Oxygen – Sometimes less is more.

Everyone loves oxygen and you might even say that you can’t get enough of it.  Well, actually you can.   Oxygen overdose is nothing new but the way we use oxygen on casualties’ needs re-thinking.

First Aid – like any body of knowledge - changes and so it should as new evidence emerges

  • CPR ratios have changed over the years as Resuscitation guidelines are reviewed periodically and new evidence gains enough credence and popularity to justify new ways of thinking.
  • Where 2 litres of IV fluid were routinely given to trauma casualties, we now apply a more measured approach.
  • Because of the long term complications which may arise from prolonged immobilisation, a more considered view of spinal management is evolving rather than collaring and boarding all casualties suspected of spinal injury.

While change can be frustrating, change in response to developing knowledge and understanding is the only way we can ensure we are providing the best possible care.


Some casualties actually prefer LESS oxygen.

Oxygen is often introduced on advanced First Aid courses and this is no bad thing – make no mistake:  Oxygen is LIFE SAVING but oxygen, like all drugs, affects the body.  We wouldn’t administer any other drug with impunity so why are we so happy to automatically put so many casualties on High Flow oxygen?

COPD Patients

The most widely known ‘exception to the rule’ of high-flow oxygen is the casualty with a Chronic Obstructive Pulmonary Disorder (COPD) such as bronchitis or emphysema.  While it is not fully understood or agreed why COPD casualties respond better to low-flow oxygen is it universally accepted. 

Where a healthy person would typically have oxygen saturations of over 95% breathing normal air, a COPD casualties would normally have saturations of 88-92%, as such we aim to oxygen to that level.  Moderating oxygen flow to a target saturation level – titrating – has been seen to reduce mortality by 58% compared to high-flow oxygen in COPD casualties.(1)


Chest Pain Patients

One of the most seemingly obvious casualty who would require high flow oxygen is the casualty with chest pain.  The consequences of high levels of oxygen include a reduction in coronary arterial flow, by as much as 30% after 5 minutes as well as reducing the effectiveness of vasodilators, such as GTN.(2, 3)  There is also evidence that high-flow oxygen can decrease cardiac output and stroke volume.(4)  In the cardiac casualty, high flow oxygen is actually reducing oxygen flow to the heart and decreasing heart output.  This is far from ideal.

As of 2010 the Resuscitation Council (UK) and American Heart Association have amended their position on Supplemental Oxygen for basic life support:

There is no evidence that oxygen administration is of benefit during basic life support in the majority of cases of cardiac arrest before healthcare professionals are available with equipment to secure the airway. Its use may lead to interruption in chest compressions, and is not recommended, except in cases of drowning.(5)

There is insufficient evidence to support [oxygen’s] routine use in uncomplicated ACS. If the patient is dyspneic, hypoxemic or has obvious signs of heart failure, providers should titrate therapy, based on monitoring of oxyhemoglobin saturation, to 94%. (6)

[We] did not find a beneficial effect of oxygen treatment with respect to all-cause mortality at 1 year. (7)


Post-Cardiac Resuscitation Patients

Let’s say we have successfully resuscitated the casualty, we know their oxygen stores are going to be depleted, cells in the heart and brain especially are going to be crying out for more so surely we push 100% O2 at 15 liters per minute into them?

We know that ischemia – a restriction of oxygen to cells – is the prime cause of cardiac arrest but managing reperfusion of ischemic cells is much more complicated than we thought; a flood of oxygen to previously ischemic cells can actually cause significant damage to the cells – ‘reperfusion injury’.

Again, the 2010 Resuscitation Council (UK) and American Heart Association Guidelines reflect this:

As soon as arterial blood oxygen saturation can be monitored reliably (by blood gas analysis and/or pulse oximetry), titrate the inspired oxygen concentration to maintain the arterial blood oxygen saturation in the range of 94 -98%.(8)

Avoid excessive ventilation. Start at 10–12 breaths/min and titrate to target PetCO2 of 35–40 mmHg. When feasible, titrate FiO2 to minimum necessary to achieve SpO2 equal to or greater than 94%.(9)


Stroke Casualties

Approximately 87% of strokes are ischemic (the rest being haemorrhagic)(10) so it is easy to see how the stroke casualty is at similar risk to cerebral reperfusion injury via the same mechanism as the cardiac casualty.


Trauma Casualties

Surely trauma casualties need Oxygen?  We don’t want them going into shock, do we?  A 2004 study monitored 5,090 trauma patients not requiring assisted ventilation to see whether supplemental oxygen improved their outcomes. The results showed those who received oxygen did no better or worse than those who did not.

Essentially, if the casualty is not in respiratory distress, there is not much evidence that 100% is of any benefit to the casualty.(12)



Current Protocols

The British Thoracic Society provide the basis for UK healthcare guidelines.  The current full guidelines can be found here with a summary of pre-hospital guidelines here.   The current BTS guidelines separates casualties into four groups based on their needs(13):

1.       Critical illnesses requiring high levels of supplemental oxygen

2.       Serious illnesses requiring moderate levels of supplemental oxygen if the patient is hypoxaemic

3.       COPD and other conditions requiring controlled or low-dose oxygen therapy

4.       Conditions for which patients should be monitored closely but oxygen therapy is not required unless the patient is hypoxaemic

Treatment is based on titrating the Oxygen to reach desired saturation levels – delivering a measured amount of Oxygen proportionate to their need.  One of the most important factors if the casualty’s saturation levels:



Whether a casualty requires oxygen or not and if so, how much, depends upon:

  • What type of casualty they are
  • What their SpO2 is

The signs of Hypoxia are everything you would expect with a casualty who does not have enough oxygen; cyanosis, shallow breathing, possibly fast, possibly slow.  These signs have however, been shown to be slow to present even when oxygen saturations levels are critically low.   Pulse oximetry is the definitive tool for delivering appropriate amounts of oxygen. (14-19)

COPD casualties are used to a lower oxygen saturation, as such they receive low doses and have a lower target saturation.   BTS Guidelines state delivery should be 4 lpm via a 28% venturi mask or 1-2lpm via a nasal mask.   We don't carry a venturi mask so we simply follow the rule for nasal masks.

The nasal mask also has another use in the medic bag.

On our First Person on Scene and FREC courses we teach Pulse Oximetry as an integral part of Supplemental Oxygen and use this protocol which is a distilled version of the JRCALC and BTS guidelines to enable the Non-Healthcare Profession to make an informed decision on how much oxygen to deliver based on how much the casualty needs.


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