Assisted Pressure-Controlled Ventilation (aPCV)

aPCV stands for assisted, pressure-controlled ventilation that synchronizes spontaneous breathing in patients with mechanical breaths. This not only increases the comfort of patients, but is also extremely versatile and can be flexibly adapted to their needs.

This form of ventilation is suitable for individuals who both have and lack spontaneous breathing and plays an important role in emergency medicine – particularly in the management of respiratory insufficiency as in acute respiratory failure or chronic obstructive pulmonary disease.

In this article, we explain how ventilation in the aPCV mode differs from normal PCV, how the aPCV mode works during ventilation and which WEINMANN devices support this form of ventilation.

Definition: Assisted pressure-controlled ventilation

Assisted pressure-controlled ventilation (aPCV) is an assisted, pressure-controlled form of ventilation. The ventilation frequency is mandatory and preset. It can, however, be altered by the patient’s spontaneous breathing, which in turn increases the minute volume.

The patient’s own efforts to breath set off a trigger that synchronizes spontaneous breathing with the mechanical breaths. Triggering is detected in an adjustable time window during expiration and is usually indicated as a percentage of the expiratory time (Te). No mechanical breath is triggered when spontaneous breathing occurs outside the time window. The inspiratory time during the process is preset and remains constant.¹

Diagram with ventilation curve aPCV mode

How aPCV ventilation works

During inspiration, air is supplied until the preset inspiratory pressure (pInsp) is reached. This pressure is determined by the aPCV ventilation parameters and should be high enough to ensure adequate ventilation.

The speed of the air supply depends on the ramp setting, which describes the rise time until the inspiratory pressure is reached. It can be indicated in time units (seconds, milliseconds) or in levels. The shorter the time or the lower the level, the faster the air flows into the lungs. Nevertheless, the rise time setting should be selected carefully because a ramp that is too steep or one that is too flat can both be associated with various risks.

As soon as the preset pressure is reached, it is maintained at a constant level for the entire inspiration time. The inspiratory-expiratory ratio (I:E) is defined as the ratio of time expended on inspiration versus that expended on expiration.

After the inspiratory time has elapsed, the air pressure is lowered to the PEEP level via the expiratory valve. Now, when ventilation is in the aPCV mode, a trigger can detect the patient’s spontaneous breathing efforts during expiration and initiate synchronization with a mechanical breath. Afterwards, a new ventilation cycle is initiated.

How the trigger works

When the trigger is switched on, the conventional PCV mode becomes aPCV, a ventilation mode that supports the patient’s breathing with a mechanical breath. The trigger recognizes the patient’s own breathing efforts in either a pressure- or flow-controlled manner.

Flow trigger: During inhalation, an air flow is generated that is detected by the ventilator above a certain threshold. The limit value is indicated in l/min. As soon as the threshold value is achieved during inspiration, the device triggers a breath-synchronized mechanical breath.
Pressure trigger: The pressure trigger reacts to the negative pressure created during inhalation. This negative pressure is specified in an air pressure unit such as mbar or in levels of 1–6. The following applies to the setting parameters:
- Air pressure unit: Due to the negative pressure, negative values are indicated for air pressure units. The greater the negative value, the more difficult it is to trigger a mechanical breath. Conversely, a smaller negative value facilitates triggering.
- Level setting: The smaller the level, the easier the triggering.

Based on this trigger, patients can initiate one or more breaths during ventilation in the aPCV mode. Synchronization supports spontaneous breathing while promoting patient comfort at the same time. This means that patients do not have to fight against the device, which prevents additional stress and reduces the risk of exhaustion.²

WEINMANN ventilators have a flow trigger that can be set either in levels or in units of l/min. The type of setting (levels or units) can be preconfigured in the operator menu.

Indications

Ventilation in the PCV mode is used in patients who have complete respiratory insufficiency and cannot breathe on their own. By contrast, ventilation in the aPCV mode is indicated in patients who cannot breathe completely independently but nevertheless have a certain amount of spontaneous respiratory activity. The aPCV mode offers more intensive ventilation support in contrast to pure pressure support (ASB). This ventilation mode is therefore particularly useful when weaning patients off ventilation or for patients being ventilated in a domestic setting in whom ASB alone is not sufficient.

Used in neuromuscular diseases that weaken the respiratory muscles, aPCV has proven itself in routine clinical practice for this setting.³ Moreover, ventilation in the aPCV mode can be administered to patients with lung diseases such as acute respiratory distress syndrome (ARDS).⁴

aPCV can be administered both for continuous as well as intermittent ventilation. The objective of intermittent, pressure-controlled ventilation is to achieve recovery of the respiratory muscles. This is all the more pronounced the longer the ventilation lasts – for example, during the night. Nevertheless, there are also phases with respiratory activity, for example during the process of connecting the patient to ventilation or during rest and recovery phases. During ventilation, such phases are taken into account by the aPCV mode.²

Advantages of aPCV

One major advantage of aPCV is that it supports spontaneous breathing. The delivery of mechanical ventilation is kept constant and effective to ensure continuous CO₂ exhalation – even under varying clinical conditions. Simultaneously, patient-driven triggering enables adaptation to the patient’s individual needs while increasing patient comfort as well.

Thanks to this pressure control, ventilation in the aPCV mode additionally reduces the risk of volutrauma and barotrauma. Therefore, this mode is particularly advantageous for lung-protective ventilation and is frequently used for home ventilation.²

Another advantage of ventilation in the aPCV mode is that it supports weaning from a respirator. Thanks to the promotion of spontaneous breathing and the additional work of breathing, the patient’s respiratory muscles are strengthened and trained, making it easier to wean the patient back to completely breathing on their own.

Disadvantages of ventilation in the aPCV mode

Despite all of the above, ventilation in the aPCV mode also has certain disadvantages. As with classic ventilation in the PCV mode, the tidal volume here is likewise also heavily dependent on the compliance and resistance of the airways and lungs. Fluctuations in the patient’s work of breathing can lead to unpredictable volume changes since ventilation in the aPCV mode integrates both assisted and controlled breaths.

Ventilation in the aPCV mode equally carries the risk of hyperventilation, especially if the triggering of mechanical breaths occurs at a too high frequency. Respiratory alkalosis or overexpansion of the lungs (barotrauma) is also a conceivable consequence.

Difference between PCV and aPCV

PCV and aPCV are both pressure-controlled forms of ventilation with a preset pressure limit. PCV is a controlled ventilation mode that does not allow any spontaneous breathing. The tidal volume depends on the compliance of the respiratory system and the patient’s airway resistance.

By contrast, aPCV represents an assisted form of ventilation that allows spontaneous breaths by the patient while administering a breath-synchronized mechanical breath during the patient’s efforts to breathe on their own. The tidal volume is similarly a function of compliance and resistance. However, the minute volume can be increased or decreased by changing the ventilation frequency through the patient’s spontaneous breathing. Ventilation in the aPCV mode can also be performed without the patient’s own breathing. This way, the ventilation frequency remains constant and the patient is ventilated under controlled conditions.

The main differences between the two modes are listed in the following table:

PCV: Pressure-controlled ventilation

Control type: Pressure-controlled
Operating mode: Controlled
Application: No spontaneous breathing
Pressure limit: Fixed pressure limit through pressure control
Volume delivery: Constant, depending on respiratory system compliance and resistance

aPCV: Assisted pressure-controlled ventilation

Control type: Pressure-controlled
Operating mode: Assisted
Application: Partial spontaneous breathing, but also possible without spontaneous breathing
Pressure limit: Fixed pressure limit through pressure control
Volume delivery: Adaptive, depending on the patient’s spontaneous breathing, compliance of the respiratory system and resistance

Ventilation in the aPCV mode: Parameter

Important ventilation parameters must be set in order to adapt ventilation in the aPCV mode to the patients’ individual needs. The following parameters can be adjusted for ventilation in the aPCV mode on WEINMANN ventilators:

Inspiratory pressure in mbar (pInsp): The pressure generated during inhalation to move air into the lungs.
Ventilation frequency in 1/min (Freq): The number of breaths performed per minute by the ventilator.
Positive end-expiratory pressure in mbar (PEEP): The pressure that keeps the alveoli open at the end of exhalation to improve gas exchange.
Maximum inspiratory pressure in mbar (pMax): The maximum pressure that can be achieved during inhalation to protect the lungs from excessive pressure.
Inspiratory trigger (InTr): The threshold value that determines when the ventilator initiates inspiration.
Inspiratory-expiratory ratio (I:E): The ratio of inhalation time versus exhalation time spent to control the respiratory cycles.
0–100% of Te (trigger window): The period of time during which the ventilator responds to the patient’s breathing attempt and triggers inspiration, indicated as a percentage of the expiratory time (Te).

Ventilation in the aPCV mode is particularly flexible and supports patients in the work of breathing. At the same time, it enables patients to train and strengthen their respiratory muscles through spontaneous breaths. aPCV thus represents an extremely versatile feature, providing personalized and safe airway management. WEINMANN ventilators support this form of ventilation with devices that can be precisely adapted to the patient’s needs by setting the parameters.

aPCV mode on WEINMANN ventilators

WEINMANN supports ventilation in the aPCV mode with the MEDUMAT Standard² ventilator and MEDUVENT Standard ventilator.

MEDUVENT Standard is one of the most light-weight and easy-to-handle emergency ventilators in the world. With a weight of a mere 2.1 kg, the MEDUVENT Standard can ventilate an adult for an average of 7.5 hours at typical ventilation settings – without an external pressurized gas supply.

With a weight of just 2.5 kg and a battery runtime of 10 hours, MEDUMAT Standard² is equipped for use in any setting; it is a reliable companion for emergency medical services, especially during longer sessions. The ventilator can also ventilate patients with a weight as low as 3 kg, which also makes it suitable for the ventilation of infants.

In an emergency - such as acute respiratory insufficiency - both devices offer a quick and guideline-compliant start to ventilation by entering the patient’s height. This way, patients are assured of rapid assistance to overcome shortness of breath in critical situations.

Additionally, the devices generate pressure and flow curves that make it possible to monitor the effectiveness of ventilation in the aPCV mode and the patient’s own work of breathing. Comprehensive monitoring increases patient safety, as does the intuitive operation and handling of the devices in use: The straightforward arrangement of symbols and the visual and acoustic warning signals ensure that patients are ventilated effectively and safely.

In addition, the devices feature a night view, which enables safe handling even in the dark. Thanks to a hygiene filter, the devices can be used on several patients during one session without fearing contamination of the device.

¹https://www.weinmann-emergency.com/de/themen/notfallbeatmung/druckkontrollierte-beatmung

² Hartmut Lang (2017): Außerklinische Beatmung. Basisqualifikationen für die Pflege heimbeatmeter Menschen. Berlin Heidelberg: Springer-Verlag, p. 120-131.

³ Groß M, Dorst J, Pelzer K. Beatmung bei neuromuskulären Erkrankungen. Neurological respiratory medicine. 2019 Sep 4:193–246. German. doi: 10.1007/978-3-662-59014-0_13. PMCID: PMC7236064: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236064/

⁴ https://www.weinmann-emergency.com/de/themen/notfallbeatmung/beatmungsformen