A total spinal block is a rare and very serious complication that occurs after excessive cephalad spread of local anasthetic. It can occur during single shot spinal anasthesia or as a result of inadvertent intrathecal spread of epidural medication after unintentional dural puncture or catheter migration. Subdural spread of the local anasthetic can also cause high block characterised by a high sensory level, sacral sparing, and incomplete or absent motor block. Single-shot spinal anaesthesia after a failed spinal or patchy epidural may also precipitate a total spinal.
There are several possible mechanisms for high spinal blocks when a spinal is attempted after failed epidurals. Expansion of the epidural space may compress the spinal canal and encourage cephalad spread of intrathecal drugs.Rapid transfer of local anaesthetic from the epidural space across the dural hole may also occur. In addition, sufficient local anasthetic may be present in the nerve roots to decrease the dose requirements of subsequent spinal anaesthesia.
In the case of a non emergency cesarean section when a patchy block is present, several options are possible without resorting to a single -shot spinal. An epidural catheter can be relocated and the drug titrated through the catheter. Alternatively, a CSE can be placed in which a fraction of the usual spinal dose can be administered; again, the catheter can be used to titrate to a desired level. other options include repeating a spinal after waiting for the original block to resolve or converting to a general anesthetic.
Factors Affecting Block height:
Unlike epidural dose requirements, weight is not trelated to block height during spinal anasthesia. Patient height is related, although the contribution in minor compared with more important factors. Age, injection rate and barbotage of isobaric and hyperbaric solutions have not shown to affect block height, although injection rates in these studies have been above 0.1 to 0.2 mL/sec. it is becoming clear that the direction of spinal needle lateral facing openings affect block height levels, even with isobaric spinal solutions.
Other maneuvers that do not appear to affect block height are coughing and straining after local anaesthetic injection. This is related to the physics of injections injecting drugs into a closed column of CSF, which instantaneously transmits pressure changes throughout the CSF column, such as those that occur with coughing or straining.
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