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Ventilation

Breathing is a process that most people take for granted. But for patients with certain illnesses or in acutely critical situations, it is often a challenge. In cases like these, mechanical ventilation is an essential support; however, it is not the same as spontaneous physiological breathing. 

Both spontaneous breathing and mechanical ventilation follow a cycle of inhalation (inspiration) and exhalation (expiration). The crucial difference is the way in which inspiration takes place.

During physiological breathing, negative pressure is created in the thorax, which draws air into the alveoli and causes the inspiratory respiratory muscles to contract. Expiration is usually performed passively by the retraction forces of the lungs and thorax as well as the expiratory respiratory muscles. During mechanical ventilation, air enters the lungs through positive pressure generated by the ventilator. Here too, expiration is passive.1

In the absence of spontaneous breathing, mechanical ventilation is a lifesaving measure, especially in the emergency medical services. In the following you will find an overview of the principles of ventilation as well as various ventilation types and parameters.

Definition: Ventilation

Ventilation is a medical procedure that ensures that gas is exchanged in the lungs when there is no or insufficient spontaneous breathing. Respiratory gas is introduced into the lungs using manual or mechanical support in order to maintain oxygenation and ventilation. Ventilation has 4 key objectives: 

  1. To ensure pulmonary gas exchange: improve O₂ uptake (oxygenation) and the elimination of CO₂ (decarboxylation) for adequate ventilation.
  2. To increase lung volume: ensure appropriate volume delivery and ventilation pressures to improve respiratory system compliance, prevent or eliminate atelectasis and minimize lung damage.
  3. To reduce the work of breathing: allow the respiratory muscles to recover, bridge states of exhaustion and eliminate respiratory distress by relieving pressure.
  4. To ensure survival: prolong survival time in critical conditions.2

Mechanical ventilation is usually performed as positive pressure ventilation, where a ventilator (respirator) generates the pressure increase. Depending on the ventilation mode, the device generates a controlled pressure and/or volume during inspiration. A distinction can therefore be made between pressure-controlled, volume-controlled and hybrid ventilation types. 

Inspiration can be triggered by the ventilator (machine-triggered) or by a patient’s spontaneous breath (patient-triggered). The end is also either machine or patient triggered. Expiration, on the other hand, is a passive process.3

Indication

The decision to ventilate is made on an individual basis and requires careful consideration. The indication is not based on individual parameters, but is the result of a combination of several factors. These include:

  • Progression of the underlying condition
  • Severity of the gas exchange disorder
  • Measurable vital signs
  • Patient’s wishes and therapeutic goals

Progression of the underlying condition

Acute respiratory failure is a basic indication for ventilation that can occur both in previously healthy patients and in patients with decompensated chronic lung diseases. There are pulmonary and extrapulmonary indications that may make ventilation therapy necessary.

Pulmonary indications

  • Respiratory ailments, e.g. asthma and COPD
  • Disorders of the lung parenchyma, e.g. ARDS, pneumonia, atelectasis, aspiration and near-drowning

Extrapulmonary indications

  • Central respiratory disorder, e.g. craniocerebral trauma
  • Peripheral respiratory disorder, e.g. neurological damage
  • Cardiovascular disorder, e.g. cardiopulmonary resuscitation
  • Severe sepsis and septic shock
  • Hypothermia

Severity of the gas exchange disorder

Respiratory insufficiency is assessed on the basis of clinical signs such as:

  • Cyanosis
  • Tachypnea
  • Bradypnea
  • Orthopnea
  • Dyspnea
  • Cold sweats

Measurable vital signs

Deviations from the normal values for ventilation parameters such as respiratory rate or oxygen saturation (SpO2) support the indication and supplement the clinical assessment.

Patient’s wishes and therapeutic goals

The patient’s prognosis and state of health play a key role. If possible, invasive measures should be avoided and alternatives such as non-invasive ventilation given preference.4

Ventilation options: Types of ventilation explained simply

Mechanical ventilation can be performed either invasively or non-invasively: 

Invasive ventilation: This is performed using airway devices that are inserted directly into the airways. The devices used include:

  • Tracheal tube: A tube that is inserted into the windpipe (trachea) during oral or nasal intubation. An inflatable cuff ensures that it is sealed.
  • Supraglottic airway devices: These are positioned above the glottis or trachea.5 Examples include the laryngeal mask airway and laryngeal tube.
  • Tracheal cannula: A cannula that is inserted into a tracheostoma – a surgically created opening between the external airspace and the trachea.

Non-invasive ventilation: This type of ventilation does not require intubation and is performed via a mask or helmet. The ventilation can only be performed mechanically with a ventilator.

Ventilation modes

The choice of ventilation mode depends on spontaneous breathing. If there is spontaneous breathing, supported or assisted modes are available, such as:

  • CPAP (continuous positive airway pressure): Positive end-expiratory pressure (PEEP) is continuously maintained in the airways, which improves oxygenation and prevents alveolar collapse.
  • ASB/PSV mode (assisted spontaneous breathing/pressure support ventilation): During ASB ventilation, pressure support is provided at a set PEEP level in synchrony with spontaneous breathing.
  • SIMV (synchronized intermittent mandatory ventilation): This volume-controlled ventilation type sets a minimum frequency of mechanical breaths per minute. Patients can also trigger a pressure-supported breath during expiration, which is administered synchronously.
  • BIPAP/BiLevelaPCV: Various pressure-controlled types of ventilation are available. With BiLevel ventilation, ventilation takes place at 2 pressure levels – the inspiratory pressure (pInsp) and the positive end-expiratory pressure (PEEP). Spontaneous breaths can be taken at any time, which are then synchronized by the mode. If the patient is unable to breathe on their own, they are ventilated under pressure control. aPCV ventilation specifies a mandatory ventilation frequency, which can be supplemented by spontaneous breaths within a trigger window during expiration.
  • PRVC (pressure-regulated volume control): With this ventilation type, a test breath is taken, which is used to select an inspiratory pressure that delivers the tidal volume to be administered in a pressure-controlled manner. PRVC ventilation is therefore a hybrid mode.

If there is no spontaneous breathing, mandatory ventilation is used. There are 2 ventilation options in this case:

  • PCV (pressure-controlled ventilation): The ventilation pressure is set; the tidal volume is determined by the compliance and resistance of the lungs.
  • VCV (volume-controlled ventilation): The tidal volume is preset and the airway pressure is limited by a maximum ventilation pressure (pMax).

Complications during ventilation

During ventilation, various complications affecting the safety and success of the treatment can occur. 

  • Pulmonary damage due to overexpansion: Weak alveoli can rupture, resulting in a pneumothorax, where air accumulates in the pleural space and the lung collapses.6
  • Baro-, volu- or biotrauma7: Lung tissue and structures can be damaged by high pressure or high volumes. Biotrauma can be caused by an excessively high oxygen concentration, as free oxygen radicals can attack the lungs. This phenomenon is known as oxygen toxicity.8

Volume and pressure limits are used to prevent risks of this kind. Flexible adjustments to the ventilation are also necessary, particularly with regard to risk factors such as oxygen levels. It is therefore important to monitor ventilation parameters.

Ventilation parameters

The following table provides an overview of the main adjustable ventilation parameters during ventilation.

FiO₂

Inspiratory oxygen concentration
Unit: vol%

RR

Respiratory rate
Unit: breaths per minute

VT

Tidal volume
Unit: liters, milliliters

PEEP

Positive end-expiratory pressure
Unit: mbar

pInsp

Inspiratory pressure
Unit: mbar

ASB/PSV

Assisted spontaneous breathing/pressure support ventilation
Unit: mbar

I:E

Ratio of inspiration to expiration
Unit: -

Trigger

Respiratory volume of the patient until the machine begins to provide support
Unit: liters per minute (flow trigger)

Pressure ramp

Time within which inspiratory pressure is reached
Unit: s

Ventilation monitoring

Ventilators offer various options for monitoring important parameters and adjusting them if necessary, thereby ensuring safer and more effective ventilation. 

One of the key tools here is capnography, which is a procedure for measuring end-tidal CO₂ concentration (etCO₂). Monitoring shows whether sufficient CO₂ is being exhaled, for example. 

Pulse oximetry measures the patient’s oxygen saturation and pulse and, alongside etCO2, is a key component in monitoring ventilation.

Pressure and flow curves can be used to visualize ventilation, making it easier to identify potential risks.

Ventilators enable important measured values to be collected. These include:

  • Expiratory tidal volume (VTe)
  • Expiratory minute volume (MVe)
  • Pressure measurements such as pPeak, pPlat, and pMean
  • Leakage volume (Vleak)
  • A blood gas analysis (BGA) provides information about the breathing and ventilation ratio. It can also indicate whether invasive ventilation should be started. The analysis is used to assess the state of oxygenation, ventilation and the acid-base balance. Values such as the CO₂ partial pressure (paCO₂) and the pH value are recorded for this purpose.9
  • To detect impending dangers at an early stage, ventilators use alarms that are triggered when defined threshold values are exceeded. The limits are determined by users and must be checked regularly. Possible alarms include:
    • Airway pressure (pAw, pMax)
    • Minute volume high/low
    • Respiratory rate high/low
    • etCO₂ high/low
    • Apnea time10

Ventilators and types of ventilationfrom WEINMANN

WEINMANN ventilators offer a wide range of ventilation options tailored to the needs of patients in various emergency situations. They cover a wide range of ventilation modes so that you can always find the right solution for each individual case.

WEINMANN ventilators

With WEINMANN ventilators, we guarantee maximum flexibility and efficiency.

MEDUVENT Standard is one of the smallest and lightest turbine-driven ventilators in the world. Weighing just 2.1 kg, it is extremely handy and can be operated for up to 7.5 hours with no need for an external compressed gas supply. Oxygen concentrations of 21% to 100% can be applied in this process.

MEDUMAT Standard² is a real all-rounder. It is equipped with a variety of ventilation modes and provides reliable ventilation for up to 10 hours – ideal for long deployments. It can also ventilate infants weighing 3 kg or more as well as adults, making the device practical and universally applicable.

Types of ventilation from WEINMANN

We offer the following ventilation types for ventilation therapy: 

Volume-controlled

  • IPPV
  • S-IPPV
  • SIMV
  • SIMV+ASB

Pressure-controlled

  • PCV
  • aPCV
  • BiLevel
  • BiLevel + ASB
  • CCSV (ventilation mode for resuscitation)

Hybrid ventilation modes

  • PRVC
  • PRVC + ASB

Spontaneous ventilation modes

  • CPAP
  • CPAP + ASB

Special ventilation functions

  • CPR
  • RSI
  • Manual via MEDUtrigger

1Larsen, R. & Mathes, A. (2023): Beatmung. 7. Aufl., Berlin Heidelberg: Springer Verlag, S. 243f. 

2Lang, H. (2020): Beatmung für Einsteiger. Theorie und Praxis für die Gesundheits- und Krankenpflege, 3. Aufl. Berlin Heidelberg: Springer Verlag, S. 25. 

3Larsen, R. & Mathes, A. (2023): Beatmung. 7. Aufl., Berlin Heidelberg: Springer Verlag, S. 243.

4Larsen, R. & Mathes, A. (2023): Beatmung. 7. Aufl., Berlin Heidelberg: Springer Verlag, S. 266ff.

5https://www.amboss.com/de/wissen/supraglottische-atemwegshilfen/

6https://www.msdmanuals.com/de/heim/lungen-und-atemwegserkrankungen/respiratorische-insuffizienz-und-akutes-atemnotsyndrom/k%C3%BCnstliche-beatmung#Alternativen_v38059371_de

7https://viamedici.thieme.de/lernmodul/6772238/4915521/beatmung

8https://www.msdmanuals.com/de/profi/intensivmedizin/respiratorische-insuffizienz-und-maschinelle-beatmung/mechanische-beatmung-im-%C3%BCberblick#Komplikationen-bei-der-mechanischen-Beatmung-und-Sicherheitsvorkehrungen_v89529514_de

9Lang, H. (2020): Beatmung für Einsteiger. Theorie und Praxis für die Gesundheits- und Krankenpflege, 3. Aufl. Berlin Heidelberg: Springer Verlag, S. 264.

10[Lang, H. (2020): Beatmung für Einsteiger. Theorie und Praxis für die Gesundheits- und Krankenpflege, 3. Aufl. Berlin Heidelberg: Springer Verlag, S. 242.