Awareness During Anesthesia DR.Mohammad Hajeyah Kuwait Board of Anesthesia R.3

IS THE PATIENT AWAKE RIGHTNOW IS THE PATIENT AWAKE RIGHTNOW ?

HOW MANY OF YOU THINK THAT ITS IMPORTANT TO MONITOR AWARENESS HOW MANY OF YOU THINK THAT ITS IMPORTANT TO MONITOR AWARENESS ?

HOW MANY OF YOU DO MONITOR AWARENESS ?

OUTLINE  Definition  Incidence  Why does it happen  Types and consequences  Modalities of monitoring  How do we prevent and manage it  Take home message

DEFINITION  The situation that occurs when a patient under general anesthesia becomes aware of some or all events during surgery or a procedure, and has direct recall of those events. patientanesthesiasurgerypatientanesthesiasurgery  Because of the routine use of neuromuscular blocking agents during general anesthesia, the patient is often unable to communicate with the surgical team if this occurs. neuromuscular

 Explicit memory may be recalled spontaneously, or may be provoked by postoperative events or questioning.  Implicit memory may not be consciously recalled, but may affect behavior or performance at a later time

INCIDINCE  Awareness during anesthesia is a very disturbing event if encountered.  Memories of the event are either remembered spontaneously or provoked by post-op events.  Recall of such events specially if awareness of paralysis and painful stimuli is the issue then ones life maybe changed permanently.

 Back in the 1970`s where nitrous oxide was used in 60-70%,incidince was 7% ( 1 in 14) pts.  In recent times awareness with recall of painful stimuli is at 0.03% (1 in 3000 )pts.  And in cases where no painful stimuli was encountered its % (1 in ) pts. Sigalovsky N. Awareness under General Anesthesia. AANA Journal/October 2003/Vol.71,No. 5,p: Sigalovsky N. Awareness under General Anesthesia. AANA Journal/October 2003/Vol.71,No. 5,p:

 The closed claim analysis of the ASA. States the incidence to be more common in women (77%).  In adults younger than 60 yrs. (89%).  In pediatrics its (0.5-1%)  In ASA physical status 1 and 2 (68%) Sigalovsky N. Awareness under General Anesthesia. AANA Journal/October 2003/Vol.71,No. 5,p: Sigalovsky N. Awareness under General Anesthesia. AANA Journal/October 2003/Vol.71,No. 5,p:

 A study in Finland done on 2,600 pts. Showed (0.4%) who experienced awareness and (0.3%) possibly experience awareness.  A Swedish study found the incidence to be (0.18%) when MR. was used and (0.10%) when no MR. was used.  A study done in the university of Iowa showed the incidence to be much higher in cases where cardiopulmonary and vascular functions were compromised. ( %) in cardiac surgery and (11-43%) in major trauma. Sigalovsky N. Awareness under General Anesthesia. AANA Journal/October 2003/Vol.71,No. 5,p:

WHY DOES IT HAPPEN WHY DOES IT HAPPEN ?

 Resistance to anesthetic agents: 1. Pyrexia/Septic 2. Hyperthyroidism 3. Obesity 4. Anxiety 5. Young age 6. Heavy alcohol and tobacco use. 7. Recreational drug usage. 8. Factors reducing the MAC. Why does it happen

Consequences  No one can tell you how bad it is but the patient himself.  Impact can be as a medico legal law sue and also as psychiatric implications.  Symptoms would range from simple insomnia and anxiety to as severe as PTSD. development.  Those symptoms are related to being helpless, feeling pain,fear,and inability to communicate nor express themselves.

Consequences

Signs of AWARENESS  Tachycardia  Hypertension  Sweating  Tear formation  Pupillary dilatation and reaction to light  Movement and grimacing

How do we monitor Awareness  Bispectral index  Electroencephalogram  Auditory Evoked Response  Ocular Microtremor  Patients State Analyzer Index

Bispectral Index

BIS  Measures patients response to sedative/hypnotics administration.  Non-invasive.  Converts the generated EEG. Data into a number.  Ideal numbers under GA. Are between

BIS  One study stated that with BIS there was a reduction of Propofol use by 32.6% with subsequent less mean time till eye opening.  According to Glass and Johansson; that BIS uses led to a more precise dosing of medication and less time till recovery leading to high turnover of patients.

BIS  Kurehara and Coworkers found claims of awareness in spite a value of 40 intra-op.  This study concluded that BIS maybe effective in measuring hypnotic state yet awareness still can occur even with a low BIS value.

BIS  A recent study concluded that values between were insufficient to prevent awareness during intubation with propofol or alfentanil use.  Barr and colleagues; studied BIS with Nitrous Oxide use. This study concluded no changes in BIS values with different conc. Of Nitrous.

EEG.

EEG.  Analyzing brain waveforms changes under GA.  Both computer-processed and un-processed EEG reading are used to analyze level of awareness.  Problems include: 1. Cost 2. Complexity of readings 3. Complexity of equipments 4. Difficult to interpret.

Auditory Evoked Potentials

AEP  Fluctuations of the (AER) latency as a sign of awareness.  It has been reported that a positive correlation exists between AER and awareness changes.  Problems: 1. Good indicator with inhalational agents rather than narcotics. 2. Complexity of equipment and analysis.

Ocular Micro tremor

OMT  A promising new device in awareness monitoring.  It measures high frequency tremors of extra-ocular muscles generated by higher brain signals from the brain stem.  Those signals are in direct relation with anesthesia depth.  Still under study and not fully under practical use.

Patient State Analyzer Index  It’s a quantitative analysis of the EEG.  Simply uses more extensive sensors to measure EEG.  Few completed studies regarding this method.

How To Manage Intra-operative:  If pt is being exposed to a noxious stimuli that maybe recalled later on then anesthesia should be deepened.  If hypotension is present then anesthesia should be deepened while supporting hemodynamics.  Benzodiazepines (Mediazolam 5mg) may reduce recall post-op. via retrograde amnesic effect. Hardman J.G., Aitkenhead A.R. Awareness during Anesthesia. Advance Access Publication, October 2005

How To Manage Post-operative:  Pt. should be interviewed post-op if claims were made of intra-op awareness.  Exact timing and experience should be identified and distinguished from dreaming.  Its important to make it clear that no confusion was made between awareness and memories at induction or emergence.  Always to take every claim seriously and to show sympathy with the patient.  If pt. started showing signs of anxiety,depression and PTSD. Then psychiatric referral shouldn’t be delayed.

Avoiding Awareness  BZD. Administered at induction reduces the incidence of awareness specially at high risk period during induction.  Adequate anesthetic drugs should be administered.  The risk of awareness is greatly reduced at a MAC  MAC. Adjustment according to patient age group reduces the risk greatly. Hardman J.G., Aitkenhead A.R. Awareness during Anesthesia. Advance Access Publication, October 2005

Avoiding Awareness  The use of NMBD. Inc. the risk of awareness.  Complete paralysis should be given only if needed and doses should e measured.  In cases that light anesthesia is suspected then monitoring is justified using BIS. and/or other modalities.  In spite of all that awareness still occurs for unknown reasons. Hardman J.G., Aitkenhead A.R. Awareness during Anesthesia. Advance Access Publication, October 2005

Take Home Message  Intra-op awareness is associated with devastating psychiatric sequelae that leads to medico-legal consequences on the anesthetist.  Awareness is twice likely if NMBD. Are used.  Inadequate anesthetic dosing is the most common cause of awareness.  Most of the time signs of awareness are often masked by drugs or patients own concomitant illnesses.  Monitoring, specialy in high risk cases is justified and reduces the risk of awareness greatly.

Thank You