The safe use of supplemental oxygen during defibrillation
On many Pre-Hospital Care and AED courses, students will be told to turn off and remove sources of supplemental oxygen before defibrillating a patient.
The rationale is that while oxygen is not flammable, it supports combustion. There have been several cases of fires occurring in hospital settings in an oxygen rich environment, for example (1)
“A patient went into cardiac arrest while on a ventilator and was defibrillated. Just before defibrillation, one of the responding staff disconnected the breathing system from the patient and left the open end flowing O2 onto the bed near the patient’s upper chest. The defibrillation discharge resulted in a visible arc, possibly because the patient was thin and had prominent ribs and the paddles were not applied with enough force to make a large low resistance contact area with the patient’s skin. This arc caused a fire to flash across the patient, who had copious chest hair, and across the bed to the O2 source. The breathing system caught fire and was not extinguished until the ventilator was shut off. The patient was only slightly burned, but subsequently died of cardiac arrest.”
There are no documented cases of fires occurring during pre-hospital resuscitation using an AED.
Since 2005 the United Kingdom Resuscitation Council has stated that the following can reduce the risks of fire (2)
Remove any oxygen mask or nasal cannulae and place them at least 1m away from the patient’s chest.
Leave the ventilation bag connected to the tracheal tube or other airway adjunct. Alternatively, disconnect the ventilation bag from the tracheal tube and move it at least 1 m from the patient’s chest during defibrillation.
The use of self-adhesive defibrillation pads, rather than manual paddles, may minimise the risk of sparks occurring.
Since 2005 UK and European guidance has not stated that the supplemental oxygen should be turned off nor should a closed system (i.e. oxygen to BVM to supraglottic airway) be disconnected.
So why are people told to turn off and disconnect oxygen?
The mechanism of oxygen enriched fires during defibrillation.
In certain situations, fires have been reported during defibrillation (and other surgical procedures involving electrical sources during surgery) (3-8) but there have been a number of small but critical factors which have culminated in the fire, each relating to the simple factors required for combustion:
In the first instance, a spark is required for the source of ignition – this comes from an air gap between the electrode and the patient’s skin. This is only a problem when flat metal paddles are used in a hospital setting which do not conform to the curves of a patient’s chest. This is especially try if the casualty is underweight, the paddles are applied to bony prominences (such as the clavicle), pads are applied over electrode pads, or other equipment) and before the regular use of gel-pads.
Piercings do not present a problem as piercings are not usually found at the sites of defibrillator pad placement.
Adhesive AED pads do not produce a spark as there is no air-gap.
A fuel source is needed to ignite – this is usually hairs on a casualty’s chest. If the casualty does not have a hairy chest or there are no combustible materials nearby, (e.g. the casualty’s chest is fully exposed) there is no fuel.
In normal atmospheric condition (20.95% oxygen) a spark will simply singe near-by hairs. Poorly applied pads may leave burns, which while unpleasant, is neither life threatening for the casualty or the responder nor is it likely with the use of soft, adhesive pads.
If pads are poorly applied while using an AED, the AED will in most cases alert the user to “Poor pad contact” or other similar verbal alert. This may be because they have not been applied firmly enough, with full coverage of the pad or there is too much chest hair between the pad and the patient’s skin.
In normal situations, chest hair does not present a fire risk as it is an inadequate fuel.
In an oxygen rich environment over 50% concentration and where the source of ignition is within 30cm of the source of supplemental oxygen (9-10), a phenomena known as "surface-fibre flame propagation (SFFP) occurs.
"the fire flashes over the oxygen-enriched surface, often without burning the skin or underlying fabric, as each small hair or fiber ignites hairs or fibers nearby until the flame front meets an edge (e.g., hem or fold of cloth, area of near-ambient oxygen concentration) and either establishes a flame at the edge or burns out. In most cases, the flame front races toward the source of the oxygen enrichment and can result in ignition of the supply tubing or device.”
For this to occur the surface of the chest must be bathed in a blanket of high concentrations of oxygen.
This exciting 1960s film from the Royal Air Force Institute of Aviation Medicine (9) demonstrates the phenomena beautifully. What is not know is the saturation of oxygen present in the demonstration required to produce the effect.
In a crowded operating theatre, resuscitation bay on in the back of an ambulance this may be possible but incredibly unlikely in a well ventilated area or with any turbulent air (such as a breeze or draft around the casualty).
Examples of this phenomena typically feature a disconnected ventilator tube placed near the casualty’s chest exist spilling out high volumes of oxygen over the casualty’s.
There are no examples of fires occurring
with a closed system (e.g. the ventilator or BVM remains attached to an ET tube or supraglottic or laryngeal airway)
in well ventilated spaces.
with low concentrations of supplemental oxygen.
As currently advised by ERC (10) and UKRC (11) 2015 Guidelines, when the responder is using supplemental oxygen during defibrillation:
Take off any oxygen mask or nasal cannulae and place them at least 1m away from the patient’s chest or
Leave the ventilation bag connected to the tracheal tube or supra-glottic airway.
ECRI. (2003) “A clinician’s guide to surgical fires: how they occur, how to prevent them, how to put them out”. Guidance Article. Health Devices. Jan; 32(1):5-24.
https://www.resus.org.uk/EasySiteWeb/GatewayLink.aspx?alId=1546 accessed 9th November 2018
Miller PH. (1972) “Potential fire hazard in defibrillation”. JAMA 221:192.
Hummel 3rd RS, Ornato JP, Weinberg SM, Clarke AM. (1988) “Spark-generating properties of electrode gels used during defibrillation. A potential fire hazard”. JAMA 260:3021–4.
ECRI. (1987) Defibrillation in oxygen-enriched environments [hazard]. Health Devices. 16:113–4.
Lefever J, Smith A. (1995) “Risk of fire when using defibrillation in an oxygen enriched atmosphere”. Medical Devices Agency Safety Notices. 3:1–3.
Ward ME. (1996) “Risk of fires when using defibrillators in an oxygen enriched atmosphere”. Resuscitation. 31:173.
Theodorou AA, Gutierrez JA, Berg RA. (2003) “Fire attributable to a defibrillation attempt in a neonate”. Pediatrics 112:677–9.
ECRI Institute. (1994) “Hazard report: fires from defibrillation during oxygen administration”. Health Devices. 23:307-309.
ECRI Institute. (2005) “Hazard report: using external defibrillators in oxygen-enriched atmospheres can cause fires”. Health Devices 34: 423-425.
https://www.youtube.com/watch?v=X8QoEzc40rg accessed 9th November 2018
https://cprguidelines.eu/sites/573c777f5e61585a053d7ba5/content_entry573c77e35e61585a053d7baf/573c78145e61585a083d7bcf/files/S0300-9572_15_00328-7_main.pdf? Accessed 9th November 2018
https://www.resus.org.uk/resuscitation-guidelines/adult-advanced-life-support/ accessed 9th November 2018