Ventilator Reference Library
Comprehensive guide to ventilator modes and waveform analysis.
Volume Control Ventilation (VCV / AC-VC)
Mechanism
The ventilator delivers a preset tidal volume at a set rate. If the patient triggers a breath, they receive the full preset tidal volume.
Indications
Initial mode for most critically ill patients requiring full ventilatory support.
Advantages
Guarantees a specific minute ventilation and tidal volume.
Limitations
Peak inspiratory pressures can vary greatly. Can lead to patient-ventilator asynchrony if the patient's flow demand is higher than set flow.
Pressure Control Ventilation (PCV / AC-PC)
Mechanism
The ventilator delivers a breath at a preset inspiratory pressure for a preset inspiratory time.
Indications
Patients with poor lung compliance (ARDS) to limit peak alveolar pressures and prevent barotrauma.
Advantages
Limits peak pressures, preventing barotrauma. Better flow synchronization as the flow is decelerating and variable based on patient demand.
Limitations
Tidal volume is variable. Minute ventilation is not guaranteed and can drop if lung compliance worsens.
Synchronized Intermittent Mandatory Ventilation (SIMV)
Mechanism
Delivers a set number of mandatory breaths synchronized with the patient's effort, but allows the patient to take spontaneous, unsupported (or pressure-supported) breaths in between.
Indications
Weaning, or for patients who need partial support.
Advantages
Prevents breath stacking. Exercises respiratory muscles.
Limitations
May increase work of breathing if mandatory rate is too low. Generally falling out of favor compared to PSV for weaning.
Pressure Regulated Volume Control (PRVC)
Mechanism
A dual-control mode. The ventilator attempts to achieve a target tidal volume by automatically adjusting the inspiratory pressure breath-by-breath.
Indications
Patients whose compliance is changing rapidly, to guarantee volume while minimizing pressure.
Advantages
Combines the benefits of VCV (guaranteed volume) and PCV (decelerating flow, pressure limit).
Limitations
If patient effort increases significantly, the ventilator may paradoxically decrease support to maintain the target volume, causing air hunger.
Pressure Support Ventilation (PSV)
Mechanism
A purely spontaneous mode. Every breath is initiated and terminated by the patient, but the ventilator provides a set pressure during inspiration to overcome airway resistance.
Indications
Weaning trials (SBTs), overcoming endotracheal tube resistance in spontaneously breathing patients.
Advantages
Very comfortable for the patient. Allows patient to control rate, inspiratory time, and tidal volume.
Limitations
No backup rate. Patient must have a reliable respiratory drive.
Airway Pressure Release Ventilation (APRV)
Mechanism
Inverse ratio ventilation using two levels of CPAP (Phigh and Plow) with brief releases to Plow to facilitate CO2 clearance.
Indications
Severe ARDS failing conventional lung-protective ventilation.
Advantages
Maximizes mean airway pressure for oxygenation (alveolar recruitment) while allowing spontaneous breathing.
Limitations
Complex to manage. Requires an expert team. High risk of pneumothorax if not carefully monitored.