FAILURE OF CPAP THERAPY IN OBSTRUCTIVE SLEEP-APNEA SYNDROME - PREDICTIVE FACTORS AND TREATMENT WITH BILEVEL-POSITIVE AIRWAY PRESSURE

Continuous positive airway pressure (CPAP) is the most widely used the rapy for obstructive sleep apnoea (OSA). Despite its general efficacy, oxygen desaturation due to hypoventilation persists in some patients. The present study analysed the factors which an associated with this primary failure and, moreover, examined the effect of a bilevel positi ve airway pressure (BiPAP) trial. In a 15-month period, 13 patients wi th OSA (Group A) failed to respond to initial CPAP therapy defined by a remaining apnoea/hypoproea index (AHI) of greater than or equal to 5 or a mean noctural SaO(2) <90%. These patients were compared to an ag e- and AHI-matched control group (Group B) successfully treated by CPA P. A logistic regression analysis was performed to identify factors wh ich are associated with initial failure to CPAP. Patients of the CPAP- failure group were treated with nasal BiPAP in the control mode. These patients were significantly more obese than patients of the control g roup (mean body mass index 44.2 +/- 7.7 vs 31.2 +/- 6.3 kg m(-2); P<0. 001). PaO2 at rest (P<0.001) and at exercise (P<0.005 was significantl y lower in Group A patients. PaCO2 at rest (P<0.001) was significantly higher in Group A patients and changed for the worse during exercise, whereas it improved in the control group. Group A patients spent sign ificantly (P<0.0001) more time with oxygen saturation <90%. The percen tage of time spent at <90% of SaO(2) was the only factor which was ind ependently associated with the initial failure of CPAP (OR 1.13: 95% C l 1.0-1.2). After 3 months of treatment with BiPAP, the patients' bloo d gas values while awake improved significantly (P<0.05) for PaO2 as w ell as for PaCO2. In conclusion, patients with OSA resistant to initia l CPAP are morbidly obese with impaired awake blood gas values. The pe rcentage of time spent at <90% of nocturall SaO(2) is independently as sociated with initial failure of CPAP. BiPAP in the control mode is ad equate for noctural ventilation, and improves awake blood gas values.