Ventilator Modes Made Easy: An Overview (2025)

Mechanical ventilation is a method of life support that uses positive pressure to assist patients who cannot breathe on their own. A ventilator mode refers to the specific settings on the machine that define how breaths are delivered, including the flow, volume, and pressure.

This guide offers an overview of the most common ventilator modes, describing how they work and the clinical situations in which each is typically used.

What is a Ventilator Mode?

A ventilator mode is a specific setting on a mechanical ventilator that determines how breaths are delivered to a patient. It defines key factors such as whether the breath is controlled by volume or pressure, how much support the machine provides, and how much the patient contributes to their own breathing.

Different modes are designed to meet different clinical needs, from providing full support to allowing partial patient effort. Understanding ventilator modes is important for tailoring therapy to the patient’s condition, ensuring adequate oxygenation and ventilation while minimizing risks like lung injury or respiratory muscle fatigue.

Primary Control Variables

Mechanical ventilation is built on two fundamental control variables:

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

Volume Control

In volume control (VC) ventilation, the operator sets a specific tidal volume to be delivered with each breath. The volume remains constant, while the patient’s peak inspiratory pressure (PIP) varies according to lung compliance and airway resistance.

The major advantage of VC is its ability to ensure consistent minute ventilation, which helps maintain stable gas exchange by precisely controlling the total volume of air entering and leaving the lungs per minute.

Pressure Control

In pressure control (PC) ventilation, the operator sets a predetermined inspiratory pressure. Here, the pressure is fixed, but the delivered tidal volume can vary depending on the patient’s lung compliance and airway resistance.

The key benefit of PC ventilation is its lung-protective nature. By limiting the maximum pressure, it reduces the risk of overdistension, barotrauma, and ventilator-induced lung injury (VILI).

Summary: Volume control and pressure control represent the two primary variables that guide mechanical ventilation. Choosing between them is the first step in the initiation of mechanical ventilation, followed by selecting the most appropriate ventilator mode for the patient’s needs.

Primary Ventilator Modes

Two of the most commonly used ventilator modes are:

1. Assist/Control (A/C)
2. Synchronous Intermittent Mandatory Ventilation (SIMV)

Assist/Control

In assist/control (A/C) mode, the ventilator delivers a preset number of mandatory breaths while also assisting any spontaneous breaths initiated by the patient. When the patient triggers a breath, the machine provides full support with positive pressure.

A/C mode offers complete ventilatory support, making it a standard choice during the early stages of mechanical ventilation. However, one drawback is the risk of hyperventilation and subsequent respiratory alkalosis if the patient receives excessive assisted breaths.

Synchronous Intermittent Mandatory Ventilation (SIMV)

The synchronous intermittent mandatory ventilation (SIMV) mode delivers a set number of mandatory breaths but allows the patient to take spontaneous breaths between them.

This approach encourages patient participation in ventilation, helping preserve respiratory muscle strength and reducing the risk of atrophy. SIMV also promotes better distribution of tidal volumes across the lungs, minimizes V/Q mismatch, and helps maintain lower mean airway pressures.

Spontaneous Ventilator Modes

Spontaneous ventilator modes are used when a patient on mechanical ventilation is capable of initiating their own breaths. These modes provide varying levels of support to assist the patient’s natural breathing efforts, rather than delivering fully mandatory breaths.

The primary spontaneous modes include:

1. Continuous Positive Airway Pressure (CPAP)
2. Pressure Support Ventilation (PSV)
3. Volume Support (VS)

Continuous Positive Airway Pressure (CPAP)

Continuous positive airway pressure (CPAP) maintains a constant pressure above atmospheric level throughout the entire respiratory cycle. The patient must breathe spontaneously, as the ventilator does not initiate mandatory breaths.

CPAP is particularly valuable during weaning from mechanical ventilation. It helps sustain airway pressure, improve oxygenation, and reduce the work of breathing without taking full control of ventilation.

Pressure Support Ventilation (PSV)

Pressure support ventilation (PSV) augments the patient’s spontaneous breaths by applying a preset level of pressure during inspiration. When the patient initiates a breath, the ventilator assists by delivering positive pressure, thereby reducing the effort required to inhale.

In PSV, breaths are pressure-limited and flow-cycled, meaning support ends once inspiratory flow decreases below a set threshold. This makes the breathing pattern more comfortable and patient-driven.

PSV is widely used in the weaning process because it helps patients overcome circuit resistance, particularly that of the endotracheal tube, while still promoting spontaneous effort.

Volume Support (VS)

Volume support (VS) is a pressure-regulated, spontaneous mode in which the ventilator adjusts inspiratory pressure from breath to breath to achieve a target tidal volume.

Unlike PSV, where pressure is fixed, the support level in VS automatically adapts to the patient’s effort. This makes it useful in situations where consistent tidal volumes are desired despite variable effort.

Although less common than CPAP and PSV, VS can be beneficial in select scenarios, such as during weaning from anesthesia or when patients require guaranteed volumes while still breathing spontaneously.

Other Modes of Mechanical Ventilation

Beyond the primary and spontaneous modes, there are additional modes of mechanical ventilation designed for specific clinical scenarios. These modes expand the functionality of modern ventilators, offering targeted strategies to meet the complex needs of critically ill patients.

Key examples include:

• 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 (CMV)

Continuous mandatory ventilation (CMV) delivers a preset tidal volume at a fixed frequency, fully taking over the patient’s breathing. It is primarily used in patients who are deeply sedated or paralyzed with neuromuscular blocking agents.

Because the patient is entirely dependent on the ventilator, CMV requires vigilant monitoring to prevent complications from accidental disconnection or machine malfunction.

Airway Pressure Release Ventilation (APRV)

Airway pressure release ventilation (APRV) alternates between two levels of continuous positive airway pressure with periodic release phases, allowing spontaneous breathing throughout the cycle. It is particularly effective in treating acute lung injury, ARDS, and severe atelectasis.

APRV improves oxygenation, promotes alveolar recruitment, and enhances patient comfort by preserving spontaneous effort while maintaining lung-protective strategies.

Mandatory Minute Ventilation (MMV)

Mandatory minute ventilation (MMV) ensures a preset minimum minute ventilation by automatically delivering additional mandatory breaths if the patient’s spontaneous effort is insufficient.

This adaptive feature is often combined with modes like SIMV to safeguard against hypoventilation while still encouraging spontaneous breathing.

Inverse Ratio Ventilation (IRV)

Inverse ratio ventilation (IRV) reverses the normal inspiratory-to-expiratory (I:E) ratio, prolonging inspiration to increase mean airway pressure and recruit alveoli.

It is reserved for severe cases such as ARDS, where conventional strategies fail. By improving alveolar recruitment and reducing shunting, IRV enhances oxygenation and corrects V/Q mismatch. However, IRV carries risks such as reduced venous return, decreased cardiac output, and auto-PEEP, requiring close hemodynamic monitoring.

Pressure Regulated Volume Control (PRVC)

Pressure regulated volume control (PRVC) combines the safety of pressure control with the reliability of volume control. It delivers a set tidal volume but automatically adjusts the inspiratory pressure on a breath-to-breath basis to achieve it with the lowest pressure possible.

This adaptive strategy provides lung-protective ventilation, especially for patients with fluctuating compliance or resistance, while ensuring consistent gas exchange.

Proportional Assist Ventilation (PAV)

Proportional assist ventilation (PAV) delivers support proportional to the patient’s spontaneous inspiratory effort. Unlike fixed-pressure modes, PAV continuously adapts in real time to match patient demand, enhancing synchrony and reducing the work of breathing.

This makes it particularly useful during the weaning process. However, careful monitoring is essential to avoid over-assistance (leading to hyperventilation) or under-assistance (causing fatigue).

Adaptive Support Ventilation (ASV)

Adaptive support ventilation (ASV) is an intelligent mode that automatically adjusts ventilatory support according to the patient’s needs. The ventilator continuously monitors parameters such as tidal volume, respiratory rate, and airway pressure, then adapts its support in real time.

The goal of ASV is to optimize patient comfort and gas exchange while reducing the risk of ventilator-induced lung injury. It is especially valuable for patients with rapidly changing respiratory mechanics, as it ensures consistent and adequate ventilation without constant manual adjustments.

Adaptive Pressure Control (APC)

Adaptive pressure control (APC) combines the principles of pressure-controlled ventilation with advanced adaptive algorithms. It targets a set tidal volume and automatically adjusts inspiratory pressure based on the patient’s lung compliance and resistance.

By tailoring pressure breath-by-breath, APC delivers the required volume with the lowest possible pressure, lowering the risk of barotrauma and ventilator-induced lung injury. This makes it particularly useful for patients who need precise tidal volume delivery while maintaining lung protection.

Volume-Assured Pressure Support (VAPS)

Volume-assured pressure support (VAPS) merges pressure support with a guaranteed tidal volume. While the ventilator provides pressure support for each spontaneous breath, it ensures that the preset tidal volume is always achieved, adjusting support as needed.

VAPS is especially beneficial for patients with irregular breathing patterns or fluctuating respiratory drive. This mode improves gas exchange, reduces the work of breathing, and accommodates spontaneous efforts while maintaining consistent ventilation.

Neurally Adjusted Ventilatory Assist (NAVA)

Neurally adjusted ventilatory assist (NAVA) is a unique mode that relies on the electrical activity of the diaphragm (EAdi) to guide ventilator support. A specialized catheter with electrodes detects the diaphragm’s signals, and the ventilator delivers assistance proportional to the patient’s neural respiratory drive.

This approach produces a more physiologic breathing pattern, enhancing synchrony between the patient and the ventilator. NAVA is particularly valuable for patients with complex respiratory patterns or neuromuscular disorders, and it can be highly effective during weaning by avoiding both over-assistance and under-assistance.

Automatic Tube Compensation (ATC)

Automatic tube compensation (ATC) is not a true ventilator mode but rather a supportive feature available on some ventilators. It offsets the resistance created by the endotracheal tube, making spontaneous breathing feel as natural as possible, as if the patient were breathing without an artificial airway.

ATC is particularly helpful during weaning, as it reduces the extra work of breathing caused by the tube and enhances patient comfort, potentially accelerating liberation from mechanical ventilation.

High-Frequency Oscillatory Ventilation (HFOV)

High-frequency oscillatory ventilation (HFOV) is a specialized mode that delivers very small tidal volumes at extremely high frequencies.
This strategy minimizes the repetitive opening and closing of alveoli, thereby reducing ventilator-associated lung injury.

HFOV is especially useful in cases of severe hypoxemia or when conventional ventilation has failed. By maintaining constant mean airway pressure, it enhances oxygenation while protecting delicate lung tissue.

It is also a valuable option in neonates with conditions such as congenital diaphragmatic hernia, diffuse alveolar disease, or pulmonary hypoplasia. Careful adjustments to frequency, amplitude, and mean airway pressure allow clinicians to tailor HFOV precisely to the patient’s gas exchange needs.

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:
CMV, A/C, IMV, SIMV, CPAP

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?
Sensitivity

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?
CPAP

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?
SIMV

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?
CPAP

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?
BiPAP

34. Is PEEP a standalone mode on ventilation?
No

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?
Volume

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?
Assist/control

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

61. What happens when sensitivity is set too low on a ventilator?
The patient may not be able to trigger a breath, leading to missed breaths and increased work of breathing.

62. What happens when sensitivity is set too high on a ventilator?
Auto-triggering may occur, causing the ventilator to deliver breaths inappropriately without patient effort.

63. What type of breath is patient-triggered, pressure-limited, and flow-cycled?
Pressure support breath

64. What does flow-cycled mean in pressure support ventilation?
The ventilator cycles to expiration when inspiratory flow drops to a preset percentage of peak flow.

65. Which ventilator mode allows spontaneous breathing with preset pressure support for each breath?
Pressure Support Ventilation (PSV)

66. What parameter primarily determines CO₂ removal in pressure control ventilation?
Respiratory rate

67. What parameter primarily determines oxygenation in pressure control ventilation?
Mean airway pressure

68. In what mode is the I:E ratio typically inverse to improve oxygenation?
Inverse Ratio Ventilation (IRV)

69. Which ventilator mode is most effective for patients with severe hypoxemia who are not responsive to conventional ventilation?
High-Frequency Oscillatory Ventilation (HFOV)

70. How is mean airway pressure affected in IRV?
It is increased due to a prolonged inspiratory time.

71. What is a normal inspiratory flow rate for volume-controlled ventilation in adults?
Typically 40–60 L/min

72. What is the significance of setting a rise time in pressure support ventilation?
It controls how quickly the pressure target is reached during inspiration.

73. What happens if the rise time is set too fast?
It may cause discomfort or sudden pressure spikes.

74. What happens if the rise time is set too slow?
It may lead to patient-ventilator asynchrony and increased work of breathing.

75. What type of cycling is used in pressure support ventilation?
Flow-cycling

76. What is the benefit of synchronized breaths in SIMV mode?
They help reduce patient-ventilator asynchrony.

77. In APRV, what does increasing the T-high do?
It increases mean airway pressure and improves oxygenation.

78. In APRV, what is the purpose of the T-low setting?
To allow brief exhalation and carbon dioxide removal without derecruitment.

79. What is the role of a backup rate in pressure support or CPAP modes?
It provides safety by delivering breaths if the patient becomes apneic.

80. What ventilator mode provides the highest level of spontaneous breathing support without mandatory breaths?
CPAP with pressure support

81. What does it mean when a ventilator breath is volume-cycled?
The breath ends when a preset tidal volume has been delivered.

82. What is the main goal of lung-protective ventilation strategies?
To minimize ventilator-induced lung injury by using low tidal volumes and limiting pressures.

83. In which mode does the patient determine both the rate and the tidal volume, with each breath supported by pressure?
Pressure Support Ventilation (PSV)

84. What parameter is adjusted to increase tidal volume in pressure support mode?
Inspiratory pressure level

85. What is the effect of increasing the inspiratory time in pressure control ventilation?
It can improve oxygenation by increasing mean airway pressure.

86. What is one advantage of SIMV over A/C mode during weaning?
SIMV allows the patient to practice spontaneous breathing between mandatory breaths.

87. What ventilator mode is best suited for neuromuscular disease patients who cannot initiate breaths?
Controlled Mandatory Ventilation (CMV)

88. What is the main difference between SIMV and A/C modes?
SIMV allows spontaneous breaths between mandatory breaths; A/C does not.

89. Why might CPAP be contraindicated in a lethargic patient with poor respiratory drive?
Because it requires the patient to maintain spontaneous ventilation.

90. What does dual control mode combine?
It combines features of pressure control and volume targeting in one breath.

91. What is a key advantage of dual control modes?
They provide the comfort of pressure ventilation with the safety of volume delivery.

92. What happens if the inspiratory flow is set too low in volume control mode?
It may lead to patient-ventilator dyssynchrony and increased work of breathing.

93. What type of ventilator cycling occurs when the machine ends inspiration after a set time?
Time-cycling

94. Which parameter is most responsible for improving oxygenation in ventilated patients?
Positive end-expiratory pressure (PEEP)

95. What does a square waveform represent in flow-time graphics during volume-controlled ventilation?
A constant inspiratory flow throughout the breath.

96. What type of waveform is typically seen in pressure-controlled ventilation?
A decelerating flow waveform

97. What is meant by “total cycle time” on a ventilator?
It is the total duration of one respiratory cycle, including inspiration and expiration.

98. What setting determines the frequency of mandatory breaths in time-cycled ventilation?
The respiratory rate

99. What is the purpose of the plateau pressure measurement?
To assess alveolar pressure and risk for barotrauma.

100. What does a high peak inspiratory pressure with a normal plateau pressure suggest?
Increased airway resistance, such as from secretions or bronchospasm

Final Thoughts

Ventilator modes are a fundamental part of mechanical ventilation, each designed to match the needs of patients with varying degrees of respiratory support. By understanding how these modes function and when they are most appropriate, clinicians and respiratory therapists can ensure safe, effective care while minimizing complications.

A clear grasp of these settings not only improves patient outcomes but also strengthens confidence in managing complex cases where precise ventilation strategies are essential.