Factors That May Influence the Spread of Local Anesthetic Solutions in the Epidural Space

Injection site: Unlike spinal anesthesia, epidural anesthesia produces a segmental block that spreads both caudally and cranially from the site of injection
Drug volume: Increasing the volume results in greater spread and density of block; increases cephalad distribution
Drug dose: Important with volume in determining spread and density of block
Drug concentration: Relatively unimportant in determining block spread
Position: Does not seem to have a clinically important effect on the spread of the block from side to side
Patient characteristics
Age: Greater spread in elderly patients perhaps because of less compliant epidural space and decreased likelihood of local anesthetic solution to escape via intervertebral foramina
Height and weight: Weak correlation except at extremes
Pregnancy: Conflicting data
Atherosclerosis: Relationship not confirmed