With some anxiety, I’m rolling out a new talk this month atEMS Today in Baltimoreon the developing science related to oxygen administration. As my research and reading took me into the realm of free-radicals, oxidative stress and reperfusion injury, I began to pick up on possible problems related to supplemental oxygenation. I tried out some earlier versions of the talk and was told that some of the material was too complex. I gave a similar lecture to a group of emergency physicians in Puerto Rico last year and found that many physicians are only partly aware of the changing science in this area of medicine. So, I spent the past few months refining it and hope it’s well received at the conference. Here’s a sneak peak.
In EMS, we’ve always emphasized two things: airway and oxygenation. In reality, we should be emphasizing ventilation. Without an airway, your patient cannot ventilate. Without ventilation, you cannot assess the airway. They’re inseparably linked.
Likewise, without ventilation, oxygenation is impossible. But ventilation involves much more than oxygenation. It involves the elimination of carbon dioxide and toxins and plays a role in other important biological processes.
We’ve always taught that a little oxygen is good and a lot of oxygen is better. We adopted pulse oximeters and really only use them to document oxygen saturations — especially low thresholds. The closer to 100%, the better — or so we thought. But is doing this in the best interest of the patients?
Several years ago we saw a change in practice in the neonatology community to limit supplemental oxygenation given to newborns and neonates. We had always known that high-concentration oxygen was associated with the development of retinopathy of prematurity (ROP), formerly called retrolental fibroplasia, in premature infants. Later, clinicians found that neonates resuscitated with high-concentration oxygen had worse outcomes than those resuscitated with room air. For example, infants resuscitated with 100% oxygen have a greater delay to first cry and a greater delay to first respiration.(1) In one study of depressed infants, mortality was 13% for those resuscitated with 100% oxygen and only 8% for those resuscitated with room air.(2) Further, neonates resuscitated with room air had a lower mortality at one week compared to those resuscitated with 100% oxygen.(3) The American Heart Association now recommends starting with room air and increasing oxygen concentration as needed to maintain an adequate oxygen saturation.(4)
Next, the phenomenon of reperfusion injury was noted. Reperfusion injury occurs when oxygen is reintroduced to ischemic tissues. Stated another way, the injury does not occur during periods of hypoxia. It occurs after oxygen is restored to the affected tissues.
The primary mechanism is thought to be the development of toxic chemicals called “reactive oxygen species” or “free radicals.” These chemicals have an unpaired electron in their outer shell and are very unstable. They occur normally, to a limited degree, but the body has enzyme systems that process the free radicals into less toxic substances, thus avoiding significant cellular damage. But following a period of hypoxia, a large number of free radicals are produced that overwhelm the protective enzyme systems (antioxidants) and cellular damage occurs. This damage is called “oxidative stress.”
The effects of aging are often due to oxidative stress. Also, some diseases such as atherosclerosis, Alzheimer’s disease, Parkinson’s disease, and others have been linked to oxidative stress and free radical induction. Thus, the evolving thought is that, in some conditions, high concentrations of oxygen can be harmful.
So, what does this mean to the future evolution of EMS practice? Well, there are several disease processes we must consider.
Stroke: The brain is very vulnerable to the effects of oxidative stress. The brain has fewer antioxidants than other tissues. Thus, should we give oxygen to non-hypoxic stroke patients? Studies have shown that patients with mild-moderate strokes have improved mortality when they receive room air instead of high-concentration oxygen.
The data on patients with severe strokes is less clear.(5) Current research indicates that supplemental oxygen should not be routinely given to patients with stroke and can, in some cases, be detrimental.(6)
Acute Coronary Syndrome:The myocardium is highly oxygen dependent and vulnerable to the effects of oxidative stress. Thus far, there’s no evidence that giving supplemental oxygen to acute coronary syndrome patients is helpful, but there’s no evidence it’s harmful.(7)
Post-Cardiac Arrest: Here, too, the evidence is too scant to tell. We do know that virtually all current therapies for cardiac arrest (drugs, airway) are of little, if any, benefit. The primary therapies remain CPR (often with limited ventilation initially) and defibrillation followed by induced hypothermia. The whole purpose of induced hypothermia is to prevent the detrimental effects of oxidative stress and the other harmful effects of reperfusion injury.
Trauma:What role should oxygen play in non-hypoxic trauma patients? Little research exists, but an interesting study out of New Orleans demonstrated that there was no survival benefit to the use of supplemental oxygen in the prehospital setting in traumatized patients who do not require mechanical ventilation or airway protection.(8)
Carbon Monoxide (CO) Poisoning:We have learned a lot about carbon monoxide poisoning in the past few years. We know that the mechanism of CO poisoning is a lot more complex than once thought. We also know that there’s no reliable evidence that hyperbaric oxygen (HBO) therapy improves outcome (although it’s still widely used).(9) But when you think about it, the goal of treatment in CO poisoning is to eliminate CO through ventilation — not hyperoxygenation. Although oxygen can displace some CO from hemoglobin, the induction of free-radicals may be worse than the effects of CO. Again, the science here is in a state of flux.
Neonates: The science is clear in regard to supplemental oxygen in neonates. It should be used only when room air ventilation fails.
Again, this is a discussion of the changing science. Always continue to follow the direction of your medical director and local protocols. That said, it’s clear that we need to use every tool possible to support, but not replace, our physical exam skills. We should use pulse oximetry and waveform capnography. Although, individually, each technology has its limitations, together they provide important information about the patient.
The goal of therapy is to avoid hypoxia and hyperoxia. If the patient s oxygen saturation and ventilation are adequate, supplemental oxygen is probably not required. If the patient is hypoxic or hypercapnic, then you must determine whether the problem can be remedied through increased ventilation, increased oxygenation, or both. Thus, you have to assess the problem, recognize and understand the pathophysiological processes involved, plan an appropriate therapy (within the scope of your protocols), and provide the needed therapy. That is what prehospital care is all about.
References
- Martin RJ, Bookatz GB, Gelfand SL, et al: “Consequences of neonatal resuscitation with supplemental oxygen.” Semin Perinatol. 32:355-366, 2008.
- Davis PG, Tan A, O’Donnell CP, et al: “Resuscitation of newborn infants with 100% oxygen or air: A systematic review and meta-analysis.” Lancet. 364:1329-1333, 2004.
- Rabi Y, Rabi D, Yee W: “Room air resuscitation of the depressed newborn: A systematic review and meta-analysis.” Resuscitation. 72:353-363, 2007.
- American Heart Association: “2005 American Heart Association guidelines for cardiopulmonary resuscitation (CPR) and emergency cardiovascular care (ECC) of pediatric and neonatal patients: Pediatric basic life support.” Circulation.13:IV1-203, 2005.
- Ronning OM, Guldvog B: “Should stroke victims routinely receive supplemental oxygen? A quasi-randomized controlled trial.” Stroke. 30:2033-2037, 1999.
- Pancioli AM, Bullard MJ, Grulee ME, et al: “Supplemental oxygen use in ischemic stroke patients: Does utilization correspond to need for oxygen therapy.” Archives of Internal Medicine. 162:49-52, 2002.
- Mackway-Jones K: “Oxygen in uncomplicated myocardial infarction.” Emergency Medicine Journal. 21:75-81, 2004.
- Stockinger ZT, McSwain NE: “Prehospital supplemental oxygen in trauma patients: Its efficacy and implications for military medical care.” Military Medicine. 169:609-612, 2004.
- Gilmer B, Kilkenny J, Tomaszewski C, et al: “Hyperbaric oxygen does not improve neurologic sequelae after carbon monoxide poisoning.” Academic Emergency Medicine. 9:1-8, 2002.
