[Nocturnal hypoxia index: a new pulse oxymetry index of nocturnal hypoventilation in neuromuscular disorders].
Respiratory insufficiency due to progressive muscle wasting is a major cause of death in various neuromuscular disorders. Morning headache and anorexia leading to slowly progressive body weight loss are frequently observed as initial symptoms of insufficient ventilation. From our experience nocturnal pulse oxymetry is a valuable study to detect early respiratory insufficiency and helpful to evaluate the effectiveness of ventilatory assistance, since ventilation is more impaired during sleep in early stage of respiratory insufficiency. Percent desaturation time (total desaturation time (SaO2 < or = 90%)/total sleep time) has been used as the most reasonable index of nocturnal hypoventilation. The criteria for introduction of nocturnal mechanical ventilation is 20% or more in Duchenne muscular dystrophy. Unfortunately, the earliest stage of hypoventilation cannot be detected by this index and it is of no use in advanced respiratory failure, because this index never exceeds 100% by definition. Here we propose a new index for nocturnal hypoventilation, which is defined as follows: nocturnal hypoxia index (NHI) = (% time of 95% > or = SaO2 > 90%) + (% time of 90% > or = SaO2 > 85%) x 2 + (% time of 85% > or = SaO2 > 80%) x 3 + (% time of 80% > or = SaO2 > 75%) x 4 + (% time of 75% > or = SaO2 > 70%) x 5.... This index is good for any stage of respiratory failure, and applicable to nocturnal hypoxia of other causes. The criteria for initiating mechanical ventilation in DMD can be substituted by "NHI is above 130."
Kawai
M
M
Department of Neurology, Shimoshizu National Hospital.
Shintani
M
M
Komiya
T
T
Yatabe
K
K
D000328:Adult; D006801:Humans; D000860:Hypoxia / Q000175:diagnosis* / Q000209:etiology; D009468:Neuromuscular Diseases / Q000150:complications*; D010092:Oximetry; D012891:Sleep Apnea Syndromes / Q000175:diagnosis* / Q000209:etiology