MECHANICAL VENTILATION WITH 100-PERCENT OXYGEN DOES NOT INCREASE INTRAPULMONARY SHUNT IN PATIENTS WITH SEVERE BACTERIAL PNEUMONIA

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Abstract
Pure O2 ventilation was shown to increase the right to left shunt .ovrhdot.QS/.ovrhdot.QT in both normal and diseased lungs. N2 absorption atelectasis, an explanatation of the phenomenon, is likely to occurin lung units with low ventilation/perfusion rato. In 11 patients with severe unilateral or bilateral bacterial pneumonia, the effects of increasing FIO2 from maintenance level (m = 0.44 .+-. 0.11) to 1.0 were assessed. Venous admixture (.ovrhdot.QVA/.ovrhdot.QT) was calculated using the O2 method, and the distribution of the .ovrhdot.VA/.ovrhdot.Q ratios were assessed with the 6 inert gas (IG) technique providing the distribution between the true shunt (.ovrhdot.QS/.ovrhdot.QT IG) and the low .ovrhdot.VA/.ovrhdot.Q units. Although a large part of perfusion was distributed preferentially to low .ovrhdot.VA/.ovrhdot.Q units, ranging from 2-43% of cardiac output,thus placing large zones of lung parenchyma at risk of absoprtion atelectasis. .ovrhdot.QVA/.ovrhdot.QT decreased from 31 .+-. 13%-25 .+-. 10% and IG shunt did not increase after 30 min of O2 ventilation. .ovrhdot.QS/.ovrhdot.QT Ig remained unalterd despite P.hivin.vO2 increase from 32-43 mmHg suggesting a poor level of hypoxic vasoconstriction in human bacterial pneumonia.

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