What is ventilation?
Ventilation replaces or supports the breathing of patients whose spontaneous breathing has stopped (apnea) or is no longer sufficient to maintain bodily functions. Due to the lack of or insufficient oxygen supply, the carbon dioxide content in the body rises while the oxygen content falls.
Ventilation counteracts this. Its effectiveness can be measured by blood gas analysis, by measuring the absorption of light when the skin is illuminated (pulse oximetry) or the concentration of carbon dioxide in the exhaled air (capnometry).
Different ventilation techniques
There are many different ventilation techniques. They can be categorized according to different criteria. In principle, there is manual ventilation with a manual ventilation bag for emergencies and mechanical ventilation with a ventilator (respirator). The latter can be divided into non-invasive and invasive ventilation depending on the access route:
- Non-invasive ventilation (NIV ventilation): This refers to mechanical ventilation via a ventilation mask or a ventilation helmet.
- Invasive ventilation (IV ventilation): This refers to mechanical ventilation via a tube or thin tube inserted into the trachea (endotracheal tube or trach cannula).
- Controlled ventilation: In this case, the respirator, i.e. the ventilator machine, performs all the breathing work – regardless of whether the patient is breathing on their own.
- Assisted ventilation: In this case, the patient performs the greater part of the work of breathing and breathing regulation. The ventilator supports the patient like an additional respiratory muscle.
There are various techniques for both controlled and assisted ventilation (more on this below).
When is ventilation performed?
Ventilation is always necessary when natural spontaneous breathing is not sufficient to inhale enough oxygen and exhale enough carbon dioxide. Depending on the cause, the doctor selects the appropriate ventilation form or technique.
For example, in people with chronic obstructive pulmonary disease (COPD) or diseases with respiratory muscle weakness, ventilation during the night is usually sufficient to allow the respiratory muscles to recover. This can also be carried out as home ventilation with respirators at home.
Acute respiratory distress syndrome (ARDS), caused for example by pneumonia, pulmonary embolism, blood poisoning (sepsis) or various medications and toxins, usually requires temporary ventilation. Sometimes nitric oxide is added to the breathing gas (NO ventilation) to increase the oxygen content of the blood.
For patients in a coma or those who are no longer breathing on their own due to paralysis, long-term mechanical ventilation ensures the oxygen supply.
What is ventilation used for?
In contrast to spontaneous breathing, artificial ventilation forces breathing gas into the lungs using positive pressure. Non-invasive artificial respiration uses masks that are placed over the mouth and nose, while invasive artificial respiration uses a tube that is inserted into the windpipe via the mouth or nose (intubation). Various forms of treatment are used.
Please note: There are no internationally standardized terms for the various forms of treatment!
Controlled ventilation
As mentioned above, in controlled mechanical ventilation (controlled mechanical ventilation or continuous mandatory ventilation, CMV), the respirator does all the work of breathing and is not influenced by any spontaneous breathing the patient may still be doing.
A distinction is made between volume-controlled and pressure-controlled ventilation:
IPPV ventilation (intermittent positive pressure ventilation) is also a volume-controlled form of ventilation. Here, the pressure in the lungs drops passively to zero during exhalation. However, this technique is rarely used today. Instead, the CPPV (continuous positive pressure ventilation) variant is usually chosen as volume-controlled ventilation: With this ventilation technique, the ventilator maintains a positive pressure in the lungs during exhalation (PEEP = positive end-expiratory pressure). This prevents the alveoli from collapsing (collapsing) at the end of each exhalation. A CPPV is therefore basically an IPPV with PEEP.
For pressure-controlled ventilation (PCV), the ventilator creates a certain pressure, which is not exceeded, in the airways and alveoli so that as much oxygen as possible can be absorbed. As soon as the pressure is high enough, exhalation starts. This protects the lungs from overstretching and the damage this can cause.
Assisted ventilation
The latter occurs with assisted spontaneous breathing (ASB). Spontaneous ventilation is pressure-supported here: The ventilator sets the pressure during inspiration (inspiratory pressure) and the volume fraction of oxygen in the gas mixture to be inhaled. It also maintains the airway pressure at the end of exhalation so that the alveoli remain open (PEEP). During ASB ventilation, the patient can determine the breathing rate and breathing depth themselves.
SIMV ventilation and CPAP ventilation are also variants of assisted ventilation:
Synchronized intermittent mandatory ventilation (SIMV ventilation)
In SIMV ventilation, assisted spontaneous breathing by the patient is combined with controlled ventilation. The respirator supports the patient when the patient triggers it through breathing efforts. The interval between two inspiration phases is defined. If the patient breathes outside these intervals, they breathe independently without support. If triggering by the patient’s own breathing fails completely, the respirator ventilates independently.
CPAP ventilation
You can read more about this form of ventilation here.
High-frequency ventilation (high-frequency oscillation ventilation; HFO ventilation)
High-frequency ventilation has a special status and is mainly used for children and newborns. With HFO ventilation, turbulence is created in the airways so that the air in the lungs is constantly mixed. This results in improved gas exchange despite the low ventilation volume.
What are the risks of ventilation?
In addition to skin irritation or wounds caused by the mask or tube, complications can arise from the ventilation itself. These include
- Damage to the lungs due to pressure
- Pneumonia
- Increase in pressure in the chest
- Stomach bloating
- Reduction in venous return to the heart
- Increase in vascular resistance in the lungs
- Reduction in the pumping capacity of the heart
- Reduction in kidney and liver blood flow
- Increase in intracranial pressure
Lung-protective ventilation reduces or prevents such damage by limiting ventilation pressures and ventilation volumes.
