Exhibiting a significant proportion of asynchronous breaths is associated with an almost five-fold increase in ICU mortality,([FOOTNOTE=Blanch L, Villagra A, Sales B, et al. Asynchronies during mechanical ventilation are associated with mortality. Intensive care medicine. 2015;41(4):633-641.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=906058]) a three-fold increase in median duration of mechanical ventilation and a greater than two-fold increase in median hospital length of stay.([FOOTNOTE=de Wit M, Miller KB, Green DA, Ostman HE, Gennings C, Epstein SK. Ineffective triggering predicts increased duration of mechanical ventilation. Critical care medicine. 2009;37(10):2740-2745.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=720867])

 

Approximately 36% of patients admitted to the ICU require mechanical ventilation.([FOOTNOTE=Dasta JF, McLaughlin TP, Mody SH, Piech CT. Daily cost of an intensive care unit day: the contribution of mechanical ventilation. Critical care medicine. 2005;33(6):1266-1271.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=959739])   Those patients who endure a prolonged time on mechanical ventilation are at-risk for greater resource utilization and length of stay.([FOOTNOTE=Zilberberg MD, Luippold RS, Sulsky S, Shorr AF. Prolonged acute mechanical ventilation, hospital resource utilization, and mortality in the United States. Critical care medicine. 2008;36(3):724-730.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203240]) Therefore a great deal of clinical focus has developed around optimizing the delivery of mechanical ventilation and subsequent weaning.   An increasing amount of evidence is revealing the relationship between patient-ventilator asynchrony and adverse outcome in mechanically ventilated patients including increased time on mechanical ventilation and mortality.1,2  Therefore, the identification, prevention and resolution of patient-ventilator asynchrony is increasingly being recognized as being integral to the optimization of quality of care for mechanically ventilated patients.

 

  • Up to 25% of patients with acute respiratory failure exhibit a significant proportion of asynchronous breaths (>10 %)([FOOTNOTE=Robinson BR, Blakeman TC, Toth P, Hanseman DJ, Mueller E, Branson RD. Patient-ventilator asynchrony in a traumatically injured population. Respiratory care. 2013;58(11):1847-1855.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203233]) [see INCIDENCE]
  • Exhibiting a significant proportion of asynchronous breaths is associated with an almost five-fold increase in ICU mortality,1 a three-fold increase in median duration of mechanical ventilation and a greater than two-fold increase in median hospital length of stay.2 [see CLINICAL IMPACT]
  • Patient-ventilator asynchrony consists of multiple types of asynchrony. The identification and treatment of each type is multifactorial, influenced by a myriad of ventilator-related and patient-specific factors.([FOOTNOTE=Pierson DJ. Patient-ventilator interaction. Respiratory care. 2011;56(2):214-228.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203232]) [see ETIOLOGY]
  • Features included in the Puritan Bennett™ 980 ventilator may help improve patient synchrony by better aligning triggering, flow, breathe delivery, and cycling with individualized patient need, promoting more natural breathing compared to conventional mechanical ventilation.([FOOTNOTE=Xirouchaki N, Kondili E, Vaporidi K, et al. Proportional assist ventilation with load-adjustable gain factors in critically ill patients: comparison with pressure support. Intensive care medicine. 2008;34(11):2026-2034.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=719462 ]) [see INTERVENTIONS]
  • Reduction of asynchrony with the Puritan Bennett 980 ventilator may improve patient outcomes compared to PS and VC.([FOOTNOTE=Bosma K, Ferreyra G, Ambrogio C, et al. Patient-ventilator interaction and sleep in mechanically ventilated patients: pressure support versus proportional assist ventilation. Critical care medicine. 2007;35(4):1048-1054.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=352110]),([FOOTNOTE=Xirouchaki N, Kondili E, Klimathianaki M, Georgopoulos D. Is proportional-assist ventilation with load-adjustable gain factors a user-friendly mode? Intensive care medicine. 2009;35(9):1599-1603.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=719463]) [see OUTCOMES]

 

The incidence of patient-ventilator asynchrony is influenced by the definition of asynchrony, patient condition, ventilator mode and method of observation.

 

Table 1. Incidence of asynchrony by condition and mode measured in percentage of patients with asynchrony in greater than 10% of total breaths.

 

Citation Number of participants Condition Mode % of patients with asynchrony index* > 10
Blanch 20151 50 ICU Invasive Ventiation > 24 hrs PCV, PSV, VCV 12
Carlucci 2013([FOOTNOTE=Carlucci A, Pisani L, Ceriana P, Malovini A, Nava S. Patient-ventilator asynchronies: may the respiratory mechanics play a role? Critical care (London, England). 2013;17(2):R54.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=956126]) 69 ICU Invasive Ventiation > 24 hrs NIV, PSV 30
Robinson 20135 35 Trauma SIMV, PSV 25.7
Vignaux 2009([FOOTNOTE=Vignaux L, Vargas F, Roeseler J, et al. Patient-ventilator asynchrony during non-invasive ventilation for acute respiratory failure: a multicenter study. Intensive care medicine. 2009;35(5):840-846.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=603142]) 60 Acute respiratory failure (Acute chonic respiratory failure, pneumonia, post-extubation, pulmonary edema, postoperative, thoracic trauma) NIV mode - ICU Ventilator 43
Vignaux 2010([FOOTNOTE=Vignaux L, Tassaux D, Carteaux G, et al. Performance of noninvasive ventilation algorithms on ICU ventilators during pressure support: a clinical study. Intensive care medicine. 2010;36(12):2053-2059.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203239]) 65 Acute respiratory failure (acute episode of chronic pulmonary disease, NIV after extubation, pneumonia, post-operative, pulmonary edema NIV mode - ICU Ventilator 38
Thille 2006([FOOTNOTE=Thille AW, Rodriguez P, Cabello B, Lellouche F, Brochard L. Patient-ventilator asynchrony during assisted mechanical ventilation. Intensive care medicine. 2006;32(10):1515-1522.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=805246]) 62 ICU Invasive Ventiation > 24 hrs ACV, PSV 24

 

*Asynchrony Index (expressed in percentage) = number of asynchrony events/total respiratory rate (ventilator cycles +wasted efforts)×100

 

Acronyms  
ACV Assist-control Ventilation
NIV Non-invasive Ventilation
PCV Pressure-control Ventilation
PSV Pressure-support Ventilation
VCV Volume-control Ventilation

 

Asynchronous breaths are associated with worsened patient outcomes

 

Exhibiting a significant proportion of asynchronous breaths is associated with an almost five-fold increase in ICU mortality,1 a three-fold increase in median duration of mechanical ventilation and a greater than two-fold increase in median hospital length of stay.2

 

Figure 1. ICU Mortality (%) in mechanically ventilated patients with asynchrony index* greater or less than 10% (p=0.011)1 [-] [+]

Blanch 2015

*Asynchrony Index = number of asynchronous breaths/total number of breaths

Figure 2. Hospital Mortality (%) in mechanically ventilated patients with asynchrony index* greater or less than 10% (p=0.044)1 [-] [+]

Blanch 2015

*Asynchrony Index = number of asynchronous breaths/total number of breaths

Figure 3. Ventilator-free survival (days) in mechanically ventilated patients with ineffective triggering index* greater or less than 10%
(p=0.02)2 [-] [+]

de Wit 2009

*Ineffective Triggering Index = number of ineffectively triggered breaths/total number of breaths

Figure 4. Median duration of mechanical ventilation (days) in mechanically ventilated patients with an ineffective triggering index* greater
or less than 10% (p=0.007)2 [-] [+]

de Wit 2009

*Ineffective Triggering Index = number of ineffectively triggered breaths/total number of breaths

Figure 5. Weaning Success (%) in mechanically ventilated patients with and without intermittent trigger asynchrony (p<0.01)21 [-] [+]

Figure 6. Median ICU length of stay (days) in mechanically ventilated patients with patients with ineffective triggering index* greater
or less than 10% (p=0.01)2 [-][+]

de Wit 2009

*Ineffective Triggering Index = number of ineffectively triggered breaths/total number of breaths

Figure 7. Median Hospital length of stay (days) in mechanically ventilated patients with ineffective triggering index* greater or less
than 10% (p=0.03)2 [-][+]

de Wit 2009

*Ineffective Triggering Index = number of ineffectively triggered breaths/total number of breaths

Figure 8. Percentage of mechanically ventilated patients discharged to home with an ineffective triggering index* greater or less
than 10% (p=0.04)2 [-][+]

de Wit 2009

*Ineffective Triggering Index = number of ineffectively triggered breaths/total number of breaths

Figure 9. Mean PEEPi (cmH20) in mechanically ventilated COPD patients with a pressure support termination criteria of 10%*
versus 70% (p<0.05)32 [-][+]

Gentile 2011

*According to this study, a pressure support termination criteria of 10% is associated with prolonged cycling, which is a type of asynchrony, in patients with obstructive lung disease.

Figure 10. Triggering pressure time product (cmH20) in mechanically ventilated COPD patients with a pressure support termination criteria
of 10%* versus 70% (p<0.05)32 [-][+]

Gentile 2011

*According to this study, a pressure support termination criteria of 10% is associated with prolonged cycling, which is a type of asynchrony, in patients with obstructive lung disease.

 

When the delivery of ventilatory support does not correspond with patient demand, patient-ventilator asynchrony is the result.

 

Types of Asynchrony

Patient-ventilator asynchrony appears in many different forms. The presence of each type of asynchrony is associated with specific patient and ventilator risk factors, and adverse effects. Each type of asynchrony can be categorized according to its relationship to specific phases of the delivered breath: breath initiation, flow delivery and breath cycling/termination.

 

Figure 3. Asynchrony Types, Definitions, Patient and ventilator-specific risk factors and associated waveforms

 

 
 

 

Asynchrony Type: Flow asynchrony

  • Asynchrony Category: Flow delivery
  • Definition: Ventilator flow output does not coincide with patient demand.
  • Adverse Effects:
    • Increased work of breathing (WOB),([FOOTNOTE=Chiumello D, Pelosi P, Croci M, Bigatello LM, Gattinoni L. The effects of pressurization rate on breathing pattern, work of breathing, gas exchange and patient comfort in pressure support ventilation. The European respiratory journal. 2001;18(1):107-114.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203222]) and increased dyspnea15
  • Patient Risk Factors:
    • High respiratory drive([FOOTNOTE=Gilstrap D, MacIntyre N. Patient-ventilator interactions. Implications for clinical management. American journal of respiratory and critical care medicine. 2013;188(9):1058-1068.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203224])
  • Ventilator Setting Risk Factors:
    • Volume control,([FOOTNOTE=MacIntyre NR, McConnell R, Cheng KC, Sane A. Patient-ventilator flow dyssynchrony: flow-limited versus pressure-limited breaths. Critical care medicine. 1997;25(10):1671-1677.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203231]) low or high level of assistance([FOOTNOTE=Vitacca M, Bianchi L, Zanotti E, et al. Assessment of physiologic variables and subjective comfort under different levels of pressure support ventilation. Chest. 2004;126(3):851-859.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=352166]) and high or low pressurization rate/rise time setting15
 
 

Asynchrony Type: Ineffective efforts

  • Asynchrony Category: Breath initiation
  • Definition: Patient effort to initiate a breath is unrecognized by ventilator.
  • Adverse Effects:
    • Increased work of breathing14
  • Patient Risk Factors:
    • Alkalosis,([FOOTNOTE=Thille AW, Rodriguez P, Cabello B, Lellouche F, Brochard L. Patient-ventilator asynchrony during assisted mechanical ventilation. Intensive care medicine. 2006;32(10):1515-1522.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=805246]) COPD,19 coma,([FOOTNOTE=de Wit M, Pedram S, Best AM, Epstein SK. Observational study of patient-ventilator asynchrony and relationship to sedation level. Journal of critical care. 2009;24(1):74-80.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=720868]) decreased Richmond Agitation-Sedation Scale,20 delirium,20 higher intrinsic respiratory rate,hypercapnia,([FOOTNOTE=Chao DC, Scheinhorn DJ, Stearn-Hassenpflug M. Patient-ventilator trigger asynchrony in prolonged mechanical ventilation. Chest. 1997;112(6):1592-1599.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=805242]) low minute volume,([FOOTNOTE=Vignaux L, Grazioli S, Piquilloud L, et al. Patient-ventilator asynchrony during noninvasive pressure support ventilation and neurally adjusted ventilatory assist in infants and children. Pediatric critical care medicine : a journal of the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies. 2013;14(8):e357-364.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203238]) older age,21 and Intrinsic PEEP (PEEPi)([FOOTNOTE=Jolliet P, Tassaux D. Clinical review: patient-ventilator interaction in chronic obstructive pulmonary disease. Critical care (London, England). 2006;10(6):236.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203227])
  • Ventilator Setting Risk Factors:
    • Airway leaks,22 delayed cycling,22 higher tidal volume,([FOOTNOTE=Thille AW, Cabello B, Galia F, Lyazidi A, Brochard L. Reduction of patient-ventilator asynchrony by reducing tidal volume during pressure-support ventilation. Intensive care medicine. 2008;34(8):1477-1486.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=352081])  higher pressure support,24 less sensitive inspiratory trigger,19 and long ventilator set inspiratory time24
 
 

Asynchrony Type: Auto-triggering

  • Asynchrony Category: Breath initiation
  • Definition: Ventilator triggers unscheduled breath that is not initiated by patient. More than one breath occurring in a single patient effort.
  • Adverse Effects: Altered gas exchange14
  • Patient Risk Factors:
    • Cardiogenic oscillations([FOOTNOTE=Imanaka H, Nishimura M, Takeuchi M, Kimball WR, Yahagi N, Kumon K. Autotriggering caused by cardiogenic oscillation during flow-triggered mechanical ventilation. Critical care medicine. 2000;28(2):402-407.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203225]) and low respiratory drive([FOOTNOTE=Sassoon C. Triggering of the ventilator in patient-ventilator interactions. Respiratory care. 2011;56(1):39-51.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=805250])
  • Ventilator Setting Risk Factors:
    • Airway leaks,([FOOTNOTE=Bernstein G, Knodel E, Heldt GP. Airway leak size in neonates and autocycling of three flow-triggered ventilators. Critical care medicine. 1995;23(10):1739-1744.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=805239]) circuit leak,26 flow triggering,([FOOTNOTE=Shoham AB, Patel B, Arabia FA, Murray MJ. Mechanical ventilation and the total artificial heart: optimal ventilator trigger to avoid post-operative autocycling - a case series and literature review. Journal of cardiothoracic surgery. 2010;5:39.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203235]) and low triggering threshold26
 
 

Asynchrony Type: Double-triggering

  • Asynchrony Category: Breath initiation
  • Definition: Two breaths occurring in interval less than half mean inspiratory time. Typically occurs when patient demand outlasts set inspiratory time, resulting in ventilator triggering second breath.
  • Adverse Effects:
    • Increased tidal volume/overdistention([FOOTNOTE=Pohlman MC, McCallister KE, Schweickert WD, et al. Excessive tidal volume from breath stacking during lung-protective ventilation for acute lung injury. Critical care medicine. 2008;36(11):3019-3023.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=805247])
  • Patient Risk Factors:
    • Unusually high ventilatory demand,([FOOTNOTE=de Wit M. Monitoring of patient-ventilator interaction at the bedside. Respiratory care. 2011;56(1):61-72.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=720866]) low Ramsay scale,19 high PaO2/FiO2,19 and longer neural inspiratory time19
  • Ventilator Setting Risk Factors:
    • Assist-controlled ventilation,19 low tidal volumes,29 low pressure support,22 and ventilator set inspiratory time too short22
 
 

Asynchrony Type: Premature cycling

  • Asynchrony Category: Breath cycling
  • Definition: Occurs when patients' neural inspiratory time exceeds ventilator set inspiratory time.
  • Adverse Effects:
    • Increased work of breathing([FOOTNOTE=Tokioka H, Tanaka T, Ishizu T, et al. The effect of breath termination criterion on breathing patterns and the work of breathing during pressure support ventilation. Anesthesia and analgesia. 2001;92(1):161-165.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203237])
  • Patient Risk Factors:
    • Longer neural inspiratory time22
  • Ventilator Setting Risk Factors:
    • Earlier machine termination of breath([FOOTNOTE=Tassaux D, Gainnier M, Battisti A, Jolliet P. Impact of expiratory trigger setting on delayed cycling and inspiratory muscle workload. American journal of respiratory and critical care medicine. 2005;172(10):1283-1289.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203236])

Asynchrony Type: Delayed cycling

  • Asynchrony Category: Breath cycling
  • Definition: Occurs when the ventilator set inspiratory time exceeds patients’ neural inspiratory time.
  • Adverse Effects:
    • Increased work of breathing and increased intrinsic PEEP32
  • Patient Risk Factors:
    • Lower minute volume22
  • Ventilator Setting Risk Factors:
    • Airway leaks22 and later machine termination of breath22
 
 

 

 

 

Asynchrony Begets More Asynchrony

As asynchrony has a negative impact on respiratory mechanics, it may predispose patients to increased and/or different types of asynchrony.

 

Figure 3. The influence of patient-ventilator asynchrony on respiratory mechanics and subsequent asynchrony23,26,29,([FOOTNOTE=Gentile MA. Cycling of the mechanical ventilator breath. Respiratory care. 2011;56(1):52-60.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203223])

 

 

 

 

Managing Patient-Ventilator Interaction

In circumstances where there is a mismatch between patient demand and ventilatory delivery, the result is frequently patient-ventilator asynchrony (e.g. fighting the ventilator), which may negatively influence patient outcome. 6,([FOOTNOTE=Epstein SK. How often does patient-ventilator asynchrony occur and what are the consequences? Respiratory care. 2011;56(1):25-38.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=805249])  Conversely, passive mechanical ventilation in which patient demand is eliminated, via sedative or neuromuscular blockade, may also produce diaphragmatic injury or ventilator-induced diaphragmatic dysfunction. 6

 

Figure 1. Scenarios of patient ventilator interaction during mechanical ventilation6

 

 

 

Figure 2. Ventilator and patient factors influencing the occurrence of asynchrony6

 

Patient Factors: Ventilator Factors:
Intrinsic Respiratory Rate Mode
Minute Ventilation Minute Ventilation
Respiratory Drive Triggering criteria
Airway Resistance Cycling criteria
Lung Volume Rise Time
Compliance Tidal Volume
Respiratory Muscle Function Expiratory Time

 

 

Influence of underlying patient condition

Respiratory mechanics significantly impact patient-ventilator interaction. Therefore, specific patient conditions that influence respiratory mechanics may predispose patients to specific types of asynchrony.

 

Chronic Obstructive Pulmonary Disease (COPD)
Patient characteristics Increased lung compliance
Higher airway resistance
Longer time constant
Prone to intrinsic PEEP
Relationship to Asynchrony Increased presence of intrinsic PEEP (PEEPi) is a common cause of ineffective efforts with flow triggering, as the patient effort required to trigger the ventilator must first overcome any alveolar pressure present at the end of exhalation23
Additional airway resistance may extend ventilator inspiratory time. Patients with a lower cycling-off threshold of peak inspiratory flow are prone to delayed cycling, shortened expiratory time (already compromised by increased expiratory resistance) and additional air-trapping.32
Acute Respiratory Distress Syndrome (ARDS)
Patient characteristics Decreased lung compliance
Higher airway resistance
Shorter time constant
Relationship to Asynchrony In contrast to COPD patients, stiff-lung ARDS patients with a higher cycling-off threshold of peak inspiratory flow are prone to premature cycling, which may or may not be accompanied by double-triggering. This premature cycling leads to decreased tidal volume delivery and consequent increases in work of breathing.31

 

 

Achieving Balance

Often the optimization of patient-ventilator interaction causes the clinician to adjust the ventilator in order find a balance between two harmful extremes. For example, determining the appropriate trigger sensitivity involves striking a balance of between ineffective efforts (i.e. overlyinsensitive trigger) and auto-trigger (i.e. overly sensitive trigger). A review of the asynchrony evidence reveals many of these scenarios. Like many circumstances related to asynchrony, the success of a given ventilator adjustment may be confounded by several related patient and ventilator factors.

 

Figure 4. Clinical consequences of asynchrony due to suboptimal breath triggering threshold, cycling threshold, pressurization rate/rise time, and level of assistance14,15,18,23,35,([FOOTNOTE=Chiumello D, Polli F, Tallarini F, et al. Effect of different cycling-off criteria and positive end-expiratory pressure during pressure support ventilation in patients with chronic obstructive pulmonary disease. Critical care medicine. 2007;35(11):2547-2552.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=655710])

 

 

 

 

Adverse Consequences of Patient-Ventilator Asynchrony

Though it is unclear whether asynchrony is a marker of disease severity or the cause of negative outcome, there is significant evidence associating asynchrony with mortality, delayed weaning and increased hospital length of stay [see CLINICAL IMPACT]. However, it is clear that asynchrony has a negative influence on gas exchange, respiratory muscle function, patient comfort, and lung protection. It is possible that these are the mechanisms of injury by which asynchrony influences patient outcome.

 

Mechanisms of injury
Respiratory Muscle Function Asynchrony may work synergistically with multiple other factors related to critical illness to impose excessive muscle loading on the respiratory muscles. Ventilatory muscle failure occurs when respiratory muscle demand overwhelms respiratory muscle capability. Therefore, additional work of breathing associated with asynchrony may have a negative impact on respiratory muscle function, potentially leading to dyspnea, discomfort and increased time on ventilator.15,([FOOTNOTE=Kallet RH. Patient-ventilator interaction during acute lung injury, and the role of spontaneous breathing: part 1: respiratory muscle function during critical illness. Respiratory care. 2011;56(2):181-189.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203228]),([FOOTNOTE=Branson RD, Blakeman TC, Robinson BR. Asynchrony and dyspnea. Respiratory care. 2013;58(6):973-989.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203221]) Likewise, sustained exposure to excessive muscle loading predisposes patients to structural damage of the respiratory muscles.34
Altered Gas Exchange Patient-ventilator asynchrony may have a negative effect on gas exchange.14
Both double-triggering and delayed cycling may result in incomplete lung emptying and consequent dynamic hyperinflation, which may lead to ventilation-perfusion mismatch, causing hypoxemia and hypercapnia.([FOOTNOTE=Kent BD, Mitchell PD, McNicholas WT. Hypoxemia in patients with COPD: cause, effects, and disease progression. International journal of chronic obstructive pulmonary disease. 2011;6:199-208.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203230])
Auto-triggering may result in hyperventilation, causing hypocapnia and alkalemia.14
Defeating lung protective ventilation In the wake of the ARDSnet trial, lung protective ventilation (lower tidal volumes, ~6-8 mL/kg/min) has become the standard of care for the prevention of additional lung injury in patients with acute respiratory distress syndrome.([FOOTNOTE=Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. The Acute Respiratory Distress Syndrome Network. The New England journal of medicine. 2000;342(18):1301-1308.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=722717])
However, lung protective ventilation in the presence of increased respiratory drive may lead to an increase incidence of double triggering.18 Double-triggering leads to significantly increased tidal volume18, resulting in the delivery of potential harmful volumes.37
Dyspnea and Discomfort Asynchrony is associated with increased dyspnea and discomfort, which may result in sleep disruption and/or increased need for sedation. Both sleep disruption and additional sedation are associated with negative outcomes in mechanically ventilated ICU patients.
Dyspnea Dyspnea results from the increased demand on respiratory muscles required to overcome imposed load. As several types of asynchrony are associated with increased work of breathing,15,31 asynchrony may play a role in the etiology of dyspnea.
Ineffective efforts,18 and flow asynchrony,15 are associated with increased dyspnea.
Schmidt et al. determined that in 35% of patients with dyspnea, ventilator asynchronies were involved in the pathogenesis of dyspnea([FOOTNOTE=Schmidt M, Demoule A, Polito A, et al. Dyspnea in mechanically ventilated critically ill patients. Critical care medicine. 2011;39(9):2059-2065.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203234])
Discomfort Multiple studies have demonstrated a relationship between discomfort and asynchrony
Vitacca et al demonstrated that increasing pressure support level was associated with an increase in both the incidence of ineffective efforts and patient discomfort.18
Vignaux et al determined that an asynchrony index of > 10% was associated with a significant increase in discomfort.11
Sleep Asynchrony has been implicated in sleep disruption.8
Interventions to decrease asynchrony have been demonstrated to increase rapid eye movement (REM) sleep by two-fold and slow wave sleep by three-fold.8
In patients with preexisting pulmonary comorbidity, sleep loss may be associated with decreased pulmonary function, which may delay weaning.([FOOTNOTE=Kamdar BB, Needham DM, Collop NA. Sleep deprivation in critical illness: its role in physical and psychological recovery. Journal of intensive care medicine. 2012;27(2):97-111.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203229])
Sedation In a study by Pohlman et al, asynchrony was responsible for 42% of all increases in sedation.29
Multiple studies have demonstrated that sedation in ICU patients is associated with increased duration of mechanical ventilation, hospital and ICU length of stay, and mortality.([FOOTNOTE=Jackson DL, Proudfoot CW, Cann KF, Walsh T. A systematic review of the impact of sedation practice in the ICU on resource use, costs and patient safety. Critical care (London, England). 2010;14(2):R59.],[ANCHOR=View Abstract],[LINK=/content/covidien/websites/medtronic/com/en/covidien/support/clinical-evidence.html?id=1203226]) (For more information, please visit Evaluate Before You Sedate)

 

 

Reduction of the incidence of patient-ventilator asynchrony requires clinician proficiency in two parallel tasks:

  • Observation of the bedside ventilator waveform in order to identify the presence and type of asynchrony
  • Implementation of the appropriate ventilator adjustment to mitigate the type of asynchrony 
 

 

Table 1. Potential resolutions for each type of asynchrony

 

Asynchrony Type Possible Resolutions
Ineffective Efforts2,13,16,([FOOTNOTE=Tobin M. Principals of mechanical ventilation. 3rd ed. China: McGraw-Hill; 2013],[ANCHOR=],[LINK=]) More sensitive trigger setting
Decrease Pressure Support
Increase flow cycling criteria
Increase PEEP setting
Double Triggering2,16,42 Increase machine Ti
Increase inspiratory flow
Increase tidal volume
Decrease flow cycling criteria
Auto-Triggering2,16,42 Decrease trigger sensitivity
Fix or compensate for system leaks
Flow Asynchrony2,16,42 Adjust flow or flow pattern to match patient demand
Change to pressure-based mode
Assess excessive or depressed drive (if present)
Delayed/Prolonged Cycling2,16,42 Adjust cycling criteria
Decrease PS Support
Assess excessive or depressed drive (if present)

 

Asynchrony-related ventilator adjustments place a significant burden on clinicians. For example, Xirouchaki et al. demonstrated that asynchrony was responsible for 42% of all ventilator adjustments related to clinical deterioration in patients undergoing pressure support ventilation.9 Furthermore, imprecise adjustments may place patients at increased risk for additional asynchrony and impaired breath delivery [see ETIOLOGY]. To lessen this burden, the Puritan Bennett™ 980 ventilator provides a comprehensive solution for the reduction of patient-ventilator asynchrony. Utilization of the PAV™*+ software has been demonstrated to reduce asynchrony and improve patient outcome. [see OUTCOMES]

 

Table 2. Asynchrony Prevention Tool on the Puritan Bennett 980 ventilator

 

Asynchrony Type Synchrony Tool
Ineffective efforts PAV™*+
Auto triggering Leak Sync
Double triggering PAV™*+
Delayed cycling PAV™*+

 

The PAV™*+ software available on the Puritan Bennett™ 980 ventilator assists clinicians in reducing patient-ventilator asynchrony and improving patient outcome.

 

Reducing Asynchrony

Figure 1. Major Asynchrony Events Per hour during sleep (median) in patients ventilated with PAV™*+ software vs. pressure support
(p=0.019)43 [-][+]

Figure 2. Major Asynchrony Events Per hour during wakefulness (median) in patients ventilated with PAV+ vs. pressure support
(p=0.001)43 [-][+]

Figure 3. Autotriggering (n/hr) in patients ventilated with PAV+ vs. pressure support (p<0.05)8 [-][+]

Figure 4. Delayed cycling (n/hr) in patients ventilated with PAV+ vs. pressure support (p<0.05)8 [-][+]

Figure 5. Total Asynchronies (n/hr) in patients ventilated with PAV+ vs. pressure support (p<0.05)8 [-][+]

Figure 6. Expiratory Trigger Delay (Msec) in patients ventilated with PAV+ vs. pressure support (p<0.01)44 [-][+]

Figure 7. Time during which patient and ventilator are in phase (Msec) PAV+ vs. pressure support (p<0.001)44 [-][+]

Improved Sleep

Figure 8. Sleep arousals per hour in patients ventilated with PAV+ vs. pressure support (p<0.05)8 [-][+]

Figure 9. Percentage of rapid eye movement sleep in patients ventilated with PAV+ vs. pressure support (p<0.05)8 [-][+]

Figure 10. Percentage of slow wave sleep in patients ventilated with PAV+ vs. pressure support8 [-][+]

Reduced Effort

Figure 11. Inspiratory effort (pressure time product at the diaphragm per liter) in patients ventilated with PAV+ vs. pressure support
under artificially imposed mechanical load (p<0.05)45 [-][+]

Reduced Workload

Figure 12. Mean number of ventilaor adjustments for clinical deterioration over a 48 hour period (p<0.0001) [-][+]

Figure 13. Failure rate (percentage of patients who required controlled ventilation) in patients ventilated with PAV+ vs. pressure support
(p=0.04)7 [-][+]

Reduced Sedative Administration

Figure 14. Mean number of adjustments in sedative administration due to clinical deterioration over 48 hrs. in patients ventilated with PAV+
vs. pressure support (p=0.015)9 [-][+]