Which Ventilator Mode Delivers a Preset Tidal Volume? (2025)

When managing patients who require mechanical ventilation, understanding how different ventilator modes function is essential. One key concept is the delivery of a preset tidal volume—the amount of air given to a patient with each breath. This ensures consistent and controlled ventilation, especially in critically ill individuals who cannot breathe effectively on their own.

In this article, we’ll explore which ventilator mode provides a preset tidal volume and why it plays such a crucial role in respiratory care.

Which Type of Ventilator Has a Preset Volume of Air to Be Delivered With Each Inspiration?

A ventilator that delivers a preset volume of air with each inspiration is known as a volume-controlled ventilator or a ventilator operating in volume-controlled mode. In this mode, the machine ensures that a specific tidal volume—determined by the clinician—is delivered to the patient with each breath, regardless of the pressure required to do so.

This provides consistent ventilation and is particularly useful in patients who require precise control of minute ventilation. While it guarantees volume delivery, airway pressures can fluctuate depending on lung compliance and resistance, which may increase the risk of barotrauma in patients with stiff or non-compliant lungs.

Understanding Preset Tidal Volume in Ventilator Modes

Preset tidal volume is a key setting in some ventilator modes, determining how much air is delivered to the patient with each breath. This setting impacts patient care, safety, and the effectiveness of ventilation.

Definition of Preset Tidal Volume

Preset tidal volume refers to a fixed volume of gas that a ventilator delivers to a patient with each mechanical breath. In volume-controlled ventilation modes, clinicians set the desired tidal volume, usually measured in milliliters (mL), and the ventilator ensures that this exact amount is given every cycle.

This feature aims to maintain stable ventilation and support predictable gas exchange, which is essential in critically ill patients. Ventilator alarms are set to alert clinicians if the preset volume is not reached, offering an additional safety check.

Clinical Significance of Tidal Volume Control

Controlling the tidal volume is vital for preventing lung injury. Delivering too high a tidal volume can cause volutrauma, whereas too little results in hypoventilation and poor gas exchange. Setting an appropriate tidal volume helps keep arterial carbon dioxide and oxygen levels within safe ranges.

Precise tidal volume delivery is especially important in patients with acute respiratory distress syndrome (ARDS) where lung-protective strategies rely on low tidal volumes. Consistent volume control also simplifies monitoring and adjustment since changes in minute ventilation are predictable.

Comparison with Pressure-Controlled Ventilation

In pressure-controlled ventilation, the ventilator delivers air until a preset pressure is reached, with the volume delivered varying based on patient lung compliance and airway resistance. This can result in fluctuating tidal volumes if lung mechanics change.

Volume-controlled ventilation guarantees the set tidal volume, making it more reliable for ensuring predictable ventilation. Pressure-controlled modes may provide better comfort for some patients but require close monitoring to avoid dangerously low or excessive volumes if the patient’s pulmonary status alters suddenly.

Common Ventilator Modes Delivering Preset Tidal Volume

Several ventilator modes are designed to consistently deliver a preset tidal volume, ensuring reliable minute ventilation and supporting various patient needs. Differences in how these modes synchronize with patient effort and control breaths are central to understanding their clinical use.

Volume-Controlled Ventilation (VCV)

Volume-controlled ventilation (VCV) delivers a fixed tidal volume with each mechanical breath. The ventilator provides this volume regardless of changes in airway resistance or lung compliance. The inspiratory flow is typically set, and airway pressures will vary based on patient condition.

This mode is widely used in anesthesia and critical care. It ensures a precise tidal volume, which is critical for patients requiring controlled ventilation. The risk of high airway pressures exists if resistance increases or compliance drops.

Alarms for high-pressure limits are essential in VCV. This protects the patient from barotrauma if airway pressures exceed safe thresholds. VCV is best suited for patients not making spontaneous efforts or those unable to maintain adequate ventilation on their own.

Synchronized Intermittent Mandatory Ventilation (SIMV)

Synchronized intermittent mandatory ventilation (SIMV) improves on IMV by synchronizing the delivery of mandatory breaths with the patient’s spontaneous efforts. Each mandatory breath still gives a preset tidal volume, but the ventilator detects when the patient initiates a breath and synchronizes the machine breath with this effort.

SIMV provides better comfort and coordination with the patient’s natural breathing pattern. Spontaneous breaths between mandatory ones are not assisted unless pressure support is added as a separate feature.

SIMV is used widely in weaning due to its flexibility. It helps maintain respiratory muscle strength and can reduce the risk of asynchrony, although careful setting adjustment is needed to avoid fatigue or inadequate ventilation.

Assist-Control Ventilation (A/C)

Assist-Control Ventilation (A/C) delivers a preset tidal volume with every breath, whether the breath is initiated by the ventilator or triggered by the patient. The ventilator is sensitive to spontaneous efforts and delivers a full preset tidal volume with each.

A/C provides complete support for the patient’s ventilation needs while allowing spontaneous initiation of breaths. If the patient does not trigger any breath, the ventilator ensures the set respiratory rate and volume are maintained.

This mode is often used in patients who require full ventilatory support, such as those with severe respiratory failure. Patients at risk of developing respiratory alkalosis or who are prone to hyperventilate may require close monitoring in A/C due to the risk of excessive ventilation.

How Volume-Controlled Modes Work

Volume-controlled ventilator modes deliver consistent tidal volumes with each breath. These modes use set parameters and specific cycling features to achieve reliable ventilation, while clinicians monitor and adjust settings to ensure safety and effectiveness.

Mechanism of Delivering a Set Tidal Volume

Volume-controlled modes function by delivering a preselected tidal volume to the patient with every breath. The operator sets the exact tidal volume (in milliliters), regardless of changes in lung compliance or airway resistance.

A flow rate is chosen, and the ventilator generates the necessary pressure to deliver the set volume within the specified inspiratory time. This method ensures every breath has the same volume, even when the pressure required to achieve this volume changes from breath to breath.

Ventilators automatically compensate for minor leaks in the circuit or slight changes in patient demand. In situations where strict control of minute ventilation is critical, such as during certain surgeries or with specific patient populations, this predictability is advantageous.

Trigger, Limit, and Cycle Variables

Each breath in a volume-controlled mode is triggered either by the ventilator itself (time-triggered) or by the patient’s own effort (patient-triggered). The trigger mechanism determines when the ventilator delivers a breath.

During inspiration, the limit variable is the flow or pressure, but the cycle variable is always volume. This means that the ventilator switches from inspiration to expiration only once the preset tidal volume is delivered.

If the patient inhales faster or slower than the set flow, the ventilator maintains the chosen flow pattern and does not adjust the volume or cycling limits. The constant cycling by volume leads to predictable breath delivery, which is vital for managing certain clinical conditions.

Monitoring and Adjustment in Clinical Practice

Clinicians closely monitor delivered tidal volume, airway pressures, and patient-ventilator synchrony. High peak or plateau pressures can signal changes in lung compliance or increased airway resistance, prompting adjustments in ventilator settings.

Alarm systems alert staff if delivered volumes deviate from target values. Regular assessment ensures that tidal volume is appropriate for patient size and clinical condition, reducing risks like barotrauma or volutrauma.

Adjustments include modifying tidal volume, inspiratory flow rate, or sensitivity settings. This helps optimize oxygenation, reduce patient discomfort, and maintain effective ventilation, especially as patient conditions change during care.

Patient Considerations for Preset Tidal Volume Modes

Preset tidal volume modes in mechanical ventilation are crucial for maintaining specific minute ventilation and supporting patients with varying levels of respiratory drive and lung mechanics.

The choice of these modes requires an understanding of their indications, associated risks, and impact on patient–ventilator interaction.

Indications for Volume Control

Volume control ventilation is used when a stable tidal volume is essential. This includes patients with acute respiratory distress syndrome (ARDS), neuromuscular disorders, or those under deep sedation. Clinicians select this mode to guarantee a minimum level of alveolar ventilation, even if the patient’s lung compliance or airway resistance changes during therapy.

Patients with severe respiratory failure often benefit from volume control modes. These modes are relied upon when reliable carbon dioxide removal is necessary, such as during hypercapnic respiratory failure. Volume control is also preferred if airway protection is compromised or spontaneous breathing efforts are minimal.

Tidal volume settings are based on predicted body weight, especially in patients with ARDS, to reduce lung injury. Careful adjustment and monitoring limit complications associated with inappropriate tidal volumes.

Risks of Barotrauma and Volutrauma

Delivering a preset tidal volume may increase the risk of barotrauma and volutrauma, particularly in patients with reduced lung compliance. Elevated airway pressures, particularly plateau and peak pressures, can cause alveolar overdistension, which may result in air leaks or pneumothorax.

Patients with heterogeneous lung disease are more vulnerable. In these cases, the least compliant regions may be damaged due to uneven distribution of delivered volume. High tidal volumes can increase the risk of ventilator-induced lung injury (VILI).

To reduce these risks, clinicians monitor plateau pressures and lung mechanics closely. Adjustments to tidal volume and positive end-expiratory pressure (PEEP) are made as needed, especially if pressure limits are exceeded or the patient’s clinical status changes.

Patient–Ventilator Synchrony

Preset tidal volume modes sometimes lead to patient–ventilator asynchrony if patient demand or inspiratory effort does not align with ventilator settings. Triggering, cycling, and flow delivery mismatches can occur, leading to discomfort, increased work of breathing, or difficulty weaning from the ventilator.

Patients who are awake or partially breathing on their own are at higher risk for asynchrony. Common signs include visible distress, use of accessory muscles, or irregular ventilator waveforms.

Adjustments to sensitivity, flow rate, or inspiratory time can help improve synchrony. Some patients may benefit from partial support modes or sedation if synchrony cannot be achieved through ventilator adjustments alone. Monitoring ventilator graphics and patient comfort is essential to address these issues promptly.

Advanced Features in Modern Ventilators

Advanced ventilators use sophisticated modes to improve synchrony, comfort, and lung protection. These features allow clinicians to tailor settings based on patient needs, lung mechanics, and disease progression.

Dual Control Ventilation

Dual control ventilation combines aspects of both pressure and volume-controlled modes. The ventilator provides a set tidal volume while adapting the pressure applied in each breath.

During inspiration, the ventilator starts with a pressure target but monitors exhaled tidal volume closely. If the delivered tidal volume falls short or exceeds the set value, the ventilator adjusts inspiratory pressure automatically for the next breath. This compensation helps maintain consistent ventilation with changing lung compliance or resistance.

The mode reduces the risk of volutrauma by limiting excessive tidal volumes. It also offers better comfort than standard volume control modes, as the ventilator responds quickly to patient effort and lung changes. Common labels for these modes include PRVC (Pressure Regulated Volume Control) and VC+ (Volume Control Plus).

AutoFlow and Adaptive Modes

AutoFlow and adaptive modes continuously adapt ventilation to dynamic changes in the patient’s condition. AutoFlow delivers a preset tidal volume with variable flow, automatically adjusting pressure if resistance or compliance changes.

Adaptive modes, such as Adaptive Pressure Ventilation (APV), blend pressure support with guaranteed volumes. These modes predict and adjust to the patient’s demands, fine-tuning inspiratory pressure for each breath while ensuring a minimum volume is delivered.

Both features promote spontaneous breathing by letting patients set their inspiratory flow. This can enhance patient comfort and synchrony, especially for those weaning from mechanical ventilation. They also minimize the risk of airway pressure peaks or breath-stacking.

Limitations and Potential Complications

Preset tidal volume modes can lead to alveolar overdistension if the patient’s lung compliance decreases. This overinflation increases the risk of barotrauma and volutrauma.

Patients with high airway resistance may experience elevated peak airway pressures. This can result in discomfort or hemodynamic instability, especially in those with underlying cardiovascular conditions.

Another limitation is the potential for patient-ventilator asynchrony. If a patient’s spontaneous breathing effort does not align with the ventilator’s cycle, it may cause discomfort or increased work of breathing.

Preset tidal volume does not adjust for changes in lung mechanics. If compliance or resistance suddenly changes, delivered pressures can rise significantly.

There is also a risk of auto-PEEP (positive end-expiratory pressure), particularly in patients with obstructive lung disease. This can compromise venous return and cardiac output.

Some patients may require frequent monitoring for signs of lung injury or ineffective ventilation, especially in acute respiratory distress syndrome (ARDS). Staff may need to adjust ventilator settings frequently to balance lung protection and adequate ventilation.

Weaning Strategies from Preset Tidal Volume Ventilation

Weaning from preset tidal volume modes, such as volume-controlled ventilation, requires careful planning and frequent assessment. The primary goal is to transition the patient to spontaneous breathing while ensuring adequate gas exchange and minimal respiratory distress.

Common weaning strategies include:

• Gradually reducing the set tidal volume or mandatory rate
• Employing spontaneous breathing trials
• Utilizing modes like Pressure Support Ventilation (PSV) for support during the transition

Spontaneous breathing trials are often performed by placing the patient on minimal ventilator support for a set period, typically 30–120 minutes. Continuous assessment of respiratory rate, tidal volume, oxygen saturation, and patient comfort is crucial during this period.

Indicators for successful weaning include stable vital signs, appropriate oxygenation, and the absence of respiratory distress. If signs of fatigue or instability occur, the patient may require continued support or a slower weaning pace.

Clinicians also monitor arterial blood gases and consider underlying conditions that could affect respiratory drive or muscle strength. Effective communication among care team members ensures an individualized approach to each patient’s readiness for extubation.

Phasing out preset tidal volume emphasizes patient safety and adaptability to changes in respiratory status. This process relies on clinical judgment and ongoing evaluation.

Final Thoughts

Selecting the appropriate ventilator mode is vital for optimizing patient outcomes, particularly when precise control over tidal volume is needed.

Volume-controlled ventilation is the mode that ensures a consistent volume of air is delivered with each breath, providing predictable support for patients with compromised respiratory function. By understanding how this mode works and when to use it, clinicians can make informed decisions to enhance patient safety and care.