As a kid growing up in Fort Worth, Texas I had little interest in ambulances or medicine. I do remember one thing about the ambulances in the late 1960s in that they always had signs on the side that stated “oxygen equipped” in big letters. Before that, the ambulances were emblazoned with the phrase “radio equipped”—but that is a different story.
The EMS love affair with oxygen goes back as far as I can recall. I went to EMT school in 1974 and we actually had a skills station where we were tested on oxygen administration and had to calculate the amount of oxygen available in oxygen cylinders of various sizes.
During 1975 and 1976, I was in paramedic school and we again taught that every patient needed oxygen. At that time, there was perceived benefit and minimal risk of harm. This went on for a decade or two before we began to recognize that too much oxygen can actually be dangerous.
The National Registry of Emergency Medical Technicians (NREMT), in their testing process, formerly considered failure to administer high-flow oxygen as a failure criterion. In their most recent skill sheets, the NREMT states: “Failure to voice and ultimately provide appropriate oxygen therapy” as a critical criterion. The whole concept of hyperoxia and oxidative stress is complex and often not explained well in the EMS educational process or in textbooks. It is something we need to remedy.
In Victorian times, medical care was often very primitive by modern standards. During that era, it was learned that oxygen was essential for many biological processes. It seemed intuitive that the more oxygen a patient received, the better they would fare overall. The concept and practice of bringing plants to hospitalized patients was based upon this belief. It was known at that time that plants utilize carbon dioxide and generate oxygen.
This is just the opposite of what animals do. Thus, placing multiple plants into a patient’s room would theoretically increase the ambient oxygen and reduce carbon dioxide levels, thus enhancing the patient’s chances of survival. This same belief led to the widespread use of supplemental oxygen in all phases of medical care (from newborn delivery to death at old age).
Again, the prevailing belief was oxygen was certainly beneficial and not at all harmful. Empiric administration had the possibility of providing some benefit with minimal risk. However, as this practice began to be examined critically, we found that there are actually risks associated with excessive oxygen administration.
Historically, in EMS, it has always been taught that hypoxia is bad and it should be treated with high concentrations of oxygen. For the most part, there was never any concern about the detrimental aspects of high concentration oxygen. In fact, the word “hyperoxia” was not even used until the last decade or so. It is been a reflexive practice to apply oxygen to virtually any patient who presents to EMS or an emergency department.
In a British study of ambulance and emergency department patients in 2008, researchers found significant overuse of supplemental oxygen in both ambulance and emergency department patients.1
A Canadian systematic review and meta-analysis, published in 2018, found high-quality evidence that demonstrated that liberal oxygen therapy increases mortality without improving other important patient outcomes. They determined that supplemental oxygen might become problematic when it results in an SpO2 exceeding 94-96%.2
Furthermore, several studies have demonstrated worsened outcomes for acute stroke and acute myocardial infarction (AMI) in patients who are hyperoxic from supplemental oxygen administration. In fact, there is an evolving body of evidence demonstrating that hyperoxia can increase infarct size in both stroke and AMI.3
Several studies have found that stroke patients who were hyperoxic had worsened outcomes than those who were normoxic or even hypoxic.4 There is an expanding body of evidence that demonstrates hyperoxia, including hyperoxia immediately after intubation, can worsen mortality in critically-ill patients.5-6
The concern about hyperoxia is based on the concept of oxidative stress. Oxidative stress occurs when the levels of toxic chemicals (free radicals) in the body exceeds the body’s capability to remove these (anti-oxidants). Free radicals are oxygen-containing molecules that have an uneven number of electrons which makes them highly-reactive and allows them to easily react with other molecules causing injury to body tissues.
Free-radicals are produced constantly by the body, but various anti-oxidant systems remove them before damage occurs. However, in critical illness and injury, flooding injured or hypoxic tissues with excess oxygen can cause an increase in free radical production that exceeds the capabilities of the body’s anti-oxidant systems thus causing often permanent damage to tissues that are high utilizers of oxygen (brain, heart).7
The introduction of pulse oximetry in the 1980s made it possible to assess hemoglobin oxygen saturation (SpO2) in peripheral vascular beds. This technology is highly accurate and can be used to guide supplemental oxygen therapy. However, for the most part, EMS providers have not been provided with desired SpO2 targets and have assumed, as have many in healthcare, that the higher the SpO2, the better. We now know that hyperoxia is not desirable and lower target values have been recommended.
Recently, several organizations and entities have published more conservative target guidelines for supplemental oxygen administration. Supplemental oxygen therapy should be considered when a patient’s SpO2 is ≤ 93% (strong recommendation) or 90-92% (weak recommendation). Supplemental oxygen administration must be titrated to assure that the SpO2 does not exceed 96%. This target does not apply to patients with possible carbon monoxide poisoning, sickle cell crisis, pneumothorax, or cluster headache. These patients can have an SpO2 > 96%. Patients with COPD and hypoxic drive should actually have a lower SpO2 target (88-92%) to avoid respiratory drive suppression.8-9
EMS providers must remember oxygen is a medication. As with any medication there are indications, contraindications, precautions, side-effects and dosing. EMS personnel should use the technologies available (pulse oximetry and capnography) to monitor a patient’s oxygenation and ventilation status.
It is important to remember that shortness of breath is a subjective symptom while hypoxia is an objective finding. Supplemental oxygen is only indicated if there is documented hypoxia (not just shortness of breath). If supplemental oxygen administration is warranted (based on evolving standards), then judicious supplemental oxygen administration may be started with a goal of maintaining the SpO2 within the target range (90-96%) and should not exceed 96%, except in the special situations detailed previously.
EMS personnel have the equipment (oxygen flow regulators, various oxygen masks and cannulas, and pulse oximetry) to adhere to these guidelines. Of course, local protocols should guide local care practices. But, if your local protocols still recommend high-flow oxygen with minimal limitations, it may be time to review the science and update the protocols.
- Hale KE, Gavin C, O’Driscoll BR. Audit of oxygen use in emergency ambulances and in a hospital emergency department. Emerg Med J 2008;25:773-6. 10.1136/emj.2008.059287 pmid:18955625.
- Chu DK, Kim LH, Young PJ, et al. Mortality and morbidity in acutely ill adults treated with liberal versus conservative oxygen therapy (IOTA): a systematic review and meta-analysis. Lancet 2018;391:1693-705. 10.1016/S0140- 6736(18)30479-3 pmid:29726345.
- Stub D, Smith K, Bernard S, et al. Air Versus Oxygen in ST-Segment-Elevation Myocardial Infarction. Circulation. 2015;131(24):2143-50.
- Rincon F, Kang J, Maltenfort M, et al. Association between hyperoxia and mortality after stroke: a multicenter cohort study. Crit Care Med. 2014;42(2):387-96.
- Stolmeijer R, Bouma HR, Zijlstra JG, Drost-de klerck AM, Ter maaten JC, Ligtenberg JJM. A Systematic Review of the Effects of Hyperoxia in Acutely Ill Patients: Should We Aim for Less?. Biomed Res Int. 2018;2018:7841295.
- Page D, Ablordeppey E, Wessman BT, et al. Emergency department hyperoxia is associated with increased mortality in mechanically ventilated patients: a cohort study. Crit Care. 2018;22(1):9.
- Pisoschi AM, Pop A. The role of antioxidants in the chemistry of oxidative stress: A review. Eur J Med Chem. 2015;97:55-74.
- Siemieniuk RAC, Chu DK, Kim LH, et al. Oxygen therapy for acutely ill medical patients: a clinical practice guideline. BMJ. 2018;363:k4169.
- O’driscoll BR, Howard LS, Earis J, Mak V. BTS guideline for oxygen use in adults in healthcare and emergency settings. Thorax. 2017;72(Suppl 1):ii1-ii90.