Background:
Thoracic epidural analgesia is a proven technique for post-operative pain control in open upper abdominal and thoracic surgeries with many potential benefits. However, successful and safe analgesia requires catheter placement in the epidural space. Inadvertent puncture and placement of an intrathecal catheter carries inherent risk; namely a high spinal, vasoplegia leading to significant hypotension, or a motor block. Thus, this case-review attempts to distinguish appropriate ways of diagnosing an intrathecal catheter.
Case description:
We present a 72 year-old man presenting for a liver mass resection via open right hepatectomy. A thoracic epidural was placed for postoperative pain management. No CSF or heme was noted during or following placement of the needle or catheter. An infusion of bupivacaine 0.05% with 0.005mg/ml of hydromorphone was started at 8ml/hr with a patient demand dose of 2ml every 10 minutes. Intraoperative hypotension was treated with a low-dose phenylephrine infusion rather than crystalloid as part of our standard hepatic resection protocol. No other significant hemodynamic changes were noted. After the operation, the basal epidural rate was titrated down over the course of 12 hours to 2 ml/hr for persistent hypotension. On morning pain rounds, the patient’s remained persistently hypotensive despite adequate resuscitation and reassuring laboratory values. The patient had adequate pain control with a sensory block up to approximately T2. Given the relatively high sensory block and significant hypotension, the team was concerned for a possible subarachnoid catheter. An epidurogram was performed, which demonstrated equivocal results, though concerning for intrathecal spread. Thus, a sample was drawn off the catheter and sent for analysis. Glucose and protein were not concerning for CSF.
Discussion:
An accidental subarachnoid puncture during epidural placement will generally result in CSF return visible either spontaneously via needle or with aspiration of the catheter. However, it is possible that the needle has only partially punctured the dura and may not return CSF with aspiration. Subsequent delivery of anesthetic to the subarachnoid space may lead to a high spinal block with hemodynamic and respiratory effects. Evaluation with epidurograms, sending aspirate for analysis, and epidural waveform analysis can assist the practitioner in confirming the placement of an epidural catheter.
When interpreting epidurograms, contrast spread through the epidural space is typically described as honeycomb in appearance and vacuolated. This irregularity of contrast spread is secondary to fat within the space. Contrast should also spread laterally under the pedicles. Lastly, the number of levels the contrast spreads caudal and rostral is less compared to intrathecal spread. In comparison, intrathecal injection of contrast would demonstrate a more homogenous spread, appearing columnar, and with greater caudal and rostral spread.
Another diagnostic tool is sending CSF for analysis. CSF glucose is typically two thirds of the serum glucose, ranging from 18 to 58 mg/dL. Epidural waveform analysis can be useful in equivocal cases. Once the needle tip enters the epidural space, the pressure tracing becomes synchronized with arterial pulsations.
