Are you ready to learn about the ventilator modes of mechanical ventilation? If so, you’re in the right place because that is what this study guide is all about.

As you will see below, we have listed out pretty much everything you need to know about Ventilator Modes as a Respiratory Therapy Student. Not to mention, you’ll get access to some helpful practice questions as well. 

So if you’re ready to get started, let’s go ahead and dive right in.

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What is a Ventilator Mode?

A ventilator mode is a way of describing how the mechanical ventilator assists the patient with inspiration. The characteristics of a particular mode controls how the ventilator functions. 

Understanding the different ventilator modes is one of the most important aspects of mechanical ventilation.

Primary Control Variables:

In mechanical ventilation, there are two primary control variables:

  1. Volume Control
  2. Pressure Control

Volume Control

Volume Control means that you can set (or control) the patient’s tidal volume.

So with a set tidal volume and a set respiratory rate, this means that there is a known minute ventilation. This is good when it comes to making adjustments to achieve a desired PaCO2.

One of the negative aspects of using Volume Control is that, since the tidal volume is preset, if the patients lung compliance were to decrease, this could result in high peak pressures.

Another drawback of Volume Control is patient-ventilator dyssynchrony.

Pressure Control

Pressure Control means that you can set (or control) the patient’s pressure in order to achieve a desired tidal volume.

As with Volume Control, a Pressure-Controlled tidal volume and set rate can help you reach a desired PaCO2.

The main disadvantage of using Pressure Control is the patient’s tidal volume can potentially be unstable if there are changes in the patient’s lung compliance or airway resistance.

So again, Volume Control and Pressure Control — those are the two control variables. When initiating mechanical ventilation on a patient, once you select the control variable, now you can choose the actual operational mode that determines the pattern of breathing for the patient.

What are the Primary Ventilator Modes?

In mechanical ventilation, there are two primary ventilator modes:

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

Assist/Control (A/C) Mode

In this mode, a minimum number of preset mandatory breaths are delivered by the ventilator but the patient can also trigger assisted breaths. The patient makes an effort to breathe and the ventilator assists in delivering the breath.

With that said, this mode of ventilation does not allow the patient to take spontaneous breaths. In this mode, the operator can set either a controlled pressure or a controlled volume.

The sensitivity control can be adjusted to make it easier or harder for the patient to initiate a breath.

When to Use Assist/Control?

This mode is most often used when mechanical ventilation is first initiated for a patient because this mode provides full ventilatory support.

That is also one of the advantages of using Assist/Control because it keeps the patient’s work of breathing requirement very low.

One of the major complications of Assist/Control is hyperventilation, which results in respiratory alkalosis. This is the result of too many breaths given to the patient, whether patient-triggered or machine-triggered.

Synchronous Intermittent Mandatory Ventilation (SIMV) Mode

In this mode, the ventilator delivers a preset minimum number of mandatory breaths. However, it also allows the patient to initiate spontaneous breaths in between the mandatory breaths.

This mode also allows the operator to set either a controlled pressure or a controlled volume. 

When to Use SIMV?

The primary indication for SIMV is when a patient needs partial ventilatory support. That is because, since the patient can takes spontaneous breaths, that means they can contribute to some of their minute ventilation.

SIMV is a mode that is used for weaning as well.

Advantages of Using SIMV:

  • Since the patient is able to take spontaneous breaths, it helps to maintain their respiratory muscle strength and avoid muscular atrophy.
  • It distributes tidal volumes evenly throughout the lung fields, which reduces V/Q mismatching.
  • It helps to decrease the patient’s mean airway pressure.
As a Respiratory Therapist (or student), SIMV and Assist/Control are the two ventilator modes that you should be most familiar with.

However, it’s also important to develop an understanding of some of the secondary modes of mechanical ventilation as well.

Ventilator Modes for Spontaneous Breathing:

Keep in mind that, in order to use any of the following modes, the patient must be breathing spontaneously.
  1. Continuous Positive Airway Pressure (CPAP)
  2. Pressure Support Ventilation (PSV)
  3. Volume Support (VS)

Continuous Positive Airway Pressure (CPAP)

In CPAP, or continuous positive airway pressure, a continuous pressure that is above atmospheric pressure is maintained throughout the breathing cycle.

The patient must be breathing spontaneously to be in this mode because no mandatory breaths are given. This is a useful mode for weaning patients off of the ventilator. 

Pressure Support Ventilation (PSV)

A mode of mechanical ventilation in which the patient’s spontaneous breaths are supported by the ventilator during the inspiratory phase of breathing. As the patient triggers a breath, the ventilator assists by adding pressure to make breathing easier.

The level of pressure is preset by the operator, so you have control over how much support you give the patient. For example, the higher the level of pressure support that is set, the easier it will be for the patient to take a breath.

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

PSV is often used to help the patient overcome the airway resistance that is caused by the endotracheal tube.

For example, let’s say there is a patient who needs to be weaned from the ventilator that is in the SIMV mode. If their endotracheal tube size is too small, the airway resistance would be increased which would make weaning difficult.

That’s when PSV would come in handy to help the patient overcome the airway resistance so that they can be extubated.

Volume Support (VS)

A mode of mechanical ventilation in which the ventilator delivers a supported breath to help the patient reach a set tidal volume. This mode is totally dependent on the patient’s effort, meaning that, the machine varies the inspiratory pressure support level with each breath in order to achieve the target volume.

This mode is not quite as common as some of the others, but it’s often used to wean patients from anesthesia.

Other Modes of Mechanical Ventilation:

Now that we’ve covered the primary and spontaneous modes of ventilation, now let’s go through the unconventional ventilator modes. These are sometimes referred to as the secondary modes of ventilation.
  1. Control Mode Ventilation (CMV)
  2. Airway Pressure Release Ventilation (APRV)
  3. Mandatory Minute Ventilation (MMV)
  4. Inverse Ratio Ventilation (IRV)
  5. Pressure Regulated Volume Control (PRVC)
  6. Proportional Assist Ventilation (PAV)
  7. Adaptive Support Ventilation (ASV)
  8. Adaptive Pressure Control (APC)
  9. Volume-Assured Pressure Support (VAPS)
  10. Neurally Adjusted Ventilatory Assist (NAVA)
  11. Automatic Tube Compensation (ATC)
  12. High-Frequency Oscillatory Ventilation (HFOV)

Control Mode Ventilation (CMV)

It’s a mode where the ventilator delivers a preset tidal volume at a set time-triggered frequency. Basically, 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 dependant on the machine for ventilation and oxygenation, it could be devastating if they were to become disconnected.

Airway Pressure Release Ventilation (APRV)

A mode of mechanical ventilation 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 an Acute Lung Injury (ALI), Acute Respiratory Distress Syndrome (ARDS), and Severe Atelectasis.

Settings for APRV:

  • High Pressure
  • Low Pressure
  • High Time
  • Low Time

Mandatory Minute Ventilation (MMV)

This is a feature of some ventilators that causes an increase in the mandatory breaths that are delivered when the patient’s spontaneous breathing level becomes inadequate.

So basically, if the patient’s spontaneous breathing decreases, the ventilator compensates in order to make sure that a safe minimal minute ventilation is delivered.

MMV is often an additional function of the SIMV mode and is intended to prevent hypercapnia.

Inverse Ratio Ventilation (IRV)

This is a mode that uses an inverse I:E ratio to improve oxygenation and gas exchange. It’s been shown to decrease shunting, improve V/Q mismatching, and decrease deadspace ventilation.

IRV is commonly recommended for patients with Acute Respiratory Distress Syndrome (ARDS).

This mode causes auto-PEEP (intrinsic PEEP) which is actually what helps improve the patient’s oxygenation and reduce shunting.

Pressure Regulated Volume Control (PRVC)

A mode of mechanical ventilation that provides volume-controlled breaths with the lowest pressure possible. It does so by altering the flow and inspiratory time. This mode 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 (PAV)

This is a mode of mechanical ventilation where the machine uses variable pressure to provide pressure support for 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.

One thing to keep in mind about this mode is that, if the patient’s lungs show rapid improvement, overdistention or barotrauma could occur because too much pressure would be delivered.

Adaptive Support Ventilation (ASV)

A mode of ventilation that changes the number of mandatory breaths and pressure support level according to the patient’s breathing pattern.

Adaptive Pressure Control (APC)

A pressure-controlled mode that utilizes a closed-loop control of the pressure setting in order to maintain a minimum delivered tidal volume.

With that said, in this mode, the delivered tidal volume will vary depending on the patient’s lung compliance.

Volume-Assured Pressure Support (VAPS)

A mode of ventilation that provides a stable tidal volume by incorporating inspiratory pressure support ventilation along with conventional volume-assisted cycles. It’s only available on certain ventilators.

This mode can cause a prolonged inspiratory time, so patients with an obstructive disease should be monitored closely in order to prevent air trapping or other cardiovascular effects.

Neurally Adjusted Ventilatory Assist (NAVA)

A ventilator mode that uses the patient’s electrical activity of the diaphragm to guide the functionality of the ventilator.

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

Automatic Tube Compensation (ATC)

While not technically a ventilator mode, this is a setting on some ventilators that offsets and compensates for the airflow resistance that is imposed by the endotracheal tube or artificial airway.

High-Frequency Oscillatory Ventilation (HFOV)

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 severe cases, such as with refractory hypoxemia.

Adjusting the Setting in HFOV:

  • Ventilation – can be increased by increasing the Amplitude (Power) or by decreasing the frequency.
  • Ventilation – can be decreased by decreasing the Amplitude (Power) or by increasing the frequency.
  • Oxygenation – can be increased by increasing the Mean Airway Pressure setting or by increasing the FiO2.
  • Oxygenation – can be decreased by decreasing the Mean Airway Pressure setting or by decreasing the FiO2.
This mode is also indicated to provide mechanical ventilatory support in neonates with conditions such as congenital diaphragmatic hernia, diffuse alveolar disease, and pulmonary hypoplasia.

Example TMC Practice Question:

A 63-year-old female patient is intubated and receiving mechanical ventilation in the pressure controlled A/C mode. If the patient’s compliance were to decrease, which of the following would you expect to occur?

A. Her delivered volume will decrease
B. Her peak pressure will increase
C. Her inspiratory time will increase
D. Her PEEP level will decrease

To get this one correct, you must have a basic understanding of lung compliance. You also have to take into account that the ventilator is in the pressure control mode, which means that the pressure is pre-set.

If there is a decrease in lung compliance when the ventilator is operating in the pressure control mode, the machine will continue delivering a constant pressure. But, since the lungs don’t expand as much when there is decreased compliance, it reaches the set pressure limit much faster. This means that there will be a decrease in the delivered tidal volume.

In this case, the inspiratory time will decrease and the PEEP levels should not be affected.

The correct answer is: A. Her delivered volume will decrease

This practice question was actually taken from our TMC Test Bank, which is a massive bank of premium practice questions that cover every topic that students must know in order to pass the TMC Exam.

As you can see, each question comes with a detailed rationale that explains exactly why the answer is correct. This is critical when it comes to actually learning the information.

If you’re interested in getting access to more practice questions like this one, definitely consider checking it out.

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Practice Questions about the Ventilator Modes:

1. What are 5 examples of ventilator modes?
CMV, A/C, IMV, SIMV, and CPAP

2. What type of pressure ventilation involves normal respirations, chest cuirass, and an iron lung?
Negative pressure

3. Positive pressure ventilators can be ____ or ____ controlled.
Pressure, Volume

4. What are 2 examples of nonconventional ventilator modes?
HFOV and APRV

5. How does positive pressure ventilation create transairway pressure?
By increasing the airway opening pressure above the alveolar pressure.

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6. List the modes of positive pressure ventilation from the most support to the least support:
CMV, A/C, IMV, SIMV, CPAP

7. What is an advantage of a volume-controlled mode?
It ensures minimal minute ventilation.

8. What are some disadvantages of a volume-controlled mode?
The pressure is variable, there is a possibility of barotrauma or volutrauma, and the volume is limited by the high-pressure alarm.

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

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

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

12. What are the four types of triggers?
Time, Patient, Pressure, and Flow.

13. What control is used to adjust the patient’s inspiratory effort?
Sensitivity

14. What are the two types of sensitivity controls?
Pressure and Flow

15. How does a pressure trigger work?
The ventilator senses a drop in pressure below the baseline and senses the patient’s negative inspiratory effort.

16. Which trigger type is more sensitive, pressure or flow?
Flow

17. How does a flow trigger work?
When a patient initiates a breath, the base flow returning to the ventilator is reduced which triggers an inspiration.

18. What is Controlled Mandatory Ventilation?
A mode that is time-triggered, gives machine breaths, and is volume or pressure cycled.

19. What are the indications for CMV?
The need to control minute ventilation completely. Also, the need to control chest expansion completely. For example, it would be helpful for a patient with a flail chest.

20. 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.

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21. 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.

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

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

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

25. What is the synchronization window?
It is the time interval just prior to time triggering in which the ventilator is responsive to the patient’s spontaneous breath.

26. What are some indications for the SIMV mode?
It is indicated for a patient who needs partial ventilatory support, and if the patient can actively contribute to their minute ventilation.

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

28. 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.

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

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

31. In this mode, the ventilator delivers a time-triggered breath and allows the patient to breathe at their own tidal volume between mechanical breaths?
SIMV

32. In this mode, the ventilator delivers 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

33. In this mode of ventilation, the patient cannot trigger a mechanical or spontaneous breath so there is no negative deflection on graphics?
Controlled Mandatory Ventilation (CMV). The patient must be sedated or paralyzed. It is not as commonly used.

34. In order for this mode to be used, the patient must be spontaneously breathing, have adequate lung function to maintain normal PaCO2, and not be at risk for hypoventilation?
CPAP

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

36. 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.

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

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

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

40. What would be considered CPAP with pressure support?
BiPAP

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41. How do you manage pressure support?
Begin with 5-10 and increase in increments of 3-5.

42. You should titrate pressure support according to what 3 things?
(1) Spontaneous tidal volume of 5 – 10 mL/kg of IBW. (2) Respiratory rate of less than 25. (3) A decrease in work of breathing.

43. Is PEEP considered a standalone mode on ventilation?
No, no it is not.

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

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

46. What is an indication for PEEP?
Refractory hypoxemia

47. How do you manage proper levels of PEEP?
The physiologic normal setting of PEEP is 5 cmH2O. You can increase the setting in increments of 3 – 5 while watching the patient’s blood pressure. You should strive to titrate to the previous level or zero in order to lower blood pressure. You can treat low blood pressure with volume expansion or vasopressors, then increase the PEEP setting again while continuing to monitor.

48. Is Inverse Ratio Ventilation (IRV) a volume-controlled or pressure-controlled mode?
IRV is a pressure-controlled mode.

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

50. What is auto-PEEP?
Air trapping that occurs when there is an incomplete expiration.

51. How does IRV prevent alveolar collapse?
The critical opening pressure is reduced, the pressure needed for ventilation is less, and it improves ventilation.

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

53. 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.

54. The method of increased ventilation with MMV varies upon what?
It depends on the ventilator model. Some ventilators increase the respiratory rate, some increase the tidal volume, and some increase the level of pressure support.

55. In mechanical ventilation, what should the minute ventilation be set to achieve?
It should be set to achieve a satisfactory PaCO2.

56. What are some advantages of MMV?
It promotes spontaneous breathing, it requires minimal support but protects against hypoventilation and respiratory acidosis, and it permits weaning but compensates for apnea.

57. What does Pressure Control generate?
It generates a flow in order to increase the airway pressure to a preset pressure limit.

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

59. What are some advantages of Pressure Control Ventilation?
The PIP is reduced while maintaining adequate oxygenation and ventilation. Also, there is a reduced risk of barotraumas.

60. How do you manage pressure control?
The PIP is set to achieve a desired tidal volume unless the patient is allowed to become hypercapnic in the interest of limiting the PIP. Tidal volume and minute ventilation must be carefully monitored in this mode.

61. What APRV stand for?
It is a mode of ventilation that stands for Airway Pressure Release Ventilation.

62. APRV is inappropriate for what kind of patients?
Those at risk for an inadequate spontaneous respiratory rate.

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

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

65. What is the description of the APRV mode?
It is time-triggered but the patient is allowed to breathe spontaneously at any time. It is mandatory and spontaneous pressure limited and it is time-cycled with a preset I-time.

66. 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.

67. 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.

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

69. What is the limit variable for VC/SIMV?
Volume

70. What is the definition of Controlled Mandatory Ventilation (CMV)?
It is a ventilator mode that is 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.

71. What is the definition of Synchronized Intermittent Mandatory Ventilation (SIMV)?
It is a ventilator mode that provides assisted mechanical ventilation synchronized with the patient’s breathing. The ventilator senses the patient taking a breath then delivers the breath. Spontaneous breathing by patient occurs between the assisted mechanical breaths which occurs at preset intervals. If the patient fails to take a breath, the ventilator will provide a mechanical breath.

72. When is the SIMV mode preferred?
When the patient has an intact respiratory drive.

73. How is SIMV is similar to CPAP and BIPAP?
SIMV, BiPAP, and CPAP are all spontaneously triggered by patient.

74. How does the trigger in Assist/Control ventilation work?
The trigger for delivery of a breath can be either by the patient or by elapsed time.

75. What is the preferred mode for patients with respiratory distress?
Assist/Control

76. This mode can be used in ARDS, paralyzed, or sedated patients?
Assist/Control Ventilation

77. During Assist/Control ventilation, what can happen to an anxious patient?
They can trigger the ventilator to hyperventilate which leads to breath stacking or auto-PEEP.

78. Which mode of mechanical ventilation can provide a precise I:E ratio?
Control Mode Ventilation (CMV)

79. What mode can make it easier for the patient to overcome the resistance of the ET tube and is often used during weaning because it reduces the work of breathing?
Pressure Support Ventilation

80. What is the definition of Pressure Support Ventilation?
It is a ventilator mode that supports ventilation during inspiration. The patient determines the tidal volume, rate, and minute volume. It requires consistent respiratory effort by the patient.

Final Thoughts

So there you have. That wraps up our study guide on the modes of mechanical ventilation. I hope that you found this information to be helpful. In fact, I’m confident that you can use this guide to boost your knowledge of the ventilator modes to a whole new level. 

And most importantly, this guide to give you a head start on preparing for the TMC Exam as well. Thank you so much for reading and as always, breathe easy my friend. 

Before you go, don’t forget to get access to our Cheat Sheet Database. It’s 100% free. 

References

The following are the sources that were used while doing research for this article:

  • Clinical Application of Mechanical Ventilation. 4th ed., Cengage Learning, 2013. [Link]
  • Pilbeam’s Mechanical Ventilation: Physiological and Clinical Applications. 6th ed., Mosby, 2015. [Link]
  • Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020. [Link]
  • Mosby’s Respiratory Care Equipment. 10th ed., Mosby, 2017. [Link]

Disclosure: The links to the textbooks are affiliate links which means, at no additional cost to you, we will earn a commission if you click through and make a purchase.