OUTCOMES:
Obesity Hypoventilation Syndrome (OHS) and Related Conditions

(Increased Work of Breathing, Myotonic Dystrophy,

Disorders of Central Control of Breathing,

Restrictive Lung Disease)

 

BACKGROUND

 

People living with neuromuscular disease (NMD) develop breathing/respiratory difficulty, insufficiency, and failure because of breathing muscle weakness. As a result, they are very compliant with noninvasive ventilatory support (NVS) because it assists them with breathing and makes them feel better. The same is true for people with increased work of breathing due to obesity hypoventilation syndrome (OHS) and restrictive lung disease.

 

On the other hand, for people with the diagnosis of myotonic muscular dystrophy, there is predominantly an impairment of muscle relaxation with weakness usually being secondary. As a result, inspiratory muscles have difficulty with reversing direction, and normal lung ventilation cannot be maintained. Breathing difficulty initially occurs during sleep, but then eventually persists around-the-clock. Often, NVS offers only partial relief from symptoms of fatigue and hypersomnolence, and patients have greater difficulty synchronizing and tolerating sleep/noctural NVS. It has been suggested that persistence of hypersomnolence despite use of NVS may be due to primary involvement of the hypothalamic-pituitary axis in addition to hypercapnia.(OHS1)

 

For people with the diagnoses of

  • Congenital hypoventilation (Ondine’s curse)

  • Obesity hypoventilation syndrome (OHS)

  • Kyphoscoliosis

  • Other conditions of central hypoventilation and/or increased work of breathing

are often treated by tracheostomy mechanical ventilation (TMV) or phrenic pacing, but these treatments are both undesirable and unnecessary. People with these diagnoses can use mouthpiece NVS at pressures necessary for full ventilatory support and normal CO2 levels.

 

We have morbidly obese patients who routinely use mouthpiece NVS to insufflate their lungs and assist their breathing muscles. Their lips can easily manage pressures greater than 60 cm H2O to achieve normal tidal volumes of ~500 mL. None should require tracheostomy tubes or pacemakers.

 

 

OUTCOMES OF CONVENTIONAL MANAGEMENT

 

A study to determine the causes of death in myotonic dystrophy over a 47-year period indicated (OHS2):

  • A median survival of 60 years for males and 59 years for females with survival to age 65 of only 18% (normal population = 78%).

  • A weakly positive correlation between the CTG codon repeat length and younger age at death was found in the 13 patients studied (P = 0.08).

  • The cause of death could be determined in 70 of the 83 deceased patients. Pneumonia and cardiac arrhythmias were the most frequent primary causes, each occurring in approximately 30%.

  • Half of the patients were partially to totally wheelchair-bound.

Despite the outcomes of this study, our clinical impression is that inadequate breathing/ventilatory and cough assistance played a strong role in the pneumonia deaths and fatal cardiac arrthythmias (from cor pulmonale and heart failure).

 

In the beginning, preferred treatment for OHS ranged from tracheotomy to continuous positive airway pressure (CPAP) and supplemental oxygen. However, CPAP has a 43% failure rate (OHS3), and neither CPAP nor breathing via an open tracheostomy tube compensates overworked diaphragms that are not up to the task of moving the abdomen against a hundred pounds or more of extra weight in order to ventilate the lungs.

 

Failure of CPAP to correct blood gases, even at a positive pressure of 14 cm H2O, is often attributed to a failure to achieve “a therapeutic pressure” during a polysomnography titration”.(OHS4) Similarly, some of our patients with neuromuscular diseases and little VC also “failed noninvasive ventilation” which has been titrated to bi-level PAP levels of 23/19 cm H2O, levels tantamount to breathing in a hurricane. Of course, the patients could not tolerate these pressures and the inspiratory assistance of 4 cm H2O (23-19 cm H2O) was insignificant for them as it is for extremely obese patients whose inspiratory muscles are overworked. While it has been recognized that bi-level PAP has the advantage over CPAP of assisting inspiratory muscle function as a function of its span, nevertheless its use has generally been restricted to spans of 8 to 10 cm H2O,(OHS3,OHS4) which are grossly inadequate to rest inspiratory muscles or normalize blood gases. Remarkably, even when clinicians refer to providing “nocturnal intermittent positive pressure ventilation” for their OHS patients they are referring to low span bi-level PAP.(OHS5) Perhaps clinicians should learn from the experience of CNVS dependent post-polio survivors who became morbidly obese over time (see below) but maintain normal blood gases without ever using bi-level PAP, O2, CPAP, or tracheostomy tubes. The authors would likely have done much better if instead of using bi-level PAP at low spans they had used portable ventilators to deliver higher volumes and pressures. They might also have been well advised to have used MIE to prevent pneumonia since many of these patients have inadequate cough flows.

A prospective study monitored 47 untreated patients with OHS for 18 months after hospital discharge. The mortality of these untreated patients was 23 versus 9% for patients with a similar degree of obesity but without hypoventilation thereby suggesting that failure to correct hypoventilation can result in untimely death. By contrast, one retrospective study of 126 patients with OHS who were adherent with NPPV “therapy” (spans higher than 10 cm H2O) reported an 18-month mortality of 3% (Figure 3), and the 2- and 5-year mortality rates were 8 and 30%, respectively, a significant improvement over using low span bi-level PAP.(OHS6) Moreover, current evidence also suggests that adherence with positive airway pressure “therapy” reduces health care expenses and hospital readmission rates among patients with OHS.(OHS6) The concept of “therapy” implies improving alveolar ventilation and CO2 levels but not necessarily correcting them by providing nonininvasive ventilatory “support” (NVS) at greater volumes and pressures than are possible by bi-level PAP. Although a few studies report use of volume preset ventilation, even they generally use it at less than the volumes needed to permit patients to air stack efficiently, to physiologically vary tidal volumes, and to optimally rest muscles and normalize CO2 and O2 sat levels.(OHS5) While it has been recognized that for “patients with OHS, factors other than sleep-disordered breathing are the driving force behind the pathogenesis of hypoventilation. These patients will most likely need more aggressive nocturnal mechanical ventilation,” the same authors fail to recognize noninvasive ventilation as ventilatory support (NVS) and the fact that it can require insufflation pressures of 50 to 60 cm H2O to counter the increased work of breathing against sometimes hundreds of pounds of surplus weight. “Barotrauma” is a misnomer. It is really volutrauma, trauma from over expansion of alveoli, and not from pressure per se. No one employing conventional management proposes ventilatory support other than via tracheostomy tubes (CTMV) even though when these patients are ventilated via invasive tubes the positive inspiratory pressures are typically over 30 cm H2O.(OHS3)

Therefore, while CPAP and low-span bi-level PAP are suboptimal for resting muscles or normalizing sleep blood gases, in one study positive inspiratory presusres of 12-30 cm H2O and positive expiratory pressures of 5-13 cm H2O were used. These pressures improved PaCO2 to less than 50 mm Hg.(OHS7) In other studies, patients on bi-level PAP 22/6 and 20/4-8 also noted significant improvements in PaCO2 and PaO2.(OHS8,OHS9) In all these studies, O2 supplementation was still used routinely to normalize O2 sat, a practice we dissuade since this should be the goal of normalizing lung ventilation. Depending on the degree of obesity, if the highest possible bi-level PAP spans of 30 cm H2O or so can not normalize O2 sat and markedly improve PaCO2 levels, then only the more powerful portable ventilators should be used.

                  Besides placing tracheostomy tubes to keep the airway open and reduce dead space ventilation it can also be used for TMV to improve or normalize alveolar ventilation. “Ventilatory support via tracheostomy for obesity-related respiratory failure has been used since the 1960s. Although effective, this was obviously not an ideal technique given the difficulties of maintaining a tracheostomy, especially in patients with markedly excessive fat in the neck region.”(OHS10) While there are reports demonstrating improved survival using NVS vs. no treatment at all we have found none that compare outcomes with TMV. Since tracheostomy tubes are undesirable, unnecessary, and the majority of, at least, ALS patients using them for TMV die from complications of the tube,(JBCV67) they should not be considered for managing OHS and when used for TMV, the users should be offered decanulation to NVS.

 

Long-Term Outcomes for Noninvasive Respiratory Management

End-tidal CO2 monitoring is not routinely a part of polysomnographic analyses. As a result, hypercapnia leading to cor pulmonale can be missed. More appropriate than polysomnography is sleep EtCO2 and O2 saturation monitoring to guide in the use of NVS to prevent severe hypercapnia and cor pulmonale.(JBCV238) Of our 7 myotonic dystrophy patients who survived beyond age 65, 5 required at least sleep NVS and 3 others required CNVS surviving thus far to age 71. Overall we have had 6 patients dependent on CNVS and all 6 were wheelchair dependent. These patients maintain normal lung ventilation throughout daytime hours as opposed to ambulatory patients who use sleep NVS but ambulated with hypercapnia during daytime hours, refusing to use mouthpiece NVS with their ventilators on walker trays. The CNVS use is at less risk for acute respiratory failure than the sleep-only NVS or bi-level PAP users. Thus, it is our strong clinical impression that the weakest wheelchair bound patients with myotonic dystrophy with the lower VCs derive the greatest benefit from NVS. Because they are able to walk, ambulatory patients do not use NVS sufficiently during daytime hours to ultimately prevent cor pulmonale. Thus, patients who tolerate NVS best may have the better prognosis despite lower VCs. As for people with other myopathies for whom episodes of respiratory failure and mortality result from ineffective coughing during respiratory tract infections, myotonic dystrophy patients with cough peak flows less than 300 L/m also need access to mechanical insufflation-exsufflation during intercurrent respiratory tract infections.

Many post-poliomyelitis survivors who were switched from body ventilator use to CNVS became obese overtime and like all our adult NVS users with neuromuscular disorders they also use 800 to 1500 ml volume-preset ventilation which often generates positive inspiratory pressures (PIPs) of 50 to 65 cm H2O for them. They usually use no expiratory PAP or positive end-expiratory pressure (PEEP). They can equally use pressure preset ventilation at these pressure settings to generate the same tidal volumes. These pressures and volumes permit them to maintain essentially normal blood gases day and night.

In 1993 we reported 3 OHS patients who were managed by CNVS including daytime mouthpiece NVS from 53.3±9.9 years of age with mean VC 876 ml (20% of predicted normal). All three had less than 1 hour of ventilator free breathing ability during up to 2 years of CNVS. Their volume preset ventilation also generated positive inspiratory pressures of 50 to 60 cm H2O.(JBCV54) The next year Piper and Sullivan also reported that volume preset nasal ventilation during sleep could improve daytime blood gases for 13 OHS patients with BMI greater than 35 and that some could subsequently be managed by CPAP.(OHS11)

Subsequently we have had at least 22 other OHS patients managed by NVS/CNVS. We transferred all of them from CPAP and O2 or inadequate span bi-level PAP that did not assuage their orthopnea sufficiently to permit them to sleep supine, to NVS. Using NVS at volumes preset for 800 to 1500 ml they could sleep reclining. Their VCs varied from as little as 200 ml supine to 3150 ml in the sitting position but in all cases VC was lower supine than when sitting. Sleep NVS was generally required when the sitting/supine VC difference exceeded 30%. Ten OHS patients extended sleep NVS throughout daytime hours to become CNVS dependent. Six of these CNVS users presented with EtCO2s of 54, 56, 51, 63, 71, 51 and corresponding O2 sat ranges of 83/84, 79/89, 86/88, 69/83, 74/89, 88/94, respectively, before extending sleep NVS into daytime hours and normalizing CO2 and O2 saturation levels. EtCO2 and O2 sats normalized only when using daytime mouthpiece NVS at PIPs of 50 to 60 cm H2O. All also used oronasal interfaces for sleep at the same preset volumes of 800 to 1500 ml that generated positive inspiratory pressures of 50 to 60 cm H2O at night as well.

In 2007 Heinemann et al. reported 35 clinically stable hypercapnic OHS patients with a mean body mass index (BMI) 45.9+/-8.8 kg/m(2) who were placed on bi-level PAP with inspiratory PAP 24±3 cm H2O, expiratory PAP 6±2 cm H2O and respiratory, rate 18.8±3.7/min. After 12 and 24 months the CO2 levels normalized, hypoxemia improved, and hemoglobin and hematocrit decreased (P<0.001 each). Daily duration of ventilator use correlated with the decrease in PaCO2 after 12 months (r = 0.37; P<0.05) and 24 months (r = 0.47; P<0.05). Vital capacity (VC) and expiratory reserve volume (ERV) significantly increased after 12 and 24 months although BMI was only slightly reduced. The 2-year survival rate was 91% with three patients (9%) discontinuing noninvasive ventilation during the study period.(OHS12)

Although patients with chronic ventilatory/respiratory failure due to kyphoscoliosis and congenital central alveolar hypoventilation (Ondine’s curse) conventionally undergo tracheotomy when treatment limited to low spans of bi-level PAP rather than NVS and failure to use MIE result in acute on chronic respiratory failure, there are no long-term efficacy studies comparing TMV to NVS. Likewise, there is a tendency for patients with conditions that result in intercurrent exacerbations, like myasthenia gravis, multiple sclerosis, and the acute Guillian-Barré syndrome, to benefit long-term from sleep NVS and access to MIE between exacerbations. Even when acute on chronic respiratory failure results in intubation, irrespective of pre-intubation access to NVS and MIE, these patients can usually be managed long-term without tracheostomy as will be considered below. Considering Ondine’s congenital central hypoventilation and idiopathic kyposcoliosis, we have had no patients placed on NVS from point of diagnosis. Small children with intact skeletal muscle function may not cooperate with nasal NVS.

 

Outcomes of Extubation

At the 18th Annual Meeting of the Society for Airway Management in Seattle, Washington, September 19-21, 2014, much of the emphasis of the conference was on preventing extubation failure for obese patients following bariatric surgery. Remarkably, none of the participants had ever heard of extubating patients to full ventilatory support via mouthpieces or nasal interfaces, avoiding supplemental O2, and using MIE to enhance airway secretion clearance. We have had the opportunity to extubate only three “unweanable” OHS patients to CNVS and MIE, thereby avoiding extubation failure and tracheotomies.(JBCV235) One other “unweanable” patient for whom the tracheostomy tube was removed (decanulated) in 2001 and who then was CNVS dependent had to be intubated for pneumonia in 2012 when we extubated him back to CNVS and MIE. He has now been CNVS dependent for 15 years during which he was hospitalized only that once once (Figure OHS1). Without question, there is little doubt that extubation of alert post-bariatric surgery patients to CNVS and MIE can only decrease if not essentially eliminate extubation failure rates for these patients. We have also recently extubated 6 patients with OHS and other restrictive syndromes to CNVS rather than have them undergo tracheotomy.(JBCV235) Since these patients, although often “unweanable,” usually have very functional bulbar-innervated musculature, they are usually not difficult to extubate to CNVS even when they have not had experience with it or bi-level PAP beforehand.

Besides causing severe ventilatory failure, acute exacerbations of multiple sclerosis, myasthenia gravis, and the Guillain-Barré syndrome can also cause severe bulbar-innervated muscle dysfunction (BIMD). While it is possible to routinely extubate people with SMA type 1 with 0 ml of VC and no bulbar-innervated muscle function at all as well as others with NMD in the same category provided that the upper airway is sufficiently patent for MIE to expulse airway secretions to maintain normal O2 sat, it is much easier to return patients with a long history of use of CNVS and MIE back to the settings they are accustomed to than to extubate acute myasthenia patients with severe BIMD to interventions that they must learn “cold” and often in panic. Nevertheless, in 2010 we reported the successful extubation of 15 consecutive “unweanable” patients with myasthenia gravis who had minimal VC and could pass no ventilator weaning parameters or spontaneous breathing trials.(JBCV197) In 2015 we reported 23 others with myasthenia, multiple sclerosis, Guillain-Barré syndrome, myotonic dystrophy and similar conditions, all unweanable from ventilatory support and with BIMD, equally successfully extubated without resort to tracheotomy. Accomplishing this, however, requires a specifically trained respiratory therapist and family instructed by the therapist to provide intensive MIE for at least the first 36 hours after extubation. It also requires an ICU prepared to accommodate this change from their usual protocols.

 

Outcomes of Decanulation

                  We have successfully decanulated eight OHS patients, all of whom depended on NVS following decanulation, and two had to be decanulated to CNVS.(JBCV232) and three became CNVS dependent with minimal ventilator free breathing ability (Figure OHS1). None have ever returned to having an indwelling tracheostomy.

Similarly, a 54 year old with chronic ventilatory failure due to Pott’s disease (tuberculosis of the spine) was decanulated to CNVS and MIE. That case demonstrated the hazards of oxygen therapy, unnecessary insistence on tracheostomy, and the fact that breathing tolerance (inspiratory muscle endurance) can initially be entirely lost while ventilatory drive resets but it can subsequently increase with the inspiratory muscle rest provided by CNVS over time.

                  A 54 year old high school teacher with a history of Pott's disease at age 3, severe kyphoscoliosis, and a 5 year history of shortness of breath, hypersomnolence, fatigue, and headaches was hospitalized for ventilatory failure, informed that he would require a tracheostomy tube or he would not survive more than a few months, and was sent home using continuous supplemental oxygen. With oxygen therapy, PaCO2 increased to 74 mm Hg and Pao2 to 55 mm Hg. Dyspnea eased, but hypersomnolence and other symptoms of hypercapnia worsened; and he complained that he frequently fell asleep while teaching classes. He had two additional hospitalizations for ventilatory failure over the next 4 months and continued to refuse to undergo tracheotomy but he became very depressed and thought that he was dying. His respiratory therapist referred him to our program. His mean nocturnal O2 sat breathing room air was 71% (Etco2 was 53); using 4 L/min of oxygen via nasal canula it was 89%; using nasal NVS in ambient air, 91%; and using nasal NVS with 2 L/min of oxygen it was 95%. Supplemental oxygen use was discontinued to optimize nocturnal nasal NVS. Using oximetry for occasional feedback he maintained O2 sat greater than 94% during daytime hours by breathing deeper and using mouthpiece NVS as need to maintain O2 sat over 94%. He has continued to use nocturnal nasal NVS with a custom molded nasal interface (see Figure 9 of Chapter 7), and used mouthpiece NVS for daytime periods for 15 years then CNVS for the next 8 years. At the age of 76 he developed Alzheimer’s disease and over the next two years became incoherent and uncooperate and died after 23 years of NVS and at least 8 of CNVS. His father was a fisherman and brought Dr. Bach fish every 2 weeks for 4 years, out of gratitude for permitting his son to avoid tracheotomy, until he himself died.

                  In 2014 we reported the decanulations of 8 CTMV dependent patients with myasthenia gravis, Guillian-Barré syndrome, multiple sclerosis, myotonic dystrophy and others with similar acute on chronic conditions having used TMV for a mean of over 18 months. After decanulation, 4 of the 8 weaned from continuous ventilatory support (CTMV to CNVS) to sleep-only NVS and their VCs significantly increased despite not having developed any ventilator-free breathing ability while previously using CTMV. Had they not been decanulated there is little doubt that they would have remained CTMV dependent for the rest of their lives. The way in which this was achieved has previously been presented for other diagnoses and is described in publications.(CVJB232)

 
 
 
 
 

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