The epidural infusion rate of morphine and bupivacaine has recently been increased, and the patient now complains of decreased sensation in the lower extremities. Which of the following is the MOST likely cause of the decreased sensation?

While morphine and bupivacaine can interact pharmacologically, the primary effect of concern in this scenario is the local anesthetic action of bupivacaine. An interaction does not necessarily lead to decreased sensation, as morphine primarily acts as an analgesic rather than a local anesthetic. Thus, it is not the most likely cause of the decreased sensation.

An epidural infection could potentially cause neurological symptoms, but it is less likely to directly result in decreased sensation due to the immediate effects of anesthesia. Infections often present with fever, pain, or neurological deficits but would not typically cause acute changes in sensation following an increase in medication infusion rates.

While excessive morphine can lead to side effects such as sedation or respiratory depression, it does not directly cause decreased sensation in the lower extremities. Morphine's primary role is pain management, and its effects are distinct from those of local anesthetics like bupivacaine.