undergoing NIV is 25%, which is the default ETS setting on Hamilton Medical ventilators (see Figure 1). With obstructive patients, for example, in a patient with chronic obstructive pulmonary disease (COPD), ETS should be set higher to increase the expiratory time and thus avoid air-trapping and intrinsic PEEP.

Incorrect ETS settings leading to expiratory asynchrony may be recognized from either delayed or premature cycling leading to double triggering.

Screenshot of flow waveform indicating maximum flow and ETS at 25% — Figure 1: Default ETS setting of 25%

Delayed cycling

Delayed cycling can be recognized from an end-inspiratory peak in the pressure curve caused by an active expiratory effort, as well as a change in the slope of inspiratory flow towards the baseline (see Figure 2). This is typically described in patients with COPD. The reduction in inspiratory flow is smaller, probably due to dynamic hyperinflation and airway resistance.

In the case of delayed cycling, increase ETS in increments of 10% to shorten the inspiratory time (TI) and adjust TI max according to the patient’s condition.

Double triggering

Along with short inspiratory times, double triggering is an indication of premature cycling (see Figure 3). During premature cycling, the inspiratory muscles continue to contract, causing the ventilator to anticipate a second effort. This leads to double triggering, with delivery of higher tidal volumes, breath stacking, and higher work of breathing. A possible solution is trying to match the neural inspiratory time with the ventilator inspiratory time. Double triggering may also be caused by insufficient pressure support.

In the case of double triggering, decrease ETS in increments of 10% to lengthen TI, adjust TI max according to the patient’s condition, or increase Psupport to achieve the desired tidal volumes.

Screenshot of flow and pressure waveform showing change in slope of flow — Figure 2: Delayed cycling

Screenshot of flow and pressure waveform showing double triggering — Figure 3: Double triggering

Trigger adjustment with IntelliSync+

The HAMILTON-C6 and HAMILTON-G5/S1 ventilators offer the option of automatic adjustment with IntelliSync+ (Standard on the HAMILTON-S1A)(Not all ventilators available in all marketsB). The ventilator monitors incoming sensor signals from the patient, continuously analyzes the waveform shapes using a set of algorithms and then dynamically adjusts the setting in real-time to address changing patient or system conditions. IntelliSync+ can be set to automate trigger adjustment for inspiration or expiration, or both.

Footnotes

A. Standard on the HAMILTON-S1
B. Not all ventilators available in all markets

References

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.