2. Introduction
• Awareness during anaesthesia can be very distressing for a patient, particularly if
accompanied by recall of the painful nature of surgery.
• Unconsciousness is the sine qua non of General Anaesthesia.
• Loss of responsiveness to verbal commands is used to assess the onset of
unconsciousness, but loss of responsiveness does not equate with loss of
consciousness.
• Patients may be able to recall events of this conscious phase during general
anaesthesia leading to intraoperative awareness.
3. Neurobiology of Consciousness and taxonomy
• The neurobiology involved in the process of sleep, wakefulness, memory,
recall and behavioural response to the impaired memory are complex with
wide speculative theories.
• The nuclei in the subcortical area of the brain- Pons, Midbrain,
Hypothalamus, basal forebrain regulate the sleep wakefulness cycle.
4.
5. Definition and Incidence of Awareness
• Awareness refers to the perception of sensory stimuli by the patient during
the course of an intended general anesthesia with explicit recall in the future.
• It involves both the presence of consciousness and memory.
• Intraoperative awareness is an uncommon complication with an incidence that
varies from 1 to 2 per 1000 general anesthetics to approximately 1 per 14,500.
National Audit Project report 5 (NAP-5) on accidental awareness during general Anesthesia from BJA.
6. Memory
• Based on time, it can also be classi
fi
ed as immediate, short term and long term
memory.
• The acquisition of memory involves learning, consolidation and retrieval.
7. Types of Awareness
• Awareness can be classi
fi
ed as explicit or implicit depending on whether it is
associated with or without explicit recall.
• Awareness without explicit recall has a higher incidence than awareness with
explicit recall but the signi
fi
cance of awareness without explicit recall is not clear.
8. Cause of awareness
• Intentional provision of light anaesthesia
• Inadvertent provision of light anaesthesia
• Increased anesthetic requirements.
9. Intentional provision of light anaesthesia
• High risk ASA-IV & V pts
• Massive bleeding and severe
hypovolemia
• Decreased cardiopulmonary reserve
( EJECTION FRACTION <30%)
• Severe ventricular dysfunction
• Low cardiac index
• Severe aortic stenosis
• Severe pulmonary hypertension.
• Trauma
• Underlying cesarean section
• Cardiac surgery
• Rigid bronchoscopy
• Microlaryngeal laser surgery without
endotracheal intubation.
• Volatile anesthetics cause depression
of myocardial contractility and
vasodilation.
10. Inadvertent provision of Light Anesthesia
• During prolonged attempts at laryngoscopy and intubation after a routine
induction dose of anesthetic agents.
• During patient transport from induction room to operating room.
• Insu
ffi
cient knowledge, especially when low
fl
ow Anesthesia is being used,
without concomitant use of anaesthesia monitors
• Indiscriminate use of non depolarising muscle relaxants, clinician fatigue and
haste due to rapid turnover of cases.
• Relying on
fi
xed MAC doses.
• Malfunction of anesthetic delivery systems such as vaporisers or infusion pumps.
11. Increased anesthetic requirements
• *24% variation with race, MAC being highest in
Caucasians and Chinese, less in Asians, and
least in Europeans.
• Tolerance can occur due to chronic exposure to
sub anesthetic concentrations of anaesthetic
agents.
• Concomitant use of drugs which increase central
catecholamine levels can all increase the MAC of
anesthetic agents.
• Use of alcohol
• Smoking
• Addiction to opioids
• Use of Amphetamines.
• Pyrexia
• Hyperthyroidism
Ezri T, et al, described the Association of ethnicity with the minimum alveolar concentration of Sevo
fl
urane in 2007.
12. Human factors attributing to awareness
• Drug errors:
-Syringe swaps
-Inadequate doses
-Failure to reconstitute drugs properly
• Inadequate dosing during maintainence (due to hemodynamic instability)
• Judgement errors
• Miscommunication
• Lack of understanding of onset and o
ff
set time of newer inhalational agents, during
emergence.
13. Risk Factors for Intraoperative Awareness
• Age: incidence in children - 0.8-1.2% recent studies -0.2%
• Gender: more in women than men.
• Weight: increased awareness in obese.
• Previous history of awareness
• Di
ffi
cult airway
• Choice of anesthetic drugs & techniques: benzodiazepines cause
anterograde amnesia, the duration of action of Midazolam is very short and
they do not contribute to awareness during maintenance phase of anesthesia.
14. • Use of nitrous oxide, opioids and muscle relaxants with avoidance of
inhalational anesthetics.
• Increased incidence of awareness with use of TIVA.
• Regional Anesthesia leads to dea
ff
erentation and suppression of the surgical
stimulus.
• Type of surgery.
15. Duration of awareness
• Is important as attention, association, knowledge and consolidation are
needed for storage in long term memory.
• If duration of intraoperative awakening and consciousness is less than 30
seconds, and if Anesthesia is immediately deepened, there is no memory of
the event and no explicit recall.
• 75% of the awareness experiences lasted for <5minutes duration, but was
associated with distress in 51% of patients and long term adverse e
ff
ects in
41% of patients.
Cook TM et al conducted a study on accidental awareness during general Anesthesia in
NATIONAL AUDIT PROJECT (NAP5) - BJA
16. Methods to prevent awareness
Preoperative measures
• Patients who are at high risk should receive prophylactic benzodiazepines
prior to induction of Anesthesia
• Anesthesia delivery system should be meticulously checked for their integrity
and output everyday and prior to start of every case, as per standard
protocols
• Regular calibration of vaporisers to ensure accurate output is necessary
• Infusion pumps should be programmed
17. Intraoperative choice of anaesthetic technique and drugs
• Use of inhalational agents titrated to a MAC of at least 0.8 MAC with alarms set for
low end tidal agent concentration would help in preventing awareness.
• As there is tendency to reduce the inhalational agent, during hemodynamic
deterioration, administration of BZD or a sub anesthetic concentration of ketamine
can produce amnesia and prevent awareness.
• Neuromuscular blockade should be used only when necessary as indiscriminate
use can lead to increased awareness
• Use of analgesics.
• When TIVA is used, advisable to use a processed EEG based monitor.
18. Role of monitoring to prevent intraoperative awareness
• There is no ideal method or monitor that is available to gauge the depth of
anaesthesia, adequacy of analgesia or the level of consciousness till date.
• Depth of Anesthesia based on clinical stages, as proposed by Guedel, Clinical
signs such as:
Sweating,
Lacrimation,
Tachycardia,
Hypertension,
Movement etc
are only indirect indicators of anesthetic depth and are confounded by several other
intraoperative factors and drugs.
19.
20. GUEDELS Clinical Stages of Anaesthesia:
Stage I (stage of analgesia or disorientation): from beginning of induction of
general anesthesia to loss of consciousness
.
Stage II (stage of excitement or delirium): from loss of consciousness to onset
of spontaneous breathing. Eyelash re
fl
ex disappear but other re
fl
exes remain
intact and coughing, vomiting and struggling may occur; respiration can be
irregular with breath-holding
.
21. Stage III (stage of surgical anesthesia): from onset of spontaneous respiration to respiratory
paralysis. It is divided into four planes
:
• Plane I - from onset of automatic respiration to cessation of eyeball movements. Eyelid
re
fl
ex is lost, swallowing re
fl
ex disappears, marked eyeball movement may occur but
conjunctival re
fl
ex is lost at the bottom of the plane
.
• Plane II - from cessation of eyeball movements to beginning of paralysis of intercostal
muscles.
• Laryngeal re
fl
ex is lost although in
fl
ammation of the upper respiratory tract increases re
fl
ex
irritability,
• Corneal re
fl
ex disappears, secretion of tears increases (a useful sign of light anesthesia
)
• Respiration is spontaneous and regular, movement and deep breathing as a response to
skin stimulation disappears.
22. • Plane III - from beginning to completion of intercostal muscle paralysis.
Diaphragmatic respiration persists but there is progressive intercostal
paralysis, pupils dilated and light re
fl
ex is abolished.
• The laryngeal re
fl
ex lost in plane II can still be initiated by painful stimuli
arising from the dilatation of anus or cervix. This was the desired plane for
surgery when muscle relaxants were not used
.
• Plane IV - from complete intercostal paralysis to diaphragmatic paralysis
(apnea)
.
Stage IV: from stoppage of respiration till death. Anesthetic overdose-caused
medullary paralysis with respiratory arrest and vasomotor collapse. Pupils are
widely dilated and muscles are relaxed.
23. Available monitors to gauge anesthetic depth are:
• Isolated forearm technique
• Gas analyzers
• Processed EEG based indices
• Evoked potentials
24. Isolated forearm technique
• Introduced by TUNSTALL to detect consciousness under general anaesthesia
using neuromuscular blockade.
• The motor response is graded from 0 to 4 that indirectly indicated the level of
consciousness, which is a graded response rather than an all or none binary
phenomenon
• LEVEL 0- No response or spontaneous movement
• LEVEL 1- Random spontaneous movement not associated with any stimulus,
where the movement does not localise the stimulus
• LEVEL 2- Movement in response to tactile stimulus, which includes a painful
stimulus; 2a- Non Localising; 2b- localising
• LEVEL 3- Movement in response to verbal commands
25. • LEVEL 4- Movement in response choice questions or conversations
• LEVEL 5- Spontaneous purposeful movement initiated by the patient with the
desire to communicate
• Level 4 & 5 indicate that the patient is de
fi
nitely fully conscious and aware and
requires immediate deepening of Anesthesia.
• Level 0- pt is unconscious
• The current guideline of NAP5 is to include isolated forearm technique in the
anaesthesia academic curriculum and as a method to detect awareness in all
patients at high risk of intraoperative awareness.
26. End Tidal Anesthetic Agent Concentration
• The use of gas analyzers to detect and display end tidal anesthetic agent
concentration is a cheap and reliable method to ensure adequate
administration of anesthetic agents.
• Amnesia is produced with sub anesthetic doses of volatile agents, at 0.3-0.5
MAC, while unconsciousness occurs with 0.8-1MAC.
• LIMITATIONS: Factors that increase alveolar dead space, such as
hypotension, emphysema and use of bronchodilators will lead the end tidal
value to lean towards the inhaled value and hence does not re
fl
ect e
ff
ect site
concentration.
• Overdosing and lack of titration of the anaesthetic agent to the surgical
stimulus.
27. Processed EEG monitors
• EEG monitors use rapid mathematical analysis of the frontal EEG to generate
a dimensionless number that can in turn be used to titration anesthetic
agents.
• Anaesthetic agents produce a biphasic e
ff
ect on the EEG.
• With Light Anesthesia, there is EEG desynchronisation with increased
frequency.
• With increasing anaesthetic depth, there is progressive desynchronisation,
decrease in frequency and an increase in amplitude, eventually leading to
burst suppression and then to silence.
• The topographic distribution of EEG also changes with induction of
Anesthesia, occipital to frontal dominance.
28. • Processed EEG monitors process the
EEG by time domain analysis, frequency
domain analysis and phase analysis.
• The BIS (Bispectral index) monitor is
most commonly used.
• BIS employs a proprietary algorithm to
convert the single channel of frontal
EEG into an index of hypnotic level by
generating a dimensionless number.
BIS VALUE CORRELATION
>93
Awake,
Intact memory
Premedicated potent
75-80 <10% event recall
65-85 Sedation
40-65 GA Maintainence
<40
Deep Sedation
29. • Limitations to BIS: BIS values are a
ff
ected by cerebral hypo perfusion,
cerebral ischemia and gas embolism.
• BIS is unreliable with use of nitrous oxide, ketamine, xenon and opioids, as
they do not produce the same changes in processed EEG metrics as
GABAergic agents.
• Beta blocker therapy, dementia, stroke and encephalopathy can a
ff
ect brain
monitoring indices.
• Others monitors include: ENTROPY, Narcotrend, patient state analyser,
SNAP INDEX, CEREBRAL state monitor, EEG and index of consciousness
30. Evoked responses as monitors of depth of anesthesia
• Auditory evoked potentials are a
ff
ected by anesthetic agents and are used to
monitor depth of Anesthesia.
• It is recorded at primary auditory cortex in response to auditory canal stimulation
by audible clicks
• The waveform consists of 15 waves which are divided into 3 parts, based on origin
sites in the brain; brainstem auditory evoked potential, middle latency auditory
evoked potential (early cortical AEP) and late latency auditory evoke potential.
31. • The middle latency auditory evoked potentials have been shown to be
signi
fi
cantly a
ff
ected by anesthetic, hypnotic drugs in a graded, reversible and
nonspeci
fi
c manner.
• Anesthetics decrease the amplitude and increase the latency of the pa and
Nb waves.
• The AEP index is calculated by a mathematical analysis of the AEP waveform
and is used as an index of Anesthetic depth.
• It is scaled from 0-100 and a value <25 indicates unconsciousness
32. Guidelines for the use of depth of Anesthesia monitors
• The National Institute for Health and Care excellence (NICE) Guidance 2012
recommends the use of depth of Anesthesia monitoring, especially BIS in situations
with high risk of intraoperative awareness.
• BIS is also a useful tool to avoid awareness when the technique of TIVA is
practised.
• BIS, E-ENTROPY and narcotrend are considered equivalent according to the NICE
guidance.
33. Brain function monitors recommended include:
• Spontaneous electrical activity based monitor namely BIS,
• Cerebral state monitoring,
• Entropy,
• Narcotrend,
• Patient state analyser,
• Snap index
• Evoked electrical activity based monitor- namely AEP monitor/2.
34. Detection of awareness
Awareness is only detected postoperatively, either by spontaneous self reporting by
patients or by direct questioning.
The gold standard for the detection of intraoperative awareness has been the
MODIFIED BRICE QUESTIONNAIRE. The questions included are
• What was the last thing you remember before Anesthesia?
• What is the
fi
rst thing you remember after waking up?
• Do you remember anything between going under Anesthesia and waking up?
• Did you dream during your procedure?
• What was the worst thing about your operation?
35. • Incidence of intraoperative awareness can be identi
fi
ed by using the
questionnaire in a prospective manner immediately after surgery, at 24-72hrs
after surgery and once again within
fi
rst 30 days.
• Repetitive questioning is likely to increase the accuracy of detection.
36. MICHIGAN AWARENESS CLASSIFICATION INSTRUMENT is another tool to
assess awareness and is also recommended by the American society of
Anaesthesiologists Anaesthesia Awareness Registry.
• Class 0- No awareness
• Class 1- Isolated auditory perceptions
• Class 2- Tactile Perceptions (surgical Manipulation, Endotracheal tube)
• Class 3- Pain
• Class 4- Paralysis (feeling that one cannot move, speak or breathe)
• Class 5- Paralysis and Pain.
• An additional D for distress is included for patients report of fear, anxiety,
su
ff
ocation, sense of doom, sense of impending death, etc.
37. Consequences of Intraoperative Awareness
• Severe psychological sequelae
• Post traumatic Stress disorder (PTSD) is a debilitating consequence of awareness
occurring in 0.03- 0.05% of patients.
• Classical Features include:
Re-experience,
Avoidance and
Physiological hyperarousal which can take the form of fear,
panic, nightmares, inability to sleep or concentrate, helplessness, anxiety, tendency
to avoid hospitals and post traumatic stress disorder.
Impairs quality of life.
38. • The risk factors include
Severe trauma,
Multiple surgeries,
Women,
Middle aged individuals,
Depression or anxiety disorders.
• When symptoms persist for more than 3 months, it is referred to as chronic
PTSD.
• Intraoperative Awareness also is associated with medicolegal consequences
for the Anesthesiologist.
40. Management of Intraoperative Awareness
• First step-intently listen to the patients experience, acknowledge and document
in the case record.
• Reassurance and explained about possibilities of bad memories, dreams and
fl
ashbacks in the near future.
• Psychologist Referral.
• Therapy for post traumatic stress disorder includes:
Cognitive behavioural therapy,
Eye movement desensitisation reprocessing (EMDR) and
Selective serotonin reuptake inhibitors.
41. • Awareness support pathway- three pronged consisting of meeting, analysis
and support.
• Meeting includes:
Face to face meeting with patient,
Carefully listening to patients story and
Accepting the story as their genuine experience,
Expressing regret for the event along with recommendation to consult
the clinical psychologist
42. • Analysis includes:
Probing into cause using NAP5 process,
Scrutinising details of patients story, and correlating it with monitoring data
and sta
ff
reports and a separate analysis by an independent observer.
• Support includes:
Checking for
fl
ashbacks,
Nightmares,
New anxiety states and
Depression which are four CARDINAL SIGNS OF IMPACT OF
INTRAOPERATIVE AWARENESS.
• The presence of these signs should be followed up for a period of 2 weeks and the
patient should be referred to a psychiatric service, if symptoms persist beyond 2 weeks.
43. KEY-POINTS
✓Explicit & Implicit Awareness.
✓Cause of Awareness.
✓GUEDELS CLINICAL SIGNS- sweating, lacrimation, tachycardia,
hypertension, movement.
✓Monitoring to prevent intraoperative awareness.
✓Detection of awareness- Modi
fi
ed Brice Questionnaire.
. Michigan Awareness Classi
fi
cation Instrument
✓Post traumatic stress disorder (PTSD)
44. Conclusion
• Although, an uncommon complication, Intraoperative Awareness is associated
with signi
fi
cant debilitating, psychological consequences for the patient,
necessitating adoption of all preventive measures.
• Further research is warranted to identify the ideal monitor to detect this state
intraoperatively itself.
45. References
• Accidental Awareness during general Anesthesia - A Narrative review by S. R.
Tasbihgou, M. F. Vogels, A. R. Absalom - December 2017
• Association of ethnicity with minimum alveolar concentration of sevo
fl
urane.-
Ezri T et al Anaesthesiology. 2007; 107: 9-14
• Yearbook of Anaesthesiology-5
46. Anaesthesia is quite remarkable,
it’s either lost time or A Painful
return to reality
.
Thank you.
