Sleep apnoea · Devices

Beyond CPAP: when to consider BiPAP or ASV

Written by Dr Ari Manuel, Consultant in Sleep & Respiratory Medicine

Continuous positive airway pressure (CPAP) is the first-line treatment for obstructive sleep apnoea, and it works well for the majority of patients. But a significant minority either cannot tolerate CPAP, have residual symptoms despite adequate compliance, or have a pattern of sleep-disordered breathing that standard CPAP does not adequately address. Understanding when to escalate — and to what — is an important part of consultant-level sleep medicine.

Treatment-emergent central apnoeas

Some patients who begin CPAP therapy develop central apnoeas that were not present before treatment. This phenomenon — sometimes called complex sleep apnoea syndrome — occurs when CPAP eliminates obstructive events but unmasks or provokes centrally-generated breathing cessation. In these patients, continuing CPAP may produce poor objective outcomes despite apparent adherence. Adaptive servo-ventilation (ASV) devices, which adjust pressure support breath-by-breath in response to the patient's own respiratory effort, are often the appropriate next step.

It is important to note that ASV is contraindicated in patients with symptomatic chronic heart failure and significantly reduced left ventricular ejection fraction (LVEF ≤45%), based on the SERVE-HF trial (Cowie MR et al., NEJM 2015). Cardiac function should be assessed before prescribing ASV in any patient with relevant cardiac history.

BiPAP and non-invasive ventilation

Bilevel positive airway pressure (BiPAP) delivers different pressures during inhalation and exhalation. It is particularly useful in obesity hypoventilation syndrome, neuromuscular respiratory disease, and severe OSA with significant hypoxaemia or nocturnal hypoventilation. Unlike CPAP, BiPAP provides genuine ventilatory support and can correct hypercapnic respiratory failure when applied correctly.

Hypoxic burden: looking beyond AHI

Apnoea-hypopnoea index (AHI) remains the most commonly reported measure from sleep studies, but accumulating evidence suggests that the total hypoxic load — the area under the desaturation curve — may be a more clinically meaningful predictor of cardiovascular, metabolic, and cognitive outcomes (Azarbarzin A et al., European Heart Journal 2019). Two patients with an identical AHI may have very different hypoxic burden depending on the depth and duration of desaturations, and therefore different risk profiles and treatment urgency.