In an attempt to restrict spinal blockade to the operative side by the use of low doses of hyperbaric bupivacaine and a directional spinal needle have become widely used for minor orthopaedic, urological and general surgery . This technique, which has also been defined as unilateral spinal anaesthesia, allows minimal effects on cardiovascular homeostasis [2-4]. The patient is placed in the lateral decubitus position with the side to be operated upon dependent. After dural puncture, the needle bevel is directed towards the dependent side of spinal canal and hyperbaric local anaesthetic solution is injected slowly(about 0.02 mL s−1) in order to facilitate the migration of anaesthetic molecules towards the nerve roots on the dependent side [1-4].
In Italy, both 0.5% and 1% concentrations of hyperbaric bupivacaine are used, and it has been suggested that increasing the concentration of local anaesthetic solution should produce a better penetration of dependent nerve roots [1,5].
We describe a case of transient neurological deficit after unilateral spinal anaesthesia using hyperbaric bupivacaine 1%.
A healthy 30-year-old male, 78 kg body weight, was scheduled for elective left spermatic vein ligature. After 750 mL of Ringer's lactate solution was given intravenously, the patient was placed in the left lateral decubitus position and dural puncture was performed at the L1-L2 interspace with a 25-gauge Whitacre spinal needle. Hyperbaric bupivacaine 8 mg 1% was then injected slowly (≈0.015 mL s−1). Neither paraesthesia nor back-pain were observed during dural puncture or administration of the local anaesthetic. Sensory (T8) and motor (modified Bromage score third degree) blocks developed on the dependent side within 10 min of the bupivacaine injection. The lateral decubitus position was maintained for 15 min before the patient was turned to the supine position. Twenty minutes after bupivacaine administration, we observed sensory block up to T11 and partial motor block (modified Bromage score first degree) also on the non-operated side. Twenty-six minutes after, dural puncture surgery started and this was successfully completed in a 45-min period.
Three days after surgery, the patient reported an area of hypoaesthesia (L3-L4 dermatomes) of the left leg with loss of pinprick sensation, but without signs of motor fibre involvement: he reported no problems with muscular strength or movement of the left lower limb. Sensation in this area returned to normal over the next 2 weeks.
A transient neurological deficit was observed after unilateral spinal block with hyperbaric bupivacaine 1% given using a slow injection rate through a pencil-point spinal needle.
No previous reports have described a transient neurological deficit after unilateral spinal anaesthesia with hyperbaric 1% bupivacaine. Cauda equina syndrome has been reported in patients receiving spinal hyperbaric lignocaine 5% through sacrally directed small-bore catheters. Data from in vitro models supported the hypothesis that hyperbaric local anaesthetic solutions injected through sacrally directed catheters may remain in high concentrations in the sacral regions because the small-bore catheters limits the injection rate. Mixing of local anaesthetic molecules in the cerebrospinal fluid is limited because of the slow injection rate . Beardsley and coworkers  described two cases of neurological deficit associated with hyperbaric lignocaine 5% spinal anaesthesia delivered via pencil-point needles (Whitacre 27-gauge), and with a slow injection rate and needle bevel introduced in a sacral direction. Using a model of the spinal canal, these authors showed evidence of anaesthetic maldistribution with slow injection when a caudally directed pencil-point needle is used . They suggested that this technique for spinal anaesthesia may potentially result in a neurotoxic concentration of intrathecal lignocaine if a 5% hyperbaric solution is employed.
Unilateral spinal anaesthesia with hyperbaric bupivacaine 1% has been used most often over recent years in our department. This is the first case of transient neurological deficit in more than 1200 unilateral spinal blocks. Prospective multicentre studies with a large population and a prolonged follow-up should be performed in order to evaluate the real incidence of this unusual side effect. However, we suggest that the lowest concentration of hyperbaric bupivacaine 0.5% should be employed in order to minimize the risk of a localized high peak local anaesthetic concentration when a pencil-point needle with a low injection rate is only used to restrict spinal block to the side for operation.
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