Mandatory ventilation

Mandatory ventilation is of key importance in emergency medical services. It supports patients with no spontaneous breathing and may be life-saving in critical situations. Controlled ventilation provides a rapid, reliable remedy at the very point when spontaneous breathing fails completely.

In this article, we explain when mandatory ventilation is used, how pressure-controlled and volume-controlled ventilation differ, and which modes WEINMANN ventilators offer to support mandatory ventilation.

What does mandatory ventilation mean?

Continuous mandatory ventilation (CMV) is a method of ventilation in which the ventilator assumes complete control of breathing. This mode is frequently also called simply “controlled ventilation”. In mandatory ventilation, the ventilator takes on the whole work of breathing and ventilation (total ventilatory support), so the patient is unable to influence ventilation in any way.¹

The term “mandatory” is to show that parameters such as respiratory rate and tidal volume/inspiratory pressure are specified in advance and are, as it were, “forced upon” the person being ventilated. The mechanical breath is initiated and ended by the ventilator. The duration of inspiration is time-controlled. 

Mandatory ventilation is indicated when there is little to no spontaneous breathing, as this is scarcely taken into account during ventilation, if at all. It can be performed on both a volume-controlled and a pressure-controlled basis.²

Volume-controlled mandatory ventilation

Volume-controlled mandatory ventilation (VC-CMV) is often referred to as VCV ventilation, though this name also includes other volume-controlled ventilation modes, e.g. IPPV.²

VCV ventilation is a form of ventilation in which a fixed tidal volume (Vt) is specified. The resulting airway pressure depends on the patient’s airway resistance (resistance) and on the degree to which the lungs can inflate (compliance). The higher the resistance/the lower the compliance, the higher the inspiratory pressure (pInsp) required.² If the specified tidal volume is not reached, inspiration is canceled and an alarm indicates the inconsistent volume supply. 

Minute volume results from tidal volume and the set ventilation frequency. Ventilation frequency is time-controlled and is determined by the ratio of inspiratory time to expiratory time (I:E) specified in the ventilator. 

At high airway resistance and low compliance, high airway peak pressures may arise. A pressure limit is set to prevent barotrauma. In this case, maximum airway pressure (pMax) limits inspiratory pressure. This should not generally exceed 30 mmHg.^3,4

IPPV ventilation

An example of volume-controlled mandatory ventilation is IPPV ventilation (intermittent positive pressure ventilation). In IPPV ventilation, positive pressure is exerted on the lungs during inspiration to make them inflate. During expiration, pressure drops to 0 (ZEEP, zero end-expiratory pressure). 

CPPV ventilation (continuous positive pressure ventilation) is a further development of IPPV ventilation. Instead of a ZEEP, in this case a positive end-expiratory pressure (PEEP) is administered to help keep the lungs and the airway open.⁵

Parameters

The following parameters are set either directly or indirectly on the ventilator in volume-controlled mandatory ventilation:

Pressure-controlled mandatory ventilation

In pressure-controlled mandatory ventilation (PC-CMV) – also called simply pressure-controlled ventilation (PCV) – the ventilation pressure is specified. 

In this case, tidal volume results from the patient’s lung resistance and compliance. This means that the higher the resistance and the lower the compliance, the lower the resulting tidal volume. Ventilation is effected by switching between a set inspiratory pressure and a lower pressure during expiration (PEEP).

In order to prevent ventilation-induced lung damage, it is possible to set a volume limit so that pressure-controlled, volume-regulated ventilation results. However, the decelerating flow means that peak pressures in PCV ventilation are in any case somewhat lower than in volume-controlled ventilation. For pressure-controlled mandatory ventilation, it is possible to ventilate in PCV mode.⁴

Parameters

Pressure-controlled mandatory ventilation requires the following parameters to be set: 

Differences between pressure-controlled and volume-controlled mandatory ventilation

When selecting between pressure-controlled and volume-controlled mandatory ventilation, a few key differences need to be noted. Both modes have specific advantages and disadvantages that need to be considered depending on the clinical situation and on patient condition. The key differences between the methods are listed in the table below: 

When is controlled ventilation used?

Controlled mandatory ventilation is used when patients are no longer conscious and are unable to breathe independently. Appropriate sedation is required in this case. As the ventilator takes on the entire work of breathing, this form of ventilation is unable to take account of potential spontaneous breathing.

Mandatory ventilation is thus in direct contrast to assisted ventilation that is used to maintain and support spontaneous breathing. Both ventilation modes have their specific applications.

Mandatory ventilation always guarantees adequate respiratory ventilation, whilst assisted ventilation trains the respiratory muscles.⁷ There are consequently also ventilation modes such as SIMV ventilation that combine both forms of ventilation with one another.

Risks of mandatory ventilation

As controlled ventilation does not permit spontaneous breathing, this form of ventilation is associated with certain risks.

If patients exhibit any spontaneous breathing at all, even if only a little, conflict may arise between the patient and the ventilator. Patients may “fight” asynchronously against the specified ventilation, leading to ineffective work of breathing, increased oxygen consumption, and discomfort. This is why heavy sedation or muscle relaxants are often required during ventilation. As mandatory ventilation takes over the entire work of breathing, it can also lead to weakening (atrophy) of the respiratory muscles after just a few days.²

What is intermittent mandatory ventilation (IMV)?

Intermittent mandatory ventilation (IMV) administers mechanical breaths at regular intervals. It is considered out of date nowadays, however, and provides few advantages in intensive care and emergency medicine, which is why it has been further developed into SIMV ventilation.

Synchronized intermittent mandatory ventilation (SIMV) combines mechanical breaths delivered by the ventilator with spontaneous breathing. This method allows patient-triggered breaths within a certain time window. Patients can breathe spontaneously between the mechanical breaths. However this is effected mainly at a PEEP level, which is why patients have to overcome a certain resistance.

As both mechanical and patient-triggered breaths are possible, IMV ventilation is considered a form of partial ventilation.⁸The trigger mechanism of SIMV ventilation allows breaths to be synchronized with spontaneous breathing so that the patient can initiate inspiration. If a breath is missed, this is delivered under machine control and unsynchronized.⁹

Mandatory ventilation with SIMV can be implemented on both a volume-controlled (VC-SIMV) and a pressure-controlled (PC-SIMV) basis. In addition, SIMV ventilation can be combined with pressure support (ASB, assisted spontaneous breathing) in order to provide additional relief for spontaneous breathing.¹⁰

Mandatory ventilation with WEINMANN

WEINMANN ventilators have a variety of ventilation modes for mandatory ventilation. IPPV mode is available for volume-controlled ventilation, whilst WEINMANN provides PCV mode for pressure-controlled ventilation. 

In addition, combined modes such as SIMV and SIMV + ASB or BiLevel + ASB can be selected. These allow patient-oriented ventilation by supporting attempts at spontaneous breathing and facilitating pressure support.

MEDUMAT Standard² and MEDUVENT Standard are available for ventilation. MEDUMAT Standard² is the ideal companion for emergency sessions as its battery runtime of 10 hours means it works reliably, even in extended sessions. The ventilator can ventilate anyone from infants weighing 3 kg or above, making it suitable for patients of all age groups. Its weight of 2.5 kg makes MEDUMAT Standard² especially lightweight; this ventilator provides a variety of ventilation modes guaranteeing flexible use in ambulances, emergency helicopters, and in the intensive care unit.

At ordinary ventilation settings for adults, MEDUVENT Standard can ventilate patients for up to 7.5 hours without an external source of compressed gas. Weighing just 2.1 kg, it is among the smallest emergency ventilators in the world, making it particularly handy.

Both devices can measure both flow and pressure, ensuring accurate patient monitoring. Clearly-arranged operating symbols and night view ensure that operation is intuitive. Patient safety is increased by visual and acoustic warning signals, together with a hygiene filter inside the ventilator. 

Mandatory ventilation can be initiated in compliance with the guidelines by entering patient height - a key advantage in critical situations. It ensures that patients in any situation obtain support as quickly as possible, improving patient outcome. 

¹ https://www.thieme-connect.de/products/ebooks/lookinside/10.1055/b-0034-41498#

² Larsen R, Mathes A (2023): Beatmung. Indikation – Techniken – Krankheitsbilder [Ventilation. Indications - Techniques - Clinical Pictures]. 7th edition Berlin Heidelberg: Springer-Verlag, p. 251f, p. 316.

³ https://viamedici.thieme.de/lernmodul/6772238/4915521/beatmung#p_Intensiv_000400_PCV

⁴ https://www.atmungbeatmung.de/index.php/beatmung/17-beatmungsformen

⁵https://flexikon.doccheck.com/de/IPPV

⁶ Larsen R, Mathes A (2023), p. 317ff.

⁷ 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. 141, p. 372

⁸ https://link.springer.com/chapter/10.1007/978-3-662-46219-5_5

⁹ Larsen R, Mathes A (2023), p. 340f.

¹⁰ 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. 138f.