Hemodynamic dysfunction in obesity hypoventilation syndrome and the effects of treatment with surgically induced weight loss

Obstructive Sleep Apnea, Obesity Hypoventilation Syndrome, and Pulmonary Hypertension: A State-of-the-Art Review

The pathophysiological interplay between sleep-disordered breathing (SDB) and pulmonary hypertension (PH) is complex and can involve a variety of mechanisms by which SDB can worsen PH. These mechanistic pathways include wide swings in intrathoracic pressure while breathing against an occluded upper airway, intermittent and/or sustained hypoxemia, acute and/or chronic hypercapnia, and obesity. In this review, we discuss how the downstream consequences of SDB can adversely impact PH, the challenges in accurately diagnosing and classifying PH in the severely obese, and review the limited literature assessing the effect of treating obesity, obstructive sleep apnea, and obesity hypoventilation syndrome on PH.

Management of Pulmonary Hypertension Associated with Chronic Lung Disease

Pulmonary hypertension (PH) is a common complication of chronic lung diseases, particularly in chronic obstructive pulmonary disease (COPD) and interstitial lung diseases (ILD) and especially in advanced disease. It is associated with greater mortality and worse clinical course. Given the high prevalence of some respiratory disorders and because lung parenchymal abnormalities might be present in other PH groups, the appropriate diagnosis of PH associated with respiratory disease represents a clinical challenge. Patients with chronic lung disease presenting symptoms that exceed those expected by the pulmonary disease should be further evaluated by echocardiography. Confirmatory right heart catheterization is indicated in candidates to surgical treatments, suspected severe PH potentially amenable with targeted therapy, and, in general, in those conditions where the result of the hemodynamic assessment will determine treatment options. The treatment of choice for these patients who are hypoxemic is long-term oxygen therapy and pulmonary rehabilitation to improve symptoms. Lung transplant is the only curative therapy and can be considered in appropriate cases. Conventional vasodilators or drugs approved for pulmonary arterial hypertension (PAH) are not recommended in patients with mild-to-moderate PH because they may impair gas exchange and their lack of efficacy shown in randomized controlled trials. Patients with severe PH (as defined by pulmonary vascular resistance >5 Wood units) should be referred to a center with expertise in PH and lung diseases and ideally included in randomized controlled trials. Targeted PAH therapy might be considered in this subset of patients, with careful monitoring of gas exchange. In patients with ILD, inhaled treprostinil has been shown to improve functional ability and to delay clinical worsening.

Characteristics of Obese Patients with Acute Hypercapnia Respiratory Failure Admitted in the Department of Pneumology: An Observational Study of a North African Population

Background. Acute hypercapnic respiratory failure (AHRF) is a common life-threatening event in patients with obesity hypoventilation syndrome (OHS). Objectives. To study the clinical pattern, noninvasive ventilatory support, as well as the short- and long-term outcomes of patients with OHS admitted in a ward because of AHRF. Methods. We conducted a retrospective cohort study including all adults with OHS $\text{aged}\ge 18-\text{year}-\text{old}$ , admitted in a 90-bed-ward for AHRF. Results. A total of 44 patients were included. Fifteen (34.1%) and 29 (65.9%) patients were diagnosed with malignant OHS (mOHS) and nonmalignant OHS (non-mOHS), respectively, while 36 (81.8%) had coexisting obstructive sleep apnea hypopnea syndrome (OSAHS). Patients with mOHS had a significantly higher rate of heart failure (100% vs. 31%; $p<0.001$ ), chronic renal insufficiency (CRI) (73.3% vs. 41.4%; $p=0.04$ ), and dyslipidemia (66.7% vs. 34.5%; $p=0.04$ ) than those with non-mOHS. The mean forced vital capacity (FVC) in our patients was of $59.5\%\pm 18.5$ of the predicted value, lower than what is usually reported in stable patients with OHS. At hospital admission, more than two-thirds ( $n=34$ , 77.3%) were misdiagnosed as having asthma exacerbation ( $n=4$ , 4.9.1%), chronic obstructive pulmonary disease (COPD) exacerbation ( $n=12$ , 27.3%) and/or heart failure ( $n=29$ , 65.9%). Acute pulmonary oedema (ACPE) ( $n=16$ , 36.4%) and acute viral bronchitis ( $n=12$ , 27.3%) were the main identified causal factors, while no cause could be determined in 5 (11.4%) patients. Noninvasive positive pressure ventilation (NIPPV) using bilevel positive airway pressure (BIPAP) was very highly effective to treat AHRF, with only 2.27% of patients failing the modality. Median overall duration of ventilation was 9 hours per day (1.3–20) and was significantly longer in patients with mOHS than in those with non-mOHS (10 [6–18] vs. 8 [1.3–20], respectively; $p=0.01$ ). Forty two of the forty-three patients discharged alive were treated with BIPAP or continuous positive airway pressure (CPAP) in 26 and 16 patients, respectively. The probability of survival was 90% at 12 months, while the probability of readmission for a new episode of AHRF was 56% at 6 months and 22% at 12 months, respectively. Conclusion. AHRF in OHS patients is a life-threatening event which can be successfully and safely treated with BIPAP, with a low long-term mortality even in patients with mOHS.

Risk factors associated with pulmonary hypertension in obesity hypoventilation syndrome

STUDY OBJECTIVES

Pulmonary hypertension (PH) is prevalent in obesity hypoventilation syndrome (OHS). However, there is a paucity of data assessing pathogenic factors associated with PH. Our objective is to assess risk factors that may be involved in the pathogenesis of PH in untreated OHS.

METHODS

In a post-hoc analysis of the Pickwick trial, we performed a bivariate analysis of baseline characteristics between patients with and without PH. Variables with a p value ≤0.10 were defined as potential risk factors and were grouped by theoretical pathogenic mechanisms in several adjusted models. Similar analysis was carried out for the two OHS phenotypes, with and without severe concomitant obstructive sleep apnea (OSA).

RESULTS

Of 246 patients with OHS, 122 (50%) had echocardiographic evidence of PH defined as systolic pulmonary artery pressure ≥40 mmHg. Lower levels of awake PaO₂ and higher body mass index (BMI) were independent risk factors in the multivariate model, with a negative and positive adjusted linear association, respectively (adjusted odds ratio 0.96; 95% CI 0.93 to 0.98; p = 0.003 for PaO₂, and 1.07; 95% CI 1.03 to 1.12; p = 0.001 for BMI). In separate analyses, BMI and PaO₂ were independent risk factors in the severe OSA phenotype, whereas BMI and peak in-flow velocity in early (E)/late diastole (A) ratio were independent risk factors in the non-severe OSA phenotype.

CONCLUSIONS

This study identifies obesity per se as a major independent risk factor for PH, regardless of OHS phenotype. Therapeutic interventions targeting weight loss may play a critical role in improving PH in this patient population.

CLINICAL TRIALS REGISTRATION

Registry: Clinicaltrial.gov; Identifier: NCT01405976.

Cardiovascular disease in obesity hypoventilation syndrome - A review of potential mechanisms and effects of therapy

Cardiovascular disease is common in patients with obesity hypoventilation syndrome (OHS) and accounts in part for their poor prognosis. This narrative review article examines the epidemiology of cardiovascular disease in obesity hypoventilation syndrome, explores possible contributing factors and the effects of therapy. All studies that included cardiovascular outcomes and biomarkers were included. Overall, there is a higher burden of cardiovascular disease and cardiovascular risk factors among patients with obesity hypoventilation syndrome. In addition to obesity and sleep-disordered breathing, there are several other pathophysiological mechanisms that contribute to higher cardiovascular morbidity and mortality in OHS. There is evidence emerging that positive airway pressure therapy and weight loss have beneficial effects on the cardiovascular system in obesity hypoventilation syndrome patients, but further research is needed to clarify whether this translates to clinically important outcomes.

Group 3 Pulmonary Hypertension: A Review of Diagnostics and Clinical Trials

Group 3 pulmonary hypertension (PH) is a known sequelae of chronic lung disease. Diagnosis and classification can be challenging in the background of chronic lung disease and often requires expert interpretation of numerous diagnostic studies to ascertain the true nature of the PH. Stabilization of the underlying lung disease and adjunctive therapies such as oxygen remain the mainstays of therapy, as there are no Food and Drug Administration-approved therapies for group 3 PH. Referral to PH centers for individualized management and clinical trial enrollment is paramount.

The association between sleep-related breathing disorders and pre-capillary pulmonary hypertension: A chicken and egg question

The level of knowledge about a direct link between sleep-related breathing disorders and pre-capillary pulmonary hypertension (PH) is low and there is a chicken and egg question to know which disease causes the other. On one hand, sleep-related breathing disorders are considered as a cause of group 3 PH, in the subgroup of patients with hypoxemia without lung disease. Indeed, isolated sleep-related breathing disorders can lead to mild pre-capillary PH on their own, although this is rare for obstructive sleep apnea and difficult to establish for obesity-hypoventilation syndrome, the evolution towards PH being observed especially in the presence of respiratory comorbidities. The hemodynamic improvement under treatment with continuous positive airway pressure or non-invasive ventilation also argues for a causal link between pre-capillary PH and sleep-related breathing disorders. On the other hand, patients followed for pre-capillary PH, particularly pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension, develop more sleep-related breathing disorders than the general population, especially sleep hypoxemia, central sleep apnea in patients with severe PH and obstructive sleep apnea in older patients with higher body mass index. The main objective of this article is therefore to answer two main questions, which will then lead us to discuss the bilateral link between these diseases: are sleep-related breathing disorders independent risk factors for pre-capillary PH and does pre-capillary PH induce sleep-related breathing disorders? In other words, who is the chicken and who is the egg?

Improvement after bariatric surgery in chronic thromboembolic pulmonary hypertension: a novel treatment target

A 66-year-old man with a medical history significant for multiple pulmonary embolism and morbid obesity was evaluated for chronic thromboembolic pulmonary hypertension. Echocardiogram and right heart catheterisation were significant for severe pulmonary hypertension. Therefore, he was started on pulmonary hypertension medical therapy with riociguat and ambrisentan, in addition to anticoagulation. He experienced a dramatic clinical response to medical therapy. Despite haemodynamic improvement, the patient remained symptomatic with significant fatigue, exertional dyspnea and poor functional status as highlighted by a 6 min walk distance of only 128 m. Patient was referred for bariatric surgery with a gastric sleeve, after which he successfully lost 95 lbs in 6 months. Postoperative right heart catheterisation demonstrated normal pulmonary  vascular resistance and cardiac output. His echocardiogram revealed normal right ventricular size and function. His 6 min walk distance also nearly quadrupled from 128 to 512 m, consistent with WHO Functional Class I.

Weight Loss Interventions as Treatment of Obesity Hypoventilation Syndrome. A Systematic Review

Rationale: Obesity hypoventilation syndrome (OHS) is an undesirable consequence of obesity. Weight loss is an important component of management based on clinical rationale, but the evidence supporting weight loss has not been summarized and the optimal approach has not been determined.Objectives: This systematic review informed an international, multidisciplinary panel of experts who had converged to develop a clinical practice guideline on OHS for the American Thoracic Society. The panel asked, "Should a weight loss intervention be performed in patients with OHS?"Methods: Medline, the Cochrane Library, and Embase were searched from January 1946 to March 2019 for studies that assessed weight loss interventions in obese adults with confirmed OHS, suspected OHS, or hypercapnia. The quality of the evidence was appraised using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach.Results: The search identified 2,994 articles. Six studies were selected, including two randomized trials and four nonrandomized studies without a comparator. Sample size ranged from 16 to 63 subjects. The studies found that a comprehensive weight loss program (including motivational counseling, dieting, and exercise) can reduce weight by 6% to 7% but confers no clinically significant effects compared with standard care. Bariatric surgery, on the other hand, is associated with more robust weight loss (15-64.6%, depending on the type of intervention), reduction of obstructive sleep apnea severity (18-44% reduction of the apnea-hypopnea index), and improvement in gas exchange (17-20% reduction in partial pressure of carbon dioxide in the arterial blood), ultimately leading to the resolution of OHS. Moreover, daytime sleepiness and pulmonary artery pressure also improve with significant weight loss. Bariatric surgery is associated with adverse effects in roughly one-fifth of patients, but serious adverse effects are very rare. The level of certainty in the estimated effects was very low for most outcomes.Conclusions: The guideline panel for which the systematic review was performed made a conditional (i.e., weak) recommendation suggesting a weight loss intervention for patients with OHS, targeting a sustained weight loss of 25% to 30% of actual body weight. This recommendation was based on very low-quality evidence. Although the weight loss target is based on the observation that greater weight loss is associated with better outcomes, there is a need for better-quality studies to ascertain the degree of weight loss necessary to achieve improvement in clinically relevant outcomes in patients with OHS.

Leptin: Master Regulator of Biological Functions that Affects Breathing

Obesity is a global epidemic in developed countries accounting for many of the metabolic and cardiorespiratory morbidities that occur in adults. These morbidities include type 2 diabetes, sleep-disordered breathing (SDB), obstructive sleep apnea, chronic intermittent hypoxia, and hypertension. Leptin, produced by adipocytes, is a master regulator of metabolism and of many other biological functions including central and peripheral circuits that control breathing. By binding to receptors on cells and neurons in the brainstem, hypothalamus, and carotid body, leptin links energy and metabolism to breathing. In this comprehensive article, we review the central and peripheral locations of leptin's actions that affect cardiorespiratory responses during health and disease, with a particular focus on obesity, SDB, and its effects during early development. Obesity-induced hyperleptinemia is associated with centrally mediated hypoventilation with decrease CO₂ sensitivity. On the other hand, hyperleptinemia augments peripheral chemoreflexes to hypoxia and induces sympathoexcitation. Thus, "leptin resistance" in obesity is relative. We delineate the circuits responsible for these divergent effects, including signaling pathways. We review the unique effects of leptin during development on organogenesis, feeding behavior, and cardiorespiratory responses, and how undernutrition and overnutrition during critical periods of development can lead to cardiorespiratory comorbidities in adulthood. We conclude with suggestions for future directions to improve our understanding of leptin dysregulation and associated clinical diseases and possible therapeutic targets. Lastly, we briefly discuss the yin and the yang, specifically the contribution of relative adiponectin deficiency in adults with hyperleptinemia to the development of metabolic and cardiovascular disease. © 2020 American Physiological Society. Compr Physiol 10:1047-1083, 2020.

Effectiveness of different treatments in obesity hypoventilation syndrome

Obesity hypoventilation syndrome (OHS) is an undesirable consequence of obesity, defined as daytime hypoventilation, sleep disorder breathing and obesity; during the past few years the prevalence of extreme obesity has markedly increased worldwide consequently increasing the prevalence of OHS. Patients with OHS have a lower quality of life and a higher risk of unfavourable cardiometabolic consequences. Early diagnosis and effective treatment can lead to significant improvement in patient outcomes; therefore, such data has noticeably raised interest in the management and treatment of this sleep disorder. This paper will discuss the findings on the main current treatment modalities OHS will be discussed.

Echocardiographic Changes with Positive Airway Pressure Therapy in Obesity Hypoventilation Syndrome. Long-Term Pickwick Randomized Controlled Clinical Trial

Rationale: Obesity hypoventilation syndrome (OHS) has been associated with cardiac dysfunction. However, randomized trials assessing the impact of long-term noninvasive ventilation (NIV) or continuous positive airway pressure (CPAP) on cardiac structure and function assessed by echocardiography are lacking.Objectives: In a prespecified secondary analysis of the largest multicenter randomized controlled trial of OHS (Pickwick Project; N = 221 patients with OHS and coexistent severe obstructive sleep apnea), we compared the effectiveness of three years of NIV and CPAP on structural and functional echocardiographic changes.Methods: At baseline and annually during three sequential years, patients underwent transthoracic two-dimensional and Doppler echocardiography. Echocardiographers at each site were blinded to the treatment allocation. Statistical analysis was performed using a linear mixed-effects model with a treatment group and repeated measures interaction to determine the differential effect between CPAP and NIV.Measurements and Main Results: A total of 196 patients were analyzed: 102 were treated with CPAP and 94 were treated with NIV. Systolic pulmonary artery pressure decreased from 40.5 ± 1.47 mm Hg at baseline to 35.3 ± 1.33 mm Hg at three years with CPAP, and from 41.5 ± 1.56 mm Hg to 35.5 ± 1.42 with NIV (P < 0.0001 for longitudinal intragroup changes for both treatment arms). However, there were no significant differences between groups. NIV and CPAP therapies similarly improved left ventricular diastolic dysfunction and reduced left atrial diameter. Both NIV and CPAP improved respiratory function and dyspnea.Conclusions: In patients with OHS who have concomitant severe obstructive sleep apnea, long-term treatment with NIV and CPAP led to similar degrees of improvement in pulmonary hypertension and left ventricular diastolic dysfunction.Clinical trial registered with www.clinicaltrials.gov (NCT01405976).

Obesity, Systemic Hypertension, and Pulmonary Hypertension: A Tale of Three Diseases

Cardiovascular disease (CVD), especially ischemic heart disease and stroke, is the major cause of death worldwide, accounting for more than one-third of all deaths annually. Hypertension is the most prevalent and modifiable risk factor of CVD-related deaths. The same is true for obesity, which is currently being recognized as a major global epidemic. The prevalence of obesity in the United States has increased dramatically, from 13.4% in 1960 to 36.5% in 2014, with as much as 70.7% of the American adult population being overweight or obese (CDC). Epidemiological studies have shown that obesity predisposes to hypertension and CVD - with the relationship between markers of obesity and blood pressure being almost linear across different populations. In this review, we discuss systemic and pulmonary hypertension in the context of obesity.

Evaluation and Management of Obesity Hypoventilation Syndrome. An Official American Thoracic Society Clinical Practice Guideline

Background: The purpose of this guideline is to optimize evaluation and management of patients with obesity hypoventilation syndrome (OHS).

Methods: A multidisciplinary panel identified and prioritized five clinical questions. The panel performed systematic reviews of available studies (up to July 2018) and followed the Grading of Recommendations, Assessment, Development, and Evaluation evidence-to-decision framework to develop recommendations. All panel members discussed and approved the recommendations.

Recommendations: After considering the overall very low quality of the evidence, the panel made five conditional recommendations. We suggest that: 1) clinicians use a serum bicarbonate level <27 mmol/L to exclude the diagnosis of OHS in obese patients with sleep-disordered breathing when suspicion for OHS is not very high (<20%) but to measure arterial blood gases in patients strongly suspected of having OHS, 2) stable ambulatory patients with OHS receive positive airway pressure (PAP), 3) continuous positive airway pressure (CPAP) rather than noninvasive ventilation be offered as the first-line treatment to stable ambulatory patients with OHS and coexistent severe obstructive sleep apnea, 4) patients hospitalized with respiratory failure and suspected of having OHS be discharged with noninvasive ventilation until they undergo outpatient diagnostic procedures and PAP titration in the sleep laboratory (ideally within 2–3 mo), and 5) patients with OHS use weight-loss interventions that produce sustained weight loss of 25% to 30% of body weight to achieve resolution of OHS (which is more likely to be obtained with bariatric surgery).

Conclusions: Clinicians may use these recommendations, on the basis of the best available evidence, to guide management and improve outcomes among patients with OHS.

A Case of Right Ventricular Dysfunction with Right Ventricular Failure Secondary to Obesity Hypoventilation Syndrome

Patient: Male, 53

Final Diagnosis: Right ventricular dysfunction secondary to obesity hypoventilation syndrome

Symptoms: Shortness of breath

Medication: —

Clinical Procedure: Echocardiogram (TTE)

Specialty: Cardiology

More than Heart Failure: Central Sleep Apnea and Sleep-Related Hypoventilation

Central sleep apnea (CSA) comprises a variety of breathing patterns and clinical entities. They can be classified into 2 categories based on the partial pressure of carbon dioxide in the arterial blood. Nonhypercapnic CSA is usually characterized by a periodic breathing pattern, while hypercapnic CSA is based on hypoventilation. The latter CSA form is associated with central nervous, neuromuscular, and rib cage disorders as well as obesity and certain medication or substance intake. In contrast, nonhypercapnic CSA is typically accompanied by an overshoot of the ventilation and often associated with heart failure, cerebrovascular diseases, and stay in high altitude. CSA and hypoventilation syndromes are often considered separately, but pathophysiological aspects frequently overlap. An integrative approach helps to recognize underlying pathophysiological mechanisms and to choose adequate therapeutic strategies. Research in the last decades improved our insights; nevertheless, diagnostic tools are not always appropriately chosen to perform comprehensive sleep studies. This supports misinterpretation and misclassification of sleep disordered breathing. The purpose of this article is to highlight unresolved problems, raise awareness for different pathophysiological components and to discuss the evidence for targeted therapeutic strategies.

Hemodynamic Effects of Weight Loss in Obesity: A Systematic Review and Meta-Analysis

OBJECTIVES

The authors aimed to explore whether weight loss may improve central hemodynamics in obesity.

BACKGROUND

Hemodynamic abnormalities in obese heart failure with preserved ejection fraction patients are correlated with the amount of excess body mass, suggesting a possible causal relationship.

METHODS

Relevant databases were systematically searched from inception to May 2018, without language restriction. Studies reporting invasive hemodynamic measures before and following therapeutic weight loss interventions in patients with obesity but no clinically overt heart failure were extracted.

RESULTS

A total of 9 studies were identified, providing data for 110 patients. Six studies tested dietary intervention and 3 studies tested bariatric surgery. Over a median duration of 9.7 months (range 0.75 to 23.0 months), a median weight loss of 43 kg (range 10 to 58 kg) was associated with significant reductions in heart rate (-9 beats/min, 95% confidence interval [CI]: -12 to -6; p < 0.001), mean arterial pressure (-7 mm Hg, 95% CI: -11 to -3; p < 0.001), and resting oxygen consumption (-85 ml/min, 95% CI: -111 to -60; p < 0.001). Central cardiac hemodynamics improved, manifested by reductions in pulmonary capillary wedge pressure (-3 mm Hg, 95% CI: -5 to -1; p < 0.001) and mean pulmonary artery pressure (-5 mm Hg, 95% CI: -8 to -2; p = 0.001). Exercise hemodynamics were assessed in a subset of patients (n = 49) in which there was significant reduction in exercise pulmonary artery pressure (p = 0.02).

CONCLUSIONS

Therapeutic weight loss in obese patients without HF is associated with favorable hemodynamic effects. Randomized controlled trials evaluating strategies for weight loss in obese patients with heart failure such as the obese phenotype of heart failure with preserved ejection fraction are needed.

Obesity hypoventilation syndrome

Obesity hypoventilation syndrome (OHS) is defined as a combination of obesity (body mass index ≥30 kg·m-2), daytime hypercapnia (arterial carbon dioxide tension ≥45 mmHg) and sleep disordered breathing, after ruling out other disorders that may cause alveolar hypoventilation. OHS prevalence has been estimated to be ∼0.4% of the adult population. OHS is typically diagnosed during an episode of acute-on-chronic hypercapnic respiratory failure or when symptoms lead to pulmonary or sleep consultation in stable conditions. The diagnosis is firmly established after arterial blood gases and a sleep study. The presence of daytime hypercapnia is explained by several co-existing mechanisms such as obesity-related changes in the respiratory system, alterations in respiratory drive and breathing abnormalities during sleep. The most frequent comorbidities are metabolic and cardiovascular, mainly heart failure, coronary disease and pulmonary hypertension. Both continuous positive airway pressure (CPAP) and noninvasive ventilation (NIV) improve clinical symptoms, quality of life, gas exchange, and sleep disordered breathing. CPAP is considered the first-line treatment modality for OHS phenotype with concomitant severe obstructive sleep apnoea, whereas NIV is preferred in the minority of OHS patients with hypoventilation during sleep with no or milder forms of obstructive sleep apnoea (approximately <30% of OHS patients). Acute-on-chronic hypercapnic respiratory failure is habitually treated with NIV. Appropriate management of comorbidities including medications and rehabilitation programmes are key issues for improving prognosis.

Obesity hypoventilation syndrome: a current review

Obesity hypoventilation syndrome (OHS) is defined as the presence of obesity (body mass index ≥ 30 kg/m²) and daytime arterial hypercapnia (PaCO2 ≥ 45 mmHg) in the absence of other causes of hypoventilation. OHS is often overlooked and confused with other conditions associated with hypoventilation, particularly COPD. The recognition of OHS is important because of its high prevalence and the fact that, if left untreated, it is associated with high morbidity and mortality. In the present review, we address recent advances in the pathophysiology and management of OHS, the usefulness of determination of venous bicarbonate in screening for OHS, and diagnostic criteria for OHS that eliminate the need for polysomnography. In addition, we review advances in the treatment of OHS, including behavioral measures, and recent studies comparing the efficacy of continuous positive airway pressure with that of noninvasive ventilation.

Vertical sleeve gastrectomy improves ventilatory drive through a leptin-dependent mechanism

Obesity hypoventilation syndrome (OHS) is a serious disorder characterized by daytime hypercapnia, disordered breathing, and a reduction in chemosensitivity. Vertical sleeve gastrectomy (VSG), a bariatric surgical procedure resulting in weight loss and weight-independent improvements in glucose metabolism, has been observed to substantially improve sleep-disordered breathing. However, it is unclear if the ventilatory effects of VSG are secondary to weight loss or the marked change in metabolic physiology. Using preclinical mouse models, we found that VSG leads to an improvement in the hypercapnic ventilatory response (HCVR) and reductions in circulating leptin levels independent of reductions in body mass, fat mass, and caloric intake. In the absence of leptin, VSG continues to improve body mass, fat mass, and glucose tolerance in ob/ob mice but no longer affects HCVR. However, the HCVR of ob/ob mice can be returned to wild-type levels with leptin treatment. These data demonstrate that VSG improves chemosensitivity and ventilatory drive via a leptin-dependent mechanism. Clinically, these data downgrade the relative contribution of physical, mechanical load in the pathogenesis of OHS, and instead point to physiological components of obesity, including alterations in leptin signaling, as key drivers in OHS.

Pulmonary Hypertension and Its Response to Treatment in a Patient with Kyphosis-related Alveolar Hypoventilation

Pulmonary hypertension (PH) with kyphoscoliosis-related alveolar hypoventilation is uncommon, so little is known about the effectiveness of treatments for this condition. A 66-year-old man with kyphosis who had been treated with nocturnal noninvasive positive-pressure ventilation developed PH with a mean pulmonary arterial pressure (PAP) of 32 mmHg and a pulmonary vascular resistance (PVR) of 5.95 Wood units. After addition of oxygen therapy and tadalafil, his condition improved. One year later, his mean PAP and PVR were 25 mmHg and 3.62 Wood units, respectively. This case shows the therapeutic potential of vasoactive medications for alveolar hypoventilation-related PH.

Pulmonary hypertension associated with lung diseases and hypoxemia

Pulmonary hypertension that develops in the setting of underlying lung diseases such as COPD or idiopathic pulmonary fibrosis (IPF) is associated with decreased functional status, worsening hypoxemia and quality of life, and increased mortality. This complication of lung disease is complex in its origin and carries a unique set of diagnostic and therapeutic issues. This review attempts to provide an overview of mechanisms associated with the onset of pulmonary hypertension in COPD and IPF, touches on appropriate evaluation, and reviews the state of knowledge on treating pulmonary hypertension related to underlying lung disease.

Echocardiographic changes with non-invasive ventilation and CPAP in obesity hypoventilation syndrome

Rationale

Despite a significant association between obesity hypoventilation syndrome (OHS) and cardiac dysfunction, no randomised trials have assessed the impact of non-invasive ventilation (NIV) or CPAP on cardiac structure and function assessed by echocardiography.

Objectives

We performed a secondary analysis of the data from the largest multicentre randomised controlled trial of OHS (Pickwick project, n=221) to determine the comparative efficacy of 2 months of NIV (n=71), CPAP (n=80) and lifestyle modification (control group, n=70) on structural and functional echocardiographic changes.

Methods

Conventional transthoracic two-dimensional and Doppler echocardiograms were obtained at baseline and after 2 months. Echocardiographers at each site were blinded to the treatment arms. Statistical analysis was performed using intention-to-treat analysis.

Results

At baseline, 55% of patients had pulmonary hypertension and 51% had evidence of left ventricular hypertrophy. Treatment with NIV, but not CPAP, lowered systolic pulmonary artery pressure (−3.4 mm Hg, 95% CI −5.3 to –1.5; adjusted P=0.025 vs control and P=0.033 vs CPAP). The degree of improvement in systolic pulmonary artery pressure was greater in patients treated with NIV who had pulmonary hypertension at baseline (−6.4 mm Hg, 95% CI −9 to –3.8). Only NIV therapy decreased left ventricular hypertrophy with a significant reduction in left ventricular mass index (−5.7 g/m2; 95% CI −11.0 to –4.4). After adjusted analysis, NIV was superior to control group in improving left ventricular mass index (P=0.015). Only treatment with NIV led to a significant improvement in 6 min walk distance (32 m; 95% CI 19 to 46).

Conclusion

In patients with OHS, medium-term treatment with NIV is more effective than CPAP and lifestyle modification in improving pulmonary hypertension, left ventricular hypertrophy and functional outcomes. Long-term studies are needed to confirm these results.

Trial registration number

Pre-results, NCT01405976 (https://clinicaltrials.gov/).

Bariatric surgery as a treatment for heart failure: review of the literature and potential mechanisms

Heart failure due to severe obesity is a complex disease due to multiple mechanisms, including increased body mass, inflammation, and impaired cardiac metabolism that is complicated by obesity-associated co-morbidities, such as type 2 diabetes and obstructive sleep apnea. Bariatric surgery significantly improves cardiac geometry, function, and symptoms related to obesity cardiomyopathy. There is a consistently positive impact of bariatric surgery on diastolic function with the potential to significantly improve systolic function as measured by ejection fraction in patients with advanced heart failure. For end-stage heart failure patients, including those requiring mechanical circulatory support who are ineligible for organ transplant due to morbid obesity, bariatric surgery has been successfully used for weight loss as a bridge to cardiac transplantation.

The prevalence of pulmonary hypertension in patients with obesity hypoventilation syndrome: a prospective observational study

BACKGROUND

One important cardiovascular morbidity that is associated with obesity hypoventilation syndrome (OHS) is the development of pulmonary hypertension (PH). However, few studies have assessed PH in OHS patients. Therefore, we prospectively assessed the prevalence of PH in a large sample of OHS patients.

METHODS

In this prospective observational study, all consecutive OHS patients referred to the sleep disorders clinic during the study period were included. All patients underwent overnight polysomnography (PSG), spirometry, arterial blood samples and thyroid tests. Transthoracic echocardiography was performed for patients who agreed to participate in the study. PH was defined as systolic pulmonary artery pressure (SPAP) >40 mmHg.

RESULTS

Echocardiographic data were available for 77 patients with a mean age of 60.5±11.7 years, a BMI of 43.2±10.4 kg/m², and an Epworth Sleepiness Scale (ESS) score of 11.4±5.5. SPAP was >40 mmHg in 53 patients (68.8%), with a mean SPAP of 64.1±17.1 mmHg. There were no differences between the OHS patients with PH and those with normal PAP in terms of age, BMI, presenting symptoms, comorbidities, arterial blood gasses (ABG), and spirometric and PSG parameters. Approximately 71.4% of women and 61.9% of men with OHS also had PH. SPAP was >40-55 mmHg in 19 (24.7%) patients (18 women), >55-70 mmHg in 15 (19.5%) patients (6 women) and >70 mmHg in 19 (24.7%) patients (16 women). Severe PH (SPAP >70 mmHg) was diagnosed in 28.6% of the women and 14.3% of the men.

CONCLUSIONS

PH is very common among patients with OHS who have been referred to sleep disorders clinics. PH should be considered in the regular clinical assessment of all patients with OHS.

The Predictors of Obesity Hypoventilation Syndrome in Obstructive Sleep Apnea

Background:

As obesity increases, the frequency of obstructive sleep apnea and obesity hypoventilation syndrome increases also. However, obesity hypoventilation syndrome frequency is not known, as capnography and arterial blood gas analysis are not routinely performed in sleep laboratories.

Aims:

To investigate the frequency and predictors of obesity hypoventilation syndrome in obese subjects.

Study Design:

Retrospective clinical study.

Methods:

Obese subjects who had arterial blood gas analysis admitted to the sleep laboratory and polysomnography were retrospectively analyzed. Subjects with restrictive (except obesity) and obstructive pulmonary pathologies were excluded. Demographics, Epworth-Sleepiness-Scale scores, polysomnographic data, arterial blood gas analysis, and spirometric measurements were recorded.

Results:

Of the 419 subjects, 45.1% had obesity hypoventilation syndrome. Apnea hypopnea index (p<0.001), oxygen desaturation index (p<0.001) and sleep time with SpO₂<90% (p<0.001) were statistically higher in subjects with obesity hypoventilation syndrome compared to subjects with eucapnic obstructive sleep apnea. The nocturnal mean SpO₂ (p<0.001) and lowest SpO₂ (p<0.001) were also statistically lower in subjects with obesity hypoventilation syndrome. Logistic regression analysis showed that the lowest SpO₂, oxygen desaturation index, apnea hypopnea index and sleep time with SpO₂ <90% were related factors for obesity hypoventilation syndrome.

Conclusion:

Obesity hypoventilation syndrome should be considered when oxygen desaturation index, apnea hypopnea index and sleep time with SpO₂ <90% are high.

Definition, discrimination, diagnosis and treatment of central breathing disturbances during sleep

The complexity of central breathing disturbances during sleep has become increasingly obvious. They present as central sleep apnoeas (CSAs) and hypopnoeas, periodic breathing with apnoeas, or irregular breathing in patients with cardiovascular, other internal or neurological disorders, and can emerge under positive airway pressure treatment or opioid use, or at high altitude. As yet, there is insufficient knowledge on the clinical features, pathophysiological background and consecutive algorithms for stepped-care treatment. Most recently, it has been discussed intensively if CSA in heart failure is a “marker” of disease severity or a “mediator” of disease progression, and if and which type of positive airway pressure therapy is indicated. In addition, disturbances of respiratory drive or the translation of central impulses may result in hypoventilation, associated with cerebral or neuromuscular diseases, or severe diseases of lung or thorax. These statements report the results of an European Respiratory Society Task Force addressing actual diagnostic and therapeutic standards. The statements are based on a systematic review of the literature and a systematic two-step decision process. Although the Task Force does not make recommendations, it describes its current practice of treatment of CSA in heart failure and hypoventilation.

The clinical characteristics and hospital and post-hospital survival of patients with the obesity hypoventilation syndrome: analysis of a large cohort

OBJECTIVE

The worldwide prevalence of obesity has reached epidemic proportions. Obesity hypoventilation syndrome (OHS) is a common yet largely undiagnosed and mistreated condition that likely carries a high mortality. The aim of this study was to determine the clinical characteristics, hospital outcome, outcome following hospital discharge and predictors of death in a large cohort of patients hospitalized with OHS. OHS is an important condition as many patients with this syndrome are misdiagnosed and receive inappropriate treatment.

METHODS

We reviewed the electronic medical records of patients with unequivocal OHS admitted to a 525-bed tertiary-care teaching hospital over a 5-year period. Demographic and clinical data as well as hospital disposition were recorded. In order to determine the patients' post-discharge status, we linked our database to the database of death certificates of the State Registrar of Vital Records.

RESULTS

We identified 600 patients who met the inclusion criteria for this study. The patients' mean age was 58 ± 15 years with a mean body mass index of 48.2 ± 8.3 kg m-2; 64% were women. Thirty-seven percent had a history of diabetes and 43% had been misdiagnosed as having chronic obstructive pulmonary disease, while none had been previously diagnosed with OHS. The most common admission diagnoses were respiratory failure, heart failure and sepsis. Ninety (15%) patients died during the index hospitalization. The patients' age, S-creatinine, respiratory failure, sepsis and admission to the ICU were independent predictors of hospital mortality. The hospital survivors were followed for a mean of 1,174 ± 501 d (3.2 ± 1.3 years) from the index hospitalization. On follow-up, 98 of the 510 (19%) hospital survivors died, with an overall cumulative mortality of 31.3%. The patients' age, S-creatinine and admission to the ICU were independent predictors of post-hospital mortality.

CONCLUSION

Obesity hypoventilation syndrome is a common disease that is frequently misdiagnosed and mistreated and carries a 3-year morality, which is significantly worse than that for most cancers combined. Considering the high mortality of this disease, all patients with a body mass index > 35 kg m-2 should be screened for OHS; those patients with both early and established OHS should be referred to a pulmonary and/or sleep specialist for evaluation for non-invasive positive pressure ventilation, to a dietician for dietary counseling and lifestyle modification and to a bariatric surgeon for evaluation for bariatric surgery.

OSA and pulmonary hypertension: time for a new look

OSA is a common yet underdiagnosed disorder encountered in everyday practice. The disease is a unique physiologic stressor that contributes to the development or progression of many other disorders, particularly cardiovascular conditions. The pulmonary circulation is specifically affected by the intermittent hypoxic apneas associated with OSA. The general consensus has been that OSA is associated with pulmonary hypertension (PH), but only in a minority of OSA patients and generally of a mild degree. Consequently, there has been no sense of urgency to screen for either condition when evaluating the other. In this review, we explore available evidence describing the interaction between OSA and PH and seek to better understand underlying pathophysiology. We describe certain groups of patients who have a particular preponderance of OSA and PH. Failure to recognize the mutual additive effects of these disorders can lead to suboptimal patient outcomes. Among patients with PH and OSA, CPAP, the mainstay treatment for OSA, may ameliorate pulmonary pressure elevations, but has not been studied adequately. Conversely, among patients with OSA, PH significantly limits functional capacity and potentially shortens survival; yet, there is no routine screening for PH in patients with OSA. We think it is time to study the interaction between OSA and PH more carefully to identify high-risk subgroups. These would be screened for the presence of combined disorders, facilitating earlier institution of therapy and improving outcomes.

A case of obesity hypoventilation syndrome with respiratory failure that improved with abdominoplasty

We report on a 70-year-old man with severe respiratory failure caused by obesity hypoventilation syndrome due to abdominal adiposis. Obesity hypoventilation syndrome is a severe condition that is diagnosed when all of the following criteria are satisfied: body-mass index >30 kg/m(2); apnea hypopnea index >30; PaCO2 >45 mm Hg (in the daytime); and marked daytime somnolence. Abdominoplasty, which is generally used for abdominal laxness, striae, and rectus muscle diastases and for women in the postpartum period, was performed for this patient to facilitate ventilator weaning and produced a satisfactory result.

Pulmonary and cardiac function in asymptomatic obese subjects and changes following a structured weight reduction program: a prospective observational study

BACKGROUND

The prevalence of obesity is rising. Obesity can lead to cardiovascular and ventilatory complications through multiple mechanisms. Cardiac and pulmonary function in asymptomatic subjects and the effect of structured dietary programs on cardiac and pulmonary function is unclear.

OBJECTIVE

To determine lung and cardiac function in asymptomatic obese adults and to evaluate whether weight loss positively affects functional parameters.

METHODS

We prospectively evaluated bodyplethysmographic and echocardiographic data in asymptomatic subjects undergoing a structured one-year weight reduction program.

RESULTS

74 subjects (32 male, 42 female; mean age 42±12 years) with an average BMI 42.5±7.9, body weight 123.7±24.9 kg were enrolled. Body weight correlated negatively with vital capacity (R = -0.42, p<0.001), FEV1 (R = -0.497, p<0.001) and positively with P 0.1 (R = 0.32, p = 0.02) and myocardial mass (R = 0.419, p = 0.002). After 4 months the study subjects had significantly reduced their body weight (-26.0±11.8 kg) and BMI (-8.9±3.8) associated with a significant improvement of lung function (absolute changes: vital capacity +5.5±7.5% pred., p<0.001; FEV1+9.8±8.3% pred., p<0.001, ITGV+16.4±16.0% pred., p<0.001, SR tot -17.4±41.5% pred., p<0.01). Moreover, P0.1/Pimax decreased to 47.7% (p<0.01) indicating a decreased respiratory load. The change of FEV1 correlated significantly with the change of body weight (R = -0.31, p = 0.03). Echocardiography demonstrated reduced myocardial wall thickness (-0.08±0.2 cm, p = 0.02) and improved left ventricular myocardial performance index (-0.16±0.35, p = 0.02). Mitral annular plane systolic excursion (+0.14, p = 0.03) and pulmonary outflow acceleration time (AT +26.65±41.3 ms, p = 0.001) increased.

CONCLUSION

Even in asymptomatic individuals obesity is associated with abnormalities in pulmonary and cardiac function and increased myocardial mass. All the abnormalities can be reversed by a weight reduction program.

Use of pulmonary arterial hypertension-specific therapy in overweight or obese patients with obstructive sleep apnea and pulmonary hypertension

Pulmonary hypertension (PH) in overweight or obese patients with obstructive sleep apnea (OSA) may be multifactorial. The effect of pulmonary artery hypertension (PAH)-specific drugs on PH and exercise capacity in such patients is unknown. We performed a retrospective review of overweight or obese patients with OSA and PH who were treated with PAH-specific therapy in our PH clinic. We identified 9 female and 2 male patients. The mean age ± SD was 54.9 ± 9.3 years. The mean pulmonary artery pressure at the time of diagnosis of PH was 39.8 ± 16.1 mmHg. The right atrial pressure was 11.1 ± 4.5 mmHg, the pulmonary artery wedge pressure was 14.1 ± 2.9 mmHg, the cardiac index was 2.6 ± 0.5 L/min/m(2), and the pulmonary vascular resistance index was 10.6 ± 7.1 Wood units/m(2). The indications for use of PAH-specific therapy were dyspnea in association with right heart failure (n = 4), persistent PH despite compliance with nocturnal positive airway pressure (PAP) therapy (n = 4), or inability to tolerate PAP therapy (n = 3). PH was treated with an endothelin receptor antagonist (n = 8) or a phosphodiesterase-5 inhibitor (n = 3). The 6-minute walk distance (6MWD) improved significantly, from 234 ± 49.7 to 258 ± 54.6 m (24 m [95% confidence interval (CI): 6.5-341.5 m]; P = 0.014) over a period of 4.4 ± 1.8 months (n = 8) and from 241.7 ± 48.5 to 289.9 ± 91 m (48 m [95% CI: 5.5-90.8 m]; P = 0.033) in those with a longer follow-up period of 12.1 ± 6.4 months (n = 7). The systolic pulmonary artery pressure dropped significantly, from 64 ± 25.2 to 42 ± 10.4 mmHg (22 mmHg [95% CI: 4-40 mmHg]; P = 0.024) over a period of 6.1 ± 4.1 months (n = 7). In conclusion, PAH-specific therapy resulted in significant improvement in both PH and 6MWD.

Clinical significance of elevated intraabdominal pressure during common conditions and procedures

INTRODUCTION

Pregnancy, obesity, peritoneal dialysis, pneumoperitoneum, prone position and application of positive end-expiratory pressure are associated with elevated intraabdominal pressure (IAP).

OBJECTIVE

To review the relation between these conditions and procedures, and intraabdominal hypertension (IAH) or abdominal compartment syndrome (ACS).

METHODS

Search of PubMed and Google Scholar and review of article bibliographies.

RESULTS AND CONCLUSION

Only obesity, peritoneal dialysis, and pneumoperitoneum are associated with symptoms related to IAH and these symptoms are reversible.

Pulmonary hypertension due to lung disease and/or hypoxia

Pulmonary hypertension may complicate the course of patients with many forms of advanced lung disease. The cause is likely multifactorial with pathogenic pathways both common and unique to the specific disease entities. The occurrence of pulmonary hypertension is associated with worse outcomes, but whether this is an adaptive or maladaptive phenomenon remains unknown. The treatment of pulmonary hypertension with vasoactive medications in lung disease remains unproved. Specific disease phenotypes that might benefit, and those in which such therapies might be deleterious, remain to be determined.

The malignant obesity hypoventilation syndrome (MOHS)

We have coined the term 'malignant obesity hypoventilation syndrome' (MOHS) to describe a severe multisystem disease due to the systemic effects of obesity. Patients with this syndrome have severe obesity-related hypoventilation together with systemic hypertension, diabetes and the metabolic syndrome, left ventricular hypertrophy with diastolic dysfunction, pulmonary hypertension and hepatic dysfunction. This syndrome is largely unrecognized as physicians do not make the association between the patients' multiple medical problems and obesity. Because of the delayed diagnosis and progressive morbidities of this condition, all patients with a body mass index of more than 40 kg m(-2) should be screened for MOHS. The management of patients with MOHS includes short-term measures to improve the patients' medical condition and long-term measures to achieve enduring weight loss. Bariatric surgery reverses or improves the multiple metabolic and organ dysfunctions associated with MOHS and should be strongly considered in these patients.

Characteristics of patients with the "malignant obesity hypoventilation syndrome" admitted to an ICU

BACKGROUND

The incidence of obesity in westernized nations is increasing at an alarming rate. We have noted an increasing number of patients admitted to our intensive care unit (ICU) with hypercapnic respiratory failure and multisystem organ dysfunction related to obesity. We have coined the term the malignant obesity hypoventilation syndrome (MOHS) to describe this entity.

METHODS

We reviewed the hospital records of all patients who were admitted to our ICU over an 8-month period, with a body mass index (BMI) greater than 40 kg/m² and a PaCO₂ greater than 45 mm Hg. We excluded patients with musculoskeletal disease, intrinsic lung disease, and those with >20 pack-year smoking history.

RESULTS

Sixty-one patients (8% of all admissions) met the inclusion criteria for our study. The patients' mean BMI was 48.9 ± 8.6 kg/m². The patients' mean age was 59 ± 11; 47 (77%) were female and 56 (92%) were black. All patients were admitted to the ICU with hypercapnic respiratory failure. The patients had been admitted to our hospital on average 6 times over the previous 2 years; 75% had been erroneously diagnosed and treated for chronic obstructive pulmonary disease (COPD)/asthma and 86% had been treated with diuretics for congestive cardiac failure. All patients had type 2 diabetes and the metabolic syndrome. Three patients had a tracheotomy in place at admission and required mechanical ventilation. All of the remaining patients were treated with noninvasive bilevel positive airway pressure (BiPAP), with 23 patients failing BiPAP and requiring mechanical ventilation. Seven patients had a tracheotomy performed. On the basis of unexplained abnormalities of liver function tests, 39 patients (64%) were presumptively diagnosed with nonalcoholic steatohepatitis (NASH). Pulmonary function tests were suggestive of a restrictive pattern in all patients tested. By echocardiography 43 (71%) patients had left ventricular hypertrophy and 37 (61%) patients had features of left ventricular diastolic dysfunction. Forty-seven (77%) patients had pulmonary hypertension, which was moderate to severe (pulmonary systolic pressure >45 mm Hg) in 25 cases. All patients had an elevated C-reactive protein (9.4 ± 6.9 mg/dL), and all but 1 were vitamin D deficient (13.5 ± 8.5 ng/mL). Eleven patients (18%) died during the index hospitalization.

CONCLUSIONS

MOHS is a serious multisystem disorder with a high mortality that appears to be relatively common, frequently misdiagnosed, and inadequately treated.

Right ventricular dysfunction in chronic lung disease

Right ventricular (RV) dysfunction arises in chronic lung disease when chronic hypoxemia and disruption of pulmonary vascular beds increase ventricular afterload. RV dysfunction is defined by hypertrophy with preserved myocardial contractility and cardiac output. RV hypertrophy seems to be a common complication of chronic and advanced lung disease. RV failure is rare, except during acute exacerbations of chronic lung disease or when multiple comorbidities are present. Treatment is targeted at correcting hypoxia and improving pulmonary gas exchange and mechanics. There are no data supporting the use of pulmonary hypertension-specific therapies for patients with RV dysfunction secondary to chronic lung disease.

Obesity and pulmonary hypertension: a review of pathophysiologic mechanisms

Pulmonary hypertension (PH) is a potentially life-threatening condition arising from a wide variety of pathophysiologic mechanisms. Effective treatment requires a systematic diagnostic approach to identify all reversible mechanisms. Many of these mechanisms are relevant to those afflicted with obesity. The unique mechanisms of PH in the obese include obstructive sleep apnea, obesity hypoventilation syndrome, anorexigen use, cardiomyopathy of obesity, and pulmonary thromboembolic disease. Novel mechanisms of PH in the obese include endothelial dysfunction and hyperuricemia. A wide range of effective therapies exist to mitigate the disability of PH in the obese.

Difficulties in managing the surgical patient who is morbidly obese

Managing patients who are morbidly obese in the intensive care unit is associated with a variety of problems uncommonly experienced with the those who are not morbidly obese. Clinicians experience a myriad of unique problems and circumstances, from the need for special beds and lifts to unusual and unknown volumes of distribution resulting in unclear drug dosing. This review examines several issues including sedation, invasive monitoring, venous thromboembolism prophylaxis, surgical infections, nutritional support, and other complications that may be of particular importance to the critically ill patient who is morbidly obese. In many cases, care is altered based on the complicating issues surrounding morbid obesity. In other cases, the presence of obesity suggests no alterations in our routine critical care delivery. A comprehensive review of the literature is undertaken, data are critically considered, and overall opinion is rendered based on the available peer-reviewed literature. In many cases, data are not available that address the specific patient population in question, so related papers (like gastric bypass data) are considered. Many issues do not have definitive answers based on randomized controlled trials, and much is left to treating clinician opinion and local practice patterns. Where good data exist, however, one should consider carefully and individually deviation from the evidence-based approach.

Bariatric surgery: a primer

OBJECTIVE

To review the management of bariatric surgical patients.

QUALITY OF EVIDENCE

MEDLINE, EMBASE, and Cochrane Library databases were searched, as well as PubMed US National Library, from January 1950 to December 2009. Evidence was levels I, II, and III.

MAIN MESSAGE

Bariatric surgery should be considered for obese patients at high risk of morbidity and mortality who have not achieved adequate weight loss with lifestyle and medical management and who are suffering from the complications of obesity. Bariatric surgery can result in substantial weight loss, resolution of comorbid conditions, and improved quality of life. The patient's weight-loss history; his or her personal accountability, responsibility, and comprehension; and the acceptable level of risk must be taken into account. Complications include technical failure, bleeding, abdominal pain, nausea or vomiting, excess loose skin, bowel obstruction, ulcers, and anastomotic stricture. Lifelong monitoring by a multidisciplinary team is essential.

CONCLUSION

Limited long-term success of behavioural and pharmacologic therapies in severe obesity has led to renewed interest in bariatric surgery. Success with bariatric surgery is more likely when multidisciplinary care providers, in conjunction with primary care providers, assess, treat, monitor, and evaluate patients before and after surgery. Family physicians will play a critical role in counseling patients about bariatric surgery and will need to develop skills in managing these patients in the long-term.

Metabolic, renal, and nutritional consequences of bariatric surgery: implications for the clinician

Management of obesity-associated comorbidities costs about $60 billion/year, about 5% of total US healthcare expenditure. Bariatric surgery is the only proven effective weight loss therapy for severely obese patients with a BMI > or =35 kg/m2. Bariatric surgery produces long-term weight loss, improves quality of life, and reduces the number of sick days and medication costs. Surgery has a profound effect on the metabolic milieu and nutritional status from the first few days after surgery, even before significant weight loss has been achieved. Metabolic effects of bariatric surgery reduce obesity-related comorbidities like type 2 diabetes, hypertension, metabolic syndrome, and cardiovascular disease risk. Improvement in renal function is seen, but adverse effects like oxalate nephropathy can lead to chronic kidney disease or end-stage renal disease (CKD/ESRD). Surgery can also lead to micronutrient deficiencies, making dietary supplementation necessary. Reduction in insulin resistance and hypertension after surgery makes medication adjustment imperative. Improvement in comorbidities and nutritional deficiencies after bariatric surgery has important clinical implications.

Big breathing: the complex interaction of obesity, hypoventilation, weight loss, and respiratory function

Obesity places a significant load on the respiratory system, affecting lung volumes, respiratory muscle function, work of breathing, and ventilatory control. Despite this, most morbidly obese individuals maintain eucapnia. However, a subgroup of morbidly obese individuals will develop chronic daytime hypercapnia, described as the obesity hypoventilation syndrome (OHS). While obesity is obviously a crucial component of this syndrome, the relationship between excess fat accumulation and the development of awake hypercapnia is complex and extends beyond simply impairments of pulmonary mechanics and lung volumes as a consequence of obesity. Various compensatory mechanisms operate to maintain eucapnia even in the presence of extreme obesity. However, if compensation is impaired, hypoventilation will ensue. While obesity alone does not account for the development of hypoventilation, weight loss will produce significant improvements in lung function and awake gas exchange. Such improvements have the potential to substantially reduce morbidity and mortality in these individuals. Nevertheless, many individuals remain overweight despite substantial weight loss, with persistence of upper airway obstruction. Attention to this residual abnormality is important given the high incidence of cardiovascular abnormalities, including pulmonary hypertension, in individuals with OHS.