Assisted ventilation

Assisted ventilation is a key component of modern emergency and intensive care medicine. It supports spontaneous breathing in patients, making the work of breathing easier and training the respiratory muscles. This makes gentler, more comfortable treatment possible.

This article tells you everything you need to know about assisted ventilation: Why and where it is used, how it differs from controlled ventilation, and which are the common ventilation modes. We also show you how WEINMANN ventilators support assisted ventilation.

Definition: What is assisted ventilation?

Supported or assisted ventilation – often also referred to as augmented ventilation in intensive care medicine – is an umbrella term for all forms of ventilation in which the patient’s spontaneous breathing is maintained in whole or in part and is synchronously supported by a ventilator.¹ In contrast to controlled ventilation, the ventilator accordingly takes on only part of the work of breathing in assisted ventilation.²

A ventilator assists with either a pressure-controlled (p-AC) or a volume-controlled (V-AC) ventilation mode. However, it is not possible to deliver assisted ventilation by means of bag mask ventilation. This is because in bag mask ventilation, the patient is ventilated entirely by an EMS field provider. This individual controls mechanical breaths by squeezing the bag and cannot generally detect efforts to breathe spontaneously, so this cannot be synchronized with ventilation with a bag mask. Only a ventilator is capable of reliably detecting independent breaths and providing technical support for them.

The mechanical breaths of assisted ventilation are both machine-controlled and triggered by patients. Ventilation frequency is preset in this case to ensure a minimum number of breaths and a minimum level of ventilation. At the same time, patients can breathe spontaneously, initiating additional breaths. Assisted ventilation thus allows frequency to be affected by the spontaneous breathing of the person being ventilated.³

A trigger is required to detect spontaneous breathing. This allows the patient to initiate a supported breath. A variety of trigger functions can be set on the ventilator for this: 

An appropriate threshold for the pressure or flow trigger is specified before commencing assisted ventilation. If this threshold is exceeded, this initiates the breath. This setting specifies how much work of breathing patients have to do themselves before they are given synchronized breathing support.⁴

When is assisted ventilation performed?

Assisted ventilation is essentially used in non-invasive ventilation. In the context of continuous weaning, it facilitates a smooth transition from controlled ventilation to spontaneous breathing and relieves strain on the respiratory muscles until they are strong enough to breathe independently. The patient can thus gradually perform more of the work of breathing and also train the respiratory muscles. 

This flexible approach allows adaptation to an individual’s condition without medical personnel continually having to reassess the time from when it makes sense to switch to assisted ventilation modes.⁵

In patients with diseases in which spontaneous breathing activity needs to be avoided, the risk/benefit ratio of assisted ventilation needs to be considered on an individual basis. Potential clinical pictures in which this might be the case include elevated intracranial pressure or right-sided heart failure.⁶

In addition, an assisted ventilation mode such as aPCV ventilation is suitable for patients with neuromuscular diseases who require support due to weakness of the respiratory muscles.⁷

Using assisted ventilation in emergency medical services

Assisted ventilation is used in emergency medical services particularly in the context of non-invasive ventilation (NIV).⁸ Assisted ventilation can furthermore be used when transporting intensively ventilated patients or those on ventilation at home. The trigger function of assisted ventilation makes particular sense in patients on ventilation at home in order to detect and support attempts at spontaneous breathing at an early stage.

Difference between assisted and controlled ventilation

Mechanical ventilation is divided into controlled and assisted ventilation. In assisted ventilation, the ventilator supports spontaneous breathing, whilst in controlled ventilation, it is not possible for the patient to breathe independently.

Mandatory ventilation is used in patients with no spontaneous breathing, which is why the ventilator takes on the entire work of breathing. If patients still try to breathe independently, the ventilator suppresses the breaths using a specified ventilation frequency.¹

The central differences between assisted and controlled ventilation are clearly shown in the table below:

Forms of assisted ventilation

Assisted ventilation includes a large number of ventilation modes. We introduce some of the key modes below.

Assisted spontaneous breathing (ASB)

Assisted spontaneous breathing (ASB) is a form of assisted ventilation in which the patient controls respiratory rate and tidal volume independently. ASB ventilation can be used alone or in combination with other modes such as CPAP, BIPAP or SIMV and, depending on the ventilation mode selected, can be fully or partly initiated by the patient.

During inspiration, the ventilator provides preset pressure support (ΔpASB) with a specified proportion of oxygen (FiO₂) in the respiratory gas. Following inspiration, airway pressure is reduced to a lower positive end-expiratory pressure (PEEP) to make it easier to breathe out. 

Biphasic positive airway pressure (BIPAP/BiLevel)

BIPAP/BiLevel ventilation is pressure-controlled ventilation at two different levels of pressure: The higher inspiratory pressure (pInsp) and the lower positive end-expiratory pressure (PEEP). 

A mandatory ventilation frequency is specified for this form of assisted ventilation. Patients can breathe spontaneously in any phase of the ventilation cycle and thus initiate a synchronized breath within a specified time window. The ventilation frequency during synchronization results from the ratio of inspiratory time to expiratory time (I:E).¹

Pressure support (ASB) can also be used to support spontaneous breathing during expiration. 

Synchronized intermittent mandatory ventilation (SIMV) 

SIMV ventilation can be volume-controlled (VC-SIMV) or pressure-controlled (PC-SIMV). This mode is a combination of controlled and assisted ventilation.

In SIMV ventilation, the number of mechanical breaths is specified. Patients can breathe spontaneously during expiration and thus initiate a synchronized breath within a specified time window.⁹ The frequency during synchronization is also determined by the I:E ratio with this form of assisted ventilation.

Pressure support (ASB) can also be used to support spontaneous breathing during expiration.

Benefits of assisted ventilation

Assisted ventilation delivers a number of benefits: The preset respiratory rate secures respiration and increases patient safety. Spontaneous breathing simultaneously trains the respiratory muscles.³

A further benefit is the reduced requirement for sedation. Assisted ventilation furthermore improves the ventilation/perfusion ratio in acute lung failure and increases cardiac output as well as available oxygen.¹⁰

Combining assisted ventilation with controlled ventilation increases flexibility and allows treatment to be adapted to suit a patient’s individual requirements. Assisted ventilation consequently increases patient comfort.

Risks of assisted ventilation

As assisted ventilation involves ventilation frequency and tidal volume being controlled either completely or partly by patients themselves, both hyperventilation and hypoventilation may occur.¹¹

During hyperventilation, an increased respiratory rate means more CO₂ is breathed out. Conversely, hypoventilation can lead to a drop in oxygen level and a rise in carbon dioxide in the blood. However, the risk of hypoventilation can be prevented by the adjustable mandatory ventilation frequency provided in most assisted ventilation modes.

What is more, safety measures such as apnea ventilation provide additional protection. For example, if spontaneous breaths fail to occur during ASB ventilation, a backup mode is automatically activated to provide the patient with controlled ventilation.¹²

Control parameters

A variety of control parameters such as respiratory rate can be used to assess the efficacy of assisted ventilation. Critical consideration of individual situations is required to determine the respiratory rate above which assisted ventilation will be successful.

Non-invasive ventilation (NIV) is essentially considered successful if respiratory rate drops by about 20%. Invasive ventilation is indicated if respiratory rate is above 35/min or below 7/min.² The following control parameters can also be used:

Assisted ventilation with WEINMANN

MEDUMAT Standard² and MEDUVENT Standard ventilators from WEINMANN have the following modes for assisted ventilation:

MEDUMAT Standard² is the ideal companion for emergency medical services. Weighing just 2.5 kg, it is especially handy and its battery runtime of 10 hours guarantees that it will be reliably available throughout the whole session. The device can be used on any patients with a body weight of 3 kg or above and is thus equally suitable for adults and infants.

At 2.1 kg, MEDUVENT Standard is among the lightest turbine-driven emergency ventilators in the world. The ventilator can ventilate an adult at typical ventilation settings for about 7.5 hours without an external source of compressed gas – without using up its own oxygen reserves in the process. This makes it possible to guarantee reliable ventilation, even in challenging situations with restricted equipment.

Both ventilators are intuitive to operate, have clearly-arranged controls, and acoustic as well as visual warning signals for maximum patient safety. In emergency situations, ventilation can be started quickly and in compliance with guidelines by entering the patient’s height. 

¹ https://www.amboss.com/de/wissen/maschinelle-beatmung/

² https://viamedici.thieme.de/lernmodul/6772238/4915521/beatmung

³ Schwab et. al (2012): Neurointensiv [Neurointensive care]. 2nd edition Berlin Heidelberg: Springer-Verlag, p. 17.

⁴ Lang, Hartmut (2020), Beatmung für Einsteiger, Theorie und Praxis für die Gesundheits- und Krankenpflege [Ventilation for beginners, theory and practice for healthcare]. Berlin Heidelberg: Springer-Verlag, p. 228 ff.

⁵ Hartmut Lang (2017): Außerklinische Beatmung. Basisqualifikationen für die Pflege heimbeatmeter Menschen [Out-of-hospital ventilation. Basic qualifications for nursing people on ventilation at home]. Berlin Heidelberg: Springer-Verlag, p. 372

⁶  https://register.awmf.org/assets/guidelines/001-021l_S3_Invasive_Beatmung_2017-12.pdf, p. 49

⁷ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236064/

⁸ Hartmut Lang (2017): Außerklinische Beatmung. Basisqualifikationen für die Pflege heimbeatmeter Menschen [Out-of-hospital ventilation. Basic qualifications for nursing people on ventilation at home]. Berlin Heidelberg: Springer-Verlag, p. 97

⁹ R. Larsen, T. Ziegenfuss (2017). Pocket Guide Beatmung [Pocket Guide to Ventilation]. Berlin Heidelberg: Springer-Verlag

¹⁰ Schwab et. al (2012): Neurointensiv [Neurointensive care]. 2nd edition Berlin Heidelberg: Springer-Verlag, p. 142.

¹¹ https://www.bildungsinstitut-rlp.drk.de/fileadmin/downloads/Rettungsdienst-weitere_Ausbildungen/Weiterbildung_Intensivtransport/Beatmung_aktuell__Schreibgeschu__tzt___Kompatibilita__tsmodus_.pdf

¹² https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7531439/