As an FY1, you will be called to review patients who are hypoxic. Here we will discuss common causes of generalised hypoxia rather than focal hypoxia/ischaemia, such as in strokes or heart attacks. Also, insufficient oxygen-carrying capacity due to anaemia or ineffective use of oxygen at the tissue level (no cyanide management here zebra hunters!) will not be dealt with here.

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Often patients who are found to be hypoxic will be referred to you with the following handovers:

  • “This patient is agitated and confused”
  • “This patient has low saturations”
  • “This patient is having difficulty breathing”

Hypoxia is a Medical Emergency 

  • you should consider calling for help early – if “should I put a (peri)arrest call out” crosses your mind, then put it out!
  • the patient assessment should be approached with the DR ABCDE system

When any patient is acutely unwell, sometimes you need more hands to manage the situation – this isn’t a question of your abilities. This might be the ward nurses, particularly for background information about the patient. Don’t be afraid to have a low threshold to pull the ward buzzer which is usually located on the wall behind the patient.

Context and history are important in assessing the hypoxic patient but avoid the temptation to pore through notes. The majority of information will be found at the patient’s bedside. Simple measures and treatments can quickly stabilise the patient giving you the time to review the notes later.

Assessment at the Bedside

An unresponsive or drowsy hypoxic patient should trigger a MET call.

Problems found with an assessment of the airways should also trigger a MET call.

Tracheostomy: remember if the patient has a tracheostomy, apply oxygen via this route. These patients usually have guides by their bedside with diagrams of where to apply oxygen. Always call for senior help with these patients as it is better to have people who know how to manage tracheostomies with you in non-ITU settings. ENT & anaesthetics are best suited to help you for this.


  • Is this patient having difficulty breathing?
  • Do they look tired?
  • What is their respiratory rate?
  • What are their saturations? – attach a pulse oximeter for continuous readings
    • Ensure the sats probe is giving a good trace otherwise adjust it

Give the patient 15L/minute via a non-rebreathe mask. This is regardless of their co-morbidities and can always be reduced later. Sit the patient upright to improve oxygenation.

Giving high flow oxygen first whilst you assess and/or seek help gives you time.

Remember: Hypoxia kills before hypercapnia.
COPD or other patients at risk of retaining CO2 will die of hypoxia first before from tissue ischaemia.

Patients to Escalate

Medical registrars will want to know about any patients who are requiring 10L/min of high flow oxygen or greater to maintain sats of >94%. However, if you’re worried, escalate regardless! Please remember patients who are maintaining saturations with lower amounts of oxygen with a high respiratory rate will eventually tire.

If they deteriorate despite being on high flow oxygen, this means either the oxygen isn’t enough or it isn’t getting in. You need a team working together to rapidly identify the underlying problem and manage it which might require advanced treatments including intubation.

Perform a Basic Assessment & Start Treatment

Clues around the bed can help you identify an aetiology.

  • IV fluids running – could this be pulmonary oedema?
  • Evidence of swallowing problems e.g. NBM sign or thickeners on table – could this be an aspiration?
  • Are they on a cardiac monitor?
  • Are they on NIV?
    • If the patient is on NIV and have deteriorated, increase the oxygen via NIV to maximum & urgently call for senior help.

Continue examining the patient.

  • Palpate the trachea
  • Percuss anteriorly (particularly over the clavicles) – does it sound the same or could this be a pneumothorax?
  • Auscultate: Is there crackles, wheeze, unequal air entry or normal breath sounds, this helps identify the cause
  • If well, complete your A to E assessment. If not, initiate treatment before moving on
  • Consider an ABG & CXR at this point
    • Portable CXR should be considered if unwell.

In the UK, pO2 on a blood gas is measured in kilopascals (kPa). Roughly, it is 10 units less than the inspired oxygen (FiO2). For example, on FiO2 60%, someone who was not having any issues with gas exchange or oxygen delivery would have a PO2 of 50KPA.

A high or normal CO2 is a very concerning sign in a hypoxic patient as this means they are not ventilating properly and often are becoming tired.

  • If they have good oxygenation, then the oxygen may be titrated down and senior help should be sought for consideration of NIV before they run into problems due to CO2 retention. 
  • If however, the oxygenation is poor, the (peri)arrest team are required to consider intubation or other treatments. 

Splitting the Causes by your Examination Findings

CRACKLES – Secretions (infection/aspiration), Pulmonary oedema, Fibrosis

Secretions, Infection, Aspiration
If there are secretions, consider suctioning (ask the nurses for a yankauer suction catheter) and nebulised bronchodilators (although remember that oxygen delivery won’t be as high via nebulisers). Patients with mucous plugging might have reduced air entry on one side, with a normal percussion noted. Deep suctioning, hypertonic saline nebulisers and physiotherapy are options for these patients, but you will need more help to do this. Usually for deep suctioning critical care outreach services are available or ITU can assist.

New findings of pneumonia or aspiration should trigger you to look for signs of sepsis in your DR ABCDE assessment and manage accordingly.  Even if there is not systemic sepsis, these patients will need blood cultures and antibiotics.

Pulmonary oedema
An outline of managing pulmonary oedema is discussed here.

Pulmonary Fibrosis
A patient with pulmonary fibrosis might have an oxygen requirement, but an acute deterioration in saturations should trigger seeking another cause.

WHEEZE – Asthma, COPD,  Anaphylaxis, Pulmonary oedema

Occasionally, pulmonary oedema can cause wheeze. Usually though, it means some form of obstructive airway disease. Peak flows are NOT realistic in acutely hypoxic patients and add little benefit.

This should always be the first thing you should consider as this is life-threatening. This is particularly true of patients with no known history of lung disease. If you suspect it (urticarial rash, facial/mucous membrane swelling, hypotension & any recent new medications) then immediately put out a MET call. Management includes

  • 0.5mg 1:1000 intramuscular adrenaline (life-saving). IV adrenaline can cause arrhythmias & should be reserved for ITU settings. 
  • 10mg IV chlorphenamine
  • 200mg IV hydrocortisone

An outline of managing asthma is discussed here.

An outline of managing COPD is discussed here.

NO AIR ENTRY ON ONE SIDE – Pneumothorax, Mucus Plugging, Effusion

No air entry and a hyper-resonant percussion signifies a pneumothorax. As an FY1 it is highly unlikely you will manage this on your own, however, be aware that in extremis a green cannula in the second intercostal space in the midclavicular line is life-saving. Remember you must remove the needle once inserted to allow air to escape via the plastic tube.

Mucus Plugging
Usually, you can hear bilateral air entry in mucous plugging but if significant, sometimes there may be reduced air entry with normal percussion. Manage this as secretions above.

No air entry and a reduced percussion note could signify a pleural effusion. It is unlikely that this would develop very acutely, but may be pre-existing in a patient you are assessing.


Respiratory depression
If hypoventilating consider opioid or benzodiazepine toxicity. For opiates, look for pinpoint pupils. Also, review the drug chart.

Pulmonary embolism
Your blood gas, ongoing assessment of the cardiovascular system, and the context of the patient will assist you with this, and you may consider further investigations such as a d-dimer. Remember that a d-dimer can be raised in any pro-inflammatory state and thus it is only helpful to rule out a PE. If suspected, following discussion with seniors and reviewing any contraindications, immediately start treatment with a treatment dose of low molecular weight heparin. Specialist treatment such as thrombolysis may be required if the patient is hypotensive or has chest pain, but by then you will have called the medical emergency team.


This means you need to escalate. Particularly if the patient is very unwell: requiring high flow oxygen or looks unwell. The most common ward dilemma is “does the patient have crackles due to infection with sepsis or are they overloaded and need diuretics”. Clinical experience can make these decisions easier to distinguish, however at times even seniors have to opt for a closely monitored therapeutic trial. Discuss this with them as they may trial a low volume 250ml bolus of crystalloid or 40mg IV furosemide with GTN spray (GTN has a very short half-life). The more unwell the patient, the higher the stakes and so you will really want support.

Further Treatment

  • Don’t forget to continue on to C, D & E as this might reveal further information about the aetiology of hypoxia & don’t miss anything.
  • Don’t forget to contact next of kin for anyone unwell (this can be done by a nurse).
  • Initially, give high flow oxygen to all patients including CO2 retainers if they are significantly hypoxic. However, prolonged saturations of >98% are toxic and so never leave patients on this and wean to their targets as soon as possible: 88-92% or 94-98%.
  • If you need to give controlled oxygen, go for a venturi mask.
  • If oxygen is going to be prolonged, humidified circuits are needed. Talk to critical care outreach services or the site manager.

The Importance of Reassessment

Some causes of hypoxia reverse & improve quickly (anaphylaxis, pulmonary oedema) however most worsen before they improve (e.g. chemical pneumonitis (lung injury) from aspiration with secondary infection). Check if their oxygen requirement is increasing (or if it can be weaned down). Thus, re-assessment can offer helpful information.

Beware of the High Respiratory Rate

Patients might not be hypoxic, but simply have a high respiratory rate. Young patients will often compensate with a high respiratory rate and are critically unwell when they eventually become hypoxic. Arterial blood gas can demonstrate the relative hypoxia and a normal pCO2 in these patients demonstrates they are tiring and critically unwell.

Non-respiratory causes can increase the respiratory rate, but they should have a normal pO2. This includes anaemia, metabolic acidosis and pain. Anxiety and overdose of drugs can also do this. Anxiety however should always be a diagnosis of exclusion!

Written by Dr Yvonne Mitchell (SpR)
Additions by Dr Paul Groves (ST7 ICM & Anaesthetics)
Edits by Dr Akash Doshi CT2

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1 thought on “Hypoxia”

  1. I am a general nurse and it was really useful to attend this session. I understand now better the ABG result interpretation.

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