Oxygen is the most commonly used drug in Emergency Medicine and, when used judiciously, it undoubtedly saves lives. It’s an essential component in the resuscitation of the critically ill, including trauma victims, patients with sepsis, cardiac arrest and myocardial infarction victims, stroke, asthma and COPD exacerbations. The goal is to correct hypoxemia (low blood oxygen levels).
When Should Emergency Oxygen be Used?
Supplemental oxygen is needed when the oxygen saturation falls below 89 % or the arterial oxygen pressure falls below 60 mmHg. However, supplemental oxygen might become unfavourable above a SpO2 range of 94-96% hence causing hyperoxia (high blood oxygen levels).
In fact, multiple randomised controlled trials have shown that hyperoxia can actually increase mortality in several subsets of critically ill patients. Hyperoxia can cause coronary vasoconstriction. Paradoxically, therefore, giving too much oxygen at the time of an acute infarction may worsen oxygen delivery to the cardiac muscle.
The use of high-flow oxygen has been associated with increased reperfusion injury, infarct size and mortality in myocardial infarction. Theoretically, hyperoxia may have similar effects on cerebral blood flow. One randomised controlled trial found that in minor or moderate stroke, oxygen administration was linked to increased mortality when compared with air.
In absence of hypoxemia, the routine use of oxygen therapy in patients with myocardial infarction, stroke, traumatic brain injury, cardiac arrest and sepsis, showed no benefit but rather it seems to be harmful.
High-flow oxygen tubing should only be used in a few diseases such as carbon monoxide poisoning, cluster headaches, sickle cell crisis and pneumothorax.
Intensive care unit patients can tolerate a conservative oxygen therapy aimed to maintain arterial oxygenation within the physiological range, which in turn may improve outcomes.
Pulse oximetry should be recorded in all patients as the ‘fifth vital sign’ and further assessment with arterial blood gases (ABGs) should be performed, if indicated. Arterial blood gases (ABGs) are recommended in all critically ill patients with unexpected or inappropriate hypoxemia (oxygen saturation <94%) or those who require supplemental oxygen to maintain this level. Although pulse oximetry is the go-to quick solution to discovering blood oxygen levels, only arterial blood gas results will give exact, precise and completely reliable results.
Who can Benefit from Emergency Oxygen?
Your choice of mask and oxygen tubing, on which the flow depends, is related to the patients' requirements.
Type 2 respiratory failure patients (T2RF) are still able to maintain normal carbon dioxide levels. In all acutely unwell patients that are not at risk of T2RF, the recommended target saturation range is 94–98%. In patients at risk of type 2 respiratory failure i.e. being both hypoxemic and hypercapnic (have high carbon dioxide levels), a target saturation range of 88–92% is recommended.
This allows a margin of safety for possible inaccuracies in pulse oximetry readings and a “safety cushion” to allow for fluctuation in the oxygen saturation. Conversely, lower oxygen levels are necessary for chronically hypercapnic patients (those at risk of type 2 respiratory failure). High oxygen levels could induce oxygen-induced hypercapnia, one of the most common and serious complications of oxygen therapy.
In conditions where there is a risk of type 2 respiratory failure, Venturi masks are the delivery device of choice as constant or known oxygen concentrations are administered, regardless of flow. These conditions include COPD exacerbations, chest-wall deformities, respiratory muscle weakness and central nervous system depression (CNS) depression.
A common cause of CNS depression is high doses of sedatives and strong opioids. Moreover, T2RF can be caused by severe asthma, myasthenia gravis, muscle disorders, obesity, hypothyroidism and adult respiratory syndrome.
In most breathless but non-hypoxaemic patients, supplemental oxygen is not required.
On the other hand, a saturation within target range but falling by ≥3%, requires prompt assessment should ensure as it may herald acute deterioration in the patient’s condition.
If patients carry an oxygen alert card, due to a previous T2RF, the patient-specific target range should be prescribed.
Comments like ‘No one ever died because they had too much oxygen – that is the first thing you learn on the trauma course’ and ‘We are resuscitating in this department – it’s different down here’ are entirely untrue and there are standards for how much oxygen does a patient need.
A100% oxygen saturation (100 ≥ mm Hg) is used only in preoxygenation, cardiac arrest until ROSC (return of spontaneous circulation), spontaneous pneumothorax in patients without COPD, cluster headache, carbon monoxide poisoning and cyanide poisoning and decompression illness prior to starting hyperbaric oxygen therapy.
A 94-98 % oxygen saturation (76–92 mm Hg) is the goal in hypoxia in the absence of risk factors for hypercapnic respiratory failure.
Lower oxygen saturation of around 90-94% (69–76 mm Hg) is achieved in acute stroke and myocardial infarction.
When there are risk factors for hypercapnic respiratory failure, the goal is 88-92% (57-68mm Hg). These include chronic lung disease (e.g., COPD bronchiectasis cystic fibrosis), chest wall deformity, morbid obesity, neuromuscular disorders (e.g., ALS), obstructive sleep apnea or central hypoventilation (reduced breathing rate and gas exchange) due to a cerebrovascular accident, traumatic brain injury or narcotic overdose.
Finally, the target oxygen saturation for Paraquat and Bleomycin poisoning is 85-88% (52-57 mm Hg).
How do You Administer Oxygen Safely?
Nonhumidified oxygen is supplied oxygen without added moisture. It’s used when low-flow (≤ 4/L minute) oxygen via nasal cannula or a mask is required. Additionally, it can be used for high-flow oxygen (> 4 L/minute) via the upper airways but only for short-term use.
Humidified oxygen is a form of oxygen delivery with a humidification device. It’s used when high-flow oxygen (> 4 L/minute) via the upper airways for > 24 hours is needed. It’s used in conjunction with a high-flow nasal cannula, tracheal cannula or other artificial airways and if patients experience discomfort with non- humidified oxygen.
If an emergency tracheostomy needs to be performed, any oxygen is acceptable until humidified oxygen becomes available again.
A nasal cannula is a basic oxygen delivery system consisting of two nasal prongs. The FiO2 delivered: ∼ 24–40% (1–6 L/minute flow) and is used in patients who are not critically ill but have low oxygen saturation.
A face mask is used if the patient requires a higher FiO2 than a basic nasal cannula can provide (i.e., FiO2 > 40%) when a nasal cannula is contraindicated (e.g., nasal blockage or facial injury) or when consistent FiO2 is desired (e.g., to prevent oxygen-induced hypercapnia in COPD). There are simple oxygen face masks, Venturi masks, non-rebreather masks and nebulizers.
Critically ill patients with no risk factors for hypercapnic respiratory failure patients and initial SpO2 < 85% should be started on high-flow oxygen (10–15 L/minute) via NRB (non-rebreather mask) and titrate down to target saturations. Patients with risk factors for hypercapnic respiratory failure should be given a Venturi mask (24–28%) or nasal cannula at 1–2 L/minute and obtain an ABG as soon as possible.
All other patients should be started on a nasal cannula or a simple face mask and titrate up to target saturations.
Oxygen is a drug and hence should be prescribed, administered and monitored by trained staff In life-threatening situations, high-flow oxygen via oxygen tubing and a reservoir (non-rebreathe) bag should be given immediately, without a prescription. However, subsequent documentation should take place. In all other situations, oxygen should be prescribed by a doctor and signed for at each drug round by trained staff.
A target saturation range should be prescribed, along with the initial delivery device, oxygen tubing and flow rate, whose effectiveness will be regularly reviewed by oximetry. Increasing oxygen requirement, decreasing saturation or increasing respiratory rate could indicate and should prompt rapid medical assessment.
As oxygen requirements decrease, supplemental oxygen can be titrated downwards and eventually discontinued. Even so, the prescription for an oxygen target range should remain active in case the patient deteriorates again.
