Awareness During Anesthesia
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Transcript Awareness During Anesthesia
Awareness During
Anesthesia
DR.Mohammad Hajeyah
Kuwait Board of Anesthesia
R.3
IS THE PATIENT AWAKE RIGHTNOW
?
HOW MANY OF YOU THINK THAT ITS
IMPORTANT TO MONITOR AWARENESS
?
HOW MANY OF YOU DO MONITOR
AWARENESS
?
OUTLINE
Definition
Incidence
Why does it happen
Types and consequences
Modalities of monitoring
How do we prevent and manage it
Take home message
DEFINITION
The
situation that occurs when a patient
under general anesthesia becomes aware of
some or all events during surgery or a
procedure, and has direct recall of those
events.
Because of the routine use of
neuromuscular blocking agents during
general anesthesia, the patient is often
unable to communicate with the surgical
team if this occurs.
Explicit
memory may be recalled
spontaneously, or may be provoked by
postoperative events or questioning.
Implicit
memory may not be consciously
recalled, but may affect behavior or
performance at a later time
INCIDINCE
Awareness
during anesthesia is a very
disturbing event if encountered.
Memories
of the event are either
remembered spontaneously or provoked by
post-op events.
Recall
of such events specially if awareness
of paralysis and painful stimuli is the issue
then ones life maybe changed permanently.
Back in the 1970`s where nitrous oxide was used in
60-70%,incidince was 7% ( 1 in 14) pts.
In recent times awareness with recall of painful
stimuli is at 0.03% (1 in 3000 )pts.
And in cases where no painful stimuli was
encountered its 0.1-0.7% (1 in 142-1000) pts.
Sigalovsky N. Awareness under General Anesthesia. AANA Journal/October 2003/Vol.71,No. 5,p:373-379.
The
closed claim analysis of the ASA. States
the incidence to be more common in women
(77%).
In
adults younger than 60 yrs. (89%).
In
pediatrics its (0.5-1%)
In
ASA physical status 1 and 2 (68%)
Sigalovsky N. Awareness under General Anesthesia. AANA Journal/October 2003/Vol.71,No. 5,p:373-379.
A study in Finland done on 2,600 pts. Showed (0.4%) who
experienced awareness and (0.3%) possibly experience
awareness.
A Swedish study found the incidence to be (0.18%) when
MR. was used and (0.10%) when no MR. was used.
A study done in the university of Iowa showed the
incidence to be much higher in cases where
cardiopulmonary and vascular functions were
compromised. (1.1-1.5%) in cardiac surgery and (11-43%)
in major trauma.
Sigalovsky N. Awareness under General Anesthesia. AANA Journal/October 2003/Vol.71,No. 5,p:373-379.
WHY DOES IT HAPPEN
?
Why does it happen
Resistance to anesthetic agents:
1.
Pyrexia/Septic
Hyperthyroidism
Obesity
Anxiety
Young age
Heavy alcohol and tobacco use.
Recreational drug usage.
Factors reducing the MAC.
2.
3.
4.
5.
6.
7.
8.
Consequences
No one can tell you how bad it is but the patient
himself.
Impact can be as a medico legal law sue and also
as psychiatric implications.
Symptoms would range from simple insomnia and
anxiety to as severe as PTSD. development.
Those symptoms are related to being helpless,
feeling pain,fear,and inability to communicate nor
express themselves.
Consequences
Signs of AWARENESS
Tachycardia
Hypertension
Sweating
Tear formation
Pupillary dilatation and reaction to light
Movement and grimacing
How do we monitor Awareness
Bispectral
index
Electroencephalogram
Auditory
Ocular
Evoked Response
Microtremor
Patients
State Analyzer Index
Bispectral Index
BIS
Measures
patients response to
sedative/hypnotics administration.
Non-invasive.
Converts
the generated EEG. Data into a
number.
Ideal
numbers under GA. Are between 40-60.
BIS
One
study stated that with BIS there was a
reduction of Propofol use by 32.6% with
subsequent less mean time till eye opening.
According
to Glass and Johansson; that BIS
uses led to a more precise dosing of
medication and less time till recovery leading
to high turnover of patients.
BIS
Kurehara
and Coworkers found claims of
awareness in spite a value of 40 intra-op.
This
study concluded that BIS maybe
effective in measuring hypnotic state yet
awareness still can occur even with a low
BIS value.
BIS
A
recent study concluded that values
between 50-60 were insufficient to prevent
awareness during intubation with propofol
or alfentanil use.
Barr
and colleagues; studied BIS with
Nitrous Oxide use. This study concluded no
changes in BIS values with different conc. Of
Nitrous.
EEG.
EEG.
Analyzing brain waveforms changes under GA.
Both computer-processed and un-processed EEG
reading are used to analyze level of awareness.
Problems include:
Cost
Complexity of readings
Complexity of equipments
Difficult to interpret.
1.
2.
3.
4.
Auditory Evoked Potentials
AEP
Fluctuations of the (AER) latency as a sign of
awareness.
It has been reported that a positive correlation
exists between AER and awareness changes.
Problems:
Good indicator with inhalational agents rather
than narcotics.
Complexity of equipment and analysis.
1.
2.
Ocular Micro tremor
OMT
A promising new device in awareness monitoring.
It measures high frequency tremors of extra-ocular
muscles generated by higher brain signals from the
brain stem.
Those signals are in direct relation with anesthesia
depth.
Still under study and not fully under practical use.
Patient State Analyzer Index
It’s
a quantitative analysis of the EEG.
Simply
uses more extensive sensors to
measure EEG.
Few
completed studies regarding this
method.
How To Manage
Intra-operative:
If pt is being exposed to a noxious stimuli that
maybe recalled later on then anesthesia should be
deepened.
If hypotension is present then anesthesia should
be deepened while supporting hemodynamics.
Benzodiazepines (Mediazolam 5mg) may reduce
recall post-op. via retrograde amnesic effect.
Hardman J.G., Aitkenhead A.R. Awareness during Anesthesia. Advance Access Publication, October 2005
How To Manage
Post-operative:
Pt. should be interviewed post-op if claims were made of
intra-op awareness.
Exact timing and experience should be identified and
distinguished from dreaming.
Its important to make it clear that no confusion was made
between awareness and memories at induction or
emergence.
Always to take every claim seriously and to show sympathy
with the patient.
If pt. started showing signs of anxiety ,depression and
PTSD. Then psychiatric referral shouldn’t be delayed.
Avoiding Awareness
BZD. Administered at induction reduces the
incidence of awareness specially at high risk period
during induction.
Adequate anesthetic drugs should be
administered.
The risk of awareness is greatly reduced at a MAC
0.8-1.0.
MAC. Adjustment according to patient age group
reduces the risk greatly.
Hardman J.G., Aitkenhead A.R. Awareness during Anesthesia. Advance Access Publication, October 2005
Avoiding Awareness
The
use of NMBD. Inc. the risk of
awareness.
Complete paralysis should be given only if
needed and doses should e measured.
In cases that light anesthesia is suspected
then monitoring is justified using BIS. and/or
other modalities.
In spite of all that awareness still occurs for
unknown reasons.
Hardman J.G., Aitkenhead A.R. Awareness during Anesthesia. Advance Access Publication, October 2005
Take Home Message
Intra-op awareness is associated with devastating
psychiatric sequelae that leads to medico-legal
consequences on the anesthetist.
Awareness is twice likely if NMBD. Are used.
Inadequate anesthetic dosing is the most common cause of
awareness.
Most of the time signs of awareness are often masked by
drugs or patients own concomitant illnesses.
Monitoring, specialy in high risk cases is justified and
reduces the risk of awareness greatly.
Thank You