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Editorial |

Postoperative Complications in Obesity Hypoventilation Syndrome and Hypercapnic OSA: CO2 Levels Matter! FREE TO VIEW

Jessica Cooksey, MD; Babak Mokhlesi, MD, FCCP
Author and Funding Information

FINANCIAL/NONFINANCIAL DISCLOSURES: B. M. has received research funds from Philips Respironics and has served as a consultant to Philips Respironics, Itamar Medical Ltd, and Zephyr Technology Corp. None declared (J. C.).

FUNDING/SUPPORT: Dr Mokhlesi has received research funds from the National Institutes of Health (R01 HL119161).

CORRESPONDENCE TO: Babak Mokhlesi, MD, FCCP, Section of Pulmonary and Critical Care, Sleep Disorders Center, University of Chicago Pritzker School of Medicine, 5841 S Maryland Ave, MC 6076, Room M630, Chicago, IL 60637


Copyright 2016, American College of Chest Physicians. All Rights Reserved.


Chest. 2016;149(1):11-13. doi:10.1016/j.chest.2015.11.001
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Obesity hypoventilation syndrome (OHS) is defined by the triad of obesity (BMI ≥ 30 kg/m2), daytime hypoventilation (Paco2 ≥ 45 mm Hg), and sleep-disordered breathing in the absence of other causes of hypercapnia, such as severe obstructive lung disease, severe interstitial lung disease, neuromuscular disease, and chest wall deformities. Although approximately 90% of patients with OHS will have concomitant OSA, roughly 10% do not have sufficient hypopneas or apneas to meet criteria for OSA. These patients are instead found to have worsening of hypoventilation during sleep, particularly rapid eye movement sleep. Furthermore, concurrent OSA and hypercapnia are by no means pathognomonic for OHS. Indeed, OHS is a diagnosis of exclusion when the two are coexistent. A significant portion of patients with both OSA and hypercapnia may have concomitant COPD, a condition known as the overlap syndrome.

The estimated prevalence of OHS in the general population is 0.3% to 0.6%. Among patients with OSA, the prevalence is considerably higher, with estimates ranging from 4% to 50% depending on the characteristics of the population studied. The prevalence of OHS increases with both increasing BMI and increasing severity of OSA, with rates reaching as high as 50% when BMI > 50 kg/m2. The global obesity epidemic will surely lead to increases in the prevalence of both OSA and OHS.,

In addition to being highly prevalent, OSA is quite consequential. Along with the well-described long-term cardiovascular consequences of untreated moderate to severe OSA, several authors have delineated the negative impact of OSA on postoperative outcomes. Large retrospective reviews have found that OSA increases the risk of postoperative pulmonary complications, including aspiration pneumonia, ARDS, emergent postoperative intubation, and need for postoperative noninvasive ventilation., These complications do not, however, necessarily translate into higher mortality or longer lengths of hospital stay., Given the increased risk of postoperative complications, the American Society of Anesthesiologists recommends preoperative screening for sleep-disordered breathing.

Also described in the literature is the overall morbidity and mortality associated with OHS, namely increased rates of pulmonary hypertension, congestive heart failure, cor pulmonale, and acute-on-chronic respiratory failure. These complications are associated with increased rates of hospital admission, ICU admission, and excess mortality., Given that OSA alone confers an increased risk of postoperative complications and that OHS is associated with these additional high-risk comorbidities, one might surmise that OHS raises the stakes in the perioperative setting.

In this issue of CHEST (see page 84), Kaw and colleagues contribute one of the first studies to demonstrate that hypercapnia coupled with OSA is indeed associated with worse postoperative outcomes than OSA alone. In this study, concomitant hypercapnia raised the risk of postoperative respiratory failure, postoperative heart failure, prolonged intubation, and postoperative ICU transfer. These complications translated into an increased length of stay, although not an increase in mortality.

This retrospective, single-center study identified obese (BMI > 30 kg/m2) patients with polysomnographically confirmed OSA who underwent elective noncardiac surgery. Outcomes for patients with concomitant hypercapnia (Paco2 ≥ 45 mm Hg or hypercapnic OSA) were compared with those without (eucapnic OSA). It is important to note that because of the retrospective nature of the study, pulmonary function testing data were not available for 77 of the hypercapnic OSA group (39.7%). A further 36 (18.6%) met spirometric criteria for alternate etiologies of hypercapnia (35 with COPD and one with severe restrictive lung disease). Although the combination of COPD and OSA (overlap syndrome) is pathophysiologically distinct from OHS, the two are linked to some of the same adverse cardiovascular outcomes, notably pulmonary hypertension.

Interestingly, OSA severity, as measured by the apnea-hypopnea index (AHI) as either a continuous or a categorical variable (ie, mild, moderate, severe), was not found to modify the risk of postoperative complications. The AHI is the number of apneas and hypopneas a patient experiences per hour of sleep. Because it is a composite score, the AHI can be driven by apneas or hypopneas scored based on oxygen desaturations, arousals, or both. The AHI, therefore, can be quite heterogeneous. Although it is the accepted metric for classifying OSA severity, the AHI is neither a perfect measure nor the only one available. Polysomnograms routinely include additional metrics of severity, such as the oxygen desaturation index (ODI), which is the number of times per hour a patient’s oxygen saturation drops by ≥ 3% below their baseline as well as the total time during a sleep study that a patient’s oxygen saturation is < 90% (T90). These additional metrics help to clarify the substantial heterogeneity that can be seen among patients with the same AHI.

To illustrate the point on the heterogeneous nature of AHI, consider three patients who all have an AHI of 45/h, placing them in the severe OSA category. The first patient’s AHI (Fig 1A) is driven primarily by hypopneas with arousals and with very few oxygen desaturations, resulting in a 3% ODI of 2/h and a T90 of 0 min. The second patient (Fig 1B) has frequent oxygen desaturations, resulting in a 3% ODI of 43/h, but most of these desaturations do not fall to < 90%, leading to a T90 of 9 min. In contrast, the third patient (Fig 1C) experiences frequent obstructive apneas and hypopneas, leading to oxygen desaturations that fall significantly to < 90% and, therefore, has a 3% ODI of 47/h and a T90 of 77 min. In fact, the third patient spends a significant proportion of sleep with oxygen saturations < 80% or even 70%. Considering AHI alone, these three patients would all be classified as having severe OSA and would all be considered to be at the same risk for complications. Their risk profiles, however, are quite different because the third patient not only has a high AHI but also experiences frequent and severe oxygen desaturations and possibly more significant sleep hypoventilation.

Figure Jump LinkFigure 1 A-C, Excerpts of hypnograms of three patients with similar severity of OSA based on the AHI but significantly different profiles of intermittent and sustained hypoxemia during sleep. AHI = apnea-hypopnea index; ODI = oxygen desaturation index; T90 = time during a sleep study with oxygen saturation < 90%.Grahic Jump Location

The previously mentioned heterogeneous nature of AHI may account for the finding of Kaw and colleagues that AHI did not modify postoperative outcomes. Rather, hypercapnia emerged as the major risk factor for complications among patients with OSA. This work provides incremental evidence that certain phenotypes of sleep-disordered breathing are at increased risk, highlighting the need to move beyond AHI to more-nuanced phenotyping of OSA in the context of postoperative risk stratification.

In addition to demonstrating that hypercapnic OSA imparts further postoperative risk, above that of OSA alone, Kaw and colleagues report that patients with hypercapnia were less likely to receive general anesthesia and more likely to receive monitored anesthesia care alone or monitored anesthesia care with local anesthesia than their counterparts without hypercapnia. This occurred despite hypercapnia frequently not being discovered before surgery. The authors theorize that perhaps suspicion of OHS led to avoidance of general anesthesia in these patients. It is also plausible that concern for the comorbid cardiac and pulmonary conditions that were more prevalent in the hypercapnic group contributed to this approach. Interestingly, the most recent guidelines from the American Society of Anesthesiologists for perioperative management of OSA recommend the use of local or regional anesthesia when feasible. These guidelines further advise general anesthesia with a secure airway over deep anesthesia without a secure airway. This recommendation is based on expert opinion because there is a dearth of high-level evidence to guide the perioperative care of patients with OSA.

Accumulating evidence shows that OSA represents a special high-risk group in the perioperative period. The work of Kaw and colleagues indicates that concomitant hypercapnia, either from OHS or from overlap syndrome, raises the risk of postoperative complications. Now that these high-risk subgroups have been identified, future research should focus on (1) efficient and accurate preoperative screening for OSA and OHS and (2) interventions to improve perioperative outcomes in these individuals, including delineating preferred anesthetic strategies. Clinicians should have a high index of suspicion for OSA and hypercapnia in patients who have a high STOP-Bang score and unexplained elevated serum bicarbonate levels., If these two risk factors are present, sleep testing and measurement of arterial blood gases should be performed before elective surgery, when feasible, to further risk stratify patients.

References

Mokhlesi B. . Obesity hypoventilation syndrome: a state-of-the-art review. Respir Care. 2010;55:1347-1362 [PubMed]journal. [PubMed]
 
Kessler R. .Chaouat A. .Schinkewitch P. .et al The obesity-hypoventilation syndrome revisited: a prospective study of 34 consecutive cases. Chest. 2001;120:369-376 [PubMed]journal. [CrossRef] [PubMed]
 
Weitzenblum E. .Chaouat A. .Kessler R. .Canuet M. . Overlap syndrome: obstructive sleep apnea in patients with chronic obstructive pulmonary disease. Proc Am Thorac Soc. 2008;5:237-241 [PubMed]journal. [CrossRef] [PubMed]
 
Balachandran J.S. .Masa J.F. .Mokhlesi B. . Obesity hypoventilation syndrome epidemiology and diagnosis. Sleep Med Clin. 2014;9:341-347 [PubMed]journal. [CrossRef] [PubMed]
 
Mokhlesi B. .Tulaimat A. .Faibussowitsch I. .Wang Y. .Evans A.T. . Obesity hypoventilation syndrome: prevalence and predictors in patients with obstructive sleep apnea. Sleep Breath. 2007;11:117-124 [PubMed]journal. [CrossRef] [PubMed]
 
Peppard P.E. .Young T. .Barnet J.H. .Palta M. .Hagen E.W. .Hla K.M. . Increased prevalence of sleep-disordered breathing in adults. Am J Epidemiol. 2013;177:1006-1014 [PubMed]journal. [CrossRef] [PubMed]
 
Heinzer R. .Vat S. .Marques-Vidal P. .et al Prevalence of sleep-disordered breathing in the general population: the HypnoLaus study. Lancet Respir Med. 2015;3:310-318 [PubMed]journal. [CrossRef] [PubMed]
 
Memtsoudis S. .Liu S.S. .Ma Y. .et al Perioperative pulmonary outcomes in patients with sleep apnea after noncardiac surgery. Anesth Analg. 2011;112:113-121 [PubMed]journal. [CrossRef] [PubMed]
 
Mokhlesi B. .Hovda M.D. .Vekhter B. .Arora V.M. .Chung F. .Meltzer D.O. . Sleep-disordered breathing and postoperative outcomes after elective surgery: analysis of the nationwide inpatient sample. Chest. 2013;144:903-914 [PubMed]journal. [CrossRef] [PubMed]
 
American Society of Anesthesiologists Task Force on Perioperative Management of patients with obstructive sleep apnea Practice guidelines for the perioperative management of patients with obstructive sleep apnea: an updated report by the American Society of Anesthesiologists Task Force on Perioperative Management of patients with obstructive sleep apnea. Anesthesiology. 2014;120:268-286 [PubMed]journal. [CrossRef] [PubMed]
 
Castro-Añón O. .Pérez de Llano L.A. .De la Fuente Sánchez S. .et al Obesity-hypoventilation syndrome: increased risk of death over sleep apnea syndrome. PLoS One. 2015;10:e0117808- [PubMed]journal. [CrossRef] [PubMed]
 
Kaw R. .Bhateja P. .Paz y Mar H. .et al Postoperative complications in patients with unrecognized obesity hypoventilation syndrome undergoing elective noncardiac surgery. Chest. 2016;149:84-91 [PubMed]journal
 
Chung F. .Chau E. .Yang Y. .Liao P. .Hall R. .Mokhlesi B. . Serum bicarbonate level improves specificity of STOP-Bang screening for obstructive sleep apnea. Chest. 2013;143:1284-1293 [PubMed]journal. [CrossRef] [PubMed]
 

Figures

Figure Jump LinkFigure 1 A-C, Excerpts of hypnograms of three patients with similar severity of OSA based on the AHI but significantly different profiles of intermittent and sustained hypoxemia during sleep. AHI = apnea-hypopnea index; ODI = oxygen desaturation index; T90 = time during a sleep study with oxygen saturation < 90%.Grahic Jump Location

Tables

References

Mokhlesi B. . Obesity hypoventilation syndrome: a state-of-the-art review. Respir Care. 2010;55:1347-1362 [PubMed]journal. [PubMed]
 
Kessler R. .Chaouat A. .Schinkewitch P. .et al The obesity-hypoventilation syndrome revisited: a prospective study of 34 consecutive cases. Chest. 2001;120:369-376 [PubMed]journal. [CrossRef] [PubMed]
 
Weitzenblum E. .Chaouat A. .Kessler R. .Canuet M. . Overlap syndrome: obstructive sleep apnea in patients with chronic obstructive pulmonary disease. Proc Am Thorac Soc. 2008;5:237-241 [PubMed]journal. [CrossRef] [PubMed]
 
Balachandran J.S. .Masa J.F. .Mokhlesi B. . Obesity hypoventilation syndrome epidemiology and diagnosis. Sleep Med Clin. 2014;9:341-347 [PubMed]journal. [CrossRef] [PubMed]
 
Mokhlesi B. .Tulaimat A. .Faibussowitsch I. .Wang Y. .Evans A.T. . Obesity hypoventilation syndrome: prevalence and predictors in patients with obstructive sleep apnea. Sleep Breath. 2007;11:117-124 [PubMed]journal. [CrossRef] [PubMed]
 
Peppard P.E. .Young T. .Barnet J.H. .Palta M. .Hagen E.W. .Hla K.M. . Increased prevalence of sleep-disordered breathing in adults. Am J Epidemiol. 2013;177:1006-1014 [PubMed]journal. [CrossRef] [PubMed]
 
Heinzer R. .Vat S. .Marques-Vidal P. .et al Prevalence of sleep-disordered breathing in the general population: the HypnoLaus study. Lancet Respir Med. 2015;3:310-318 [PubMed]journal. [CrossRef] [PubMed]
 
Memtsoudis S. .Liu S.S. .Ma Y. .et al Perioperative pulmonary outcomes in patients with sleep apnea after noncardiac surgery. Anesth Analg. 2011;112:113-121 [PubMed]journal. [CrossRef] [PubMed]
 
Mokhlesi B. .Hovda M.D. .Vekhter B. .Arora V.M. .Chung F. .Meltzer D.O. . Sleep-disordered breathing and postoperative outcomes after elective surgery: analysis of the nationwide inpatient sample. Chest. 2013;144:903-914 [PubMed]journal. [CrossRef] [PubMed]
 
American Society of Anesthesiologists Task Force on Perioperative Management of patients with obstructive sleep apnea Practice guidelines for the perioperative management of patients with obstructive sleep apnea: an updated report by the American Society of Anesthesiologists Task Force on Perioperative Management of patients with obstructive sleep apnea. Anesthesiology. 2014;120:268-286 [PubMed]journal. [CrossRef] [PubMed]
 
Castro-Añón O. .Pérez de Llano L.A. .De la Fuente Sánchez S. .et al Obesity-hypoventilation syndrome: increased risk of death over sleep apnea syndrome. PLoS One. 2015;10:e0117808- [PubMed]journal. [CrossRef] [PubMed]
 
Kaw R. .Bhateja P. .Paz y Mar H. .et al Postoperative complications in patients with unrecognized obesity hypoventilation syndrome undergoing elective noncardiac surgery. Chest. 2016;149:84-91 [PubMed]journal
 
Chung F. .Chau E. .Yang Y. .Liao P. .Hall R. .Mokhlesi B. . Serum bicarbonate level improves specificity of STOP-Bang screening for obstructive sleep apnea. Chest. 2013;143:1284-1293 [PubMed]journal. [CrossRef] [PubMed]
 
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