From the Journals

Guideline: Blood CO2 can be used to screen for OHS



A blood test for elevated carbon dioxide may be used in screening adults for obesity hypoventilation syndrome, according to new guidelines.

Obese adults with sleep-disordered breathing and increased blood carbon dioxide levels during the day are likely to have obesity hypoventilation syndrome (OHS), a result of shallow or slow breathing that can lead to respiratory failure, heart failure, pulmonary hypertension, and death. Pulmonologists and sleep specialists may be the first to see and diagnose patients with OHS in the outpatient setting, while other cases are diagnosed in the hospital when patients present with hypercapnic respiratory failure.

Screening for OHS usually involves measuring arterial blood gases, which is not standard practice in outpatient clinics. Patients often remain undiagnosed and untreated until late in the course of the disease, according to the American Thoracic Society, which in August published a new diagnosis and management guideline aiming to boost early diagnosis and reduce variability in treatment (Am J Respir Crit Care Med. 2019;200:3,e6–e24).

The guideline authors, led by Babak Mokhlesi, MD, of the University of Chicago, recommend a simpler screening method – measuring serum bicarbonate only – to rule out OHS in obese patients with nighttime breathing problems.

Serum bicarbonate should be measured in obese patients with sleep-disordered breathing and a low likelihood of OHS, Dr. Mokhlesi and colleagues recommend in the guideline. If serum bicarbonate is below 27 mmol/L, it is not necessary to conduct further testing as the patient is unlikely to have OHS.

In patients whose serum bicarbonate is higher than 27 mmol/L, or who are strongly suspected of having OHS at presentation because of severe obesity or other symptoms, arterial blood gases should be measured and a sleep study conducted. The guideline authors said that there is insufficient evidence to recommend that pulse oximetry be used in the diagnostic pathway for OHS.

First-line treatment for stable, ambulatory patients with OHS should be positive airway pressure during sleep, rather than noninvasive ventilation, Dr. Mokhlesi and colleagues concluded. For patients with comorbid obstructive sleep apnea – as many as 70% of OHS patients also have OSA – the first-line treatment should be continuous positive airway pressure (CPAP) at night, the guideline states.

Patients hospitalized with respiratory failure and suspected of having OHS should be discharged with noninvasive ventilation until diagnostic procedures can be performed, along with PAP titration in a sleep lab.

In patients initially treated with CPAP who remain symptomatic or whose blood carbon dioxide does not improve, noninvasive ventilation can be tried, the guidelines say. Finally, patients diagnosed with OHS should be guided to weight loss interventions with the aim of reducing body weight by 25%-30%. This can include referral for bariatric surgery in patients without contraindications.

Dr. Mokhlesi and colleagues acknowledged that all of the recommendations contained in the guideline are classed as “conditional,” based on the quality of evidence assessed.

The American Thoracic Society funded the study. Dr. Mokhlesi and 7 coauthors disclosed financial conflicts of interest, while an additional 13 coauthors had none. Disclosures can be found on the AJRCCM website.

SOURCE: Mokhlesi B et al. Am J Respir Crit Care Med. 2019;200:3,e6-e24

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