What is the difference between type 1 and type 2 respiratory failure?

Type 1 is defined by the British Thoracic Society as a PaO2 below 8 kPa with a normal or low PaCO2, so it is a problem of oxygenation. Type 2 is any PaCO2 above the normal range of 4.6 to 6.1 kPa, which is a problem of ventilation and can occur with a normal oxygen saturation.

Should a patient with COPD who is critically ill get 15 litres of oxygen?

Yes, initially. The British Thoracic Society says patients with COPD and other risk factors for hypercapnia who develop critical illness should have the same initial target saturations as any other critically ill patient, starting with a reservoir mask at 15 litres per minute, pending blood gas results. The range is then reset to 88 to 92% or controlled therapy if the gas shows hypercapnia.

When does CPAP beat non-invasive ventilation?

CPAP is for oxygenation failure, and the guideline recommendation is cardiogenic pulmonary oedema not responding to standard treatment, with entrained oxygen targeting 94 to 98%. Hypercapnic acidosis needs bilevel non-invasive ventilation rather than CPAP, because CPAP does not augment alveolar ventilation.

What pH triggers non-invasive ventilation in COPD?

A pH below 7.35 with a PaCO2 above 6.5 kPa persisting despite optimal medical therapy, which in practice means after 60 minutes of treatment targeting a saturation of 88 to 92%. That is a grade A recommendation in the 2016 BTS and Intensive Care Society guideline.

Can non-invasive ventilation be used in acute asthma?

No. Recommendation 39 of the BTS and Intensive Care Society guideline states that non-invasive ventilation should not be used in patients with acute asthma exacerbations and acute hypercapnic respiratory failure. Acute or acute on chronic hypercapnia complicating chronic asthma resembles COPD and is managed as such.

Oxygen Therapy, CPAP and When to Intubate — CT1 Anaesthetics Interview Clinical Judgement Answer

Q: Is there a pH at which you must intubate?

The guideline says there is insufficient evidence for absolute values as intubation criteria, but suggests a pH of 7.25 as the level below which invasive ventilation should be considered and 7.15 as the level at which it is indicated, after initial resuscitation and controlled oxygen. Respiratory arrest, a conscious level with a Glasgow Coma Scale score below 8, and an unusable interface are separate indications.

Type 1 respiratory failure is a PaO2 below 8 kPa with a normal or low PaCO2, and type 2 respiratory failure is a PaCO2 above the normal range of 4.6 to 6.1 kPa even when the saturation looks fine. According to the British Thoracic Society guideline for oxygen use in adults, the target saturation is 94 to 98% for most acutely ill patients and 88 to 92% for those at risk of hypercapnic respiratory failure. At the CT1 anaesthetics interview the marks are for setting a target, choosing a device, and naming the point at which you stop titrating oxygen and start supporting ventilation.

Key takeaways

Type 1 respiratory failure is a PaO2 below 8 kPa (60 mmHg), roughly a saturation of 90%, with a normal or low PaCO2 (British Thoracic Society, 2017)
Type 2 respiratory failure is any PaCO2 above the normal range of 4.6 to 6.1 kPa, and it can exist with a normal oxygen saturation
Target 94 to 98%, or 88 to 92% for known COPD and other risk factors for hypercapnia pending blood gases; a critically ill patient starts on a reservoir mask at 15 litres per minute whatever their COPD history
CPAP with entrained oxygen to maintain 94 to 98% is considered in cardiogenic pulmonary oedema that is not responding to standard treatment
Non-invasive ventilation starts when a pH below 7.35 and a PaCO2 above 6.5 kPa persist despite optimal medical therapy, which in acute COPD means after 60 minutes
A pH of 7.25 is the level at which invasive ventilation should be considered and 7.15 the level at which it is indicated, after resuscitation and controlled oxygen (BTS and Intensive Care Society, 2016)

How do you recognise which type of respiratory failure this is?

You recognise the type of respiratory failure from a blood gas, not from the saturation probe. The British Thoracic Society defines type 1 as a PaO2 below 8 kPa with a normal or low PaCO2, and type 2 as hypercapnia.

The guideline is explicit that a patient has type 2 respiratory failure once the PaCO2 is above 4.6 to 6.1 kPa, even if the oxygen saturation sits in the normal range. Oximetry does not detect hypercapnia.

That is why a breathless patient on oxygen with a comfortable-looking saturation still needs a gas. In practice the saturation may be normal precisely because supplemental oxygen is masking a rising carbon dioxide.

What do you do in the first few minutes?

In the first few minutes of a respiratory failure scenario you work through ABCDE, give oxygen, attach monitoring and take a blood gas, while asking for help. The Resuscitation Council UK approach treats each life-threatening problem before moving on.

Airway: look for see-saw movement, accessory muscle use and noisy or absent breath sounds; airway obstruction is a medical emergency needing immediate expert help
Breathing: count the rate, note that above 25 breaths per minute or rising is a marker of illness, then percuss and auscultate
Oxygen: a reservoir mask at 15 litres per minute in critical illness, enough flow that the bag does not collapse on inspiration
Monitoring: pulse oximetry, blood pressure and ECG, plus an arterial or arterialised gas
Circulation and disability: blood pressure, capillary refill, conscious level and a bedside glucose
Handover: SBAR or RSVP, so the person you are calling knows the target and the trend

However, the anaesthetic contribution in a respiratory failure scenario is rarely the oxygen itself. It is deciding whether this patient needs a mask, a machine or a tube, and saying so out loud.

What oxygen target do you set, and why?

The oxygen target in acute respiratory failure is 94 to 98%, or 88 to 92% in those with known COPD or other risk factors for hypercapnic respiratory failure, pending blood gas results. Both figures come from the British Thoracic Society.

There is a trap inside that sentence. The guideline says patients with COPD who develop critical illness should have the same initial target as any other critically ill patient until their gases are back.

After the gas, the range is reset. If the PaCO2 is normal, move to 94 to 98% unless there is a history of hypercapnic failure needing ventilation, and recheck gases after 30 to 60 minutes.

Which delivery device do you choose?

The device in a respiratory failure scenario follows the target, not the diagnosis. The British Thoracic Society starts hypoxaemic patients on nasal cannulae at 2 to 6 litres per minute or a simple face mask at 5 to 10 litres per minute.

Saturation below 85%, or critical illness: reservoir mask at 15 litres per minute, with urgent senior assessment
At risk of hypercapnia and no prior respiratory acidosis: a 24% Venturi mask at 2 to 3 litres per minute, a 28% Venturi at 4 litres per minute, or nasal cannulae at 1 to 2 litres per minute, aiming for 88 to 92%
Respiratory rate above 30 breaths per minute: increase the Venturi mask flow by up to 50%
A simple face mask should never run below 5 litres per minute, because of rebreathing, and is not suitable for type 2 failure

Saying the flow rate as well as the device is what separates a CT1-level answer from a list. The guideline attaches a number to every mask it names.

When is CPAP the right answer?

CPAP is the right answer in this scenario when the problem is oxygenation in cardiogenic pulmonary oedema rather than ventilation. The British Thoracic Society recommends considering CPAP with entrained oxygen to maintain 94 to 98% when standard treatment is not working.

The evidence statement behind that recommendation is that CPAP with oxygen improves gas exchange early in cardiogenic pulmonary oedema. Reported falls in short-term mortality and intubation rates were not confirmed in the largest trial.

That said, CPAP does not clear carbon dioxide the way bilevel ventilation does. A hypercapnic, acidotic patient is not a CPAP patient, and mixing the two up is a classic interview error.

What are the numbers that say start non-invasive ventilation?

Non-invasive ventilation starts when a pH below 7.35 and a PaCO2 above 6.5 kPa persist or develop despite optimal medical therapy. That is recommendation 25 of the 2016 guideline from the British Thoracic Society and the Intensive Care Society.

In an acute exacerbation of COPD, optimal medical therapy means treatment with the saturation targeted at 88 to 92%, reassessed after 60 minutes. Research shows about one in five patients, 20%, correct their acidosis on that alone.

The same guideline says non-invasive ventilation should not be used in acute asthma with hypercapnic failure, and that severe acidosis alone does not rule out a trial in an area with ready access to safe intubation.

When do you stop escalating and intubate?

You intubate in this scenario when non-invasive support has failed, is impossible, or was never going to be enough. The BTS and Intensive Care Society guideline names respiratory arrest or peri-arrest as an immediate indication unless there is rapid recovery.

Persistent or deteriorating acidosis despite attempts to optimise the delivery of non-invasive ventilation
Severe respiratory distress, or a persisting pH below 7.15 or deterioration in pH despite non-invasive ventilation
A depressed conscious level, quoted in the guideline as a Glasgow Coma Scale score below 8
An interface that cannot be fitted or used: severe facial deformity, fixed upper airway obstruction, facial burns
A risk and benefit judgement by an experienced clinician that favours invasive ventilation

The guideline suggests a pH of 7.25 as the level below which invasive ventilation should be considered and 7.15 as the level at which it is indicated, following initial resuscitation and controlled oxygen therapy.

Who do you call, and when?

In a respiratory failure scenario you call early and you call twice: the medical registrar for the disease and critical care for the ventilation decision. Calling once the pH has fallen below 7.15 is calling late.

The BTS and Intensive Care Society guideline asks for an individualised plan, agreed with the patient where possible, documenting what happens if non-invasive ventilation fails. That conversation belongs at the start of treatment, not at 3 am.

For an anaesthetic CT1 the specific offer is your own skill set: a difficult airway assessment, the intubation itself, and a safe transfer to a level 3 bed. Say what you personally would do.

What do the assessors score besides the escalation ladder?

Beyond the ladder, the assessors in a respiratory failure scenario score whether you noticed that a ceiling of treatment is a decision someone has to make, and whether you would make it with the patient rather than about them.

Reflective practice is a named domain. A usable example is a patient you started on non-invasive ventilation without an agreed plan for failure, and the escalation conversation that then happened under pressure.

Working under pressure is scored in how you speak while the numbers worsen. Naming the next trigger out loud, for instance a repeat gas in 60 minutes, shows a plan rather than a reaction.

Which mistakes cost marks here?

The mistakes in an oxygen and respiratory failure scenario are the ones the British Thoracic Society text was written to close, and most of them are about fixing a number to the wrong patient.

Withholding oxygen from a critically ill patient with COPD: the initial target is the same as anyone else until the gas is back
Reading a normal saturation as a normal gas, when type 2 failure can exist at any saturation
Offering CPAP for hypercapnic acidosis, where bilevel support is the treatment
Quoting a single pH for intubation: the guideline gives 7.25 to consider and 7.15 to indicate, after resuscitation
Using non-invasive ventilation for acute asthma with hypercapnic failure, which the guideline advises against
Never naming a reassessment time, so nobody knows when the plan failed

How this comes up at the CT1 anaesthetics interview

Oxygen and respiratory failure reach the clinical judgement station as a referral: a breathless ward patient with a falling saturation, or a COPD patient whose gas has just come back acidotic. The station is 15 minutes after five minutes of reading, marked out of 50.

Clinical judgement and decision making is scored on the target, the device and the ventilation trigger. Reflective practice is scored on the ceiling-of-treatment conversation, and working under pressure on whether you keep reassessing while the pH falls.

The follow-up usually moves the goalposts: the mask does not fit, the patient pulls it off, or there is no level 3 bed. anaestheticinterview's bank of 340 questions includes AI-marked spoken practice, so these numbers can be said aloud until they are automatic.

Oxygen Therapy, CPAP and When to Intubate: Type 1 vs Type 2 Failure