Spinal Muscle Atrophy Type 1:
Noninvasive Respiratory Management Approach

Also see: SMA1: Management and Outcomes

Contents

Abstract

Study Objective

Design

Methods

Results

Conclusion

Key Words

Introduction

Methods

Results

Discussion

References

Table 1 - Protocol Vs. Conventional Management of Intubated SMA 1 Patients

Conventional

Protocol

Table 2 - Spinal Muscular Atrophy 1: Noninvasive Management Outcomes

Spinal Muscle Atrophy Type 1:
Noninvasive Respiratory Management Approach

Published in Chest 2000; 117:1100-1105.

John R. Bach, M.D., F.C.C.P., F.A.A.P.M.R., Professor of Physical Medicine and Rehabilitation, Professor of Neurosciences, University of Medicine and Dentistry of New Jersey (UMDNJ)-New Jersey Medical School, Newark, N.J.

Vis Niranjan, M.D., Assistant Professor, Department of Pediatrics, UMDNJ-New Jersey Medical School, Newark, NJ

Brian Weaver, B.S., R.R.T., University Hospital, Newark, NJ

This work was performed at the University Hospital of the University of Medicine and Dentistry of New Jersey-New Jersey Medical School in Newark, N.J.    

Abstract

Study Objective

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To determine whether SMA type 1 can be managed without tracheostomy and to compare extubation outcomes using a respiratory muscle aid protocol vs. conventional management

Design

A retrospective cohort study  

Methods

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Eleven SMA type 1 children were studied during episodes of respiratory failure. Nine children required multiple intubations. Along with standard treatments, these children received manually and mechanically assisted coughing to reverse airway mucus-associated decreases in oxyhemoglobin saturation (SaO2). Extubation was not attempted until there was no oxygen requirement to maintain SaO2 greater than 94%. Upon extubation all patients received nasal ventilation with positive end-expiratory pressure (PEEP). Successful extubation was defined by no need to reintubate during the current hospitalization.  

Results

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Two children have survived for 37 and 66 months, and have never been intubated despite requiring 24-hour nasal ventilation since 5 and 7 months of age, respectively. One other child underwent tracheostomy for persistent left lung collapse and inadequate home care, another for need for frequent readmission and intubation, and one child was lost to follow-up 3 months after successful extubation. The other 6 children have been managed at home for 15 to 59 (mean 30.4) months using nocturnal nasal ventilation following their initial episode of respiratory failure. The nine children were successfully extubated by our protocol 23 of 28 times. The same children managed conventionally were successfully extubated 2 of 20 times when not using this protocol (p<0.001 by the two tailed Fisher's exact t-test).  

Conclusion

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Although intercurrent chest colds may necessitate periods of hospitalization and intubation, tracheostomy can be avoided throughout early childhood for some children with SMA type 1.  

Key Words

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Spinal Muscular Atrophy; Mechanical Ventilation; Respiratory Failure; Pulmonary Complications; Noninvasive Ventilation; Bi-level Positive Airway Pressure; Survival.  

Introduction

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Autosomal recessive spinal muscular atrophy (SMA) is the most common inherited neuromuscular disease of the floppy newborn and along with Duchenne muscular dystrophy, one of the two most commonly inherited neuromuscular diseases. It is caused by a chromosome 5 defect. About one in 40 people carry the defective gene and the overall incidence has been reported to be 1/5000.1 It has been categorized into four types according to severity. The SMA type 1 infant never attains the ability to sit independently. Less than 20% of these children survive 4 years and then only with indwelling tracheostomy tubes.2 Virtually all die from respiratory complications. SMA type 2 children can sit independently but never walk and, they too, usually have periods of respiratory failure during early childhood. Other SMA types have milder courses.

The lungs of patients with neuromuscular disease can be ventilated noninvasively by intermittent positive pressure ventilation (IPPV) provided by volume-cycled or by pressure-cycled ventilators. However, with or without using ventilatory assistance, 3-5 SMA patients are usually stable until an intercurrent chest cold results in pneumonia and acute respiratory failure because of inability to cough effectively.6 For SMA type 1 infants this usually occurs between birth and 2 1/2 years of age. Clinicians are often reluctant to intubate them because they often lose breathing autonomy with the correction of compensatory metabolic alkalosis that accompanies normalization of arterial carbon dioxide tensions. Further, once intubated, tracheostomy is thought to be mandatory when ventilator weaning is delayed or thought to be impossible. Since it is considered to be unavoidable for survival, tracheostomy is often recommended during the initial episode of respiratory failure.3 If these infants wean from ventilator use, are extubated, and the parents persist in refusing tracheostomy, the parents are often advised to avoid future intubations and to simply let the children die.3

Because we have succeeded in using continuous noninvasive ventilation long-term as an alternative to tracheostomy6-8 and have used a home respiratory muscle aid protocol to avoid pneumonias and hospitalizations for older patients who can cooperate,9 when several parents refused tracheostomies for their infants, we attempted to modify this protocol for their children.9 We hypothesized that we could use noninvasive aids for SMA type 1 children who require endotracheal intubation and, thereby, maintain the children free of tracheostomy until they are old enough to cooperate fully with the home protocol. In this way it may be possible to avert tracheostomy indefinitely.9 We also hypothesized that extubation would more likely be successful for patients managed by our protocol than for patients managed conventionally.  

Methods

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Eleven consecutively referred SMA type 1 children in respiratory failure were managed as per a protocol (Table 1) that was approved by our Institutional Review Board. All eleven patients had severe skeletal and bulbar muscle weakness to the extent that none had functional extremity movements or ability to take any nutrition by mouth. Two have not developed the ability to verbalize. All 11 patients' parents had refused tracheostomies on multiple occasions.

Nine of the 11 patients have required one or more intubations. All were intubated in respiratory failure with oxygen requirement and managed conventionally with respect to hydration and nutrition via feeding tubes but not with respect to respiratory care (Table 1). Since oxygen administration can mask oxyhemoglobin desaturations that would otherwise signal airway mucus accumulation or hypoventilation, its use was restricted to patients who were acutely ill and intubated or who required emergency resuscitation.

Immediately upon extubation the patients received nasal ventilation with PEEP at a rate slightly greater than the patients' spontaneous breathing rate. This was provided by BiPAP-ST™ ventilator (Respironics Inc., Murrysville, PA) for 10 children and by volume cycled ventilator (Bird VIP™, Exeter, UK) on assist/control for one patient who breathed more rapidly than the maximum rate of the BiPAP™ device. Initially an inspiratory positive airway pressure (IPAP) of 10 cm H2O was used but the IPAP was quickly increased to 20 cm H2O or to the point that the patient demonstrated good chest expansion and the spontaneous respiratory rate decreased to a machine set rate. The machine set rate was decreased as the patient's spontaneous rate slowed. Thus, although the small infants could not trigger the BiPAP-ST™, provided that IPAP EPAP spans were adequate, they breathed in synchrony with it unless their spontaneous rate exceeded the machine's capabilities. The expiratory positive airway pressure (EPAP) was 3 cm H2O. An EPAP of 3 cm H2O was used to prevent excessive CO2 rebreathing while minimizing any decrease in the IPAP EPAP span.10

All patients were eventually weaned to nocturnal only nasal ventilation and discharged using a BiPAP-ST™. Following discharge daytime end-tidal CO2 remained normal for all patients. Bi-level spans were adjusted during sleep to achieve good chest expansion during inspiration, SaO2 greater than 94% without supplemental oxygen, and to better rest inspiratory muscles. All children received IPAP greater than 14 cm H2O.

We often used modified Hudson size 4 or 5 Infant Nasal CPAP Cannulas (Hudson Respiratory Care Inc., Temecula, CA) as nasal interfaces (Figure 1). The nasal seal had to be adequate for the infants to trigger or synchronize with the ventilator otherwise there were often precipitous oxyhemoglobin desaturations that necessitated brief manual resuscitation. The nasal interface was connected to the ventilator circuit using intervening tubing adapters. The restraints for these prongs were originally designed for infants less than 2 kg and, therefore, had to be improvised. For our children between 6 months and 5 years of age, when tolerated and effective (with minimal leak), we used the Respironics (Murrysville, PA) pediatric nasal mask.

While nasal ventilation aided inspiratory muscle function, expiratory aid was provided by manual abdominal compressions during the exsufflation phase of MI-E. MI-E was used via indwelling tubes and following extubation, via oral-nasal interfaces.11 Manual thrusts were not performed or were performed gingerly for two hours following meals.

The caregivers were trained in all aspects of noninvasive support including in chest percussion and postural drainage. They provided the bulk of the care within hours of extubation and through discharge. The children were discharged home with pulse oximeters, In-exsufflators, and BiPAP-ST™ machines. Following initial hospitalization arrangements were made for 24 hour nursing for one week. The home nurses were trained by specifically trained respiratory therapists and ultimately by the parents. Patients were considered to be able to cooperate successfully with the protocol during future chest colds when they could avoid hospitalizations despite requiring continuous nasal ventilation and have airway mucus associated oxyhemoglobin desaturations reversed by using respiratory muscle aids.9 The patients presented for physician evaluation when SaO2 persisted below 95% despite use of nasal ventilation and expiratory support, when fever persisted, or when dehydration was suspected.

We defined a failed extubation as that resulting in reintubation during the same hospitalization. We used a contingency table with Instat Software (Graphpad, CA) and developed an odds for success ratio for protocol vs. non-protocol extubations using the Woolf approximation.12 The two tailed Fishers exact t-test for unpaired data was used to determine significance. A p value less than 0.05 was considered significant.  

Results

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In all, eleven consecutively referred patients were treated by the respiratory aid protocol. The demographic data and the results of management are summarized in Table 2. They had 28 distinct episodes of respiratory compromise necessitating hospitalizations: two postoperative, two associated with insidiously progressive inspiratory muscle dysfunction, and 24 sudden episodes mostly due to chest colds. These resulted in a total of 48 intubations. Non-protocol therapy and extubation were attempted 20 times including eight times at our institution by non-participating physicians. Protocol therapy was used 28 times. On nine occasions children were extubated to continuous nasal ventilation despite having no autonomous breathing capability. These patients weaned to nocturnal-only nasal ventilation up to 3 weeks post-extubation. In three cases, the infants weaned to nocturnal-only nasal ventilation after discharge home. Two patients (Table 2 #10 and #11) remained 24 hour ventilator dependent.

Protocol care was generally well tolerated although two children had periods of abdominal distention while using nasal ventilation and required frequent burping of gastrostomy tubes. MI-E expulsed the secretions into the endotracheal tube or adapter or the mouth from where they were suctioned and oxyhemoglobin desaturations were reversed. Two patients received intramuscular glycopyrrolate (Robinul™) to decrease secretions prior to extubation.

Comparing the success of protocol vs. non-protocol extubations, the two tailed Fishers exact t-test p value of 0.001 was very significant. The odds ratio was 18.72 with a confidence interval from 2.85 to 92.56.12

One child (#6) succeeded in being extubated and discharged home with normal SaO2 and using only nocturnal nasal ventilation but was re-hospitalized in respiratory failure 3 times in 5 months because of persistent left lung collapse. She underwent tracheostomy and used nocturnal tracheostomy ventilation but died suddenly at home 3 months later. Another patient who developed respiratory failure at only 3 months of age (Table 2 #8) underwent tracheostomy at 7 months of age after 6 intubations during 3 months of almost continuous hospitalization. Another patient (#2) was lost to follow-up subsequent to relocation 3 months after successful extubation. The other seven patients are alive a mean of 34.7 months since their first episodes of respiratory failure. This includes one 6 year old boy who has been hospitalized and intubated 6 times during intercurrent chest colds. Over the last two years, however, he has required continuous nasal ventilation and successfully reversed airway mucus associated oxyhemoglobin desaturations during two chest colds and has, thus, avoided at least two hospitalizations.9 Two children have required continuous nasal ventilation and have had no autonomous breathing ability for 59 and 32 months, respectively, without ever being intubated. Although we do not have the hospital length of stay data for the patients managed at other institutions, the mean number of days our protocol patients were intubated was 8.23.2 and the mean hospital stay was 16.57.4 days.

Untreated SMA type 1 child have paradoxical breathing and develop pectus excavatum that worsens with time. Pectus excavatum disappeared with institution of nocturnal nasal ventilation for all 11 children.  

Discussion

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This study suggests that it may be possible for infants with SMA type 1 to avoid tracheostomy long enough to be able to cooperate with the use of respiratory muscle aids and possibly safely avoid tracheostomy indefinitely.6,9 This is important because the parents of children with neuromuscular disease often refuse tracheostomy but want their children to survive.

Hypercapnia can cause oxyhemoglobin desaturation. We have noted that neuromuscular disease patients tend to become symptomatic for hypercapnia only when it causes SaO2 to decrease below 95%. Likewise, desaturation can be caused by accumulating airway mucus. Thus, oxygen administration can eliminate oximetry as an important monitor of airway plugging and clinically significant alveolar hypoventilation and it can result in exacerbation of hypercapnia. It was only used post-extubation in conjunction with manual resuscitation to treat precipitous desaturations as nasal interfaces were being fit, ventilator synchronization achieved, and airway secretions exsufflated and suctioned. Its avoidance played an important role in the success of this protocol.

The use of nasal ventilation was reported to have failed to prolong life for children with SMA type 1.3 However, in this latter attempt, the low bi-level spans used may not have been adequate and MI-E was not used. All four patients who died did so from inadequate ventilatory assistance or failure to intubate or use expiratory aids during chest colds once the parents were resigned to let their children die.3 Indeed, MI-E via an indwelling tube has never before been reported. However, whether via a tube or via the upper airway its use succeeded in eliminating airway mucus and the children neither showed discomfort nor was there any evidence of barotrauma. It is appropriate for SMA type 1 children to nocturnally use high span bi-level positive airway pressure to prevent pectus excavatum and promote more normal lung growth.

Shortcomings of this study include the small number of patients and the lack of controls. However, performing a randomized, controlled trial in adequate numbers would be extremely difficult, if not impossible, considering the rarity of the disease, and the ethical issues involved in getting parents to permit such a trial. We excluded SMA type 2 patients to maintain sample homogeneity and because SMA type 2 patients are much easier to manage by this approach. Despite the small population, however, these 11 children had 48 interventions.

It might also be argued that a selection bias existed. Patients who repeatedly succeed in being extubated with conventional care might not have been referred to us and this might have resulted in children surviving without tracheostomy and without use of this protocol. However, greater than 3 year survival has not been reported for children with SMA type 1 without tracheostomy and only one other center has reported 24 hour ventilator users (none with SMA type 1) managed strictly noninvasively.13 Thus, most of the seven SMA type 1 infants known to continue to be managed noninvasively and who now have a mean age of 43.4 months would have been expected to have died or undergone tracheostomy by this time.

Larger issues at hand are those of quality of life, cost, and survival comparisons with children ventilated via tracheostomies. Tracheostomy IPPV has permitted children with SMA type 1 to survive more than 4 years.14 While "do not resuscitate" may be an acceptable alternative to tracheostomy for some parents, noninvasive ventilation can prolong life,6 is more desirable than tracheostomy,15 and in our experience, has not been refused. Patients who have used both tracheostomy and noninvasive ventilatory support almost invariably prefer the latter for safety, convenience, and facilitation of speech, sleep, swallowing, appearance, comfort, and overall acceptability.16 Besides the disadvantages of tracheostomy ventilation,6,9 the imposition of a tube often results in the need for continuous, rather than nocturnal-only ventilator use.16 This along with need for tracheal suctioning have untoward consequences on quality of life.17 Further, considering the ethics of ventilator use, unlike for tracheostomy ventilation users, individuals using noninvasive aids can discontinue them on their own.

On the other hand, the introduction of noninvasive ventilation often requires effort intensive ventilator synchronization, interface preparation and fitting, and airway secretion management, especially when the patient cannot cooperate. Thus, following extubation, patients can require close surveillance and intensive intervention for days until they wean to nocturnal-only nasal ventilation and their airway secretions have dissipated. The first few hours post-extubation can require the continuous presence and intense efforts of a highly skilled respiratory therapist to manage sudden, precipitous oxyhemoglobin desaturations. Since it can be virtually impossible to achieve this level of ongoing respiratory-nursing care for more than the initial post-extubation hours in our understaffed intensive care units, we train the infants' parents and rely heavily on them to eventually provide much if not most of the intensive care. Having a thoroughly trained and totally dedicated family member or care provider is critical for successful noninvasive home management. It must be emphasized that the parent must be comfortable managing sudden oxyhemoglobin desaturations by manually resuscitating the patient, using MI-E and oral suctioning, re-adjusting nasal interfaces, re-positioning, and applying other therapies to facilitate lung ventilation and airway secretion elimination. It is unlikely that this approach can succeed long-term if both parents work or have difficulty learning or performing the interventions required. Both of our patients who underwent tracheostomy had suboptimal parent involvement.

Cost is a difficult issue. For patients with milder neuromuscular conditions such as Duchenne muscular dystrophy, the avoidance of respiratory complications and hospitalizations with the use of noninvasive respiratory muscle aids create considerable cost savings by comparison with the prolonged hospitalizations associated with conventional management and tracheostomy.1,9,18 However, at least until SMA patients are old enough to cooperate with the noninvasive protocol, essentially every chest cold must be treated by hospitalization and intubation. This may be more costly and effort intensive than managing intercurrent chest colds via a tracheostomy tube. Cost, quality of life, and survival issues deserve further study.

In summary, the need to intubate an SMA type 1 infant does not mean that tracheostomy is inevitable. These patients have a better chance of successful extubation when they are extubated in the manner used in this study. Although intubation may be required during intercurrent chest colds, tracheostomy can usually be avoided if respiratory muscle aids are used by highly trained and dedicated parents both in the acute and home setting as needed.  

References

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1. Brooke MH: A Clinician's View of Neuromuscular Diseases, ed. 2. Baltimore: Williams & Wilkins, 1986, p. 243-331.

2. Zerres K, Rudnik-Schoneborn S. Natural history in proximal spinal muscular atrophy: clinical analysis of 445 patients and suggestions for a modification of existing classifications. Arch Neurol 1995: 52;518-23

3. Birnkrant DJ, Pope JF, Martin JE, et al. Treatment of type 1 spinal muscular atrophy with noninvasive ventilation and gastrostomy feeding. Pediatr Neurol 1998; 18:407-10

4. Wysocki M, Tric L, Wolff MA, et al. Noninvasive pressure support ventilation in patients with acute respiratory failure. Chest 1993; 103:907-13

5. Antonelli M, Conti G, Rocco M, et al. A comparison of noninvasive positive pressure ventilation and conventional mechanical ventilation in patients with acute respiratory failure. N Engl J Med 1998; 339:429-35

6. Bach JR, Rajaraman R, Ballanger F, et al. Neuromuscular ventilatory insufficiency: the effect of home mechanical ventilator use vs. oxygen therapy on pneumonia and hospitalization rates. Am J Phys Med Rehabil 1998; 77:8-19

7. Bach JR, Alba AS, Saporito LR. Intermittent positive pressure ventilation via the mouth as an alternative to tracheostomy for 257 ventilator users. Chest 1993; 103:174-82

8. Bach JR, Alba AS. Management of chronic alveolar hypoventilation by nasal ventilation. Chest 1990; 97:52-57

9. Bach JR, Ishikawa Y, Kim H. Prevention of pulmonary morbidity for patients with Duchenne muscular dystrophy. Chest 1997; 112:1024-28

10. Kacmarek RM. Characteristics of pressure-targeted ventilators used for noninvasive positive pressure ventilation. Respir Care 1997; 42:380-88

11. Bach JR. Update and perspectives on noninvasive respiratory muscle aids: part 2--the expiratory muscle aids. Chest 1994; 105:1538-44

12. Woolf B. On estimating the relation between blood group and disease. Ann Human Genet 1955; 19:251-53

13. Viroslav J, Rosenblatt R, Morris-Tomazevic S. Respiratory management, survival, and quality of life for high-level traumatic tetraplegics. Respir Clin N Am 1996; 2:313-22

14. Wang TG, Bach JR, Avilez C, Alba AS, Yang GF. Survival of individuals with spinal muscular atrophy on ventilatory support. Am J Phys Med Rehabil 1994; 73:207-211

15. Bach JR. A comparison of long-term ventilatory support alternatives from the perspective of the patient and care giver. Chest 1993; 104:1702-06

16. Haber II, Bach JR. Normalization of blood carbon dioxide levels by transition from conventional ventilatory support to noninvasive inspiratory aids. Arch Phys Med Rehabil 1994; 75:1145-50

17. Bach JR. Ventilator use by muscular dystrophy association patients: an update. Arch Phys Med Rehabil 1992; 73:179-83

18. Bach JR, Intintola P, Alba AS, et al. The ventilator-assisted individual: cost analysis of institutionalization versus rehabilitation and in-home management. Chest 1992; 101:26-30    

Table 1 - Protocol Vs. Conventional Management of Intubated SMA 1 Patients

Conventional

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1. Oxygen administrated arbitrarily in concentrations that maintain SaO2 well above 95%.

2. Frequent airway suctioning via the tube.

3. Supplemental oxygen increased when desaturations occur.

4. Ventilator weaning attempted at the expense of hypercapnia.

5. Extubation not attempted unless the patient appears to be ventilator weaned.

6. Extubation to CPAP or low span bi-level positive airway pressure and continued oxygen therapy.

7. Deep airway suctioning by catheterizing the upper airway along with postural drainage and chest physical therapy.

8. With increasing CO2 retention or hypoxia supplemental oxygen is increased and ultimately the patient is reintubated.

9. Following re-intubation tracheostomy is thought to be the only long-term option
...or following successful extubation bronchodilators and ongoing routine chest physical therapy are used.

10. Eventually discharged home with a tracheostomy, often following a rehabilitation stay for family training.  

Protocol

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1. Oxygen administration limited only to approach 95% SaO2.

2. Mechanical insufflation-exsufflation used via the tube at 25 to 40 cm H2O to -25 to -40 cm H2O pressures up to every 10 minutes as needed to reverse oxyhemoglobin desaturations due to airway mucus accumulation and when there is auscultatory evidence of secretion accumulation. Abdominal thrusts are applied during exsufflation. Tube and upper airway are suctioned following use of expiratory aids as needed.

3. Expiratory aids used when desaturations occur.

4. Ventilator weaning attempted without permitting hypercapnia.

5. Extubation attempted whether or not the patient is ventilator weaned when meeting the following:

A. Afebrile

B. No supplemental oxygen requirement to maintain SaO2 >94%

C. Chest radiograph abnormalities cleared or clearing

D. Any respiratory depressants discontinued

E. Airway suctioning required less than 1-2x/eight hours

F. Coryza diminished sufficiently so that suctioning of the nasal orifices is required less than once every 6 hours (important to facilitate use of nasal prongs/mask for post-extubation nasal ventilation)

6. Extubation to continuous nasal ventilation and no supplemental oxygen.

7. Oximetry feedback used to guide the use of expiratory aids, postural drainage, and chest physical therapy to reverse any desaturations due to airway mucus accumulation.

8. With CO2 retention or ventilator synchronization difficulties nasal interface leaks were eliminated, pressure support and ventilator rate increased or the patient switched from BiPAP-ST™ to using a volume cycled ventilator. Persistent oxyhemoglobin desaturation despite eucapnia and aggressive use of expiratory aids indicated impending respiratory distress and need to re-intubate.

9. Following re-intubation the protocol was used for a second trial of extubation to nasal ventilation
...or following successful extubation bronchodilators and chest physical therapy were discontinued and the patient weaned to nocturnal nasal ventilation.

10. Discharge home after the SaO2 remained within normal limits for 2 days and when assisted coughing was needed less than 4 times per day.  

Table 2 - Spinal Muscular Atrophy 1: Noninvasive Management Outcomes

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   Age (months)  Conventional Outcomes  Protocol Outcomes 
#SexabcSuccessFailureSuccessFailure
1F621440020
2M628*310320
3M626812540
4F411420031
5F413420031
6F67**150320
7F1112270342
8M33***120411
9M628580020
10M2537    
11M4766    

Age: a = first diagnosed, b = first intubation or episode requiring ventilatory support, c = last follow up, c-b = except for #6 and #8, months of use of nocturnal nasal ventilation;

*--lost to follow up; **--deceased suddenly after 3 months of tracheostomy ventilation; ***--underwent tracheostomy following an unsuccessful extubation using the protocol


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