I have recently seen this 75 y/o woman with significant obesity for persistent hypoxemia. She has no TOB Hx and not a lot of structural lung Dz. Her PFTs were remarkable for a pettern consistent with obesity. I thought alveolar hypoventilation might account for much of her hypoxemia and obatined an ABG. Her mid-day ABG revealed normal pH, paCO2 of 57 and a low paO2. Because of the hypoventilation, obesity and history of loud snoring I thought she might also have OSA. However, her sleep study showed nocturnal hypoxemia but no OSA.
Have you seen many cases of OHV without OSA or structural lung disease?
Would you start her on BiPAP? If so would you try and get a titration study even though she does not meet OSA criteria? Otherwise how would you choose her settings?
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I would do a BiPAP titration and then prescribe BiPAP. The pt meets Medicare criteria for BiPAP since he has a restrictive thoracic disorder (obesity hypoventilation) and an awake PaCO2 greater than 45. I would titrate BiPAP to eliminate hypoxemia and then tachypnea.
Michael Rack, MD
I have not seen many cases, but the little I have read specifically points out that OHS and OSA are separate entities, and although OSA is usually present in those with OHS, that does not HAVE to be the case. This does not mean that BiPAP wouldn't be worth a try though...
Have you tried to do a nocturnal oximetry study on 2L of oxygen as a start?
This may eliminate the hypoxemia and prevent the need for a NPPV machine.
Does she have an CSA's on the study?
Starting BiPAP at night without a backup rate will probably offer nothing more than CPAP alone. And, patients hate it much more.
I don't know that the O2 alone will help with the high PaCO2. Michael Rack's point about Medicare criteria is an excellent one. Even with no OSA, she more than meets criteria and Medicare would pay for her BiPAP. I find many (not all, obviously) patients prefer BiPAP, especially at higher pressures since they don't have to exhale against a high PEEP.
I had seen this article on the Am J of Med (the green journal) on prevalence and complications of OHV (without or with OSA): Nowbar et al Am J Med. 2004 Jan 1;116(1):1-7 It also had a nice accompanying editorial.
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