What parameters can be adjusted in Pressure Support (PS) mode of a ventilator?

Adjustable Parameters in Pressure Support Ventilation Mode

In pressure support ventilation (PSV) mode, the key adjustable parameters include inspiratory positive airway pressure (IPAP), expiratory positive airway pressure (EPAP), pressure support level, rise time, cycling criteria, trigger sensitivity, and backup rate when using spontaneous-timed mode. 1

Primary Parameters

1. Pressure Settings

• IPAP (Inspiratory Positive Airway Pressure)

  • Range: Minimum starting of 8 cm H₂O, maximum of 30 cm H₂O for adults and 20 cm H₂O for pediatric patients 1
  • Controls the pressure delivered during inspiration
  • Directly affects tidal volume delivery

• EPAP (Expiratory Positive Airway Pressure)

  • Range: Minimum starting of 4 cm H₂O 1
  • Helps maintain airway patency during exhalation
  • Counteracts intrinsic PEEP in COPD patients 1
  • Promotes lung recruitment and stents open the upper airway

• Pressure Support (PS = IPAP - EPAP)

  • Range: Minimum of 4 cm H₂O, maximum of 20 cm H₂O 1
  • Augments ventilation by increasing tidal volume
  • Should be increased if tidal volume is low (<6-8 mL/kg) 1

2. Triggering and Cycling Parameters

• Inspiratory Trigger Sensitivity

  • Determines how easily the patient can initiate a breath
  • Can be flow-triggered or pressure-triggered
  • More sensitive triggers reduce work of breathing 2

• Cycling Criteria (Expiratory Trigger)

  • Range: Can be fixed (typically 5-40% of peak inspiratory flow) or automatically adjusted 3
  • Determines when inspiration ends and expiration begins
  • Adjustable cycling improves patient-ventilator synchrony 3

• Rise Time (Pressurization Rate)

  • Controls how quickly the ventilator reaches the set pressure support level
  • Shorter rise times reduce inspiratory work of breathing 4
  • Adjustable on most current-generation ventilators 5

3. Backup Parameters (for Spontaneous-Timed Mode)

• Backup Rate

  • Starting rate: Equal to or slightly less than spontaneous sleeping respiratory rate (minimum 10 breaths/min) 1
  • Provides mandatory breaths if patient fails to trigger within set time window
  • Essential for patients with central hypoventilation, muscle weakness, or significant central apneas 1

• Inspiratory Time (IPAP Time)

  • Should be set to provide 30-40% of the cycle time 1
  • Calculated as: 60/respiratory rate in breaths per minute

Additional Adjustable Features

1. Supplemental Oxygen

• Can be added when SpO₂ remains <90% despite optimized pressure settings 1
• Starting at 1 L/minute, increased in 1 L/minute increments until SpO₂ >90%

2. Advanced Comfort Settings (Ventilator-Dependent)

• Pressure Relief: Reduces pressure during specific parts of the breath cycle
• Maximum and Minimum IPAP Durations: Limits how long inspiration can last
• Flow Waveform Adjustments: Can improve triggering sensitivity 2

Practical Adjustment Approach

1. Start with appropriate mask interface and initial settings:

   • IPAP: 8-12 cm H₂O
   • EPAP: 4-5 cm H₂O
   • Rise time: Medium setting
   • Cycling: Default setting (usually 25% of peak flow)

2. Adjust EPAP first:

   • Increase to eliminate obstructive events (apneas, hypopneas, snoring)
   • In COPD patients, adjust to overcome intrinsic PEEP (typically 4-5 cm H₂O) 1

3. Adjust pressure support (IPAP-EPAP):

   • Increase if tidal volume is inadequate (<6-8 mL/kg)
   • Increase if PCO₂ remains elevated above goal
   • Increase if respiratory muscle rest is not achieved 1

4. Fine-tune trigger and cycling:

   • Adjust inspiratory trigger sensitivity to minimize effort but avoid auto-triggering
   • Adjust cycling criteria to match neural inspiration termination
   • For obstructive patients: consider higher cycling threshold (40-50%)
   • For restrictive patients: consider lower cycling threshold (10-20%)

5. Consider adding backup rate if:

   • Patient has central hypoventilation
   • Significant central apneas are present
   • Patient has muscle weakness affecting reliable triggering 1

Common Pitfalls and Solutions

• Auto-triggering: Occurs when trigger sensitivity is too high

  • Solution: Decrease trigger sensitivity, check for leaks

• Ineffective triggering: Patient effort fails to trigger breath

  • Solution: Increase trigger sensitivity, adjust EPAP to counteract intrinsic PEEP 1

• Premature cycling: Ventilator cycles to expiration before patient is ready

  • Solution: Decrease cycling threshold (% of peak flow)

• Delayed cycling: Ventilator continues inspiration after patient wants to exhale

  • Solution: Increase cycling threshold, consider shorter inspiratory time

• Excessive leakage: Compromises ventilator performance

  • Solution: Adjust mask fit, consider different interface type

By understanding and appropriately adjusting these parameters, clinicians can optimize patient-ventilator synchrony, minimize work of breathing, and improve patient comfort during pressure support ventilation.