A computed tomographic study of the dog lung during hemorrhagic shock and after resuscitation

A shock model was used to explore the capability of computed tomography (CT) to detect changes in lung density during hypovolemia and after resuscitation. The same level of the lower thorax was scanned repeatedly during base-line, shock (aortic pressure 60 mmHg), and after resuscitation with shed blood. The average baseline CT number (+/- SEM) for 5 areas of interest for four prone dogs was -754 +/- 16 (air = -1000, water = 0). This decreased 7.4% to -810 +/- 15 (P less than .05) during shock. After resuscitation CT density was -773 +/- 17 or 2.5% less than baseline (P greater than .1). A dorsal to ventral gradient of increasing CT density during baseline was maintained in all five areas during shock and post-resuscitation. From baseline to shock there were also significant changes in heart rate, mean aortic pressure, cardiac output, and vascular volume. Extravascular lung volume after resuscitation was equal to baseline volume. We conclude that CT is sufficiently sensitive to detect rapid physiological changes leading to increased or decreased lung density.