Calvo et al identified factors that can be used to identify a patient with amyotrophic lateral sclerosis (ALS) who is at risk for respiratory failure. This may be associated with worse overall survival. The authors are from Torino and Orbassano in Italy.
Risk factors for decreased survival::
(1) respiratory rate > 25 breaths per minute
(2) hypercapnia
(3) low vital capacity (as percent of predicted)
A patient with a respiratory rate > 25 breaths per minute has an increased risk of hypercapnia. This was relatively specific (82%) but not very sensitive (46%).
Vital Capacity
Hazard Ratio for Death
> 76%
1.0
50 - 76%
1.7
< 50%
3.6
where:
• According to Tietz's Clinical Guide for Laboratory Tests (1995), the upper limit to the normal reference range for PaCO2 is 48 mm Hg in men and 45 mm Hg in females.
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