Introduction
Supplemental oxygen is used to increase oxygen concentration in inspired air, above the normal 21%, in order to treat or prevent hypoxia.
Oxygen therapy is frequently applied when there is concern for cardiovascular diseases of various types. Even though temporary use is unlikely to be dangerous, there are some conditions, described below, that can result in a life-threatening deterioration following the application of oxygen. Accordingly, frequent re-evaluation of the patient’s condition is warranted, including by PaO2 (partial pressure of arterial oxygen) or SaO2 (arterial saturation of oxyhemoglobin).
Indications
Oxygen administration is one of the most frequently used treatments in a hospital setting. Indications for supplemental oxygen normally focus on hypoxemia, rather than symptomatic dyspnea.
The rationale of providing supplemental oxygen is to:
- treat hypoxemia, as measured by pulse oximetry or arterial saturation
- treat localized tissue hypoxia, eg MI, stroke
- decrease the work of breathing
There are many conditions that can lead to requirement for oxygen administration. These include:
- acute or chronic respiratory disease, eg pneumonia, COPD, asthma, pulmonary embolism
- decreased respiratory drive: anaesthesia, overdose, brain injury, etc
- acute or chronic heart disease, eg MI, heart failure
- anemia
- shock
- carbon monoxide poisoning
The cause of a patient’s condition may not be immediately evident. Accordingly, reasons to begin oxygen include:
- measured hypoxemia
- signs and/or symptoms of respiratory distress (ie, dyspnea, chest pain, diaphoresis, cyanosis, increased respiratory rate/effort)
- signs and/or symptoms of decreased respiratory drive
Cautions
Ensure you are plugged into an oxygen source, and not an air line – a mistake commonly made in hospitals.
Oxygen will help improve hypoxia, though will not increase ventilation, or removal of waste CO2. For some patients with chronically high CO2 levels (“CO2 retainers”), respiratory drive depends on oxygen levels. Accordingly, improving oxygenation through oxygen administration can reduce or eliminate respiratory drive, creating life-threatening compromise. For these patients, the goal of oxygen therapy should be a saturation of 88-92%.
An FiO2 of >50% can lead to tissue toxicity, absorptive atalectasis, and decreased function of airway cilia.
Oxygen supports combustion and can be explosive. Accordingly, extreme care should be taken around open flames, and petroleum-based products should not be used on the lips or face.
Assessing Oxygen Needs
The easiest and most frequent method of assessing oxygen need is by pulse oximetry, in which a probe is to place on the fingertip (or toe, or earlobe, at times). Light at two wavelengths, normally red and infrared, is transmitted through the body. Deoxygenated blood preferentially absorbs red light, while oxygenated light preferentially absorbs infrared light. The ratio of wavelengths passing through the body is therefore measured, and saturation can be calculated.
Ensure the measured pulse rate is very close (within 5 bpm) of the actual pulse rate, and that the measured saturation is stable.
A pulse oxygen saturation (SpO2) of 92% correlates with a PaO2 of ~62 mmHg; below this, the oxygen saturation begins to drop off more steeply on the oxygen saturation curve. Accordingly, SpO2 is normally kept above 92%, unless chronic CO2 retention is suspected (see above).
If SpO2 is <80%, results will be inaccurate, but represents a life-threatening situation. Ensure emergency response is activated if resuscitation is warranted (eg, the patient is not palliative), increase oxygenation using available techniques, and assess arterial saturation.
Pulse oximetry can also be limited by:
- nail polish
- a very bright environment
- low perfusion states (ie shock)
- very pigmented skin
- elevated bilirubin in the blood
- intravascular dyes
During treatment, assess the effect of oxygen on the patient’s symptoms, respiratory effort, and vital signs, and adjust as necessary.
Nasal Prongs
Nasal prongs are usually the first approach to providing oxygen. Small prongs fit into the nostrils and provide low-flow oxygen. They are the least constraining, as they allow talking and eating, and are normally the best tolerated.
Flow rates are generally 1-6L/min. Above this, the higher flows can dry the nasal passages and cause pain.
FiO2 is generally 4%/L; accordingly, percentages of inhaled oxygen range from 24-44%.
Simple Mask
Simple masks, which normally use flow rates of 5-8 LPM, can attain FiO2 of 35-55%.
Aerosols can often be given as well.
Venturi Mask
The Venturi mask is useful for providing mid-range levels of oxygen, and is one of the most accurate methods of providing a set FiO2.
Percentage depends on which connector is used, with ranges from 24-50%.
Non-Rebreather Mask
The non-rebreather mask provides 80-100% oxygen, based on flows of 12-15L/min of oxygen.
Before using, pinch the mask closed and allow the reservoir to fill. Once on the patient, it is important that the reservoir not collapse.
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Resources and References
Royal Children’s Hospital, Melbourne
British Thoracic Society – Guideline for emergency oxygen use in adult patients.