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Numerous complications of Obstructive Sleep Apnea Syndrome (OSAS) have included systemic and pulmonary hypertension, chronic obstructive airway disease, respiratory failure, right-sided heart failure, irregular heart rhythms, and increased risk of heart attacks and strokes, as well as poorer outcome after strokes. The major treatment for OSAS, nasal CPAP, has shown signs of decreasing mortality. CPAP is expensive and sometimes economic resources limit access to it, but it seems to have a very favorable cost-to-utility ratio that well justifies the expense. This study aimed to investigate one aspect of its utility that adds to the evidence for this favorable ratio: reduced need for acute hospitalization for cardiovascular or respiratory disease.
This was a retrospective study of all 88 patients prescribed CPAP for OSAS at the Skovde Central Hospital from 1988 through 1994, at least two years prior to gathering of data for the study; the time span under study was two years prior to and two years subsequent to prescription of CPAP. All patients had been initially admitted for initiation of treatment, based on a Respiratory Distress Index higher than 10/hr with daytime symptoms including excessive sleepiness. Admission was for CPAP titration to the point of eliminating oxygen desaturations. All patients then received information about the mechanism and function of CPAP, and were told to use it throughout the night every night. Follow-up was undertaken within six months and yearly thereafter. Six patients were eliminated because of serious confounding diseases, such as brain tumor, so the actual number of subjects evaluated was 82, divided into two groups, depending on their acceptance of CPAP. Regular CPAP users were defined by self-reported minimum use of 4 hours per night for at least 4 nights per week. Data was obtained from interviewing patients and reviewing clinical charts.
There were 58 CPAP users (71%) and 24 nonusers (29%). Of the nonusers, 15 returned the CPAP withn the first month and another nine admitted to using CPAP less than a few hours per week. No serious side effects were observed. Reasons given for treatment interruption were common ones such as runny nose, disturbance from noise of the machine, and claustrophobia from the mask.
The average ages of users (54 yrs SD=11) and nonusers (56 yrs SD=8) were essentially the same. Users were 81% male, nonusers 83% male, again essentially the same. Body Mass Index was slightly lower for users (33 SD=6) than nonusers (36 SD=9). Prescribed CPAP pressure levels were identical for the two groups (7.8). Prior to treatment, they had similar Oxygen Desaturation Indices or ODI (events/hour) of 36 and 37, and identical lowest oxygen saturations of 70. On treatment, users showed much lower ODI of 3/hr and much higher minimum oxygen saturation of 90; of course, parallel treatment data was not available for nonusers. Nonusers had slightly more cardiovascular and pulmonary disease than users (75% vs. 62%). In other words, users and nonusers were quite similar on a number of measures prior to treatment.
Out of all 82 studied patients, 54 (66%) had an additional diagnosis of cardiovascular or pulmonary disease. During the 4-year period under study, 31 (57%) of these patients required hospitalization for this reason. Hospitalizations occured in 33% of users vs. 50% of nonusers. Users required a median of 10 hospital days (range=3-66) before CPAP, vs. a significantly lower median of 0 hospital days (range 0-25) after CPAP. Among nonusers, median durations of hospitalization were 8.5 days (0-42) before CPAP prescription, 9.5 days (0-47) after. Among the users, total number of hospital admissions decreased from a median of 3 (range 1-8) to a median of 0 (range 0-3), whereas among the nonusers it increased from a median of 1 (0-3) to a median of 2 (0-14). The reduction of hospital days was statistically significant for the users, but not the increase of days for nonusers. Over the 4 years, the mean number of medications prescribed for users remained the same (3.6 before CPAP vs. 3.3 after CPAP) whereas the median number of medications prescribed for nonusers increased from a mean of 1.5 to 2.8. One patient in the nonuser group, but none in the user group, died in the two years after prescription of CPAP.
From an economic perspective, the yearly cost of hospital treatment for users due to cardiovascular and pulmonary disease dropped from about $60,800 U.S. to about $7,900 U.S. after CPAP, whereas the cost in nonusers increased from $20,300 U.S. to $27,600 U.S.
The authors noted the high prevalence of concurrent cardiovascular and pulmonary disease in their OSAS patients. Their compliance rate of 70% corresponded well with results of other studies, although the lack of counters on some of their early CPAP machines left them short on an objective measure of compliance, though only for 6 patients and only during their first two years of treatment. They noted that their limitation to an Oxygen Desaturation Index prevented them from distinguishing obstructive and central apneas. There may have been a confounding effect of the slightly higher BMI in nonusers, but this decreased in the following two years. There was no significant difference in BMI between users and non-users in the subgroup of patients with cardiovascular and pulmonary disease and hospitalization during the follow-up after CPAP was started. Nevertheless, their data demonstrated a reduction in number of admissions to hospital for cardiovascular and pulmonary disease, as well as a reduction in the amount of time spent in hospital for these admissions, among CPAP users. It is likely that other benefits, such as reduction of blood pressure, occurred that were not assessed; these may have helped reduce frequency and length of hospitalizations. Furthermore, from an economic perspective alone, the savings in yearly inpatient treatment costs largely offset the cost of CPAP devices.
The repeated findings of different studies from different countries demonstrating that the economic benefits of prescribing CPAP outweigh its costs is a useful fact in persuading government and third party insurance payers of the importance of doing everything possible to make CPAP maximally accessible to everyone with OSA.
These results should also help convince those reluctant to put up with the usual side effects of CPAP that these are well worth the potential health benefits of the treatment.
Bear in mind that this study has focused on only two of the many different complications of OSA--cardiovascular and pulmonary disease--but that its use of hospitalization and hospital days as a measure of outcome indicates that the impact of CPAP is on illness of substantial severity.
The authors' admission to the weaknesses of their study--the lack of an objective measure of compliance for some patients and the use of only an oxygen desaturation index to titreate CPAP--is well stated, but the implications are not made fully clear. It is possible that some patients without objective monitoring who reported regular CPAP use actually used it much less frequently; had these individuals been identifiable, the difference in outcome between users and nonusers might have been enhanced. Also, the narrow focus on oxygen desaturation probably underrepresented the frequency of apneas and especially hypopneas, to say nothing of completely ignoring the upper airway resistance syndrome, the net effect of which design limitations would be to limit the range of measurable frequency of arousals related to respiratory events, which if it were wider might have allowed better correlation with medical consequences.
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