Although severe spinal deformities may make epidural or spinal puncture impossible, lesser degrees of scoliosis, kyphosis, kyphoscoliosis, increased lumbar Iordosis or disc disease usually allow satisfactory access to the epidural (Chapter 1) or subarachnoid space (Chapter 68). However, the resulting block may fail (3) or produce only patchy analgesia (4). Moderately severe scoliosis may be associated with persistent unilateral epidural analgesia (9) and kyphosis frequently predisposes to an excessively high level of sensory block.
Similarly, blocks may be difficult to insert and spread may be inadequate in patients who have undergone surgical correction of these spinal deformities (5). Scar tissue and bone grafts may disrupt the ligamentum flavum or impede the spread of local anaesthetic. The epidural space may even be obliterated by adhesions.
The presence of Harrington rods or similar instrumentation provides another challenge. One group of workers were only able to satisfactorily overcome the technical difficulties in 5 out of 9 parturients receiving epidural block and one of these parturients suffered an inadvertent dural puncture (6). These patients are unable to flex their spines making any approach technically more difficult. In those patients who have not had a laminectomy, insertion of a block needle may be attempted adjacent to a single rod or between the two rods. In one patient with a Harrington rod, a subdural block followed an L5 - S1 epidural puncture (7).
In patients who have undergone laminectomy, insertion of a block needle may be attempted above or below, but not through, the scar. In these individuals, fibrous tissue has completely replaced the epidural space. A midline or paramedian approach may be used but caution is always required.
In those with spinal deformity, a planned subarachnoid block may be undertaken, but this can result in a patchy block (Chapter 98). This may necessitate the use of either a continuous technique or repeated subarachnoid puncture (4). The presence of abnormal spinal curves makes the effect of posture on the distribution of a spinally administered drug difficult to predict (Chapter 30). Caution is required because excessively high levels of block, with respiratory insufficiency, have been reported. This is especially so when a subarachnoid injection is used to correct an inadequate epidural block (8). In one case, the spinal component ascended rapidly even though only normal saline was injected into the epidural space (8).
Two epidural catheters may be inserted at different levels to overcome the poor spread of epidural solutions in patients with spinal deformity (4). There is a minor theoretical concern that the catheters might become knotted together, or that the second epidural needle insertion might damage the first catheter. An alternative to the double lumbar catheter technique is the addition of a caudal (Figure 22.1), low spinal or, very occasionally, paravertebral block to provide analgesia for delivery.
A combination of various techniques together with some ingenuity is required for these difficult patients!
References:
3. MORAN DH, JOHNSON MD. Continuous spinal anesthesia with combined hyperbaric and isobaric bupivacaine in a patient with scoliosis. Anesthesia and Analgesia 1990; 70:445-447.
4. SCHACHNER SM, ABRAM SE. Use of two epidural catheters to provide analgesia of unblocked segments in a patient with lumbar disc disease. Anesthesiology 1982; 56:150-151.
5. PASCOE HF, JENNINGS GS, MARX GF. Successful spinal anesthesia after inadequate epidural block in a parturient with prior surgical correction of scoliosis. Regional Anesthesia 1993; 18:1 91-192.
6. CROSBY ET, HALPERN SH. Obstetric epidural anaesthesia in patients with Harrington instrumentation. Canadian J Anaesthesia 1989; 36:693-.
7. LEE Y-S J, BUNDSCHU RH, MOFFAT EC. Unintentional subdural block during labor epidural in a parturient with prior Harrington rod insertion for scoliosis. Regional Anesthesia 1995; 159-162.
8. BECK GN, GRIFFITHS AG. Failed extradural anaesthesia for caesarean section: complication of subsequent spinal block. Anaesthesia 1992; 47:690-692.
9. COLLIER CB Why obstetric epidurals fail. International Journal of Obstetric Anaesthesia. 1996 5:19-31