Obstructive sleep apnea (OSA) steals much of the sleep medicine limelight, while less attention is typically paid to obesity hypoventilation syndrome (OHS). Sure, OSA is more prevalent, but the clinical implications of undiagnosed OHS are far worse.
As its name implies, OHS occurs when excessive weight gain leads to respiratory changes. The mechanisms that cause some obese patients, but not others, to retain carbon dioxide (CO2) are complex. It takes more than an elevated body mass index (BMI), but BMI is positively and linearly related to OHS prevalence. As BMI increases, so does risk for OHS. Naturally, then, as obesity rates have reached epidemic proportions, OHS diagnoses have increased proportionately.
OHS is progressive, it's clearly related to adverse cardiopulmonary changes, and if untreated, it leads to hypercapnic respiratory failure.[1,2] Given its consequences and rising prevalence, it's time we give OHS the attention it deserves.
The American Thoracic Society (ATS) recently published a critically important clinical practice guideline for the evaluation and management of OHS.
This guideline provides recommendations in response to five specific questions:
Question 1: Should serum bicarbonate (HCO3 -) and/or oxygen saturation by pulse oximetry (SpO2) rather than partial pressure of carbon dioxide (PaCO2) in arterial blood be used to screen for OHS in obese adults with sleep-disordered breathing?
Question 2: Should adults with OHS be treated with positive airway pressure (PAP)—either continuous positive airway pressure (CPAP) or noninvasive ventilation (NIV)—or not be treated with PAP?
Question 3: Should adults with OHS be treated with CPAP or with NIV?
Question 4: Should hospitalized adults suspected of having OHS, in whom the diagnosis has not yet been made, be discharged from the hospital with or without PAP treatment until the diagnosis of OHS is either confirmed or ruled out?
Question 5: Should a weight-loss intervention or no such intervention be used for adults with OHS?
The recommendation for Question 1 pertains to OHS screening. The guidelines recommend using serum bicarbonate, which is readily available via standard laboratory testing (CHEM-7 panel, also known as a basic metabolic panel), to screen when the pre-test probability (PTP) for OHS is low to moderate (baseline probability < 20%). If the bicarbonate value is < 27 mmol/L and the BMI is < 40 kg/m2 (ie, OHS PTP is < 20%), no further evaluation for OHS is required. If bicarbonate is ≥ 27 mmol/L, a measurement of arterial blood gas should be considered, particularly as BMI increases toward and above 40 kg/m2. It's important to note that these screening criteria do not apply to the general population but rather to patients diagnosed with OSA or referred for suspected OSA.
The recommendation for Question 3 addresses an issue that the sleep medicine community has long debated: Do all OHS patients require noninvasive positive pressure ventilation (NIPPV), or can some (or all) be treated with CPAP? This is important because CPAP is less expensive in some health systems.[4,5] The guidelines favor CPAP over NIPPV in all patients with OHS and comorbid severe OSA. Of note, 70% of OHS patients will have severe OSA, so the recommendation would apply to more than two thirds of all OHS patients, meaning that most OHS patients can be treated with CPAP. This recently published systematic review that informed the guideline provides more detail.
An important caveat is that the cost savings from using CPAP over NIPPV are debatable. The two studies cited to support the cost benefits from CPAP do not include robust cost-efficacy analyses.[4,5] In addition, both compare CPAP to NIPPV with a back-up rate. NIPPV without a back-up rate is considerably less expensive. Last, they were done in European healthcare systems (Spain and France), where payment structures are likely to be different from in the United States. Despite this, the fact remains that CPAP has similar clinical efficacy to NIPPV for OHS patients with severe OSA.
Although I can see why they asked the questions they did in the guideline, the remaining three recommendations (for Questions 2, 4, and 5) aren't clinically helpful. They are: Stable, ambulatory OHS patients should be treated with PAP during sleep; hospitalized OHS patients should be discharged on NIPPV; and OHS patients should pursue strategies to obtain a sustained loss of 25%-30% of actual body weight.
The recommendation for Question 2 seems obvious and has long been standard of care.
The recommendation for Question 4 is clearly the right thing to do, especially when the reason for the hospitalization is hypercapnic respiratory failure, but it's unrealistic. Good luck getting NIPPV paid for prior to the diagnosis, no matter how apparent the clinical need.
The recommendation for the last question (Question 5) is important as well, but I wish the ATS Assembly on Sleep and Respiratory Neurobiology wouldn't waste their time (or ours) by reviewing the weight loss literature. There are too many other questions pertaining to OHS to be answered that fall directly under their purview. Let an endocrinologist or perhaps even a nutritionist discuss the benefits of weight loss.
The recommendation for Question 1 should increase recognition, and the one for Question 3 should save money, so these guidelines are important. The other recommendations are unlikely to influence practice.
Despite some shortcomings, this guideline is a solid resource. Table 2 lists 14 additional questions that the panel believes are important to clinicians but were not addressed. Hopefully such questions can be used to drive forward the research agenda, thus improving the next iteration of these guidelines.
Dr Aaron Holley is an associate professor of medicine at Uniformed Services University and program director of pulmonary and critical care medicine at Walter Reed National Military Medical Center. He covers a wide range of topics in pulmonary, critical care, and sleep medicine.
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Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.
Cite this: Aaron B. Holley. Pay Attention to the New Obesity Hypoventilation Syndrome Guidelines - Medscape - Oct 01, 2019.