Chronic pain unmasked by subarachnoid anesthesia
There are multiple potential causes (all uncommon) of pain immediately following a combined spinal-epidural (CSE), including direct mechanical nerve injury, neurotoxicity from unintended injection of toxic substances, and hematoma. Published in Anesthesiology News, the authors present this case because the aetiology proved to be more obscure than initially anticipated.

A 37-year-old man with avascular necrosis of the left hip was scheduled for a left total hip arthroplasty. His past surgical history included a right total hip arthroplasty and right wrist arthroplasty, both of which he initially described as having proceeded uneventfully.

On the day of surgery, the patient’s only complaint was persistent pain in his left (surgical) hip, for which he had been prescribed oxycodone 10 mg every 6 hours as needed and naproxen 500 mg every 6 hours as needed.

Given the absence of a history of abnormal bleeding or bruising, there was judged to be no absolute contraindication to regional anesthesia. The authors anticipated that the benefits of reducing perioperative opioid administration, especially in an opioid-tolerant patient, far outweighed the risks of neuraxial anesthesia. Therefore, they proceeded with our usual anesthetic for patients undergoing hip arthroplasty: a CSE with intraoperative sedation. They planned for postoperative IV hydromorphone patient-controlled analgesia after spinal anesthesia had worn off.

The patient was placed in a sitting position and given 5 mg of IV midazolam and 50 mcg of fentanyl in divided doses. A 3.5-inch, 17-gauge Tuohy needle was easily placed in the epidural space at the L3-4 level. Neither blood nor cerebrospinal fluid could be aspirated. There were no paresthesias. Next, a 25-gauge spinal needle was easily inserted through the epidural needle. After confirming correct placement by withdrawal of clear cerebrospinal fluid, 15 mg (3 mL) of 0.5% isobaric bupivacaine was injected. With the patient still in the sitting position, a 19-gauge catheter was threaded 4 cm past the tip of the epidural needle (10.5 cm at the skin), whereupon the epidural needle was withdrawn and the catheter was taped in place. The patient was then repositioned supine.

Almost immediately, the patient began to complain of crushing hip and leg pain. A quick sensory and motor examination demonstrated appropriate signs of a developing spinal anesthesia. Despite his excruciating pain, which from his description appeared to extend bilaterally from T12-L3, he had no sensation to either pinprick or cold below the T10 dermatome. He had a dense motor block (unable to move his feet or bend his knees). His blood pressure decreased from 133/89 to 98/41 mmHg secondary to the sympathectomy, requiring treatment with IV phenylephrine.

Upon considering the differential diagnosis, these rapidly developing symptoms seemed inconsistent with epidural hematoma, accidental direct nerve damage, or cauda equina syndrome. The neurology team recommended 500 mg of IV methylprednisolone to reduce any swelling around the spine, and this was administered.

The epidural catheter was removed prior to imaging. The MRI study showed disk herniation at T8-9 and L3-S1 without any significant spinal stenosis, and no fluid collection was identified (Figure). In general, the radiologist considered the images to be unremarkable.

After ruling out the most urgent cause of the patient’s pain, he was transported to the PACU for observation and pain control. Over the next few hours, as the spinal anesthetic resolved, so did his pain.

To their amazement, the patient returned to his baseline condition and could move his lower extremities without difficulty. It was at this time that he described to us a somewhat similar, but less extreme, event that occurred with his previous hip replacement surgery under neuraxial anesthesia. Later during the week, he had his scheduled surgery under general anesthesia without incident and was discharged home on postoperative day 3. At a 3-month postoperative visit, he was free of pain and off all opiates and alcohol.

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