Acute neuromuscular respiratory failure: Viva

Q1. Why is his saturation 98 percent when he is clearly failing?

Because neuromuscular respiratory failure is a failure of the respiratory pump, not the lungs. The lung tissue is structurally normal, so the alveoli that are still ventilated continue to oxygenate the blood reaching them and the saturation stays high. What fails is the bellows: the weak diaphragm and intercostals move less air, so carbon dioxide climbs while oxygenation is preserved. The saturation is therefore reassuring in the wrong direction, and the child can arrest with a normal saturation. [4][1]

Probe: So what does the saturation tell you? It tells me almost nothing useful at this stage. I drive the decision from the bedside forced vital capacity and the bulbar assessment, never from the saturation or a single blood gas, which are both late and confirmatory. [3]

Q2. How do you monitor him, and at what point do you intubate?

I measure serial bedside spirometry every two to six hours, recording forced vital capacity, maximum inspiratory pressure, and maximum expiratory pressure, plotting them on a trend, and acting on the Lawn thresholds. A forced vital capacity under 20 mL per kilogram, a fall of over 30 percent in twenty-four hours, a maximum inspiratory pressure weaker than minus 30 cmH2O, and a maximum expiratory pressure under 40 cmH2O each predict the need for ventilation. He meets them all, so I intubate now. [1][2]

Probe: What if the bulbar function were intact? Then I could trial non-invasive bilevel positive airway pressure for pure pump failure, with cough augmentation and close spirometry, intubating only if it failed or bulbar weakness developed. But this child has bulbar weakness, so the mask will not protect his airway, and the answer is intubation. [9]

Q3. What drug do you avoid at intubation, and what do you use instead?

I avoid suxamethonium entirely. In denervating or chronically diseased muscle, extrajunctional immature acetylcholine receptors proliferate across the muscle membrane, so depolarisation by suxamethonium releases potassium from a large muscle mass and can cause hyperkalaemic cardiac arrest. I use rocuronium one milligram per kilogram intravenously for rapid sequence intubation instead. [10]

Probe: Is this only for diagnosed disease? No. I avoid suxamethonium in any child with a known or suspected neuromuscular disorder, because the upregulation of receptors begins early in denervation and the first arrest may be the presenting event. [10]

Q4. Run me through the differential of acute neuromuscular respiratory failure.

I frame it by the tempo and the level of the motor unit. In a previously well child over hours to days, Guillain-Barre syndrome leads with ascending symmetrical areflexic weakness, acute flaccid myelitis with focal asymmetric polio-like weakness after a viral illness, myasthenic crisis with fatigable ocular-bulbar weakness, and infant botulism with descending weakness, cranial-nerve palsies, and constipation. Tick paralysis is ascending and areflexic but resolves on tick removal, and periodic paralysis is metabolic, reversible, and electrolyte-driven. Chronic disease that decompensates with an infection brings spinal muscular atrophy, the muscular dystrophies, and the congenital myopathies. [4][3]

Probe: What must you exclude urgently? A surgical cord compression from tumour, abscess, or haematoma, which produces back pain and a sensorimotor level and needs an urgent spinal MRI. [4]

Q5. What disease-specific therapy applies, and what do you tell the family?

For Guillain-Barre syndrome I give intravenous immunoglobulin two grams per kilogram over two to five days; corticosteroids have no role. I tell the family that children recover faster and more completely than adults, that the intensive-care course is dominated by weaning ventilation and managing autonomic instability, and that recovery runs over weeks to months with the majority walking independently within a year. I am honest about residual fatigue and weakness, and I give a clear safety-net for relapse and autonomic instability with paediatric neurology and rehabilitation follow-up. [4][1]

Probe: How does this change in a chronic disease such as spinal muscular atrophy or Duchenne muscular dystrophy? In chronic disease the respiratory reserve is silently eroded, so I institute proactive non-invasive ventilation and cough augmentation, use disease-modifying therapy where it applies, and hold the family-centred conversation about tracheostomy and long-term ventilation against quality of life rather than rushing to intubate every intercurrent infection. [4]