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Intraoperative awareness
This document provides information about general anesthesia and intraoperative awareness. It discusses what general anesthesia is, how its depth is determined, and the different stages of awareness and memory formation. It also covers risk factors for awareness, its incidence and impact on patients. Monitoring techniques like BIS, entropy and EEG patterns are described. Finally, it discusses approaches to preventing and managing cases of intraoperative awareness.
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Intraoperative awareness
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- 2. • Privation ofsenses 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 cruxof 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— • Postoperativerecall 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 thepostoperative 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: Consciousawareness 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 ofthe 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 resultsfrom 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 malfunctionor 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 thepatient: • 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: • Temporaryeffects: • Sleep disturbances • Nightmares • Daytime anxiety • Sustained • Post traumatic stress disorder
- 26. • PTSD(post-traumatic stressdisorder) • 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 Advisoryfor Intraoperative Awareness and Brain Function Monitoring: • Pre op evaluation • Pre indution phase • Post operative period
- 33. • Clinical techniquesand conventional monitoring: • Assess intraoperative consciousness • checking for movement, • response to commands, • eyelash reflex, • pupillary responses, • respiratory pattern, • perspiration and tearing.
- 34. • Conventional monitoringsystems • ECG, • blood pressure, • heart rate, • end tidal anaesthetic analyzer • capnography
- 35. • I. SpontaneousEEG 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 describesthe 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 rangeis 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 classificationof 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 StateAnalyser • SNAP index • Cerebral State Monitor
- 41. • From amathematical 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 • Aloneuse • 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 andketamine • 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 patientseriously • 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’scomplaint seriously • Visit patient as soon as possible, along with a witness • Detailed history – modified Brice interview • Document patient’s exact memory
- 48. • Attempt toconfirm 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.