4.2 Awareness Flashcards
a) Define the types of unintentional awareness that may occur during general anaesthesia. (20%)
Explicit awareness:
» May have spontaneous recall,
or recall prompted by questioning.
> > May occur with or without pain.
> > May result in psychological harm,
sleep disturbance, nightmares, anxiety
or even post-traumatic stress disorder (PTSD).
Implicit awareness:
» No conscious recall but may affect behaviour and performance in the future.
b) What factors may increase the likelihood of intraoperative awareness? (55%)
- Surgical factors
Emergency surgery
casesarean section
cardiothoracic surgery
- Anaesthetic factors
Use of muscle relaxant
Use of TIVA
Junior / inexperienced anathetist - Patient factors
Younger patients
Previous awareness/ fh awareness
c) What monitoring techniques can be employed to reduce the risk of awareness during general
anaesthesia? (25%)
Clinical monitoring:
» Presence of the anaesthetist throughout the case.
> > Eye position.
> > Pupillary dilatation and reactivity to light.
> > Sweating.
> > Lacrimation.
> > Tachypnoea.
> > Movement.
> > Retching on tube/LMA.
General monitoring:
» Full equipment checks and
ongoing monitoring during anaesthesia
(pumps, anaesthetic machine, vaporisers).
> > Heart rate, respiratory rate and tidal volume (if not paralysed), blood pressure.
> > End tidal anaesthetic gas (ETAG) monitoring.
> > TIVA pump effect-site or plasma-site concentration.
> > Train-of-four monitoring to ensure that neuromuscular blockade is reversible before ending anaesthesia.
Specific depth of anaesthesia monitoring:
» Processed EEG monitors convert the frontal signal into a dimensionless number, 1–100 (100 = fully awake).
BIS (target 40–60 for absence of postoperative recall),
M-Entropy and Narcotrend.
> > Other specific monitors use auditory evoked potentials as a measure of depth of anaesthesia.
Various incidence of AAGA
Incidence of AAGA: approximately 1/19,000.
Incidence of AAGA if NMBD used: 1/8,000.
Incidence of AAGA if no NMBD used: 1/36,000.
Incidence of AAGA in obstetrics: 1/670.
Incidence of AAGA in cardiothoracics: 1/8,600.
Exectuive summary of increased awareness
The following is lifted straight from the executive summary of the NAP5 report:
Drug factors: NMBD, thiopentone, TIVA.
Patient factors:
female gender, young adults, obesity, previous AAGA,
possibly difficult airway.
Surgical factors:
obstetric, cardiac, thoracic, neurosurgical.
Organisational:
emergencies, junior anaesthetists, out of hours
operating.
Awareness drug factors AAGA
Drug factors:
>> TIVA results in a full range of human and equipment error issues: tissued cannula, pump failure, failure to switch the pump on, pump wrongly programmed.
>> Neuromuscular blocking drug (NMBD): 97% of the episodes of awareness reported to NAP5 included use of NMBD. Failure to reverse, failure to monitor depth of block, human error causing syringe switches, failure to label syringes properly, mixed up ampoules.
> > Increased incidence of awareness associated with thiopentone use.
> > RSI.
Patient factors: AAGA
> > Female gender.
> > Young adults.
> > Difficult airway
> > Obesity:
difficulties with drug dosing and
increased risk of difficult airway.
> > Previous awareness:
possible genetic component.
> > Sick, cardiovascularly compromised patients in whom lower doses of anaesthetic agents were given.
Surgical factors AAGA
Surgical factors: >> Obstetrics, especially emergency LSCS: anxiety, no pre-medication, physiological changes of pregnancy mask awareness, NMBD used, thiopentone commonly used, may underdose due to failure to take account of body weight, rapid sequence induction, emergency (increased risk of error), junior anaesthetist, out of hours, short period between intubation and commencement of surgery, not giving adequate time for drugs to work. Failed regional is a risk factor according to the reports submitted.
>> Cardiac: not many cases in NAP5, but previously high level of awareness reported at start of cardiopulmonary bypass. May also relate to cardiac anaesthesia technique (low hypnotic dose, high opioid dose).
May be less likely to report as patients are warned of waking in cardiac ICU with tube still in situ, and older patients may possibly be more tolerant.
> > Thoracics:
NMBD usually used.
Switching tubes (single lumen to double
lumen) and failing to maintain anaesthesia by volatile technique.
Rigid bronchoscopy – episodes of intense stimulation, intermittent interruption to anaesthesia administration if volatile used, NMBD needed.
> > Neurosurgical.
Organisational:
> > Out of hours.
Junior anaesthetist.
Emergency surgery.
c) What are the possible
consequences to the patient of an
episode of AAGA? (4 marks)
> > There may be immediate, delayed or no recall.
> > Experiences may be auditory or tactile;
may include pain and awareness
of paralysis.
> > Response very varied:
neutral feelings about experience to extreme
distress at the time and
also subsequently in the form of post-traumatic stress disorder with flashbacks, anxiety and depression , with impact on personal, social and work life.
> > May cause avoidance of all medical settings
or specifically anaesthesia and
loss of trust of healthcare professionals.
> > No recall may still cause long-term
problems with e.g.
unexplained anxiety due to implicit memory
> > Patients tend to benefit from explanation and cognitive behavioural therapy.
