Autoregulation maintains cerebral blood flow of 50 cc/100g/min over MAPs ranging from 50 – 150 cc/hr, although in hypertensives this range is shifted upward. While neurologic symptoms may arise at CBP > 20 cc/100g/m, the brain is critically compromised (electrical impairment ensues) at CBP < 20 cc/100g/m, and pump failure occurs at CBF < 12 cc/100g/m. CPP > 55 mm Hg is adequate provided that signs of cerebral dysfunction are adequate, although in patients with injured brains CPP requirements may be higher. [Cucchiara: Brain Tumors, 1996]

Cerebral Edema

Vasogenic

Impairment of the blood brain barrier. Occurs in brain tumors, trauma, intracerebral hemorrhage, inflammation. Responds to steroids – dexamethasone at 8-32 mg/day (2-8 mg q6h) responds as early as one hour and lasts approximately 12 hours. ALWAYS start GI prophylaxis along with steroids.

Cytotoxic

Pump failure following reductions in CBF

Interstitial

Caused by high pressure hydrocephalus

Hydrostatic

Caused by an increase in transmural vascular pressure, loss of cerebral autoregulation

Osmotic

Secondary to a critical fall in osmolality or hyponatremia

Preoperative Considerations

2% of patients with brain tumors will hemorrhage spontaneously [J Neurosurg 67: 852, 1987; Neurosurgery 10: 437, 1982]. A study of 1028 glioma patient showed the incidence of seizures was 85%, 69%, and 49% for grade II, III, and IV gliomas, respectively [28]. Location matters as well, with frontal, temporal, and parietal lesions causing 3-fold as many seizures as occipital lobe lesions [31]. Still, metaanalyses suggest that patients with newly diagnosed brain tumors do not require AEDs [Neurology 54: 1886, 2000], although those who suffer an intracerebral hemorrhage probably do [Andrews]. Tumor edema, if present, is treated with corticosteroids and ventricular drainage if needed.

Postoperative Considerations

The risk of post-operative seizures is significant [15]. Oligodendrogliomas [29], extraaxial lesions such as meningiomas [21] as well as slow growing lesions [13] carry a higher risk of post-operative seizure activity. Location matters as well – a study of 100 patients with grade III gliomas showed the incidence of seizures in occipital lobe lesions is 1/3 that of frontal, temporal, or parietal lobe lesions [31]. The standard approach, not necessarily based on any data, is to give AEDs preoperatively and continue them for 3-6 months. The data (North et. al.) suggest starting at surgery and continuing for 10 weeks [J Neurosurg 58: 672, 1983] Post-operative antibiotics have been proven in these cases, however there is no data to support empiric gram negative coverage [17].

INR is routinely elevated after tumor removal secondary to release of tissue thromboplastin. DIC = PTT, INR, fibrin split product elevations with decreases in platelets and fibrinogen – treat with fresh frozen plasma, cryoprecipitate, platelets, and blood if needed.

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Preoperative Considerations

2% of patients with brain tumors will hemorrhage spontaneously [J Neurosurg 67: 852, 1987; Neurosurgery 10: 437, 1982]. A study of 1028 glioma patient showed the incidence of seizures was 85%, 69%, and 49% for grade II, III, and IV gliomas, respectively [28]. Location matters as well, with frontal, temporal, and parietal lesions causing 3-fold as many seizures as occipital lobe lesions [31]. Still, metaanalyses suggest that patients with newly diagnosed brain tumors do not require AEDs [Neurology 54: 1886, 2000], although those who suffer an intracerebral hemorrhage probably do [Andrews]. Tumor edema, if present, is treated with corticosteroids and ventricular drainage if needed

Anesthetic Goals

Two unique goals in caring for patients with intracranial mass lesions are 1) minimization of changes in cerebral blood flow (secondary to elevated ICP) and 2) facilitation of rapid awakening so that a prompt neurologic exam can be performed

Cerebral Edema

Vasogenic: impairment of the blood brain barrier. Occurs in brain tumors, trauma, intracerebral hemorrhage, inflammation. Responds to steroids – dexamethasone at 8-32 mg/day (2-8 mg q6h) responds as early as one hour and lasts approximately 12 hours. ALWAYS start GI prophylaxis along with steroids Cytotoxic: pump failure following reductions in CBF Interstitial: caused by high pressure hydrocephalus Hydrostatic: caused by an increase in transmural vascular pressure, loss of cerebral autoregulation Osmotic: secondary to a critical fall in osmolality or hyponatremia

Postoperative Considerations

The risk of post-operative seizures is significant. Oligodendrogliomas, extraaxial lesions such as meningiomas as well as slow growing lesions carry a higher risk of post-operative seizure activity. Location matters as well – the incidence of seizures in occipital lobe lesions is ~ 1/3 that of frontal, temporal, or parietal lobe lesions. Post-operative antibiotics have been proven in these cases, however there is no data to support empiric gram negative coverage. INR is routinely elevated after tumor removal secondary to release of tissue thromboplastin

Special Cases

Sitting Position

Benefits include better surgical view and anesthetic access. That said, the sitting position is associated with several complications, the worst of which is venous air embolism (VAE). Most commonly the air is expelled, but it can also pass through a R-L shunt or collect in the SVC/atrial junction. Rarely, it passes all the way through the pulmonary circulation to the systemic. In order to avoid a VAE, consider screening with a preoperative doppler/Valsalva maneuver, or a TEE with contrast (if positive, avoid the sitting position).

Also beware of quadriplegia from excessive cervical flexion (always leave 2 finger breadths between the chin and sternum), avoidance of pressure point necrosis, the risk of pneumocephalus (which is increased), and oral trauma (increased lingual and laryngeal trauma). Absolute contraindications to this position include an open ventriculo-atrial shunt, severe CV disease, large patent foramen ovale, cerebral ischemia, and unfamiliarity with the position [Anaesth Intensive Care 33: 323, 2005]. Patients who have posterior fossa operations must be monitored closely post-operatively, as brainstem nuclei may be damaged during surgery.

If the patient is in sitting position, consider a central venous catheter (peripherally inserted) and a precordial doppler (detects 0.25 mL) or TEE (most sensitive, but invasive), also look for a drop in ETCO2. Late signs of VAE include hypotension, arrhythmias, cyanosis, and mill wheel murmurs – VAE incidence is ~ 25% in sitting position. Transpulmonary passage of venous air is possible even in patients without a patent FO [Byrick RJ et. al. Anesthesiology 94: 163, 2001]

Diagnosis of VAE

Diagnosis of VAE: TEE (gold standard), precordial Doppler (recently displaced by TEE as the mainstay of diagnosis), capnography (ETCO2 will drop, not as sensitive as TEE), and PA catheter (PA pressure will rise, similar sensitivity to capnography) can all be useful. TEE is particularly useful because it can often diagnose a shunt, if present. Measures such as neck compression (tourniquet) and volume loading can be helpful in preventing VAE. PEEP increases the risk of VAE. Precordial doppler can detect 0.25 cc of air, however this amount is not necessarily clinically significant – check ETCO2 (will drop) to determine if significant.

Treatment of VAE

Treatment of VAE: stop the VAE (saline flood, wax, jugular compression, repositioning, turn off all PEEP), address hemodynamics (100% O2, volume, possible vasopressors), and attempt removal (possible air aspiration, which is usually not successful). A PICC is more advantageous than a standard TLC – single lumen allows easier aspiration of air.

Transphenoidal Surgery

Although non-functioning pituitary adenomas are the most common, many of these patients will have endocrine abnormalities (ex. Cushing’s sydrome). Patients with acromegaly may have extremely difficult airways. These patients rarely have ICP issues – the greatest concern is the unlikely scenario of intraoperative bleeding (ex. carotid puncture) which can be almost impossible to stop. These patients should have throat packs which prevent accumulation of blood in the stomach but must be removed prior to extubation. These patients will also have nasal packs which prevent nasal breathing

Stereotactic Surgery

Usually done under local with sedation. Beware, as the stereotactic frame obstructs easy access to the airway. Fiberoptic bronchoscopes should be available

Awake Craniotomy

Requires balancing the opposing goals of minimizing patient discomfort while ensuring cooperation in intraoperative neurologic examinations. ALWAYS be ready to treat stimulation-induced seizures (ask the neurosurgeon to irrigate the cortex with iced saline, then consider midazolam or thiopental). Never place an IV across a joint, because in a grand mal situation IV access is critical