Brian W Locke, MD MSCI

Brian W Locke, MD MSCI

Pulm/CC Clinical Investigator: Respiratory Failure, Clinical Reasoning, and Research Informatics

Changes in Bicarbonate in Patients at Risk for Obesity Hypoventilation Undergoing Bariatric Surgery AUTHORS: Brian W Locke, MD; Conrad Addison, MD; Somya Mishra, MD; Krishna M Sundar, MD. The University of Utah. Division of Pulmonary and Critical Care; Division of Sleep Medicine; Department of Anesthesiology

Date:

The ERS proposed spectrum of hypoventilatory disorders:

  • Randerath W, Verbraecken J, Andreas S, Arzt M, Bloch KE, Brack T, Buyse B, De Backer W, Eckert DJ, Grote L, Hagmeyer L. Definition, discrimination, diagnosis and treatment of central breathing disturbances during sleep. European respiratory journal. 2017 Jan 1;49(1).
  • Link to paper

Evidence supporting isolated elevated daytime bicarbonate (without frank hypercapnia) as intermediary stage toward hypoventilation.

  • Manuel AR, Hart N, Stradling JR. Is a raised bicarbonate, without hypercapnia, part of the physiologic spectrum of obesity-related hypoventilation?. Chest. 2015 Feb 1;147(2):362-8.
  • Link to paper

Most recent ATS OHS Diagnosis Management guideline suggesting 25-30% body weight loss, which usually requires surgery, and also systematically reviews evidence around test characteristics of 27 mEq/L as a cutoff for OHS screening.

  • Mokhlesi B, Masa JF, Brozek JL, Gurubhagavatula I, Murphy PB, Piper AJ, Tulaimat A, Afshar M, Balachandran JS, Dweik RA, Grunstein RR. Evaluation and management of obesity hypoventilation syndrome. An official American Thoracic Society clinical practice guideline. American journal of respiratory and critical care medicine. 2019 Aug 1;200(3):e6-24.
  • Link to paper

Systematic review suggesting that serum HCO3- decreased 0.55 and 1.5 mEq/L per 3281 ft above sea level

  • Ramirez-Sandoval JC, Castilla-Peón MF, Gotés-Palazuelos J, Vázquez-García JC, Wagner MP, Merelo-Arias CA, Vega-Vega O, Rincón-Pedrero R, Correa-Rotter R. Bicarbonate values for healthy residents living in cities above 1500 meters of altitude: A theoretical model and systematic review. High Altitude Medicine & Biology. 2016 Jun 1;17(2):85-92.
  • Link to paper

Small study showing the analytic sensitivity for serum bicarbonate measurement is within 0.5 mEq/L, while the change that constitutes a significant difference is 2.6 mEq/L

  • Harding PJ, Fraser CG. Biological variation of blood acid-base status: consequences for analytical goal-setting and interpretation of results. Clinical chemistry. 1987 Aug 1;33(8):1416-8.
  • Link to paper

Cleveland Clinic Bariatric Surgery Cohort with an estimated prevalence of OHS (Stage 2 and Above) of 68.4% (though EtCO2 over 45 mmHg was also included)

  • Tran K, Wang L, Gharaibeh SD, Kempke N, Rao Kashyap S, Cetin D, Aboussouan LS, Mehra R. Elucidating predictors of obesity hypoventilation syndrome in a large bariatric surgery cohort. Annals of the American Thoracic Society. 2020 Oct;17(10):1279-88.
  • Link to paper
  • Editorial by Randerath and BaHammam including discussion of ERS classification system and its rationale
  • Link to paper

Estimate of the prevalence of each ERS stage of obesity-related hypoventilation among obese patients (BMI 40 kg/m^2 or higher): Stage 0 (no hypoventilation) 61%; Stage 1 or 2 (nocturnal hypoventilation) 19%; Stage 3 or 4 (daytime hypoventilation) 17%.

  • Sivam S, Yee B, Wong K, Wang D, Grunstein R, Piper A. Obesity hypoventilation syndrome: early detection of nocturnal-only hypercapnia in an obese population. Journal of Clinical Sleep Medicine. 2018 Sep 15;14(9):1477-84.
  • Link to paper

Support for exclusions:

Review articles on kidney factors influencing the development of metabolic acidosis: GFR < 40 ml/min/1.73m^2 is when risk of acidosis begins to increase, but below 60 ml/min/1.73m^2 (~sCr 1.3 by CKD-EPI) is likely when acid-base handling begins to decrease. Additionally, medications influencing the RAAS system (e.g. spironolactone) influence metabolic acid-base.

  • Raphael KL. Metabolic acidosis in CKD: core curriculum 2019. American Journal of Kidney Diseases. 2019 Aug 1;74(2):263-75.
  • Link to paper
  • Kraut JA, Madias NE. Metabolic acidosis of CKD: an update. American Journal of Kidney Diseases. 2016 Feb 1;67(2):307-17.
  • Link to paper

Topiramate is carbonic anyhydrase inhibitor and lowers serum bicarbonate concentration

  • Welch BJ, Graybeal D, Moe OW, Maalouf NM, Sakhaee K. Biochemical and stone-risk profiles with topiramate treatment. American journal of kidney diseases. 2006 Oct 1;48(4):555-63.
  • Link to paper