What Does a CPAP Machine Do? Benefits & NHS Access

What does a CPAP machine do? A CPAP (continuous positive airway pressure) machine delivers a steady, pressurised stream of air through a mask to keep your upper airway open while you sleep, preventing the repeated breathing interruptions caused by obstructive sleep apnoea (OSA). Used by millions of people worldwide, CPAP is the first-line treatment recommended by NICE for moderate to severe OSA in adults. This article explains how CPAP works, who it is prescribed for on the NHS, the health benefits of consistent use, common side effects, and how to access a machine through NHS or private routes.

What does a CPAP machine actually do while you sleep?

A CPAP machine pressurises room air and delivers it continuously through a mask to prevent the airway from collapsing in obstructive sleep apnoea. Pressure is prescribed in cmH2O and tailored to the severity of your apnoea.

A CPAP (continuous positive airway pressure) machine delivers a steady, pressurised stream of air through a mask to keep your upper airway open throughout the night. In obstructive sleep apnoea (OSA), the muscles of the throat relax during sleep, causing the airway to narrow or collapse repeatedly. Each collapse briefly stops breathing, fragments sleep, and drops blood oxygen levels. CPAP prevents this by acting as a pneumatic splint: the continuous air pressure holds the soft tissues of the throat apart so they cannot fall inward.

The machine itself consists of a small motorised unit that draws in room air, filters it, and pressurises it to a level set by your sleep specialist. This pressurised air travels along a flexible tube to a mask worn over the nose, the mouth, or both. The prescribed pressure is measured in centimetres of water (cmH2O) and is tailored to the severity of your apnoea.

UK sleep services commonly assess severity using the apnoea-hypopnoea index (AHI, the number of breathing interruptions per hour of sleep) and the oxygen desaturation index (ODI, the number of times per hour that blood oxygen falls by a defined amount). Both measures inform diagnosis and treatment decisions alongside your symptoms.

Many modern devices are auto-titrating (APAP), meaning they continuously monitor your breathing and adjust the pressure moment to moment rather than delivering a fixed level all night. Some machines also incorporate heated humidifiers, which add moisture to the air to reduce dryness and improve comfort. These devices record data, including a calculated residual AHI, which your sleep team reviews to check that therapy is working effectively. This figure is an estimate and is always interpreted by a clinician rather than used in isolation.

Who is a CPAP machine prescribed for in the UK?

CPAP is the first-line NHS treatment for adults with moderate to severe OSAHS, and may be offered for mild OSAHS where symptoms significantly affect quality of life. Diagnosis follows a GP referral to a specialist sleep service and a diagnostic sleep study.

CPAP is the first-line treatment recommended by NICE for adults with moderate to severe obstructive sleep apnoea hypopnoea syndrome (OSAHS), and it may also be offered to people with mild OSAHS whose symptoms significantly affect their quality of life (NICE NG202; NICE TA139).^[1][2] Severity is classified by the sleep service using AHI or ODI alongside symptoms such as excessive daytime sleepiness, unrefreshing sleep, or witnessed apnoeas.

Diagnosis in the UK is typically made through a sleep study arranged by a GP referral to a specialist sleep service. This may be a home-based oximetry or respiratory polygraphy study, or a full in-laboratory polysomnography for more complex cases. The Epworth Sleepiness Scale is commonly used alongside objective testing to quantify daytime sleepiness.^[21][1]

CPAP is also used in some presentations of overlap syndrome (OSAHS combined with chronic obstructive pulmonary disease). Central sleep apnoea is a distinct condition requiring specialist assessment: CPAP is not generally the first-line approach, and management may involve bilevel positive airway pressure (bilevel) in spontaneous-timed mode, adaptive servo-ventilation, or other modalities depending on the underlying cause.^[16][17] Children with OSA are usually managed differently, most often with adenotonsillectomy in the first instance; families should be guided by a paediatric or ENT specialist.^[22][23]

People with OSA who drive have a legal obligation to report their condition to the DVLA (or DVA in Northern Ireland) and must not drive while excessively sleepy, regardless of whether treatment has started. Group 2 licence holders (lorry and bus drivers) face stricter requirements and should consult the DVLA guidance on assessing fitness to drive for the specific standards that apply to them.

How does CPAP therapy improve your health over time?

Consistent CPAP use reduces sleep fragmentation, improving daytime sleepiness, blood pressure, and cognitive function over weeks to months. Cardiovascular and metabolic benefits are also associated with effective therapy, though adherence is the key determinant of outcome.

Consistent CPAP use reduces the number of breathing interruptions during sleep, which in turn produces a range of measurable health benefits over weeks to months. The most immediate improvement most people notice is reduced daytime sleepiness: because sleep is no longer fragmented by repeated arousals, restorative slow-wave and REM sleep can occur normally. Partners often report that snoring stops on the first night of effective therapy.

Beyond symptom relief, there is good evidence that CPAP lowers blood pressure, particularly in people with resistant hypertension whose elevated readings are partly driven by the repeated surges in sympathetic nervous system activity that accompany each apnoea.^[9][10] Cardiovascular risk, including the risk of atrial fibrillation and stroke, is associated with untreated OSA.^[7][8] CPAP use is considered an important part of managing that risk, though evidence on reduction of hard cardiovascular events is mixed, and CPAP is not a substitute for other cardiovascular risk factor management.^[6][7]

Metabolic benefits have also been observed. Untreated OSA is linked to impaired glucose regulation and worsened insulin resistance, and CPAP therapy may modestly improve glycaemic control in people with type 2 diabetes, though the magnitude of benefit varies between individuals.^[12][13] Mood, concentration, and cognitive function frequently improve as sleep quality is restored.

Adherence is the key determinant of benefit. Your sleep service will agree usage goals with you based on your individual circumstances and the evidence available; if you have questions about how much use is needed to see benefit, discuss this with your sleep physiologist or specialist nurse.

What side effects and discomfort can a CPAP machine cause?

Mask discomfort, airway dryness, and aerophagia are the most common side effects, particularly in the early weeks of treatment. Most issues can be resolved by changing mask style, adding a heated humidifier, or enabling expiratory pressure relief.

CPAP therapy is generally safe, but side effects are common in the early weeks and are the main reason some people struggle to continue treatment. Mask discomfort is the most frequently reported problem: pressure sores on the bridge of the nose, air leaks around the seal, and a feeling of claustrophobia can all occur. Trying different mask styles (nasal pillows, nasal masks, or full-face masks) often resolves fit-related issues, and your sleep service should offer mask fitting support.

Airway dryness and congestion are also common, particularly if the machine is used without a humidifier. A heated humidifier attachment, available on most modern devices, significantly reduces nasal dryness, nosebleeds, and sore throats. Nasal saline sprays can provide additional relief. Condensation in the tubing (sometimes called rainout) can be reduced by adjusting humidifier settings or using heated tubing. Air leaks around the mask can occasionally cause dry or irritated eyes; improving the mask seal usually resolves this.

Some people experience aerophagia (swallowing air), which causes bloating or discomfort; adjusting the pressure setting or switching to an APAP device may help. A small number of people find the sensation of pressurised air difficult to tolerate, particularly on exhalation. A feature called expiratory pressure relief (EPR, or an equivalent function depending on the manufacturer) reduces pressure slightly during the out-breath and can improve comfort without compromising efficacy.^[18][19] Skin irritation from mask materials is occasionally reported and may respond to hypoallergenic mask liners.

Regular cleaning of the mask, tubing, and humidifier chamber according to the manufacturer's instructions and your sleep service's guidance helps to reduce the risk of irritation and infection.

If you experience chest pain, significant shortness of breath, or worsening symptoms after starting CPAP, contact your GP or sleep service promptly. For urgent concerns outside normal hours, NHS 111 can provide advice. Suspected adverse incidents involving CPAP equipment can be reported to the MHRA via the Yellow Card scheme (yellowcard.^[20]mhra.gov.uk).

How do you get a CPAP machine on the NHS?

A GP referral to a specialist sleep service is the standard NHS pathway; if OSAHS is confirmed, the service loans a CPAP machine, mask, and consumables at no charge. Waiting times vary by Integrated Care Board area, and private assessment is an option to reduce delays.

To obtain a CPAP machine on the NHS, the usual pathway begins with a GP referral to a specialist sleep service after a clinical assessment suggests obstructive sleep apnoea. Your GP will typically ask about symptoms such as loud snoring, witnessed pauses in breathing, and excessive daytime sleepiness, and may use a validated questionnaire such as the STOP-BANG or Epworth Sleepiness Scale to support the referral decision.

Once referred, the sleep service will arrange a diagnostic sleep study. If OSAHS is confirmed and meets the threshold for treatment, the service will prescribe and loan a CPAP machine to you. On the NHS, the machine, mask, and consumables such as filters and tubing are provided on loan at no charge to the patient; there is no standard prescription charge for CPAP equipment because it is supplied as a medical device rather than a medicine.^[3] The provision of humidifiers and the replacement schedule for consumables can vary between local sleep services. Follow-up appointments, which may be face-to-face or remote, allow the team to review your usage data and troubleshoot any difficulties.

Waiting times for NHS sleep services vary by Integrated Care Board (ICB) area. Some people choose to pursue a private sleep study and CPAP assessment to reduce waiting time, after which they may be able to return to NHS follow-up. If you are considering private assessment, look for a service using an accredited sleep laboratory (such as those meeting ARTP or British Sleep Society standards) and led by a clinician registered with the General Medical Council (gmc-uk.org). Whichever route you take, ongoing support from a sleep physiologist or specialist nurse is an important part of achieving good adherence and long-term benefit from therapy.

If you hold a Group 2 driving licence, your sleep service can advise on the evidence of effective treatment that the DVLA requires before you may resume driving.

Scientific References

1. Obstructive sleep apnoea/hypopnoea syndrome and obesity hypoventilation syndrome in over 16s (NG202).
2. Continuous positive airway pressure for the treatment of obstructive sleep apnoea/hypopnoea syndrome (TA139).
3. Sleep apnoea.
4. Excessive sleepiness and driving.
5. Miscellaneous conditions: assessing fitness to drive.
6. CPAP for Prevention of Cardiovascular Events in Obstructive Sleep Apnea.
7. PAP therapy is associated with reduced all-cause and cardiovascular mortality in people with OSA: systematic review and meta-analysis.
8. Association of Positive Airway Pressure With Cardiovascular Events in Patients With Obstructive Sleep Apnea.
9. Effect of CPAP therapy on blood pressure in patients with obstructive sleep apnoea.
10. Effect of Continuous Positive Airway Pressure on Blood Pressure in Patients With Resistant Hypertension and Obstructive Sleep Apnea.
11. Continuous Positive Airway Pressure in Patients With Obstructive Sleep Apnea and Resistant Hypertension: A Meta-Analysis of Randomized Controlled Trials.
12. Effect of Continuous Positive Airway Pressure on Glycemic Control in Patients With Obstructive Sleep Apnea and Type 2 Diabetes.
13. Benefits of continuous positive airway pressure on glycaemic control and insulin resistance.
14. Effects of continuous positive airway pressure therapy on glucose metabolism in patients with obstructive sleep apnoea and type 2 diabetes: a systematic review and meta-analysis.
15. CPAP in patients with obstructive sleep apnea and type 2 diabetes mellitus: Systematic review and meta-analysis.
16. Adaptive Servo-Ventilation for Central Sleep Apnea in Systolic Heart Failure.
17. Treatment of central sleep apnea in adults: an American Academy of Sleep Medicine clinical practice guideline.
18. Pressure-Relief Features of Fixed and Autotitrating CPAP: Effects on Efficacy.
19. Efficacy and patient satisfaction with autoadjusting CPAP with variable expiratory pressure vs standard CPAP: a two-night randomized crossover trial.
20. The Yellow Card scheme: guidance for healthcare professionals, patients and the public.
21. Use of the Epworth Sleepiness Scale to demonstrate response to treatment with nasal CPAP in patients with obstructive sleep apnoea.
22. Heated High-Flow Nasal Cannula Therapy for Pediatric Obstructive Sleep Apnea: Physiology, Clinical Evidence, and Future Directions.
23. Is watchful waiting an alternative to adenotonsillectomy in children with mild to moderate obstructive sleep apnoea?.
24. Role of Continuous Positive Airway Pressure in the Prevention of Cardiovascular Events in Patients With Obstructive Sleep Apnea: A Systematic Review and Meta-analysis.
25. Impact of Continuous Positive Airway Pressure on Cardiovascular Health in Patients With Obstructive Sleep Apnea: A Systematic Review and Meta-Analysis.

Frequently Asked Questions