Describe the advantages and disadvantages of subarachnoid and epidural opioids

Describe the advantages and disadvantages of subarachnoid and epidural opioids.

The advantages of subarachnoid opioids include sim-plicity of administration and small dose requirement. Although they can be administered through a subarach-noid catheter, it is more common to inject subarachnoid opioids as a bolus dose through a needle. Thus the ability to titrate small amounts of a medication to the desired effect is lost. In addition, the one-shot dosing provides analgesia of only a specified duration, with morphine last-ing from 8 to 24 hours. The incidence of side-effects is greater with subarachnoid opioids compared with epidural opioids.

Epidural opioid via a continuous infusion is the pre-ferred way to administer neuraxial opioids in the postoper-ative period. Because access to the epidural space is often provided through an indwelling catheter, multiple small doses or continuous infusions may be administered. If placed in a sterile fashion, the catheter can be kept in place for many days, allowing for a long duration of analgesia. The use of PCA via the epidural route adds the ability for a patient to self-administer additional boluses when pain increases, such as prior to mobilization. Combinations of opioid and local anesthetic can be used to enhance analgesia.

Disadvantages of epidural opioids include larger dose requirements, predisposing patients to higher plasma narcotic concentrations with lipid-soluble opioids. Indwelling catheters may migrate into the CSF or a blood vessel, placing patients at risk for complications. Any indwelling catheter can become a source of infection. If a patient is to receive an anticoagulant in the postoperative period, the catheter must be removed prior to institution of the medication, or, if appropriate, within the safe window of the drug’s administration. If a patient develops a coagulopathy in the postoperative period, it must be decided on a risk–benefit basis whether or not to remove the catheter, for fear of dislodging a clot and causing an epidural hematoma. In addition, it is imperative to use tubing without ports or other access, to prevent inappro-priate injections into the epidural space. Also, the epidural catheter may be difficult to place in some patients, such as the obese or those with a curvature of the spine.