A NEW LOOK AT THE STRESS INDEX FOR LUNG INJURY

Abstract

Ranieri and colleagues1,2 have proposed a simple mathematical equation (Paw(t) ≈ atb+c) where a, b, and c are constants that relates airway pressure, Paw(t), over inspiration (0 ≤ t ≤ ti) in constant flow mechanical ventilation to ventilator-induced lung injury. They have correlated b with low-volume stress (b ≤ 0.9), high-volume stress (b ≥ 1.1), and minimal stress (0.9 ≤ b ≤ 1.1) in the lungs. In this paper we examine the theoretical underpinnings of this empirical equation and show that it has a relationship to the upper and lower inflection points of the Pelastic - V curve during inspiration. An alternative equation [Formula: see text] that comes from the theoretical analysis of this type of mechanical ventilation is presented. Both equations are compared using experimental data.