Does changing the continuous positive airways pressure (CPAP) interface alter pressure requirements in patients with obstructive sleep apnoea

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Continuous positive airways pressure (CPAP) is the treatment of choice for patients who have obstructive sleep apnoea (OSA). The patient wears an interface attached to a pump which delivers pressurized air to the upper airway, thereby splinting the airway open. The interface is usually one of three types, nasal pillows which sit directly in the nostrils, a nasal mask which covers the nose or a full-face mask which covers the nose and mouth. The nasal pillows and nasal mask require the patient to keep their mouth closed during treatment as opening the mouth releases pressure and this mouth leak results in less air pressure in the upper airway where it is required to splint the airway. The full-face mask ensures the nose and mouth are both in the pressurised area and thus prevents mouth leak from being a problem. Although the difference in dead space between the interfaces has been examined, the effect of the mechanical pressure from the headgear on the position of the lower jaw which is required to seal the full-face mask has not been clearly assessed. The force applied to the headgear to seal the full-face mask may result in the lower jaw being pushed back and thus the diameter of the upper airway being reduced. If this occurs, a higher CPAP pressure would be required to splint the airway. An alternative treatment for OSA is the mandibular advancement splint which relies on a dental device to pull the jaw forward to enlarge the airway opening. It is not unreasonable to presume that pressure in the reverse direction would have the opposite effect. This study aims to assess the pressure requirements of nasal versus full-face mask in patients with OSA by using auto-titrating continuous positive airways pressure (APAP).The APAP devices sense flow limitation and snore and respond to these by increasing or decreasing the positive airways pressure as required. The downloaded data can be examined to assess the pressure requirements of the patient. Patients will be assessed in a random order, crossover study comprising a two week period each of a suitably fitted nasal interface and a suitably fitted full-face interface. As the data will be collected over a two week period, night to night variation should be minimised. The APAP will assess the pressure requirements for each period to examine if there is any difference in pressure requirements between the two interfaces. The Mallampati score and pharyngeal dimensions will also be evaluated to examine if this is a possible pre-disposing factor.

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