When to switch from volume control (VC) to pressure control (PC) on a ventilator?

When to Switch from Volume Control to Pressure Control Ventilation

Switch from volume control (VC) to pressure control (PC) ventilation when transitioning from passive/controlled ventilation to assisted spontaneous breathing as the patient recovers and begins triggering breaths, prioritizing patient comfort and synchrony. 1

Primary Clinical Algorithm for Mode Selection

Start with Volume Control When:

• Initiating mechanical ventilation in acute respiratory failure - VC guarantees fixed tidal volume delivery (6 mL/kg predicted body weight) and allows measurement of plateau pressure and driving pressure, which are essential for lung-protective ventilation 1, 2
• Managing early ARDS - VC facilitates automatic collection of plateau pressure during inspiratory pause, critical for titrating PEEP and assessing lung stress 1
• Plateau pressures exceed 30 cmH₂O - VC is essential when reducing tidal volume from 6 to 4 mL/kg predicted body weight 1
• Compliance or airway resistance changes rapidly - VC better ensures consistent alveolar ventilation when lung mechanics are unstable 3, 1
• Significant air leaks are present - VC compensates better for leaks, though tidal volumes must be increased arbitrarily 3, 1

Switch to Pressure Control When:

• Patient begins spontaneous breathing efforts - PC provides superior respiratory comfort because it does not limit inspiratory flow, allowing the ventilator to match variable patient demand 1, 4
• Work of breathing becomes excessive - PC significantly reduces patient work of breathing (0.59 vs 0.70 J/L) due to higher peak inspiratory flow (103 vs 44 L/min) 4
• Patient comfort is compromised - PC offers better patient-ventilator synchrony during assisted breathing phases 1, 5
• Weaning sedation and allowing spontaneous efforts - This represents the natural transition point from controlled to assisted ventilation 1

Critical Nuances and Monitoring Requirements

When Using Volume Control:

• Monitor plateau pressure continuously - Perform inspiratory hold maneuvers (0.5-1 second pause) to measure static pressure and ensure it remains ≤30 cmH₂O 1, 2
• Calculate driving pressure - Plateau pressure minus PEEP should be kept <15 cmH₂O regardless of mode, as this predicts outcomes 1
• Set appropriate flow patterns - If available, use decelerating flow waveform during VC to achieve similar benefits as PC for oxygenation and peak pressures 6

When Using Pressure Control:

• Accept variable tidal volumes - PC limits maximum airway pressure but tidal volume will vary with changes in compliance and resistance 5, 7
• Monitor for hypoventilation - In severely obstructed patients with high airway resistance, PC may fail to deliver programmed tidal volume, leading to inadequate ventilation 7
• Watch for rebreathing - PC bi-level systems have significant rebreathing potential that worsens hypercapnia, especially when respiratory rate exceeds 20/min 1
• Ensure exhalation ports function properly - Occlusion by sputum can exacerbate hypercapnia through rebreathing 3, 1

Common Pitfalls to Avoid

Don't Switch to PC Too Early:

• During passive ventilation in early ARDS - VC is superior for measuring respiratory mechanics and implementing lung-protective strategies 1
• When ensuring consistent minute ventilation is critical - VC guarantees tidal volume delivery even when lung mechanics change 3, 1

Don't Assume PC is Always Better:

• Both modes achieve equivalent lung protection when tidal volume, plateau pressure, and driving pressure are appropriately managed 1
• For the same tidal volume, there is no outcome advantage between PC and VC in terms of stress and strain generated in the lung 1
• Some patients who fail PC may be successfully treated with VC - particularly "difficult patients" where ensuring alveolar ventilation is crucial 3, 1

Special Consideration for Obese Patients:

• Either mode can be used based on procedural factors, though VC allows better tidal volume control during procedures that intermittently affect chest wall compliance 1

Practical Implementation Strategy

Begin with VC during the acute phase → Monitor plateau pressure, driving pressure, and patient effort → Transition to PC when reducing sedation and allowing spontaneous breathing → Monitor arterial blood gases closely after transition for unexpected hypercapnia → Consider returning to VC if patient fails to maintain adequate ventilation on PC 3, 1