Nov 082019

sleep apnea obesity hypoventilation syndrome ohs osaTens of millions of adults in the U.S. have obstructive sleep apnea (OSA), but most are mild cases that pose low health risks. A greater danger is faced by the smaller number of people with sleep apnea that progresses to obesity hypoventilation syndrome (OHS), a life-threatening condition.

Obesity hypoventilation syndrome -- an impairment in resting respiration resulting in an increase in carbon dioxide levels in the blood  ≥ 45 mm Hg -- develops for unclear reasons in a minority of obese patients, 90% of whom also have OSA.

Diagnosis requires arterial blood gas (ABG) measurement of carbon dioxide, a test not performed in most doctors’ offices or outpatient laboratories. For this and other reasons, OHS usually goes unrecognized for prolonged periods. OHS can cause or complicate respiratory exacerbations that are often misdiagnosed as chronic obstructive pulmonary disease, delaying appropriate treatment. People with untreated OHS are at higher risk for hospitalization, respiratory failure and death.

A new professional society guideline gives advice to physicians on the screening and treatment for OHS. They advise:

  • Screen for OHS in obese patients using serum bicarbonate on a routine blood chemistry. A value below 27 mmol/L rules out OHS for most patients.
  • For patients with bicarbonate ≥27 mmol/L or where there is a suspicion for OHS, obtain arterial blood gas and a sleep study. PCO2  ≥ 45 mm Hg (without other reasons for hypoventilation) is diagnostic for OHS.
  • First-line treatment for OHS when OSA is present is continuous positive airway pressure (CPAP) during sleep.
  • Noninvasive ventilation should be used for patients initially treated with CPAP who remain symptomatic or whose pCO2 on ABGs does not improve.

Many patients’ OHS first comes to light during a hospitalization for acute-on-chronic hypercarbic and hypoxemic respiratory failure, frequently treated with noninvasive ventilation (BiPAP or other modalities). These patients should be discharged home with non-invasive ventilation, with sleep testing to be performed as soon as feasible after discharge.

Weight loss advice and support should be provided, with a target of 25-30% reduction in body weight. This would be 50 to 100 pounds in most patients. Bariatric surgery can be considered in selected patients.

The evidence for all the recommendations was considered very low quality and so all the advice was considered “conditional” with a “very low level of certainty.”

Source: Society guideline

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New guidelines on obesity hypoventilation syndrome released