In general, almost all the adverse effects seen with spinal anaesthesia are due to the nerve blockade itself and not to the drug used. These effects include hypotension, bradycardia and postdural puncture headache.
High or Total Spinal Blockade:
Severe adverse reactions following spinal anaesthesia are rare, but may occur in connection with extensive (total) spinal blockade.
Total spinal blockade will result in cardiovascular and respiratory depression. The cardiovascular depression is caused by an extensive sympathetic blockade which may result in profound hypotension and bradycardia, or even cardiac arrest. Ventilatory depression is caused by blockade of the innervation of the respiratory muscles, including the diaphragm.
Neurological damage is rare, though recognized, consequence of regional and particularly spinal anaesthesia. It may be due to several causes eg, direct injury to the spinal cord or nerves, anterior spinal artery syndrome, injection of an irritant substance and nonsterile solution or the development of a space occupying lesion (hematoma or abscess) within the spinal canal. These may result in localized areas of paresthesia or anaesthesia, motor weakness, loss of sphincter control or paraplegia. Occasionally, these are permanent.
Neurological complications of this type have been reported with all local anaesthetics used for spinal anaesthesia.
Allergy to amide type local anesthetics is very rare but may be present as allergic dermatitis, bronchospasm or anaphylaxis.
Acute Systemic Toxicity:
Like all local anesthetic drugs, bupivacaine may have acute toxic effects on the central nervous and cardiovascular systems if given in high doses. The first manifestation of CNS toxicity is drowsiness merging into unconsciousness and respiratory arrest. The cardiovascular reactions are depressant and may be characterized by hypotension, myocardial depression, bradycardia and possibly cardiac arrest. In view of the low dosage employed, systemic adverse reactions are rarely associated with spinal anesthesia, but may occur after accidental intravascular injection. Systemic adverse reactions are characterized by numbness of the tongue, lightheadedness, dizziness and tremors, followed by convulsions and cardiovascular disorders.