Published ahead of print on October 11, 2007, doi:10.1164/rccm.200703-484OC Am. J. Respir. Crit. Care Med., Volume 177, Number 3, February 2008, 292-300 A more recent version of this article appeared on February 1, 2008
Submitted on March 24, 2007 Relation between Shunt, Aeration and Perfusion in Experimental Acute Lung InjuryGuido Musch1*,1 Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA, 2 Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA; Department of Experimental Medicine, Ospedale San Gerardo and Universita Milano-Bicocca, Monza, Milano, Italy, 3 Department of Medicine, Pulmonary and Critical Care Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA * To whom correspondence should be addressed. E-mail: gmusch{at}partners.org.
Rationale: In a pulmonary process characterized by spatially heterogeneous loss of aeration, the impairment of gas exchange is expected to depend on the regional distribution of perfusion relative to that of aeration. Objective: To investigate how regional aeration, shunt and perfusion are interrelated at different levels of end-expiratory pressure and how their interplay relates to global shunt fraction, in acute lung injury. Methods: Regional shunt and perfusion were assessed by imaging with Positron Emission Tomography the pulmonary kinetics of [13N]nitrogen infused in saline solution in 5 sheep after lung lavage. The lung field was divided in 6 horizontal regions. Results: Each animal showed an inverse relation between regional shunt (Fs) and gas (FG) fractions: Fs = -m xFG+Fso. This relation was similar among animals (m = 1.25±0.14, Fso = 0.75±0.15) and invariant with end-expiratory pressure, despite lack of correlation between global shunt and gas fractions and large interanimal variability in global shunt fraction. When this relation was used to estimate global shunt fraction as a perfusion-weighted average of the estimates of regional shunt fraction derived from regional gas fraction, 72% of the interanimal variability in global shunt fraction could be explained. Conclusion: Despite large interanimal variability in global shunt fraction, there was a consistent inverse relation between regional shunt and gas fractions, independent of end-expiratory pressure. Most of the interanimal variability in global shunt fraction could be explained by the combined effect of this relation and of the distribution of perfusion on regional shunt, rather than by differences in global aeration. Key words: Key words: artificial respiration, adult respiratory distress syndrome, positron-emission tomography, mechanical ventilators, x-ray computed tomography
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