EFFECT OF 2 TIDAL VOLUMES ON OXYGENATION AND RESPIRATORY SYSTEM MECHANICS DURING THE EARLY-STAGE OF ADULT-RESPIRATORY-DISTRESS-SYNDROME

Purpose: To study the effect of two tidal volumes on gas exchange, lun g mechanics, and hemodynamics in 12 patients with acute respiratory di stress syndrome (ARDS) within the first 72 hours of mechanical ventila tion. Methods: Tidal volume (VT) was increased by 40% from the initial value at fixed positive end-expiratory pressure (PEEP) and matched mi nute ventilation by adjusting the respiratory rate (RR) of the ventila tor. Initial VT and RR were 592 +/- 42 mL and 19 +/- 1 min 1, respecti vely. High VT amounted to 825 +/- 54 mL with a RR of 12 +/- 1 min-1. R esults: We found that at high VT (1) the index of oxygenation increase d from 0.22 +/- 0.03 to 0.32 +/- 0.04 (P < .001) with a parallel decre ase in the right to left venous admixture from 0.26 +/- 0.02 to 0.23 /- 0.02 (P < .001), and in the ratio of physiological dead space to ti dal volume (VDS/VT) from 0.53 +/- 0.05 to 0.46 +/- 0.04 (P < .01), wit hout impairment to hemodynamics and (2) respiratory system compliance improved significantly from 34.8 +/- 2.8 mL/cm H2O to 37.2 +/- 2.9 mL/ cm H2O (P < .05). In 4 patients, we performed pressure-volume curves o n PEEP with the ventilator finding an upward concavity reflecting prog ressive alveolar recruitment with increasing inflation volume in 3. Co nclusions: High-tidal ventilation in the early stage of ARDS improved gas exchange, suggesting recruitment during the inspiratory phase. How ever, the benefit of better oxygenation should be weighed against the potential risk of barotrauma induced at high VT. Copyright (C) 1994 by W.B. Saunders Company