neuro anaesthesia post fossa surgery.ppt

neuro ananesthesia

1. Management of Posterior Fossa
Surgery
Anjum Naz
MD, PDCC (Neuroanaesth.)

2. Anatomy
Surrounded by
•Anteriorly by clivus and
petrous bone
•Laterally and posteriorly by
ocipital squamosa
•Inferiorly by foramen
magnum
•Superiorly by tentorium
cerebelli

3. Contents
•Cerebellar hemispheres
•Large portion of brainstem
(upper medulla, pons, lower
midbrain)
• Third to twelfth cranial nerves
•Vertibrobasilar arteries

Major highway for the afferent and efferent
pathways to the brain

4. Surgical Conditions
Cerebellar hemisphere:
Hemangioblastoma
Astrocytoa
Metastasis
CP angle:
Schwanoma- facial,acoustic
Meningioma
Epidermoid
Brain stem:
Glioma
Fourth ventricle:
Medulloblastoma
Ependymoma
Choroid plexus papilloma
Cerebellar vermis:
Astrocytoma
Dermoid
Clivus:
Meningioma
Chordoma
Tumours:

6. Others
Cranial nerve compression syndromes
Trigeminal neuragia
Hemifacial spasm
Disabling positional vertigo
Developmental anamolies
Chiari malformation
Craniovertebral junction anamoly
Vascular lesions
Aneurysms
AV malformations
Infarcts and hemorrhages

7. Presentation
Elevated ICP- mass effect, hydrocephalus
Headache
Reduced visual activity
Truncal/limb ataxia
Hypotonia, intension tremor
Opisthotonus due to herniation
Respiratory changes due to brain stem involvement
Multiple cranial nerve involvement

8. Preoperative evaluation and preparation
•Physical status
•Cardiopulmonary problems
•Previous operations- VP shunt, carotid end arterectomy
•Hydration status
•Vascular access for right atrial catheter placement
•Echocardiography- PFO for sitting position

9. Monitoring
Preinduction and induction:
–ECG
–NIBP
–Pulse oximetry
–Capnography
–Precordial stethoscope
Postinduction
–Central venous/ RA/ PA catheter
–Invasive BP
–Esophageal/ nasopharyngeal temperature probe
–ETCo2, ETN2
–Precordial doppler probe
–TEE

10. Choice of Patient Position
•Sitting
•Prone
•Lateral
•Three quarter prone
•Park bench

11. Sitting position
•Head secured in three pin holder
•Legs folded at knees with thigh high compression
stockings
•Elbows supported by pillows and pads
•Legs freed at pressure points
•1 inch space between chin and chest prevent cervical
cord streching and venous obstruction
•Avoid large bite blocks or airways
•Tranducer relocation

13. Advantages
•Low air way pressures
•Ease of diapghramatic excursion
•Improved Access to ETT
•Access of extremities for fluid and blood
administration blood sampling
•Visualisation of face for examination during
nerve stimulation

14. Complications
•Cerebral ischemia – decreased CPP
•Cervical spine ischemia
•Nerve palsies – brachial, sciatic, peroneal
•Tube migration
•Tension pneumocephalus
•Hypotension – decreased CO, venous return
•Venous air embolism, paradoxical air embolism
•Edema of face and tongue

15. Contraindications
•Intracardiac defects
•Pulmonary AV malformations
•Severe hypovolemia
•Severe hydrocephalus
•Poor cardiac reserve
•Carotid artery stenosis
•Cervical PIVD

16. Prone position
•Head elevated above body
•Head resting in a padded head rest or three
pin holder
•1 inch distance between chin and chest
•Abdomen free
•Padding at pressure points
•Arms on the side

18. Complications
•Dismantling of monitors during poistioning
•Access not so good for surgery
•Facial and tongue edema
•Increased airway pressures
•Hypotension dysrrhythmias
•Eye compression
•Blindness – retinal artery thrombosis
•Venous air embolism
•Paradoxical air embolism

20. Anaesthetic considerations
•Maintenance of CPP
•Preservation of cardiovascular responses to
surgical manipulation of brain stem
•Avoidance of nitrous oxide

21. Premedication
•Individualised acc to physical status
•Evidence of raised ICP
•Level of anxiety
•Narcotic premedication to be avoided
•Chronic antihypertensives to be continued
•Corticosteroids

22. Induction
•Thiopentone/ Propofol
•Vecuronium/ rocuronium
•Smooth laryngoscopy
•Blunt sympathetic response short acting beta
blockers/ vasodilators
•Need of vasopressors during positioning
•Verification of tube after final position

23. Maintenance
•CPPV
•Avoid N2O
•Adequate depth and pain relief during pin insertion and
craniotomy
•Propofol infusion, isoflurane, sevoflurane
•Low normocarbia
•Low normothermia
•Liberal use of fluids preferably colloid after sitting
position
•Avoidance of osmotic and loop diuretics

24. Emergence and extubation
•Prevent abrupt rise of blood pressure
•Minimise coughimg and straining on tube
•Immediate extubation if patient has good air way
reflexes
•Extensive manipulation of brain stem or edema keep
the air way secured till the patient is fully awake
• look for persistent postoperative hypertension,
bradycardia in the post operative period

25. Venous air embolism
•Pathophysiologic effects are that of ischemic
reperfusion injury – depend on
•Volume of entrained air
•Rate of accumulation.
•Height of the vein above the right heart
>>50 ml for clinical changes50 ml for clinical changes
200-300 ml or 3-5 ml/kg200-300 ml or 3-5 ml/kg
The closer the vein of entrainment to the The closer the vein of entrainment to the
right heart the lower the critical volumeright heart the lower the critical volume

26. •Slow continuous entrainment goes in to
peripheral pulmonary circulation
–Sympathetic reflex vasoconstriction
–Endothelial mediators
•Rapidly entered air bolus causes blockage of
right ventricular outflow tract

27. Presentation
•Cardiovascular: decreased venous return, CO,
dysrrhythmias, acute right ventricular failure
cardiovascular collapse
•Respiratory: bronchoconstristion, pulmonary
hypertension, hypoxemia, CO2
retension ,increased pulmonary dead space,
pulmonary edema
•Neurological: cerebralischemia, hyperemia,
stroke, neurological deficit, coma.

28. High risk procedures
•Sitting position craniotomy
•Posterior fossa/neck surgery.
•Laparoscopic procedures
•Total hip arthroplasty.
•Cesarean section
•Central venous access

29. Detection
•Trans-oesophageal echocardiography can detect
0.02ml/kg, requires expertise
•Pre-cordial Doppler can detect 0.05ml/kg. Affected
by cautery.
•End-tidal nitrogen-0.04% is significantly faster than E-
tidal C02 by 30-90 seconds, specific for air.
•End-tidal C02; decrease by 2mm Hg significant?
•RA/ PA catheter- rise in pressure. Aspiration of air.
•Vigilance

30. Prevention
•Patient positioning, e.g. “park bench” versus sitting for
posterior fossa craniotomy
•High index of suspicion in any surgery where there is a
negative gradient between surgical field and heart.
•Adequate hydration
•Meticulous surgery with liberal use or bone wax
• Avoid nitrous oxide
•Avoid drugs which increase venous capacitance, eg
nitroglycerine

31. Treatment
•Inform surgeon
•Prevent further air entrainment
•100% oxygen
•Provide jugular venous compression
•Trendelenberg position
•CPR/ inotropes.
•Aspiration of air.
-Swan Ganz Catheter 6-16%
- Multi-orifice catheter 30-60%

32. Postoperative goals
•Provide supplemental oxygen
•Perform ECG, chest X ray
•Measure serial ABGs
•If arterial air emboli are suspected provide
hyperbaric compression.

33. Thank you ..

34. Sitting Position