Benefits at 1 year of nocturnal intermittent positive pressure ventilation in patients with obesity-hypoventi lation syndrome

Effectiveness of CPAP vs. Noninvasive Ventilation Based on Disease Severity in Obesity Hypoventilation Syndrome and Concomitant Severe Obstructive Sleep Apnea

RATIONALE

Obesity hypoventilation syndrome (OHS) with concomitant severe obstructive sleep apnea (OSA) is treated with CPAP or noninvasive ventilation (NIV) during sleep. NIV is costlier, but may be advantageous because it provides ventilatory support. However, there are no long-term trials comparing these treatment modalities based on OHS severity.

OBJECTIVE

To determine if CPAP have similar effectiveness when compared to NIV according to OHS severity subgroups.

METHODS

Post hoc analysis of the Pickwick randomized clinical trial in which 215 ambulatory patients with untreated OHS and concomitant severe OSA, defined as apnoea-hypopnea index (AHI)≥30events/h, were allocated to NIV or CPAP. In the present analysis, the Pickwick cohort was divided in severity subgroups based on the degree of baseline daytime hypercapnia (PaCO₂ of 45-49.9 or ≥50mmHg). Repeated measures of PaCO₂ and PaO₂ during the subsequent 3 years were compared between CPAP and NIV in the two severity subgroups. Statistical analysis was performed using linear mixed-effects model.

RESULTS

204 patients, 97 in the NIV group and 107 in the CPAP group were analyzed. The longitudinal improvements of PaCO₂ and PaO₂ were similar between CPAP and NIV based on the PaCO₂ severity subgroups.

CONCLUSION

In ambulatory patients with OHS and concomitant severe OSA who were treated with NIV or CPAP, long-term NIV therapy was similar to CPAP in improving awake hypercapnia, regardless of the severity of baseline hypercapnia. Therefore, in this patient population, the decision to prescribe CPAP or NIV cannot be solely based on the presenting level of PaCO₂.

Diagnosis and Management of Obesity Hypoventilation Syndrome during Labor

Obesity hypoventilation syndrome (OHS) is a disorder in which patients with a body mass index ≥30 kg/m² develop awake hypercapnia with a partial pressure of carbon dioxide ≥45 mm Hg, in the absence of other diseases that may produce alveolar hypoventilation. Additional clinical features include sleep disordered breathing, restrictive lung disease, polycythemia, hypoxemia, and an increased serum bicarbonate concentration (≥27 mEq/L). Anesthesia providers should be familiar with OHS because it is often undiagnosed, it is associated with a higher mortality rate than obstructive sleep apnea, and it is projected to increase in prevalence along with the obesity epidemic. In this case, a 33-year-old obese woman with presumed OHS developed respiratory acidosis during induction of labor. Continuous positive airway pressure treatment was initiated, but the patient continued to have hypercapnia. A cesarean delivery was recommended. The patient had baseline orthopnea due to her body habitus; thus, despite adequate labor analgesia, a cesarean delivery was completed with general endotracheal anesthesia. We believe this patient had OHS despite a serum bicarbonate <27 mEq/L, a partial pressure of oxygen >70 mm Hg, and a hemoglobin <16 g/dL, which would typically rule out OHS. Pregnant women experience a decrease in serum bicarbonate concentration due to progesterone-mediated hyperventilation, an increase in arterial oxygenation from increased minute ventilation and higher cardiac output, and a decrease in hemoglobin due to the physiologic anemia of pregnancy. Thus, OHS may be defined differently in pregnant than in non-pregnant patients.

A network meta-analysis of different positive airway pressure interventions in obesity hypoventilation syndrome

Continuous positive airway pressure (CPAP) and different types of non-invasive ventilation (NIV) have been studied in obesity hypoventilation syndrome such as bi-level PAP with back-up rate (BPAP-BUR), BPAP without BUR, and the new hybrid devices that target a pre-set volume by adjustment of pressure support (VT-PS). Although several studies have compared one PAP intervention with the other, none has compared all four in a head-to-head design, which formed the basis of this network meta-analysis. PubMed and Web of Science were searched for potentially includable randomised active comparator trials. Changes in partial pressure of carbon dioxide (PaCO₂ ) and Epworth Sleepiness Score (ESS) were the primary outcomes of interest. Network meta-analysis was done in R program using the 'frequentist' framework. A total of seven trials were included. Only VT-PS and BPAP-BUR showed statistically significant reductions in PaCO₂ compared to control, with no significant inter-PAP differences except for the comparison between VT-PS and CPAP. Only VT-PS showed a statistically significant improvement in ESS as compared to control, with no other significant inter-PAP differences. P-score ranking (based on effect size and standard errors) and Hasse diagram ranked VT-PS and BPAP as superior to other PAPs for both primary outcomes. There were no significant differences between the different PAP interventions for hospital or emergency department admissions. The results of this network meta-analysis suggest superiority of VT-PS and BPAP over other PAP interventions at least for daytime hypercapnia and subjective daytime somnolence.

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.

Long-term Noninvasive Ventilation in Obesity Hypoventilation Syndrome Without Severe OSA: The Pickwick Randomized Controlled Trial

BACKGROUND

Noninvasive ventilation (NIV) is an effective form of treatment in obesity hypoventilation syndrome (OHS) with severe OSA. However, there is paucity of evidence in patients with OHS without severe OSA phenotype.

RESEARCH QUESTION

Is NIV effective in OHS without severe OSA phenotype?

STUDY DESIGN AND METHODS

In this multicenter, open-label parallel group clinical trial performed at 16 sites in Spain, we randomly assigned 98 stable ambulatory patients with untreated OHS and apnea-hypopnea index < 30 events/h (ie, no severe OSA) to NIV or lifestyle modification (control group) using simple randomization through an electronic database. The primary end point was hospitalization days per year. Secondary end points included other hospital resource utilization, incident cardiovascular events, mortality, respiratory functional tests, BP, quality of life, sleepiness, and other clinical symptoms. Both investigators and patients were aware of the treatment allocation; however, treating physicians from the routine care team were not aware of patients' enrollment in the clinical trial. The study was stopped early in its eighth year because of difficulty identifying patients with OHS without severe OSA. The analysis was performed according to intention-to-treat and per-protocol principles and by adherence subgroups.

RESULTS

Forty-nine patients in the NIV group and 49 in the control group were randomized, and 48 patients in each group were analyzed. During a median follow-up of 4.98 years (interquartile range, 2.98-6.62), the mean hospitalization days per year ± SD was 2.60 ± 5.31 in the control group and 2.71 ± 4.52 in the NIV group (adjusted rate ratio, 1.07; 95% CI, 0.44-2.59; P = .882). NIV therapy, in contrast with the control group, produced significant longitudinal improvement in Paco₂, pH, bicarbonate, quality of life (Medical Outcome Survey Short Form 36 physical component), and daytime sleepiness. Moreover, per-protocol analysis showed a statistically significant difference for the time until the first ED visit favoring NIV. In the subgroup with high NIV adherence, the time until the first event of hospital admission, ED visit, and mortality was longer than in the low adherence subgroup. Adverse events were similar between arms.

INTERPRETATION

In stable ambulatory patients with OHS without severe OSA, NIV and lifestyle modification had similar long-term hospitalization days per year. A more intensive program aimed at improving NIV adherence may lead to better outcomes. Larger studies are necessary to better determine the long-term benefit of NIV in this subgroup of OHS.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT01405976; URL: www.clinicaltrials.gov.

Integrated Care Intervention Supported by a Mobile Health Tool for Patients Using Noninvasive Ventilation at Home: Randomized Controlled Trial

BACKGROUND

Home-based noninvasive ventilation has proven cost-effective. But, adherence to therapy still constitutes a common clinical problem. We hypothesized that a behavioral intervention supported by a mobile health (mHealth) app could enhance patient self-efficacy. It is widely accepted that mHealth-supported services can enhance productive interactions among the stakeholders involved in home-based respiratory therapies.

OBJECTIVE

This study aimed to measure changes in self-efficacy in patients with chronic respiratory failure due to diverse etiologies during a 3-month follow-up period after the intervention. Ancillary objectives were assessment of usability and acceptability of the mobile app as well as its potential contribution to collaborative work among stakeholders.

METHODS

A single-blind, single-center, randomized controlled trial was conducted between February 2019 and June 2019 with 67 adult patients with chronic respiratory failure undergoing home-based noninvasive ventilation. In the intervention group, a psychologist delivered a face-to-face motivational intervention. Follow-up was supported by a mobile app that allowed patients to report the number of hours of daily noninvasive ventilation use and problems with the therapy. Advice was automatically delivered by the mobile app in case of a reported problem. The control group received usual care. The primary outcome was the change in the Self Efficacy in Sleep Apnea questionnaire score. Secondary outcomes included app usability, app acceptability, continuity of care, person-centered care, and ventilatory parameters.

RESULTS

Self-efficacy was not significantly different in the intervention group after the intervention (before: mean 3.4, SD 0.6; after: mean 3.4, SD 0.5, P=.51). No changes were observed in adherence to therapy nor quality of life. Overall, the mHealth tool had a good usability score (mean 78 points) and high acceptance rate (mean score of 7.5/10 on a Likert scale). It was considered user-friendly (mean score of 8.2/10 on a Likert scale) and easy to use without assistance (mean score of 8.5/10 on a Likert scale). Patients also scored the perception of continuity of care and person-centered care as high.

CONCLUSIONS

The integrated care intervention supported by the mobile app did not improve patient self-management. However, the high acceptance of the mobile app might indicate potential for enhanced communication among stakeholders. The study identified key elements required for mHealth tools to provide effective support to collaborative work and personalized care.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03932175; https://clinicaltrials.gov/ct2/show/NCT03932175.

Cost-effectiveness of positive airway pressure modalities in obesity hypoventilation syndrome with severe obstructive sleep apnoea

BACKGROUND

Obesity hypoventilation syndrome (OHS) is treated with either non-invasive ventilation (NIV) or CPAP, but there are no long-term cost-effectiveness studies comparing the two treatment modalities.

OBJECTIVES

We performed a large, multicentre, randomised, open-label controlled study to determine the comparative long-term cost and effectiveness of NIV versus CPAP in patients with OHS with severe obstructive sleep apnoea (OSA) using hospitalisation days as the primary outcome measure.

METHODS

Hospital resource utilisation and within trial costs were evaluated against the difference in effectiveness based on the primary outcome (hospitalisation days/year, transformed and non-transformed in monetary term). Costs and effectiveness were estimated from a log-normal distribution using a Bayesian approach. A secondary analysis by adherence subgroups was performed.

RESULTS

In total, 363 patients were selected, 215 were randomised and 202 were available for the analysis. The median (IQR) follow-up was 3.01 (2.91-3.14) years for NIV group and 3.00 (2.92-3.17) years for CPAP. The mean (SD) Bayesian estimated hospital days was 2.13 (0.73) for CPAP and 1.89 (0.78) for NIV. The mean (SD) Bayesian estimated cost per patient/year in the NIV arm, excluding hospitalisation costs, was €2075.98 (91.6), which was higher than the cost in the CPAP arm of €1219.06 (52.3); mean difference €857.6 (105.5). CPAP was more cost-effective than NIV (99.5% probability) because longer hospital stay in the CPAP arm was compensated for by its lower costs. Similar findings were observed in the high and low adherence subgroups.

CONCLUSION

CPAP is more cost-effective than NIV; therefore, CPAP should be the preferred treatment for patients with OHS with severe OSA.

TRIAL REGISTRATION NUMBER

NCT01405976.

Long-term clinical effectiveness of continuous positive airway pressure therapy versus non-invasive ventilation therapy in patients with obesity hypoventilation syndrome: a multicentre, open-label, randomised controlled trial

BACKGROUND

Obesity hypoventilation syndrome is commonly treated with continuous positive airway pressure or non-invasive ventilation during sleep. Non-invasive ventilation is more complex and costly than continuous positive airway pressure but might be advantageous because it provides ventilatory support. To date there have been no long-term trials comparing these treatment modalities. We therefore aimed to determine the long-term comparative effectiveness of both treatment modalities.

METHODS

We did a multicentre, open-label, randomised controlled trial at 16 clinical sites in Spain. We included patients aged 15-80 years with untreated obesity hypoventilation syndrome and an apnoea-hypopnoea index of 30 or more events per h. We randomly assigned patients, using simple randomisation through an electronic database, to receive treatment with either non-invasive ventilation or continuous positive airway pressure. Both investigators and patients were aware of the treatment allocation. The research team was not involved in deciding hospital treatment, duration of treatment in the hospital, and adjustment of medications, as well as adjudicating cardiovascular events or cause of mortality. Treating clinicians from the routine care team were not aware of the treatment allocation. The primary outcome was the number of hospitalisation days per year. The analysis was done according to the intention-to-treat principle. This study is registered with ClinicalTrials.gov, number NCT01405976.

FINDINGS

From May 4, 2009, to March 25, 2013, 100 patients were randomly assigned to the non-invasive ventilation group and 115 to the continuous positive airway pressure group, of which 97 patients in the non-invasive ventilation group and 107 in the continuous positive airway pressure group were included in the analysis. The median follow-up was 5·44 years (IQR 4·45-6·37) for all patients, 5·37 years (4·36-6·32) in the continuous positive airway pressure group, and 5·55 years (4·53-6·50) in the non-invasive ventilation group. The mean hospitalisation days per patient-year were 1·63 (SD 3·74) in the continuous positive airway pressure group and 1·44 (3·07) in the non-invasive ventilation group (adjusted rate ratio 0·78, 95% CI 0·34-1·77; p=0·561). Adverse events were similar between both groups.

INTERPRETATION

In stable patients with obesity hypoventilation syndrome and severe obstructive sleep apnoea, non-invasive ventilation and continuous positive airway pressure have similar long-term effectiveness. Given that continuous positive airway pressure has lower complexity and cost, continuous positive airway pressure might be the preferred first-line positive airway pressure treatment modality until more studies become available.

FUNDING

Instituto de Salud Carlos III, Spanish Respiratory Foundation, and Air Liquide Spain.

Non-invasive ventilation in obesity hypoventilation syndrome without severe obstructive sleep apnoea

Background

Non-invasive ventilation (NIV) is an effective form of treatment in patients with obesity hypoventilation syndrome (OHS) who have concomitant severe obstructive sleep apnoea (OSA). However, there is a paucity of evidence on the efficacy of NIV in patients with OHS without severe OSA. We performed a multicentre randomised clinical trial to determine the comparative efficacy of NIV versus lifestyle modification (control group) using daytime arterial carbon dioxide tension (PaCO₂) as the main outcome measure.

Methods

Between May 2009 and December 2014 we sequentially screened patients with OHS without severe OSA. Participants were randomised to NIV versus lifestyle modification and were followed for 2 months. Arterial blood gas parameters, clinical symptoms, health-related quality of life assessments, polysomnography, spirometry, 6-min walk distance test, blood pressure measurements and healthcare resource utilisation were evaluated. Statistical analysis was performed using intention-to-treat analysis.

Results

A total of 365 patients were screened of whom 58 were excluded. Severe OSA was present in 221 and the remaining 86 patients without severe OSA were randomised. NIV led to a significantly larger improvement in PaCO₂ of −6 (95% CI −7.7 to −4.2) mm Hg versus −2.8 (95% CI −4.3 to −1.3) mm Hg, (p<0.001) and serum bicarbonate of −3.4 (95% CI −4.5 to −2.3) versus −1 (95% CI −1.7 to −0.2 95% CI)  mmol/L (p<0.001). PaCO₂ change adjusted for NIV compliance did not further improve the inter-group statistical significance. Sleepiness, some health-related quality of life assessments and polysomnographic parameters improved significantly more with NIV than with lifestyle modification. Additionally, there was a tendency towards lower healthcare resource utilisation in the NIV group.

Conclusions

NIV is more effective than lifestyle modification in improving daytime PaCO₂, sleepiness and polysomnographic parameters. Long-term prospective studies are necessary to determine whether NIV reduces healthcare resource utilisation, cardiovascular events and mortality.

Trial registration number

NCT01405976; results.

Respiratory management of the obese patient undergoing surgery

As a reflection of the increasing global incidence of obesity, there has been a corresponding rise in the proportion of obese patients undergoing major surgery. This review reports the physiological effect of these changes in body composition on the respiratory system and discusses the clinical approach required to maximize safety and minimize the risk to the patient. The changes in respiratory system compliance and lung volumes, which can adversely affect pulmonary gas exchange, combined with upper airways obstruction and sleep-disordered breathing need to be considered carefully in the peri-operative period. Indeed, these challenges in the obese patient have led to a clear focus on the clinical management strategy and development of peri-operative pathways, including pre-operative risk assessment, patient positioning at induction and under anesthesia, modified approach to intraoperative ventilation and the peri-operative use of non-invasive ventilation (NIV) and continuous positive airways pressure.

Obesity hypoventilation syndrome in the critically ill

This article summarizes available data on the obesity hypoventilation syndrome and its pertinence to intensivists, outlines clinical and pathophysiologic aspects of the disease, discusses multidisciplinary treatments, and reviews the available literature on outcomes specific to the critically ill patient.

Obesity Hypoventilation Syndrome

Obesity hypoventilation syndrome is a respiratory consequence of morbid obesity that is characterized by alveolar hypoventilation during sleep and wakefulness. The disorder involves a complex interaction between impaired respiratory mechanics, ventilatory drive and sleep-disordered breathing. Early diagnosis and treatment is important, because delay in treatment is associated with significant mortality and morbidity. Available treatment options include non-invasive positive airway pressure (PAP) therapies and weight loss. There is limited long-term data regarding the effectiveness of such therapies. This review outlines the current concepts of clinical presentation, diagnostic and management strategies to help identify and treat patients with obesity-hypoventilation syndromes.

Noninvasive mechanical ventilation in patients with obesity hypoventilation syndrome. Long-term outcome and prognostic factors

INTRODUCTION

Obesity is associated with 2 closely related respiratory diseases: obesity hypoventilation syndrome (OHS) and obstructive sleep apnea-hypopnea syndrome (OSAHS). It has been shown that noninvasive ventilation during sleep produces clinical and functional improvement in these patients. The long-term survival rate with this treatment, and the difference in clinical progress in OHS patients with and without OSAHS are analyzed.

METHODOLOGY

Longitudinal, observational study with a cohort of patients diagnosed with OHS, included in a home ventilation program over a period of 12 years, divided into 2 groups: pure OHS and OSAHS-associated OHS. Bi-level positive airway pressure ventilation was administered. During the follow-up period, symptoms, exacerbations and hospitalizations, blood gas tests and pulmonary function tests, and survival rates were monitored and compared.

RESULTS

Eighty-three patients were eligible for analysis, 60 women (72.3%) and 23 men (27.7%), with a mean survival time of 8.47 years. Fifty patients (60.2%) were included in the group without OSAHS (OHS) and 33 (39.8%) in the OSAHS-associated OHS group (OHS-OSAHS). PaCO₂ in the OHS group was significantly higher than in the OHS-OSAHS group (P<.01). OHS patients also had a higher hospitalization rate (P<.05). There was a significant improvement in both groups in FEV₁ and FVC, and no differences between groups in PaCO₂ and PaO₂ values. There were no differences in mortality between the 2 groups, but low FVC values were predictive of mortality.

CONCLUSIONS

The use of mechanical ventilation in patients with OHS, with or without OSAHS, is an effective treatment for the correction of blood gases and functional alterations and can achieve prolonged survival rates.

Respiratory mechanics and ventilatory control in overlap syndrome and obesity hypoventilation

The overlap syndrome of obstructive sleep apnoea (OSA) and chronic obstructive pulmonary disease (COPD), in addition to obesity hypoventilation syndrome, represents growing health concerns, owing to the worldwide COPD and obesity epidemics and related co-morbidities. These disorders constitute the end points of a spectrum with distinct yet interrelated mechanisms that lead to a considerable health burden. The coexistence OSA and COPD seems to occur by chance, but the combination can contribute to worsened symptoms and oxygen desaturation at night, leading to disrupted sleep architecture and decreased sleep quality. Alveolar hypoventilation, ventilation-perfusion mismatch and intermittent hypercapnic events resulting from apneas and hypopneas contribute to the final clinical picture, which is quite different from the “usual” COPD. Obesity hypoventilation has emerged as a relatively common cause of chronic hypercapnic respiratory failure. Its pathophysiology results from complex interactions, among which are respiratory mechanics, ventilatory control, sleep-disordered breathing and neurohormonal disturbances, such as leptin resistance, each of which contributes to varying degrees in individual patients to the development of obesity hypoventilation. This respiratory embarrassment takes place when compensatory mechanisms like increased drive cannot be maintained or become overwhelmed.

Although a unifying concept for the pathogenesis of both disorders is lacking, it seems that these patients are in a vicious cycle. This review outlines the major pathophysiological mechanisms believed to contribute to the development of these specific clinical entities. Knowledge of shared mechanisms in the overlap syndrome and obesity hypoventilation may help to identify these patients and guide therapy.

Correlates of a prescription for Bilevel positive airway pressure for treatment of obstructive sleep apnea among veterans

INTRODUCTION

The acceptance of portable home-based polysomnography together with auto-titrating CPAP has bypassed the need for a laboratory polysomnography. Since bilevel airway pressure (BPAP) is titrated in the sleep lab, patients diagnosed using portable home-based polysomnography may not have the opportunity to receive BPAP. It is unknown whether the patients who would have ordinarily received a BPAP would benefit from it. We determine correlates of receiving BPAP and of being switched from BPAP to CPAP. We examine whether patients with these correlates have better adherence to BPAP versus CPAP.

METHODS

Retrospective Cohort Study (Correlates at baseline) of 2,513 VA patients with a sleep study between January 2003 and October 2006 and receiving continuous or bilevel positive airway pressure (CPAP [N = 2,251]) or BPAP [N = 262]) by the end of 2007. PAP adherence up to 30 months was assessed.

RESULTS

Significant correlates of BPAP were older age (p < 0.001), higher BMI and CHF (p < 0.01), COPD (p < 0.001), higher blood CO₂ (p < 0.05), higher AHI and OSA severity (p < 0.001), lower nadir SpO₂ (p < 0.001), and greater sleepiness (ESS) (p < 0.01). Patients on BPAP were more adherent to PAP therapy (p < 0.01), but the association largely disappeared following adjustment for BPAP correlates. There was preliminary evidence that these correlates predict long-term adherence to PAP therapy regardless of mode.

CONCLUSIONS

We identified baseline factors that can help clinicians decide whether to prescribe an auto-BPAP as first-line therapy and that predict good long-term PAP adherence.

Efficacy of noninvasive mechanical ventilation in obese patients with chronic respiratory failure

Chronic respiratory failure (CRF) develops in a minority of obese patients. Noninvasive mechanical ventilation (NIMV) is a new optional treatment for such patients. The aim of this study was to evaluate the effectiveness of NIMV in obese patients with CRF. The material of the study consisted of 34 obese patients (body mass index 47.3 ± 7.9 kg/m(2)) with CRF (PaO2 = 6.40 ± 0.93 kPa and PaCO2 = 8.67 ± 2.13 kPa) who were hypoxemic despite an optimal therapy. Thirteen patients had an overlap syndrome (OS) - chronic obstructive pulmonary disease (COPD) coexisting with obstructive sleep apnea syndrome (OSAS) and 21 patients had obesity-hypoventilation syndrome (OHS). Ventilation parameters were determined during polysomnography. The efficacy of NIMV was evaluated on the fifth day and after 1 year's home treatment. We observed a significant increase in the mean blood oxygen saturation during sleep in all patients; the increase was greater in patients with OHS (92.6 ± 1.4 %) than in patients with OS (90.4 ± 1.8 %). There was a significant improvement of diurnal PaO2 and PaCO2 on the fifth day of NIMV (mean PaO2 increase 2.1 kPa and PaCO2 decrease 0.9 kPa) and also after 1 year of home NIMV (mean PaO2 increase 1.9 kPa and PaCO2 decrease 2.4 kPa). Only one patient stopped treatment because of lack of tolerance during the observation period (1-3 years). In conclusion, NIMV is an effective and well tolerated treatment option in obese patients with CRF resulting in a rapid relief of respiratory disorders during sleep and a gradual, long-term improvement of gas exchange during the day, particularly in patients with OHS.

Positive pressure for obesity hypoventilation syndrome

Obesity is increasing world-wide; obesity hypoventilation syndrome (OHS), formerly Pickwickian syndrome, has increased in parallel. Despite its prevalence, OHS has not been studied well, but there is abundant evidence that it is tightly linked with sleep-disordered breathing, most commonly obstructive sleep apnea. This article reviews the pathophysiology of OHS as well as the literature regarding the benefits of treating this disorder with positive airway pressure. We also emphasize that while positive pressure treatments may temporize cardiopulmonary disease progression, simultaneous pursuit of weight reduction is central to long-term management of this condition.

Noninvasive ventilation in mild obesity hypoventilation syndrome: a randomized controlled trial

OBJECTIVE

Open studies suggest that treatment of obesity hypoventilation syndrome (OHS) by noninvasive ventilation (NIV) restores sleep quality and daytime vigilance and reduces cardiovascular morbidity. However, to our knowledge no randomized controlled trial (RCT) comparing NIV to conservative measures is available in the field. The goal of this study was to assess in patients with OHS, during an RCT, effects of 1-month NIV compared with lifestyle counseling on blood gas measurements, sleep quality, vigilance, and cardiovascular, metabolic, and inflammatory parameters.

METHODS

Thirty-five patients in whom OHS was newly diagnosed were randomized either to the NIV group or the control group represented by lifestyle counseling. Assessments included blood gas levels, subjective daytime sleepiness, metabolic parameters, inflammatory (hsCRP, leptin, regulated upon activation normal T-cell express and secreted [RANTES], monocyte chemoattractant protein-1, IL-6, IL-8, tumor necrosis factor-α, resistin) and antiinflammatory (adiponectin, IL-1-RA) cytokines, sleep studies, endothelial function (reactive hyperemia measured by peripheral arterial tonometry [RH-PAT]), and arterial stiffness.

RESULTS

Despite randomization, NIV group patients (n = 18) were older (58 ± 11 years vs 54 ± 6 years) with a higher baseline Paco(2) (47.9 ± 4.2 mm Hg vs 45.2 ± 3 mm Hg). In intention-to-treat analysis, compared with control group, NIV treatment significantly reduced daytime Paco(2) (difference between treatments: -3.5 mm Hg; 95% CI, -6.2 to -0.8) and apnea-hypopnea index (-40.3/h; 95% CI, -62.4 to -18.2). Sleep architecture was restored, although nonrespiratory microarousals increased (+9.4/h of sleep; 95% CI, 1.9-16.9), and daytime sleepiness was not completely normalized. Despite a dramatic improvement in sleep hypoxemia, glucidic and lipidic metabolism parameters as well as cytokine profiles did not vary significantly. Accordingly, neither RH-PAT (+0.02; 95% CI, -0.24 to 0.29) nor arterial stiffness (+0.22 m/s; 95% CI, -1.47 to 1.92) improved.

CONCLUSIONS

One month of NIV treatment, although improving sleep and blood gas measurements dramatically, did not change inflammatory, metabolic, and cardiovascular markers.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT00603096; URL: www.clinicaltrials.gov.

Respiratory complications of obesity

Obesity, well known as a cardiovascular risk factor, can also lead to significant respiratory complications. The respiratory changes associated with obesity extend from a simple change in respiratory function, with no effect on gas exchange, to the more serious condition of hypercapnic respiratory failure, characteristic of obesity hypoventilation syndrome. More recently, it has been reported that there is an increased prevalence of asthma which is probably multifactorial in origin, but in which inflammation may play an important role. Hypoventilation in the obese subject is the result of complex interactions that involve changes in the ventilatory mechanics and anomalies in breathing control. Two other conditions (COPD and sleep apnea-hypopnea syndrome [SAHS], often present in obese patients, can trigger or aggravate it. The prevalence of hypoventilation in the obese is under-estimated and the diagnosis is usually established during an exacerbation, or when the patient is studied due to suspicion of SAHS. Ventilatory management of these patients includes either CPAP or NIV. The choice of one or another will depend on the underlying clinical condition and whether or not there is another comorbidity. Both NIV and CPAP have demonstrated their effectiveness, not only in the control of gas exchange, but also in improving the quality of life and survival of these patients.

Hypoventilation syndromes

A wide variety of mechanisms can lead to the hypoventilation associated with various medical disorders, including derangements in central ventilatory control, mechanical impediments to breathing, and abnormalities in gas exchange leading to increased dead space ventilation. The pathogenesis of hypercapnia in obesity hypoventilation syndrome remains somewhat obscure, although in many patients comorbid obstructive sleep apnea appears to play an important role. Hypoventilation in neurologic or neuromuscular disorders is primarily explained by weakness of respiratory muscles, although some central nervous system diseases may affect control of breathing. In other chest wall disorders, obstructive airways disease, and cystic fibrosis, much of the pathogenesis is explained by mechanical impediments to breathing, but an element of increased dead space ventilation also often occurs. Central alveolar hypoventilation syndrome involves a genetically determined defect in central respiratory control. Treatment in all of these disorders involves coordinated management of the primary disorder (when possible) and, increasingly, the use of noninvasive positive pressure ventilation.

Can improving sleep influence sleep-disordered breathing?

Sleep-disordered breathing (SDB) encompasses a group of disorders that include obstructive sleep apnoea (OSA), central sleep apnoea (CSA) and nocturnal hypoventilation. SDB commonly coexists with sleep disorders such as insomnia and restless legs syndrome, and sleep deprivation has been shown to play a role in the pathogenesis of SDB. Participants of a workshop, held at the 6th annual meeting of The International Sleep Disorders Forum: The Art of Good Sleep in 2008, evaluated whether the effective management of sleep disorders could result in a reduction in SDB. Following the workshop, a critical review of the literature in the field of sleep and SDB was conducted in order to assess the impact of improving sleep on SDB, and to determine whether measures taken to improve sleep result in a subsequent improvement in SDB. Results showed that studies evaluating the influence of improved sleep on respiratory abnormalities in patients with SDB are lacking. Studies in patients with OSA, with or without obesity-hypoventilation syndrome, show that therapy with continuous positive airways pressure and non-invasive ventilation improves sleep parameters with beneficial effects on SDB. Studies involving small numbers of patients have shown that the antidepressants fluoxetine and mirtazapine produce improvements in sleep parameters and the apnoea-hypopnoea index, and that acetazolamide may improve CSA. The benzodiazepines flurazepam, temazepam and nitrazepam, the hypnotic zolpidem, the melatonin receptor agonist ramelteon and gamma-hydroxybutyrate have all been shown to improve sleep, but are not associated with reductions or worsening in SDB. It is clear that there is a distinct knowledge gap with regard to the benefit of improving sleep disturbances for subsequent improvements in SDB. Randomized controlled clinical trials investigating the effect of pharmacological and non-pharmacological improvement of sleep disorders focusing on whether there is improvement in coexisting OSA/SDB are clearly needed. Furthermore, well-designed clinical trials investigating the role of hypnotic agents in improving SDB in certain phenotypes will enable the development of treatment recommendations for primary care physicians managing these patients in routine clinical practice.

The pickwickian syndrome-obesity hypoventilation syndrome

Obesity-hypoventilation syndrome (OHS), also historically described as the Pickwickian syndrome, consists of the triad of obesity, sleep disordered breathing, and chronic hypercapnia during wakefulness in the absence of other known causes of hypercapnia. Its exact prevalence is unknown, but it has been estimated that 10% to 20% of obese patients with obstructive sleep apnea have hypercapnia. OHS often remains undiagnosed until late in the course of the disease. Early recognition is important because these patients have significant morbidity and mortality. Effective treatment can lead to significant improvement in patient outcomes, underscoring the importance of early diagnosis. The authors review the definition and epidemiology of OHS, in addition to the current multifaceted understanding of the pathophysiology, and provide useful clinical approaches to diagnosis and treatment.

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.

Upper airway mechanics

This review discusses the pathophysiological aspects of sleep-disordered breathing, with focus on upper airway mechanics in obstructive and central sleep apnoea, Cheyne-Stokes respiration and obesity hypoventilation syndrome. These disorders constitute the end points of a spectrum with distinct yet interrelated mechanisms that lead to substantial pathology, i.e. increased upper airway collapsibility, control of breathing instability, increased work of breathing, disturbed ventilatory system mechanics and neurohormonal changes. Concepts are changing. Although sleep apnoea is considered more and more to be an increased loop gain disorder, the central type of apnoea is now considered as an obstructive event, because it causes pharyngeal narrowing, associated with prolonged expiration. Although a unifying concept for the pathogenesis is lacking, it seems that these patients are in a vicious circle. Knowledge of common patterns of sleep-disordered breathing may help to identify these patients and guide therapy.

Assessment and management of patients with obesity hypoventilation syndrome

Obesity hypoventilation syndrome (OHS) is characterized by obesity, daytime hypercapnia, and sleep-disordered breathing in the absence of significant lung or respiratory muscle disease. Compared with eucapnic morbidly obese patients and eucapnic patients with sleep-disordered breathing, patients with OHS have increased health care expenses and are at higher risk of developing serious cardiovascular disease leading to early mortality. Despite the significant morbidity and mortality associated with this syndrome, diagnosis and institution of effective treatment occur late in the course of the syndrome. Given that the prevalence of extreme obesity has increased considerably, it is likely that clinicians will encounter patients with OHS in their clinical practice. Therefore maintaining a high index of suspicion can lead to early recognition and treatment reducing the high burden of morbidity and mortality and related health care expenditure associated with undiagnosed and untreated OHS. In this review we define the clinical characteristics of the syndrome and review the pathophysiology, morbidity, and mortality associated with it. Last, we discuss currently available treatment modalities.

Current perspectives on the obesity hypoventilation syndrome

PURPOSE OF REVIEW

Identifying and treating obesity hypoventilation syndrome is an important therapeutic goal, especially given the high morbidity and mortality associated with untreated disease. Significant weight loss or effective treatment of upper airway obstruction will reverse daytime hypoventilation, suggesting that these two mechanisms play key roles in the development and progression of this disorder. Only a subset of morbidly obese patients will develop awake hypercapnia, however, even in the presence of sleep disordered breathing. This implies that complex interplay between a number of known and unknown mechanisms is needed to produce daytime respiratory failure in this patient population.

RECENT FINDINGS

Work in the mouse model of obesity has been central in advancing our understanding of the role leptin plays in stimulating ventilation. Leptin deficiency or development of leptin resistance in obesity leads to alterations in central respiratory drive and reduced ventilatory responsiveness, permitting development of carbon dioxide retention. Changes in neuromodulators resulting from the effects of hypoxia may further exacerbate the problem by depressing arousal from sleep in the face of abnormal breathing.

SUMMARY

Understanding the various mechanisms contributing to development of obesity hypoventilation is important in order to identify new approaches to effective long-term management of this disorder.

Sleep-related hypoventilation/hypoxemic syndromes

The latest edition of The International Classification of Sleep Disorders: Diagnostic and Coding Manual subsumes a broad range of disorders under the heading "Sleep Related Hypoventilation/Hypoxemic Syndromes." Some are quite common, such as COPD with worsening gas exchange during sleep; while some are exceedingly rare, such as congenital central hypoventilation syndrome. All share the attribute of abnormal gas exchange that worsens, or may only be present, during sleep. The sleep state, the sleeping posture, and the circadian rhythm driving sleep all may affect respiration by altering control of breathing and/or pulmonary mechanics. These changes are largely inconsequential in the normal individual but interact with respiratory, neurologic, or neuromuscular disease to manifest as the sleep-related hypoventilation/hypoxemic syndromes. In addition to optimal treatment of the underlying disorder (when known and when possible), treatment usually involves nocturnal ventilatory support that is now most commonly provided by noninvasive positive pressure ventilation.

Obesity hypoventilation syndrome: hypoxemia during continuous positive airway pressure

BACKGROUND

Polysomnography findings between matched groups with obstructive sleep apnea (OSA) and OSA plus obesity-hypoventilation syndrome (OHS) before and after continuous positive airway pressure (CPAP), particularly in the extremely severe obese (body mass index [BMI] >or= 50 kg/m2), are unclear.

DESIGN

Prospective study of subjects (BMI >or= 50 kg/m2) undergoing diagnostic polysomnography. Subjects with an apnea-hypopnea index (AHI) >or= 15/h underwent a second polysomnography with CPAP. The effect of 1 night of CPAP on sleep architecture, AHI, arousal indexes, and nocturnal oxygenation was assessed. OHS was defined as those subjects with obesity, PaCo2 > 45 mm Hg, and PaO2 < 70 mm Hg in the absence of lung disease.

RESULTS

Twenty-three subjects with moderate-to-severe OSA and 23 subjects with moderate-to-severe OSA plus OHS underwent a 1-night trial of CPAP. Both groups were matched for spirometry, BMI, and AHI, but oxygen desaturation was worse in the OSA-plus-OHS group. CPAP significantly improved rapid eye movement (REM) duration (p < 0.005), AHI (p < 0.005), arousal indexes (p < 0.005), and percentage of total sleep time (TST) with oxygen saturation (SpO2) < 90% (p < 0.005) in both groups. In subjects with OSA plus OHS, 43% continued to spend > 20% of TST with SpO2 < 90%, compared to 9% of the OSA group, despite the adequate relief of upper airway obstruction.

CONCLUSIONS

Extremely severe obese subjects (BMI >or= 50 kg/m2) with moderate-to-severe OSA plus OHS exhibit severe oxygen desaturation but similar severities of AHI, arousal indexes, and sleep architecture abnormalities when compared to matched subjects without OHS. CPAP significantly improves AHI, REM duration, arousal indexes, and nocturnal oxygen desaturation. Some subjects with OHS continued to have nocturnal desaturation despite the control of upper airway obstruction; other mechanisms may contribute. Further long-term studies assessing the comparative role of CPAP and bilevel ventilatory support in such subjects with OHS is warranted.

Clinical Heterogeneity among Patients with Obesity Hypoventilation Syndrome: Therapeutic Implications

BACKGROUND

Obesity hypoventilation syndrome (OHS) can be treated with noninvasive positive pressure ventilation (NIPPV). Once clinical stability is achieved, continuous positive airway pressure (CPAP) can be recommended in many cases. However, some patients respond only partially to CPAP and NIPPV is a better option for them.

OBJECTIVES

To assess treatment effectiveness in 2 groups of patients: those who could be switched to CPAP after polysomnographic titration and those who required NIPPV.

METHODS

A prospective study of 24 OHS patients was conducted, 11 were treated with CPAP and 13 with NIPPV. Morning and evening arterial blood gases were measured. Daytime and overnight oximetric recordings were performed. A post hoc analysis compared both groups.

RESULTS

Neither group exhibited deterioration on morning-to-evening blood gases. All patients in the CPAP group presented SaO(2) of less than 90% (CT90%) for <15% of the time on nocturnal and daytime recordings. In the NIPPV group, 8 patients had either daytime or nocturnal CT90% >or=15%. There were no intergroup differences regarding age, body mass index, Epworth scale values or PaO(2)/PaCO(2) prior to treatment. FVC in the NIPPV group was lower than in the CPAP group (p = 0.01). Apnea-hypopnea index was higher (56 +/- 23 vs. 36 +/- 23, p = 0.049) and baseline CT90% was lower (76 +/- 19% vs. 92 +/- 14%, p = 0.03) in the CPAP group.

CONCLUSIONS

Two patient subtypes can be identified. Those controlled with CPAP have better spirometry and a significantly higher apnea-hypopnea index. None of these patients showed daytime hypoxemia and all exhibited satisfactory overnight oxygenation. However, 61% of the NIPPV group had suboptimal oximetry results. Nocturnal/diurnal oximetries should be made to assess treatment efficacy in stable OHS patients who fail to achieve good control with CPAP.

Non-invasive positive ventilation in the treatment of sleep-related breathing disorders

This chapter addresses the use of long-term non-invasive positive pressure ventilation (NIPPV) (to the exclusion of continuous positive airway pressure) in the different clinical settings in which it is currently proposed: principally in diseases responsible for hypoventilation characterized by elevated PaCO(2). Nasal masks are predominantly used, followed by nasal pillow and facial masks. Mouthpieces are essentially indicated in case daytime ventilation is needed. Many clinicians currently prefer pressure-preset ventilator in assist mode as the first choice for the majority of the patients with the view of offering better synchronization. Nevertheless, assist-control mode with volume-preset ventilator is also efficient. The settings of the ventilator must insure adequate ventilation assessed by continuous nocturnal records of at least oxygen saturation of haemoglobin-measured by pulse oximetry. The main categories of relevant diseases include different types of neuromuscular disorders, chest-wall deformities and even lung diseases. Depending on the underlying diseases and on individual cases, two schematic situations may be individualized. Either intermittent positive pressure ventilation (IPPV) is continuously mandatory to avoid death in the case of complete or quasi-complete paralysis or is used every day for several hours, typically during sleep, producing enough improvement to allow free time during the daylight in spontaneous breathing while hypoventilation and related symptoms are improved. In case of complete or quasi-complete need of mechanical assistance, a tracheostomy may become an alternative to non-invasive access. In neuromuscular diseases, in kyphosis and in sequela of tuberculosis patients, NIPPV always significantly increases survival. Conversely, no data support a positive effect on survival in chronic obstructive pulmonary disease.