Ventilator Modes Made Easy Vector

Ventilator Modes Made Easy: An Overview (2024)

by | Updated: Mar 14, 2024

Mechanical ventilation is a form of life support that uses positive pressure to help patients who are unable to breathe on their own.

A ventilator mode is a specific setting on the machine that determines the characteristics of the breaths delivered to the patient.

This guide provides a comprehensive overview of the most common ventilator modes and their uses, explaining how each mode functions and the clinical situations in which it is most appropriately applied.

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What is a Ventilator Mode?

A ventilator mode is a set of parameters that determines how a mechanical ventilator supports a patient’s breathing. These parameters include the timing, volume, and pressure of breaths delivered to the patient, allowing for customization based on the patient’s respiratory needs and condition.

Ventilator Modes Vector Illustration

Primary Control Variables

Mechanical ventilation operates through two primary control variables:

  1. Volume control (VC)
  2. Pressure control (PC)

Volume Control

In volume control (VC) ventilation, the operator presets a specific volume of air to be delivered to the patient.

The volume remains constant, leading to fluctuations in the patient’s peak inspiratory pressure (PIP), influenced by their lung compliance and airway resistance.

The primary benefit of VC is its ability to maintain consistent minute ventilation, ensuring stable gas exchange by regulating the total volume of air entering and exiting the lungs per minute.

Pressure Control

Pressure control (PC) ventilation involves setting a predetermined pressure level, controlled by the operator.

In this mode, the pressure remains constant, but the volume of air the patient receives during each breath can change, depending on their lung compliance and airway resistance.

The primary advantage of PC is its lung-protective nature, preventing overdistension and potential damage by limiting the maximum pressure applied to the lungs, thereby reducing the risk of barotrauma and ventilator-induced lung injuries.

Summary: Volume control and pressure control represent the primary control variables in mechanical ventilation. The choice of control variable is the first step in the initiation of mechanical ventilation. Subsequently, selecting a specific operational mode determines the nature and extent of respiratory support provided to the patient.

Primary Ventilator Modes

The two primary modes of mechanical ventilation include:

  1. Assist/control (A/C)
  2. Synchronous intermittent mandatory ventilation (SIMV)


In assist/control (A/C) mode, the ventilator delivers a predetermined number of mandatory breaths and simultaneously permits the patient to initiate additional assisted breaths.

In this scenario, when the patient attempts to breathe, the machine actively supports the breath with positive pressure.

A/C mode provides full ventilatory support, making it a common choice during the initial phase of mechanical ventilation, as it significantly reduces the patient’s respiratory effort.

One potential issue with A/C mode is hyperventilation, which can lead to respiratory alkalosis if the patient receives too many breaths.

Synchronous Intermittent Mandatory Ventilation

The synchronous intermittent mandatory ventilation (SIMV) mode delivers a preset number of mandatory breaths but allows the patient to initiate spontaneous breaths in between the mandatory breaths.

By enabling spontaneous breathing, SIMV facilitates the patient’s contribution to their own minute ventilation, making it suitable for those requiring partial respiratory support.

This mode is beneficial for preserving respiratory muscle strength and preventing muscular atrophy.

Additionally, SIMV promotes a more uniform distribution of tidal volumes across the lung fields, minimizing V/Q mismatch and effectively reducing the mean airway pressure.

Types of Ventilator Modes Illustration

Spontaneous Ventilator Modes

Spontaneous ventilator modes are those used when a mechanically ventilated patient is capable of initiating breaths on their own.

These modes support the patient’s spontaneous breathing efforts to varying degrees.

The primary types include:

  1. Continuous positive airway pressure (CPAP)
  2. Pressure support ventilation (PSV)
  3. Volume support (VS)

Continuous Positive Airway Pressure

In continuous positive airway pressure (CPAP), a constant level of pressure above atmospheric pressure is maintained throughout the entire breathing cycle.

This mode requires the patient to breathe spontaneously, as the ventilator does not deliver mandatory breaths.

CPAP is particularly useful for weaning patients off mechanical ventilation, as it can help maintain airway pressure and improve oxygenation without completely taking over the breathing process.

Pressure Support Ventilation

Pressure support ventilation (PSV) supports the patient’s spontaneous breaths by providing a preset level of pressure during the inspiratory phase.

When the patient initiates a breath, the ventilator assists by adding positive pressure to ease the breathing effort.

The breaths in PSV are time-cycled and pressure-limited, meaning the duration of the support and the maximum pressure are predetermined.

PSV is often used for weaning because it helps patients overcome the resistance of the breathing circuit, including the endotracheal tube.

Volume Support

In volume support (VS), the ventilator delivers supported breaths to help the patient achieve a set tidal volume.

The level of inspiratory pressure support varies with each breath to meet the target tidal volume, depending on the patient’s effort.

VS mode is less common than PSV and CPAP but is used in certain situations, such as weaning patients from anesthesia.

Other Modes of Mechanical Ventilation

The modes of mechanical ventilation that go beyond the primary and spontaneous ventilator modes are designed for specific clinical situations.

These modes offer a range of functionalities to cater to the unique respiratory needs of patients.

This includes:

  • Continuous Mandatory Ventilation (CMV)
  • Airway Pressure Release Ventilation (APRV)
  • Mandatory Minute Ventilation (MMV)
  • Inverse Ratio Ventilation (IRV)
  • Pressure Regulated Volume Control (PRVC)
  • Proportional Assist Ventilation (PAV)
  • Adaptive Support Ventilation (ASV)
  • Adaptive Pressure Control (APC)
  • Volume-Assured Pressure Support (VAPS)
  • Neurally Adjusted Ventilatory Assist (NAVA)
  • Automatic Tube Compensation (ATC)
  • High-Frequency Oscillatory Ventilation (HFOV)

Continuous Mandatory Ventilation

Continuous mandatory ventilation (CMV) is a mode in which the ventilator takes full control of the patient’s breathing by delivering a preset tidal volume at a specific, time-triggered frequency.

This mode is predominantly used for patients who are fully sedated and have received neuromuscular blocking agents.

The primary concern with CMV is the total dependence of the patient on the ventilator, which necessitates careful monitoring to prevent accidental disconnection or machine failure.

Airway Pressure Release Ventilation

Airway pressure release ventilation (APRV) is a mode designed to enhance oxygenation and treat refractory hypoxemia.

It operates by applying two levels of continuous positive airway pressure, with an intermittent release phase allowing for spontaneous breathing.

This mode is particularly beneficial in managing patients with acute lung injuries, acute respiratory distress syndrome (ARDS), and severe atelectasis.

The primary objective is to improve oxygenation while maintaining spontaneous breathing, thereby promoting lung protection and patient comfort.

Mandatory Minute Ventilation

Mandatory minute ventilation (MMV) is an adaptive feature found in some ventilator models. It ensures a minimum level of minute ventilation by automatically adjusting the frequency of mandatory breaths based on the patient’s spontaneous respiratory effort.

If the patient’s spontaneous breathing decreases, leading to inadequate ventilation, the MMV feature compensates by increasing the ventilator support.

This mode is typically used as an adjunct to other modes like SIMV to prevent hypoventilation and ensure stable gas exchange.

Inverse Ratio Ventilation

Inverse ratio ventilation (IRV) is a specialized mode where the I:E ratio is reversed, meaning the inspiratory phase is longer than the expiratory phase.

This uncommon approach is primarily used to improve oxygenation and gas exchange in patients with severe respiratory conditions like acute respiratory distress syndrome (ARDS).

IRV increases the mean airway pressure and alveolar recruitment, reducing shunting and dead space ventilation, thus improving the V/Q mismatch.

However, it’s essential to monitor patients closely as IRV can lead to increased intrathoracic pressure, potentially affecting cardiac output and causing auto-PEEP.

Pressure Regulated Volume Control

Pressure regulated volume control (PRVC) is a mode that combines the benefits of both volume control and pressure control ventilation.

It delivers breaths that are volume-cycled but uses a feedback system to adjust the inspiratory pressure for each breath.

The goal is to deliver the set tidal volume at the lowest possible pressure, thus minimizing the risk of lung injury.

PRVC adjusts the flow rate and inspiratory time dynamically based on the patient’s lung mechanics and is particularly useful for patients with varying respiratory compliance and resistance, ensuring lung-protective ventilation while maintaining adequate gas exchange.

Proportional Assist Ventilation

Proportional assist ventilation (PAV) is an advanced mode that provides assistance proportional to the patient’s spontaneous breathing effort.

The ventilator assists with variable levels of pressure support, adapting in real-time to the patient’s inspiratory demand.

The level of assistance changes with the patient’s respiratory mechanics, thus mimicking the natural variability of human breathing.

PAV is particularly beneficial for patients in the weaning phase of mechanical ventilation, as it can improve patient-ventilator synchrony and reduce the work of breathing.

However, careful monitoring is required to ensure that the assistance provided matches the patient’s needs, preventing issues like over-assistance leading to hyperventilation or under-assistance resulting in respiratory muscle fatigue.

Adaptive Support Ventilation

Adaptive support ventilation (ASV) is a mode that automatically adjusts ventilatory support based on the patient’s respiratory needs.

It’s a form of ventilation in which the ventilator continuously monitors various patient parameters, such as tidal volume, respiratory rate, and airway pressure, and then adjusts the ventilation support accordingly.

The primary goal of ASV is to optimize patient comfort and gas exchange while minimizing the risk of ventilator-induced lung injuries.

It’s particularly useful for patients with rapidly changing respiratory mechanics, as it adapts to ensure consistent and adequate ventilation.

Adaptive Pressure Control

Adaptive pressure control (APC) is a mode that combines the principles of pressure control ventilation with advanced monitoring and adaptive algorithms.

It aims to deliver a target tidal volume by automatically adjusting the inspiratory pressure based on the patient’s lung compliance and resistance.

This mode ensures that the patient receives the necessary ventilation with minimal pressure, reducing the risk of barotrauma and ventilator-induced lung injury.

APC is beneficial for patients who require precise control of tidal volume and pressure, offering a balance between ensuring adequate gas exchange and protecting the lungs from excessive stress.

Volume-Assured Pressure Support

Volume-assured pressure support (VAPS) is a ventilatory mode that guarantees a certain tidal volume while providing pressure support ventilation.

It combines the advantages of both volume-controlled and pressure-controlled ventilation by assuring a preset volume is delivered even as it adjusts the pressure support level to meet the patient’s demand.

VAPS is particularly helpful for patients with irregular breathing patterns or those who have a fluctuating respiratory drive.

It ensures a consistent tidal volume delivery, improving gas exchange and reducing the work of breathing, while also being flexible enough to accommodate the patient’s spontaneous breathing efforts.

Neurally Adjusted Ventilatory Assist

Neurally adjusted ventilator assist (NAVA) is a unique mode of ventilation that uses the electrical activity of the diaphragm (EAdi) to control the ventilator.

A specialized catheter with electrodes is placed near the diaphragm to capture its electrical activity, and the ventilator assists the breathing in proportion to this signal.

This results in a more physiologically natural breathing pattern, ensuring better synchrony between the patient and the ventilator.

NAVA is particularly beneficial for improving patient-ventilator interaction, reducing the risk of over-assistance and under-assistance, and is considered useful in weaning patients from mechanical ventilation, especially those with complex respiratory patterns or neuromuscular disorders.

Automatic Tube Compensation

Automatic tube compensation (ATC) is technically not a standalone ventilator mode but a supportive feature available in some ventilators.

It compensates for the resistance imposed by the endotracheal tube during spontaneous breathing, making it feel as if the patient is breathing without an artificial airway.

This feature is especially useful during the weaning process, as it helps to overcome the additional work of breathing caused by the presence of the tube, thereby improving patient comfort and potentially expediting the weaning process.

High-Frequency Oscillatory Ventilation

High-frequency oscillatory ventilation (HFOV) is a highly specialized ventilator mode that delivers very small tidal volumes at extremely high frequencies (rates), reducing the risk of lung injury associated with larger tidal volumes.

HFOV is particularly useful in treating patients with severe hypoxemia and those who have not responded well to conventional mechanical ventilation strategies.

It’s known for its ability to improve oxygenation while minimizing lung injury by maintaining constant mean airway pressures and reducing the cyclic opening and closing of alveoli.

Adjustments in HFOV settings, like frequency and amplitude, can significantly affect gas exchange and are tailored based on the patient’s specific needs and responses to the therapy.

This mode is also useful in supporting neonates with conditions such as congenital diaphragmatic hernia, diffuse alveolar disease, and pulmonary hypoplasia.

Ventilator Modes Practice Questions

1. Positive pressure ventilators are controlled by what?
Pressure or volume

2. What type of mechanical ventilation involves the chest cuirass or iron lung?
Negative pressure

3. List the common modes of positive pressure ventilation from the most support to the least support:

4. What is an advantage of volume-controlled modes?
They ensure minimal minute ventilation.

5. What are the disadvantages of volume-controlled mode?
The pressure is variable, barotrauma is possible, and the volume is limited by the high-pressure alarm.

6. What is an advantage of a pressure-limited mode?
There is less risk of barotrauma.

7. What are the disadvantages of pressure-controlled modes?
This type of mode doesn’t ensure minute ventilation, and the tidal volume is variable.

8. What two things are variable in pressure-controlled modes?
The volume, which is dependent on a set pressure, and the flow.

9. What are the four types of triggers?
Time, patient, pressure, and flow.

10. What control is used to adjust a patient’s inspiratory effort?

11. What are the two types of sensitivity controls?
Pressure and flow

12. What is controlled mandatory ventilation (CMV)?
A ventilator mode that is time-triggered, gives machine breaths, and is volume or pressure-cycled.

13. What are the indications for CMV?
The need to have total control of chest expansion and minute ventilation.

14. What are some complications of CMV?
The patient is totally ventilator-dependent, alarms are essential, you may be unable to assess weaning, and seizures may interrupt the delivery of a breath.

15. What are some indications for the A/C mode?
The patient needs full ventilatory support, the need to support a high minute ventilation with low oxygen consumption, and the need for sedation after intubation.

16. What is an advantage of the A/C mode?
It keeps the patient’s work of breathing requirement low.

17. What is the IMV mode?
It was the first widely used ventilator mode that allowed partial ventilatory support. It facilitates weaning and increases respiratory muscle strength, but is not widely used today.

18. What are some complications of the IMV mode?
Breath stacking, a spontaneous effort immediately followed by a mechanical breath, which leads to increased PIP, barotrauma, and cardiac compromise.

19. What is the primary indication for the SIMV mode?
It is indicated for patients who need partial ventilatory support.

20. What happens if the rate is set high in the SIMV mode?
This would provide full ventilatory support because SIMV with no spontaneous rate is essentially the same as A/C.

21. What happens if the rate is set low in the SIMV mode?
It facilitates weaning, strengthens the respiratory muscles, and decreases the mean airway pressure, making spontaneous breaths have a lower peak pressure than mandatory breaths.

22. What are some complications of the SIMV mode?
A low rate can increase the patient’s work of breathing causing respiratory muscle fatigue.

23. What mode has a positive baseline pressure continuously applied to the circuit and airway during both inspiration and expiration?

24. In which mode does the ventilator deliver a time-triggered breath and allow the patient to breathe at their own tidal volume between mechanical breaths?

25. In which mode does the ventilator deliver a set tidal volume or pressure at a time-triggered rate, but the patient can trigger a mechanical breath above the preset rate?
Assist/control (A/C)

26. In which mode can the patient not trigger a mechanical or spontaneous breath, and there is no negative deflection on the ventilator graphics?
Continuous mandatory ventilation (CMV)

27. Which mode requires the patient to be spontaneously breathing, have adequate lung function to maintain normal PaCO2, and not be at risk for hypoventilation?

28. What does pressure support do?
It augments spontaneous tidal volume, decreases spontaneous respiratory rate, and reduces the patient’s work of breathing.

29. How does pressure support decrease the patient’s spontaneous respiratory rate?
An increased volume decreases the need for a high respiratory rate in order to achieve the required minute ventilation. Also, it decreases deadspace ventilation.

30. What is the desired respiratory rate during mechanical ventilation?
Less than 25

31. What is tidal volume dependent upon in a pressure support mode?
It is dependent on the set inspiratory pressure, lung compliance, and airway resistance.

32. What makes flow variable in pressure support?
It’s dependent upon the flow needed to maintain the plateau pressure.

33. CPAP with pressure support is essentially what?

34. Is PEEP a standalone mode on ventilation?

35. What are some of the positive effects of PEEP?
It helps recruit alveoli and increases the FRC, alveolar surface area, and oxygenation.

36. What are some complications of PEEP?
Cardiac compromise, increased intrathoracic pressure, decreased venous return, decreased cardiac output, and decreased blood pressure

37. What is an indication for PEEP?
Refractory hypoxemia

38. Is inverse ratio ventilation (IRV) a volume-controlled or pressure-controlled mode?
IRV is a pressure-controlled mode.

39. During mechanical ventilation, a long inspiration and short expiration causes what?
It causes air trapping, auto-PEEP, and prevents alveolar collapse.

40. What is auto-PEEP?
It is air trapping that occurs when there is an incomplete expiration.

41. What are some complications of IRV?
Barotrauma, requires paralysis sedation, and cardiovascular compromise

42. When is mandatory minute ventilation activated?
MMV is activated when the patient’s spontaneous breathing is less than the minimum set minute ventilation. When this occurs, the ventilator increases ventilation.

43. What are some advantages of MMV?
It promotes spontaneous breathing, requires minimal support, protects against hypoventilation and respiratory acidosis, and permits weaning while compensating for apnea.

44. What are some indications for pressure control?
It is indicated for patients with low lung compliance, high PIP during volume-controlled ventilation, and in patients with ARDS.

45. What are some advantages of pressure-controlled ventilation?
In PCV, the PIP is lower while maintaining adequate oxygenation and ventilation. There is also a lower risk of barotraumas.

46. Which mode of mechanical ventilation can provide a precise I:E ratio?
Continuous mandatory ventilation

47. APRV is inappropriate for what type of patient?
It should not be used in patients with an inadequate spontaneous respiratory rate.

48. When does APRV resemble IRV?
APRV resembles IRV when the expiratory pressure release time is less than the spontaneous effort.

49. Why is APRV a beneficial alternative to IRV?
Because it does not require paralytic medications.

50. What is HFOV?
It is a mode of ventilation that stands for high-frequency oscillatory ventilation. It reduces the risk of lung destruction by keeping alveoli open at a constant pressure. It oscillates very rapidly and provides a high respiratory rate at very small tidal volumes.

51. What is amplitude in HFOV?
It refers to the change in stroke volume and the force delivered by the piston. Adjusting the amplitude setting helps control the patient’s ventilation.

52. What are the trigger variables for VC/SIMV?
Time, volume, and pressure.

53. What is the limit variable for VC/SIMV?

54. What is the definition of CMV?
CMV stands for controlled mandatory ventilation and is a ventilator mode used in sedated, apneic, or paralyzed patients. All breaths are triggered, limited, and cycled by the ventilator. The patient has no ability to initiate their own breaths.

55. What is the definition of SIMV?
SIMV stands for synchronized intermittent mandatory ventilation and is a ventilator mode that provides assisted support that is synchronized with the patient’s breathing. The ventilator senses when the patient is taking a breath and then helps deliver the breath. Spontaneous breathing by the patient can occur between the assisted mechanical breaths, which occur at preset intervals. If the patient fails to take a spontaneous breath, the ventilator will provide a mechanical breath.

56. When is the SIMV mode preferred?
It is preferred when the patient has an intact respiratory drive.

57. How is SIMV similar to CPAP and BIPAP?
They use breaths that are spontaneously triggered by the patient.

58. How does the trigger in assist/control ventilation work?
It can be time-triggered or initiated by the patient.

59. What is the preferred ventilator mode for patients in respiratory distress?

60. Which mode can be used in ARDS, paralyzed, or sedated patients?

Final Thoughts

The various modes of mechanical ventilation play an essential role in the management of patients who require breathing support.

The choice of a particular mode depends on the patient’s respiratory status and the clinical objectives, such as improving oxygenation or weaning from the ventilator.

Therefore, understanding and utilizing ventilator modes effectively is a key aspect of patient care in critical care settings.

John Landry, BS, RRT

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.


  • Clinical Application of Mechanical Ventilation. 4th ed., Cengage Learning, 2013.
  • Pilbeam’s Mechanical Ventilation: Physiological and Clinical Applications. 6th ed., Mosby, 2015.
  • Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020.
  • Advanced modes of mechanical ventilation and optimal targeting schemes. Intensive Care Medicine Experimental. Matthias van der Staay and Robert L. Chatburn, 2018.

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