Intracranial pressure during recovery from nitrous oxide and halothane anaesthesia in neurosurgical patients.

Seven patients with intracranial disorders were studied during recovery from anaesthesia with nitrous oxide and halothane. Arterial, intracranial, and central venous pressure, and arterial carbon dioxide tension were measured and compared with the patient's clinical state. No patient had evidence of increased brain volume when the dura was closed. All had been hyperventilated during the surgical procedure. Cessation of hyperventilation and the continued administration of anaesthetics was followed by a moderate increase in intracranial pressure and a reduction in cerebral perfusion pressure, but critically low values were not seen. Spontaneous respiration returned when the PaCO2 was in the range of 33-51 mm Hg. When spontaneous respiration was judged to be normal, anaesthesia was interrupted and the endotracheal tube was removed. In the following minutes, until the patients were awake, the intracranial pressure decreased to normal or near normal values, with minimal change in PaCO2. In these seven patients in whom there were no signs of brain swelling, the skull was closed, the patients were allowed to resume spontaneous respiration, and anaesthesia was terminated without major changes in intracranial pressure or cerebral perfusion pressure. However, hyperventilation is advocated after operation in patients with marked brain swelling.