What are the different ventilation (vent) modes?

Ventilation Modes: A Comprehensive Guide

Ventilation modes should be selected based on the patient's underlying pathophysiology, with pressure-controlled modes generally preferred in pediatric patients to minimize barotrauma risk while ensuring adequate gas exchange. 1

Basic Ventilation Modes

Volume-Controlled Ventilation

• Assist-Control Ventilation (ACV/VC-CMV)
  • Delivers set tidal volume with each breath
  • Provides backup rate if patient doesn't trigger
  • Benefits: Guarantees minute ventilation
  • Drawbacks: Risk of barotrauma, less comfortable for awake patients 2
  • Best for: Initial ventilation in critically ill patients 3

Pressure-Controlled Ventilation

• Pressure Control (PC)

  • Delivers set inspiratory pressure for fixed time
  • Tidal volume varies based on lung compliance
  • Benefits: Limits peak airway pressure, may reduce barotrauma
  • Drawbacks: Variable tidal volumes
  • Best for: Patients with poor lung compliance, pediatric patients 1

• Pressure Support Ventilation (PSV)

  • Patient-triggered, pressure-limited, flow-cycled mode
  • Patient controls respiratory rate and inspiratory time
  • Benefits: More comfortable, better patient-ventilator synchrony 2
  • Drawbacks: Risk of central apneas during sleep if excessive support 1
  • Best for: Weaning, awake patients, NIV 1

• Bi-level Positive Airway Pressure (BiPAP/BPAP)

  • Provides IPAP (inspiratory) and EPAP (expiratory) pressures
  • Can be used with or without backup rate (ST mode)
  • Benefits: Simpler, cheaper, more flexible than other ventilators 1
  • Best for: NIV, initial setup of acute NIV service 1

Advanced Ventilation Modes

Hybrid Modes

• Pressure-Regulated Volume Control (PRVC)

  • Volume-targeted, pressure-controlled mode
  • Automatically adjusts pressure to achieve target volume
  • Benefits: Combines advantages of volume and pressure modes
  • Less comfortable than PSV for awake patients 2

• Volume-Assured Pressure Support (VAPS/AVAPS)

  • Pressure support with volume guarantee
  • Benefits: Ensures minimum tidal volume while maintaining pressure limits
  • Useful for: Obesity hypoventilation syndrome, neuromuscular disease 1

Proportional Modes

• Proportional Assist Ventilation (PAV)

  • Delivers pressure proportional to patient effort
  • Benefits: Improved patient-ventilator synchrony, potentially better sleep quality 1
  • Best for: Patients with asynchrony on conventional modes

• Neurally Adjusted Ventilatory Assist (NAVA)

  • Uses diaphragmatic electrical activity to trigger and cycle ventilation
  • Benefits: Improved patient-ventilator synchrony
  • Drawbacks: Requires special nasogastric tube with electrodes

High-Frequency Modes

• High-Frequency Oscillatory Ventilation (HFOV)
  • Delivers very small tidal volumes at high frequencies (3-15 Hz)
  • Benefits: May reduce ventilator-induced lung injury
  • Drawbacks: No mortality benefit shown in AHRF 1
  • Consider when conventional ventilation fails, using open lung strategy 1

Mode Selection Based on Pathophysiology

Healthy Lungs

• Initial mode: Volume-cycled ventilation in assist-control mode
• Settings: Tidal volume 6 mL/kg PBW, plateau pressure ≤30 cmH2O 3
• Target: SpO2 ≥95%, PCO2 35-45 mmHg 1

Obstructive Airway Disease (Asthma, COPD)

• Preferred mode: Pressure support or pressure control
• Considerations:
  • Set sufficient EPAP (4-5 cmH2O) to overcome intrinsic PEEP 1
  • Avoid excessive pressure support to prevent central apneas 1
  • Consider longer expiratory times to prevent air trapping
  • NIV can be considered before intubation 1

Restrictive Disease (ARDS, Pulmonary Edema)

• Preferred mode: Volume-controlled with lung-protective strategy
• Settings:
  • Tidal volume 4-8 mL/kg PBW
  • Plateau pressure ≤30 cmH2O
  • Driving pressure (plateau - PEEP) <15 cmH2O 3
  • PEEP based on severity: higher PEEP for severe ARDS 3
• Target: SpO2 92-97% when PEEP <10 cmH2O, 88-92% when PEEP ≥10 cmH2O 1

Neuromuscular Disease

• Preferred mode: Pressure control or volume control with backup rate
• Considerations:
  • Timed/controlled mode important as respiratory effort may be insufficient to trigger breaths 1
  • Consider NIV in acute exacerbations 1
  • Consider cough-assist devices 1

Practical Considerations for Ventilator Management

Monitoring

• Essential parameters:
  • Peak inspiratory pressure and plateau pressure
  • Mean airway pressure and PEEP
  • Tidal volume and minute ventilation
  • Pressure-time and flow-time scalars 1

Preventing Asynchrony

• Common causes:
  • Trigger asynchrony (missed or auto-triggering)
  • Flow asynchrony (inadequate flow)
  • Cycle asynchrony (premature or delayed cycling)
• Solutions:
  • Adjust trigger sensitivity
  • Optimize flow settings
  • Consider proportional modes (PAV, NAVA) for difficult cases 1
  • Adjust level of assistance to meet patient's demands 1

Weaning Considerations

• Start weaning as soon as possible
• Perform daily extubation readiness testing
• Pressure support mode may be beneficial during weaning 1, 3
• Consider NIV post-extubation in selected patients 1

Pitfalls to Avoid

1. Excessive pressure support causing central apneas during sleep 1
2. Inadequate EPAP in obstructive disease failing to overcome intrinsic PEEP 1
3. Excessive tidal volumes causing ventilator-induced lung injury
4. Poor patient-ventilator synchrony leading to increased work of breathing
5. Delayed recognition of weaning readiness prolonging mechanical ventilation
6. Inappropriate use of home ventilators during acute phase in ICU 1

While there are many ventilation modes available, the choice should be guided by the patient's underlying pathophysiology, with pressure-controlled modes generally preferred in pediatric patients to minimize barotrauma risk. Regular assessment of patient-ventilator synchrony and adjustment of settings based on patient response is essential for optimal outcomes.