How would you induce and maintain anesthesia in this patient?
The preoperative assessment of this patient includes an evaluation of mental status and determination of acute increased ICP. Co-existing diseases should be optimally treated before arrival in the operating room. The MRI examination reveals a large mass which has slowly increased in size.
This patient can be induced in the typical manner with caution to avoid additional increases in ICP. Intravenous anesthetic induction is followed by moderate hyperventilation until neuromuscular blockade is achieved. Thiopental or propofol are commonly used for induction with an opioid, such as fentanyl, to blunt the hemody-namic response to laryngoscopy and intubation. Moderate hyperventilation is achieved to an ETCO2 of 28–30 mmHg. A radial artery catheter and additional intravenous lines may be placed after endotracheal intubation. A CVP catheter is useful but not essential for this case unless required for intravenous access. The potential for blood loss may be considerable and, thus, large-bore intravenous catheters are needed. Mannitol is commonly started at a dose of 0.5–1.0 g/kg.
Maintenance of anesthesia may proceed with low doses of volatile agent (less than 1 MAC), continuous infusion or bolus doses of an opioid and muscle relaxant. N2O may be administered at a concentration of 50%, if surgical conditions do not indicate a “tight brain”. Intravenous fluid administration generally requires isotonic crystalloid solu-tions; colloids are also useful for maintenance of intravascu-lar volume. Extensive blood loss is replaced with packed red blood cells. Hypotonic solutions exacerbate cerebral edema and are generally contraindicated, while glucose-containing solutions are avoided unless truly necessary.
Neurosurgery is characterized by periods of intense stimulation followed by minimal pain during brain resec-tion. Hypertension may occur and is treated promptly to prevent bleeding and potential cerebral swelling. The use of β-blockers in addition to adequate anesthesia is recom-mended throughout. Upon closure and emergence, blood pressure control is especially important. Patients who have had an uneventful procedure are expected to emerge promptly at the end of surgery for neurologic evaluation. Extubation is managed carefully, after assurance of airway reflexes and stable hemodynamics. Postoperative respira-tory insufficiency adversely affects cerebral physiology.