Anatomic spread of india ink in the human intercostal space with radiographic correlation

In a study designed to determine the spread of anesthetic solutions in the intercostal space, the spread of india ink was studied in fresh cadavers. They were turned prone and had epidural catheters placed at ribs 4, 6, 8 and 10, 7-8 cm lateral to the midline, by two different techniques. Group 1 had epidural catheters directed laterally into the subcostal groove. Group 2 had catheters directed medially into the intercostal space. A window was dissected in the anterior chest wall to visualize the location of the catheters and the spread of india ink. Catheters in Group 1 were observed to be lateral to the medial border of the intercostalis intimus muscle and injection of india ink resulted in spread entirely within a single intercostal space. Catheters in Group 2 were observed to be 2-3 cm medial to the border of the intercostalis intimus muscle and injection of ink resulted in concentric spread over 3-5 intercostal spaces. Posteroanterior and lateral radiographs taken with contrast material in live patients confirmed these patterns of spread. The catheters in Groups 1 and 2 were within the same tissue plane. The results indicate that the pattern of spread obtained by injection of fluid in the intercostal space is dependent upon the site of injection in relation to the angle of the rib.