Ward based CPAP machines use air (different to ICU where they can use oxygen driven CPAP), so oxygen has to be entrained separately using an oxygen entrainment port (in the tubing or in the patient’s mask). The concentration of oxygen delivered to the patient should be increased up to 15 litres/minute. The air that drives the CPAP pressure dilutes the oxygen delivered to the patient; the higher the CPAP pressure, the lower the fractional inspired concentration of oxygen (FiO2).
This relationship between CPAP pressure and FiO2 has been illustrated in the table below.
By monitoring the patient’s oxygen saturations, the CPAP pressure support should be titrated up and down to achieve target oxygen saturations (90 – 94%); some patients may need higher CPAP pressure, and some may need higher FiO2.