The parents of infants with neuromuscular disorders, most often, infants with SMA types 1 and 2, are told that their children will not survive infancy. Typically, these children are well until a cold causes airway secretions to accumulate in the lungs because of a weak cough mechanism. Bacteria multiply in the secretions and the child develops pneumonia and respiratory failure. After hospital admission, the child is typically intubated (a tube is passed via the nose or mouth into the lungs) for ventilatory support and airway suctioning. Attempts to remove the tube usually fail because the methods used to do so are appropriate for children with primarily lung disease rather than muscle weakness. Once extubation has failed, the parents are told to either let the child die or to agree to tracheotomy (placing a tube permanently in the neck for ventilatory support and suctioning). We have found that this is usually unnecessary when noninvasive inspiratory and expiratory muscle aids are used appropriately.
Infants cannot air stack delivered volumes of air or cooperate to receive maximal insufflations. All SMA type 1 babies, SMA type 2 infants and others with infantile neuromuscular weakness who have paradoxical chest wall movement (inward movement of the chest when the belly goes outward during inspiration), require nocturnal high span bi-level positive airway pressure to prevent pectus excavatum (chest deformity) and promote lung growth (See Further Information and Article 143 in the Bibliography). Nocturnal high span bi-level positive airway pressure prevents or reverses pectus excavatum. It should be introduced to the small child once he or she is asleep. The child gradually becomes accustomed to it. Inspiratory pressures should begin at 15 cm H2O and be gradually increased to 18 to 20 cm H2O. Expiratory pressures should be left at the minimum or 2 cm H2O. In addition to nocturnal aid, deep insufflations are provided via oral-nasal interface for children over 1 year of age along with concomitant abdominal thrusts to prevent abdominal expansion so as to direct the air into the upper chest. These insufflations need to be timed to the child's inspirations. Children can become cooperative with deep insufflation therapy by 14 to 30 months of age.
We have routinely used MI-E via translaryngeal and tracheostomy tubes in children with SMA under 1 year of age. Although we have been using approximately the same pressure settings as for adults, that is, +40 to -40 cm H2O, its use through the very narrow gauge pediatric tubes results in a severe pressure drop off that may not permit the generation of optimal exsufflation flows. However, even at these probably inadequate pressures secretions are expulsed and dSaO2s reversed. It needs to be determined how to compensate the pressure drop offs through very narrow tubes.
The use of MI-E via the upper airway can be effective for children as young as 13 months of age. Children this young can become accustomed to MI-E and permit its effective use by not crying or closing their throats. Between two and one-half and five years of age most children become able to cooperate and cough on queue with MI-E and they can then avoid hospitalizations and pneumonias during their intercurrent chest infections. Exsufflation timed abdominal thrusts are also used for infants.
Children to small to cooperate with manually and mechanically assisted coughing or those who are not introduced to these methods before a cold develops into pneumonia and respiratory failure are hospitalized and usually intubated (a catheter is passed via the nose or mouth into the lungs for ventilatory support and airway secretion evacuation). Often, each time that small children develop chest infections until they are old enough to cooperate they need to be hospitalized and intubated. Our Intensive Care Protocol must be used to return these children home without the need to do a surgical tracheostomy. Patients using these methods as outpatients can also avoid respiratory complications and hospitalizations.
Whether used via the nose or mouth or via invasive indwelling airway tubes, routine airway suctioning misses the left lung about 90% of the time so that 80% of pneumonias are in the left lung. MI-E via an airway tube provides the same exsufflation flows in both left and right airways without the discomfort or airway trauma of tracheal suctioning and it can be effective when suctioning isn't. Patients invariably prefer MI-E to suctioning for comfort and effectiveness and they find it less tiring. Deep suctioning, whether via airway tube or via the upper airway, can essentially be discontinued for most patients.
The use of MI-E has permitted us to consistently extubate people with neuromuscular disease following general anesthesia despite their lack of any ability to breathe on their own, and to manage them with noninvasive IPPV. It has also permitted us to avoid intubation or to quickly extubate people in acute ventilatory failure and with profuse airway secretions due to intercurrent chest infections. MI-E in a protocol with manually assisted coughing, oximetry feedback, and home use of noninvasive IPPV was shown to effectively decrease hospitalizations and respiratory complications and mortality for people with neuromuscular diseases. It may not be effective if the user cannot cooperate sufficiently to keep the airway open, if there is a fixed upper airway obstruction, or if upper airway dilator muscles cannot maintain sufficient patency to allow for PCF to exceed 160 L/m. This is most often seen in advanced amyotrophic lateral sclerosis with severe throat muscle weakness. MI-E has been demonstrated to be extremely safe even when used many times at pressures of 40 to 60 cm H2O. It is rarely effective for people of any age at pressures less than 35 cm H2O.
For other techniques that assist respiratory muscle effort including the use of oro-nasal interfaces, see Further Information. People with generalized weakness living at home need to be trained and equipped to follow the Outpatient Protocol of respiratory muscle aids to remain free of pneumonia, respiratory failure, hospitalization, and tracheostomy and read appropriate articles and books.
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