NEUROANAESTHESIA

1. Anaesthetic management
for Posterior fossa surgery
Dr.ZIKRULLAH

2. What are boundries
of
post.cranial fossa?

3. ANATOMY
Boundaries :
Anteriorly : clivus, petrous part of temporal
bone
Posteriorly : occipital bone
Laterally : squamous and mastoid part of
the temporal bone
Superiorly : tentorium cerebelli
Inferiorly : Foramen magnum

4. What are the contents of
post.cranial fossa?

5. Contents :
Cerebellar hemispheres,
Brainstem (lower midbrain, pons and upper
medulla)
 3rd to 12th cranial nerves nuclei efferent
and afferent fiber tracts - connect the brain
with the rest of the body.
Blood supply :
Vertebrobasilar system.

6. CLINICAL PHYSIOLOGY
• Cerebellum ,mid brain, pons, medulla and
multiple cranial nerves - lesions in this area
with a multitude of possible signs and
symptoms.
• Mass effects of lesion,hydrocephalus
secondary to obstruction of CSF flow through
aqueduct of sylvius leads to increased ICP.

7. What are the signs and symptoms
of post.fossa tumour?

8. SIGNS AND SYMPTOMS
Non specific symptoms include
• Headache
• Fatigue
• Vomiting
• Anorexia
• Personality changes
• Cerebellar or brainstem– dysmetria,
hemiparesis and cranial nerve deficits.

9. • More specific clinical syndromes
(tumors -rapidly involve neural structures )
-acoustic neuromas,
-other CP angle tumors
-brainstem glioma
-carotid body tumor.
• SOL( posterior fossa)-elevated ICP-CSF outflow
obstruction.
• In infants an enlarged head or bulging
fontanelle may indicate hydrocephalus.

10. DISTINCT SET OF SIGNS AND
SYMTOMS IN RELATION TO
LOCATION OF LESION

11. Midline and 4th ventricle ?

12. • Truncal ataxia
• Wide based gait
• Nystagmus
• extraocular movement abnormalities
• Truncal titubation
• Hydrocephalus- early and common
• Frequent papilledema
• Signs of brainstem lesion are common

13. Lesion of lateral cerebellar
hemisphere??

14. • Hypotonia
• Intention tremor
• Limb ataxia
• Dysmetria
• Dysdiadochokinesia
• Dysarthria
• Ocular abnormalities like nystagmus, gaze
paresis, skew deviation
• Hydrocephalus less common and appear
later

15. Herniation of the cerebellar
tonsils through foramen magnum
(especially in children) appear
as??

16. • Meningismus
• Head tilt
• Muscle spasm
• Opisthotonus
• Vomiting

17. • Skew deviation of the eyes
• Downbeat nystagmus (vertical nystagmus)
• Typical ‘posturing’ from tonsillar
herniation may be mistaken for “cerebellar
fits”
• Bulbar palsies with vocal cord paralysis

18. • Swallowing and gag dysfunction
• Occipital headache
• Neck pain
• Coughing--loss of consciousness as the
tonsils are further impacted into the
foramen magnum
• Further herniation compresses the
medulla
irregular respiration and death

19. Brainstem involvement
produces??

20. • Ocular problems related to pupil size,
ocular mobility, nystagmus
• Sensory or motor deficits
• Respiratory changes vary depending on
brainstem compression :
Hyperventilation
as compression passes caudally apneustic
and ataxic breathing

21. • Multiple cranial nerve problems(bulbar
palsies)
• Progressive external compression- brainstem
from midline or 4th ventricle lesions
Gaze and facial palsies develop
rapid loss of consciousness
respiratory changes
bradycardia
hypertension

22. Classify Post.Fossa tumor??

23. Posterior fossa neoplasms
CHILDREN
1.)Brainstem:-Glioma
Ganglioma
Astrocytoma
2.)Tectum & cerebellum:-Pilocytic astrocytoma
Meduloblastoma

24. 3.)Fourth ventricle:-Meduloblastoma
Ependymoma
Choroid plexus papilloma
4.)CP angle:-Schwannoma
Meningioma
Choroid plexus papilloma

25. ADULT
1.)Extra axial:-Vestibular Schwannoma
Metastasis
Meningioma
Glomus jugulare
Paraganglioma

26. 2.)Intra axial:-
A.)Parenchymal:-Metastasis
Hemangioblastoma
B.)Intraventricular:-Subependymoma
Choroid plexus papilloma

27. Anaesthetic considerations
• Create challenges to the
anaesthesiologists, whose intraoperative
goals - facilitate surgical access, minimise
nervous tissue trauma and maintain
respiratory and cardiovascular stability.

29. 1) Complete Medical History
• Mainly for function of the heart and the
lungs.
• History of CNS Disorders – Seizure disorders
(type and for adequacy of therapy)
• Cerebral hemorrhage or prior strokes are
noted.

30. • Any residual speech, sensory or motor
dysfunction are recorded
• recent intracranial or diagnostic
procedure and consider possibility of
residual pneumocephalus.

31. • What drug history you will like to
know??

32. 2) Review the patient list of medications:
• Steroid,
• Mannitol
• Diuretics
• Antihypertensive
• Tricyclic antidepressants
• L –dopa
• Benzodiazepines
• Phenothiazines

33. 3 ) Physical examination :
• Patient physical status
• Particularly in reference to cardiovascular and
pulmonary stability
• Airway manageability, is a determinant of the
choice of patient position for posterior fossa
surgery.

34. 4) Neurological Examination :
• Level of consciousness
• Document any focal motor or sensory
deficit.
• Examination of sign and symptom of
increased ICP.

35. 5) Routine Investigations:
• CBC
• Blood Chemistry
• Coagulation profile
• ECG and CXR

36. 6)Imaging
• Bony artefacts -seen in CT scan but MRI scan
has greatly improved diagnosis
• Imaging allows intraaxial and extraaxial
lesions to be differentiated and allows
visualization of the surrounding anatomic
structures and they provide information for
pathologic diagnosis of lesion.

37. EXTRAAXIAL LESION INTRAAXIAL LESION
•Displacement of
parenchymal structures
•Presence of bone erosion
•Well delineated margins
•Contiguity with surrounding
dural or bony structures
•Do not erode bone
•Have indistinct margins

38. • How will you monitor the patient?

39. Monitoring
• The goals of monitoring are to ensure adequate CNS
perfusion maintain cardiovascular stability and
detect and treat VAE ( venous air embolism )
Five lead ECG
Pulse oximetry
NIBP
EtCO2 monitoring
Invasive BP

40. Capnography
Temperature
Precordial stethoscope
Central venous catheter
Precordial doppler probe
Esophageal stethoscope
TEE

41. Positioning???

42. Common neurosurgical positions are:
• Sitting position
• Lateral (park bench)
• Semilateral (Janetta)
• Prone
• Supine

43. Patient position
Sitting position :
• Patient head secured in a three pin head
holder.
• Bony prominences are padded
• Legs placed in thigh high compression
stockings to limit pooling of blood

44. • Elbows and leg supported by pillows or
pads.
• Maintain 1 inch space between the chin and
chest to prevent cervical cord stretching and
obstruction of venous drainage from the
face and tongue

45. • Avoid large airway and bite block placements
• Avoidance of excessive neck rotation
• Avoid excessive flexion of knees towards the
chest to prevent abdominal compression,
lower extremity ischemia and sciatic nerve
injury

47. Advantages of sitting position ??

48. • Lower airway pressure
• Easy of diaphragmatic excursion
• Improved ability for hyperventilation
• Increased access to ETT and thorax for
monitoring
• Access to extremities for monitoring fluid or
blood administration and blood sampling

49. • Visualisation of the face for observation of
motor responses during cranial nerve
stimulation
• Better surgical exposure
• less tissue retraction
• less cranial nerve damage
• complete resection of tumor possible.

50. Problem with sitting position?

51. • High chance of venous air embolism
• Hemodynamic instability
• Compressive Peripheral neuropathy
• Cervical spine injury

52. • Contraindications for sitting
position??

53. • Intracardiac defects
• Severe hypovolemia
• Cachexia
• Severe hydrocephalus
• Lesion vascularity
• Extremes of age / impaired cardiac
function
• Degenerative diseases of cervical spine
• Significant CVD.

54. • Physiologic changes in sitting
position??

55. • CVS-cardiovascular instability and arterial
hypotension ass.with upright position
• Aggravated by I.v.induction & volatile
agent
• Due to hydrostatic effect permit the
drainage of blood and csf – systemic
arterial pressure

56. Head elevation above the rt. atrium
decrease in dural sinus pressure upto 10 mm Hg
Increased risk of VAE decreases
venous bleeding
(45 % in sitting position)

57. • What are the advantages and
disadvantages in prone position??

58. Prone position
• Patient’s head elevated to decrease venous
bleeding
• Face compression - prevented by keeping
head elevated and shoulders at or above the
edge of the operating table
• Lower incidence of VAE

59. Disadvantages :
• Surgical field is not as clear as in sitting
• Eye compression can produce blindness from
retinal artery thrombosis
• Conjunctival edema.
• Venous pooling in the lower extremities

61. Lateral Or Park Bench Position
Can be used for access
• To the post parietal
• Occipital lobes
• Lat. Post fossa (CP Angle)
• Aneurysms of the vertebral & basilar
arteries.

63. • How to premedicate the patient??

64. Premedication
• Preoperative premedication is
individualized by patients’
Physical status
Evidence of increased ICP
Level of patient anxiety
Continue antihypertensives
Corticosteroids
Antibiotics

65. • Oral benzodiazepines 60 minutes prior are
effective in reducing anxiety and do not
have sufficient effect on ICP
• Narcotic premedication to be avoided in pts
with SOL or hydrocephalous

66. • How will you induce the patient??

67. Induction
• Achieved with drugs ( thiopental, etomidate,
propofol)
produce rapid, reliable onset of
unconsciousness without increasing ICP.
• In presence of raised ICP, thiopental is
commonly used
• Smooth and gentle induction of general
anaesthesia is more important.

68. • Lidocaine (1.5 mg/kg) IV 90sec before
intubation to suppress laryngeal reflexes
• Adequate depth & profound skeletal muscle
paralysis should be achieved prior to
laryngoscopy
• Gentle laryngoscopy & intubation.

69. Maintenance??

70. Maintenance of Anaesthesia
• These technique generally fall in to two
categories –
• 1.) Primarily Volatile agent and
• 2.) Narcotics
• Either technique can be used.

71. • In narcotics based anaesthetic technique
with either N2O or low dose (< 1%)
isoflurane in O2 is optimum .
• Fentanyl or sufentanil may be used.
• Volatile agent preferably isoflurane with
little or no narcotic supplementation can
also be used.

72. • Hyperventilation combination with < 1%
isoflurane-stable intracranial dynamics.
• N2O may be used in anaesthetic regimen but
it is contraindicated if the patient is suspected
to have pneumocephalus
• HTN or tachycardia near the end of surgery, it
is best to treat with either Labetalol or
Esmolol.

73. Fluid Management
• A balanced salt solution - fluid of choice
• volume of fluid administered should be
minimized
• Use no dextrose containing solution.
• Maintain hematocrit at 30 to 35 %.

74. • Patients who present for tumor surgery
should be kept on the dry side of normal.
• Excess fluid administered -may cause
brain edema at the sites of blood brain
barrier disruption.

75. Emergence
• It should be smooth and gentle.
• Lidocaine 1.5 mg/kg IV decrease cough and
strain.
• If surgery is superficial and performed without
much traction on the brain stem, it is assumed
safe to extubate.

76. • If lesion is deep seated with frequent
traction on the brain stem - danger of apnea
or decrease sensorium with diminish airway
reflexes
• remain intubated and be allowed to awaken
slowly in the ICU after a period of
monitoring and continued ventilation.

77. COMPLICATIONS??

78. 1. Brainstem and CN stimulation
2. Venous air embolism
3. Pneumocephalus
4. Macroglossia
5. Quadriplegia

79. 1.Brainstem & CN stimulation
• Hypertension d/t stimulation of Vth CN,
periventricular gray area, reticular
formation, or nucleus of tractus solitarius.
• Bradycardia and escape rhythms - vagus N
stimulation

80. • Hypotension - pontine or medullary
compression.
• Ventricular and supraventricular
arrhythmias - brain stem stimulation.
• Close attention to cardiovascular
parameters during critical periods of
surgery is essential
• surgeon may inform of brainstem
encroachment

81. 2.Venous Air Embolism
• Most Feared Complication associated with
sitting position.
• CAUSES:
open veins & non collapsible venous channels
gravitational effects of low CVP
neg. I.V. pressure relative to atm. Pressure
poor surgical technique
• Incidence- 25-50%

82. 3.Pneumocephalus
• Air into the epidural or dural space sufficient
to exert a mass effect.
• Incidence- 3%
• Sometimes life threatening brain herniation.

83. CAUSES:
• Diminition of brain volume secondary to
mannitol
hyperventillation
removal of SOL
• contraction of intravascular blood vol.
associated with acute hemorrhage
• Gravitational effect of sitting position
• Intraop drainage of CSF

84. • “Inverted Pop Bottle Analogy” as CSF pours
out, air bubbles to the top of the
container(cranium)
 So that is why slow cont. gravitational
drainage of CSF in sitting position can result
in accumulation of air in subdural space

85. • ROLE OF NITROUS OXIDE:
major contributing factor
avoidance would not eliminate the risk
it increases the size of air filled space
S/S:
• Confusion
• Headache
• Convulsions
• Neurological deficits
• Failure to regain conciousness

86. CT scan confirms the diagnosis and
localisation of intracranial air, if untreated
Brain herniation and death.
T/T:
• IMMEDIATE twist drill aspiration of air
through burr holes on either side of the
vertex.

87. 4.MACROGLOSSIA
CAUSES:
• Extreme flexion of head with chin resting on
the chest
• Prolong presence of an oral airway
Obstruction of its venous and lymphatic
drainage
Airway obstruction
hypoxemia
hypercapnia postop

88. 4.QUADRIPLEGIA
CAUSES:
• Flexion of head on the neck causes
streching of the spinal cord at C5 level,
regional cord perfusion may be
compromised if MAP is decreased.

89. Thank you