Ventilator Modes Made Easy: Mechanical Ventilation (2023)

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 that are delivered to the patient.

In this guide, we’ll go over the most common ventilator modes and what they’re used for. This includes advantages, disadvantages, and indications for each mode.

What is a Ventilator Mode?

A ventilator mode is a way of describing how the mechanical ventilator assists the patient with taking a breath. The characteristics of a specific mode control how the machine uses positive pressure to deliver air to the patient’s lungs.

Therefore, respiratory therapists and medical professionals who work with mechanically-ventilated patients must understand the various modes in order to provide optimal patient care.

Primary Control Variables

In mechanical ventilation, there are two primary control variables:

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

Volume Control

Volume control (VC) is a type of ventilation where a delivered volume is set (i.e., controlled) by the operator. Since the delivered volume is fixed, the patient’s peak inspiratory pressure (PIP) will vary depending on their lung compliance and airway resistance.

The primary advantage of volume-controlled ventilation is that a set volume allows the operator to regulate the patient’s minute ventilation.

Pressure Control

Pressure control (PC) is a type of ventilation where the delivered level of pressure is set (i.e., controlled) by the operator. Since the delivered pressure is fixed, the patient’s tidal volume will vary depending on their lung compliance and airway resistance.

The primary advantage of pressure-controlled ventilation is that it protects the lungs from overinflation due to too much pressure, which prevents barotrauma and ventilator-induced lung injuries. 

Recap: Volume control and pressure control are the two primary control variables. Selecting the control variable is the first step in the initiation of mechanical ventilation. Then you can choose an operational mode to determine the type and amount of support the patient receives.

Primary Ventilator Modes

There are two primary modes of mechanical ventilation:

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

Assist/Control

The assist/control (A/C) mode delivers a minimum number of preset mandatory breaths by the ventilator, but the patient can also trigger assisted breaths. Therefore, the patient can make an effort to breathe, and the machine will use positive pressure to assist in delivering the breath.

This mode provides full ventilatory support; therefore, it is often used when mechanical ventilation is first initiated. This helps keep the patient’s work of breathing requirement very low.

Hyperventilation is a complication of assist/control, which may occur when too many breaths are delivered to the patient. This results in respiratory alkalosis.

Synchronous Intermittent Mandatory Ventilation

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

Therefore, by being able to initiate spontaneous breaths, the patient is contributing to some of their minute ventilation. This mode is indicated when a patient only needs partial ventilatory support.

The SIMV mode helps patients maintain their respiratory muscle strength and avoid muscular atrophy. It distributes tidal volumes evenly throughout the lung fields, which reduces V/Q mismatching. It also helps to decrease the patient’s mean airway pressure.

Spontaneous Ventilator Modes

A spontaneous ventilator mode is used when a mechanically ventilated patient is capable of breathing on their own. The different types include:

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

Continuous Positive Airway Pressure

Continuous positive airway pressure (CPAP) is a mode used to deliver a constant level of pressure above atmospheric pressure throughout the entire breathing cycle.

The patient must breathe spontaneously when this mode is in use because no mandatory breaths are delivered by the ventilator. This is a useful mode for weaning patients off of the ventilator.

Pressure Support Ventilation

Pressure support ventilation (PSV) is a mode in which the patient’s spontaneous breaths are supported by the ventilator during the inspiratory phase of breathing. When the patient triggers a breath, the ventilator assists by adding pressure to make breathing easier.

In this mode, the breaths are time-cycled and pressure-limited.

Therefore, the level of pressure support is preset by the operator to control how much support the patient receives. For example, the higher the level of pressure support that is set, the easier it will be for the patient to take a breath.

PSV can help patients overcome the airway resistance caused by the endotracheal tube, making this another helpful mode for weaning.

Volume Support

Volume support (VS) is a mode in which the ventilator delivers a supported breath to help reach a set tidal volume. This mode is totally dependent on the patient’s effort.

This means that the inspiratory pressure support level varies with each breath to achieve the target volume. This mode isn’t as common as PSV and CPAP but is often used to wean patients from anesthesia.

Other Modes of Mechanical Ventilation

Aside from the primary and spontaneous ventilator modes, there are several other types that are indicated in specific situations. These 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

Continuous mandatory ventilation (CMV) is a mode in which the ventilator delivers a preset tidal volume at a set time-triggered frequency. Therefore, the ventilator controls both the rate and tidal volume, which means that it’s in total control of the minute ventilation.

This mode should only be used on patients who are fully sedated and have been administered neuromuscular blocking agents.

That is also the biggest hazard of using this mode because, since the patient is fully dependent on the machine, it could be devastating if they were to become disconnected.

Airway Pressure Release Ventilation

Airway pressure release ventilation (APRV) is a mode in which two levels of continuous positive airway pressure are applied with an intermittent release phase for spontaneous breaths. This mode is often recommended to improve oxygenation and treat refractory hypoxemia.

Other indications for APRV include acute lung injuries, acute respiratory distress syndrome (ARDS), and severe atelectasis.

Mandatory Minute Ventilation

Mandatory minute ventilation (MMV) is a feature of some ventilators that causes an increase in the mandatory breaths delivered when the patient’s spontaneous breathing level becomes inadequate.

For example, if the patient’s spontaneous breathing decreases, the ventilator compensates to make sure that a minimal minute ventilation is delivered. MMV is often an additional function of the SIMV mode and is intended to prevent hypercapnia.

Inverse Ratio Ventilation

Inverse ratio ventilation (IRV) is a mode that uses an inverse I:E ratio to improve oxygenation and gas exchange. It’s been shown to decrease shunting and deadspace ventilation while improving V/Q mismatching.

IRV is commonly used to treat patients with acute respiratory distress syndrome (ARDS). This mode causes auto-PEEP (i.e., intrinsic PEEP) and helps improve the patient’s oxygenation while reducing shunting.

Pressure Regulated Volume Control

Pressure regulated volume control (PRVC) is mode that provides volume-controlled breaths with the lowest pressure possible. It does so by altering the flow and inspiratory time.

PRVC is used to keep the peak airway pressure at the lowest possible level. This mode is volume-cycled and can be patient triggered-or time-triggered.

Proportional Assist Ventilation

Proportional assist ventilation (PAV) is a mode in which the machine uses varying levels of pressure to provide support to a patient’s spontaneous breaths. The level of pressure support is adjusted depending on the patient’s work of breathing.

PAV is either pressure-triggered or flow-triggered, and the breathing cycle ends once the patient’s volume or flow demands are met. If the patient’s lungs show rapid improvement while this mode is in use, too much pressure may be delivered, resulting in overdistention or barotrauma.

Adaptive Support Ventilation

Adaptive support ventilation (ASV) is a dual control mode that changes the number of mandatory breaths and pressure support level according to how the patient is breathing.

Therefore, this mode increases or decreases the level of support based on the monitored patient parameters, such as flow, pressure, inspiratory and expiratory time, compliance, resistance, and time constants.

Adaptive Pressure Control

Adaptive pressure control (APC) is a mode that maintains a minimum delivered tidal volume by utilizing a closed-loop control of the pressure setting. In other words, it uses variable inflation pressures to deliver a minimum targeted tidal volume.

Volume-Assured Pressure Support

Volume-assured pressure support (VAPS) is a mode of ventilation that uses inspiratory pressure support and volume-assisted cycles to deliver a stable tidal volume.

VAPS provides optimal inspiratory flows, reducing the patient’s work of breathing, and delivers stable tidal volumes in patients with irregular breathing patterns.

Neurally Adjusted Ventilatory Assist

Neurally adjusted ventilator assist (NAVA) is a mode that uses the patient’s electrical activity to control how the ventilator functions.

A catheter with electrodes is positioned in the patient’s esophagus at the level of the diaphragm. This is how the electrical activity is picked up from the phrenic nerves. The ventilator uses this information to ventilate the patient.

NAVA is often used for weaning in patients with spinal cord injuries. It helps reduce the incidence of diaphragmatic atrophy.

Automatic Tube Compensation

Automatic tube compensation (ATC) is technically not a ventilator mode, but it’s a feature that can be found on some ventilators. Its primary role is to compensate for the airflow resistance that is caused by the endotracheal tube.

High-Frequency Oscillatory Ventilation

High-frequency oscillatory ventilation (HFOV) is a type of mechanical ventilation that delivers very small tidal volumes at an extremely fast rate, which minimizes the chances of a lung injury.

This mode has been shown to improve oxygenation in patients with refractory hypoxemia.

The settings for HFOV are different than conventional mechanical ventilation. For example, the patient’s ventilation can be increased or decreased by adjusting the oscillation frequency or amplitude setting. Oxygenation can be increased or decreased by adjusting the FiO2 or mean airway pressure setting.

This mode is also indicated to provide mechanical ventilatory support to neonates with conditions such as congenital diaphragmatic hernia, diffuse alveolar disease, and pulmonary hypoplasia.

Ventilator Modes Practice Questions

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

2. Positive pressure ventilators can be ____ or ____ controlled.
Pressure, volume

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 a volume-controlled mode?
It ensures minimal minute ventilation.

5. What are some disadvantages of a volume-controlled mode?
The pressure is variable, there is a possibility of barotrauma, 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 some 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?
It is 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 the 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?
One complication is breath stacking, which is a spontaneous effort immediately followed by a mechanical breath. This leads to an increased PIP, barotrauma, and cardiac compromise.

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

20. What happens if the rate is set high in the SIMV mode?
This would provide total 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

26. In which mode can the patient not trigger a mechanical or spontaneous breath and there is no negative deflection on the 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 a low lung compliance, high PIP during volume-controlled ventilation, and in patients with ARDS.

45. What are some advantages of pressure control ventilation?
In PCV, the PIP is lower while maintaining adequate oxygenation and ventilation. Also, there is 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 is 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 continuous 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 delivers the breath. Spontaneous breathing by 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 is similar to CPAP and BIPAP?
They are all spontaneously triggered by 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

Final Thoughts

There are many different modes of mechanical ventilation that may be used in various clinical situations. The mode that is chosen will be based on the patient’s individual needs.

Understanding the different modes is important for respiratory therapists and medical professionals who care for patients on the ventilator.

It’s also important to understand the capabilities and limitations of each mode, as well as the ventilator settings that can be adjusted to optimize the support a patient receives. Thanks for reading, and, as always, breathe easy, my friend.