Intraoperative awareness

1. Dr Himanshu Jangid

2. • Privation of senses or Lack of sensory perception
• What is General Anaesthesia ?
• State of unconsciousness or the lack of thought
processing.

3. • Hypnosis ( unconsciousness)
• Analgesia (decreasing pain)
• Amnesia (preventing recall)
• Impairment of skeletal muscle (preventing movement)
• Physiologic support (maintaining respiratory and
• cardiovascular function, fluid management, electrolyte
• control, and thermoregulation )

5. • The crux of the difficulty in defining “anesthetic depth” is
that unconsciousness cannot be measured directly.
• What can be measured is response to stimulation.

6. • The “depth” of anesthesia is determined by
• the stimulus applied,
• the response measured,
• the drug concentration at the site of action that blunts
responsiveness.eg.
• MAC AWAKE
• MAC
• MAC BAR

10. • Awareness—
• Postoperative recall of events occurring during general
anesthesia
• Amnesic wakefulness—
• Responsiveness during general anesthesia without
postoperative recall
• Dreaming—
• Any experience (excluding awareness) that patients are able
to recall postoperatively that they think occurred during
general anesthesia and that they believe is dreaming

11. • Explicit memory—
• Conscious recollection of previous experiences
(“awareness” is evidence of explicit memory)
• Implicit memory—
• Changes in performance or behavior that are produced
by previous experiences but without any conscious
recollection of those experiences (“unconscious memory
formation” during general anesthesia)

12. • is the postoperative recall of sensory perception during
general anaesthesia.
• Rare but serious
• May occur despite apparently sound anaesthetic
management
• Usually not associated with pain.

13. Stage 1: Conscious awareness with explicit memory
Stage 2: Conscious awareness without explicit memory
Stage 3: Subconscious awareness with implicit memory
Stage 4: No awareness

14. • “Definite” awareness
• Recall conversations or music that they hear in the OR during the
period of awareness
• “Probable” awareness
• Hearing voices or feeling discomfort asso with intubation or
surgery
• “Near miss” awareness
• More vague and dream-like

15. • In 1845, Horace Wells
• N2O anesthesia
• Pt moved and cried out
• No recall of his operation
• In 1846, W.T.G. Morton
• Ether anesthesia
• Surgeons considered it a success
• Pt. had been aware, no pain.
• From a pt’s perspective, Well’s anesthetic may
be considered more successful than Morton’s.

16. • Estimation of the incidence of awareness
• Multiple post anesthetic interviews, usually using a modified Brice
interview
The Modified Brice Interview
• What is the last thing you remember before surgery?
• What is the first thing you remember after surgery?
• Do you remember anything happening during surgery?
• Did you have any dreams during surgery?
• What was the worst thing about your surgery?

17. • Over all
• 1 or 2 cases out of every 1000 patients (0.2%)
• Obstetric 0.4%
• Cardiac cases 1.1-1.5%
• In children 0.8-1.2%.

18. • Awareness results from an imbalance between
anesthetic requirement and anesthetic delivery
• Normal Requirement—Low Delivery
• Low Requirement—Very Low Delivery
• High Requirement—Normal Delivery

19. • Patient related:
• Age
• Sex
• Genetics
• ASA physical status
• Drug resistance or tolerance(substance abuse and chr.
Pain treated with high dose opoids)
• Concurrent medications
• Past history of awareness
• Difficult intubation

20. • Surgery related
• High Risk Surgeries
• Caesarian section (0.4%)
• Major trauma/Emergency (11-43%)
• Cardiac surgery (1.1-1.5%)

21. • Anaesthesia related
• Reduced anesthetic doses in presence of paralysis
• Rapid sequence induction
• total intravenous anaesthesia.
• Nitrous Opioid anesthesia
• Pharmacological masking of signs of inadequate depth of
anaesthesia-
• Use of muscle relaxants

22. • Machine malfunction or misuse resulting in an
inadequate delivery of anaesthesia:
• Drug administration errors
• Mis-labeled drug syringes
• Empty vaporizers
• Leaky gas delivery circuits
• Dysfunctional or misused drug infusion pumps
• Intravenous lines that stopping running

23. • To the patient:
• Intraoperative:
• Most common
• • Sounds and conversation
• • Sensation of paralysis
• • Anxiety and panic
• • Helplessness and powerlessness
• • Pain

24. • Least common
• • Visual perceptions
• • Intubation or tube
• • Feelings operation without pain

25. • Postoperatively:
• Temporary effects:
• Sleep disturbances
• Nightmares
• Daytime anxiety
• Sustained
• Post traumatic stress disorder

26. • PTSD(post-traumatic stress disorder)
• Most harmful consequence
• Depression, anxiety attacks, sleep disorders,
flashbacks to the experience, and nightmares.
• Pt who have no explicit recall of intraop events, but
who develop symptoms suggestive of intra operative
awareness, such as recurrent dreams about being
buried alive.
• A pt’s understanding of their experiences can affect the
psychological impact of awareness.
• Pt may think their awareness is impossible
• Leading them to become confused or question their own sanity.

27. • Towards anaesthesiologist:
• Medicolegal implications
• 2% of total claims
• ASA closed claim database
• 1971 -2001 : 1% - 3% continue growing.
• Reported awards to pts for awareness with recall
• $1000 –$600, 000

28. • Practice Advisory for Intraoperative Awareness and
Brain Function Monitoring:
• Pre op evaluation
• Pre indution phase
• Post operative period

33. • Clinical techniques and conventional monitoring:
• Assess intraoperative consciousness
• checking for movement,
• response to commands,
• eyelash reflex,
• pupillary responses,
• respiratory pattern,
• perspiration and tearing.

34. • Conventional monitoring systems
• ECG,
• blood pressure,
• heart rate,
• end tidal anaesthetic analyzer
• capnography

35. • I. Spontaneous EEG activity monitors:
BIS:
• BIS converts a single channel of frontal EEG into an
index of hypnotic level
• Targeting a range of BIS values 4060 to prevent
awareness

37. • Entropy describes the irregularity, complexity or
unpredictability characteristics of a signal.
• A single sine wave represents a completely predictable
signal (entropy=0)
• A noise from a random number generator represents
• entropy =1
• SE is computed from the EEG in the 0.8- to 32-Hz
range
• RE is computed from facial EMG 0.8 to 47 Hz

38. • SE range is 0 (isoelectric EEG) to 91 (fully awake)
• RE range is 0 to 100.
• The anesthetic range is 40 to 60
• SE outside this range may require a change in hypnotic
dosing.
• whereas if the SE is in this range but the RE is more than
10 above the SE, more analgesic may be required.

39. • Visual classification of the EEG patterns associated with
various stages of sleep.
• The original electronic algorithm classified the frontal
EEG according to:
• A (awake),
• B (sedated),
• C (light anaesthesia),
• D (general anaesthesia),
• E(general anaesthesia with deep hypnosis),
• F (general anaesthesia with increasing burst
suppression).

40. • Patient State Analyser
• SNAP index
• Cerebral State Monitor

41. • From a mathematical analysis of the AEP waveform, the
device generates a AEP index (AAI) that provides a cor-
relate of anaesthetic concentration.
• This AEP index is scaled from 0-100 and the AAI
corresponding with a low probability of consciousness is
<25.

42. • Opioids
• Alone use
• Do not suppress awareness
• Large doses
• Unresponsive to pain
• Respond to loud noises and remain aware of their surroundings
• when added to N2O
• Do not alter the incidence of awareness
• Do not alter basal BIS measurements
• Opioids
• Reduce the amount of cortical arousal asso. with peripheral pain
• Reduce the possibility that surgical pain will cause pt to awaken.
• Psychological trauma asso. with awareness and pain is greater than that
of awarenes without pain

43. • Propofol, barbiturates, etomidate, and
halogenated volatile agents
• Modulate GABA R. activity
• Shift the cortical EEG to lower frequencies
• BIS and EEG based monitor
• Provide strong correlation with hypnosis for this group

44. • N2O and ketamine
• Do not modulate GABA R., but they do produce
hypnosis
• Unchanged or increased high frequency EEG signals
• High reported incidence of dreaming during anesthesia
• BIS and EEG monitors
• Do not accurately predict the depth of anesthesia
• New “ correlates of consciousness”
• Lead to development of more universally applicable monitors
for anesthetic depth.
• Potent analgesia- NMDA receptor inhibition in spinal
cord.
• Suppress cortical arousal during painful stimulation – reduce
the prabability of awareness

45. • N2O-volatile mixtures
• MAC for N2O and voaltile agent
• Additive
• Eg, mixture of 0.5 MAC N2O + 0.5 MAC volatile agent
• Supress movement in response to pain like 1 MAC volatile
• Hypnotic activities of N2O and volatile agent
• Sub-additive
• Eg, mixture of 0.5MAC awake N2O + 0.5 MAC awake volatile
agent
• Is not as hypnotic as 1 MAC awake volatile
• N2O
• Antagonizes the hypnosis induced by volatile agent, perhaps
via direct cortical arousal.

46. • Take patient seriously
• Investigate previous anaesthetic technique &
circumstances
• Comorbidity / medications
• Reassure
• Sedative pre med
• Intraop ET agent monitoring / BiS
• Postop visit
• Good Peri op records

47. • Take patient’s complaint seriously
• Visit patient as soon as possible, along with a witness
• Detailed history – modified Brice interview
• Document patient’s exact memory

48. • Attempt to confirm validity of account
• Patient anaesthetic records / theatre circumstances
• Try to determine cause
• Reassure / offer explanation / document
• Keep a copy of records
• Offer psychological support

49. Thank you!