chapter  12
22 Pages

Interaction of VILI with Previous Lung Alterations

WithJean-Damien Ricard, Didier Dreyfuss, Georges Saumon

Initial description of ventilator-induced lung injury (VILI) was made by

ventilating normal lungs with high peak inspiratory pressures (PIP) (1). However, mechanical ventilation is most often used in patients with dis-

eased lungs. These lungs are inhomogenous, normal zones coexisting with

edematous or atelectatic ones (2). Thus it is conceivable that inflation of

lungs with heterogeneously distributed lesions may lead to greater regional

stress and local overinflation than that of uniform uninjured ones. Mead

et al. were the first to conceptualize the increased risk of tissue injury during

inflation when lungs had zones of atelectasis (3). They calculated that the

pressure tending to expand an atelectatic region surrounded by a fully expanded lung would be approximately 140 cmH2O at a transpulmonary

pressure of 30 cmH2O (3). They further speculated that ‘‘mechanical venti-

lators, by applying high transpulmonary pressure to the nonuniformly

expanded lungs of some patients who would otherwise die of respiratory

insufficiency, may cause the hemorrhage and the formation of hyaline mem-

branes found in such patients’ lungs at death’’ (3). Other abnormalities that

may increase lung tissue stress are the presence of significant areas excluded from the ventilation. In that case, the bulk of ventilation is delivered to

smaller (and likely less damaged) lung volume that thus would be at a

greater risk of overinflation.