Logo Hamilton Medical Hamilton Logo
Retour

Déclenchement double ‑ Diagnostic, différenciation et résolution

Article

Auteur: David Grooms

Date: 08.07.2019

Un décalage dans l'interface patient‑ventilateur est un phénomène qui se produit fréquemment chez les patients ventilés mécaniquement de façon invasive et non invasive. Le terme « dyssynchronie » implique une anomalie de la synchronie attendue entre le patient et le ventilateur.
Déclenchement double - Diagnostic, différenciation et résolution

Messages à retenir

  • Des décalages entre le patient et le ventilateur, également appelés dyssynchronies, surviennent souvent chez des patients ventilés mécaniquement.
  • L'une des formes les plus courantes est le déclenchement double, qui est généralement dû à un décalage des temps inspiratoires des cycles mécaniques par rapport aux temps inspiratoires des cycles neuraux, ce qui est particulièrement préoccupant chez les patients SDRA car cela peut entraîner l'administration d'un volume courant excessif.
  • Diagnostiquer un déclenchement double et établir une différentiation entre les trois différents types peut représenter un défi considérable. En outre, il requiert une surveillance étroite et une analyse des formes d'ondes scalaires du ventilateur.
  • Les nouvelles technologies peuvent aider les médecins à éviter le déclenchement double en ajustant automatiquement le temps inspiratoire en fonction des besoins du patient.

Qu'est‑ce qu'un déclenchement double ?

La fréquence des dyssynchronies a été étudiée et on estime qu'elles surviennent au moins une fois chez au moins 50 % des patients recevant une ventilation mécanique (VM) pendant plus de 24 heures. Les deux dyssynchronies les plus courantes sont le déclenchement inefficace (manqué) et le déclenchement double (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​). Le déclenchement double est défini comme deux insufflations délivrées par le ventilateur sur un effort inspiratoire du patient (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​). La cause de cette dyssynchronie est un temps inspiratoire (temps I) disproportionnellement plus court du cycle mécanique par rapport au temps inspiratoire neural du patient. Le cyclage prématuré résultant du premier cycle peut entraîner l'administration involontaire du deuxième cycle suivant au cours d'une seule activation inspiratoire. Ce problème touche surtout les patients souffrant d'un syndrome de détresse respiratoire aiguë et survient le plus souvent lors de la ventilation à volume cible et à débit fixe, car elle peut entraîner l'administration d'un volume courant excessif résultant d'une « superposition » des cycles (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​). Bien que le concept semble simple, l'identification de ce problème est souvent négligée et non diagnostiquée par l'utilisateur (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​).

Diagnostic et résolution

La principale méthode de diagnostic d'un déclenchement double consiste à observer et à évaluer les formes d'ondes scalaires du ventilateur. Une forme d'ondes scalaire correspond à toute variable affichée dans le temps. La plupart des ventilateurs mécaniques permettent en général d'afficher la pression, le débit et/ou le volume dans le temps. Pour faciliter l'analyse de ces formes d'ondes, certains ventilateurs permettent l'affichage de la pression œsophagienne (approximation de la pression pleurale) dans le temps. Les captures d'écran des formes d'ondes du ventilateur ci‑dessous permettent d'identifier correctement un déclenchement double. La figure 1 affiche des formes d'ondes courantes de pression, de débit et de volume révélant le phénomène d'un déclenchement double au cours d'une ventilation invasive. Au départ, il est possible que l'œil non averti ne diagnostique pas ce phénomène, ni ne détermine correctement l'origine du problème. Ce problème, généralement interprété comme un second cycle généré activement par le patient (Cycle 2) après l'administration d'un cycle mécanique (Cycle 1) ou une rétention d'air, peut entraîner de graves effets indésirables associés à la ventilation mécanique s'il n'est pas résolu.  Par conséquent, il est recommandé d'effectuer une analyse plus approfondie, laquelle peut être réalisée en utilisant une manométrie œsophagienne pour comparer et mettre en évidence la pression pleurale et les variations de débit et de pression des voies aériennes du ventilateur. Un autre exemple ci‑dessous montrant un ventilateur avec des formes d'ondes scalaires de pression et de débit dans le temps, fournit un petit indice d'un possible déclenchement double, mais peut également être interprété comme un effort inspiratoire actif supplémentaire (figure 2). L'ajout d'une forme d'ondes scalaire de pression œsophagienne (forme d'ondes Pes‑Paux) révèle en fait la présence d'un déclenchement double en raison de l'administration suivante de cycles au cours d'un seul effort inspiratoire actif (voir la diminution de la pression pleurale à la figure 3).

Formes d'ondes de pression, de débit et de volume affichant un déclenchement double
Figure 1
Formes d'ondes de pression et de débit affichant un déclenchement double
Figure 2
Forme d'ondes de pression œsophagienne affichant une diminution de la pression pleurale
Figure 3

Différenciation

La distinction et la classification du type de déclenchement double relèvent également du défi au chevet du patient. Les recherches actuelles suggèrent que le déclenchement double peut être répertorié en trois catégories (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​):

  • Déclenché par le patient (DT‑P) : le premier cycle déclenché présente une diminution de la pression œsophagienne de >1 cmH2O et peut être associé à un effort inspiratoire important
  • Déclenché automatiquement (DT‑A) : le premier cycle déclenché survient avant le déclenchement dans le temps réglé sur le ventilateur, sans baisse concomitante de la pression œsophagienne
  • Déclenché par le ventilateur (DT‑V) : le premier cycle survient au moment du déclenchement dans le temps réglé sur le ventilateur sans baisse concomitante de la pression œsophagienne

Les données ont montré qu'il y avait souvent un décalage compris entre 0,07 et 0,13 seconde dans le déclenchement de la phase préinspiratoire (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​). L'évaluation de la baisse de la pression des voies aériennes est plus importante que la variation du débit au point de décalage du déclenchement de 0,13 seconde (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​). Par conséquent, la diminution de la pression de > 0,49 cmH2O à ce stade permet de distinguer les cycles DT‑P des cycles DT‑A et DT‑V (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​). D'autres données ont indiqué que le temps inspiratoire neural, qui peut être calculé à partir de l'apparition d'un déclin rapide de la pression œsophagienne jusqu'au nadir, était bien plus long dans le premier cycle DT-P que dans les cycles précédents (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​). Par conséquent, les diminutions de pression des voies aériennes couplées aux calculs de temps inspiratoire neural peuvent permettre l'identification de déclenchement double chez le patient.

Résolution : IntelliSync+

Les causes les plus courantes de déclenchement double sont le fait d'un décalage des temps inspiratoires des cycles mécaniques par rapport aux temps inspiratoires neuraux et d'un niveau d'aide inspiratoire insuffisant avec les activités respiratoires élevées  (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​). Plus spécifiquement, le temps inspiratoire du cycle mécanique est trop court par rapport au temps inspiratoire neural plus long. Par conséquent, l'allongement du temps inspiratoire du cycle mécanique pour correspondre au temps inspiratoire neural du patient ou l'augmentation du volume courant et de la pression de sortie du ventilateur peut réduire ou supprimer le déclenchement double (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​). Cependant, cela nécessite que l'utilisateur final soit présent pour observer ce phénomène et manipuler le ventilateur. L'automatisation de ce réglage est rendue possible grâce à la fonction IntelliSync+ ( Non commercialisé dans certains paysA​) implémentée sur les ventilateurs Hamilton Medical .  IntelliSync+ accorde une attention particulière aux critères de cyclage de chaque cycle et ajuste le temps inspiratoire en fonction des besoins du patient. Cette option réduit le nombre d'asynchronies, améliorant ainsi le confort du patient, voire les résultats obtenus avec le patient.

Notes en bas de page

  • A. Non commercialisé dans certains pays

Références

  1. 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. 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. 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. 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. 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. 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. 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. 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

Related articles. Get a deeper look

16-3_Tip_Figure_2

How to diagnose and avoid ineffective efforts

An ineffective effort is defined as a patient effort that is unable to trigger the delivery of a mechanical breath.

Formes d'ondes de pression, de débit et de volume affichant un déclenchement double
Figure 1
Formes d'ondes de pression et de débit affichant un déclenchement double
Figure 2
Forme d'ondes de pression œsophagienne affichant une diminution de la pression pleurale
Figure 3

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



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



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



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



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



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

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



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



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.