Ventilation-perfusion distribution related to different inspiratory flow patterns in experimental lung injury.
In acute lung injury (ALI), controlled mechanical ventilation with decelerating inspiratory flow (.V(dec)) has been suggested to improve oxygenation when compared with constant flow (.V(con)) by improving the distribution of ventilation and perfusion (.V(A)/.Q). We performed the present study to test this hypothesis in an animal model of ALI. Furthermore, the effects of combined decelerating and constant flow (Vdot;(deco)) were evaluated. Thus, 18 pigs with experimental ALI were randomized to receive mechanical ventilation with either .V(con), .V(dec) or a fixed combination of both flow wave forms (.V(deco)) at the same tidal volume and positive end-expiratory pressure level for 6 h. Hemodynamics, gas exchange, and .V(A)/.Q distribution were determined. The results revealed an improvement of oxygenation resulting from a decrease of pulmonary shunt within each group (P < 0.05). However, blood flow to lung areas with a normal .V(A)/.Q distribution increased only during ventilation with .V(con) (P < 0.05). Accordingly, PaO(2) was higher with .V(con) than with .V(dec) and .V(deco) (P < 0.05). We conclude that contrary to the hypothesis, .V(con)provides a more favorable .V(A)/.Q distribution, and hence better oxygenation, when compared with .V(dec) and .V(deco) in this model of ALI.


CONCLUSIONS
In acute lung injury, mechanical ventilation with decelerating flow has been suggested to improve ventilation-perfusion distribution when compared with constant flow. We tested this hypothesis in an animal model. Contrary to the hypothesis, we found a more favorable ventilation-perfusion distribution during constant flow when compared with decelerating flow.
Dembinski
Rolf
R
From the Department of Anesthesiology, University Hospital of the RWTH Aachen, Pauwelsstrasse 30, 52074 Aachen, Germany.
Henzler
Dietrich
D
Bensberg
Ralf
R
Prüsse
Berit
B
Rossaint
Rolf
R
Kuhlen
Ralf
R
D000403:Airway Resistance / Q000502:physiology; D000818:Animals; D004573:Electrolytes / Q000097:blood; D006439:Hemodynamics / Q000502:physiology; D006895:Hydroxyethyl Starch Derivatives; D055370:Lung Injury; D005741:Noble Gases; D010366:Peak Expiratory Flow Rate / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012121:Respiration, Artificial; D012129:Respiratory Function Tests; D015656:Respiratory Mechanics / Q000502:physiology*; D013552:Swine; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*
D004573:Electrolytes; D006895:Hydroxyethyl Starch Derivatives; D005741:Noble Gases