OUTCOMES:
Type 2 and 3 Neuromuscular Disease* including
Spinal Muscular Atrophy* types 2 and 3

*NMD

*SMA

(Exclusive of Duchenne Muscular Dystrophy)

 

INTRODUCTION

 

Incidence in the New Jersey "Center for Noninvasive Respiratory Management":

 

Spinal muscular atrophy type 2: 179

Congenital myopathies: 75

Spinal muscular atrophy type 3: 71

Congenital muscular dystrophies: 29

Congenital polyneuropathies: 8

Congenital myotonic dystrophy: 8

Glycogen storage disease: 4

 

NMD types 1-3 by severity:

 

  1. NMD type 1: The children can never roll or sit independently.

  2. NMD type 2: The children can sit but never walk.

  3. NMD type 3: The children can walk for some period of time.

  4. NMD type 4: The patient’s onset is in adolescence or as an adult.

(Type 5 Kennedy’s disease is adult onset.)

 

Children with SMA and other NMD type 2 disorders achieve the ability to sit and with type 3, the ability to walk. While virtually all infants with SMA type 1 have paradoxical breathing and require sleep noninvasive ventilatory support (NVS), 50% of children with SMA type 2 and many with other type 2 NMDs also have paradoxical breathing and require sleep NVS to prevent pectus excavatum and promote lung and chest wall growth (JBCV214). For these more mildly affected children with type 2 and 3 disorders, vital capacities plateau (plateau VC) after age 10 and ongoing lung ventilation is not generally a problem until adolescence or adulthood (JBCV214).

 

However, like children with type 1 disorders, children with type 2 and 3 often develop pneumonia and acute respiratory failure (ARF) as the result of otherwise benign upper respiratory tract infections (URIs) (e.g. respiratory syncytial virus) that, because of inability to cough effectively, can necessitate intubation despite optimal use of NVS and mechanical insufflation-exsufflation (MIE) by expert parents using the oximetry feedback protocol. This can occur at any age and even before age 2 for children with NMD type 2. Although children who do not have paradoxical breathing may not need sleep NVS when well, they may need it around-the-clock (continuously on CNVS) when ill because of fatigue and debility caused by trying to cough out airway sputum for days to weeks to even months. They will use portable ventilators for this with active ventilator circuits that are volume-preset to permit air stacking if the patients’ throat muscle strength permits or for those who cannot air stack, pressure-preset ventilation with set pressures of about 20 cm H2O and physiologic backup rates. For older children and adults, the assist-control mode volumes are set at about 700 to 1500 mL, so that the user can take as much air as needed for each breath and let the rest leak. These large volumes can be used to increase cough flows, increase voice volume, and maintain lung health (compliance and elasticity).

 

While these children may not need ongoing sleep NVS, when their cough flows cannot expulse airway secretions, airway mucus plugging can cause their O2 sat to decrease below 95% when they are ill. Their families and care providers then may need to use MIE up to every 15 minutes, essentially almost continuously, along with oximetry feedback to clear the airways day and night until the secretions decrease. Use of MIE as per the protocol expulses the sputum and re-normalizes O2 sat and usually pneumonia and respiratory failure can be avoided in this way. For infants and all patients who cannot cooperate with it, MIE must be timed to the child’s breathing or the “Cough Track” setting on the CouthAssist[TM] can be used. That is, when the belly goes out (inhalation), insufflation at 50 to 60 cm H2O pressure is given via an oronasal interface and when the belly goes in (exhalation), the negative pressure exsufflation is applied at 50 to 60 cm H2O. Cycles from positive to negative may need to be delivered more than once per second for rapidly breathing children.

 

When the O2 sat baseline decreases below 95% despite optimal CNVS and MIE use and the children and parents are exhausted, hospitalization becomes necessary. Although usually the combination of CNVS and MIE successfully prevents pneumonia and respiratory failure and hospitalization and intubation are avoided, at least when the children are old enough to fully cooperate with MIE, the oximetry feedback protocol may be unknown to the parents, be inadequately used, or may simply fail to renormalize O2 sat (JBCV193).

 

Typically, parents call to say that their child is ill after calling their local doctors and having a difficult to interpret chest x-ray done and broad spectrum antibiotics administered to help prevent secondary community-acquired bacterial infections. However, when the parents do not know the child’s O2 sat, they are blind to the child’s ventilation, airway secretion congestion, and extent of lung disease. If the O2 sat is normal, then, although the antibiotics may be useful, the x-ray rarely if ever is, and supplemental O2 must be avoided. If the O2 sat is not normal (≥ 95%) and the child is not in distress, then he or she is usually better off staying home for effective protocol use by parents expert in CNVS and MIE rather than travel to an emergency room without frequent and immediate access to MIE. High fever and dehydration, however, can certainly be reasons for referral to pediatricians.

 

The greatest danger is when upon contact with emergency personel, supplemental O2 is administered in the ambulance or emergency room and the child’s CO2 levels typically soar; they lose consciousness, stop breathing, and require emergency intubation. Intubated children for whom MIE is used via the endotracheal tube at 70 cm H2O pressures usually get healthy in a few days whereas struggling to clear airway secretions without intubation can continue for weeks and sometimes months. Local doctors fail to appreciate that intubated unweanable patients can almost invariably be extubated back to CNVS once their lungs are healthy again so they think that once intubated these patients will need tracheostomy tubes. Since few children with SMA type 1 need tracheostomy tubes for continuous ventilatory support, virtually none with the milder NMDs ever need tracheostomy tubes.

 

None of the over 400 NMD type 2 or 3 NVS users from the New Jersey and Porto centers have tracheostomy tubes even though over 50 are CNVS dependent. This includes two people with SMA type 2, CNVS dependent for over 10 years and over age 60, and 7 SMA type 3 patients into their 60s and 70s.

 

 

EXTUBATION OF SMA TYPE 2 AND OTHER NMD TYPE 2 CONDITIONS

 

While children with SMA type 2 or 3 may need to be intubated on occasion, since CNVS dependent children with SMA type 1 do not need tracheostomy tubes, children with the milder NMDs virtually never need them when properly managed with NVS and MIE. Extubation should be done only when the child:

 

  • Is afebrile,

  • Has a normal white blood cell count,

  • O2 sat baseline over 94% in ambient air, AND

  • A clearing chest x-ray.

 

Ambient air O2 sat must be normal (≥ 95%) for at least 12 hours before any extubation attempt. Although average volume assured pressure support (AVAPS) and other bi-level PAP systems can be used, they are suboptimal because patients can not physiologically vary their tidal volumes, air stack, or get large breaths for coughing and increasing speech volume, and the pressure cycling gushes air into the throat to compensate for leakage during sleep, often waking up the patient.

 

Pressure-control CMV with active circuits on portable ventilators is preferred. In either case, full ventilatory support settings of either CMV 20 cm H2O or high-span bi-level PAP (IPAP 24, EPAP 4) and backup rates that facilitate patient synchrony must be used. No supplemental O2 or sedative medications must be given and the child extubated to a nonvented nasal interface as described (JBCV197,JBCV235).

 

Through 2015, 85 consecutive unweanable patients with NMD types 2 and 3 including 40 with SMA and 45 with myopathies and muscular dystrophies exclusive of DMD were extubated successfully, not including 3 more recently successfully extubated in 2015.(JBCV197,JBCV235) None have undergone tracheotomy then or subsequently. Of our 762 patients with myopathic and neuromuscular junction disorders, including 113 with myasthenia gravis and two with congenital and pre-receptor myasthenia gravis, only 7 with myotonic dystrophy whose principal problem was myotonia rather than muscle weakness and 2 muscular dystrophy patients with concommittant lung disease (bronchiectasis) were converted from CNVS to continuous tracheostomy mechanical ventilation (TMV) for ongoing ventilatory support.

 

 

DECANNULATION OF CHILDREN WITH NMD TYPES 1-3

 

Children dependent on either part-time or continuous TMV should only be evaluated for decannulation if they will cooperate with CNVS and MIE. Generally, CTMV dependent children who wish to be decannulated can be after 15 years of age provided that they can rotate their heads 30 degrees to grab a mouthpiece for NVS. If they have less than 200 ml of VC and cannot rotate their heads sufficiently to grab a mouthpiece, they should first be evaluated for a phrenic pacemaker.

 

We are aware of no NVS dependent children with NMD type 1 who have been decannulated of their tracheostomy tubes. In theory this is possible for babies and small children by intubating the child, decannulating him/her, suturing the ostomy closed, then extubating to CNVS and MIE as is done for intubated children with NMD type 1.

 

On the other hand, children with NMD types 2 and 3 who do not use ventilators and who achieve MIE-exsufflation flows (MIE-EF) of 150 L/min or greater can safely have their tubes removed and MIE should effectively expulse airway secretions when necessary. For children using sleep TMV, who may require post-decannulation sleep NVS, the clinician must be certain that the child will be cooperative with it once the tube is out. If the child has paradoxical breathing, this will be necessary; otherwise, as long as the VC is over ~150 mL for a small child and 200 mL for an older child, it might be best to leave the child off of TMV for one night and study EtCO2 and O2 sat.

 

Children without paradoxical breathing with VCs over 250 mL, unless grossly obese or scoliotic, are likely to be completely weanable. CTMV dependent children who are not weanable should not be evaluated for decannulation until over age 12 when they may be less frightened and more cooperative. The steps for decannulation of children who use NVS are the same as for adults:

 

  1. Switch to a cuffless, fenestrated tube.

  2. Use nasal NVS with the tube capped for at least one week.

  3. Decannulate.

 

Our New Jersey "Center for Noninvasive Respiratory Management" have reported decannulating 43 patients with myopathies other than DMD, most of which were done in the outpatient setting, despite 32 having no ventilator-free breathing ability (JBCV232).