Final answer:
The spread of opioids in the epidural space is determined by their lipophilicity, with lipophilic opioids having limited spread and hydrophilic opioids having a wider spread.
Step-by-step explanation:
The property of opioids that will determine their spread in the epidural space is primarily related to their physicochemical properties, particularly lipophilicity. Highly lipophilic opioids tend to have a more limited spread in the epidural space as they are rapidly absorbed into the epidural fat and the vascular system. Conversely, more hydrophilic opioids have a wider spread due to their slower absorption. Other factors that can affect the spread of opioids in the epidural space include the volume and concentration of the injected solution, the specific gravity of the opioid solution compared to cerebrospinal fluid, and the addition of vasoconstrictors.