This document provides an overview and update on issues in neuroanesthesia. It discusses recurrent issues such as patient positioning, monitoring, fluid management and more that have not changed significantly over time. It also reviews cerebral physiology concepts like blood flow regulation and the effects of anesthetic agents. The document outlines current surgical trends like minimally invasive procedures and equipment trends like intraoperative CT. It concludes by emphasizing the importance of multidisciplinary team training to continually improve neuroanesthesia care.

1. UPDATE IN NEUROANAESTHESIA
DOUGLAS FAHLBUSCH
MBBS, FANZCA, GDM, GAICD
WWW.PERIOPERATIVE.COM.AU
Improving cost, risk and the healthcare experience
MAY 2015
1

2. INTRODUCTION
• Neuroscience underpins
• Neuroanaesthesia and
• Neurocritical care
• ‘… advance the art and science of the care of the
neurologically impaired patient through education,
training and research in perioperative neuroscience’
2
SNACC, RCOA

3. OVERVIEW
PRACTICAL UPDATE
• Brain: defines who we are
• Loss of function defines
death
• Function routinely
manipulated in
anaesthesia
• Critical considerations
when operating on this
target organ
Gelb AW 2015
• What’s not new
• Surgical trends
• Cerebral oximetry
• Intraoperative CT
• Pursuit of excellence
3

4. RECURRENT ISSUES
WHAT’S NOT NEW
• Patient positioning
• Neurophysiologic monitoring
• Intravenous fluid management
• Arterial blood pressure target
• PaCO2 target
• Hypothermia
• Control of intracranial pressure/
brain relaxation
• Use of steroids
• Use of osmotherapy
Miller 8th Edn, Ch 70
• Use of diuretics
• Use of anticonvulsants
• Pneumocephalus
• Venous air embolism
• Glucose management
• Emergence from anaesthesia
4

5. WHAT’S NOT NEW
CEREBRAL PHYSIOLOGY
• Cerebral metabolic rate (CMR) is high:
• 60% function, 40% cellular homeostasis
• 15% of cardiac output
• Cerebral blood flow (CBF) is ~50 mL/100 g/min
• grey 80%, white 20%
• CBF and local metabolism highly coupled over MAP 65-
150 mmHg (est), else passive
5Miller 8th Edn, Ch 17

6. WHAT’S NOT NEW
CBF AUTOREGULATION
• Chemical regulation
• PaCO2 range of 25 to 70 mm Hg direct effect on CBF
• PaO2 < 60 mm Hg CBF decreases dramatically
• Temperature affects metabolic rate primarily, CBF secondarily
• Systemic vasodilators affect the cerebral circulation and can,
depending on the MAP, increase CBF
• Vasopressors affect arterial blood pressure - CBF secondarily
6Miller 8th Edn, Ch 17

7. WHAT’S NOT NEW
SELECTION OF ANAESTHETICS
• Intravenous
• Barbiturates, etomidate, and propofol decrease the CMR
• Opiates and benzodiazepines effect minor decreases in CBF and
CMR
• Ketamine can significantly increase the CMR and therefore CBF
• Volatiles reduce CMR
• above 1 MAC increase CBF
• reduce/ omit if brain ‘tight’
7Miller 8th Edn, Ch 17

8. WHAT’S NOT NEW
CEREBRAL ISCHAEMIA
• Barbiturates, propofol, ketamine, volatile anaesthetics, xenon
neuroprotective
• animal models, mild ischaemic insult
• not with moderate-to-severe injury (delays apoptosis)
• Etomidate can decrease regional blood flow, can exacerbate
ischaemia
• Brain stores of O2/ substrates limited, extremely sensitive to decr CBF
• Severe decreases in CBF = rapid neuronal death
• early excitotoxicity, and delayed apoptosis
8Miller 8th Edn, Ch 17

9. CONTROL OF INTRACRANIAL
PRESSURE/ BRAIN RELAXATION
Miller 8th Edn, Table 70-1 & Box 70-3
(often overlooked)
JVP -> AWP -> PCO2 & O2 -> ABP ->
CMRO2 -> vasodilators -> mass lesions
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10. SURGICAL TRENDS
• Minimally invasive
procedures
• Transphenoidal
• DBS
• Intraventricular
• Discectomy
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11. GUIDELINES FOR
PERCUTANEOUS ENDOSCOPIC
SPINAL SURGERY
• Lumbar, Thoracic, Cervical disc herniations
• Lateral spinal canal/ foraminal stenoses
• Degen facet joint cysts with radiculopathy
• Symptomatic central stenosis (experienced hands)
• C/I
• Cauda equina
• Instabilities/ deformities/ non-neural back pain
• Very large herniations relatively C/I
ISMISS 2010 12

12. TRANSFORAMINAL ENDOSCOPIC DISCECTOMY
Michael Y Wang, MD FACS; Professor, Departments of Neurological Surgery & Rehab Medicine,
University of Miami Miller School of Medicine
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13. ENDOSCOPIC SPINAL SURGERY
• Duration 45-80 mins,
• LA 1.9 mg/kg
• ‘Discomfort’ - ok if
nerve roots avoided
• Discharge < 24 hrs
possible (Chan)
14
Surg Neurol Int. 2014; 5(Suppl 3): S62–S65

14. ENDOSCOPIC
SPINAL SURGERY
• LA/ sedation has been used
since 1926 (Towne)
• Well-tolerated (Hsien-Te Chen)
• Indicated for multiple comorbidities (Khan), ASA I-IV,
geriatrics
• Intraop evaluation of surgical progress
• Early discharge
• The future ‘gold standard’ for discectomy? (Gibson 2012)
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15. DBS
STEREOTACTIC SCAN PREOP
• > 50 cases (Matthew
McDonald,
Neurosurgeon Calvary
Wakefield)
• Propofol/ LA for placing
frame (+/- opioid for
tremor suppression)
• Avoid benzo’s
16
Picture courtesy of A/Professor Wilcox, FMC

16. DBS
THEATRE SETUP
• Dexmedetomidine
infusion
• Propofol ceased once
scalp reflected
17
Picture courtesy of A/Professor Wilcox, FMC

17. Picture courtesy of A/Professor Wilcox, FMC
DBS
INTRAOP
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18. DBS
BATTERY/ LEADS
• LMA
• Propofol
• Fentanyl
• Volatile
• Battery most commonly
right on men and left on
women (seatbelts)
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19. EQUIPMENT TRENDS
• Cerebral oximetry
• Intraoperative CT
20

20. INTRACRANIAL MONITORING
Near-Infrared
oximetry
ICP (ventricular
or parenchymal)
Brain tissue
oximetry
Jugular venous
oximetry
Microdialysis
21

21. NEAR INFRARED
SPECTROSCOPY
• Two wavelengths
• Substract superficial
tissues
• Left with deep tissue
signal
• Non-pulsatile
• Ratio of arterial to venous blood dictates ‘saturation’
• Multiple sites (cerebral, kidneys, thigh)
22

22. NEAR INFRARED OXIMETRY
• Relative indices of
perfusion
• Baseline set pre-
induction (usu. 58-82)
• Relative decline
< 20% ok
• Absolute thresholds
• 50 intervene
• 40 critical
23
up to 6 channels

23. NEAR INFRARED
SPECTROSCOPY
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• Perioperative
morbidity not
correlated with
cerebral desaturation
• Reassurance for
• elderly, paeds
• vasculopaths
• ACDF, carotids
Cowie et al 2014 (AIC)

24. INTRAOP CT
‘O-ARM’
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25. INTRAOP CT
USES - DBS
• Confirm
stimulator
placement
& track
• Exclude
bleeding
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26. INTRAOP CT
USES - SPINAL FUSION
• screw placement
• alignment
• bleeding
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27. CONCLUSION
• Interplay of CNS with other organ systems/ physiology/
pathology
• Unit Excellence:
• Staff training, retention
• Cross-functional processes (breaking down the silos)
• IT: increase reach and engagement
• Closed loop delivery systems: anaesthesia, fluids …
28
Puri 2015

28. FURTHER INFORMATION
• Neuroanaesthesia SIG - ANZCA/ ASA/ NZSA
• Neuroanaesthesia Society of Great Britain and Ireland
https://nasgbi.org.uk/
• Royal College of Anaesthetists http://www.rcoa.ac.uk/document-
store/guidance-the-provision-of-services-neuroanaesthesia-and-
neurocritical-care-2015
• Society for Neuroscience in Anesthesiology and Critical Care
http://www.snacc.org/#
• Perioperative Solutions www.perioperative.com.au
• Dr Douglas Fahlbusch - drfahlbusch@perioperative.com.au
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29. 1. Gelb AW. Actualización en neuroanestesia. Rev Colomb Anestesiol. 2015;43:1-2.
2. Gibson JNA, et al. Transforaminal endoscopic spinal surgery: The future ‘gold standard’
for discectomy? A review, The Surgeon (2012)
3. Hsien-Te Chen et al. Endoscopic discectomy of L5-S1 disc herniation via an interlaminar
approach: Prospective controlled study under local and general anesthesia. Surg Neurol
Int. 2011; 2: 93.
4. Khan MB et al. Thoracic and lumbar spinal surgery under local anesthesia for patients with
multiple comorbidities: A consecutive case series. Surg Neurol Int. 2014; 5(Suppl 3): S62–
S65.
5. Li ZZ et al. The strategy and early clinical outcome of full-endoscopic L5/S1 discectomy
through interlaminar approach. Clin Neurol Neurosurg. 2015 Mar 14;133:40-45
6. Miller RD (Ed). Miller’s Anesthesia. 8 Edn. Reed Elsevier 2014
7. Peng CWB et al. Percutaneous endoscopic lumbar discectomy: clinical and quality of life
outcomes with a minimum 2 year follow-up. Journal of Orthopaedic Surgery and Research
2009, 4:20
8. Puri et al. A Multicenter Evaluation of a Closed-Loop Anesthesia Delivery System: A
Randomized Controlled Trial.Anesth Analg. 2015 Apr 21
9. Towne EB. Laminectomy and removal of spinal cord tumors under local anesthesia. Cal
West Med. 1926;24:194.
References
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