Brainstem anesthesia after retrobulbar block under brief analgosedation: Evidence for the underlying patho-mechanism

Background: Retrobulbar block is a popular regional anesthetic technique in modern eye surgery due to its excellent anesthetic properties and the provision of globe akinesia. Severe complications including inadvertent subarachnoidal injection, expulsive retrobulbar hemorrhage, and intoxication with local anesthetic, are very rare. However, most reports date back several decades, mechanisms of action are not fully understood, and in recent years the procedure has changed towards facilitating the retrobulbar injection by a brief analgosedation. We therefore describe a case with inadvertent brainstem anesthesia after retrobulbar block concealed behind an analgosedation and provide cCT (cranial computed tomography) images with characteristic pathological findings. Therapy and outcome: A man in his mid-60´s presenting with retinal detachment was scheduled for surgery. After uneventful retrobulbar injection under brief analgosedation, a severe increase of blood pressure and tachycardia occurred while unconsciousness (originally induced by analgosedation) persisted. Hemodynamic alterations were treated with betablockers and antihypertensive agents, and the patient was intubated and mechanically ventilated. The diagnostic workup revealed a dural fissure with intracranial air in the cCT-scan compatible with a perforation of the dura and accidental injection of local anesthetics into the subarachnoidal space. The patient was kept intubated on ICU throughout the respiratory depression and fully recovered without neurological deficits. The vitreoretinal procedure was performed under general anesthesia 36 h after the event. Conclusion: Albeit rare, inadvertent brainstem anesthesia remains a serious adverse event of retrobulbar block. As an important aspect, analgosedation may mask the typical clinical signs making the diagnostic work-up challenging. Furthermore, for the first time we present radiographic imaging findings providing insightful evidence for a possible mechanism of action. Serious complications, such as prolonged hypoxia with potential neurological damage, can successfully prevented by ensuring the presence of a fully equipped and skilled anesthetic team throughout the regional anesthetic procedure.