CPAP TREATMENT OF OBSTRUCTIVE SLEEP APNEA PAPERS

Further information on use of CPAP may be obtained from the following web based article:http://www.aafp.org/afp/20040201/561.html

Redline S, Adams N, Strauss M, Roebuck T, Winters M and Rosenberg C. Improvement of mild sleep-disordered breathing with CPAP compared with conservative therapy. Am J Respir Crit Care Med 1998;157:858-865.
Studied 111 obese adult men and women with RDIs between 5 and 30, without subjective EDS were randomized to CPAP (C 7.4 ± 1.8 cm H20) or conservative therapy CT; nasal dilators, optimal body position and sleep hygiene). Continuous Positive Airway Pressure was used 44± 34% of the time. While there was no changed in measured daytime sleepiness (MSLT @ 10 minutes) the subjective sleepiness as measured with the Epworth Sleepiness Scale (ESS) improved significantly in the CPAP group over the CT cohort. In addition, the Continuous Positive Airway Pressure improved in domains measuring changes in mood, functional status/general health and energy/fatigue. In general, the higher the BMI, the better the response in both groups. When asked whether they would want to continue therapy after the study ended 92% of the Continuous Positive Airway Pressure patients vs. 75% of the CT patients responded affirmatively. CONCLUSION; Continuous Positive Airway Pressure improves subjective measures in mild Obstructive Sleep Apnea over conservative measures.

Oliver Z and Hoffstein V; Predicting effective continuous positive airway pressure CHEST 2000; 117:1061-1064.

329 patients with OSA underwent CPAP titration; used the following regression equation to predict final CPAP pressure.

Pressure predicted (Ppred) = (0.16 X BMI) + (0.13 X NC) + (0.04 X AHI) – 5.12

Methods
Started CPAP titration with predicted. If AHI < 10 at that pressure the pressure was lowered by 1 cm H20 increments until the AHI > 10. If AHI > 10 at predicted then the pressure was raised similarly. The effective CPAP (Peff) pressure was the lowest pressure at which the patient had an AHI of < 10.
The study analyzed the relationship between the predicted and the effective pressure. Adequate titrations were achieved in 276/329 of the patients. In general, patients in whom the algorithm overestimated the pressure tended to be less overweight and had milder OSA than other pts. Fifty percent of the over predicted group had an AHI of < 27, whereas 50% of the under predicted and successful groups AHIs of > 44 and >41 respectively. FINAL INTEPRETATION OF DATA: 63% of pts, Ppred was within ± 1 cm H20 of Peff; in 83% the two pressures were within ± 2 cm H20 and in 95% within ± 3 cm H20.
A few useful points were made in the discussion section. The authors estimate that sleep labs using 1 cm increments of CPAP changes would typically have between 3 and 10 pressure changes necessary for optimal CPAP level achievement. Using the above prediction equation the mean number of changes to be 1 with a range of zero to five.

Ball EM, Banks MB; Determinants of compliance with nasal continuous positive airway pressure treatment applied in a community setting. Sleep Medicine 2001; 2:195-205.

From the Department of Internal Medicine; Wala Wala Clinic; Wala Wala Washington. Data is part of the Wala Wala project, a community-based program of sleep disorders evaluation and treatment…

Introduction;
One third of OSA pts eventually refuse CPAP therapy.

Results
Rates of CPAP use were not significantly different between patients managed solely by their primary care doctor or by a sleep consultant.

Determinants of CPAP failure; RDIs lower in CPAP failure patients and the level of reduction in the RDI with CPAP less. Same with the level of increase in saturation nadir. PLMS were higher in the CPAP failure group. In addition the CPAP failure group had poorer sleep hygiene.
Patients that were CPAP failures were more dissatisfied with all aspects of their care. Other studies have shown non-compliant patients to have higher levels of depression and hypochondriasis.

Conclusions;
See above
1. Data from this study suggests that CPAP failure patients have more than one sleep disorder (PLMS and sleep hygiene problems)
2. CPAP failure rates and usage rates same whether sleep physician or primary care doctor-managing patient.
3. Primary care physicians may be ideally suited to manage OSA because of their increased follow up opportunities.

Jones DJ, Braid GM and Wedzicha JA Nasal masks for domiciliary positive pressure ventilation; patient usage and complications. Thorax 1994;49:811-812
Introduction
A study of skin complications; done by pt. Questionnaire; All patients returned the questionnaire.
Results
35 pts or 53% had disruption of Rx due to mask discomfort. 4/66 could not wear mask at all. 17% pts had major complications with broken skin or open sores and 38% had minor problems with persistent erythematous areas or pain. Patients on steroids had higher incidence of complications (p < 0.05).

Sanders MH and Kern N; Obstructive sleep apnea treated by independently adjusted inspiratory and expiratory positive airway pressures via nasal mask; Physiologic and clinical implications CHEST 1990;98:317-324.

Saunders hypothesizes that “forces acting to collapse the upper airway during inspiration and expiration are of different magnitudes …(and OSA)…could be eliminated at lower levels of EPAP (expiratory positive airway pressure) than IPAP (inspiratory positive airway pressure…expiratory phase events are important in the pathogenesis of OSA…”. Work from Saunder’s laboratory suggests the airway narrows, or totally occludes, during the expiratory phase of the breaths preceding the occlusive apnea. Such narrowing of the upper airway at end-expiration may set the stage for total occlusion with the generation of subatmospheric intrapharyngeal pressure during the ensuing inspiratory effort…the application of EPAP alone, without IPAP, reduced the frequency of apneas in patients with OSA”
Methods
15 OSA patients treated with BiPap (Bi level positive airway pressure); Patients were started on 5 cm H20 and increased at 2.5 cm H20 increments. IPAP was alternatively increased with EPAP if apnea persisted. Increments were 2.5 cm H20 pressure. If in non-apneic desaturations occurred, then IPAP was increased by like amount. If pressures were equal, and an apnea occurred, IPAP was increased first. DEF represents the average number of destructions events per hour of sleep.

Results
All patients were obese, normocapneic with BMIs +57.4±17. About 10 days separated CPAP from BiPap trials. The final level of EPAP during the nasal BiPap trials was significantly lower than the final level of CPAP (8.85 ± 2.6 vs. 14.04 ± 2.4 cm H20, respectively, P < 0.0001) The final level of IPAP was not significantly different from the CPAP pressure. At optimal setting on nasal BiPap, 10/13 (77%) had a 5 cm H20 or greater difference between the level of IPAP and EPAP and 4 patients (31%) exhibited a difference of at least 7.5 cm H20. Despite lower EPAP the Apnea indices at optimal settings were equivalent between the two modalities. (0.54 ± 1.3 vs. 1.79 ± 2.3 apneas per hour, nasal BiPap and nasal CPAP respectively.
Interesting finding; episodes of ox hemoglobin desaturations that persisted after eliminating apnea on nasal BiPap were substantially reduced or eliminated when IPAP alone was increased. During the nasal BiPap trial, it was observed that virtually all apneas were associated with failure of the patient to trigger the IPAP, consistent with pre-existing occlusion of the upper airway at the initiation of the patient’s inspiratory effort. THE FOLLOWING COULD BE ANOTHER REASON TO USE BIPAP; two patients received supplemental 02 during trials of CPAP because of unacceptably lows of saturation (80-85%) on maximal achievable or tolerated pressures…(up to 15 cm H20)…When BiPap was applied, sufficient flows were generated by the device to achieve 17.5 cm H20 IPAP and 12.5 of EPAP with relief of apnea and maintenance of saturation.

Fromm RE Jr, Varon J, Lechin AE and Hirshkowitz M CPAP machine performance and altitude CHEST1995;108:1577-80

Introduction; Some patients on CPAP complain of sleep-related breathing problems when at high altitudes. Present study examined effect of simulated altitudes using mannequins in an altitude chamber.
Pressure adjustment involves either changing fan speed or using a valve regulator to alter flow velocity.

Methods; Three simulated assents to altitudes of up to 12,000 feet with machines set at 5, 10 and 12 cm H20 pressure. Given constant power and variable gas density, a fan-generated pressure is predicted by the following equation;

P2 = P1 X d2/d1

Where P1 = pressure under condition 1. P2 = pressure under condition 2, d1 = density under condition one and d2 = density under condition 2.

Conclusions; Altitude significantly alters delivered pressure according to predictions made by the fan laws, unless the unit had pressure compensating features. “Pressures delivered by CPAP devices decrease as a function of altitude increase unless they are equipped with pressure-compensating sensors and circuitry. The absolute decrease in delivered CPAP is greater with higher CPAP settings. Thus, patients requiring higher pressure may be affected more.

.”…Symptom recurrence associated with altitude changes reported by our pts with (OSA) may relate to delivered mask pressure”

In general, the higher the altitude the greater the measured pressure from the mask differed from the official setting of pressure on the mask.

Shoenur PJ, Kerr P, Micflikier AB, Yamashiro Y, Kryger MH; The effect of nasal CPAP on nocturnal reflux in patients with aperistaltic esophagus. CHEST 1994; 106:738-41.
CPAP has been shown to reduce nocturnal Gastroesophageal reflux in both patients with obstructive sleep apnea and in patients without obstructive sleep apnea but abnormal nocturnal Gastroesophageal reflux disease. The above study compared the ability of CPAP to treat Gastroesophageal reflux disease in scleroderma patients who have esophageal pressures (LES) less than 10 to those with aperistaltic esophagus (achalasia) and found that a residual resting LES pressure > 10 mm Hg may be necessary for nasal CPAP to effect nocturnal reflux.

Prosise GL and Berry RB Oral-nasal continuous positive airway pressure as a treatment for obstructive sleep apnea CHEST 1994;106:180-86.

Occasionally patients may not tolerate nasal CPAP due to discomfort from breathing totally though the nose. Often such patients have nasal congestion (partial obstruction) present either at baseline or developing during therapy with NCPAP

Methods
Study was done in two parts. In part one 10 male pts with significant obstructive sleep apnea who were unable to tolerate NCPAP has a trial with oro-nasal CPAP(ONCPAP). All complained of nasal congestion or rhinitis. All patients had successful resolution of obstructive sleep apnea. Six of the 10 were eventually weaned back to NCPAP, but four continued long term on the ONCPAP without problems
Subsequently five of the patients were restudied with a dual chamber ONCPAP measuring oral and nasal flow over a 24-hour period. Mouth breathers tended to breath more frequently through the nose but had much time breathing through both. It was thought by the authors that the lower flow rates and increase tolerance to resistive loads made nasal breathing more comfortable.

Part II of the study found that an effective level of pressure administered as NCPAP was also effective when administered via full-face mask.

The authors mention one complication of the full-face mask, which is the tendency of the cheeks to puff out, especially at the higher pressures.

My comment; Frequently we treat patients who complain of nasal congestion and rhinitis with some form of added humidity. Most will respond to room air or the heated variety. Those with mechanical obstruction from nasal septal deviation, turbinate hypertrophy or polyposis may need the full face mask as well as those who cannot keep their mouth closed while sleeping and in the perioperative period from nasal surgery. The Sanders article below further clarifies this issue.

Sanders MH, Kern NB, Stiller RA, Strollo PJ, Martin TJ and Atwood CW, CPAP therapy via or nasal mask for obstructive sleep apnea CHEST 1994; 106:774-79.
Reviewed records of 245 patients with obstructive sleep apnea with an AI>5 or AHI >10 who underwent a trial of CPAP or BiPap. 30 patients had a successful trial with an oral-nasal mask. Eight of the patients were placed on the oral-nasal mask as the result of a split-night study. The oral-nasal mask was offered only after patients demonstrated intolerance of conventional nasal interfaces due to nasal congestion that was refractory to humidification ”… inability to breathe exclusively through the nose and/or intractable mouth leaks that either precluded maintenance of the target pressure or precipitated repeated arousals from sleep. Unacceptable mouth leaks, despite the use of a chin strap, that either precluded maintenance of adequate positive pressure, caused repeated arousals fro sleep, or throat discomfort due to dryness…, inability of the patient to breathe nasally….”

The patients in this series tended to have more severe obstructive sleep apnea, but did respond to CPAP similarly in terms of reduction in RDI etc as did patients with NCPAP
The majority of these patients had obstructive sleep apnea, but three had ALS and one MD as well as OSA. Article mentions aspiration as potential complication of the oronasal mask

Rosenthal Leon, Nykamp K, Guido P, Syron ML, Day Ryan, Rice M and Roth T. Daytime CPAP titration; a viable alternative for patients with severe obstructive sleep apnea CHEST 1998; 114:1056-1060.

Introduction
Study done to determine if daytime CPAP titration is a viable alternative for the implementation of CPAP treatment in a group of patients with severe OSA

Methods

Eligible patients were those with severe OSA, with a RDI > 40 (with 80% of events being obstructive or mixed, associated with significant desaturations and an index of desaturations < 85% of at least 15. All patients had a nocturnal sleep schedule. Thirty men and 2 women participated in the study. Patients were matched with 18 patients with nocturnal CPAP trials. Individuals were started at 5 cm H20 and increased in increments of 1 cm H20 at intervals of about 10 minutes in order to alleviated respiratory events and arousals. Nocturnal studies were 8 hours, while daytime studies 5 hours because of staffing problems.

Relevant to the viability of the daytime CPAP titration is the amount REM sleep these patients accrued at their therapeutic CPAP pressures. Patients in the daytime titration group slept for a mean of 192 ± 76 min at their therapeutic CPAP settings (i.e., the prescribed pressure ± 1 cm H20), this amount of sleep was comparable to the 211 ± 111 min recorded at therapeutic CPAP settings for the nocturnal CPAP titration group. REM sleep accrual at the therapeutic CPAP settings was also comparable for the two groups. Follow up for one week showed comparable usage of the CPAP machines nor was there a difference in reported symptoms and sleep/wake characteristics. . Patients did not have difficulty sleeping 8 hours during the nocturnal study and then sleeping for the CPAP adjustment, even though they were typically nighttime sleepers. CPAP pressures of this group compared to the control group were comparable. Conclusions
From the laboratory point of view, this strategy facilitated the use of resources and shortened the waiting time for patients with severe OSA. Authors conclude that patients with milder forms of OSA would not be likely to tolerate this procedure.

§ p < 0.05 vs titration ¥ Main effect of CPSG study, P< 0.05

Table Polysomnographic Characteristics During Diagnostic and Titration Studies (Data presented as mean ± SD)

Introduction; up to 30% of patients reject CPAP, usually during the first 2 to 4 weeks of treatment. Many of the common complaints are pressure related, including nasal or sinus pressure, flatulence, and chest discomfort. The article quotes two papers that state that there is a correlation between numbers of complaints about CPAP and the level of pressure; certainly there are more difficulties with mask fitting and air leaking with the higher pressures. BiPap and auto-CPAP have been strategies to reduce the level of mask pressure. There have been articles showing that there is a reduction in mucosal edema after CPAP therapy. (Ryan CF, Lowe AA, Li D et al. MRI of the upper airway in OSA before and after chronic nasal continuous positive airway pressure therapy. Am Rev Respir Dis 1991 144:939-944.
Aim of the study; compare CPAP requirement at the time of diagnosis and after 2 and 4 weeks of therapy of CPAP. The authors reasoned that the reduction in mucosal edema would likely occur soon after commencing CPAP treatment for OSA. In addition, the authors sought to see if these changes affected outcome measures such as alertness, sleepiness and mood.
The criteria for selection in the study was a AHI of at least 40 and a CPAP level required to abolish events of +9 cm H20. Three PSGs were done; the diagnostic night T0, (split night study) two weeks later T2, and four week later T4.
Results; ANOVA revealed a significant fall in CPAP requirement over the 4 weeks of the study (ANOVA, p=0.002) As evident from figure below, there was a significant fall in CPAP requirement between T0 (median, 12; range, 9-15 cm H20) and T2 (9.5 cm H20; range 8-11 cm H20; median difference, 1.5 cm H20; p=0.0004), but CPAP requirement did not change appreciably between T2 and T4. THE CPAP REQUIRMENT WAS LOWER AFTER 2 WEEKS OF CPAP TREATMENT IN ALL 10 PATIENTS. All CPAP titrations in this study were done as part of a “split-night” study ,T0. All patients had at least 3.5 hours of sleep during CPAP titrations. In the discussion section, the authors comment that the split-night protocol would tend to underestimate initial CPAP and tend to bias against the positive results in the current study. Epworth Sleepiness Scales were similar in the two groups