ORIGINAL ARTICLE

Compliance to continuous positive airway pressure therapyin a group of Portuguese patients with obstructive sleepapnea syndrome

Claudia Alves & José Manuel Pinto Chaves Caminha &

Antonio Martins da Silva & Denisa Mendonça

Received: 17 September 2010 /Revised: 5 May 2011 /Accepted: 6 June 2011 /Published online: 21 June 2011# Springer-Verlag 2011

AbstractIntroduction Obstructive sleep apnea–hypopnea syndrome(OSAHS) is an emerging public health concern. Althoughdifferent treatments for OSAHS had been proposed,continuous positive airway pressure (CPAP) is the first-line treatment in moderate to serious OSAHS in whichsuccess can be achieved by increasing compliance toCPAP.

Materials and methods This study analyzes long-termCPAP compliance in patients with OSAHS on CPAPtherapy for at least 1 month, who began CPAP therapybetween January 2004 and December 2006, followed up ata Portuguese Sleep Outpatient Clinic in Santo AntónioHospital. Only effective data of CPAP use had beenconsidered. During the first year of CPAP therapy, 96patients were enrolled and followed up, but 15 patients haddiscontinued CPAP treatment. CPAP was used on average5.1 h per day and in 80.1% of the total follow-up days.When compliance is defined as the use of CPAP for aminimum of 4 h per day in at least 70% of the follow-updays, only 54% of patients were classified as compliantsduring the first year.Results and conclusion No statistically significant differ-ences were found throughout the first year (p>0.05) interms of the percentage of compliants, controlling fordemographic and clinic variables. None of the demographicand clinical baseline variables studied were found to besignificant predictor of CPAP compliance (p>0.05). Thisstudy diagnosed a low compliance to CPAP therapy in thestudied sample, warning to the need of developing furtherstudies in this area and to the need of implementingstrategies to increase CPAP compliance.

Keywords Obstructive sleep apnea–hypopnea syndrome .

CPAP treatment . CPAP compliance

Introduction

Obstructive sleep apnea–hypopnea syndrome (OSAHS),characterized by repeated episodes of complete or partialbreathing pauses during sleep, is an emerging public healthconcern [1]. Despite being one of the most common causes

Preliminary data on some aspects from this study were presented atthe 20th Congress of the European Sleep Research Society (Lisbon,Portugal, 14–18 September 2010).

C. AlvesDepartment of Orthopedics, Santo António Hospital,Oporto, Portugal

J. M. P. C. Caminha (*)Department of Intensive Care, Santo António Hospital,Largo Prof. Abel Salazar,4099-001 Oporto, Portugale-mail: jcaminha@netcabo.pt

A. M. da SilvaDepartment of Neurophysiology, Santo António Hospital,Oporto, Portugal

A. M. da SilvaUMIB, Abel Salazar Biomedical Sciences Institute (ICBAS),University of Porto,Oporto, Portugal

D. MendonçaDepartment of Population Studies Institute of BiomedicalSciences Abel Salazar (ICBAS), University of Porto,Oporto, Portugal

D. MendonçaInstitute of Public Health, University of Porto,Oporto, Portugal

Sleep Breath (2012) 16:555–562DOI 10.1007/s11325-011-0542-9

of daytime sleepiness, and associated with cardiovascular,neurovascular, metabolic, neurocognitive disturbances, andtraffic accidents [2–6], OSAHS is frequently undiagnosed[7]. Although different treatments for OSAHS had beenproposed, such as changes in lifestyle [8–11], pharmaco-logical [12, 13] or surgical treatment [14, 15], continuouspositive airway pressure (CPAP) therapy is the first-linetreatment in moderate to serious OSAHS [16, 17]. Thecorrect use of CPAP provides a reduction in daytimesleepiness [18–25], normalizes sleep architecture [26], andimproves some comorbidities [8, 24, 27–41]. Thus, CPAPtreatment reduces health care costs and decreases hospitaluse rates [42–45]. The effectiveness of CPAP in treatingOSAHS has been documented in several studies, butcompliance to CPAP treatment can be low [46]. Weaverand Grunstein [46] have reported in a review article that 5–50% of patients had rejected or abandoned CPAP treatmentduring the first week, and 12–25% of the remaining patientshad refused CPAP throughout the first 3 years [46]. Theseauthors have also found that the estimated rate of non-adherents was between 29% and 83% [46] when CPAPcompliance was defined as the use of CPAP greater than 4 hper day. According to several studies [46–49], the successof CPAP therapy may be obtained by increasing patientadherence to treatment. Adherence patterns, as well aspredictors of nonadherence, may constitute a crucialinformation to improve CPAP treatment results [48, 49].In spite of the large number of studies conducted to studyCPAP compliance, the variability of results observed andthe lack of detailed information about CPAP compliance inPortugal justified the present study. This study aimed tostudy long-term CPAP compliance in patients with OSAHS,who began CPAP therapy and were followed up at aPortuguese Sleep Outpatient Clinic in Santo António Hospital(SAH)—Oporto.

Materials and methods

Patients

This is a retrospective study including patients withOSAHS followed up at Sleep Outpatient Clinic of SAH,who started CPAP therapy between January 2004 andDecember 2006. In order to obtain effective CPAPcompliance data, the sample comprised all patients onCPAP therapy for at least 1 month with effective data ofCPAP use in sleep outpatient clinic database. OSAHSdiagnosis was defined as apnea–hypopnea index (AHI) ≥5events per hour of sleep, as shown by overnight poly-somnography (PSG). Sleep PSG included frontal, centraland occipital, right and left mastoid referential electroen-cephalography (EEG) leads (electrodes placed according to

10–20 system), bilateral electrooculogram, submental andtibialis electromyogram, and electrocardiography. Respira-tion was assessed with nasal and oral airflow, thoracicrespiratory effort recordings, and oximetry. Sleep wasscored according to standard criteria. PSG was scoredmanually according to Rechtschaffen and Kales [50] by aregistered EEG technician and report confirmed by amedical doctor–clinical neurophysiologist. Two types ofevents were scored. An apnea was a ≥75% decrease inairflow for at least 10 s. Hypopnea was a 50–75% decreasein airflow coupled with either a 4% oxygen desaturation oran arousal. Arterial oxygen saturation (SaO2) was recordedby pulse oximetry. Snoring patterns were assessed qualita-tively by the technician as constant, frequent, intermittent,and infrequent.

Follow-up

Data of patients enrolled in this study were analyzed for1 year. CPAP use data were collected for four periods afterthe beginning of treatment: period I, the first month; period II,the first 3 months; period III, the first 6 months; andperiod IV, the first year. Such data refer to cumulativevalues throughout the entirely specific periods. To obtainmore detailed information on temporal variations and toconsider periods which do not overlap, data referring tothe last 15 days of each of the mentioned periods were alsocollected.

CPAP device

CPAP devices were the REM Star Pró, the REM StarAuto (Respironics), and the Spirit models (Resmed).Different nose masks, facemasks, nasal pillows, and headharnesses had been used, according to the individualfacial structure and preference. When justified, heatedhumidifiers were added. In all CPAP devices, there was abuilt-in monitoring chip for collection and storage ofCPAP use data. With this system it was possible to obtaineffective data on CPAP use, because it only registereduse when the set pressure was maintained and not justwhen the CPAP device was turned on.

Data recording

The device provided the number of the days of CPAP useand the hours of daily use. Patients were recommended tobring the device or the memory card, according to themodel in use, to the sleep outpatient clinic to download therecords. CPAP use information, available in sleep outpatientclinic database, was collected during 2008. The collecteddata allowed to calculate mean of CPAP daily use (hours),rate of CPAP use, rate of CPAP use for at least 4 h per day,

556 Sleep Breath (2012) 16:555–562

rate of CPAP use for at least 4 h per day, considering onlythe days when CPAP was used, according to the followingformulas:

Mean of CPAP daily use ¼ total hours of CPAP use

number of follow � up days

Rate of CPAP use ¼ number of days of CPAP use

number of follow � up days� 100

Rate of CPAP use � 4 h=day

¼ number of days of CPAP use for at least 4 h

number of follow� up days� 100

Rate of CPAP use � 4 h=day;when CPAP was used

¼ number of days of CPAP use for at least 4 h

number of days of CPAP use� 100

Different cut points were defined to study CPAPcompliance (≥3, 3.5, 4, 4.5, and 5 h). Patients who usedCPAP for a minimum of 4 h per day for at least 70% of totalfollow-up days were defined as compliants. Data ondemographics (age, sex, and occupation), smoke andalcohol consumption, concomitant diseases, body massindex (BMI), AHI, registered by overnight PSG, and meanand lowest SpO2 (pulse oximeter oxygen saturation) wereobtained from clinical records. The collected data wereused only for the purpose of this study, having been assuredanonymity and confidentiality. This study was approved bythe ethics committee of the SAH.

Statistical analysis

Absolute and relative frequencies of categorical variableswere calculated. For continuous variables, central tendencyand dispersion measures were determined. Student's two-tailed t test was used to compare means of continuousvariables after Kolmogorov–Smirnov test assured nosignificant differences from normal distribution. Proportionswere compared using a chi-square test with Yates' correctionfor continuity. If the expected values in more than 20% ofthe cells of the contingency tables were below five, Fisher'sexact test was used. Multivariable analysis using linear andlogistic regression models were also carried out to findpredictors of CPAP daily use in hours and CPAP compliance.Linear mixed models and generalized estimating equationswere performed to analyze temporal variation of CPAP dailyuse in hours and CPAP compliance, respectively. All p values

less than 0.05 were considered to indicate statisticallysignificant results. For statistical analysis, Statistical Packagefor the Social Sciences V16 (SPSS V16) for Windows wasused.

Results

Description of sample

Ninety-six patients were included in this study. Patientdemographic and clinical baseline data are shown in Table 1.Participants were mostly male (78.1%) with a mean age of53.5 years. Professional activity was known for 83 patients,67 were working population (64.2% blue-collar and 35.8%white-collar workers). The AHI ranged between 5.5 and81.2 events per hour of sleep, with a mean of 36.5 eventsper hour. Lowest SpO2 ranged between 43% and 90% witha mean of 73.5%. Concomitant OSAHS-related diseases wereobesity (64.6%), arterial hypertension (56.2%), diabetesmellitus (20.8%), hyperlipidemia (45.8%), hypothyroidism(2.1%), cardiovascular disease (15.6%), respiratory disease(11.5%), and otorhinolaryngological disease (41.7%). Alcoholconsumption was known for 49 participants and 4.9% referredalcohol consumption at night. Tobacco consumption wasknown for 43 patients: 18 smokers, 3 ex-smokers, and 22nonsmokers.

Before the end of the first year, 15 patients haddiscontinued CPAP treatment (Fig. 1). Four patientsdropped out between the 1st and the 3rd month, fourbetween the 4th and 6th month, and seven between 7th and12th month, corresponding to rates of abandon of 4.2%,

Table 1 Patient baseline characteristics

Characteristics Number Valuea

Sex 96

Male 78.1%

Female 21.9%

Age (year) 96 53.54 (9.23)

Professional activity 83

Active 80.7%

Inactive 19.3%

BMI (kg/m2) 96 33.6 (6.3)

AHI (events per hour) 36.5 (17.8)

OAHS severity 96

AHI ≤30 events per hour 43.8%

AHI >30 events per hour 56.2%

Lowest SteO2 (%) 96 73.5 (12)

Mean SteO2 (%) 96 92.7 (3.2)

a Categorical data are expressed as percentage of patients andcontinuous data are expressed as mean (SD)

Sleep Breath (2012) 16:555–562 557

8.3%, and 15.6%, during the first 3 months, the first6 months, and the first year, respectively. Reasons for suchabandon included “difficulty or incapacity to use the mask,”“dry mouth,” “nasal symptoms,” and “claustrophobia.” Atthe end of the first year, 31 patients out of 81 on CPAPtherapy had no complete database records of effectiveCPAP use (Fig. 1). The comparison of baseline data of these31 patients to the remaining group showed no significantdifferences in demographic and clinical variables (p>0.05).

Compliance to CPAP therapy

Table 2 shows CPAP use data over the 12 months of follow-up. The average of CPAP daily use in hours ranged from5 h during the first month to 5.1 h during the first year.Comparing the last 15 days of each of the four studiedperiods, linear mixed models showed no statisticallysignificant differences in mean of CPAP daily use (p>0.05),even when controlling for the demographic and clinicalvariables above described.

We observed a mean rate of CPAP use of 80.1% duringthe first year and 84.4% during the last 15 days of thisperiod. Considering the cut point of 4 h, the mean rate ofCPAP use decreases. During the first year, CPAP was usedfor at least 4 h in 68.4% of the follow-up days and in 82.1%of the days of CPAP use. Similar values were observedanalyzing the last 15 days of the first year (69.9% and 80%,respectively).

Compliance to CPAP was also analyzed according todifferent cut points (Table 3). Only 64% of the patients usedCPAP for at least 3 h per day during the first year. The valuedecreases to 48%, considering a mean of CPAP daily use≥5 h per day.

Patients who used CPAP a minimum of 4 h for at least70% of follow-up days were classified as compliants. Inthis study, 56.2% of the studied sample was consideredcompliant during the first month and 54% during the firstyear (Table 2). For the last 15 days of these periods, thevalues are 58.3% and 58%, respectively. Analyzing thepercentage of compliants for the last 15 days of the four

Fig. 1 Flow diagram showingthe sample during the studyperiod

Table 2 CPAP utilization data over the 12-month period

Variables First month Third month Sixth month First year

Mean daily use, h 5.0 5.0 4.9 5.1

CPAP use rate 81.6 80.1 79.7 80.1

CPAP use at least 4 h rate 65.9 67.0 67.9 68.4

CPAP use at least 4 h rateon days CPAP was used

75.0 79.1 80.8 82.1

Compliants to CPAP therapya 56.2 54.1 52.2 54.0

Variables Last 15 days ofthe first month

Last 15 days ofthe third month

Last 15 days ofthe sixth month

Last 15 days ofthe first year

Mean daily use, h 4.9 5.0 4.9 5.1

CPAP use rate 79.5 80.4 78.3 84.4

CPAP use at least 4 h rate 64.6 67.5 67.8 69.9

CPAP use at least 4 h rateon days CPAP was used

72.2 76.5 78.2 80.0

Compliants to CPAP therapya 58.3 60.0 63.8 58.0

a Data are presented as percentage of patients

558 Sleep Breath (2012) 16:555–562

studied periods, no statistically significant differences werefound throughout the first year (p>0.05), controlling fordemographic and clinic variables. Similar results wereobtained considering only the 50 patients who were undertreatment for 1 year and who had complete data available inthe database during this year.

Association between demographic and clinical variablesand compliance to CPAP therapy

The differences in mean of CPAP daily use betweenprofessionally active and non active patients were statisticallysignificant during the 1st, 3rd, and 12thmonths and during thelast 15 days of the 1st month. CPAP usage, on average, washigher in professionally active patients. Blue-collar workersused on average CPAP more hours than white-collar workers,but statistically significant differences were only found duringthe first 3 months and their last 15 days. Individuals withoutknown cardiovascular disease also used CPAP, on average,over a longer period of time compared to those with diagnosedcardiovascular disease. However, the differences were onlystatistically significant during the 12-month period and its last15 days. No statistically significant differences were found interms of age, sex, and clinical variables. Multiple regressionmodels, including demographic and clinical variables andfirst-order interactions between them, revealed no furtherstatistically significant associations. The differences found interms of cardiovascular disease and employment statusremain significant when adjusted for age and sex.

Patients were classified as “compliants” and “noncom-pliants” according to the study criteria above mentioned.None of the demographic and clinical baseline variables,considered in this study, were found to be significantpredictors of CPAP compliance (p>0.05).

Discussion

Despite therapeutic benefits of CPAP treatment described inseveral studies, compliance to CPAP remains a challenge.

Satisfactory therapeutic results could only be achieved byan effective CPAP use. In this study, CPAP compliance wasdefined as the CPAP use for a minimum of 4 h in at least70% of the follow-up days. CPAP daily use in hours, rate ofCPAP use, and rate of CPAP use for at least 4 h, consideringthe total follow-up days and only the days when CPAP wasused, were also analyzed. Only recorded effective data ofCPAP usage have been considered.

At the end of the first year, 87.5% of patients treatedwith CPAP during the first month remained under treat-ment. During this period, CPAP was used on average,80.1% of the total follow-up days, but used for at least 4 hper day only in 68.4% of the total follow-up days. Thevalue increases to 82.1%, considering only the days whenCPAP was used. This means that when CPAP was used, itwas mostly used for at least 4 h. Only 54% of patients wereclassified as compliants, using a minimum of 4 h in at least70% of the follow-up days.

Comparing to the study performed by Kribbs et al. [51],our results showed a higher rate of CPAP use (80.1% vs.66%) during 3 months. Sin et al. [52], in a cohort studyperformed to assess compliance to CPAP in 296 patientswho began CPAP therapy, found a higher mean of CPAPdaily use, comparing to the same periods of our study (5.7 hat 1 month, 5.9 h at 3 months, and 5.8 h at 6 months). Themean of CPAP daily use was also lower than that obtainedby Amfilochiou et al. [53] (5.3 h at 12 months) in a studywith 98 patients under CPAP treatment. Analyzing CPAPuse during the first 3 months, Kribbs et al. [51] andEngleman et al. [54] found a mean of CPAP daily use lower,4.9 and 4.7 h, respectively. Reeves-Hoche et al. [55] alsoobserved a mean of CPAP daily use of 4.3 h during6 months, slightly lower than the observed in this study forthe same period. Pieters et al. [56] in a retrospective long-term study, selecting 95 patients treated with CPAP morethan 1 year, observed a mean of CPAP daily use similar toour study (5 h).

CPAP use has been analyzed using different cut pointswith no consistent results in published studies. Comparingwith our results, the percentage of patients with a mean ofCPAP daily use ≥4 h was much higher in the studyperformed by Sin et al. [52] for the same periods (80.9%at 1 month, 87.1% at 3 months, and 83.8% at 6 months)and in the study by Pieters et al. [56] during 12 months(74%).This difference could be explained because Pieters etal. [56] selected patients who were under CPAP therapymore than 1 year and we performed this study with patientswho had started CPAP therapy. Adopting a more stringentcriterion (i.e., ≥4.5 h/day), the results obtained by Sin et al.[52] were also better (75.6% of the studied patients useCPAP ≥4.5 h per day at first month, 83.1% of patients usedit ≥4.5 h per day at 3 months, and 78.5% of the patientsused it ≥4.5 h per day at 6 months). Results obtained by

Table 3 Percentage of patients in CPAP therapy, according to differentcut point

Mean dailyuse, ha

Firstmonth

Thirdmonth

Sixthmonth

Firstyear

≥3 75.0 78.8 71.0 64.0

≥3.5 71.9 74.1 66.7 60.0

≥4 68.8 68.2 59.4 58.0

≥4.5 59.4 61.2 55.1 52.0

≥5 57.3 54.1 46.4 48.0

a Data are presented as percentage of patients

Sleep Breath (2012) 16:555–562 559

Alarcón et al. [57] during 3 months were close to ours.They concluded that only 60% of patients used CPAP, onaverage, more than 4.5 h per day. Poor results wereobtained in Amfilochiou et al.'s study [53]. Defining as“more compliants” patients who used CPAP in mean morethan 4.5 h per day, they observed that only 25% of thestudied patients were classified as “more compliants.”

Considering a minimum of 4 h in at least 70% of thefollow-up days, only 56.2% of our patients were classifiedcompliants at 1 month, 54.1% at 3 months, 52.2% at6 months, and 54% at 12 months. Kribbs et al. [51] at3 months found even a lower value (46.0%).

Assuming that the values of CPAP use rates and CPAPcompliance mentioned above could be influenced by thepattern of the CPAP use from the start of treatment to the endof the first year, we also analyzed the last 15 days of eachperiod. These additional assessments avoided cumulativeeffects and allowed the analysis of temporal variations.However, only a small variation in the CPAP use was observedduring the first year. This suggests a similar pattern of useduring the first year in patients under CPAP treatment duringthe first month.

Sample demographic and clinic baseline characteristicswere studied in order to find predictors of CPAP compliance.According with published studies, there are no consistentconclusions about the role of age on CPAP compliance.Although there were studies where older patients were morecompliant to CPAP therapy [52, 53, 58], older patients werealso associated with less compliance [59].

In the present study, the proportion of compliantsbetween male and female was similar. Previous studies inthis area had not found a consistent association between sexand CPAP use. Some studies found that women are morecompliant than men [53, 58], and others reported thatwomen are less compliant [59]. On the other hand, somestudies revealed no differences in mean of CPAP daily usein hours, between male and female [60], similar to whatwas observed in our study.

AHI is also frequently studied to predict CPAP compliance.A higher AHI is usually associated with more compliance toCPAP therapy [58, 59, 61], but our study showed nosignificant association between AHI and CPAP compliance.

Although the present study revealed no predictors ofCPAP compliance, there was an interesting observation. Inthe study performed by Kribbs et al. [51], the mostcompliant patients had more years of schooling (p=0.05),while in the present study blue-collar workers, who wereprobably less educated, showed a slightly higher proportionof compliants (p=0.055).

This investigation was conditioned by several obstaclesand limitations. In order to obtain an effective CPAP usedata, only patients using CPAP models with capacity tostore CPAP use data could be included. This work was

performed during the implementation of the sleep outpatientclinic database at SAH in which occurred flaws in databasesystem, with consequent loss of records. In spite of theselimitations, this study could be considered a preliminary studyto determine CPAP compliance in patients followed up atSleep Outpatient Clinic of SAH.

In conclusion, the present study diagnosed a lowcompliance to CPAP therapy in the studied sample ofPortuguese population. Considering clinic, financial, andlegal implications of the suboptimal use of CPAP, the resultsof this work revealed that CPAP compliance was below thedesirable, suggesting the need of developing further studiesin this area and implementing strategies to increase CPAPcompliance. Ours results showed a good rate of CPAP useat least 4 h, considering only the days of CPAP use (82.1%).This can suggest that when CPAP was used, it was mostlyused for at least 4 h. However, it is not satisfactory that only54% of patients were classified as compliants for usingCPAP for a minimum of 4 h in at least 70% of the follow-updays. Another interesting finding is the similar pattern ofCPAP use during the first year for the studied sample,which means that strategies to improve CPAP complianceshould be implemented since the beginning of treatment.

Conflict of interest The authors declare that they have no conflict ofinterest.

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