Generalized seizures and transient contralateral hemiparesis following retrobulbar anesthesia: a case report

A rare but serious systemic complication related to retrobulbar anesthesia is generalized
seizures. The incidence of central nervous system complications in a series of 6000
retrobulbar blocks was 1 in 375 1], while in another study the incidence of systemic adverse events associated with
local anesthesia for intraocular surgery was 0.9 % 2].

Several mechanisms may lead to central nervous system spread of the local anesthetic
agent during retrobulbar block. One mechanism is the inadvertent injection of the
anesthetic solution in the ophthalmic artery or its branches. Central nervous system
toxic responses can result from retrograde passage of a local anesthetic injected
under pressure from the ophthalmic artery to internal carotid artery and delivery
to the thalamus and other midbrain structures 5]–7]. The ophthalmic artery usually runs above the optic nerve but in 15 % of patients
it lies inferior to the optic nerve in the orbital cavity 8], where retrobulbar anesthesia is usually performed. Clinical signs vary from convulsions
to cardiopulmonary arrest and the onset is rapid 1], 9], 10].

Another possible mechanism leading to central nervous system intoxication is the unintentional
injection of anesthetic in the optic nerve sheath and entry into the subdural or subarachnoid
space 11], 12]. The onset of symptoms range from 2 to 40 min after the retrobulbar anesthesia in
most cases 1]. The use of long needles of 31 mm or more 1], 13] or an uncooperative patient unable to keep the eyes in primary gaze position during
the injection increases the risk of the optic nerve puncture.

Our patient had no history of allergy, epilepsy, alcoholism, was not on any medication
and also all the biochemical investigations pro- and after the incidence were normal.
Therefore, no causative factor which may potentiated seizures 14] was detected. Furthermore, brain computed tomography and electroencephalogram were
normal, eliminating the possibility of a brain damage or stroke. It is also unlikely
that the seizures and hemiparesis were caused by an accidental intravenous injection
of the anesthetic during retrobulbar block, since the total dose of local anesthetic
used in our case was less than the intravenous toxic dose described to cause systemic
toxicity 15], 16].

In our case, generalized tonic-clonic seizures developed during retrobulbar block
before withdrawal of the needle and completion of the injection of the anesthetic
agent. Using a 38 mm long needle, we cannot exclude the central spread of local anesthetic
through an accidental puncture of the optic nerve sheath. Although a blunt needle
might be less likely to penetrate the optic nerve sheath, there is a report of unintentional
injection of local anesthetic in subarachnoid space with this type of needle 11]. However, in our patient, the omission of needle aspiration test before the injection
and the immediate onset of seizures (before needle withdrawal) are in favor of the
inadvertent intra-arterial injection of ropivacaine in the ophthalmic artery or its
branches with retrograde flow into the internal carotid artery and delivery to brain
structures.

A variable onset of neurological signs after retrobulbar or peribulbar anesthesia
has been reported, ranging from the time of needle withdrawal 9] to 40 min later 1]. Meyers et al.9] presented two cases in which grand mal seizures with respiratory obstruction developed
immediately after retrobulbar injection of 3 ml of lidocaine with epinephrine in the
first case and 5 ml of a solution contained bupivacaine, lidocaine and epinephrine
in the second case. Bensghir et al.17] reported a case in which generalized convulsions occurred 6 min following peribulbar
injection of a mixture contained lidocaine and bupivacaine. In our case, 6 ml of ropivacaine
were injected in the inferior temporal retrobulbar space which immediately initiated
generalized seizures.

Several anesthetics responsible for central nervous system toxicity following local
anesthesia for intraocular surgery have been reported; among them bupivacaine was
the most frequently associated with seizures 18]. Ropivacaine is considered to cause less central nervous system and cardiac toxicity
than bupivacaine 15], 16], 18] and constitutes an effective alternative to bupivacaine 19]. Pragt et al.12] in 2006 reported one patient with localized convulsions and brief contralateral hemiparesis
9 min after retrobulbar injection of 5 ml 1 % ropivacaine. The authors could not determine
the exact cause of convulsions and hemiparesis but suspected the subarachnoid injection
of ropivacaine.

In our case, midazolam 2 mg was administrated intravenously by the anesthesiologist
4 min after the commencement of seizures. No additional dose was needed, since the
seizures were immediately controlled. It is likely that a great amount of anesthetic
agent was rapidly eliminated from the vascular bed leading to cessation of seizures
and the administration of midazolam played a minimal role in controlling the seizures.