Oxygen in Emergency Medicine
Acute myocardial infarction:
The O2 administration is a standard of AHA emergency therapy. O2 administration leads to improved oxygen supply in ischemic tissue. In addition, there are indications that the size of the infarct and the increase in the ST route are decreasing.
"Indication:" Always on suspicion of acute cardiac syndrome. Note: MONA greets all patients: Morphin, O2, Nitrat and ASS.
Dosage:' by nasal probe not more than 4-6 l O2/min are applied, otherwise the mucous membranes will dry out. If no saturation of at least 95% can be achieved under this dose, the O2-Flow via mask must be increased to 8-10 l/min.
Caution: In chronic obstructive pulmonary disease, O2 can cause respiratory depression. In these rare cases, start with 1-2 l O2/min.
Oxygen should be given to any patient with thoracic pain, suspected oxygen deficiency of any cause and cardiac arrest as an initial measure (Class I recommendation of the AHA and ERC). There are no toxic side effects of oxygen in the acute care of the patient. Damage caused by excessive oxygen intake can only be observed after more than three to five days. During resuscitation, there is no dosage other than 100% oxygen, regardless of the cause of clinical death. In still responsive patients with acute airway obstruction (exacerbated COPD, asthmatic status), there is a certain caution when applying too high doses of oxygen. Because the respiratory drive caused by hypoxia can be inhibited by too high doses of oxygen - usually only over two litres per minute - and CO2anaesthesia results. However, it should also be borne in mind that severe hypoxia caused by acute obstruction of the respiratory tract (asthma, COPD) leads to an oxygen deficiency of the myocardium and thus to severe ischemia, which leads to circulatory shock and ultimately to the death of the patient. Therefore, even in severe asthma attacks with hemodynamic impairment, the administration of high doses of oxygen is necessary to counteract this mechanism. As a side effect, the patient can recover in the same way as he could become intubated, which is unavoidable in this situation. The dosage here ultimately depends only on the haemodynamic situation of the patient. Including oxygen even in this situation, the severe status of asthma, would therefore be a mistake due to ignorance - under the banal common idea that oxygen in high doses is contraindicated in acute respiratory obstruction.
Why oxygen in cardiac emergencies? The ultimate therapeutic goal of any cardiac emergency is to improve oxygenation in all tissues of the body. Oxygen is a drug like any i.v. or orally administered drug. It's just easier in the way it's applied. Therefore, oxygen is the first measure in any cardiac emergency and is considered a Class I recommendation of the AHA, even if there are no reliable studies on mortality improvement, etc., as these are difficult to prepare in such situations it is not ethically possible to provide a cardiac emergency without oxygen. Always remember "Oxygen - i.v.access - ECG" as a first measure in a cardiac emergency.
How is oxygen administered?
In a cardiac emergency, oxygen is usually administered at 4 (-6) liters per minute via a nasal probe. The oxygen saturation should reach 97 to 98 %. If it is not possible to reach this level, the method of application should be transferred to a mask, since oxygen in a higher supply dries out the nasal mucous membranes and is very unpleasant for the patient. Below this the dosage can be increased as required. However, it is also crucial that a mask should never be used for the application of oxygen doses of less than 5 to 6 litres, as this involves relevant rebreathing of CO2. In ventilation situations there is only one dosage: 100% oxygen.
What are the dangers of oxygen?
Alleine bei V.a. eine obstruktive Atemwegserkrankung ist eine Initialdosierung von 1 bis 2 Litern/Minute Sauerstoff, ebenfalls über Nasensonde – niemals über Maske – , zu verabreichen. Daneben gilt das oben Gesagte (siehe erster Abschnitt).
Welche inspiratorischen Sauerstoffkonzentrationen können mit den im Notfall üblichen Applikationen erreicht werden?
| Mund zu Mund-Beatmung | ca.17 % 4 Liter/Minute |
| Sauerstoff über Nasensonde | ca. 30 % 10 Liter/Minute |
| über Maske | ca. 70 % |
| Maskenbeatmung ohne Sauerstoffreservoir (flow 10 Liter/Minute) | ca. 60 % |
| Maskenbeatmung mit Sauerstoffreservoir (flow 10 Liter/Minute) | ca. 100 % |
| Beatmungsbeutel bei Maskenbeatmung mit Oxydemand-Ventil | ca. 100 % |
Bei allen Spontanatmungsformen hängt die inspiratorische Sauerstoffkonzentration im Gegensatz zu den Beatmungen natürlich vom Atemminutenvolumen des Patienten ab, weshalb hier nur Schätzwerte angegeben werden können.