Self-Reported Use of CPAP and Benefits of CPAP Therapy

Self-Reported Use of CPAP and Benefits of CPAP Therapy* A Patient Survey+ Heather M. Engleman, BSc; Nima Asgari-Jirhandeh, BSc; Andrew L. McLeod, MBChB; Crichton F. Ramsay, MRCP; Ian]. Deary, PhD; and Neil]. Douglas, MD

The benefits of continuous positive aiiWay pressure (CPAP) therapy in patients with the sleep apnealhypopnea syndrome (SAHS) are poorly documented and patients use CPAP less than physicians recommend. To establish patients' perceptions ofhenefit from CPAP and to identify detenninants of CPAP use, 204 CPAP users completed a questionnaire relating to use of CPAP therapy, sleepiness, and road traffic incident rate before and after CPAP, perceived change in daytime function and nocturnal symptoms with treatment, and problems with CPAP. Variables from these domains of interest were examined, reduced through principal components analysis and correlated to assess associations between these and polysomnographic measures of illness severity. Self-reported CPAP use averaged 5.8::!::SD 2 h a night. Subjective sleepiness rated by the Epworth sleepiness scale and road traffic incident rate were significantly reduced by CPAP (p
Nasal-continuous positive airway pressure (CPAP) therapy is the treatment of choice for the sleep apnea/hypopnea syndrome (SAHS) and related disorders. CPAP is effective in reducing nocturnal events of

For editorial comment see page 1416 SAHS and may improve objective daytime sleepiness,1-4 cognitive function, 1-3 and well-being.l· 2 Yet CPAP is frequently rejected by patients,5·6 at least partly because of the unwieldy and inconvenient nature of the treatment. Patients' use of CPAP is likely to be determined by perceived benefits and drawbacks *From the Department of Respiratory Medicine (Ms. En_gleman and Mrsr. Asgari-Jirhandeh, McLeod, Ramsey, and Dou_glas) and Department of Psychology (Dr. Deary), University of Edinburgh, Edinburgh, UK. tcopies ot the survey are available from the authors by contacting Heather Engleman, Scottish National Sleep Laboratory, Scottisli Infirm!")' orEdinburgh, Lauriston Place, Edinburgh EH3 9YW, UK; phone (+44)131 "536-2355; fax (+44)131 536-3'255. Supported by a grant from the British Lung Foundation (H.M. Eng1eman). Manuscript received July 5, 1995; revision accepted November 29. 1470

of treatment, but the composition of these factors is not well understood. Studies of CPAP use, its determinants, and effects are highly variable in terms of patient selection and outcome measures employed, and thus in results reported. 1-20 Studies based primarily on objective measures of function may neglect patient assessment ofbenefit.l-4·7 Those studies using self-reported measures5·6.18-20 usually examine limited areas of function, often sleepiness alone, while open-ended questionnaire formats 12 restrict comparability between studies. With two exceptions, 15·20 studies of the effects of CPAP have been performed in small patient samples of less than 100 patients. Average CPAP use rate varies from 3.2 to 6.7 h a night, depending on whether new CPAP users, 1·8·9·16 cross-sectional CPAP clinic populations, 15.18·20 or selected long-term acceptors of CPAP 14.l 7•19 are studied. The literature on the determinants of CPAP compliance and acceptance is contradictory, with CPAP use predicted by polysomnographic severity in some6.18.19 Clinical Investigations

and not in other studies, 5·8·9· 12 ,14 · 16 by prior sleepiness in some5·6 but not in others, 8•9,l 2 ,1 8 and compliance adversely affected by side effects in some8·12,1 8 but not in other studies. 5·9 · 1u 4 ·20 A particular area of interest is the effect of CPAP on driving competence. The road traffic accident rate in SAHS is increased by a factor of two to seven times that of the normal population,21 ·22 and a report has related driving accident rate to SAHS severity. 23 A proportion of accidents in SAHS patients will be sleep related, causing more fatalities than other accidents. 24 Laboratory-based studies, whether using monotonous driving-based vigilance tasks 1·13 or more realistic simulators,25 suggest improved driving performance after CPAP 1·13 and uvulopalatopharyngoflasty. 25 ~revious small studies, conducted with 22 2 and 1421 SAHS patients, respectively, have indicated fewer reported road traffic incidents following CPAP. This questionnaire-based study therefore assessed reported use of CPAP and a wide range of perceived benefits and drawbacks of CPAP therapy in our clinic population, so that these factors could be described and relationships between them could be examined. MATERIALS AND METHODS

Study Design A questionnaire was sent in June 1994 to all patients issued CPAP units by the Scottish National Sleep Laboratory (SNSL) for 2 weeks or longer. Questionnaire data were supplemented with infonnation, obtained from SNSL records, on age, sex, polysomnographic SAHS severity, objective CPAP use from run-time clock readings, and objective daytime sleepiness on the multiple sleep latency test (MSLT). 28 Posttreatment MSLTs were conducted after at least 4 weeks of receiving CPAP. Information from the questionnaire and SNSL sources was grouped into domains of illness severity, CPAP compliance, road traffic incidents and sleepiness before and after CP AP, perceived change in function and symptoms, problems with CPAP use, and weight change. CPAP users underwent polysomnography before commencing treatment. The criteria for prescribing CPAP were reported symptoms ofSAHS in association with an apnea+ hypopnea index (AHI) of greater than 5/h sleep, or in association with snoring and recurrent microarousals. Patients received practical demonstration and experience during the daytime in the mechanisms and use of CPAP and underwent a mask fitting before a night of CPAP titration. Telephone advice and appointments \vith nursing staff were available during oflice hours for patients experiencing problems. Patients were reviewed in an outpatient clinic 4 weeks after commencement of therapy, when problems \vith CPAP were sought. Subsequent follow-up interval varied between 2 and 6 months depending on whether problems were present. Questionnaire All 253 patients issued a CPAP unit by the SNSL, and their partners, were sent a four-page questionnaire inquiring about use of CPAP, sleepiness and road traffic incidents before and after CPAP, changes in nocturnal and daytime function, problems with CPAP therapy, and weight change. Self-Reported CPAP Use: Patients were asked how many nights per week and f(Jr how long each night CPAP was used.

Epworth Sleepiness Score: Patients' subjective sleepiness after and, retrospectively, before CPAP was rated by patients and their partners using the Epworth sleepiness scale. 29 ·30 Road Traffic Incidents: Drivers were asked their yearly mileage and the frequency of road traffic incidents in the 5 years before starting CPAP and in the time since CPAP was commenced. Self~ reported incidents were divided into near-misses, casualty-free collisions ("minor" collisions), and accidents causing injury ("major" collisions) and further subdivided for those believed to be sleep related or not. The rates of road traffic incidents per 10,000 miles were calculated for each class of event. Function and Symptoms: Patients were asked to rate changes in function and symptoms on a bipolar five-point scale with options of much worse, worse, no change, better, and much better, coded -2,-1,0,+1, and +2, respectively. Items rated by patients were snoring, breathing pauses, daytime sleepiness, sleep quality, tiredness, concentration ability, ability to drive long distances safely, work efficiency, time taken off work, sex drive, and general health. Partners were asked to rate change in patients' snoring, breathing pauses, daytime sleepiness, and temper. Problems With CPAP Use: Patients were presented with a 12-item list of side effects and problems with CPAP use, and asked to indicate on a four point-scale whether each problem was absent, a minor problem, a significant problem but not inteifering with CPAP use, or a significant problem inteifering with CPAP use. The items comprised nasal stuffiness, dry throat, red/sore eyes, leaking mask, cold airstream, nosebleeds, mask rubbing, difficulty exhaling, more frequent awakenings, excessive noise from CPAP unit, stomach bloating/flatulence, and chest wheeze. Change in Weight: Patients were asked to report any weight gain or loss since the commencement of CPAP treatment. Items not completed by or inapplicable to individuals were excluded from relevant item analyses. Statistics The significance of interindividual differences was assessed using \Vilcoxon tests. Principal components analysis 31 was conducted to reduce the number of variables for a rank correlation analysis, which examined associations between domains. All analyses were performed using specific software (SPSS-PC+ ):32 RESULTS

Questionnaire Response

Of 253 patients (26 female) issued CPAP units, 215 (85%) returned questionnaires. Nonresponders were significantly younger (mean [±SD] age, 46:±:9 years) than responders (53± 10 years; p
1471

Table !-Sleepiness Before and After CPAP Pre-CPAP, Mean:<::SD

Post-CPAP, Mean:<::SD

p Value

15:<::6 14:<::6 4.6:<::3.4

7:<::5 8:<::5 6.6:<::3.2

<0.0001 <0.0001 <0.001

Epworth sleepiness score (patient) Epworth sleepiness score (partner) MSLT, min

Table 2-Mileage-Adjusted Road Traffic Incident Rates Before and After CPAP Pre-CPAP, Mean:<::SD Incident rate (per 10,000 miles) 0.92:<::2.96 Near-miss 0.09:<::0.44 Minor 0.005±0.027 Major 1.02:<::3.17 Total incidents Sleep-related incident rate (per 10,000 miles) Near-miss 0.86±2.94 Minor 0.07±0.43 Major 0.003±0.021 0.93:<::3.15 Total incidents

indicated that they were continuing with CPAP therapy were analyzed. Self-Reported and Objective CPAP Use Self-reported compliance in 204 CPAP users averaged 5.8±2.0 h per night, ranging from 0.1 to 9.5 h per night. Synchronous CPAP run-time clock readings, available in 62 patients, yielded an average objective CPAP use of 5.1±2.5 h per night, significantly lower than that reported by the same patients (6.0±1.9 h per night; p=0.0003). Subjective and objective compliance data were significantly correlated (r=0.68; p<0.0001).

..

~

50

]...

..

IE f

•

Sleep-related incidents

0

All incidents

1 l ~

~

If After MAJOR COLLISIONS

Before

1472

0.32:<::1.53 0.09:<::0.52 0.001:<::0.015 0.41:<::1.63

<0.0001 >0.3 >0.2 0.0001

0.11:<::0.63 0.03±0.20 0 0.14:<::0.68

<0.0001 >0.2 >0.1 <0.0001

Change in Subjective and Objective Sleepiness With CPAP Patients' sleepiness, whether subjectively rated by patient or partner, was significantly improved with CPAP, as was objective daytime sleepiness assessed by MSLT (Table 1). Pre-CPAP MSLT data were available in 52 patients and post-MSLT data were available in 41 patients. Pre-CPAP scores on Epworth scale and MSLT correlated significantly (r=-0.38; p=0.01), but post-CPAP scores for the two measures of sleepiness did not (r=0.06; p>0.3). Changes in Road Traffic Incidents With CPAP Information on road traffic incidents was obtained from 147 driving patients. Sleep-related near-miss incidents, unadjusted for time receiving CPAP therapy, were reported by 39% and 5% of patients, respectively, before and after therapy (Fig 1). No sleep-related major collisions were reported after the commencement of CPAP treatment. Mileage- and time-adjusted road traffic incident rates showed a significant reduction in the rate of near-miss incidents after CPAP therapy (Table 2). All items relating to function and symptoms, rated by patients and partners (Table 3), showed highly significant improvements with CPAP, except sex drive.

~

FIGURE

p Value

Change in Function and Symptoms With CPAP

~

CPAP.

Post-CPAP, Mean:<::SD

1. Prevalence of road traffic incidents before and after

Problems With CPAP Patients' reports of problems with CPAP use are shown in Table 4. No life-threatening complications, such as meningitis, pneumoencephaly, or pneumothorax, were seen. Clinical Investigations

Change in Weight Reported weight rose significantly but trivially from treatment commencement (mean gain, 1 :±:8 kg; p=0.005). Most patients (55%) reported no change in weight.

Principal Components Analysis Principal components analysis was conducted to examine the structure of intercorrelations between responses within the function/symptom items and CPAP-related problem items, respectively. By specifYing patterns of similarities in responses on the multiple items within these two domains, this technique allows cognate variables, all associating significantly with an underlying component, to be identified. Items loading significantly on a component can thyn be consolidated into a summary score, thus allowing the number of variables for subsequent correlation to be rationally reduced. Items with excessively skewed distributions (nosebleeds, wheezing, sore eyes, difficulty exhaling) orwith reduced sample sizes (sex drive, bloating, work efficiency, days taken off work, ability to drive long distances safely) were excluded from the principal components analyses. Components with eigenvalues greater than 1 were extracted and rotated, to increase interpretability, using the varimax method. Significance for variable factor loadings was set at 0.30. The items relating to change in function and symptoms with CPAP reduced to two rotated components, the first having significant loadings on tired/sleep quality/general health/concentration ability/excessive daytime sleepiness (called "daytime function") and the second on snoring/breathing pauses (called "nocturnal symptoms"). All seven items in this analysis also had high loadings on the first unrotated principal component. This indicated that, in addition to the two clearly separable components, daytime function and nocturnal symptoms, the total score from the seven items could be used as a "general function" measure. Principal components analysis revealed that problems with CPAP use formed three rotated components, with significant loadings on frequent awakenings/noise/sore eyes (called "nuisance"), leaking mask! mask rubbing (called "mask problems"), and dry throat/nasal stuffiness (called "side effects"). Scores for created variables named daytime function, nocturnal symptoms, general function, nuisance, mask problems, and side effects were constructed by summing item scores loading on each of these components. General function, nocturnal symptoms, and daytime function were all highly significantly improved with CPAP (p
Table 3-Change in Function and Symptoms With CPAP

Measure

Percentage Reporting Improvement

Patient rating Breathing pauses Snoring Daytime sleepiness Sleep quality Tiredness Ability to drive long distances safely Concentration Work efficiency General health Time taken off work Sex drive Partner rating Snoring Breathing pauses Daytime sleepiness Temper

94 92 84 81 79

77 68 66 61 32

Change in Score. Mean±SD 1.6±0.6* 1.6±0.7* 1.3±0.8* 1.2±0.9* 1.0±0.8* 1.3±0.9*

22

0.9±0.9* 0.9±0.9* 0.8±0.9* 0.5±0.8* 0.1±0.9

95 90 79 49

1.6±0.7* 1.4±0.8* 1.1±0.9* 0.6±1.0*

*p
and side effects were rated as present in some degree by 66%, 72%, and 73% of patients, respectively.

Rank Correlation Putative predictive associations among domains of illness severity, sleepiness, road traffic incident rates, change in symptoms and function, and problems with CPAP use were assessed with rank correlation (Table 5). Subjective CPAP use was not significantly correlated witl1 any objective index of severity of SAHS, but was positively correlated with pre-treatment Epworth sleepiness score and negatively correlated with the degree of nuisance of CP AP therapy reported. CPAP nuisance was negatively correlated with SAHS severity. Improvements in daytime function and nocturnal symptoms correlated with baselineEpworth sleepiness Table 4-Percentage of Patients Reporting Problems With CPAP Use Percentage Reporting Percentage Reporting Problem Severe Problem Nasal stuffiness Mask leak Dry throat Cold airstream Noise from CPAP unit Mask mbbing Bloating/flatulence More frequent awakenings Hed/sore eyes Chest wheeze Difficulty exhaling Nosebleeds

64 63 62 4.'5 41 41 37 32 31 21 18 10

4
1 d

2

1
0

CHEST I 109 I 6 I JUNE, 1996

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Table 5-Rank Correlation Among Polysomnography, CPAP Use, Sleepiness, Changes in Function and Symptoms, Road Traffic Incidents, and CPAP Programs* AHI AHI AROUSALS MIN02 SUBJUSE PRE-ESS POST-ESS NUISANCE MASK PROB SIDE EFF dDAYFUNC dNOCTSYMP dGENFUNC

X 0.61 1 -0.471 0.04 0.11 -0.11 -0.131 -0.03

O.D7 0.03 0.13 0.09

AROUSALS

MIN02

SUBJUSE

PREESS

POSTESS

NUISANCE

MASK PROB

SIDE EFF

X X -0.271 0.00 0.13 -0.03 -0.12 -0.06 0201 -0.02 0.11 0.04

X X X -0.08 -0.29 1 0.20§ -0.04 0.00 0.01 -0.211 -0.05 -0.191

X X X X 0.221 -0.181 -0.15! 0.171 -0.07 0.441 0.35 1 0.461

X X X X X

X X X X X X 0.11 -0.07 0.11 -0.43! -0.201 -0.44 1

X X X X X X X 0.28 1 0.191 -0.171 -0.221 -0.20§

X X X X X X X X 0.05 0.10 0.12 0.09

X X X X X X X X X -0.10 -0.07 -0.09

O.ll -0.03 0.09 0.06 0.201 0.131 0.191

BNMSLP

BNMNON

0.15 0.201 -0.251 0.54 1

BMINSLP

BMINNON

0.04 0.12

0.06 0.08 -0.10

-0.01 -0.02 0.10

-0.12

0.291

om

-0.271

*Cell sample size varies from 117 to 203 patients; p values are adjusted accordingly; X~ redundant cell; short horizontal line (-)~nonpredictive cell. AROUSALS~microarousal index; MIN02~minimum oxygen saturation; SUBJUSE~subjective CPAP use; PRE-ESS~pre-CPAP Epworth sleepiness score; POST-ESS~post-CPAP Epworth sleepiness score; NUISANCE=nuisance-type problems with CPAP use; MASK PROBS=mask-related problems with CPAP use; SIDE EFF =CPAP side effects; dDAYFUNC=change in daytime function; dNOCTSYMP=change in nocturnal symptoms; dGENFUNC~change in general function/symptoms; BNMSLP=sleep-related near-miss incidents before CPAP; BNMNON=nonsleep-related near-miss incidents before CPAP; BMINSLP=sleep-related minor collisions before CPAP; BMINNON =sleep-related minor collisions before CPAP. 1p=0.00l. lp=O.OS. lp=O.Ol.

score and reported CPAP use, and negatively with Epworth sleepiness score on CPAP. The frequency of driving incidents before treatment was correlated with Epworth sleepiness score, the frequency of microarousals, and the extent of nocturnal hypoxemia. DISCUSSION

This study documents experience and perceptions of CPAP in a large sample of unselected CPAP users with a wide range of illness severity. Although necessarily limited by its use of mainly self-reported and retrospective information, the study provides evidence of patient-perceived, CPAP-induced improvement across a wide range of function, including sleepiness, driving competence, cognitive function, work efficiency, well-being, and nocturnal symptoms. Furthermore, coherent correlations linked pre-CPAP driving e:ompetence, use of CPAP, and benefit from CPAP to predictive variables. The study is based on retrospective, self-reports from CPAP users, which may be compromised by poor memory of past events occurring prior to treatment or by a tendency to overreport improvements, having psychologically "invested" in CP AP therapy. Despite these drawbacks, retrospective ratings of pretreatment status may provide counterbalancing benefits. A lack of awareness of impairment before treatment, noted by others, 16·35 may result from the absence of a normal frame of reference in constantly sleepy, untreated patients. In these, retrospective measures may be more reliable. The reversal of sleepiness and driving impair1474

ment with treatment may also encourage greater frankness on the part of patients regarding their previous deficits, who need no longer fear being banned from driving. The results of this study, showing wideranging improvements in daytime function and nocturnal symptoms, are unlikely to be due only to retrospective inaccuracies and placebo-like effects, having been shown also in a prospective, randomized, placebo-controlled study of the effects of CPAP .1 CPAP Use

Self-reported CPAP use was significantly associated with outcome measures assessing posttreatment sleepiness and improvement in function and symptoms, confirming and extending findings of others showing correlations between compliance and subjective change in sleepiness with treatment. 18 ) 9 The observed triangular association among pre-CPAP sleepiness, subsequent compliance, and posttreatment sleepiness (Table 5) is suggestive of a positively reinforcing loop. Poorer compliance was associated with greater rates of sleep-related collisions after treatment, providing additional corroboration of the benefits of CPAP. Mean objective CPAP compliance demonstrated in this study (5.1 h a night) was closely in agreement with that of others in cross-sectional CPAP clinic series, 15 ,1 8·20 which included both new and long-term users. Patients overestimated CPAP use by around 1 h per night, a finding that is consistent across this and other studiesY· 18·20 Degree of CPAP compliance was linked only to prior sleepiness and not to illness severClinical Investigations

ity, confirming the hypothesis that sleepiness is the primary determinant of CPAP acceptance.5•6 Apart from the nuisance problem factor (see below), problems with CPAP use were not associated with reduced compliance. Sleepiness

Subjective sleepiness, assessed by the Epworth sleepiness scale, was significantly improved with CPAP, with average scores after treatment falling within the normal range. 30 The Epworth sleepiness scale, although subjective and completed retrospectively, may be a relatively robust measure of sleepiness, dealing with memorable behavior of napping rather than transient mood states of sleepiness. Sleep onset latency on the MSLT was improved but was not normalized by CPAP. This observation has been reported previously by ourselves and others, 1-3·7•8•10 with only one study showinf normalization of sleep onset latency with CPAP. The small magnitude of change in objective daytime sleepiness, with posttreatment scores lying in the range associated with moderate sleepiness,28 may indicate only partial resolution of sleepiness with CPAP. Alternatively, it may reflect insensitivity of the MSLT to treatment-induced changes in sleepiness, as has been suggested by others. 10 Road Traffic Incidents

The survey documents a high prevalence of sleeprelated road traffic incidents in untreated patients, with 39% of all driving patients being aware of sleep-related near-miss incidents before treatment (Fig 1). These results are compatible with the findings of others of increased accident rates in SAHS patients. 21 •22 Selfreported mileage-adjusted rates of near-miss incidents were significantly improved after CPAP. Thus, the study shows significant improvement in actual driving competence with CPAP, consistent with studies suggesting that treatment may improve driving skills on simulators. 1•13•25 These findings confirm previous smaller-scale re~orts of lowered driving incidents following CPAP. 2 ·27 Although no significant difference in sleep-related collision rate after CPAP was observed, the low frequency of such events before CPAP in a small population (Fig 1) may contribute to this finding. Road traffic incidents before treatment were significantly correlated with sleepiness and polysomnographic measures of sleep fragmentation and hypoxemia. These findings of putative predictors for driving competence in both sleepiness and illness severity in SAHS extend those of Findley et al. 23 Function and Symptoms

CPAP-treated patients reported highly significant improvements in all symptom and function items, ex-

cept sex drive. The high frequency of reported improvements in daytime function items, especially those relating to concentration, work efficiency, absence from work, and ability to drive distances safely, suggests that these areas of function are compromised in a significant proportion of patients with SAHS (Table 4). Together with the data on road traffic incidents, the above findings suggest a high cost to community and industry from SAHS and a substantial preventive value for CPAP. The magnitude of reported improvement in daytime function and nocturnal symptoms was related to severity of initial illness. Greater reported improvements in daytime function and in nocturnal symptoms were associated with greater reported CPAP use, greater sleepiness before treatment, and lesser sleepiness after treatment. Problems With CPAP Use

Reported problems with CPAP use, which most patients classified as "minor" in nature, were remarkably frequent, despite intervention during patient follow-up. Problems with CPAP use have been associated previously with reduced compliance by ourselves and others, 8.18 but significant relationships between problems and reported CPAP use were limited to the nuisance problem complex. In contrast to nuisance problems, mask problem and side effect scores were not associated with lower SAHS severity, reported CPAP use, or satisfaction with treatment. Nuisance Problems

The nuisance complex, describing complaints relating to noise, frequent awakenings, and sore eyes with CPAP treatment, exhibited an interesting pattern of association with putative determinants and effects (Table 5). This problem complex was weakly correlated with milder polysomnographic illness, lower subsequent CPAP use, and lesser perceived benefit. One of the nuisance complex items, noise from CPAP units, has been associated with lower SAHS severity,20 but not previously with lesser CPAP compliance. Although high scorers for nuisance problems had milder initial illness and poorer subsequent CPAP compliance, recent research suggests that even patients with milder indexes of illness severity receive objective benefits for cognitive function from CPAP. 1 Thus patients' unawareness of the benefits of CPAP is insufficient justification for withholding treatment. The lack of correlation between polysomnographic indexes of illness severity and CPAP use confirms the value of CPAP therapy in "heavy snorers disease" 36 or "upper airway resistance syndrome"37 as well as SAHS. It may be that patient education can aid insight into illness-induced impairment and thus promote improved compliance with and benefit from CPAP. CHEST /109/6/ JUNE, 1996

1475

ACKNOWLEDGME~T: We thank the nursing, technical, and

administrative staff of the SNSL for their contributions to this project

18

REFERENCES

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19

20

21 22

23 24 2.5

26

27

28 29 .30 31 .32 .3.3 34

.35

36

37

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Clinical Investigations