Assist Control (AC) ventilation, also known as Continuous Mandatory Ventilation (CMV), is a mode of mechanical
ventilation where the ventilator delivers a preset number of breaths per minute at a guaranteed tidal volume or
pressure. These breaths can either be initiated by the patient or by the machine itself if the patient fails to
initiate a breath within a set time. It is a commonly used mode in critical care settings for patients who are
unable to sustain adequate spontaneous breathing.
AC ventilation is typically used in patients with severe respiratory distress or failure, such as those
suffering from
Acute Respiratory Distress Syndrome (ARDS), pneumonia, or after major surgeries
requiring mechanical support. It is also used during
anesthesia and in patients who need full
ventilatory support.
In AC ventilation, the ventilator is set to deliver a specific number of breaths per minute (the respiratory
rate) and a predetermined tidal volume or pressure. If the patient initiates a breath, the ventilator assists by
delivering the preset tidal volume or pressure. If the patient does not initiate a breath, the ventilator will
automatically deliver the breaths at the preset rate.
Advantages of Assist Control Ventilation
One of the primary advantages of AC ventilation is that it ensures a minimum level of ventilatory support,
reducing the work of breathing for the patient. It is particularly beneficial for patients who are
critically ill and unable to sustain adequate spontaneous ventilation. Additionally, it allows
for better control of
blood gas levels and can be easily adjusted to meet the changing needs of
the patient.
Disadvantages of Assist Control Ventilation
Despite its advantages, AC ventilation can also have some drawbacks. One of the main concerns is the risk of
barotrauma or volutrauma due to the delivery of preset tidal volumes or pressures, especially if
the patient's lung compliance changes. Moreover, it can lead to respiratory alkalosis if the patient is
hyperventilating. There is also the potential for patient-ventilator dyssynchrony, where the patient's
spontaneous breaths do not align well with the ventilator's cycles.
Nursing Considerations with Assist Control Ventilation
Nurses play a critical role in the management of patients on AC ventilation. Here are some key considerations:
Monitoring: Continuous monitoring of the patient's
respiratory status,
including respiratory rate, tidal volume, and blood gas levels, is essential.
Assessment: Regular assessment of the patient’s lung sounds, chest expansion, and signs of
respiratory distress or dyssynchrony is crucial.
Adjustments: Collaborate with the respiratory therapist and physician to make necessary
adjustments to the ventilator settings based on the patient's condition.
Comfort: Ensure the patient's comfort by managing pain, anxiety, and providing
sedation if necessary.
Education: Educate the patient and family about the purpose and function of AC ventilation
to alleviate anxiety and improve cooperation.
Prevention: Implement strategies to prevent complications such as ventilator-associated
pneumonia (VAP), including proper oral care and head-of-bed elevation.
Conclusion
Assist Control ventilation is a vital tool in the management of patients with severe respiratory conditions.
While it offers significant benefits in terms of ensuring adequate ventilation and reducing the work of
breathing, it also requires careful monitoring and management to prevent potential complications. Nurses play an
instrumental role in the successful implementation of AC ventilation, ensuring that patients receive optimal
care and support during their critical illness.
