Pulmonary gas exchange response to oxygen breathing in acute lung injury.
The mechanisms and time course of the pulmonary gas exchange response to 100% O(2) breathing in acute respiratory failure needing mechanical ventilation were studied in eight patients with acute lung injury (ALI) (48 +/- 18 yr [mean +/- SD]) and in four patients (66 +/- 2 yr) with chronic obstructive pulmonary disease (COPD). We postulated that, in patients with ALI while breathing 100% O(2), the primary mechanism of hypoxemia, i.e., increased intrapulmonary shunt, would further worsen (increase) as a result of reabsorption atelectasis. Respiratory and inert gases, and systemic and pulmonary hemodynamics were measured at maintenance fraction of inspired oxygen (FI(O(2))-m), at 30 and 60 min while breathing 100% O(2), and then at 30 min of resuming FI(O(2))-m. During 100% O(2) breathing, in patients with ALI, Pa(O(2)) (by 207 and 204 mm Hg; p < 0.01 each), Pa(CO(2)) (by 4 mm Hg each) (p < 0.05 each), and intrapulmonary shunt (from 16 +/- 10% to 22 +/- 11% and 23 +/- 11%) (p < 0.05 each) increased respectively. By contrast, in patients with COPD, Pa(O(2)) (by 387 and 393 mm Hg; p < 0.001 each), Pa(CO(2)) (by 4 and 5 mm Hg) and the dispersion of pulmonary blood flow (log SDQ) (from 1.33 +/- 0.10 to 1.60 +/- 0.20 and 1.80 +/- 0.30 [p < 0.05]) increased, respectively. In patients with ALI, the breathing of 100% O(2) deteriorates intrapulmonary shunt owing to collapse of unstable alveolar units with very low ventilation-perfusion (V A/Q) ratios, as opposed to patients with COPD, in whom only the dispersion of the blood flow distribution is disturbed, suggesting release of hypoxic pulmonary vasoconstriction.
Santos
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C
Servei de Pneumologia i Al.lèrgia Respiratòria, Departament de Medicina, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Hospital Clínic, Universitat de Barcelona, Barcelona, Spain.
Ferrer
M
M
Roca
J
J
Torres
A
A
Hernández
C
C
Rodriguez-Roisin
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R
D000368:Aged; D001784:Blood Gas Analysis; D005260:Female; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D018496:Hyperoxia / Q000097:blood / Q000503:physiopathology; D008173:Lung Diseases, Obstructive / Q000150:complications / Q000503:physiopathology / Q000628:therapy; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D010102:Oxygen Inhalation Therapy; D011175:Positive-Pressure Respiration; D011659:Pulmonary Gas Exchange / Q000187:drug effects*; D012128:Respiratory Distress Syndrome / Q000150:complications / Q000503:physiopathology* / Q000628:therapy; D012131:Respiratory Insufficiency / Q000209:etiology / Q000503:physiopathology / Q000628:therapy
D010100:Oxygen