Is VC+ (Volume Control Plus) mode suitable for mechanical ventilator patients with tachypnea (high respiratory rate)?

VC+ Mode for Patients with Tachypnea

VC+ (Volume Control Plus) mode is NOT recommended as the initial ventilator mode for patients with high respiratory rates, and volume-cycled assist-control (AC) ventilation should be used instead. 1

Why AC Mode is Preferred Over VC+ for Tachypnea

The American Thoracic Society explicitly recommends starting with volume-cycled assist-control ventilation when initiating mechanical ventilation, as this provides complete ventilatory support immediately after intubation and ensures a backup respiratory rate that prevents central apneas. 1 This is critical because:

• AC mode guarantees a set number of mandatory breaths per minute while allowing patient-triggered breaths, all delivering the same preset tidal volume. 1, 2
• In tachypneic patients, AC ensures consistent tidal volume delivery with every breath—whether machine-triggered or patient-triggered—preventing the hypoventilation risk that can occur with pressure-based modes. 1

The Problem with VC+ (PRVC) in High Respiratory Rates

VC+ mode, also known as pressure-regulated volume control (PRVC), is a dual-control mode that attempts to deliver a target volume at the lowest possible pressure. However, in high-resistance conditions or when respiratory rates are elevated, PRVC may fail to provide the programmed tidal volume, ultimately leading to hypoventilation. 3

• Experimental data shows that in high-resistance simulations, the delivered volume was significantly lower when using PRVC modes compared to volume control ventilation (VCV). 3
• At high respiratory rates, the shortened expiratory time and increased auto-PEEP create high-resistance conditions where PRVC struggles to deliver adequate volumes. 3
• With tachypnea, the risk of rebreathing increases, especially when respiratory frequency increases, which can exacerbate hypercapnia. 4

Lung-Protective Strategy Regardless of Mode

Regardless of which mode you ultimately use, target 6 mL/kg predicted body weight to reduce mortality in ARDS and sepsis-induced respiratory failure (strong recommendation with high-quality evidence). 1, 5

• Calculate predicted body weight using: Men = 50 + 2.3 × (height in inches - 60); Women = 45.5 + 2.3 × (height in inches - 60). 1, 2
• Maintain plateau pressure ≤30 cmH₂O to prevent alveolar overdistension and ventilator-induced lung injury. 1, 5
• Low tidal volume strategy (6 mL/kg PBW) decreases the risk of systemic cytokine-mediated nonpulmonary organ dysfunction, which may be particularly important in critically ill patients. 4

When PRVC Might Be Considered

PRVC may offer lower work of breathing and improved comfort for patients with increased and variable respiratory demand who are breathing spontaneously. 6 However, this applies to stable patients during weaning, not acute tachypnea requiring initial ventilatory support.

• PCV (and by extension PRVC) offers no advantage over VCV in patients who are not breathing spontaneously, especially when decelerating flow is available during VCV. 6
• In controlled studies comparing PCV and VCV in ARDS patients, no short-term beneficial effect of PCV could be demonstrated over conventional VC with PEEP. 7

Critical Pitfalls to Avoid

• Do not use actual body weight for tidal volume calculations—always use predicted body weight. 1, 5
• Do not assume that pressure-limited modes automatically protect against ventilator-induced lung injury—plateau pressure monitoring is essential regardless of mode. 4
• In tachypneic patients, ensure that exhalation ports or valves are functioning properly, as occlusion can exacerbate hypercapnia through rebreathing. 4
• Monitor for patient-ventilator dyssynchrony closely in tachypneic patients, as even assisted ventilation can induce VILI through generation of high tidal volumes and transpulmonary pressures. 4

Algorithm for Ventilator Mode Selection in Tachypnea

1. Start with volume-cycled AC mode with tidal volume 6 mL/kg PBW and appropriate PEEP. 1
2. Monitor plateau pressures to ensure ≤30 cmH₂O. 1, 5
3. If the patient develops severe dyssynchrony despite optimization of AC settings, consider sedation before switching modes. 4
4. Only after stabilization and during weaning should you consider transitioning to pressure support or PRVC modes. 1