Clive Collier

Accidental subdural injection during attempted lumbar epidural block may present as a failed or inadequate block: Radiographic evidence

Background and Objectives: Until now, case reports after accidental subdural injection during attempted epidural block have usually described extensive neuraxial blocks with a delayed onset, after low doses of local anesthetic, with a characteristic radiographic appearance on contrast injection. Our radiographic investigation of atypical “epidural” blocks has revealed that subdural injection may go unrecognized clinically and may be a cause of inadequate blocks. The mechanism is explored. Case Reports: A radiographic study of 35 cases of atypical or inadequate blocks for cesarean delivery has unexpectedly revealed four instances of subdural contrast injection. On imaging, only localized posterior spread of subdural contrast was detected in these 4 cases, unlike the more widespread distribution previously reported after extensive neuraxial blocks. Recent findings on the ultrastructure of the subdural space are reviewed and related to the new clinical findings, which include inadequate blocks and pain developing on postoperative reinjections. Conclusions: Accidental subdural injection may now be added to the list of causes of failed or inadequate “epidural” block. Clinicians should be aware of the diagnosis of a possible subdural injection, if a poor quality block with restricted spread and slow onset is associated with pain on postoperative reinjection of the catheter.

Why obstetric epidurals fail: a study of epidurograms

In a study of the factors involved in the occasional failure of continuous obstetric epidural blockade, contrast injections through epidural catheters and radiographic screening were undertaken in 35 postpartum patients. The two major causes of inadequate block were found to be transforaminal escape of the catheter tip, and persistent unilateral block associated with an obstructive barrier in the epidural space. Recommendations for overcoming these problems are discussed.

Bilateral trigeminal nerve palsy during an extensive lumbar epidural block

A rare case of trigeminal nerve blockade arising in the course of obstetric lumbar epidural anaesthesia is described. There was extensive bilateral spread of nerve-block up to the C4 level with respiratory distress after top-up for caesarean section, and subsequent epidurography revealed high epidural spread of contrast. The mechanism of the trigeminal nerve palsy was the source of some controversy, particularly as to whether intracranial spread of local anaesthetic had occurred, possibly following accidental subdural or subarachnoid injection.

The bending and stiffness of epidural catheters

To the Editor: Dr. Eckmann has done well to bring some scientific input to our choice of the ideal epidural catheter, by measuring bending and stiffness,1 but some extra information regarding his work would greatly help clinicians. Firstly, it would be of value to learn which particular manufacturer produced each type of tested catheter because designs vary considerably. For instance, the Duraflex coiled reinforced catheter from SIMS Portex (Keene, NH) features reduced reinforcement in the terminal 5 cm of the catheter, resulting in more bending and less stiffness of this part of the catheter. Other catheters of this type have constant reinforcement and may produce different test results. The Soft Tip from B.Braun (Melsungen, Germany) may also show more distal bending and less terminal stiffness than the rest of the catheter. Secondly, although Dr. Eckmann has provided the outer diameter measurements of the tested catheters, it would be of value to know what gauge values these represent because this is a more familiar figure to anesthesiologists. Dr. Eckmann mentioned the development of catheters having a novel cross-sectional shape. One such catheter is the Perisafe from Becton Dickinson (Franklin Lakes, NJ), which has a most unusual ribbed lumen (Fig 1). We trialled this catheter in 1997, but the 20-gauge type proved unsatisfactory in our hands because of kinking and obstruction. Measurement of the cross-sectional area of this catheter might be a little complex! Now that Dr. Eckmann has drawn our attention to the ideal mechanical characteristics of epidural catheters, it may be worthwhile to request that the manufacturers publish the relevant data on each catheter type because these parameters will almost certainly have been measured during catheter development and reassessed during quality control procedures.