Clinical implications of residual sleep apnoea after chronic CPAP therapy Several recent studies have documented residual sleep apnoea in continuous positive airway pressure-treated patients, and the term complex sleep apnoea has been used by some to describe this phenomenon. The consequences of residual sleep apnoea are unknown but could be significant, since patients with even mild obstructive sleep apnoea may be at increased risk of cardiovascular complications and motor vehicle crashes. The current study aimed at evaluating the prevalence and clinical implications of residual sleep apnoea. Materials and methods Prospective randomised clinical trial in 61 moderate-to-severe obstructive sleep apnoea (OSA) patients who were assigned to standard continuous positive airway pressure (CPAP) titra- tion during polysomnograpy (PSG) or ambulatory titration using auto-CPAP and home sleep test- ing, at University of British Colombia (Vancouver, Canada). Residual sleep apnoea was defined by an apnoea–hypopnoea index (AHI) of .10 events ? h -1 on CPAP, after 3 months of CPAP therapy. Results 30 patients received standard CPAP titration (baseline AHI 37.3¡3.6), while 31 underwent ambulatory titration (baseline AHI 43.4¡8.1). Residual sleep apnoea was present in seven of 30 PSG patients (23%) and in eight of 31 ambulatory patients (26%), overall in 25% of the study population. Periodic breathing was prevalent among patients with residual sleep apnoea. The most frequently observed residual respiratory events were classified as obstructive hypopnoeas (66% of all events), while central apnoeas accounted for only 10% of events. Age, sex distribution, body mass index, Epworth sleepiness scale (ESS), Sleep Apnea Quality of Life Index (SAQLI) and severity of OSA did not differ at baseline between patients with and without residual sleep apnoea. The combination of an ESS .8 and a machine downloaded AHI .10 had a sensitivity of 45%, a specificity of 97% and a positive-likelihood ratio of 14.5 for the presence of residual sleep apnoea. Outcomes ESS (9¡6 versus 5¡4; p,0.001), SAQLI (4.6¡1.7 versus 5.6¡0.8; p,0.002) and CPAP compliance (4.6¡2.2 versus 5.7¡1.8; p50.04) were worse for patients with residual sleep apnoea compared to those without. Conclusion Residual sleep apnoea appears common in patients with moderate-to-severe OSA, despite careful CPAP titration, and is associated with worse outcomes. Original article Mulgrew AT, Lawati NA, Ayas NT, et al . Residual sleep apnea on polysomnography after 3 months of CPAP therapy: clin- ical implications, predictors and patterns. Sleep Med 2010; 11: 119–125. Editorial comment This prospective randomised study in 61 moderate-to-severe OSA patients clearly illustrates the high prevalence of residual sleep apnoea after 3 months of CPAP therapy, independent of pressure or mouth leakage. Equal pro- portions of residual disease have been reported (17%, predominantly hypopnoeas, AHI .10 [1]; 19%, AHI .15 [2]). A similar phenomenon was described by Gilmartin et al. [3] and termed complex sleep apnoea (CompSAS). Its prevalence reported in some recent papers by different groups was also high (15%, USA [4]; 20%, USA [5]; 13%, Australia [6]). Not all groups have however reported such high prevalence data (6.5%, USA [7]; 5%, Japan [8]; 5.7%, Japan [9]), but can be considered still high when taking into account that the term CompSAS is restricted to persistence or emergence of central apnoeas or hypopnoeas (central apnoea index . 5) on exposure to continuous positive airway pressure in OSA, or at follow up. This also points at a lack of a clear definition to describe persisting events, or may reflect its heterogeneity. There is also some controversy around residual sleep apnoea, especially CompSAS, on whether it actually exists to any great extent and on its clinical relevance [10, 11]. In residual sleep apnoea, Baltzan et al . [1] reported no difference in sleepiness (ESS) between CPAP responders (6.1¡ 3.6) and non responders (7.2¡5.4), but more morning headache, nonrestorative sleep, higher CPAP pressures, more mouth leaks and mask leaks and lower compliance) [1]. Surprisingly, residual sleepiness was not associated with an increase in arousals. On the other hand, in the current study more sleepiness (ESS 9¡6 versus 5¡4), lower compliance and equal pressures were found in residual sleep apnoea. Finally, Pittman et al. [2] found no relationship between sleepiness (ESS 8 (5–12)) and residual AHI. In CompSAS, Pusalavidyasagar et al . [12] found equal therapy compliance and clinical improvement, while Morgenthaler et al. [13] found inferior effects of CPAP in Message Residual sleep apnoea presents independent of the choosen CPAP titration procedure, and may have clinical implications. Due to its high prevalence, repeated sleep studies could be recommended. Competing interests None declared. DOI: 10.1183/20734735.022010 Breathe | March 2011 | Volume 7 | No 3 289 Hot Topic