The most useful information on neurosurgery anesthesia

How to treat cerebral edema

Intracranial hypertension results from cerebral edema & it develops following sustained ICP of >15mmHg. Below are treatments for cerebral edema:

• Head elevation; IV corticosteroids (dexamethasone) in case of vasogenic edema from neoplasms, & frequent measurement of glucose level; 
• Mannitol, in doses of 0.25-1g/kg reduces intracranial fluid volume & ICP. It’s weak vasodilating effects temporarily decreases BP, & increases intravascular fluid volume. It worsens pulmonary edema in patients with cardiac & renal dysfunction;
• Avoid mannitol in patients with arteriovenous malformations, intracranial hemorrhage, & intracranial aneurysms until craniotomy is performed;
• Avoid rapid infusions of osmotic agents to old patients to avoid rupture of fragile bridging veins, resulting in subdural hematoma;
• Hypertonic saline-3% NaCl also reduces cerebral edema & ICP. Ensure cautious administration of hypertonic saline to avoid central pontine myelinolysis or osmotic demyelination syndrome in hyponatremic patients;
• Moderate hyperventilation with PaCO2 of 30-33mmHg to reduce CBF, CBV, & ICP. Be cautious to prevent worsening ischemia in patients with existing focal ischemia.
• Measure serum sodium concentration & osmolality as necessary. 300-315mOsm/kg is a desirable range for osmolality following the use of osmotic agents;
• In patients with TBI, ventriculostomy, metabolic suppression with barbiturates. Perform decompressive craniectomy following ICP >25mmHg.

Preoperative evaluation & premedication

Preoperative evaluation requires: neurological examination for sensory or motor deficits; MRI or CT scans for evidence cerebral edema (brain herniation >0.5cm); lab evaluations including ABG, BGT, & electrolyte tests. Avoid sedatives & opioids on suspicion of ICH.  

Intraoperative monitoring

Patients monitoring requires: standard monitors; direct intraarterial pressure monitoring; bladder catheterization; neuromuscular functioning & visual evoked potential monitoring; central venous catheterization & pressure monitoring through subclavian vein; PETCO₂ measurement & arterial-ETCO₂ gradient; ventriculostomy catheter.

Zero the transducers of the intraarterial & ventricular line at the level of the external auditory meatus to enable calculation of the CPP. Ventricular catheters also enable direct calculation of the ICP, CSF drainage, & decreasing ICP.

Bladder catheterization enables guidance of fluid therapy & measurement of core body temperature. PETCO₂ measurement & arterial-ETCO₂ gradient to ensure accurate regulation of ventilation.

Visual evoked potential monitoring is helpful in preventing optic nerve damage during resection of large pituitary tumors. Central venous catheterization & pressure monitoring are useful in patients receiving vasoactive agents.  

Positioning, induction, & maintenance of anesthesia

Patient is placed in a supine position with head elevation at 15-30^o, for craniotomies involving frontal, parietooccipital, & temporal access. Minimally turn the head to the side to enable exposure as necessary.       

Induction requires IV opioids, propofol, neuromuscular blocking agents, & moderate hyperventilation with controlled ventilation. Succinylcholine is useful in rapid sequence intubation.

Tachycardia associated with intubation in lightly anesthetized patients can be prevented with esmolol 0.5-1.0mcg/kg. Treat hypertension with β₁-blockers, deepening doses of propofol, or sevoflurane. Vasopressors including phenylephrine is useful in managing hypotension.

Maintenance may occur with use of either sevoflurane, remifentanil + propofol, or a combination of remifentanil+ propofol+ low-dose sevoflurane. Dexmedetomidine is also beneficial in both sleep & awake craniotomies.

Continue hyperventilation (PaCO₂ of 30-35mmHg₎ intraoperatively. Avoid high mean airway pressures (low RR, & large VT) as they may increase CVP & ICP. Ensure the use of IV glucose-free isotonic crystalloid fluids.