PORTABLE MONITORING OF OBSTRUCTIVE SLEEP APNOEA

The controversy about streamlined diagnosis & treatment of obstructive sleep apnoea has been raging on for more than one and a half decade. Opponents of portable monitoring demand more and better proof that indeed portable monitoring is reliable despite the excellent results with this technology in earlier two studies – Cleveland family study (1) & the sleep heart heath study(2).

Several critics argue that the diagnosis of obstructive sleep apnoea outside a sleep lab will only be cost effective if autotitrating positive airway pressure (APAP) “works”. A recent meta analysis of nine randomized trials comprising of 282 patients showed that APAP and standard CPAP were similar in adherence and equally effective(3).

The cost difference between APAP and in-lab CPAP titration is huge & favours routine APAP in those with high index of clinical suspicion for OSA in the present era of cost cuttings.

Sleep medicine continues to evolve rapidly. The current emphasis is on expedited diagnosis & management of OSA. In several parts of Europe & recently in North America it is now an acceptable practice to use portable monitoring device for determining which patients are eligible for CPAP treatment. New information about CPAP application seems likely to demystify and probably eliminate routine use of in-lab CPAP titrations. However the American Academy of Sleep Medicine continues to oppose the use of portable monitoring in diagnosis of OSA (4,5).

Recently, a multi centre study comparing unsupervised polysomnography (PSG) in patient’s home with PSG supervised at an academic sleep centre showed effectively that portable monitoring is a better predictor of morbidity & mortality than in-lab PSG (6). Similarly another study by Japanese authors showed that simple nocturnal oximetry can be a “valid tool” in selected subgroup of patients when the pretest probability is high as shown by them in obese patients (7). The clinical value of performing full night 16 channel PSG on patients with possible OSA has been questioned by several authors. Douglas et al(8) prospectively analysed sleep data of 200 patients to determine which signals contributed to diagnostic accuracy. Respiratory variables & leg movement sensors were helpful, whereas neuro physiological signals did not contribute significantly to the diagnosis. There is therefore an increasing tendency to use less complicated diagnostic techniques to confirm the diagnosis of OSA. These limited home studies measure more than single channel of oximetry & mostly include respiratory signals. Commonly measured combinations are oximetry, airflow, thoraco abdominal movements & heart rate measurement. There are several new portable devices in the market & this field is changing rapidly (9,10). Many of these portable devices can be conveniently used in patient’s home after adequate instructions. Studies performed in this way can be cost effective, convenient & accurate. However there are several problems with portable devices such as equipment failure, night to night reproducibility & reliability(11). The sensitivity ranges from 32% to 100% & specificity from 33% to 100% compared with full PSG in a sleep centre (12).

A review article published by American academy of sleep medicine gives a classification system for portable monitors based upon the number & type of parameters recorded by each machine(13). Further details about this classification system shall be discussed in my talk & its utility shall be highlighted. It is of paramount importance to understand that clinicians caring for patients with sleep disorders should be familiar with all the limitations associated with any individual sleep monitoring device, particularly if the potential diagnosis of sleep apnoea is refuted. It is equally important to appreciate that the specific technology used for making the diagnosis is less important than the level of experience & training available for interpreting the results.

REFERENCES :

1. Redhine S, Tosteson T, Boucher MA et al. Measurement of sleep related breathing disturbances in epidemiologic studies: Assessment of validity & reproducibility of a portable monitoring device. Chest 1991;100:1281-86
2. Quan SF & the Sleep Heart Health Study (SHHS) Research group; short term variability of respiration & sleep during unattended non laboratory polysomonography. The Sleep Heart Health Study. Sleep 2002;2:843-849.
3. Ayar NT, Patel SR, Malhotra A et al. Auto titrating versus standard CPAP for treatment of OSA results of meta analysis. Sleep 2004;27:249-53.
4. Chesson AL, Berry RB, Pack AP. Practice parameters for use of portable monitoring devices in investigation of suspected OSA in adults. Sleep 2003;26:907-913.
5. Position statement of American Academy of J.Clin.Sleep Med.2006;2:274
6. Iber C, Redhine S, Kaplan Gilpin AM et al. Polysomnography performed in the unattended home versus the attended laboratory setting – Sleep Heart Health Study Methodology. Sleep 2004;27:536-40.
7. Nakano H, Ikeda T, Hayashi M et al. Effect of Body Mass Index on overnight oximetry for diagnosis of obstructive sleep apnoea. Respir Med.2004;98:421-27.
8. Douglas NJ, Thomas S, Jan MA clinical value of polysomnography. Lancet 1992; 339;347-50.
9. Whittle AT, Finch SP, Mortimer IL, Machay TW & Douglas NT use of home sleep studies for diagnosis of sleep apnoea / hypopnoea syndrome. Thorax 1997;52:1968-73.
10. Rees K, Wraith PK, Besthon Jones M & Douglas NJ. Detection of apnoea, hypopnoea & arousals by the Auto set in sleep apnoea/ hypopnoea syndrome Eur. Respir J. 1998;12:76-9.
11. American Academy of Sleep Medicine, American College of Chest Physicians & American Thoracic Society, Evidence review on Home diagnosis of sleep apnoea: a systematic review of literature Chest 2003;124:1543-79.
12. Ross SD, Allan IE, Harrison KJ et al. Systematic review of literature regarding diagnosis of sleep apnoea. Rockville, MD: Agency for Health care policy & Research 1999.
13. Li CK, Ward Flemons W. State of home sleep studies. Clin.Chest Med.2003;24(2):283-95.


FURTHER READING:

1. Douglas NJ Home diagnosis of obstructive sleep apnoea. Sleep Med.Rev.2003;7(1)53-9.
2. Davidson TM, Gehrman P, Ferreyra H. Lack of night to night variability of sleep disordered breathing measured during home monitoring. Ear Nose Throat J. 2003;82:135-8.
3. Dingli K, Coleman EL, Vennelle M et al. Evaluation of a portable device for diagnosing sleep apnoea / hypopnoea syndrome. Eur Respir J. 2003;21:253-9.
4. Bradley PA, Morimone IL, Douglas NJ. Comparison of polysomnography with Res.Care auto set in the diagnosis of sleep apnoea / hypopnoea syndrome. Thorax 1995;50:1201-3.