Megamind Readers:

Megamind Readers:
Monitoring the brain into the future.
Hamish Gray
Anaesthetist
Canterbury District Health Board
NZATS 2014
“Super-Heros”
Aims
y Should all patients have a “megamind” reader as part of their anaesthetic?
1. Does depth of anaesthesia (DOA) monitoring reduce the chance of awareness?
2. Can DOA monitoring affect outcome (morbidity & mortality) after
anaesthesia/surgery
3. Is there a role for brain O2 monitoring in “at risk” surgery?
What is anaesthesia?
y Traditionally envisaged as a balanced triad:
y Amnesia
y Analgesia
y Muscle relaxation
y We have assumed that:
y Still patient
y Stable autonomic signs (HR/BP/RR)
y =“Anaesthesied”
y Does: unresponsiveness = unconscious?
The fact that the body is lying down is no reason for supposing that the
mind is at peace……..Rest is far from restful” Seneca 60AD
Sleep/anaesthesia
Awareness with recall
Dreaming under anaesthesia
Dr Jamie Sleigh Waikato Clinical School University of Auckland
Anaesthesia
y Suppressing connected consciousness
y +analgesia
y +blocking CVS responses
y +immobility
Anaesthesia
y Aims:
y Prevent connected consciousness (ie. just amnesia isn’t enough)
y Prevent the experience of surgery
1. Preventing awareness
2. Balancing “depth of anaesthesia”
Are we any good at this?
If you look for the problem you will
find it………
y Awareness: defined?
y “Memories of events that could only have occurred in the operating room”
y Brice interview
y Only 35% reported in PACU
y About 1/3rd are “neutral events”
y For many “the worst ever hospital experience”
Awareness:
Reports:
y 1st report “Insufficient Anaesthesia” 1950
y ?0.8-1.2% 1960’s-1970’s
y ?0.1-0.2% 2000’s
y NAP 5 (2014) 1:20,000
y Muscle relaxant 1:8,000
y No relaxant 1:136,000
y C/section 1:670
So here’s the answer……..?
Are depth of anaesthesia monitors any good?
y No?
y 34 women
y BIS guided 55-60
y Isolated forearm technique
y 11 women responded on 32 occasions
y BIS detected about 50% (“toss a coin”)
y Suggesting:
y Consciousness
y Connected to the environment (“respond to command”)
IF Russell Hull UK Anaesthesia 2013
Are depth of anaesthesia monitors any good?
y No?
y 34 women
y BIS guided 55-60
y Isolated forearm technique
y 11 women responded on 32 occasions
y BIS detected about 50% (“toss a coin”)
y Suggesting:
y Consciousness
y Connected to the environment (“respond to command”)
y But no “awareness”
IF Russell Hull UK Anaesthesia 2013
B-Aware trial
Paul Myles (Alfred, Melbourne) Lancet 2004
B-Unaware trial
Michael Avidan (Washington) NEJM 2008
BAG-RECALL trial
Michael Avidan (Washington) NEJM 2008
Michigan Awareness Control trial
George Mashour (Ann Arbour) NEJM 2012
?BIS reduces awareness compared to clinical
signs alone
y NICE 2012
y BIS is an option in high risk patients:
y Awareness
y XS anaesthesia
y Recommended in TIVA
y Recommended in patients at risk of
“adverse outcomes”
What about BIS & outcome?
y Decline in cognitive function after
surgery/anaesthesia
y “Grandad wasn’t quite the same after
his operation”
y POCD
y Could close titration of anaesthetic
agents reduce POCD?
y Time BIS <45
y Cumulative deep hypnotic time
y Are anaesthetic agents neurotoxic?
y Children <2
y Elderly
“Triple Low”
Daniel Sessler (Cleveland Clinic) Anesthesiology 2012
How does it work?
y 2 wavelengths (shallow & deep) of
near-infrared light via transcutaneous
sensor
y Oxy & deoxy Hb in venous (75%) and
arterial (25%) blood
y Capillary bed O2 saturation
y Venous O2 reserve/O2 extraction
Cerebral oximetry
y Estimates regional oxygenation in the frontal cortex
y “Early warning” of decreased O2 delivery to the brain
y ?relationship between rSO2 and POCD/neurological injury
y Allows institution of a strategy to improve blood flow/O2 delivery…………..eg:
y BP
y FiO2
y Hb
Cerebral Autoregulation
y Maintains adequate blood flow despite
changes in BP
y CBF is constant between ?MAP 60140mmHg
y Regulation based on small (100250um) arterioles changing diameter
to alter vascular resistance
y Blood flow is closely related to
oxygenation
What is the “correct” BP?
y Can we rely on knowing the cerebral autoregulation curve?
y What effect does sitting have on cerebral perfusion?
y Does BP have to be “corrected” to take account of the high difference
between the brain and the arm (BP cuff)?
1. Open model: Waterfall concept
Blood “falls” onto the venous side
2. Closed model: Siphon concept
Continuous column of blood
Do you really know your patient?
y Cardiovascular disease
Can cerebral oximetry help?
y Studies have shown:
1. Approx 10% of patients will have cerebral desaturation
2. Associated with:
y
Hypotension
y
Cerebrovascular disease
3. ?May indicate pressure-passive CBF in beach chair position
y
Supports the idea that we need to “correct” BP for height
y
Ie. The “waterfall” concept
y Currently the data is too unreliable to
allow definitive management
y Sensitivity 60%
y Specificity 25%
Conclusions
y BIS (Awareness)
y Maybe?
y BIS (Outcome)
y Possibly?
y Cerebral oximetry
y The future?