anesthesia awarness

1. By
Abdelrahman Mahmoud Soliman

2.  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)

3.  Awareness—Postoperative recall of events
occurring during general anesthesia.
 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.

4.  Incidence of awareness ranges from 0.01- 2%
in different studies according to type of
surgery and anesthetics.
 1 in 100 in cardiac surgery
 1 in 20 in trauma surgery
 1 in 250 in emergency C-Section under GA
 Awareness is doubled with use of muscle
relaxant.

5.  PTSD.
 Anxiety.
 Fear of future surgery.
 Legal responsibilities.

6.  Awareness results from an imbalance
between anesthetic requirement and
anesthetic delivery
1. Normal Requirement—Low Delivery
 Errors in knowledge.
 Anesthetic machine failure.

7. 2. Low Requirement—Very Low Delivery
 Trauma patients.
 C- section under GA.
 Hypovolemic patients.

8. 3. High Requirement—Normal Delivery
 Normal variability in the population.
 Patients tolerant to sedative, hypnotic and
analgesic drugs.
 Alcohol use
 Hyperthyroidism and hyperthermia.

9. 1. Anesthesia training and continuing
education
 Physiology and pharmacology
 Equipment and clinical measurement.

10. 2- Preoperative Phase
 Identify patients at risk
 Conduct preoperative checklist-based
equipment check.
 Inform, consent, reassure as appropriate.

11. 3- Intraoperative phase
 scan equipment regularly during each case.
 Take care to avoid wrong drug
administration
 Administer adequate hypnotic drug
 Minimize use of muscle relaxant
 Respond rapidly to suspected inadequate
anesthesia
 Consider using an EEG-based monitor

12. 4- postoperative phase
 Conduct a postoperative interview.
 Provide counseling for aware patients.

13.  Use of benzodiazipines can decrease the
postoperative recall in case of unanticipated
awareness.
 Respond rapidly to signs of inadequate
anesthesia by deeping level of anesthesia.
 Benzodiazipines although have no retrograde
amnesic properties can decrease
postoperative recall.

14. 1. Clinical signs

15. 2- End tidal agent monitoring:
The minimum alveolar concentration (MAC): the
minimum concentration at ambient pressure
to prevent movement in 50% of non
premedicated subjects to standard painful
stimulus (skin incision).

16. Increase MAC:
Pyrexia, hyperthyroidism, obesity, young age,
tobacco, chronic alcohol, chronic sedative
use.
Decrease MAC
Pregnancy , hypotension, old age,
hypothyroidism, hypothermia, opioids,

17. 1. EEG:
Can be used as a measure of the depth of
anesthesia for several reasons:
 Represent cortical activity which affected by
anesthetics drugs, CMR and CBF, both are
affected by anesthetics drugs and surgical
stimulation.
 It fails to measure clinical depth of
anesthesia.

18.  Based on Fourier spectral analysis and
bispectral analysis
 Monitor provide number on a scale 0-100
 85-100: awake, light sedation.
 85-60: deep sedation, impairment of memory
processing, arousable on stimulation.
 40-60: surgical anesthesia, decrease
probability of postoperative recall

19.  0-40: burst suppression > cortical electrical
silence.
 It is recommended to be maintained 40- 55
 BIS decrease the incidence but don’t eliminate
awareness risk

20.  BIS limitation
 Interindividual variability in depth of
anesthesia for a given BIS value.
 Minimally affected by opioids, therefore may
not reflect balanced anesthetic regimen.
 Changes in consciousness from ketmine and
nitrous oxide are not faithfully represented.

21.  Based analysis of irregularities in EEG signals
which decreased as level of anesthesia
increase, incorporating Fourier analysis.
 EMG from facial muscles.
Two readings are displaced
1- State enotropy ( SE): 0-91 based on EEG
2- Rsponse enotropy ( RE): 0-100 based on
EMG

22.  RE is hypothesized to represent analgesic
component.
 Studies showed that the device produce
results comparable to those of BIS.
 Anesthetic range from 40-60.

23.  Other monitors
 Evoked potentials
 Patient state index
 narcoted