Discontinuance of nitrous oxide does not prevent tension pneumocephalus.

A 9-year-old, 30 kg, white girl was admitted for evaluation of an acute onset of malaise, vomiting, and seizure activity which rapidly progressed to coma. On physical examination, the patient was febrile and comatose with mild decerebrate posturing. Pupils were pinpoint and nonreactive. Cranial nerve examination revealed symmetrical facies with absent gag and corneal reflexes. Deep tendon and oculocephalic reflexes were absent. The rest of the physical examination was normal. Computed tomography (CT) scan showed massive intraventricular hemorrhage. Carotid arteriograms revealed a posterior fossa arteriovenous malformation. A ventriculostomy was performed and treatment with aminocaproic acid, phenobarbital, dexamethasone, cimetidine, methacillin, and chloramphenicol was initiated. Ten days after admission, a Hakin standard valve ventriculoperitoneal shunt was inserted. The patient’s mental status improved such that she could occasionally respond to simple commands. A posterior fossa craniotomy and reseFtion of the arteriovenous malformation was scheduled on the 44th hospital day. Preoperative CT scan and skull x-ray showed no intracranial air. Anesthesia was induced with sodium thiopental, 100 mg, and maintained with diazepam, fentanyl, and 66% nitrous oxide in oxygen. Endotracheal intubation was facilitated with pancuronium and controlled hyperventilation was instituted. A lumbar subarachnoid drain was inserted and the patient was then placed in the sitting position. Surgery progressed without incident until midway through the procedure when venous air embolism was evidenced by a change in the precordial Doppler signal, a decrease in PE COz, and an increase in Paco,. The patient was given 100% oxygen. Aspiration through the right atrial catheter was negative for air. Blood pressure remained stable and PE COZ returned to normal within 10 minutes. Nitrous oxide, 6670, was resumed, but was discontinued Y-2 hour before dural closure. Total duration of exposure to NzO was 5% hours. At the end of the operation the patient was taken to the neurosurgical intensive care unit where controlled ventilation with 100% 0 2 was maintained. Two hours after arrival in the intensive care unit the patient developed a right hemiparesis and dilated left pupil. An emergency CT scan showed a large frontal pneumocephalus (Figure). This was released by bilateral twist drill holes in the cranium. The procedure was noted “to be productive of gas under pressure.” The hemiparesis resolved over the ensuing 12 hours and the left pupil returned to normal after 2 days. The remainder of the postoperative course was unremarkable.