CPAP

Indications:

Respiratory failure (pO2 < 55mgHg, pCO2 > 60mmHg) despite high flow oxygen/maximal medical treatment

    e.g.

    Acute pulmonary oedema

    COAD (BIPAP is better)

    Pneumonia

    Asthma (controversial and may worsen hyperinflation)

Contraindications (these patients will need intubation and mechanical ventilation)

    Loss of gag reflex

    Obtundation

    Pre-arrest

Procedure

Connect CPAP machine to oxygen and air wall source

Set FiO2 initially  to 100% (using oxygen/air blender and calculation table on machine)

    Attempt to achieve maximum total flow rate allowable for any given FiO2

    N.B. Avoid SaO2 > 93% in CO2 retention and titrate FiO2 downward quickly aiming around 93% and check ABG early

Set PEEP at 5 cmH2O increasing 1-2 cmH2O every minute until SaO2 > 93% to Maximum of 15cmH2O

Sit patient upright (unless hypotensive)

Place mask harness behind patient's head

Attach mask firmly to patient's face ensuring air-tight seal (hold mask to face temporarily whilst straps being fastened)

Patient requires nurse special

Observe closely for aspiration/vomiting, hypotension, non-response to treatment, hypoxia, worsening mental status

Nursing observations (minimum)

•     Continuous SaO2
•     5 minutely BP monitoring
•     Continuous assessment of mental state - eyes open, obeying commands
•     Evidence of vomiting

Complications

•     Hypotension
•     Pneumothorax
•     Gastric distension/Aspiration
•     Pressure necrosis around face (after > 48 hrs use)
•     Non-tolerance of mask

Problems - how to address

    Hypotension

• Review drugs administered e.g. GTN and reduce infusion rate
• Treat hypovolaemia/septic shock/anaphylaxis
• Treat tension pneumothorax
• Reduce PEEP
• Consider starting inotropes

    Hypoxia

• Increase FiO2 to 100%
• Treat hypotension
• Treat pneumothorax
• Maximise medical therapy
• If no response then intubate and ventilate

    Worsening mental state

• Treat hypoxia (SaO2 < 90%)
• Treat hypercarbia - reduce oxygen until SaO2 reaches 93% but no lower
• Escalate medical therapy
• If no response then intubation and mechanical ventilation required

    Patient 'fights' mask

•     Continuous verbal assurance required
•     Strongly avoid sedatives in patient already in respiratory failure

Weaning (under medical instruction)

• Continue medical therapy
• Titrate FiO2 downward whilst maintaining SaO2 > 93% until FiO2 50% reached (reduce by 10% every 5 min)
• Titrate PEEP down 1-2 cmH2O every 10-15 min to a minimum of PEEP 5cmH2O

Criteria for stopping CPAP

• Patient can speak in sentences
• Patient fully alert and orientated
• Respiratory rate normalises
• SaO2 > 93% on FiO2 50% & PEEP 5cmH2O or less
• pCO2 < 60mmHg

Criteria for starting mechanical ventilation

• Loss of gag reflex
• Mental obtundation
• Pre-arrest
• No improvement or worsening despite maximal medical therapy  and 100% FiO2 and maximal PEEP
• Increasing fatigue and sleepiness
• CPAP required for > 48 hrs