Anesthesia for supratentorial tumors

Preoperative assessment

General assessment  and  review of all systems

Medications  ,allergies

Neurological assessment including MRI, CT scan

Past anesthetic history and  anesthetic family history

Lab, EKG and Chest x-ray as indicated

Informed consent and preoperative orders

Check blood availability      

                                                       

Planned surgery

The following parameters are considered when anesthesia is planned:

The pathology (vascularization)and  site  of the tumor,its mass effect , edema, closeness to  venous sinuses , and positioning of the patient

Premedication

 Generally not indicated. For very anxious patients , small doses of midazolam are administered before entering the OR

Anesthesia  plan

General endotracheal anesthesia

IV induction,

Maintenance:  IV and inhalatory  ( sevoflurane  or Isoflurane)

Goals

Control  of brain tension

 Optimization of brain perfusion : Normovolemia , adequate CPP and CBF, adequate positioning, normoventilation , avoidance of hypoosmolarity,

Cerebral protection, normoglycemia

Hematocrit  is kept around 30% . In younger patients we may let it go down to 22-24% ,always keeping normovolemia

Specially in anterior fossa procedures : prevention of retractor  ischemia by maintenance of MAP at least 80 mmHg,  moderate hyperventilation , mannitol  and lumbar drainage of CSF

Anesthesia  technique

Monitoring

Monitoring:  EKG ,Pulse oximetry ,non invasive blood pressure, esophageal thermometer,ETCO₂, FIO₂,ET anesthetic agent

Invasive  blood pressure : arterial line, generally Lt radial ,20G after induction.The  arterial line is placed before induction under local anesthesia and light IV sedation in cardiac and unstable patients. Volemia is assessed by  the subjective analysis of the arterial wave contour and by measuring   systolic variation (delta down)

Urinary catheter , esophageal  thermometer

1  or 2 wide bore IV's (depending on the vascularity  and site of the tumor ) placed after induction

Central venous line : In CRF, in hemodinamically unstable patients,if massive bleeding  is expected,generally placed after induction

Our preferred site is right internal jugular, anterior approach

IV induction  After preoxygenation, via  existing iv line

Fentanyl  1-2 mcg/kg

Propofol   2mg/kg or Thiopental or Etomidate until loss of eyelid reflex.

Facilitation of intubation  Rocuronium 0.6 mg/kg.

The ET tube is safely fixated and eyes are taped
Maintenance The patient is ventilated with a mixture of O₂/air  to provide normoventilation and normal oxygenation.A potent inhalatory agent , sevoflurane or isoflurane is added at less than  1 MAC.
Analgesia: Remifentanyl infusion, aprox. between 0.1 and 0.2 mcg/kg/min.
Muscle relaxation Generally atracurium, 0.5 mg/kg/h.

Positioning –Final check : No jugular compression, head and thorax slightly elevated, pressure points padded. Prevent nerve compression

Pin head holder application: Local Lidocaine 1%  and IV boluses of propofol/remifentanyl

Fluids- Normal saline ( mildly hyperosmolar).  Metabolic acidosis is common with this fluid regime

Mannitol –before dura opening, 0.5-1 g/kg

Prophylactic antibiotics  Cefazoline 1g IV .In penicillin allergic patients, clindamycin 600 mg.

Seizure prophylaxis  Phenytoin or  Valproate (loading or maintenance)

Laboratory. In stable patients, Arterial blood gases and Ht are measured at  least   once every 2  hours .In bleeding patients, a full coagulation profile and a CBC is sent  at the beginning of the episode and  then  hourly. In massive bleeding   we inform the blood bank which enters in a "massive transfusion mode" providing us  with all the blood components needed.

Intraoperative problems

Hypotension

  Is corrected by treating its cause and by IV ephedrine 5- 10 mg or phenylephrine  50-100 mcg bolus  as needed

Hypertension

Generally  due   to light anesthesia, is treated accordingly. Except for poorly controlled hypertensive patients  we generally do not  give antihypertensive drugs during anesthesia ,except in emergence.

Brain bulging

Causes: the tumor itself , peritumoral  edema, problems of positioning ,trendelemburg, jugular vein compression ,extreme turning of the neck, hypoventilation, PEEP, hypoxemia, hypotension

Iatrogenic use of hypotonic fluids before surgery

Treatment . After correcting  extracranial  factors ,  hyperventilate ,reduce inspiratory time,give another dose of mannitol  or hypertonic saline and /or furosemide

The surgeon may drain CSF from the ventricle.

If it does not help, deepen the anesthesia with thiopental, which generally demands  the concomitant use of vasopressors

Bleeding

Check   frequently : Operating field, suctions , CUSA,  monitors. Communication with surgeon is essential.

Bleeding  can be profuse ,so be ready .The main problems are underestimation of blood loss and unreadiness.

 Early  blood orders and  available blood in the OR .

Arterial  wave contour and systolic variation are  the most important parameters for diagnosing hypovolemia and for continuous assessment of  volume  replacement.

In a  second place, pH and bicarbonate. Do fine tuning of the Ht  and other components when bleeding  is stopped and volemia corrected.

Children  have an almost adult head size "connected" to a small volemia reservoir, so acute bleeding  can  quickly bring a child to hypovolemic shock.

Emergence from anesthesia

In Rambam we prefer early awakening in the OR

 Goals :patient awake, responds to simple orders, minimal cough,hemodinamically stable,no risk of hypoxia  or hypoventilation

In the following situations we will not awaken the patient in the OR, and instead will transfer him to  the ICU via CT scan:

Patients which are no fully awake before surgery, long procedures, difficult hemostasis, hypothermia, massive transfusion, major hemodynamic instability, increased  pulmonary shunt , big AV malformations.

Waking up the patient

Stop atracurium infusion 30 min before end of procedure

Fentanyl  1.5 mcg/kg   and droperidol  for PONV prevention 1 mg 10 minutes before end of procedure

These will cause almost always  hypotension ,be ready with ephedrine

After pin removal (on supine position to avoid VAE) and dressing , close inhalatory agent and remifentanyl.Reverse  residual curarization with atropine/neostigmine

The patient will awake in about 10-15 minutes.Emergency hypertension  is common and is treated with Labetalol, beginning with 0.25-0.50 mg/kg .

Cough -IV lidocaine  1.5 mg/kg

Extubate when patient is awake, normal Vt ,obeys orders ,no signs of residual curarization.

Transfer the patient to Recovery Room