双重触发——诊断、区分和解决

文章

作者: David Grooms

日期: 08.07.2019

病人-呼吸机接口的不匹配是一种常见于有创和无创机械通气病人的现象。术语“不同步”表示病人和呼吸机之间预期同步性的异常。

要点

病人和呼吸机之间不匹配（也称为不同步）在机械通气病人中经常发生。
最常见的形式之一是双重触发，这通常是由机械呼吸吸气时间与自然吸气时间匹配不当引起的，尤其是 ARDS 病人，因为它可能导致潮气量输送过多。
诊断双重触发并区分三种不同类型可能是一项相当大的挑战，需要密切观察和分析呼吸机的标量波形。
新的技术可以根据病人的需求自动调整吸气时间，从而帮助临床医生避免双重触发。

什么是双重触发？

已对不同步的频率进行了研究，估计在接受机械通气 (MV) 超过 24 小时的病人中，不少于 50% 的病人至少会发生一次不同步。两种最常见的不同步是无效（错过）触发和双重触发 (DT) (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/s00134-006-0301-81)。双重触发定义为在一次病人吸气努力内输送两次呼吸机送气 (Liao KM, Ou CY, Chen CW. Classifying different types of double triggering based on airway pressure and flow deflection in mechanically ventilated patients. Respir Care.2011;56(4):460-466. doi:10.4187/respcare.007312)。这种不同步的根本原因是与病人自然吸气时间相比，机械呼吸的吸气时间 (I-time) 更短且不成比例。由此产生的首次呼吸过早切换可能导致在单次吸气激活期间意外地输送随后的二次呼吸。这是急性呼吸窘迫综合征病人特别关注的问题，最常见于固定流量定容通气，因为它会导致呼吸堆积引起的潮气量输送过多 (Pohlman MC, McCallister KE, Schweickert WD, et al. Excessive tidal volume from breath stacking during lung-protective ventilation for acute lung injury. Crit Care Med.2008;36(11):3019-3023. doi:10.1097/CCM.0b013e31818b308b3)。尽管在概念上被认为很简单，但对这个问题的认识往往被终端用户忽视和无法诊断 (Colombo D, Cammarota G, Alemani M, et al.Efficacy of ventilator waveforms observation in detecting patient-ventilator asynchrony.Crit Care Med.2011;39(11):2452-2457. doi:10.1097/CCM.0b013e318225753c4)。

诊断和解决

双重触发 (DT) 诊断的主要方法是观察和评估呼吸机标量波形。标量波形是随时间显示的任何变量。大多数机械通气机通常允许随着时间的推移显示压力、流量和/或容量。为进一步方便对这些波形的分析，一些呼吸机允许随时间显示食道压（近似胸腔压）。为演示正确识别 DT 的步骤，下面提供了呼吸机波形的截图。图 1 显示常见的压力、流量和容量波形，揭示了有创通气过程中的 DT 现象。最初，未经训练的眼睛可能无法诊断出这种现象，也无法正确确定问题的根源。通常被误认为是病人在机械定时呼吸（呼吸 1）输送或呼吸困难后主动产生二次呼吸（呼吸 2），如果这种问题持续存在，可能会导致与机械通气相关的严重不良影响。因此，建议进行更仔细的分析，而且可以利用食道测压法进行，以比较和对比胸腔压和呼吸机的气道压力和流量变化。下面另一个示例表明显示压力和流量时间标量的呼吸机，提供了可能的 DT 的微妙提示，但也可能被误认为是额外的主动吸气努力（图 2）。食道压标量波形（Pes-Paux 波形）的增加表明，事实上，由于在单次主动吸气努力过程中随后的呼吸输送，因此存在双重触发（见图 3 中胸腔压的降低）。

区分

在床旁区分和分类 DT 的类型也是一项挑战。目前的研究表明，DT 可以分为三种不同的类型 (Liao KM, Ou CY, Chen CW.Classifying different types of double triggering based on airway pressure and flow deflection in mechanically ventilated patients.Respir Care.2011;56(4):460-466. doi:10.4187/respcare.007312)：

病人触发 (DT-P)：首次触发的呼吸食道压降低 >1 cmH2O，并且可能与强烈的吸气努力有关
自动触发 (DT-A)：首次触发的呼吸发生在呼吸机设置时间触发之前，且未伴随食道压降低
呼吸机触发 (DT-V)：首次呼吸发生在呼吸机设定时间触发时，且未伴随食道压降低

数据显示，在吸气前阶段触发的延迟通常在 0.07–0.13 之间 (Takeuchi M, Williams P, Hess D, Kacmarek RM. Continuous positive airway pressure in new-generation mechanical ventilators: a lung model study. Anesthesiology.2002;96(1):162-172. doi:10.1097/00000542-200201000-000305)。气道压力下降的评估比 0.13 秒触发延迟阶段的流量变化更有力 (Liao KM, Ou CY, Chen CW.Classifying different types of double triggering based on airway pressure and flow deflection in mechanically ventilated patients.Respir Care.2011;56(4):460-466. doi:10.4187/respcare.007312)。因此，此时压力降低 > 0.49 cmH2O 可以区分 DT-P 呼吸与 DT-A 和 DT-V 呼吸 (Liao KM, Ou CY, Chen CW.Classifying different types of double triggering based on airway pressure and flow deflection in mechanically ventilated patients.Respir Care.2011;56(4):460-466. doi:10.4187/respcare.007312)。其他数据显示，自然吸气时间（可计算为食道压迅速下降至最低点的开始）在首次 DT-P 呼吸中明显长于前几次呼吸 (Parthasarathy S, Jubran A, Tobin MJ. Assessment of neural inspiratory time in ventilator-supported patients. Am J Respir Crit Care Med.2000;162(2 Pt 1):546-552. doi:10.1164/ajrccm.162.2.99010246)。因此，气道压力降低与自然吸气时间计算结合可以帮助识别病人的双重触发。

解决：IntelliSync+

DT 最常见的原因是机械呼吸吸气时间与自然吸气时间匹配不当，以及高呼吸驱动的压力支持水平不足 (Kallet RH, Campbell AR, Dicker RA, Katz JA, Mackersie RC. Effects of tidal volume on work of breathing during lung-protective ventilation in patients with acute lung injury and acute respiratory distress syndrome. Crit Care Med.2006;34(1):8-14. doi:10.1097/01.ccm.0000194538.32158.af7)。具体而言，与较长的自然吸气时间相比，机械呼吸吸气时间太短。因此，延长机械呼吸吸气时间以匹配病人自然吸气时间或增加呼吸机输出压力和潮气量可以最大限度地减少或消除 DT (Vignaux L, Vargas F, Roeseler J, et al. Patient-ventilator asynchrony during non-invasive ventilation for acute respiratory failure: a multicenter study. Intensive Care Med.2009;35(5):840-846. doi:10.1007/s00134-009-1416-58)。然而，这需要终端用户在场观察这种现象，以及手动操作呼吸机。Hamilton Medical 哈美顿医疗公司呼吸机上的 IntelliSync+ 功能（并非在所有市场均有提供A）实现了这种调整的自动化。ntelliSync+ 密切关注每次呼吸的切换标准，并根据病人需求调整吸气时间。此选项减少了不同步次数，从而改善病人的舒适度，也可能对病人治疗效果产生有益影响。

脚注

A. 并非在所有市场均有提供

参考文献

1. 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
2. Liao KM, Ou CY, Chen CW. Classifying different types of double triggering based on airway pressure and flow deflection in mechanically ventilated patients. Respir Care. 2011;56(4):460-466. doi:10.4187/respcare.00731
3. Pohlman MC, McCallister KE, Schweickert WD, et al. Excessive tidal volume from breath stacking during lung-protective ventilation for acute lung injury. Crit Care Med. 2008;36(11):3019-3023. doi:10.1097/CCM.0b013e31818b308b
4. Colombo D, Cammarota G, Alemani M, et al. Efficacy of ventilator waveforms observation in detecting patient-ventilator asynchrony. Crit Care Med. 2011;39(11):2452-2457. doi:10.1097/CCM.0b013e318225753c
5. Takeuchi M, Williams P, Hess D, Kacmarek RM. Continuous positive airway pressure in new-generation mechanical ventilators: a lung model study. Anesthesiology. 2002;96(1):162-172. doi:10.1097/00000542-200201000-00030
6. Parthasarathy S, Jubran A, Tobin MJ. Assessment of neural inspiratory time in ventilator-supported patients. Am J Respir Crit Care Med. 2000;162(2 Pt 1):546-552. doi:10.1164/ajrccm.162.2.9901024
7. Kallet RH, Campbell AR, Dicker RA, Katz JA, Mackersie RC. Effects of tidal volume on work of breathing during lung-protective ventilation in patients with acute lung injury and acute respiratory distress syndrome. Crit Care Med. 2006;34(1):8-14. doi:10.1097/01.ccm.0000194538.32158.af
8. Vignaux L, Vargas F, Roeseler J, et al. Patient-ventilator asynchrony during non-invasive ventilation for acute respiratory failure: a multicenter study. Intensive Care Med. 2009;35(5):840-846. doi:10.1007/s00134-009-1416-5

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.

Classifying different types of double triggering based on airway pressure and flow deflection in mechanically ventilated patients.

Liao KM, Ou CY, Chen CW. Classifying different types of double triggering based on airway pressure and flow deflection in mechanically ventilated patients. Respir Care. 2011;56(4):460-466. doi:10.4187/respcare.00731

Pubmed

BACKGROUND

Double-triggering (DT) is a frequent type of patient-ventilator asynchrony and has potentially severe consequences, such as alveolar overdistention or the generation of intrinsic PEEP. However, the first breath of DT could be patient-triggered (DT-P), auto-triggered (DT-A), or ventilator-triggered (DT-V).

OBJECTIVE

To differentiate DT-P, DT-A, and DT-V using airway pressure or flow changes during the trigger-delay phase in ventilated patients.

METHODS

Fourteen mechanically ventilated patients with DT were included. All patients were on flow-triggered ventilation modes and received either continuous mandatory ventilation or pressure support ventilation. Breaths in which the first breath was associated with an esophageal pressure drop of > 1 cm H(2)O were categorized as DT-P. Breaths in which the first breath occurred at the ventilator set cycle were categorized as DT-V. Breaths in which the first breath occurred earlier than the ventilator set cycle without esophageal pressure drop were categorized as DT-A. The pressure drop and flow change at 0.13 s (PD(0.13) and F(0.13), respectively) in the trigger-delay phase were calculated from the nadir.

RESULTS

There were 507 double-triggered breaths: 271 DT-V (53%), 50 DT-A (10%), and 186 DT-P (37%). The PD(0.13) for DT-V, DT-A, and DT-P were 0.16 ± 0.12 cm H(2)O, 0.25 ± 0.17 cm H(2)O, and 1.34 ± 0.67 cm H(2)O, respectively. The F(0.13) for DT-V, DT-A, and DT-P were 2.11 ± 2.31 L/min, 2.64 ± 2.07 L/min, and 16.51 ± 8.02 L/min, respectively. The best discriminatory criteria for differentiating DT-P from DT-V and DT-A, based on the Youden index (sensitivity + specificity - 1) was PD(0.13) ≥ 0.49 cm H(2)O, which had a Youden index of 95%.

CONCLUSION

DT-P can be distinguished from DT-V and DT-A by using airway pressure deflections in the trigger-delay phase.

Excessive tidal volume from breath stacking during lung-protective ventilation for acute lung injury.

Pohlman MC, McCallister KE, Schweickert WD, et al. Excessive tidal volume from breath stacking during lung-protective ventilation for acute lung injury. Crit Care Med. 2008;36(11):3019-3023. doi:10.1097/CCM.0b013e31818b308b

Pubmed

RATIONALE

Low tidal volume ventilation strategies for patients with respiratory failure from acute lung injury may lead to breath stacking and higher volumes than intended.

OBJECTIVE

To determine frequency, risk factors, and volume of stacked breaths during low tidal volume ventilation for acute lung injury.

DESIGN, SETTING, AND PATIENTS

Prospective cohort study of mechanically ventilated patients with acute lung injury (enrolled from August 2006 through May 2007) treated with low tidal volume ventilation in a medical intensive care unit at an academic tertiary care hospital.

INTERVENTIONS

Patients were ventilated with low tidal volumes using the Acute Respiratory Distress Syndrome Network protocol for acute lung injury. Continuous flow-time and pressure-time waveforms were recorded. The frequency, risk factors, and volume of stacked breaths were determined. Sedation depth was monitored using Richmond agitation sedation scale.

MEASUREMENTS AND MAIN RESULTS

Twenty patients were enrolled and studied for a mean 3.3 +/- 1.7 days. The median (interquartile range) Richmond agitation sedation scale was -4 (-5, -3). Inter-rater agreement for identifying stacked breaths was high (kappa 0.99, 95% confidence interval 0.98-0.99). Stacked breaths occurred at a mean 2.3 +/- 3.5 per minute and resulted in median volumes of 10.1 (8.8-10.7) mL/kg predicted body weight, which was 1.62 (1.44-1.82) times the set tidal volume. Stacked breaths were significantly less common with higher set tidal volumes (relative risk 0.4 for 1 mL/kg predicted body weight increase in tidal volume, 95% confidence interval 0.23-0.90).

CONCLUSION

Stacked breaths occur frequently in low tidal volume ventilation despite deep sedation and result in volumes substantially above the set tidal volume. Set tidal volume has a strong influence on frequency of stacked breaths.

Efficacy of ventilator waveforms observation in detecting patient-ventilator asynchrony.

Colombo D, Cammarota G, Alemani M, et al. Efficacy of ventilator waveforms observation in detecting patient-ventilator asynchrony. Crit Care Med. 2011;39(11):2452-2457. doi:10.1097/CCM.0b013e318225753c

Link to article

OBJECTIVES

The value of visual inspection of ventilator waveforms in detecting patient-ventilator asynchronies in the intensive care unit has never been systematically evaluated. This study aims to assess intensive care unit physicians' ability to identify patient-ventilator asynchronies through ventilator waveforms.

DESIGN

Prospective observational study.

SETTING

Intensive care unit of a University Hospital.

PATIENTS

Twenty-four patients receiving mechanical ventilation for acute respiratory failure.

INTERVENTION

Forty-three 5-min reports displaying flow-time and airway pressure-time tracings were evaluated by 10 expert and 10 nonexpert, i.e., residents, intensive care unit physicians. The asynchronies identified by experts and nonexperts were compared with those ascertained by three independent examiners who evaluated the same reports displaying, additionally, tracings of diaphragm electrical activity.

MEASUREMENTS AND MAIN RESULTS

Data were examined according to both breath-by-breath analysis and overall report analysis. Sensitivity, specificity, and positive and negative predictive values were determined. Sensitivity and positive predictive value were very low with breath-by-breath analysis (22% and 32%, respectively) and fairly increased with report analysis (55% and 44%, respectively). Conversely, specificity and negative predictive value were high with breath-by-breath analysis (91% and 86%, respectively) and slightly lower with report analysis (76% and 82%, respectively). Sensitivity was significantly higher for experts than for nonexperts for breath-by-breath analysis (28% vs. 16%, p < .05), but not for report analysis (63% vs. 46%, p = .15). The prevalence of asynchronies increased at higher ventilator assistance and tidal volumes (p < .001 for both), whereas it decreased at higher respiratory rates and diaphragm electrical activity (p < .001 for both). At higher prevalence, sensitivity decreased significantly (p < .001).

CONCLUSIONS

The ability of intensive care unit physicians to recognize patient-ventilator asynchronies was overall quite low and decreased at higher prevalence; expertise significantly increased sensitivity for breath-by-breath analysis, whereas it only produced a trend toward improvement for report analysis.

Continuous positive airway pressure in new-generation mechanical ventilators: a lung model study.

Takeuchi M, Williams P, Hess D, Kacmarek RM. Continuous positive airway pressure in new-generation mechanical ventilators: a lung model study. Anesthesiology. 2002;96(1):162-172. doi:10.1097/00000542-200201000-00030

Pubmed

BACKGROUND

A number of new microprocessor-controlled mechanical ventilators have become available over the last few years. However, the ability of these ventilators to provide continuous positive airway pressure without imposing or performing work has never been evaluated.

METHODS

In a spontaneously breathing lung model, the authors evaluated the Bear 1000, Drager Evita 4, Hamilton Galileo, Nellcor-Puritan-Bennett 740 and 840, Siemens Servo 300A, and Bird Products Tbird AVS at 10 cm H(2)O continuous positive airway pressure. Lung model compliance was 50 ml/cm H(2)O with a resistance of 8.2 cm H(2)O x l(-1) x s(-1), and inspiratory time was set at 1.0 s with peak inspiratory flows of 40, 60, and 80 l/min. In ventilators with both pressure and flow triggering, the response of each was evaluated.

RESULTS

With all ventilators, peak inspiratory flow, lung model tidal volume, and range of pressure change (below baseline to above baseline) increased as peak flow increased. Inspiratory trigger delay time, inspiratory cycle delay time, expiratory pressure time product, and total area of pressure change were not affected by peak flow, whereas pressure change to trigger inspiration, inspiratory pressure time product, and trigger pressure time product were affected by peak flow on some ventilators. There were significant differences among ventilators on all variables evaluated, but there was little difference between pressure and flow triggering in most variables on individual ventilators except for pressure to trigger. Pressure to trigger was 3.74 +/- 1.89 cm H(2)O (mean +/- SD) in flow triggering and 4.48 +/- 1.67 cm H(2)O in pressure triggering (P < 0.01) across all ventilators.

CONCLUSIONS

Most ventilators evaluated only imposed a small effort to trigger, but most also provided low-level pressure support and imposed an expiratory workload. Pressure triggering during continuous positive airway pressure does require a slightly greater pressure than flow triggering.

Assessment of neural inspiratory time in ventilator-supported patients.

Parthasarathy S, Jubran A, Tobin MJ. Assessment of neural inspiratory time in ventilator-supported patients. Am J Respir Crit Care Med. 2000;162(2 Pt 1):546-552. doi:10.1164/ajrccm.162.2.9901024

Pubmed

Neural inspiratory time (TI) is a measurement of fundamental importance in studies of patient-ventilator interaction. The measurement is usually based on recordings of flow, esophageal pressure (Pes), and transdiaphragmatic pressure (Pdi), but the concordance of such estimates of neural TI with a more direct measurement of neural activity has not been systematically evaluated. To address this issue, we studied nine ventilator-supported patients in whom we employed esophageal electrode recordings of the diaphragmatic electromyogram (EMG) as the reference measurement of neural TI. Comparison of the indirect estimates of neural TI duration, based on flow, Pes, and Pdi against the reference measurement, revealed a mean difference (bias) ranging from -54 to 612 ms during spontaneous breathing and from -52 to 714 ms during mechanical ventilation; the respective precisions (standard deviations of the differences) ranged from 79 to 175 ms and from 74 to 221 ms. Because an indirect estimate of neural TI duration could be identical to that of the reference measurement and yet be displaced in time, this lag or lead was quantified as the phase angle of neural TI onset. Flow-based estimates of the onset of neural TI displayed a systematic lag, which may be explained at least in part by concurrent intrinsic positive end-expiratory pressure. In conclusion, the indirect estimates of the onset and duration of neural TI in ventilator-dependent patients displayed poor agreement with the diaphragmatic EMG measurement of neural TI.

Effects of tidal volume on work of breathing during lung-protective ventilation in patients with acute lung injury and acute respiratory distress syndrome.

Kallet RH, Campbell AR, Dicker RA, Katz JA, Mackersie RC. Effects of tidal volume on work of breathing during lung-protective ventilation in patients with acute lung injury and acute respiratory distress syndrome. Crit Care Med. 2006;34(1):8-14. doi:10.1097/01.ccm.0000194538.32158.af

Pubmed

OBJECTIVE

To assess the effects of step-changes in tidal volume on work of breathing during lung-protective ventilation in patients with acute lung injury (ALI) or the acute respiratory distress syndrome (ARDS).

DESIGN

Prospective, nonconsecutive patients with ALI/ARDS.

SETTING

Adult surgical, trauma, and medical intensive care units at a major inner-city, university-affiliated hospital.

PATIENTS

Ten patients with ALI/ARDS managed clinically with lung-protective ventilation.

INTERVENTIONS

Five patients were ventilated at a progressively smaller tidal volume in 1 mL/kg steps between 8 and 5 mL/kg; five other patients were ventilated at a progressively larger tidal volume from 5 to 8 mL/kg. The volume mode was used with a flow rate of 75 L/min. Minute ventilation was maintained constant at each tidal volume setting. Afterward, patients were placed on continuous positive airway pressure for 1-2 mins to measure their spontaneous tidal volume.

MEASUREMENTS AND MAIN RESULTS

Work of breathing and other variables were measured with a pulmonary mechanics monitor (Bicore CP-100). Work of breathing progressively increased (0.86 +/- 0.32, 1.05 +/- 0.40, 1.22 +/- 0.36, and 1.57 +/- 0.43 J/L) at a tidal volume of 8, 7, 6, and 5 mL/kg, respectively. In nine of ten patients there was a strong negative correlation between work of breathing and the ventilator-to-patient tidal volume difference (R = -.75 to -.998).

CONCLUSIONS

: The ventilator-delivered tidal volume exerts an independent influence on work of breathing during lung-protective ventilation in patients with ALI/ARDS. Patient work of breathing is inversely related to the difference between the ventilator-delivered tidal volume and patient-generated tidal volume during a brief trial of unassisted breathing.

Patient-ventilator asynchrony during non-invasive ventilation for acute respiratory failure: a multicenter study.

Vignaux L, Vargas F, Roeseler J, et al. Patient-ventilator asynchrony during non-invasive ventilation for acute respiratory failure: a multicenter study. Intensive Care Med. 2009;35(5):840-846. doi:10.1007/s00134-009-1416-5

Pubmed

OBJECTIVE

To determine the prevalence of patient-ventilator asynchrony in patients receiving non-invasive ventilation (NIV) for acute respiratory failure.

DESIGN

Prospective multicenter observation study.

SETTING

Intensive care units in three university hospitals.

METHODS

Patients consecutively admitted to ICU were included. NIV, performed with an ICU ventilator, was set by the clinician. Airway pressure, flow, and surface diaphragmatic electromyography were recorded continuously for 30 min. Asynchrony events and the asynchrony index (AI) were determined from visual inspection of the recordings and clinical observation.

RESULTS

A total of 60 patients were included, 55% of whom were hypercapnic. Auto-triggering was present in 8 (13%) patients, double triggering in 9 (15%), ineffective breaths in 8 (13%), premature cycling 7 (12%) and late cycling in 14 (23%). An AI > 10%, indicating severe asynchrony, was present in 26 patients (43%), whose median (25-75 IQR) AI was 26 (15-54%). A significant correlation was found between the magnitude of leaks and the number of ineffective breaths and severity of delayed cycling. Multivariate analysis indicated that the level of pressure support and the magnitude of leaks were weakly, albeit significantly, associated with an AI > 10%. Patient comfort scale was higher in pts with an AI < 10%.

CONCLUSION

Patient-ventilator asynchrony is common in patients receiving NIV for acute respiratory failure. Our results suggest that leaks play a major role in generating patient-ventilator asynchrony and discomfort, and point the way to further research to determine if ventilator functions designed to cope with leaks can reduce asynchrony in the clinical setting.