As apnea or apnea , a more or less long suspension or stop willful breathing is referred to. This technical expression comes from ancient Greek ἄπνοια ápnoia "non-breathing" (to πνοή pnoé "breathing, breath" with alpha privativum ) and is pronounced three-syllable "A-pno-e" [ aˈpnoːə ], which is sometimes made clear by the spelling Apnoë .
Respiratory arrest can last from a few seconds to several minutes. Several respiratory arrests of different lengths, unnoticed by the patient, are the eponymous symptom of sleep apnea syndrome .
Possible causes of respiratory paralysis can be:
- Damage to the respiratory center
- Paralysis of the respiratory muscles
- Electricity accident
- Blockage of the airways (airway obstruction)
- neurological diseases
- Trauma , especially chest compression as a result of an accident or after an avalanche
- Intoxication , e.g. B. with potassium cyanide
- Result of a burial, for example in a mine accident
The volume of gas in the lungs initially remains unchanged. The gas exchange within the lungs and cellular respiration are initially unaffected by apnea. Respiratory failure quickly leads to a dangerous lack of oxygen in the blood ( hypoxemia ), regardless of the cause, which can quickly lead to a further failure of important vital functions. Respiratory arrest leads to an insufficient supply of oxygen to the brain.
Breathing and CO 2
Untrained individuals cannot willingly hold their breath for more than a minute or two. The reason for this lies in the very strict regulation of CO 2 and blood pH by the respiratory center. In the case of apnea, no more CO 2 is exhaled; it accumulates in the blood. This strong stimulus on the respiratory center can be overcome at will. Trained apnea divers can hold their breath for over 10 minutes.
In the blood of dissolved CO 2 in physiological and slightly increased concentration of the respiratory center of the brain is activated. In a significantly higher concentration, on the other hand, it leads to a reduction or elimination of the reflex breathing stimulus up to respiratory arrest. There is a risk of poisoning from carbon dioxide.
Since the gas exchange between blood and lung contents is independent of the gas flow between the lungs and the outside air, sufficient oxygen can even be administered to an apneaic person. This phenomenon is called apneaic oxygenation . During apnea, more oxygen is absorbed from the volume of gas in the lungs than carbon dioxide diffuses into the lungs. When the airway is open, an administered gas follows the pressure gradient from the upper airway into the lungs. If pure oxygen is given, this is sufficient to fill up the oxygen stores in the lungs. The uptake of oxygen into the blood thus remains in the usual range. However, no CO 2 is exhaled during an apnea . The partial pressure of carbon dioxide in the blood will therefore rise and a respiratory acidosis cause. In addition, the oxygen in the lungs is gradually being replaced by CO 2 .
Under ideal conditions - that is, when pure oxygen was breathed to remove all nitrogen and pure oxygen was insufflated before the apnea began - a healthy adult could theoretically be adequately oxygenated for an hour. The limiting factor here is the accumulation of carbon dioxide.
Apneaic oxygenation is used in thoracic surgery as well as for manipulation of the airways such as bronchoscopy , intubation or surgical interventions. Due to the restrictions described, however, apnea oxygenation is inferior to the extracorporeal circulation method and is only used in emergencies and for short processes up to a maximum of 10 minutes.
Apnea test (brain death diagnosis)
The so-called “apnea test” is one of the criteria used to determine brain death in the context of organ donation , along with angiography , electroencephalograms and others . Here is comatose patient with pure oxygen ventilation and mechanical ventilation drastically reduced so that there is an increase of carbon dioxide - the partial pressure is in the blood. For the receptors in the brainstem , this increase represents a maximum incentive to trigger a spontaneous breath. If spontaneous breathing does not start at a specified limit, one can assume a complete failure of the respiratory center .
Apnea ventilation is also called backup ventilation (here the names of the various manufacturers of ventilators varied ).
Spontaneous (or augmented) forms of ventilation help the patient to breathe without taking them over completely. The apnea setting on the ventilator serves as a safety measure; if the patient fails to breathe, the machine automatically jumps to apnea mode, i.e. continues to ventilate in a controlled (or mandatory) manner.
- Hugo Karel van Aken, Konrad Reinhart, Tobias Welte, Markus Weigand: Intensive Care Medicine . Georg Thieme Verlag, 2014, ISBN 978-3-13-151143-0 ( limited preview in Google book search).
- Reinhard Larsen: Anesthesia and intensive medicine in cardiac, thoracic and vascular surgery. (1st edition 1986) 5th edition. Springer, Berlin / Heidelberg / New York a. a. 1999, ISBN 3-540-65024-5 , p. 501 ( Apnoic oxygenation ).