Management of Failed Spinal Anesthesia
➧ This can be a source of pain, anxiety, and psychological trauma to the patient and a cause of stress, complaints, and medico-legal sequelae to the anesthetist.
Prevention is better than cure:
➧ The spinal block should be performed with meticulous attention to detail.
➧ If there is any doubt about the nature or duration of the proposed surgery, a method other than standard spinal anesthesia should be used.
Management of failed spinal block:
-The precise management of failed spinal block will depend on the nature of the inadequacy and the time at which it becomes apparent.
-The slower the onset of either motor or sensory block, the more likely is the block to be inadequate, so the more detailed assessment should be.
-While the onset of spinal anesthesia is rapid in most patients, it can be slow in some; so, ‘transient time’ should always be allowed.
-However, if the expected block has not developed within 15 min., some additional maneuver is needed, as follows:
1-No block:
Causes:
-Incorrect or ineffective solution was injected.
-Solution has been deposited in the wrong place.
Management:
-Repeating the block or conversion to general anesthesia is the only option.
2-Spinal block of inadequate height:
Causes:
-Some injectate has been lost or misplaced.
-The level of injection was too low.
-Anatomical abnormality has restricted spread.
Management:
-If a hyperbaric solution was used, flex the patient’s hips and knees and tilt the table head down (Trendelenburg position). This straightens out the lumbar lordosis, but maintains a cephalad ‘slope’ and allows any solution ‘trapped’ in the sacrum to spread further.
-In an obstetric situation, turn the patient to the full lateral position with a head-down tilt and reverse the side after 2–3 min.
-If a plain (and usually slightly hypobaric) solution has been used, it may help to sit the patient up but beware of peripheral pooling of blood.
-If an intrathecal catheter injection results in an inadequate spread, do not inject more of the same solution because the dose has minimal effect on the intrathecal spread.
-Either posture should be manipulated as above, or a different baricity of solution should be tried, or the catheter should be withdrawn before the injection is repeated.
3-Unilateral block:
Causes:
-This is most likely because of positioning.
-The longitudinal ligaments supporting the cord have blocked spread.
Management:
-If the operation is on the anesthetized limb, the surgeon should know that the other leg has sensation, and the patient should be reassured and closely monitored.
-Otherwise, turning the patient onto the unblocked side if a hyperbaric solution was used (or the reverse for plain solutions) may facilitate spread.
4-Patchy block:
The block appears adequate in extent, but the sensory and motor effects are incomplete.
Causes:
-The local anesthetic (LA) dose was inadequate.
-The LA was partially misplaced.
Management:
-If this becomes apparent before surgery starts, the options are to repeat the spinal injection or to use IV analgesia, the latter being the only option after skin incision.
-It may not be necessary to recourse to general anesthesia, as sedation or analgesic drugs are often sufficient especially when patient anxiety is a major factor.
-Infiltration of the wound and other tissues with LA by the surgeon may also be useful in such situations.
5-Inadequate duration:
Causes:
-An inadequate dose of LA was delivered to the CSF.
-Syringe swap; Lidocaine (intended for skin infiltration) was confused for bupivacaine.
-The operation has taken longer than expected.
Management:
-Sedation, IV analgesia, or infiltration of LA may be adequate, but often the only option is to convert to general anesthesia.
Repeating the spinal block:
➧ If no effect at all was seen 15-20 min. following the injection, it seems reasonable to repeat the block, paying close attention to avoiding the potential pitfalls.
➧ In all other situations besides total failure, there must be some LA already in the CSF, and anxieties relating to several issues have to be taken into account:
1-A restricted block may be due to an anatomical factor, impeding the physical spread of the solution, and it may have the same impact on a second injection, resulting in a high concentration of LA at or close to the site of injection leading to neurotoxicity.
2-Barriers to spread within the subarachnoid space may also affect epidural spread (and vice versa), so an attempt at epidural block may not succeed either.
3-Repeated injection in response to a poor quality block may lead to excessive cephalad spread with the potential for cardiovascular instability, respiratory embarrassment, or total spinal anesthesia, so a lower dose should be used to reduce this risk.
4-A good quality, but unilateral block, might lead to an attempt to place a second injection into the ‘other’ side of the theca, but the risk of placing the second dose on the same side must be significant.
5-A block of inadequate cephalad spread might be overcome by repeating the injection at a higher level, but should only be attempted when there is a considerable indication for a regional technique.
6-When a repeat block is considered, the adjacent nerve tissue is already affected by LA action, so the risk of direct needle trauma is increased.
Recourse to general anesthesia:
➧ There are many ways in which an inadequate block might be ‘rescued’:
-General anesthesia must be considered if one or two simple measures have not rectified matters.
-Common sense and clinical experience are usually the best indicators of exactly when to convert to general anesthesia.
-If general anesthesia is induced to supplement a partially effective spinal anesthesia, any degree of sympathetic nerve block will make hypotension more likely.
Postoperative Management:
1-Documentation and follow-up:
-The anesthetic complication details should be fully documented in the notes.
-The patient should be provided with an apology and a full explanation after the operation.
-Giving the patient a written summary of events for presentation to a future anesthetist can be very helpful, although care should be taken to prevent medico-legal recourse.
-Rarely, the inadequate spread has been the first indication of pathology within the vertebral canal, so if there is any suspicion, look for symptoms and signs of neurological disease, and consult a neurologist.
-During follow-up of a patient in whom no block was obtained, the possibility of LA ‘resistance’ may seem an attractive explanation.
2-Investigating LA effectiveness:
-Performing skin infiltration with some of the solutions intended for the spinal injection should demonstrate that it is effective.
-If the concern continues the operating theater, pharmacy, and anesthetic department records should be cross-checked to see whether other practitioners in the hospital have experienced any problems.
-Similarly, distributors should be able to check whether other hospitals, which have been supplied with material from the same batch, have reported difficulty.
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