1. ANESTHESIA FOR NEUROSURGERY
Dr Sonam Norbu
Dr Jyoti Pathania

2. 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

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

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

5. INTRACRANIAL PRESSURE
ICP is determined by the raltionship of the volume of intracranial contents(brain+blood+CSF= cm3) 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).

7. 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

8. 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.

9. 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

10. 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

11. 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

12. INTRACRANIAL HYPERTENSION (2)
TREATMENT 
  - underlying cause
    - vasogenic edema :  corticosteroids → BBB repair
    - fluid restriction, osmotic agents, loop diuretics
    - moderate hyperventilation(PaCO mmHg) :↓ CBF & ↔ ICP
     
  1)Mannitol
     - dose : g/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.

13. 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.

14. 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 .

15. ANESTHESIA & CRANIOTOMY FOR PATIENTS WITH MASS LESIONS
Positioning
Frontal, temporal, parietooccipital craniotomies : supine position
head elevation : (∵ 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 : PaCO mmHg
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.
    

16. 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

17. 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

18. 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

19. 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
     

20. 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!

21. 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 )

22. 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

23. 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...

24. 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

25. 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

26. 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

27. 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)

28. 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.

29. 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.

30. 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

31. THANK YOU…….