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Disparo doble: diagnóstico, diferenciación y resolución

Artículo

Autor: David Grooms

Fecha: 08.07.2019

Una discrepancia en la interfaz entre el paciente y el respirador es un fenómeno que suele producirse en pacientes con ventilación mecánica tanto invasiva como no invasiva. El término "asincronía" denota una anomalía de la sincronía que se espera que haya entre el paciente y el respirador.
Disparo doble: diagnóstico, diferenciación y resolución

Mensajes importantes

  • Las discrepancias entre el paciente y el respirador —también denominadas asincronías— son habituales en pacientes con ventilación mecánica.
  • Una de las formas más extendidas es el disparo doble, que suele deberse a una discrepancia entre los tiempos inspiratorios de la respiración mecánica y los tiempos inspiratorios neurales y reviste especial preocupación en los pacientes con SDRA, ya que puede llevar a un suministro de volumen tidal excesivo.
  • El diagnóstico del disparo doble y la diferenciación de los tres distintos tipos existentes pueden suponer un reto considerable, y requieren la observación y evaluación minuciosas de las formas de onda escalares del respirador.
  • Las nuevas tecnologías pueden ayudar a los profesionales sanitarios a evitar el disparo doble ajustando dinámicamente el tiempo inspiratorio según las necesidades del paciente.

¿Qué es el disparo doble?

La frecuencia de las asincronías ha sido objeto de estudio y se calcula que se producen como mínimo una vez en al menos la mitad de los pacientes que reciben ventilación mecánica durante más de 24 horas. Las dos asincronías más comunes son el disparo ineficaz (perdido) y el disparo doble (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). El disparo doble se define como dos insuflaciones del respirador suministradas en un mismo esfuerzo inspiratorio del paciente (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 causa fundamental de esta asincronía es un tiempo inspiratorio de la respiración mecánica desproporcionadamente más breve que el tiempo inspiratorio neural del paciente. Los ciclos prematuros resultantes de la primera respiración pueden desembocar en un suministro inadvertido de una segunda respiración posterior durante una misma activación inspiratoria. Esto reviste especial preocupación en pacientes con síndrome de dificultad respiratoria aguda, y ocurre con mayor frecuencia con la ventilación por volumen objetivo de flujo fijo, ya que puede derivar en un suministro de volumen tidal excesivo como consecuencia de la acumulación de respiraciones (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). Aunque parece un concepto sencillo, es un problema que a menudo pasa desapercibido para los usuarios finales y se queda sin diagnosticar (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).

Diagnóstico y resolución

El método principal para diagnosticar el disparo doble es la observación y evaluación de las formas de onda escalares del respirador. Una forma de onda escalar es cualquier variable cuyo desarrollo se muestra a lo largo del tiempo. La mayoría de los respiradores mecánicos permite ver normalmente la presión, el flujo o el volumen a lo largo del tiempo. Para simplificar aún más el análisis de estas formas de onda, en algunos respiradores se puede ver la presión esofágica (una estimación de la presión pleural) a lo largo del tiempo. Más abajo se muestran capturas de pantalla de las formas de onda de un respirador para ilustrar los pasos que permiten identificar correctamente un problema de disparo doble. En la figura 1 se muestran formas de onda de presión, flujo y volumen comunes que revelan la existencia de un fenómeno de disparo doble durante una ventilación invasiva. En un principio, un ojo no entrenado no es capaz de diagnosticar este fenómeno ni tampoco de determinar correctamente el origen del problema. Este problema, que suele confundirse con que el paciente está generando activamente una segunda respiración (Respiración 2) tras el suministro de una respiración temporizada mecánicamente (Respiración 1) o porque está «hambriento de aire», puede acabar provocando efectos adversos graves derivados de la ventilación mecánica si esta continúa.  En consecuencia, se recomienda realizar un análisis más exhaustivo, que puede realizarse a través de una manometría esofágica para comparar y contrastar la presión pleural y los cambios de flujo y de presión en la vía aérea del respirador. Otro de los ejemplos de abajo (donde aparece un respirador en el que se muestran los valores escalares de tiempo de flujo y presión) apunta sutilmente a un posible problema de disparo doble, pero también podría confundirse con un esfuerzo inspiratorio activo adicional (figura 2). La incorporación de la forma de onda escalar de la presión esofágica (forma de onda Pes-Paux) revela que, de hecho, existe un problema de disparo doble, dado el posterior suministro de respiraciones durante un mismo esfuerzo inspiratorio activo (véase la reducción de la presión pleural en la figura 3).

Formas de onda de presión, flujo y volumen que revelan un disparo doble
Figura 1
Formas de onda de presión, flujo y volumen que revelan un disparo doble
Figura 1
Formas de onda de presión y flujo que revelan un disparo doble
Figura 2
Formas de onda de presión y flujo que revelan un disparo doble
Figura 2
Forma de onda de presión esofágica que revela una reducción de la presión pleural
Figura 3
Forma de onda de presión esofágica que revela una reducción de la presión pleural
Figura 3

Diferenciación

La diferenciación y clasificación del tipo de disparo doble también plantean ciertas complicaciones a pie de cama. Varias investigaciones en curso sugieren que el disparo doble se puede clasificar en tres tipos distintos (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):

  • Activado por el paciente (DT-P): la primera respiración activada presenta una reducción de la presión esofágica de >1 cmH2O y puede asociarse a un esfuerzo inspiratorio intenso.
  • Disparo automático (DT-A): la primera respiración activada tiene lugar antes del tiempo de disparo establecido por el respirador, sin la consiguiente caída de la presión esofágica.
  • Activado por el respirador (DT-V): la primera respiración sucede durante el tiempo de disparo establecido por el respirador, sin la consiguiente caída de la presión esofágica.

Diversos datos han puesto de manifiesto que suele haber un retraso en la activación del disparo en la fase preinspiratoria de entre 0,07–0,13 segundos (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). La evaluación de la caída de la presión en la vía aérea es más eficaz que el cambio de flujo en la fase de retraso del disparo de 0,13 segundos (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). En consecuencia, la reducción de la presión >0,49 cmH2O en este punto permite distinguir las respiraciones DT-P de las respiraciones DT-A y 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). Otros datos adicionales han revelado que el tiempo inspiratorio neural, que se puede calcular como el inicio de un descenso rápido de la presión esofágica a su punto más bajo, fue considerablemente más prolongado en la primera respiración DT-que en las respiraciones anteriores (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). Como resultado, las reducciones de la presión en la vía aérea, junto con los cálculos de los tiempos inspiratorios neurales, pueden ayudar a identificar problemas de disparo doble en el paciente.

Resolución: IntelliSync+

Las causas más comunes del disparo doble son una discrepancia entre los tiempos inspiratorios de la respiración mecánica y los tiempos inspiratorios neurales, y un nivel de presión de soporte insuficiente con unos impulsos respiratorios elevados (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). En concreto, el tiempo inspiratorio de la respiración mecánica es demasiado breve en comparación con el tiempo inspiratorio neural más prolongado. En consecuencia, prolongar el tiempo inspiratorio de la respiración mecánica para que coincida con el tiempo inspiratorio neural, o bien aumentar la presión de salida del respirador y el volumen tidal, podrían minimizar el disparo doble o directamente eliminarlo (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). Sin embargo, esto requiere la presencia del usuario final para observar este fenómeno, así como manipular manualmente el respirador. La automatización de este ajuste ahora es posible gracias a la función IntelliSync+ (No disponible en todos los mercadosA) de los respiradores de Hamilton Medical. IntelliSync+ presta mucha atención a los criterios de ciclado de cada respiración y ajusta el tiempo inspiratorio según las necesidades del paciente. Esta opción reduce el número de asincronías y, por tanto, proporciona una mayor comodidad a los pacientes, además de que puede tener un efecto positivo en los resultados del paciente.

Notas al pie

  • A. No disponible en todos los mercados

Referencias

  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

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.

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