Pressure-controlled ventilation

Pressure-controlled ventilation (PCV) is a mode of mechanical ventilation where the ventilator switches between inspiration and expiration based on the set inspiratory pressure and time. Unlike volume-controlled ventilation, where the primary goal is to deliver a set volume of air with each breath, PCV aims to deliver breaths by reaching a preset inspiratory pressure. This approach can be particularly beneficial in patients with stiff lungs, such as those with acute respiratory distress syndrome (ARDS), where it can help minimize lung injury by avoiding high ventilatory pressures.

Overview

In pressure-controlled ventilation, the ventilator delivers gas until a preset airway pressure is reached, then maintains this pressure for the duration of the inspiratory time before allowing expiration. The actual volume of gas delivered during each breath can vary, depending on the patient's lung compliance and airway resistance. This mode of ventilation is often used in situations where protecting the lung from high pressures is a priority, as it allows for better control of peak airway pressures.

Indications

PCV is indicated in patients who require mechanical ventilation but are at risk of ventilator-induced lung injury (VILI) due to high ventilatory pressures. This includes patients with:

• Acute Respiratory Distress Syndrome (ARDS)
• Severe asthma
• Pneumonia
• Conditions leading to reduced lung compliance

Advantages

The primary advantage of PCV is the ability to limit peak airway pressures, potentially reducing the risk of barotrauma and volutrauma to the lungs. Other advantages include:

• Improved oxygenation in certain patient groups
• Potentially better distribution of ventilation
• Reduced risk of ventilator-induced lung injury in specific scenarios

Disadvantages

While PCV has its benefits, there are also disadvantages to consider, such as:

• The potential for variable tidal volumes, especially if lung compliance changes
• The need for close monitoring to ensure adequate ventilation and oxygenation
• May not be suitable for patients who require a guaranteed volume delivery

Settings

When setting up a patient on PCV, several parameters must be adjusted, including:

• Inspiratory pressure (above PEEP)
• Inspiratory time
• Positive end-expiratory pressure (PEEP)
• Respiratory rate
• FiO2 (Fraction of inspired oxygen)

Comparison with Volume-Controlled Ventilation

Volume-controlled ventilation (VCV) and PCV are both commonly used modes of mechanical ventilation, but they have key differences. In VCV, the primary goal is to deliver a set volume, which can lead to variable peak pressures, especially in patients with poor lung compliance. In contrast, PCV focuses on limiting peak pressures, which can result in variable tidal volumes.

Clinical Considerations

Clinicians must carefully monitor patients on PCV to ensure they are receiving adequate ventilation (measured by PaCO2 levels) and oxygenation (measured by PaO2 and SpO2 levels). Adjustments to the ventilator settings may be necessary based on the patient's clinical status and blood gas results.

Conclusion

Pressure-controlled ventilation is a valuable mode of mechanical ventilation for patients at risk of lung injury due to high ventilatory pressures. By focusing on limiting peak airway pressures, PCV can offer a safer ventilation strategy for patients with compromised lung function. However, it requires careful monitoring and adjustment to ensure optimal patient outcomes.