ANESTHESIA FOR NEUROSURGERY Dr Sonam Norbu Dr Jyoti Pathania

Goals of Neuroanesthesia Deep anesthetic level with adequate muscle relaxation and blunting response to intubation, pins and craniotomy No increase ICP, CBV, BP and No decrease in CPP, CBF, BP No hypoxia No coughing

The Adult Brain: Blood Flow CBF= 10-300 ml/100gm/min 750 ml/min(20%co) CSF=150 ml, entire volume replaced 3-4 times/day

Intracranial components Brain tissue- 80% Blood- 12% CSF- 8%

INTRACRANIAL PRESSURE ICP is determined by the raltionship of the volume of intracranial contents(brain+blood+CSF=1200-1500cm3) and the volume of the cranial vault (fixed by rigid dura and skull bone). ELASTANCE is the relationship of pressure and volume (dP/dV). In normal condition a small increase in intracranial volume will not result in ↑ICP. COMPLIANCE is the relationship of volume and pressure (dV/dP) i.e. inverse of Elastance. Initially, as intracranial volume increases, no change in ICP occurs (point A, well compensated) until point B where any further increase will cause dramatic increase in ICP (point C).

ASA TASK FORCE IN POSITIONING 2000 LIMIT ARM ABDUCTION TO 90 AND CAREFUL PADDING OF VULNERABLE PRESSURE POINTS CAREFFULL PAD AND ASSESS AREAS SENSITIVE TO PRESSURE NECROSIS e.g. EYES, EARS, NOSE, GENITALIA AND BREASTS. FEMALE BREASTS DISPLACED MEDIAL AND INFERIOR IN RELATION TO CHEST SUPPORTS PATIENTS WHO HAVE POSITION-DEPENDENT NEUROLOGIC SYMPTOMS OR EXTREMELY OBESE BENEFIT FROM AWAKE INTUBATION FOLLOWED BY AWAKE POSITIONING

PROBLEMS RELATED TO PRONE POSITION BRACHIAL PLEXUS INJURY AIR EMBOLI AND CV COLLAPSE BLINDNESS OBSTRUCTION OF FEMORAL VEINS AND IVC→↓VR→↓CVP AND ↓COP ENGORGEMENT OF PERIVERTEBRAL VENOUS PLEXUSES→DIFFICULT SURGICAL EXPOSURE AND ↑BLOOD LOSS ABDOMEN HANG FREE→NEGATIVE PRESSURE WITHIN IVC→ PERIVERTEBRAL VENOUS PLEXUSES-→ AIR EMBOLIZATION FROM SUPINE TO PRONE→↑ PVR AND ↑SVR.

PROBLEMS RELATED TO PRONE POSITION ABDOMINAL PRESSURE → DISPLACE DIAPHRAGM→ REDUCE LUNG COMPLIANCE→ POSITIVE PRESSURE VENTILATION→BAROTRAUMA. POSITIVE INSPIRATORY EFFECT ON DIAPHRAGM-→ INCREASE FRC AND DESRIABLE EFFECT ON GAS EXCHANGE VISUAL LOSS 1:100 SPINE SURGERIES DUE TO ISCHEMIC OPTIC NEUROPATHY ( ↑BLOOD LOSS, ↑IOP , ↓PERFUSION PRESSURE) FACIAL EDEMA

INTRACRANIAL HYPERTENSION (1) ICP> 15mmHg ① expanding tissue or fluid mass  ② depressed skull fracture    ③ CSF absorption interference    ④ brain edema: systemic disturbance,inc CBF Headache, nausea, vomiting, papilledema, focal neurological deficits,altered consciousness Cushing response : periodic increases in arterial BP with reflex slowing of the HR, abrupt increases in ICP lasting 1~15min

CEREBRAL EDEMA ↑Brain water content BBB:(vasogenic edema) m/c 1) Vasogenic edema : mechanical trauma, inflammatory lesion,brain tumors, hypertension, infarction 2) cytotoxic edema : hypoxemia or ischemia   3) interstitial cerebral edema :obstructive hydrocephalus, entry of CSF into brain interstitium

INTRACRANIAL HYPERTENSION (2) TREATMENT    - underlying cause     - vasogenic edema :  corticosteroids → BBB repair     - fluid restriction, osmotic agents, loop diuretics     - moderate hyperventilation(PaCO2 30-33mmHg) :↓ CBF & ↔ ICP         1)Mannitol      - dose : 0.25-0.5g/kg      - disadventage : transient increase intravascular volume ↔  pul. edema     : contra: intra cranium Aneurysms, AVM, intracranial Hemorrhage   2)Loop diuretics(furosemide)     -  less effective requiring up to30 min, ↓CSF formation.      - mannitol synergistic effect        but, serum potassium close monitoring.

ANESTHESIA & CRANIOTOMY FOR PATIENTS WITH MASS LESIONS Intracranial mass : ① congenital ② neoplastic ③ infectious ④ vascular Common sx : headache, seizures, a general decline in cognitive or specific neurological function , focal neurological deficits PREOPERATIVE MANAGEMENT preanesthetic evaluation : Intracranial HTN (CT,MRI) Neurologic assessment : mental status, any existing sensory or motor deficits Medication reviwed : corticosteroid, diuretic, anticonvulsant therapy laboratory evaluation :  steroid-induced hyperglycemia                              electrolyte disturbance by diuretics or ADH                             anticonvulsant level should be measured.  Premedication normal ICP : benzodiazepine intracranial hypertension : Avoid premedication (∵ respiratory depression : hypercapnia → ICP ↑ ) Corticosteroid and anticonvulsant: cont until surgery.

ANESTHESIA & CRANIOTOMY FOR PATIENTS WITH MASS LESIONS INTRAOPERATIVE MANAGEMENT Monitoring     1) standard monitoring   2) direct intraarterial pr. monitoring  - arterial blood gas measure : PaCO2, ETCO2     3) bladder catheterization (∵ diuretics )     4) central venous access & pressure monitoring - vasoactive drug     5) visual evoked potential -  pituitary tumor resection →optic n. damage Induction anesthesia and tracheal intubation – SLOW without inc ICP and CBF. m/c induction technique ① thiopental or propofol together with hyperventilation           ② NMBAs : facilitate ventilation and prevent straining or coughing →↑ICP           ③ IV opioid : sympathetic response blunts          ④ esmolol : preventing tachycardia .

ANESTHESIA & CRANIOTOMY FOR PATIENTS WITH MASS LESIONS Positioning Frontal, temporal, parietooccipital craniotomies : supine position head elevation : 15-30 (∵ venous drainage and CSF drainage ) Positioning: Tube disconnection .  Maintenance of Anesthesia Nitrous oxide - opioid - NMBA technique HTN : low- dose (1<MAC) Iso,Sevo, Des. opioid + low dose inhalation agents  or total IV technique continued hyperventilation : PaCO2 30-35mmHg avoid - PEEP & High mean airway pr (low rate and large tidal vol.) (∵↑ CVP) fluid - glucose-free isotonic crystalloid(ex. N/S) or colloid solution              * hyperglycemia-> ischemic brain damage, Colloid solution : restore intravascular vol. deficits Isotonic crystalloid solution : maintenance fluid requirements   Emergence  like intubation, emergence SLOW and CONTROLLED  IV lidocaine 1.5mg/kg or small dose propofol(20-30mg) or thiopental(25-50mg) before suctioning.     

ANESTHESIA FOR SURGERY IN THE POSTERIOR FOSSA(1) Obstructive Hydrocephalus infratentorially located mass : obstruct flow of CSF & increase ICP ∴ ↓ ICP prior to induction GA → ventriculostomy (↓LA) Brain Stem Injury posterior fossa operation : cranial nerve injury circulatory and respiratory brain stem center Damage to respiratory center : circulatory change, abrupt change in BP, HR, cardiac rhythm abnormal respiratory pattern or inability to maintain a patent airway following extubation → brain stem injury Brain stem auditory evoked potentials – useful(8th N). Positioning Modified lateral, prone, sitting position (preferred) Position head is always above heart. Careful positioning – avoid injuries

ANESTHESIA FOR SURGERY IN THE POSTERIOR FOSSA(2) Pneumocephalus sitting position -  pneumocephalus ↑ CSF is lost → air enters subarachnoid space Dural closeure →pneumocephalus → compress the brain Postoperative pneumocephalus : delayed awakening and impairment of neurological function Venous Air Embolism (1) Wound is above heart level sitting craniotomy (20-40%) Physiological consequences depend on – vol. and rate of air entry , patent foramen ovale ( paradoxical air embolism ) Air bubble → venous sys. → pul. Circulation (diffuse into the alveoli ) Sign : ↓ ETCO2 and o2 saturation sudden hypotension rapid & large amounts of air – sudden circulatory arrest

ANESTHESIA FOR SURGERY IN THE POSTERIOR FOSSA(3) Venous Air Embolism (2)   A. Central Venous Catheterization : allow aspiration of entrained air    catheter confirm : TEE or intravascular electrocardiography(biphasic P wave)           B. Monitoring For Venous Air Embolism  most sensitive intraop. Monitor : TEE and precordial Doppler sonography    changes ETCO2 and pul. a. pr. : less sensitive but can detect venous air embolism before clinical signs are present sx. : sudden decrease in ETCO2 ( pul. Dead space ↑ ) mean pulmonary artery pressure ↑ change in BP, & Heart sound – late manifestation

ANESTHESIA FOR SURGERY IN THE POSTERIOR FOSSA(4) Venous Air Embolism (3) C.Treatment Of Venous Air Embolism  1. surgeon notify : surgical field can be flooded with saline or packed and bone wax( entery site identified)      2. N2O stopped, 100%O2      3. CVP Cath. aspirated      4. volume infusion -> CVP      5 .vasopressor:( to treat hypotension)      6. Bilateral jugular vein compression ( ↑cranial venous pr.)      7. PEEP( ↑CVP)      8. Head down position & wound closed quickly      

ANESTHESIA FOR STREOTACTIC SURGERY Indication : invountary movement disorders intractable pain epilepsy diagnosing and treating tumor- located deep within the brain local anesthesia sedation and amnesia : propofol Stereotactic head frame : awake intubation with a fiberoptic bronchoscope!

ANESTHESIA FOR HEAD TRAUMA(1)  Significance of a head injury 1) Irreversible neuronal damage    2) 2 insults       (1) hypoxemia, hypercapnia or hypotension            (2) epidural,subdural,intracerebral hematoma       (3) intracranial HTN     --> surgical & anesthetic management directed at preventing these 2 insults.    Glasgow Coma Scale (GCS) score : severity of injury and outcome ( ex. GCS score < 8 → 35 % mortality )

ANESTHESIA FOR HEAD TRAUMA(2) PREOPERATIVE MANAGEMENT(1) Patency of the airway, adequacy of ventilation & oxygenation, correction of systemic hypotension Airway Obx and hypoventilation are common. Pul. contusion, fat emboli, or neurogenic pul.edema : complication 70% hypoxemia    Pt with hypoventilation, absent gag reflex, or GCS< 8           -> Tracheal intubation and hyperventilation      Intubation full stomach , in-line axial stabilization. Following preoxygenation and hyperventilation thiopental or propofol and rapid-onset NMBA: biunt intubation response. Hypotensive(sys <100mmHg)        : small dose thiopental or propofol, or etomidate Succinylcholine in closed head injury – controversial ( ICP ↑, hyperkalemia) If difficult intubation : awake intubation, fiberoptic techniques, or tracheostomy

ANESTHESIA FOR HEAD TRAUMA(3) Hypotension    Head trauma: hypotension : related to other associated injury (intra-abdominal) spinal cord injury ; sympathectomy associated with spinal shock Hypotension :         -  by colloid solution and blood (preventing brain edema)         -  severe hypotension: vasopressor glucose-containing or hypotonic solution should not be used Hct >30% invasive monitoring – intraarterial pr. , central venous or pul. a. pr, ICP...

ANESTHESIA FOR HEAD TRAUMA(4) INTRAOPERATIVE MANAGEMENT Similar to other mass lesion asso with intracranial HTN barbiturate-opioid-nitrous oxide-NMBA technique. PaCO2 <30 avoided as hyperventilation (↓CBF) HTN with tachycardia : b- blocker Excessive vagal tone – treated atropine or glyco. DIC ,ARDS, pulmonary aspiration, neurogenic pul. edema, G-I hemorrhage, Diabetic Insipidus

ANESTHESIA & CRANIOTOMY FOR INTRACRANIAL ANEURYSMS & ARTERIOVENOUS MALFORMATION(1) CEREBRAL ANEURYSMS(1) Preoperative Consideration rupture of a saccular aneurysms: m/c cause of subarachnoid hemorrhage acute mortality following rupture : 10% survivors – 25% subsequently die within 3 months from delayed cx. 50% survivors : left with significant neurological deficits “ prevention of rupture ”  > 7mm :surgical Ix Unruptured Aneurysms m/c sx : Headache m/c sign : 3rd nerve palsy Others : brain stem dysfunction, visual field defects, trigeminal neuralgia,  cavernous sinus syndrome, seizure, hypothalamic-pituitary dysfunction Dx : angiography, MRI angiography, helical CT angiography

ANESTHESIA & CRANIOTOMY FOR INTRACRANIAL ANEURYSMS & ARTERIOVENOUS MALFORMATION(2) Ruptured Aneurysms Usually present: acute subarachnoid hemorrhage less commonly epidural space or brain hemorrhage Sx. : sudden severe headache often associated with nausea, vomiting, transient loss of consciousness ( ∵ ↑ ICP and ↓ CPP) Delayed Cx : cerebral vasospasm (30%) , rerupture, hydrocephalus symptomatic vasospasm Tx : triple H therapy – hypervolemia, hemodilution, HTN neurosurgical management : complicated by risk of rebleeding, vasospasm. rerupture : 10~30% early surgical obliteration of the aneurysm : recommended for stable patient

ANESTHESIA & CRANIOTOMY FOR INTRACRANIAL ANEURYSMS & ARTERIOVENOUS MALFORMATION(3) PREOPERATIVE MANAGEMENT Preanesthetic evaluation : determine whether rupture has occurred Neurological findings , coexisting disease. controlled hypotension :relative contraindication to      : preexisting HTN and renal, cardiac or ischemic cerebrovascular disease ECG Abn. - commonly seen in subarachnoid hemorrhage (not heart dis.) Pt with Persistent elevation in ICP : little or no premedication to avoid hypercapnia INTRAOPERATIVE MANAGEMENT(1) Surgery can result in rupture or rebleeding :blood should be available anesthetic Mx focus : preventing rupture or rebleeding  intraarterial and central venous(or pulmonary artery) pressure monitoring  mannitol : dura is opened ( to facilitate surgical exposure & reduce tissue trauma)

ANESTHESIA & CRANIOTOMY FOR INTRACRANIAL ANEURYSMS & ARTERIOVENOUS MALFORMATION(5) INTRAOPERATIVE MANAGEMENT(2) controlled hypotension is useful       (1) decrease transmural tension across the aneurysm        (2) rupture less likely and facilitates surgical clipping        (3) ↓blood loss head-up position with volatile anesthesia(Iso.) enhance the effect of hypotensive agent. Thiopental and mild hypothermia : protect Brain during prolonged or excessive hypotension. Depending upon neurological condition:most pt extubated at the end of surgery Rapid awakening : allow neurological evaluation before transfer to ICU.

ANESTHESIA FOR SURGERY ON THE SPINE(1) PREOPERATIVE MANAGEMENT Any existing ventilatory impairment and airway anatomic abn. and limited neck movement complicate airway management. neurological deficits (DOCUMENTED) Patients with Degenerative dis. : pain ←  opioid with premedication INTRAOPERATIVE MANAGEMENT(1) Positioning prone position       : corneal abrasion or retinal ischemia , pressure necrosis of           nose, ear, forehead, chin, breast(female) or genitalia(male)         arm - comfortable position or extended with elbow flexed    supine position : ant. approach to cervical spine : ass. with injuries to the trachea, esophagus, recurrent laryngeal n. , sympathetic chain, carotid a. or jugular vein sitting and lateral decubitus position may used occasionally.

ANESTHESIA FOR SURGERY ON THE SPINE(1) INTRAOPERATIVE MANAGEMENT(2) Monitoring  Intraarterial & possibly central venous pr. Monitoring – before positioning or turning (when significant blood loss is anticipated and pt preexisting cardiac dis. ) Elective hypotension or weak epinephrine infiltration of the wound - intraoperative blood loss ↓ Monitoring somatosensory evoked potentials and motor evoked potentials - detect intraoperatively spinal cord injury from excessive distraction

THANK YOU…….