Table 2 Acute effects (<3 months) of positive airway pressure in OHS

Author	N	Study type	Intervention	Duration	Outcomes	Comments
Sullivan74	2	Case reports	CPAP	1–3 months	↑Pao₂; ↓Paco₂; ↓oedema; ↓EDS; ↑mentation	↓Reduced SDB off therapy
Piper78	13	Retrospective	NIV	3 months	Improved ABGs	Long-term CPAP effective in 9/13 subjects
Berg37	20	Retrospective	BPAP or CPAP	2 years	68% ↓hospitalisations following therapy
Hida38	26	Before/after	CPAP	3 months	↓EDS; improved QoL
de Miguel Diez57	12	Before/after	BPAP withdrawal	3 months	No change in weight, daytime or nocturnal ABGs with treatment withdrawal; slight ↓ΔP_0.1/ΔPaco₂, ΔVE/ΔPaco₂	12/22 patients managed off BPAP; 7/12 demonstrated OSA and required CPAP therapy
Storre80	10	RCT, crossover	BPAP-S/T ±AVAPS	6 weeks	Improved sleep quality on BPAP; improved QoL; ↓Ptcco₂ during sleep on BPAP	BPAP with AVAPS more effective in ↓ CO₂ but no additional effects on sleep or QoL. CPAP non-responders studied
Banerjee77	23	Prospective	CPAP	1 night	Improved sleep quality, ↓AHI and improved oxygenation compared with baseline	43% of OHS patients studied continued to desaturate <90% for >20% of TST
Piper79	36	RCT	CPAP vs BPAP	3 months	Comparable improvements in awake CO₂ and Spo₂; subjective sleep quality better with BPAP; no difference in compliance	Subset of OHS patients without severe persistent REM hypoventilation on CPAP. Majority of patients managed longer term with CPAP
Chouri-Pontarollo50	15	Before/after	BPAP	5 nights	↓EDS; ↓AHI; improved objective vigilance in those with low CO₂ responses	Daytime ventilatory responses to CO₂ associated with amount of REM hypoventilation and daytime sleepiness

ABG, arterial blood gas; AHI, apnoea-hypopnoea index; AVAPS, average volume assured pressure support; BPAP, bilevel positive airway pressure; CPAP, continuous positive airway pressure; EDS, excessive daytime somnolence; NIV, non-invasive ventilation; OHS, obesity hypoventilation syndrome; OSA, obstructive sleep apnoea; P_0.1, occlusion pressure; Paco₂, Pao₂, arterial carbon dioxide and oxygen tensions; QoL, quality of life; RCT, randomised controlled trial; REM, rapid eye movement; SDB, sleep-disordered breathing; Spo₂, oxygen saturation; TST, total sleep time; VE, minute ventilation.