Awareness in Anesthesia

Lean Chung Yee Advisor: Dr Cheah Saw Kian

General Anesthesia

A drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation.

General Anesthesia

Main components:

Hypnosis ( unconsciousness) Analgesia (decreasing pain) Amnesia (preventing recall) Muscle relaxation (preventing movement) Physiologic support (maintaining respiratory and cardiovascular function, fluid management, electrolyte control, and thermoregulation )

The Sedation Continuum

Anxiolysis Procedural Procedural Sedation

Deep Sedation

General Anesthesia

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Stages of Anaesthesia

• Stage I : Stage of analgesia or disorientation: Beginning of induction of general anesthesia to LOC.

• Stage II : Stage of excitement or delirium : From LOC to onset of automatic breathing. Eyelash reflex dissapears but other reflexes remain intact( cough, vomit, struggling)

• Stage III (Stage of Surgical Anesthesia) : 4planes - Plane 1 : Onset of automatic respiration →

cessation of eyeball movement Eyelid reflex lost, swallowing reflex disappears, marked eyeball movement may occur.

- Plane 2 : cessation of eye movement → beginning of intercostal muscles paralysis

laryngeal reflex lost, corneal reflex disappears, tear secretion ↑, resp is automatic & regular, movement & deep breathing a a response to skin stimulation disappear.

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- Plane 3 : Beginning to completion of intercostal musc paralysispupils dilated, light reflexes abolished desired plane for surgery when musc paralysis were not used.

- Plane 4 : Complete intercostal paralysis → diaphragmatic paralysis

Stage IV : Stoppage of respiration till death. Medullary paralysis with resp arrest and vasomotor collapse.Pupils widely dilated, musc are paralysed.

Incidence of Awareness

0.1-0.2 % of all adult patients undergoing GA

0.8-1.2% children

20 000 to 40 000 of the 20 million GA patients

33% of those patients develop serious psychological sequelae

Definitions

• Consciousness

• Memory and Awareness

Consciousness

A state in which a patient is able to process information from surroundings.

Assessed by purposeful responses:

• Following voice commands

• Response to noxious stimuli

Memory

Classifications:

Explicit (or conscious) memory refers to conscious recollection of previous experiences, equivalent to “remembering”.Implicit memory refers to the changes in performance or behavior that are produced by previous experiencewithout any conscious recollection of those experiences.

AWARENESS used to describe explicit memory during Anaesthesia.

Perceptions of AwarenessMost common

• Sounds and conversation• Sensation of paralysis• Anxiety and panic• Helplessness and powerlessness• Pain

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

Signs of Awareness

Michigan Awareness Classification

• Class I – isolated auditory perceptions• Class 2- tactile perceptions (perception of surgical

manipulation or endotracheal tube)• Class 3- pain• Class 4 –paralysis• Class 5- paralysis and pain• D- associated with distress (report of fear, anxiety,

suffocation, sense of doom, or sense of impending death)

Anesth Analg 2010;110: 813-5

Psychological Sequelae

• Sleep disturbances

• Nightmares

• Anxiety and panic attacks

• Flashbacks

• Avoidance of medical care

• Post-traumatic stress disorder ( PTSD)

High Risk Patient Characteristics

Substance use or abuse Limited hemodynamic reserve ASA IV – V Previous episode of intraoperative awareness Chronic pain patients Younger age Tobacco smoking Anxiety preoperation

High Risk Surgeries

Caesarian section (0.4%)

Major trauma/Emergency (11-43%)

Cardiac surgery (1.1-1.5%)

High Risk Anesthetic Techniques

Reduced anesthetic doses in presence of paralysis

Total intravenous anesthesia

Nitrous oxide-opioid anesthesia

Rapid sequence induction

Detection of Awareness

• Clinical signs• IFT• Lower oesophageal contractility• Frontalis EMG• Respiratory sinus arrhythmia• MAC value• EEG

– Raw EEG– Processed EEG

• BiS• AEP

PRST SCORE

• poor indicator of depth of anaesthesia.• haemodynamic responsiveness to noxious

stimuli does not necessarily signify awareness, nor does lack of haemodynamic changes guarantee unconsciousness.

Isolated Forearm Technique (IFT)

• First used by Tunstall• Isolate forearm with BP cuff before giving NMB• Patients asked to squeeze hand for ‘Yes’• Limitations: non-specific subtle movement; surgery

on the hand; heard command, couldn’t move.• Even when patients responded, rarely did they have

any memory of this after the operation

EEG

BiS (Bispectral Index Monitoring)

• Direct measure of the effects of anaesthetics on the brain

• BIS monitoring allows anaesthesia providers to administer the appropriate amount of drug that each patient needs

Definition : BIS uses a proprietary algorithm to convert a single channel of frontal EEG into an index of hypnotic level, ranging from 100 – 0 (isoelectric EEG)

The Bispectral IndexTM (BiS) Aspect Medical Systems

Bis Number

Relatives contributors to BIS number :- Time domain analysis ( β wave activity; burst

suppression)- Frequency domain analysis ( as ↑depth

anaesthesia – move from low freq high amp – high frequency low amp), spectral edge freq.

- Bispectral analysis – look at the phase relationships between different frequencies

Minimum Alveolar Concentration

For assurance of lack of awareness..

• Opioid + N2O + Volatile agent >0.6• Volatile agent only >0.8

Auditory Evoked Potential

Mid-latency AEP

ANY ideal system/monitor to measure adequate depth of anesthesia ???

Preventing Awareness

Preventing Awareness

Modified Brice Interview

1. What is the last thing you remember before surgery?

2. What is the first thing you remember after surgery?

3. Do you remember anything happening during surgery?

4. Did you have any dreams during surgery?

5. What is the worst thing about your surgery?

Dealing with patients who have a history of Awareness during Anaesthesia

• Take patient seriously• Document patient’s exact memory• Attempt to confirm validity of account• Investigate previous anaesthetic technique & circumstances• Comorbidity / medications• Patient anaesthetic records / theatre circumstances• Try to determine cause• Reassure• Postop visit• Keep a copy of records• Offer psychological support• Intraop ET agent monitoring / BiS• Sedative premed

Thank you !

www.asahq.org/~/media/IntraoperativeAwareness.ashx

1) Pre-op: Identification of risk factors- pt, surgical, anaesthesia plan

2) Preinduction: Checklist protocol, verifying function of equipments

3) Intraoperative monitoring: conventional monitoring, clinical observations, brain function monitoring

4) Postoperatively: Interview patient, counselling and report

Take Home Message