Awareness During Anesthesia

Report
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

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