## 4 Discussion  
The International Classification of Sleep Disorders-Third Edition (ICSD-3) has included treatment emergent central sleep apnea as a syndrome that requires OSAS diagnosis followed by significant resolution of the obstructive apnea and emergence or persistence of central apnea during PSG after CPAP treatment, not related with other comorbidities [27]. Although currently the classification does not include the development of treatment emergent central sleep apnea with other kind of therapies these are to date increasingly used. A clinical review by [PERSON] et al. reveals that TECSA is a rare phenomenon that can occur with all alternative OSA treatments, mandibular advancement devices, all types of surgery including tracheostomy, maxillomandibular advancement surgery and hypoglossus nerve stimulator [28]. In the scientific literature an important variability in TECSA's prevalence is reported, ranging from 5% to 20%. One of the reasons for this large range is the lack of established diagnostic criteria or protocols that define it and the different methodologies used in the studies [18]. Another reason can be the different use of split-night or full-night CPAP; split night studies seem to report a higher prevalence that may be connected to the lower capacity to evaluate breathing disorder's severity [29]. [PERSON] et al. reported an increased risk of developing TECSA in male and older patients who had a high baseline AHI: patients with a higher AHI had an increased risk of developing TECSA compared to patients with a lower index [20]. An increased CAI (central apnea index) can also predict TECSA emergence, so the presence of a high number of central apneas at diagnosis is a possible risk factor. Lower body mass index and chronic opiate use can also predict TECSA according to an article review by [PERSON] et al. [18]. Cardiovascular issues are common in patients with TECSA such as congestive heart failure, ischemic heart disease, coronary artery disease and hypertension [20], even if [PERSON] et al. reported that one-third of patients do not have any pathology before the sleep test and still develop TECSA [30]. According to [PERSON] et al. risk factors are male gender, hypertension and history of cardiac disease, coronary artery disease, stroke, congestive heart failure, increasing age, higher baseline apnea-hypopnea index and central apnea index and opioid use [31]. Another matter reported by [PERSON] et al. is that TECSA can occur at any CPAP setting, according to their results there are no statistically significant differences between patients with TECSA and those without TECSA in CPAP settings [20]. The results of the present study do not confirm the observation reported by the previous literature regarding CPAP therapy; indeed, no differences in terms of OSA, ODI, AHI, age, BMI and amount of mandibular advancement  
Figure 4: Descriptive variables table in patients who developed or increased the number of CSA. were observed between those subjects that showed CSA events compared to those who did not show signs of CSA. Moreover, central sleep apnea values showed a significant decrease from T0 to T1 when the whole sample--excluding the three outlier cases--was evaluated. The American Academy of Sleep Medicine define TECSA or \"complex sleep apnea\" as a disorder characterized by persistence or emergence of central apneas with CPAP treatment while obstructive sleep apneas are mainly resolved. Treatment emergent central sleep apnea, according to some studies, is a transitory condition that could resolve after some weeks of treatment with CPAP [32; 33]. According to [PERSON] et al. it would be preferable to divide subjects undergoing treatment with CPAP and that have TECSA into two different categories: on the one hand those who develop central apneas following treatment on the other hand those who have persistence of central apneas with treatment, this would be an indication of failure of therapy and the need to switch to another type of treatment [34].