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CPAP - How and when to use it?

Reading time: 10 minutes

Indications for CPAP

Acute hypoxaemic respiratory failure – as ceiling of care (including COVID-19)
Acute cardiogenic pulmonary oedema
Sleep disordered breathing (chronic use)
As a bridge to invasive intubation and ventilation

Contra-indications for CPAP

Absolute (Can’t put the mask on the face)

Severe facial deformity
Facial burns
Upper airway obstruction

Relative

Vomiting/excess secretions (risk of aspiration)
Confusion/agitation
GCS < 8 – Inability to protect airway
Pneumothorax (undrained)
Not a candidate for escalation of care to ICU. However, can be used as ceiling of care in itself

Note the undrained pneumothorax. The corollary is, it is vital to get a CXR before you start CPAP!

Interfaces

Masks come in different shapes and sizes. It is really important to get a good fit. Mask leaks increase patient discomfort and intolerance reducing success rates.

The order of likelihood for the masks to leak include: Oro-nasal mask (Figure 1a) > Full face mask (Figure 1c) > Helmet mask (Figure 1b).

The helmet mask can be claustrophobic while the full face mask can make it difficult to avoid aspiration in case the patient vomits, although the last can happen with any mask.

Practical tip: Before abruptly strapping the mask to the face, it can be helpful to start the CPAP machine with just 5cm of H₂O and hold the mask in front of the face while calmly explaining how the machine will help breathing. Once they understand what to expect, it will be easy to strap it in. It will certainly increase tolerance and success.

Figure 1

Once the mask has been strapped in, ensure there is little leak by using the dorsal surface of your hand to feel the rush of air around the mask (Figure 2).

Figure 2

Settings to start with

Start at 5 cm of H₂O
Increase in increments of 5 cm of H₂O every 10-15 minutes titrating it to saturations. Aim for saturations > 94%
Maximum of 20 cm of H₂O

Beware of too much CPAP! Read blog here.

Monitoring

Figure 3

Weaning

There is no right or wrong way. Suffice it to say that it is individualised.

Scenario 1: If patient has responded very quickly

Could take longer breaks around meal times while on supplementary oxygen and just use CPAP overnight.
Later on in the course of illness, if tolerating daytime on supplementary oxygen alone – only nocturnal use for one or two nights.

Scenario 2: If patient is responding slowly/ is at least stable:

Shorter meal-time breaks while on supplementary oxygen + nocturnal use.
Gradually increase meal-time breaks and follow as above in scenario 1.

If remains on CPAP for > 48 hours without adequate nutrition, consider naso-gastric tube feeding but avoid abdominal distension as this can splint the diaphragm and cause hypoventilation (push the diaphragm up and squash the lungs preventing air from entering). It can also increase the risk of vomiting and aspiration.

What is the significance of deciding ceiling of care before starting CPAP? Put your answers below in the comments section

and I will respond 🙂

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medbookprof

I'm a Consultant Pulmonologist having experienced medicine first-hand across two continents stretching from the South Indian peninsula to the British Isles, the emerald nation of Ireland, to the Mediterranean climes of Italy and to the happiest country on earth, Denmark. Along the way, I have served as an honorary Associate Clinical Teacher and Royal College Associate tutor at University Hospital of Wales, collected a Masters in Medical Education and a passion for teaching. My enthusiasm is matched only by my thirst for simplifying clinical knowledge for medical students and making it accessible on a global scale.