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Original Research: Sleep Disorders |

Is a Raised Bicarbonate, Without Hypercapnia, Part of the Physiologic Spectrum of Obesity-Related Hypoventilation?Bicarbonate and Obesity Hypoventilation

Ari R. G. Manuel, MBBS; Nicholas Hart, PhD; John R. Stradling, MD
Author and Funding Information

From the Oxford Centre for Respiratory Research (Drs Manuel and Stradling), Oxford Biomedical Research Centre, Churchill Campus, Oxford University Hospitals NHS Trust, Oxford; and Lane Fox Clinical Respiratory Physiology Centre (Dr Hart), St. Thomas’ Hospital, Guy’s and St. Thomas’ NHS Foundation Trust, London, England.

CORRESPONDENCE TO: Ari R. G. Manuel, MBBS, Oxford Centre for Respiratory Medicine, Churchill Hospital, Headington Old Rd, Oxford, OX3 7LJ, England; e-mail: ari.manuel@ouh.nhs.uk


FOR EDITORIAL COMMENT SEE PAGE 282

FUNDING/SUPPORT: This work was supported by the Oxford Health Services Research Committee, the Oxford Biomedical Research Centre, and the Oxford Radcliffe Hospital Charitable Funds. The NICO 2 device was kindly donated by Koninklijke Philips N.V.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2015;147(2):362-368. doi:10.1378/chest.14-1279
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BACKGROUND:  Obesity hypoventilation syndrome (OHS) conventionally includes awake hypercapnia, but an isolated raised bicarbonate, even in the absence of awake hypercapnia, may represent evidence of “early” OHS. We investigated whether such individuals exhibit certain features characteristic of established OHS.

METHODS:  Obese subjects (BMI > 30 kg/m2) were identified from a variety of sources and divided into those with (1) normal blood gas measurements and normal acid-base balance, (2) an isolated raised base excess (BE) (≥ 2 mmol/L), and (3) awake hypercapnia (> 6 kPa; ie, established OHS). Two-point ventilatory responses to hypoxia and hypercapnia were performed. Polygraphic sleep studies were done to identify intermittent and prolonged hypoxia.

RESULTS:  Seventy-one subjects (BMI, 47.2; SD, 9.8; age, 52.1 years; SD, 8.8 years) were recruited into three groups (33, 22, and 16 respectively). The Paco2 and BE values were 5.15, 5.42, 6.62 kPa, and +0.12, +3.01, +4.78 mmol/L, respectively. For nearly all the ventilatory response and sleep study measures, group 2 (with only an isolated raised BE) represented an intermediate group, and for some of the measures they were more similar to the third group with established OHS.

CONCLUSIONS:  These data suggest that obese individuals with a raised BE, despite normocapnia while awake, should probably be regarded as having early obesity-related hypoventilation. This has important implications for clinical management as well as randomized controlled treatment trials, as they may represent a group with a more reversible disease process.

TRIAL REGISTRY:  ClinicalTrials.gov; No.: NCT01380418; URL: www.clinicaltrials.gov


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