Neuroanesthesia Fundamentals

Preoperative Considerations


Avoid sedatives and/or opiates if elevated ICP is a concern (decreased RR leading to elevated ICP, obscuration of neurologic exam – for every 1 mm Hg decrease in pCO2, CBF decreases by 1-2 mL/100g/min).


Most of these patients are at high risk for electrolyte abnormalities (mental status changes, steroids, diuretics, contrast dye), which should be corrected prior to surgery.


Note that mannitol (0.25-1 g/kg) is a vascular smooth muscle relaxant and causes a transient increase in ICP, thus it must be given slowly (over ~ 10 mins). Also can cause hypotension. Consider giving furosemide as opposed to mannitol or HTS in neurosurgical patients with cardiac disease, as they may not tolerate a volume load

Primary Pathology

Always think of the primary pathology: vascular lesions can bleed extensively. Tumors can lead to ICP issues both during and after surgery. Steroids may be indicated in patients with brain tumors. Patients on chronic steroids may be hypoadrenal, always consider this in the face of refractory hypotension. Anticonvulsants may also be required


Almost all of these patients require an arterial catheter (frequent lab draws), a second IV, and urinary catheterization. Central lines, if needed, should be placed in the subclavian or brachial veins, as access to the neck is often limited


Opiates are often recommended in order to blunt the response to DL and craniotomy, so consider giving fentanyl (5-10 ucg/kg) as soon as you are ready to control the airway (ie before the induction agents). Lidocaine 1.5 mg/kg may help blunt the response to DL, as mat low dose volatile anesthetics. Etomidate (0.2-0.3 mg/kg) or midazolam (0.2-0.4 mg/kg) may help provide a more hemodynamically stable induction. Consider initiating hyperventilation immediately after induction (gives you a margain of safety in case DL is stimulating). Most practitioners prefer a non-depolarizing NMBD. Take extra care in securing the airway as it will most likely be inaccessible.

Intraoperative Considerations


Fluid of choice is 0.9% NS without dextrose, although be aware of the potential for hyperchloremic metabolic acidosis – send ABGs after several liters of NS and consider converting to lactated ringer’s solution of an acidosis is developing. Volume restriction is no longer used to treat elevated ICP as it is only moderately effective and comes with the side effects of hypotension, subsequent cerebral and renal hypoperfusion, and electrolyte and acid-base disturbances. In fact, preoperatively many neurosurgical patients are volume resuscitated

During surgery, blood loss should be replaced at a 3:1 ratio (3L crystalloid per 1L EBL) to a hematocrit of 25-30%. Glucose is avoided as it exacerbates ischemia (increases neuronal lactate production) and edema. Patients are usually kept at 15-30 degrees during surgery to facilitate venous drainage. PEEP > 10 cm H2O is avoided, above which venous drainage and ICP are affected. For major neurosurgical procedures, the following monitors are recommended – arterial line / ABG, central venous catheter, urine output. Paralyze adequately and achieve deep general anesthesia before DL, maintain PaCO2 of 30-35 mm Hg during surgery, avoiding PEEP if possible, as it can impair venous return from the brain. Avoid agitation on emergence


Brain relaxation can be achieved with hyperventilation, increasing the depth of anesthsia, administration of 10-20 mg furosemide IV, or mannitol (1 mg/kg), PRIOR to opening of the dura. Additional means include administration of thiopental or lumbar catheter drainage (if available)

Following the craniotomy and dural incision, anesthetic requirements drop substantially, as the brain itself is insensate. Propofol at 50 -150 ucg/kg/min and remifentanil at 0.1-0.5 ucg/kg/min can produce adequate anesthesia with rapid awakening (IVA in craniotomies should incorporate remifentanil, as it allows for rapid awakening). Relaxants should be held until the head dressing is completely on, as movement in response to the endotracheal tube can be detrimental

IV versus volatile anesthesia

Note that propofol is often recommended over volatile agents for intracranial neurosurgery as it was originally thought to produce less vasodilation/increase in ICP [Petersen KD et al. Acta Neurochir Suppl 81: 89, 2002]. Two recent studies have cast doubt on this common assumption – first, in a follow up study, Petersen et al. studied 117 patients and found no difference in ICP between fentanyl/volatile and fentanyl/propofol-based anesthesia. Interestingly, fentanyl/volatile led to a significantly higher jugular venous oxygen saturation and a significantly lower AVDO2 as compared to the fentanyl/propofol group, both before and after hyperventilation [Petersen KD et al. Anesthesiology. 98: 32, 2003]. More recently, Gelb et al. examined the effects of hyperventilation on operating conditions and ICP (both in propofol and isoflurane-based anesthetics), finding no difference between propofol and isoflurane in terms of ICP or surgeon-assessed brain bulk [Gelb AW et al. Anesth Analg 106: 585, 2008; FREE Full-text at Anesthesia & Analgesia]

Elements of Intracranial Neuroanesthesia to Keep in Mind

Elements of Intracranial Neuroanesthesia to Keep in Mind – CNS: minimize opiates and benzos (elevated pCOs). Avoid ICP changes. Bed at 15-30 degrees facilitates venous draininge from brain. Always infuse mannitol over 10 minutes – CV: a-line is almost always recommended – Pulm: maintain pCO2 30-35 mm Hg. Hyperventilation only lasts 4-6 hrs. Keep PEEP < 10 – Renal: volume restriction is not recommended – FEN: avoid glucose – Anesthesia: consider a pseudocardiac induction (midazolam + fentanyl) to minimize hypotension. Deeply paralyze for intubation, avoid agitated emergence


Total IV Anesthesia


There is a known association between emergence hypertension and post-operative hemorrhage – Basali et. al. reviewed 16 years of craniotomy data from the Cleveland Clinic, and found 69 cases of post-operative intracranial hemorrhage, which they matched in a 2-1 ratio by age, DOS, pathology, procedure, and surgeon. 62% of POH patients had intraoperative HTN (> 160/90), as opposed to only 32% of those who did not develop POH (p < 0.001, OR 4.6). Mortality rate in patients who suffered POH increased from 1.6 to 18.2%. Note, however, that the overall POH rate was only 0.77% [Basali et. al. Anesthesiology 93: 48, 2000]

In order to prevent intraoperative hemorrhage on emergence, consider the following techniques: 1. do not reverse paralytics until the head dressing is on 2. give 1.5 mg/kg IV lidocaine 90 seconds before suction/extubation 3. consider prophylactic labetalol on emergence

A neurologic exam should be performed prior to taking the patient from the operating room. If the patient does not wake up, consider elevated ICP (bleeding, swelling, HCP), residual anesthesia or paralysis, CO2 narcosis, hypoxia, and hypercarbia. Consider giving physostigmine (0.01-0.03 mg/kg) and/or naloxone (0.04 – 0.4 mg) to facilitate awakening

Post-Operative Care

Elevate the head of bed 30 degrees immediately. Consider checking serum electrolytes and osmolalities. Other critical PACU concerns include diabetes insipidus, SIADH, seizures, and tension pneumocephalus.