Effects of non-invasive ventilation on sleep in chronic hypercapnic respiratory failure

Chronic respiratory disease can exacerbate the normal physiological changes in ventilation observed in healthy individuals during sleep, leading to sleep-disordered breathing, nocturnal hypoventilation, sleep disruption and chronic respiratory failure. Therefore, patients with obesity, slowly and rapidly progressive neuromuscular disease and chronic obstructive airways disease report poor sleep quality. Non-invasive ventilation (NIV) is a complex intervention used to treat sleep-disordered breathing and nocturnal hypoventilation with overnight physiological studies demonstrating improvement in sleep-disordered breathing and nocturnal hypoventilation, and clinical trials demonstrating improved outcomes for patients. However, the impact on subjective and objective sleep quality is dependent on the tools used to measure sleep quality and the patient population. As home NIV becomes more commonly used, there is a need to conduct studies focused on sleep quality, and the relationship between sleep quality and health-related quality of life, in all patient groups, in order to allow the clinician to provide clear patient-centred information.

Ketogenic diet acutely improves gas exchange and sleep apnoea in obesity hypoventilation syndrome: A non-randomized crossover study

BACKGROUND AND OBJECTIVE

Obesity hypoventilation syndrome (OHS) causes hypercapnia which is often refractory to current therapies. We examine whether hypercapnia in OHS can be improved by a ketogenic dietary intervention.

METHODS

We conducted a single-arm crossover clinical trial to examine the impact of a ketogenic diet on CO2 levels in patients with OHS. Patients were instructed to adhere to 1 week of regular diet, 2 weeks of ketogenic diet, followed by 1 week of regular diet in an ambulatory setting. Adherence was assessed with capillary ketone levels and continuous glucose monitors. At weekly visits, we measured blood gases, calorimetry, body composition, metabolic profiles, and sleep studies. Outcomes were assessed with linear mixed models.

RESULTS

A total of 20 subjects completed the study. Blood ketones increased from 0.14 ± 0.08 during regular diet to 1.99 ± 1.11 mmol/L (p < 0.001) after 2 weeks of ketogenic diet. Ketogenic diet decreased venous CO2 by 3.0 mm Hg (p = 0.008), bicarbonate by 1.8 mmol/L (p = 0.001), and weight by 3.4 kg (p < 0.001). Sleep apnoea severity and nocturnal oxygen levels significantly improved. Ketogenic diet lowered respiratory quotient, fat mass, body water, glucose, insulin, triglycerides, leptin, and insulin-like growth factor 1. Rebound hypercapnia was observed after resuming regular diet. CO2 lowering was dependent on baseline hypercapnia, and associated with circulating ketone levels and respiratory quotient. The ketogenic diet was well tolerated.

CONCLUSION

This study demonstrates for the first time that a ketogenic diet may be useful for control of hypercapnia and sleep apnoea in patients with obesity hypoventilation syndrome.

Effects of sex, age, and body mass index on serum bicarbonate

Rationale

Obesity hypoventilation syndrome (OHS) is often underdiagnosed, with significant morbidity and mortality. Bicarbonate, as a surrogate of arterial carbon dioxide, has been proposed as a screening tool for OHS. Understanding the predictors of serum bicarbonate could provide insights into risk factors for OHS. We hypothesized that the bicarbonate levels would increase with an increase in body mass index (BMI), since the prevalence of OHS increases with obesity.

Methods

We used the TriNetX Research Network, an electronic health record database with de-identified clinical data from participating healthcare organizations across the United States, to identify 93,320 adults without pulmonary or advanced renal diseases who had serum bicarbonate and BMI measurements within 6 months of each other between 2017 and 2022. We used linear regression analysis to examine the associations between bicarbonate and BMI, age, and their interactions for the entire cohort and stratified by sex. We also applied a non-linear machine learning algorithm (XGBoost) to examine the relative importance of age, BMI, sex, race/ethnicity, and obstructive sleep apnea (OSA) status on bicarbonate.

Results

This cohort population was 56% women and 72% white and 80% non-Hispanic individuals, with an average (SD) age of 49.4 (17.9) years and a BMI of 29.1 (6.1) kg/m2. The mean bicarbonate was 24.8 (2.8) mmol/L, with higher levels in men (mean 25.2 mmol/L) than in women (mean 24.4 mmol/L). We found a small negative association between bicarbonate and BMI, with an expected change of -0.03 mmol/L in bicarbonate for each 1 kg/m2 increase in BMI (p < 0.001), in the entire cohort and both sexes. We found sex differences in the bicarbonate trajectory with age, with women exhibiting lower bicarbonate values than men until age 50, after which the bicarbonate levels were modestly higher. The non-linear machine learning algorithm similarly revealed that age and sex played larger roles in determining bicarbonate levels than the BMI or OSA status.

Conclusion

Contrary to our hypothesis, BMI is not associated with elevated bicarbonate levels, and age modifies the impact of sex on bicarbonate.

Arterial bicarbonate is associated with hypoxic burden and uncontrolled hypertension in obstructive sleep apnea - The ESADA cohort

OBJECTIVE

Blood bicarbonate concentration plays an important role for obstructive sleep apnea (OSA) patients to maintain acid-base balance. We investigated the association between arterial standard bicarbonate ([HCO3^-]) and nocturnal hypoxia as well as comorbid hypertension in OSA.

METHODS

A cross-sectional analysis of 3329 patients in the European Sleep Apnea Database (ESADA) was performed. Arterial blood gas analysis and lung function test were performed in conjunction with polysomnographic sleep studies. The 4% oxygen desaturation index (ODI), mean and minimum oxygen saturation (SpO₂), and percentage of time with SpO₂ below 90% (T90%) were used to reflect nocturnal hypoxic burden. Arterial hypertension was defined as a physician diagnosis of hypertension with ongoing antihypertensive medication. Hypertensive patients with SBP/DBP below or above 140/90 mmHg were classified as controlled-, uncontrolled hypertension, respectively.

RESULTS

The [HCO3^-] level was normal in most patients (average 24.0 ± 2.5 mmol/L). ODI, T90% increased whereas mean and minimum SpO₂ decreased across [HCO3^-] tertiles (ANOVA, p = 0.030, <0.001, <0.001, and <0.001, respectively). [HCO3^-] was independently associated with ODI, mean SpO₂, minimum SpO₂, and T90% after adjusting for confounders (β value [95%CI]: 1.21 [0.88-1.54], -0.16 [-0.20 to -0.11], -0.51 [-0.64 to -0.37], 1.76 [1.48-2.04], respectively, all p < 0.001). 1 mmol/L elevation of [HCO3^-] was associated with a 4% increased odds of uncontrolled hypertension (OR: 1.04 [1.01-1.08], p = 0.013).

CONCLUSION

We first demonstrated an independent association between [HCO3^-] and nocturnal hypoxic burden as well as uncontrolled hypertension in OSA patients. Bicarbonate levels as an adjunctive measure provide insight into the pathophysiology of hypertension in OSA.

A Novel Nomogram and Online Calculator for Predicting the Risk of Obesity Hypoventilation Syndrome in Bariatric Surgery Candidates

BACKGROUND

Obesity hypoventilation syndrome (OHS) is frequently misdiagnosed and undertreated, increasing the risk of perioperative complications. We aimed to determine the predictors of OHS and to develop and validate a novel nomogram and online calculator for identifying patients at risk of OHS in bariatric surgery candidates.

METHODS

We retrospectively analyzed the data of patients undergoing bariatric surgery between March 2017 and June 2020. Predictors were identified using univariate and multivariate analyses to establish the nomogram. The discriminative ability, calibration, and clinical value of the nomograms were tested using C-statistics, calibration plots, and decision curve analysis. The nomogram was internally validated using bootstrap resampling.

RESULTS

A total of 577 patients were enrolled, and OHS was presented in 17.9% (103/577). Body mass index (BMI) (odds ratio [OR], 1.11; 95% confidence interval (CI), 1.04-1.18; p = 0.001), neck circumference (OR, 1.09; 95% CI, 1.01-1.18; p = 0.035), type 2 diabetes (T2D) (OR, 2.02; 95% CI, 1.17-3.45; p = 0.011), serum bicarbonate (OR, 1.47; 95% CI, 1.30-1.67; p < 0.001), and C-reactive protein (CRP) (OR, 1.03; 95% CI, 1.01-1.06; p = 0.017) were independent risk factors for OHS and incorporated to develop the nomogram. The nomogram revealed good discrimination, with a C-index of 0.830 (95% CI: 0.784-0.876) (0.8227 through internal validation), and good calibration. Decision curve analysis further confirmed the nomogram's clinical usefulness.

CONCLUSIONS

The novel nomogram and online calculator provided an excellent preoperative individualized prediction of OHS in patients undergoing bariatric surgery, hereby potentially assisting clinicians and surgeons in the early detection and intensive monitoring of OHS.

OSA and Chronic Respiratory Disease: Mechanisms and Epidemiology

Obstructive sleep apnea (OSA) is a highly prevalent disorder that has profound implications on the outcomes of patients with chronic lung disease. The hallmark of OSA is a collapse of the oropharynx resulting in a transient reduction in airflow, large intrathoracic pressure swings, and intermittent hypoxia and hypercapnia. The subsequent cytokine-mediated inflammatory cascade, coupled with tractional lung injury, damages the lungs and may worsen several conditions, including chronic obstructive pulmonary disease, asthma, interstitial lung disease, and pulmonary hypertension. Further complicating this is the sleep fragmentation and deterioration of sleep quality that occurs because of OSA, which can compound the fatigue and physical exhaustion often experienced by patients due to their chronic lung disease. For patients with many pulmonary disorders, the available evidence suggests that the prompt recognition and treatment of sleep-disordered breathing improves their quality of life and may also alter the course of their illness. However, more robust studies are needed to truly understand this relationship and the impacts of confounding comorbidities such as obesity and gastroesophageal reflux disease. Clinicians taking care of patients with chronic pulmonary disease should screen and treat patients for OSA, given the complex bidirectional relationship OSA has with chronic lung disease.

Defining obesity hypoventilation syndrome

With increasing prevalence of obesity, the substantial contribution of obesity hypoventilation syndrome (OHS) to morbidity and mortality is likely to increase. It is therefore crucial that the condition has a clear definition to allow timely identification of patients. OHS was first described as “Pickwickian syndrome” in the 1950s; in subsequent decades, case reports did not clearly delineate between patients suffering from OHS and those suffering from obstructive sleep apnoea. In 1999, the American Academy of Sleep Medicine published a guideline that delineated the cause of daytime hypercapnia as either predominantly upper airway or predominantly hypoventilation. This was the first formal definition of OHS as the presence of daytime alveolar hypoventilation (arterial carbon dioxide tension >45 mmHg) in patients with body mass index >30 kg·m⁻² in the absence of other causes of hypoventilation. This definition is reflected in the most recent guidelines published on OHS. Recent developments in defining OHS include proposed classification systems of severity and demonstrating the value of using serum bicarbonate to exclude OHS in patients with a low index of suspicion.

Obesity hypoventilation syndrome is defined as daytime alveolar hypoventilation in obese patients in the absence of other causes of hypoventilation. Classifications of severity are now needed to target treatment at the most appropriate individuals.https://bit.ly/3yLuiL9

Severity stages of obesity-related breathing disorders - a cross-sectional cohort study

INTRODUCTION

There is a general underappreciation of the spectrum of obesity-related breathing disorders and their consequences. We therefore compared characteristics of obese patients with eucapnic obstructive sleep apnea (OSA), OSA with obesity-related sleep hypoventilation (ORSH) or obesity hypoventilation syndrome (OHS) to identify the major determinants of hypoventilation.

PATIENTS AND METHODS

In this prospective, diagnostic study (NCT04570540), obese patients with OSA, ORSH or OHS were characterized applying polysomnography with transcutaneous capnometry, blood gas analyses, bodyplethysmography and measurement of hypercapnic ventilatory response (HCVR). Pathophysiological variables known to contribute to hypoventilation and differing significantly between the groups were specified as potential independent variables in a multivariable logistic regression to identify major determinants of hypoventilation.

RESULTS

Twenty, 43 and 19 patients were in the OSA, ORSH and OHS group, respectively. BMI was significantly lower in OSA as compared to OHS. The extent of SRBD was significantly higher in OHS as compared to OSA or ORSH. Patients with ORSH or OHS showed a significantly decreased forced expiratory volume in 1 s and forced vital capacity compared to OSA. HCVR was significantly lower in OHS and identified as the major determinant of hypoventilation in a multivariable logistic regression (Nagelkerke R² = 0.346, p = 0.050, odds ratio (95%-confidence interval) 0.129 (0.017-1.004)).

CONCLUSION

Although there were differences in BMI, respiratory mechanics and severity of upper airway obstruction between groups, our data support HCVR as the major determinant of obesity-associated hypoventilation.

Determinants of bilevel therapy in the management of obstructive sleep apnea

BACKGROUND

The aim of this study was to investigate potential patient or polysomnogram (PSG) characteristics that can help determine who might benefit from bilevel positive airway pressure (BPAP) in the treatment of uncomplicated OSA.

STUDY DESIGN

This was a single center, retrospective, observational study in which 19 patients who met our inclusion criteria for BPAP were matched to 40 patients in the control group. Data on patient baseline characteristics as well as PSG results were analyzed.

RESULTS

Baseline patient and PSG characteristics were similar with the exception of shorter sleep time in the BPAP group, 290 min compared with 351 min (p = 0.005). Analysis of oxygen saturations revealed that the percent of total sleep time (TST) spent below 90% (SpO₂ < 90%) was statistically higher in BPAP group (mean 21.4% ± 23.6%) compared with CPAP (mean 9.1% ± 11.1%, p = 0.045). For every 5% increase in TST at SpO₂ < 90%, there is a 28% increase in the odds of BPAP prescription (OR = 1.276, 95%CI 1.029, 1.582, p = 0.027), and for every 10% increase, there is an increase of 63% (OR 1.627, 95%CI 1.058-2.502). The Hosmer-Lemeshow goodness-of-fit test revealed a good fit (p = 0.23). The AUC was 0.7.

CONCLUSION

There is an association between duration of hypoxemia on the PSG and the likelihood of requiring BPAP for the treatment of uncomplicated OSA. More research is needed to understand the best patient-centered therapy when initiating PAP in the management of OSA.

Predicting CPAP failure in patients with suspected sleep hypoventilation identified on ambulatory testing

STUDY OBJECTIVES

Home sleep apnea testing (HSAT) is commonly used to diagnose obstructive sleep apnea, but its role in identifying patients with suspected hypoventilation or predicting their response to continuous positive airway pressure (CPAP) therapy has not been assessed. The primary objective was to determine if HSAT, combined with clinical variables, could predict the failure of CPAP to correct nocturnal hypoxemia during polysomnography in a population with suspected hypoventilation. Secondary objectives were to determine if HSAT and clinical parameters could predict awake or sleep hypoventilation.

METHODS

A retrospective review was performed of 142 consecutive patients who underwent split-night polysomnography for suspected hypoventilation after clinical assessment by a sleep physician and review of HSAT. We collected quantitative indices of nocturnal hypoxemia, patient demographics, medications, pulmonary function tests, as well as arterial blood gas data from the night of the polysomnography . CPAP failure was defined as persistent obstructive sleep apnea, hypoxemia (oxygen saturation measured by pulse oximetry < 85%), or hypercapnia despite maximal CPAP.

RESULTS

Failure of CPAP was predicted by awake oxygen saturation and arterial blood gas results but not by HSAT indices of nocturnal hypoxemia. Awake oxygen saturation ≥ 94% ruled out CPAP failure, and partial pressure of oxygen measured by arterial blood gas ≥ 68 mmHg decreased the likelihood of CPAP failure significantly.

CONCLUSIONS

In patients with suspected hypoventilation based on clinical review and HSAT interpretation by a sleep physician, awake oxygen saturation measured by pulse oximetry and partial pressure of oxygen measured by arterial blood gas can reliably identify patients in whom CPAP is likely to fail. Additional research is required to determine the role of HSAT in the identification and treatment of patients with hypoventilation.

Prevalence and correlates of sleep apnea among US Veterans with chronic kidney disease

The prevalence and correlates of sleep apnea (SA) among Veterans with chronic kidney disease (CKD), a population at high risk of both SA and CKD, are unknown. We performed a cross-sectional analysis of 248 Veterans (18-89 years) selected only for presence of moderate to severe CKD. All participants underwent full, unattended polysomnography, measurement of renal function and a sleepiness questionnaire. Logistic regression with backward selection was used to identify predictors of prevalent SA (apnea-hypopnea index [AHI, ≥15 events/hr] and prevalent nocturnal hypoxia [NH, % of total sleep time spent at <90% oxygen saturation]). The mean age of our cohort was 73.2 ± 9.6 years, 95% were male, 78% were Caucasian and the mean body mass index (BMI) was 30.3 ± 4.8 kg/m² . The prevalence of SA was 39%. There was no difference in daytime sleepiness among those with and without SA. In the final model, older age, higher BMI and diabetes mellitus (DM) were associated with higher odds of SA, after controlling for age, BMI, race and sex. Higher BMI, DM, unemployed/retired status, current smoking and higher serum bicarbonate level were associated with prevalent NH. To sum, SA was common among Veterans with moderate to severe CKD. Although some traditional risk factors for SA were associated with SA in this population, sleepiness did not correlate with SA. Further study is needed to validate our findings and understand how best to address the high burden of SA among Veterans with CKD.

Obesity hypoventilation syndrome treated with non-invasive ventilation: Is a switch to CPAP therapy feasible?

BACKGROUND AND OBJECTIVE

Obesity hypoventilation syndrome (OHS) can be treated with either continuous positive airway pressure (CPAP) or non-invasive ventilation (NIV) therapy; the device choice has important economic and operational implications.

METHODS

This multicentre interventional trial investigated the safety and short-term efficacy of switching stable OHS patients who were on successful NIV therapy for ≥3 months to CPAP therapy. Patients underwent an autotitrating CPAP night under polysomnography (PSG); if the ensuing parameters were acceptable, they were sent home on a fixed CPAP for a 4-6-week period. It was hypothesized that blood gas analysis, PSG parameters and lung function tests would remain unchanged.

RESULTS

A total of 42 OHS patients were recruited, of whom 37 patients were switched to CPAP therapy. All patients had a history of severe obstructive sleep apnoea syndrome; chronic obstructive pulmonary disease (COPD) (Global Initiative for Obstructive Lung Disease (GOLD) I/II) was present in 52%. Regarding the primary outcome, 30 of 42 patients (71%, 95% CI: 55-84%) maintained daytime partial pressure of carbon dioxide (PaCO₂ ) levels ≤45 mm Hg after the home CPAP period. There was no further impairment in quality of life, sleep parameters or lung function. Interestingly, 24 patients (65%) preferred CPAP as their long-term therapy, despite the high pressure levels used (mean: 13.8 ± 1.8 mbar). After the CPAP period, 7 of 37 patients were categorized as CPAP failure, albeit only due to mild hypercapnia (mean: 47.9 ± 2.7 mm Hg).

CONCLUSION

It is feasible to switch most stable OHS patients from NIV to CPAP therapy, a step that could significantly reduce health-related costs. The auto-adjusted CPAP device, used in combination with the analysis of the PSG and capnometry, is a valid titration method in OHS patients.

Diagnosing obstructive sleep apnea patients with isolated nocturnal hypoventilation and defining obesity hypoventilation syndrome using new European Respiratory Society classification criteria: an Indian perspective

BACKGROUND

Recently, new classification criteria for obesity hypoventilation syndrome (OHS) have been described. OHS prevalence according to new criteria has not been reported in obstructive sleep apnea (OSA). Prevalence of OHS has not been previously reported from India.

METHODS

Retrospective study was carried out in OSA patients for whom both arterial blood gases (ABG) and end-tidal CO₂ (etCO₂) records were available. OHS was defined according to old and new criteria. Analysis was carried out among various groups: patients without OHS (Group A), patients with sleep hypoventilation but without daytime hypercapnia (Group B) and patients with daytime hypercapnia (Group C).

RESULTS

Out of 367 patients with OSA (body mass index, BMI) 31.9 ± 12.27 kg/m²), finally 128 obese OSA patients were included for analysis. Of those, 15 (5.9%, 95% confidence interval (CI) 3.5-9.4) and 45 patients (17.8%, 95% CI 13.4-22.9) fulfilled prevalence of OHS according to old and new criteria, respectively. Continuous positive airway pressure (CPAP) titration failed in 9.6%, 53.3% and 66.7% in Groups A, B, and C, respectively. For all parameters of OSA severity (apnea-hypopnea index (AHI), Nadir O₂, T90) and positive airway pressure (PAP) requirements, patients in Group B were in between those in Groups A and C. Statistically significant difference was seen between Group A and Group B, and between Groups A and C, but not between Groups B and C.

CONCLUSION

One in six OSA patients and one in three obese OSA patients (BMI >30 kg/m²) have OHS according to new criteria. Since patients with isolated nocturnal hypoventilation were as sick as patients with daytime hypercapnia, screening for sleep hypoventilation should be carried out in all obese OSA patients.

Identifying Patients Experiencing Opioid-Induced Respiratory Depression During Recovery From Anesthesia: The Application of Electronic Monitoring Devices

BACKGROUND

Postsurgical patients experiencing opioid-related adverse drug events have 55% longer hospital stays, 47% higher costs associated with their care, 36% increased risk of 30-day readmission, and 3.4 times higher risk of inpatient mortality compared to those with no opioid-related adverse drug events. Most of the adverse events are preventable.

GENERAL AIM

This study explored three types of electronic monitoring devices (pulse oximetry, capnography, and minute ventilation [MV]) to determine which were more effective at identifying the patient experiencing respiratory compromise and, further, to determine whether algorithms could be developed from the electronic monitoring data to aid in earlier detection of respiratory depression.

MATERIALS AND METHODS

A study was performed in the postanesthesia care unit (PACU) in an inner city. Sixty patients were recruited in the preoperative admissions department on the day of their surgery. Forty-eight of the 60 patients wore three types of electronic monitoring devices while they were recovering from back, neck, hip, or knee surgery. Machine learning models were used for the analysis.

RESULTS

Twenty-four of the 48 patients exhibited sustained signs of opioid-induced respiratory depression (OIRD). Although the SpO₂ values did not change, end-tidal CO₂ levels increased, and MV decreased, representing hypoventilation. A machine learning model was able to predict an OIRD event 10 min before the actual event occurred with 80% accuracy.

LINKING EVIDENCE TO ACTION

Electronic monitoring devices are currently used as a tool to assess respiratory status using thresholds to distinguish when respiratory depression has occurred. This study introduces a potential paradigm shift from a reactive approach to a proactive approach that would identify a patient at high risk for OIRD. Capnography and MV were found to be effective tools in detecting respiratory compromise in the PACU.

Obesity Hypoventilation Syndrome: Early Detection of Nocturnal-Only Hypercapnia in an Obese Population

STUDY OBJECTIVES

Hypoventilation in obesity is now divided into five stages; stage 0 (pure obstructive sleep apnea; OSA), stages I/II (obesity-related sleep hypoventilation; ORSH) and stages III/IV (awake hypercapnia, obesity hypoventilation syndrome; OHS). Hypercapnia during the day may be preceded by hypoventilation during sleep. The goal of this study was to determine the prevalence and to identify simple clinical measures that predict stages I/II ORSH. The effect of supine positioning on selected clinical measures was also evaluated.

METHODS

Ninety-four patients with a body mass index > 40 kg/m² and a spirometric ratio > 0.7 were randomized to begin testing either in the supine or upright seated position on the day of their diagnostic sleep study. Arterialized capillary blood gases were measured in both positions. Oxygen saturation measured by pulse oximetry was also obtained while awake. Transcutaneous CO₂ monitoring was performed during overnight polysomnography.

RESULTS

Stages I/II ORSH had a prevalence of 19% in an outpatient tertiary hospital setting compared with 61%, 17%, and 3% for stages 0, III/IV, and no sleep-disordered breathing respectively. Predictors for sleep hypoventilation in this group were an awake oxygen saturation of ≤ 93% (sensitivity 39%, specificity 98%, positive likelihood ratio of 22) and a partial pressure of carbon dioxide ≥ 45 mmHg (sensitivity 44%, specificity 98%, positive likelihood ratio of 24) measured in the supine position.

CONCLUSIONS

ORSH has a similar prevalence to OHS. Awake oxygen saturation and partial pressure of carbon dioxide performed in the supine position may help predict obese patients with sleep hypoventilation without awake hypercapnia.

COMMENTARY

A commentary on this article appears in this issue on page 1455.

CLINICAL TRIAL REGISTRATION

Registry: Australian New Zealand Clinical Trials Registry, Identifier: ACTRN 12615000135516, URL: https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=367493&isReview=true, Title: A cross-sectional study to identify obese patients who are at risk for developing obesity hypoventilation syndrome (OHS) by investigating the relationship between daytime measures (including supine hypercapnia, distribution of body fat and lung volumes) with the presence of hypoventilation during sleep.

Noninvasive auto-titrating ventilation (AVAPS-AE) versus average volume-assured pressure support (AVAPS) ventilation in hypercapnic respiratory failure patients

Auto-titrating noninvasive ventilation (NIV) has been developed as a new mode applying variable expiratory-positive airway pressure (EPAP) in addition to variable inspiratory pressures (IPAP), both to deliver targeted tidal volume (VT) and to eliminate upper airway resistance. The purpose of this study is to evaluate whether NIV with auto-titrating mode will decrease more PaCO₂ within a shorter time compared to volume-assured mode in hypercapnic intensive care unit (ICU) patients. The hypercapnic respiratory failure patients treated with average volume assured pressure support- automated EPAP mode (group1) were compared with those treated with average volume-assured pressure support mode (group2). Two groups were matched with each other according to baseline diagnoses, demographic characteristics, arterial blood gas values, target VT settings and daily NIV usage times. Built-in software was used to gather the ventilatory parameters. Twenty-eight patients were included in group 1, and 22 in group 2. The decrease in PaCO₂ had been achieved within a shorter time period in group 1 (p < 0.05). This response was more pronounced within the first 6 h (mean reduction in PaCO₂ was 7 ± 7 mmHg in group 1 and 2 ± 5 mmHg in group 2, p = 0.025), and significantly greater reductions in PaCO₂ (18 ± 11 mmHg in group 1 and 9 ± 8 mmHg in group 2, p = 0.008) and plasma HCO₃ levels (from 32 to 30 mEq and from 35 to 35 mEq, p = 0.007) took place within first 4 days. While mean IPAP was similar in both groups, maximum EPAP, mean VT and leak were significantly higher in group 1 than in group 2 (p < 0.05). Results of this preliminary study suggest that, this new auto-titrating NIV mode may provide additional benefit on volume-assured mode in decreasing PaCO₂ more efficiently and rapidly in hypercapnic ICU patients.

Knowledge Gaps in the Perioperative Management of Adults with Obstructive Sleep Apnea and Obesity Hypoventilation Syndrome. An Official American Thoracic Society Workshop Report

The purpose of this workshop was to identify knowledge gaps in the perioperative management of obstructive sleep apnea (OSA) and obesity hypoventilation syndrome (OHS). A single-day meeting was held at the American Thoracic Society Conference in May, 2016, with representation from many specialties, including anesthesiology, perioperative medicine, sleep, and respiratory medicine. Further research is urgently needed as we look to improve health outcomes for these patients and reduce health care costs. There is currently insufficient evidence to guide screening and optimization of OSA and OHS in the perioperative setting to achieve these objectives. Patients who are at greatest risk of respiratory or cardiac complications related to OSA and OHS are not well defined, and the effectiveness of monitoring and other interventions remains to be determined. Centers involved in sleep research need to develop collaborative networks to allow multicenter studies to address the knowledge gaps identified below.

Anaesthetic Preparation of Obese Patients: Current Status on Optimal Work-up

PURPOSE OF REVIEW

With the prevalence of obesity rapidly growing, bariatric anaesthesia becomes everyday anaesthesia rather than a subspecialty. In this review, we are aiming to draw attention to this complex group of patients and their comorbidities, relevant to everyday practice for contemporary anaesthetists.

RECENT FINDINGS

We wanted to focus greatly on sleep-related breathing disorders, because preoperative screening, diagnosis and treatment of the aforementioned make a huge impact in the improvement of preoperative morbidity and mortality, including positive effects on the cardiovascular system. The overview is touching on main obesity-related comorbidities and guides the anaesthetist and associated health professionals on how to approach and manage them. A multidisciplinary approach widely used in bariatric care may be adopted in the care of obese patients in order to reduce preoperative morbidity and mortality. We advocate the early involvement of the anaesthetic team in the preoperative assessment of obese patients in order to achieve appropriate risk stratification and optimise the care.

Independent associations between arterial bicarbonate, apnea severity and hypertension in obstructive sleep apnea

Background

Obstructive sleep apnea is characterized by intermittent hypoxia and hypercapnia. CO₂ production, transport and elimination are influenced by the carbonic anhydrase enzyme. We hypothesized that elevated standard bicarbonate, a proxy for increased carbonic anhydrase activity, is associated with apnea severity and higher blood pressure in patients with obstructive sleep apnea.

Methods

A retrospective analysis of a sleep apnea cohort (n = 830) studied by ambulatory polygraphy. Office systolic/diastolic blood pressure, lung function, and arterial blood gases were assessed during daytime.

Results

Arterial standard bicarbonate was increased with apnea severity (mild/moderate/severe 24.1 ± 1.8, 24.4 ± 1.7 and 24.9 ± 2.9 mmol/l, respectively, Kruskal-Wallis test p < 0.001). Standard bicarbonate was independently associated with apnea hypopnea index after adjustment for sex, age, body mass index, smoking, alcohol, hypertension, pO₂ and pCO₂ (standard bicarbonate quartile 1 vs. quartile 4, β = 10.6, p < 0.001). Log-transformed standard bicarbonate was associated with a diagnosis of hypertension or diastolic blood pressure but not systolic blood pressure adjusting for cofounders (p = 0.007, 0.048 and 0.45, respectively).

Conclusions

There was an independent association between sleep apnea severity and arterial standard bicarbonate. The link between high standard bicarbonate and daytime hypertension suggests that carbonic anhydrase activity may constitute a novel mechanism for blood pressure regulation in sleep apnea.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-017-0607-9) contains supplementary material, which is available to authorized users.

Determinants of Wake Pco2 and Increases in Wake Pco2 over Time in Patients with Obstructive Sleep Apnea

RATIONALE

The progression from obesity and obstructive sleep apnea to obesity with hypoventilation and daytime hypercapnia may relate to features of sleep-disordered breathing events that affect loading and unloading of carbon dioxide.

OBJECTIVES

To determine whether the wake Pco2 increases over time in untreated obstructive sleep apnea, and whether that increase is explained by changes in sleep-disordered breathing event duration, interevent duration, or postevent ventilation amplitude.

METHODS

We selected 14 adults who had two polysomnographic studies more than 1 year apart because of untreated or suboptimally treated moderate to severe obstructive sleep apnea. Demographic and polysomnographic data were reviewed for both sets of studies, including the evening wake end-tidal CO2, the ratio of mean event to mean interevent duration (subsuming apneas and hypopneas), and the ratio of mean post- to preevent breath amplitude.

MEASUREMENT AND MAIN RESULTS

The mean (SD) wake end-tidal Pco2 increased between studies from 35.9 (4.2) to 39.5 (3.9) mm Hg (P < 0.005). The wake end-tidal CO2 correlated inversely with the post- to pre-event breath amplitude and positively with the ratio of mean event to mean interevent duration and with body mass index. However, those three variables were not significantly changed between the two studies. The wake end-tidal CO2 did not correlate with the apnea-hypopnea index or age. There was a significant increase in bicarbonate level between studies (median, 24.0-26.5 mmol/L; P = 0.01).

CONCLUSIONS

In our study cohort, wake end-tidal CO2 correlated with body mass index and features of sleep apnea that influence the balance of loading and unloading of CO2. However, those features remained fixed over time, even as the wake Pco2 and bicarbonate levels increased with untreated sleep apnea.

Avoiding Management Errors in Patients with Obesity Hypoventilation Syndrome

The prevalence of obesity hypoventilation syndrome and obstructive sleep apnea are increasing rapidly in the United States in parallel with the obesity epidemic. As the pathogenesis of this chronic illness is better understood, effective evidence-based therapies are being deployed to reduce morbidity and mortality. Nevertheless, patients with obesity hypoventilation still fall prey to at least four avoidable types of therapeutic errors, especially at the time of hospitalization for respiratory or cardiovascular decompensation: (1) patients with obesity hypoventilation syndrome may develop acute hypercapnia in response to administration of excessive supplemental oxygen; (2) excessive diuresis for peripheral edema using a loop diuretic such as furosemide exacerbates metabolic alkalosis, thereby worsening daytime hypoventilation and hypoxemia; (3) excessive or premature pharmacological treatment of psychiatric illnesses can exacerbate sleep-disordered breathing and worsen hypercapnia, thereby exacerbating psychiatric symptoms; and (4) clinicians often erroneously diagnose obstructive lung disease in patients with obesity hypoventilation, thereby exposing them to unnecessary and potentially harmful medications, including β-agonists and corticosteroids. Just as literary descriptions of pickwickian syndrome have given way to greater understanding of the pathophysiology of obesity hypoventilation, clinicians might exercise caution to consider these potential pitfalls and thus avoid inflicting unintended and avoidable complications.

Exploratory study into the effect of abdominal mass loading on airways resistance and ventilatory failure

Objective

We hypothesised that the airway resistance during tidal breathing would correlate with a particular pattern of increasing obesity, particularly when supine, and would differ between participants with and without ventilatory failure.

Methods

In our cross-sectional cohort study, 72 morbidly obese patients (40 males, 32 females, mean body mass index (BMI) 47.2) had measurements of both airways resistance (by impulse oscillometry (IOS)) and adiposity (by dual-energy X-ray absorptiometry (DXA)).

Results

All measures of airways resistance increased in the supine position: total airways resistance (R5) +37% (p<0.0005); large airways resistance (R20) +29% (p<0.0005); and small airways resistance (R5–R20) +52% (p<0.0005). BMI was correlated with seated R5, seated R5–R20, supine R5 and supine R5–R20 (r=0.33 p<0.006, r=0.32 p<0.004, r=0.30 p<0.02 and r=0.36 p<0.04, respectively). Visceral adipose tissue mass was correlated with supine R5–20 (r=0.46 p<0.05). Supine measures of total airways resistance (R5) and large airways resistance (R20) differed between those with and without ventilatory failure, as did mean weight and BMI.

Conclusions

Our study identifies a potentially detrimental effect of the supine posture on tidal breathing airways resistance in obese patients. This change is correlated most with visceral adipose tissue mass and the small airways. We were able to demonstrate that supine increases in airways resistance during tidal breathing, within obese patients, are different between those with and without ventilatory failure.

Trial registration number

NCT01380418; pre-results.

Drugs influencing acid base balance and bicarbonate concentration readings

Serum bicarbonate dosage is sensitive to pharmacological interferences. However, elevated bicarbonate concentration reflects chronic hypoventilation and has been proposed as a simple marker for screening patients with Obesity Hypoventilation Syndrome (OHS), a currently underdiagnosed multimorbid and high mortality disease. We provide a practical overview of the different drugs acting on the acid-base equilibrium to aid clinicians to interpret bicarbonate concentration readings. Little is known about the chronic impact of the usual doses of these drugs on serum bicarbonate concentration and further studies are needed. It is essential to take into account drugs that could interfere with this parameter to avoid misinterpretation of serum bicarbonate levels.

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.

Correlates of obesity-related chronic ventilatory failure

Introduction

Only a third of obese patients develop chronic ventilatory failure. This cross-sectional study assessed multiple factors potentially associated with chronic ventilatory failure.

Materials/patients and methods

Participants had a body mass index (BMI) >30 kg/m², with or without chronic ventilatory failure (awake arterial partial pressure of carbon dioxide >6 kPa or base excess (BE) ≥2 mmols/L). Factors investigated were grouped into domains: (1) obesity measures, (2) pulmonary function, (3) respiratory and non-respiratory muscle strength, (4) sleep study derivatives, (5) hypoxic and hypercapnic responses, and (6) some hormonal, nutritional and inflammatory measures.

Results

71 obese participants (52% male) were studied over 27 months, 52 (SD 9) years and BMI 47 (range 32–74) kg/m². The best univariate correlates of BE from each domain were: (1) dual-energy X-ray absorptiometry measurement of visceral fat (r=+0.50, p=0.001); (2) supine forced expiratory volume in 1 s (r=−0.40, p=0.001); (3) sniff maximum pressure (r=−0.28, p=0.02); (4) mean overnight arterial oxygen saturation (r=−0.50, p<0.001); (5) ventilatory response to 15% O₂ breathing (r=−0.28, p=0.02); and (6) vitamin D (r=−0.30, p=0.01). In multivariate analysis, only visceral fat and ventilatory response to hypoxia remained significant.

Conclusions

We have confirmed that in the obese, BMI is a poor correlate of chronic ventilatory failure, and the best independent correlates are visceral fat and hypoxic ventilatory response.

Trial registration number

NCT01380418.

Obesity Hypoventilation Syndrome: Weighing in on Therapy Options

Obesity hypoventilation syndrome is becoming an increasingly encountered condition both in respiratory outpatient clinics and in hospitalized patients. The health consequences and social disadvantages of obesity hypoventilation syndrome are significant. Unfortunately, the diagnosis and institution of appropriate therapy is commonly delayed when the syndrome is not recognized or misdiagnosed. Positive airway pressure therapy remains the mainstay of treatment and is effective in controlling sleep-disordered breathing and improving awake blood gases in the majority of individuals. Evidence supporting one mode of therapy over another is limited. Both continuous and bilevel therapy modes can successfully improve daytime gas exchange, with adherence to therapy an important modifiable factor in the response to treatment. Despite adherence to therapy, these individuals continue to experience excess mortality primarily due to cardiovascular events compared with those with eucapnic sleep apnea using CPAP. This difference likely arises from ongoing systemic inflammation secondary to the morbidly obese state. The need for a comprehensive approach to managing nutrition, weight, and physical activity in addition to reversal of sleep-disordered breathing is now widely recognized. Future studies need to evaluate the impact of a more aggressive and comprehensive treatment plan beyond managing sleep-disordered breathing. The impact of early identification and treatment of sleep-disordered breathing on the development and reversal of cardiometabolic dysfunction also requires further attention.

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.

A prospective survey for insulinomas in a neurology department

Purpose

Obesity is associated with both obstructive sleep apnea (OSA) and obesity hypoventilation. Differences in adipose tissue distribution are thought to underlie the development of both OSA and hypoventilation. We explored the relationships between the distribution of upper airway, neck, chest, abdominal and muscle fat in very obese individuals.

Methods

We conducted a cross-sectional cohort study of individuals presenting to a tertiary sleep clinic or for assessment for bariatric surgery. Individuals underwent magnetic resonance (MR) imaging of their upper airway, neck, chest, abdomen and thighs; respiratory polygraphy; 1 week of autotitrating CPAP; and morning arterial blood gas to determine carbon dioxide partial pressure and base excess.

Results

Fifty-three individuals were included, with mean age of 51.6 ± 8.4 years and mean BMI of 44.3 ± 7.9 kg/m²; there were 27 males (51%). Soft palate, tongue and lateral wall volumes were significantly associated with the AHI in univariable analyses (p < 0.001). Gender was a significant confounder in these associations. No significant associations were found between MRI measures of adiposity and hypoventilation.

Conclusions

In very obese individuals, our results indicate that increased volumes of upper airway structures are associated with increased severity of OSA, as previously reported in less obese individuals. Increasingly large upper airway structures that reduce pharyngeal lumen size are likely to lead to OSA by increasing the collapsibility of the upper airway. However, we did not show any significant association between regional fat distribution and propensity for hypoventilation, in this population.

Electronic supplementary material

The online version of this article (10.1007/s11325-017-1599-x) contains supplementary material, which is available to authorized users.