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HST: The Elephant in Sleep Medicine

A Perspective and an Algorithm

Reporting and Data Analysis
While some manufacturers' scored data reports are more flexible (customizable) than others, most include a good summary of the usual and customary parameters and indices.

Whether the HST is scored manually or automatically, the raw data should be reviewed by a qualified sleep physician who is ultimately responsible for the interpretation. It is interesting that some professional associations and payers have not made formal recommendations in this regard.

We have all seen situations where a HST (or PSG for that matter) shows an AHI < 5, but during a particular portion of the recording -- perhaps 30 minutes or during supine and/or REM sleep -- 20 respiratory events are scored, equivalent to an AHI of 40 for that segment. Thismay be associated with O2 desaturation of 80% or less. I would maintain that such a patient is in need of treatment as much or more than a patient with an AHI (TST) of 8 with no such "effectively increased" AHI period and with only mild desaturations. I don't understand why certain third party payers do not cover PAP therapy in the former but do cover CPAP based on the "rule" of 4 hours for 70% of the nights (discussed below). CPAP adherence using this "rule" is not always ideal, as frequent respiratory events can occur during non-PAP-compliant sleep in the latter half of the night, particularly during REM sleep. However, this guideline persists because it is seen as better than nothing, although it could be detrimental to patient care.

Although many PSG systems report AHI for TST, NREM and REM, this is not always adequate to identify all situations in which AHI (TST) < 5 is associated with periods of more frequent respiratory events. In this regard, I suggest that all HST (or PSG) manufacturers include in their scored report a "maximum density index" or MDI which would display, for example, a 10 to 30 minute period from the recording during which the index is maximum for respiratory events (e.g. OA, HYP, CA or "AHI"), O2 desaturations, possibly snoring, heart rate, and arousals and leg movements (in the case of PSG). Some manufacturers do this already, in part. This would be particularly useful for HST with no true sleep staging. Other parameters, such as maximum, minimum, and mean (SD) O2 saturations and respiratory event durations,  may aid in the HST interpretation and decision to recommend PSG.

The Algorithm
The algorithm is designed to analyze and act on data obtained by HST for the diagnosis of OSA and is generally based on a Level III, limited channel HST. It is not confirmed by controlled studies or consensus, since none exist at this time, nor has it been reviewed by committee. However, it has been modified based on input from several well qualified sleep specialists and from Internet thread discussions with others from various disciplines in the sleep industry. The suggested decision tree is not intended to be the last word but rather a roadmap for a reasonable approach. It is hoped that these suggestions, which may not always be in precise agreement with the policies of a particular payer, regulatory body or professional society, be taken in the light for which they are intended, modified as the provider sees fit, and incorporated into patient care plans more specifically tailored to the needs of a particular physician, patient population, industry, facility or organization. Of course, as with any diagnostic study, the patient's treating physician should use the HST interpretation and recommendations in conjunction with the overall clinical evaluation and treatment of the patient. Hopefully with increased HST experience, outcome evaluations, clinical studies and advancements in technology, the approach suggested here will continue to evolve and be refined.

The Big Picture

Education -->  Screening --> Testing -->  Treatment --> Monitoring --> Outcome Evaluation --> Follow Up

The first part of the larger picture is the education of the medical community, the public and payers about the risks for and understanding of the consequences of undiagnosed and untreated obstructive sleep apnea as well as the many benefits of treatment. This subject has been covered extensively in many other venues.

Subjective validated questionnaires for assessing the risk of OSA such as the Epworth, STOP, STOP-BANG, Berlin, and/or other subjective screening tools should be used as they apply to specific patient groups or industries. Other considerations should include conventional history and physical examination as well as objective measures like  BMI, neck circumference, cardio-pulmonary, upper airway and craino-facial evaluation. Specific inclusion criteria for medical necessity for HST may be important for reimbursement issues. There should also be screening criteria for exclusion of patients with certain co-morbidities or suspected co-existing sleep disorders in whom HST may not be appropriate. Unfortunately, some of the published exclusion criteria for COPD , CHF and heart disease are not well defined with respect to the severity of those conditions. Furthermore, some have excluded other suspected sleep disorders even in patients that are at high risk for OSA.  No questionnaire or set of physical findings is perfect.  It is clear that  patients classified as "low risk'' based on a particular set of signs and symptoms may in fact be at very high risk for OSA based on numerous  other factors that are not included in commonly  used criteria. The ultimate decision for HST should be based on the overall clinical evaluation by the patient's treating physician.

HST- Sleep Apnea Decision Tree


< 5 Pre-Test Risk High  »»  Attended PSG or split night study if criteria met [1]

< 5 Pre-Test Risk Low  »»  Attended PSG or trial of conservative management as clinically indicated [1,2]

≥ 5 With Increased CA or CSR  »»  Attended PSG + Consider sleep specialist and/or cardio or neuro evaluation [3]

≥ 5 Using HST device that does not measure respiratory effort  »»  Attended PAP titration [4] 

≥ 5 if none of above  »»  Begin Auto-PAP (APAP) trial (or Oral Appliance if not willing or able to tolerate APAP)

and if high AH or low SpO2  »»   Attended PAP titration [5]

O2 Saturation (SpO2)

SpO2 during HST Normal  »»  Adherence program + Monitoring Downloads + Outcome evaluations [6,7]

SpO2 during HST Low  »»  Overnight Oximetry during APAP (or OA) + consider pulmonary function test (PFT) [8]

SpO2 corrected with APAP (or OA)

    - Yes  »»  Adherence program + Monitoring Downloads + Outcome evaluations [7]

    - No  »»  Adjust APAP (or OA) à Repeat overnight oximetry or attended PAP titration or per physician

1. High and low risk for OSA should be defined by the healthcare professional for specific patient groups or by industry requirements/standards
2. Weight loss, good sleep hygiene, education etc. and otherwise symptom related as determined by the treating physician
3. Evidence of Cheyne-Stokes Respiration (CSR) or increased central apneas (e.g. CA index ≥ 10 or ≥ 50% total respiratory events or per physician)
4. Caution should be used starting APAP if the HST device does not reflect central apneas and generally an attended PAP titration is recommended.
5. As defined by physician e.g. AHI ≥ 40 (example only) or SpO2 < 85% for ≥ 5 minutes or lowest SpO2 < 80% (example only)
6. Lowest SpO2 ≥ 90% (example only) or as defined by physician
7. See below for monitoring downloads
8. Any SpO2 during HST < 85-89% or mean <90% (examples only) or as defined by physician

HST: The Elephant in Sleep Medicine

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Your article is timely, but I still think the elephant is being missed.
We are supposed to only use HST on those pts who are LIKELY to have OSA, based on the constellation of symptoms. The trucking industry has myriad of issues regarding the self-disclosure of symptoms that would risk their driving viability as Dr. Rack has commented, but yet we see that industry purveyors of sleep testing will use HST adlibitum in an effort to fill the breach.
My writing is to ask the field if it really wants to throw the baby out with the bathwater? Meaning, ARE we really going to allow the bean counters to tell us that we HAVE to use HST when there are myriad issues pointing to it being used as a way to get a negative test on those with low likelihood of OSA, those possibly not willing to use it correctly (on themselves, as has been noted), and to avail the patient of the efficiency of their time?
Are we really looking to force the field to use HST, even if it means to wait for it (there can never be enough devices to fit the need) while the sleep lab down the block goes starving while they suffer from the practice of medicine by checkbook that the medical insurance companies are doing? I still believe that there IS benefit from performing CPAP titration in a laboratory setting, and the objective final pressure is only part of it. There is a big issue with masks/interfaces. One of the biggest issues with adherence is mask selection. The benefit in undergoing a lab based titration IS the availability of different masks/interfaces. Does the Autopap model even address this? How have we come, as a field, to leave the patients to fend for themselves, to self-apply a, possibly lifelong, therapy with no clinical interaction? Did we, as a field, really intend to do this to our patients?
I still believe that the field will recognize that we need to utilize ALL the testing/treating modalities available to us, and streamline the sleep testing request process to place the patient into the next appropriately available slot, be it Split lab study or HST.
I do not see us to be that short-sighted that we will allow the bean counters to make us throw the baby out with the least I hope so.

Claude Albertario,  Owner,  ApneaNetwork.comMay 12, 2013
Oceanside, NY

Nice article. After years of testing Truck drivers with both PSG and HSTs, we do have not found a lot of "false negatives" due to subjective reporting or devices. It is all about medical management. If Sleep MD is involved in consult and ordering the appropriate PSG or HST, rarely have we seen any issues.
You can effective manage and treat the Occ Med industry by shipping out HST devices for sure!

Mary  Convey,  Director of Risk Mitigation & ,  Sleepsafe DriversApril 27, 2013
St. Petesburg, FL

All comments are appreciated.
Most of the issues raised are addressed in the article. It's rather long so it may need to be reviewed a few times. For better or worse the country, CMS and other payers are moving to HST specifically for testing individuals at high risk for OSA. One failsafe here (which is also the position of the AASM)is that if the HST is "normal" for ANY reason then an attended PSG should be recommended.

Edward D. Michaelson, MD FACP FCCP FAASM April 24, 2013

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