A ventilator requirement index.

OBJECTIVE To determine the efficacy of vital capacity (VC) and a proposed ventilator requirement index (VRI) for justifying ventilator prescription and use for patients with neuromuscular/chest wall diseases (NMD). DESIGN Prospective observational study in which 319 patients with NMD, including 187 ventilator users, were separated into four groups: (1) asymptomatic, (2) abnormal specific screening factors and/or symptomatic, (3) ventilator use 8-20 hrs/day, and (4) >20 hrs/day of ventilator use. The VRI was defined as 60 x Ti/(Ttot)2 x (Vt/VC) x RR, where Ti = inspiratory time of one breath (secs), Ttot = total time of one breath (secs), Vt = tidal volume (ml) at rest, VC = vital capacity (ml), and RR = respiratory rate. RESULTS The overall analysis of variance F-tests and post hoc pairwise contrasts were significant (P < 0.001) for differences in the VC and VRI across groups. Thus, VC and VRI are independent predictors of group membership. Satisfying VC or VRI criteria signaled the highest number of patients benefiting from ventilator use. CONCLUSIONS The prescription of one or two ventilators can be justified by both VC and VRI, with the combination being most sensitive.