How to manage asynchrony in a ventilated patient?

Managing Patient-Ventilator Asynchrony

Ventilator asynchrony should be systematically addressed by first examining pressure/flow waveforms to identify the specific type of asynchrony, then making targeted ventilator adjustments—prioritizing flow triggers over pressure triggers, optimizing pressure support levels, and setting PEEP to offset intrinsic PEEP without exceeding it. 1

Initial Detection and Assessment

Waveform analysis is essential. Patient-ventilator asynchrony requires careful examination of pressure and flow waveforms displayed on the ventilator 1. The most sensitive detection method involves simultaneous recordings of diaphragm electrical activity and esophageal pressure changes, though this is not routinely available 1.

Key Types to Identify:

• Ineffective triggering: Patient inspiratory efforts that fail to trigger the ventilator, often due to intrinsic PEEP (iPEEP) acting as an inspiratory threshold load 1
• Delayed triggering: Lag between patient effort and ventilator response 1
• Premature or delayed cycling: Mismatch in the transition from inspiration to expiration 2
• Flow asynchrony: Inadequate flow delivery during inspiration 2

Systematic Management Approach

Step 1: Optimize Trigger Settings

Use flow triggers instead of pressure triggers as they reduce the incidence of asynchrony 1. Flow sensors detect changes in machine-produced bias flow and generally provide better patient comfort 1.

Step 2: Address Intrinsic PEEP in Obstructive Disease

In patients with COPD or airflow obstruction:

• Set EPAP/PEEP to offset intrinsic PEEP (typically 3-5 cm H₂O), which reduces the effort required to trigger a breath and improves patient comfort 1
• Critical warning: Setting PEEP greater than intrinsic PEEP can be harmful and worsen hyperinflation 1, 3
• Intrinsic PEEP in severe COPD may reach 10-15 cm H₂O, but EPAP levels >5 cm H₂O are rarely tolerated 1
• Prolong expiratory time to reduce dynamic hyperinflation and gas-trapping 1

Step 3: Adjust Pressure Support Appropriately

Inadequate pressure support causes increased respiratory rate and patient distress 1. Titrate pressure support upward while monitoring:

• Patient comfort and respiratory rate 1
• Tidal volume delivery 1
• Work of breathing 1

Avoid excessive pressure support, which can cause hyperventilation during sleep, central apneas, and paradoxically worsen asynchrony 1.

Step 4: Consider Ventilator Mode Changes

When standard adjustments fail:

Switch to timed/assist-control mode for patients with:

• Advanced respiratory failure who cease spontaneous effort when "captured" 1
• Neuromuscular disease with insufficient respiratory effort to trigger breaths 1
• Dependence on hypoxic respiratory drive 1

Consider proportional modes (PAV or NAVA):

• Proportional Assist Ventilation (PAV) delivers pressure proportional to inspiratory muscle pressure and has been shown to reduce asynchrony and improve sleep quality 1
• Neurally Adjusted Ventilatory Assist (NAVA) delivers pressure proportional to diaphragmatic electrical activity and minimizes asynchrony 1, 4
• Important caveat: While these modes improve synchrony and comfort, they have not yet demonstrated improved clinical outcomes regarding duration of mechanical ventilation or mortality 1, 5

Step 5: Manage Sedation Strategically

Light sedation with dexmedetomidine preserves sleep-wake cycles and may improve patient-ventilator interaction better than benzodiazepines 1. However:

• Avoid over-sedation, which prolongs mechanical ventilation and ICU stay 1
• Consider sedation protocols targeting higher levels of alertness 1
• In agitated patients, always consider asynchrony as the underlying cause before increasing sedation 1

Disease-Specific Considerations

Obstructive Lung Disease (COPD, Asthma):

• Prioritize prolonged expiratory time 1
• Use modest PEEP (3-5 cm H₂O) to offset iPEEP 1
• Never exceed intrinsic PEEP with applied PEEP 1, 3

Restrictive Disease (Neuromuscular, Chest Wall):

• Adequate tidal volume achievable with relatively low pressures (10-15 cm H₂O) in neuromuscular disease 1
• Higher pressures needed in chest wall disease due to reduced compliance 1
• May require controlled ventilation when triggering is inadequate or tiring 1

ARDS:

• Use low tidal volume strategy (6-8 mL/kg ideal body weight) 1, 4
• Consider lung recruitment with PEEP for persistent hypoxia 1

Monitoring Response

Check patient comfort and respiratory rate immediately after any ventilator adjustment 1. If the breathing rate falls after adjusting pressure support, the support was inadequate 1.

Reassess waveforms continuously to ensure the intervention resolved the specific asynchrony type 1, 5.

Common Pitfalls to Avoid

• Excessive oxygen flow rates (>4 L/min) can cause mask leak and delayed triggering, promoting asynchrony 1
• Ignoring waveforms: Subtle asynchronies are only detectable through waveform examination 1
• Treating agitation with sedation first: Always rule out asynchrony as the cause of agitation before escalating sedation 1
• Setting PEEP too high in obstructive disease: This worsens air trapping rather than helping 1, 3
• Assuming proportional modes automatically improve outcomes: While they reduce asynchrony, clinical outcome benefits remain unproven 1, 5