GA - Anaesthesia Flashcards
Why are there so many drugs for GA and sedation?
No single perfect agent
Combos of anaesthetics = used for synergistic and additive therapeutic effects
Risk of increasing adverse effects
Why sedation?
Reduce pt anxiety
Increase acceptability to prolonged/extensive procedures - still an effective time limit; <2hrs
Looking for anxiolysis, cooperation, street fitness (may need time to recover before leaving)
Why GA?
Extensive/prolonged procedures
Brief painful procedures - Extractions
Total lack of pt cooperation - intellectual impairment, children
Drugs available for sedation? Side effects/negatives?
Alcohol - disinhibition, nausea, slow recovery
Tetrahydrocannabinol (THC) - Nausea, illegal
Opiates - europhia, nausea, resp depression
Major tranquillisers - chlorpromazine - profound anxiety, hypotension
Minor tranquillisers - benzodiazepines - drowsiness, prolonged effect
Features of oral benzodiazepines?
Long interval, variable, small effect
Often enough for most pts
Features of intravenous benzodiazepines?
Competence in IV cannulation
Limited duration of action - repeat doses
Need for monitoring - SpO2 mandatory
Written record - pulse BP SpO2
Diazepam features?
Irritant
Skin necrosis
Diazemuls features?
Rapid onset
Brief duration of action
Psychoactive metabolites with long half life
Midazolam features?
Slower onset
Less predictable effect
Rapid metabolism
How do benzodiazepines and barbiturates work?
Bind to GABA receptor
Changes frequency of opening and closing of GABA channel
- Benzodiazepine increases frequency of opening of Cl channel
- Barbiturates increase duration of opening
Membrane hyperpolarised
CNS depression
How does propofol work in sedation?
Work at least partly with GABA receptor
Short acting
Fast recovery
Can be used in sub-anaesthetic doses
Negatives of propofol as sedation?
No analgesia
Continuous infusion - secure IV access
Expensive delivery system
What are the differences between sleep and unconsciousness?
Unrousability
Loss of protective reflexes
= Potential for - aspiration, obstruction, nerve damage due to prolonged pressure
What is the process of GA?
Induction
- Rapid pleasant production of consciousness - Iv or gaseous/volatile
Secure airway
- Optimum head position, LMA, ETT
- Endotracheal tube to keep airway open
Maintenance
- Gaseous/volatile or IV
Analgesia
Muscle relaxant
Emergence
- Reversal of muscle relaxation
What drugs are used for the induction of GA?
IV:
- Propofol
- Thiopentone
- Ketamine
- Etomidate
Volatile: sevoflurane
Characteristics of propofol?
Rapid pleasant onset
Non cumulative
Hypotension (vasodilation)
Painful on injection
Characteristics of thiopentone?
Rapid onset Offset due to redistribution Slow metabolism Cumulative Hypotension (myocardial depression) Odd complications - Arterial spasm - Porphyria - Anaphylaxis rare but serious
Characteristics of ketamine?
Rapid onset Hypertension Powerful analgesic Non cumulative Muscle rigidity Unpleasant hallucinations
Characteristics of etomidate?
CV stability Noncumulative Odd (major) complications - Inhibition of steroid synthesis - Death due to induced addison's
How to maintain the airway?
Optimum head position - neck flexed, head extended
Laryngeal mask - does not prevent aspiration
Tracheal intubation - eliminates danger of aspiration BUT
- Use muscle relaxant to overcome laryngeal reflexes = these have side effects
- Suxamethonium
- Atracurium
- Cisatracurium
- Rocuronium
- Pancuronium
Features of suxamethonium?
Rapid onset and offset Depolarising Muscle pain Occasional prolonged paralysis Malignant hyperthermia
Atracurium features?
Reliable spontaneous hydrolysis
Histamine release
Hypotension
Cisatracurium features?
Not so much histamine release
Slow onset
Rocuronium features?
Long duration
Specific reversal agent
Histamine release
Pancuronium features?
Medium duration
Tachycardia
Renally excreted
Unchanged
How to maintain gaseous/volatile and intravenous anaesthesia?
Gaseous/volatile
- Nitrous oxide
- Isoflurane, sevoflurane, desflurane
Intravenous
- Propofol
Issues with nitrous oxide?
Dysphoria
Association with miscarriage
Issues with seveflurane?
Acceptable for volatile induction
Issues with desflurane?
Rapid onset/offset
Issues with propofol?
IV agent - access required
Microprocessor controlled infusion pump - expensive
Can be used for sedation
Why do a preop assessment?
Perfect prep prevents poor performance
Max pt safety - optimise pts condition, postpone if necessary
Toxic drugs with significant side effects
- All have lifethreatening effects at therapeutic doses
- CV depressant
- Resp depressant
Complications encountered during an operation?
Pt
Anaesthetic
Surgeon
What pt problems can occur during an op?
Pre-existing disease
Cardiac
- Aortic stenosis
- Coronary artery disease
Resp
- COPD
- Asthma
Diabetes
- Common
- Associated with renal, CV pathology
What history to take for anaesthesia?
Proposed procedure
PMH
- Drugs/allergies
- Surgical: previous GA, problems (pt/fam)
- Medical - cardiac, resp, GI (aspiration risk - Hiatus hernia), renal (impairs drug handling), diabetes
Airway assessment
What are the complications of anaesthesia? How to reduce them?
Awareness/OD - agent monitoring: brain func monitors; neuromuscular blockage
Anaphylaxis
Hypoxia - SpO2
Resp depression - CO2 monitoring
Aspiration (preop starvation, intubation)
Peripheral nerve damage (careful positioning)
Problems that can occur in surgery? How to treat this?
Haemorrhage - Signs:
- Falling BP
- Rising HR
- Suction container full of blood
- Loads of wet swabs
Tx:
- Permissive loss of haemoglobin (to Hb=80)
Restore circulation with crystalloid
Chloride is the current unfashionable anion
