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Monitored anesthesia care in awake craniotomy for brain tumor surgery.

Monitored anesthesia care during brain surgery was introduced more than 60 years ago for surgical treatment of epilepsy. The procedure was proposed mainly for patients whose pathology was located in the anterior temporal or frontal lobes, near motor, language, or memory areas of the brain [1]. Intraoperative cortical mapping during such ``awake craniotomies'' allows detection and sparing of these important brain regions. In recent years this technique of intraoperative brain mapping in the awake patient has been used more frequently, especially in patients undergoing surgery for resection of brain tumors located in close proximity to eloquent cortex [2±4]. Identification of cortical areas essential for motor or language functions can guide the surgeon during corticotomy and tumor resection and prevent significant functional disabilities. Moreover, identifying the functional brain regions may allow the resection of lesions that would otherwise be considered inoperable based on classical anatomical landmarks. Such landmarks have been shown to be inaccurate due to the variability in the anatomic location of brain functions and the displacement caused by the tumor mass itself. The cortical organization of language, for example, has been historically defined by correlating structural abnormalities caused by stroke or tumor, with resulting language deficits [5,6]. On this basis, Broca's area responsible for expressive aphasia was located in the posterior portion of the inferior frontal gyrus, and Wernicke's area responsible for receptive aphasia was located in the presilvian region in the temporoparietal cortex [7,8]. More recently, Ojemann et al. [9] used electrical stimulation mapping to demonstrate speech areas within 3 cm of the temporal lobe up in the superior and middle temporal gyri. No specific region of the temporal lobe cortex was found to be essential for language in more than 55% of 117 patients. Haglund et al. [10] found a similar variability in cortical language sites, and demonstrated that intraoperative mapping allowed for more extensive resection of gliomas. Although this technique is beneficial, it requires a fully awake and cooperative patient during surgery and exposes the patient to several potential anesthetic hazards. While adequate analgesia and sedation are necessary during the painful initial stages of the procedure, the patient must be fully conscious and cooperative during the periods of brain mapping and tumor resection. Uncontrolled pain during head-frame positioning and craniotomy may lead to hemodynamic instability, emotional distress, and loss of cooperation on the part of the patient. Alternatively, excessive sedation may lead to hypoventilation and hypoxemia, both hazardous to the patient with intracranial pathology and increased intracranial pressure. Moreover, urgent endotracheal intubation for the management of airway, hypoventilation, or "tight brain" might be impossible in patients in the lateral position while the head holder tightly fixes the head. Other serious potential problems during surgery may include convulsions that may be caused by the cortical stimulation itself, nausea and vomiting, particularly associated with traction on the dura, and emotional distress leading to loss of control by the patient with an exposed brain.