- Becky Maxwell, EM Consultant, Bristol.
- Chris Connolly, EM Consultant, Sheffield
Codes: CAP6, HAP6,
Right now we have given you enough time to digest all the clever definitions, let’s drill down into the benefits and risks of oxygenation.
Firstly, we must prescribe oxygen…. Would you expect the nursing staff in the department to administer any other drug without you prescribing it – of course not! Oxygen has its side effects just like any other drug and we need to be more rigid about prescription and administration. This can’t happen without a basic understanding…..
But hold on second, oxygen is good right?? I need it to live, how could there be any bad effects to such a vital thing?? What are the risks of over oxygenating a patient?
- The most significant effect that we talk about with oxygen administration is hypercapnic respiratory failure in those patients who are deemed at risk – COPD patients, NMDs – we know this and it doesn’t come as any surprise, we are pretty good at this. The pathophysiology of this is complex from loss of respiratory drive through to V/Q mismatch and absorption atelectasis and none of this lends itself easily to discussing in this podcast.
What we don’t talk about so often is those other effects:
- Rebound Hypoxaemia – in those who have developed T2RF if you suddenly withdraw the oxygen therapy you can get a rebound hypoxia which is often worse that the position you started in before you administered the oxygen!
- Coronary and cerebral vasoconstriction – there have been studies showing hyperoxia is bad for strokes and MI’s secondary to this phenomenon. Potentially worse outcome have been demonstrated in those patients who have had a mild to moderate stroke in studies.
- Damage from free oxygen radicals – leading to alveolar damage and reperfusion injury post MI to name a few.
There are times when it is good to administer oxygen to patients who aren’t hypoxic in the ED.
- Spontaneous pneumothorax – probably the most common one we’ll come across in the ED. high-concentration inhaled oxygen can also increase the rate of reabsorption of air from a pneumothorax up to fourfold.
- Carbon monoxide and cyanide poisoning
- Cluster headache – immensely painful, oxygen is a wonder drug in these patients and should be administered at 12L per minute. One study comparing oxygen delivery via reservoir bag at 12L /min found that headache reduced by 78% in 15 minutes compare to 20% in those breathing air.
Ok so we’ve talked about definitions and those who aren’t hypoxic who benefit from oxygen. Lets talk about the more common reason to want to give oxygen – hypoxic hypoxaemia.
- The first thing to say is that recognition is key. The guideline calls SpO2 the 5th vital sign, poor sats. Only 5th! A timely reminder to use a validated track and trick tool such as NEWS score when assessing unwell adults.
- Rapid assessment including history and examination should happen in conjunction with vital sign monitoring.
- Don’t take the oxygen off to get an ‘air’ reading on those who are clearly requiring oxygen therapy.
- Use an ABG in all critically unwell patients, in those who you are concerned are hypoxemic and those at risk of hypercapnic respiratory failure.
So when are we giving oxygen?
- When we suspect or prove the patient is hypoxic.
- Of unknown cause give 15l NRB is SpO2 <85%, if higher than this a NC 2-6L or Hudson 5-10L – this is good advice IMHO – starting with ALL the oxygen if its clearly all bad, if not then start medium and crank it up as needed.
- If you know the cause is either Asthma, pneumonia, acute change in lung Ca or fibrosis, then the advice is the same.
- If there’s a pneumothorax causing the hypoxemia – give high flow oxygen whilst prepping to get it drained, likewise pleural effusion.
- All of these patients should be treated with a target of 94-98% saturation.
- If your patient has risk factors for T2RF then start low and target 88-92% prior to blood gases. The guidance recommends venture 24 or 28% or nasal cannulae at 1-2L.
- These folks are as you’d expect
- IECOPD, CF, those with neuromuscular disorders, chest wall deformity and morbid obesity. This last category is one we seem to be seeing more and more of up here. They ventilate terribly, have a multitude of difficulties with obtaining a safe gas balance being just one! In terms of reversible disease they’re really tricky too – I’d be interested to know about long term ICU outcomes in those who are obese but have no underlying lung disorder.
So we’re going to start oxygen in lots of patient and then we’re going to do some blood gases.
The guidance recommends the first sample is done arterially and then subsequent gases can be an arteriloised lobe sample, warning that these can under-estimate the pO2 by 0.5-1kpa
We should try and remember to use LA unless it’s a dire emergency – I’ll be honest I only started doing this about a year or so ago after seeing some talk about it on twitter. Unlike with cannula which I find the LA makes it more difficult the ABG is sooooo much easier with a cooperative patient that has a numb wrist!
So lets talk COPD
- The first point the guidance raises which is welcome is that you don’t have to have a formal diagnosis of COPD to treat a patint as though they have COPD – this is great advice.
- If someone is over 50, smokes ‘properly’ and has a hsitroy of exertional SOB, and there isn’t another cause idenitifable then assume COPD.
- remember we said to start low and slo with these guys. 24 or 28% venture. But if this isn’t working then increase to 5L via face mask or a 2-6L NC.
- Remebeer that if the RR is >30 then you need to increase the flow rate on a venturi mask to higher than on the packaging – this is something I remember some of the time I’ll be honest!!
- If the pH and PCO2 were normal on your COPD patients first gas then aim at saturation 94-98 and repeat the gas in 30-60 minutes. If you know their usual resting sats are <94 then aim at 88-92%.
- If the pCO2 is raised but the pH is normal aim sats at 88-92% and recheck at 30-60 minutes.
- If the pH <7.35 and PCO2 > 6 then start NIV if no improvement at 30 mins from starting medical therpay.
This is great advice. Although I’m never that optimistic I’ll get the repeat gas done at minute 30. I often start NIV early doors, as they usually had salbutamol and Atrovent a couple of times in the ambulance. Means the medics can do the repeat ga at 60mins post BIPAP…….
Another useful bit of advice sneaked away at the bottom – consider NIV for all patients with hypercapnoeic respiratory failure due to CF/obesity/ NMDs. Wooohoooo. Gone are the days of the chest doctors rolling their eyes and only wanting it started on those with COPD. Obvs we’ve been ignoring them for years, but now I can send them away to read this 100 page epic!!
So that all sounds pretty important right? Yep well it is. Patients can get harmed by too much or too little oxygen. So it needs prescribing. It’s a bloody drug!!
The guidance says we should have a standardised prescription chart for this. This prescription should be for/to a target saturation rather than a specific flow rate of oxygen. If the situation is emergent then just giving the 15L O2 via NRB is fine, and shouldn’t be delayed for a formal prescription – similar to anaphylaxis adrenaline really. Last thing to say on prescribing is oxygen alert cards. If your patient has one then use it, flow the targets on it until you have a blood gas back. I saw on twitter a while back (I think in Stoke) ‘livestrong’ style bracelets for people in hospital for target saturations – I liked this although obvs is open to abuse/failure. We just have a acahrt above the drugs bit on our ED card with 88-92, 94-98 and ‘other’ with space for a signature. I’m a pedant when it comes to oxygen prescription. One day I’ll audit our practice. Not sure I’ll like the results…..