Anaesthesia Flashcards
What are the 3 types of anaesthesia?
- General (total loss of sensation)
- Regional (loss of sensation to a region or part of the body e.g. spinal anaesthesia or BP block)
- Local (topical, infiltration)
What is amnesia?
A lack of response and recall to noxious stimuli - unconsciousness
What is analgesia?
Pain relief
What is akinesis?
Immobilisation/paralysis
What is an induction agent?
Induce loss of consciousness in one/two arm-brain circulation time (intravenous)
10-20 seconds
duration of action: 4-10 minutes
What are inhalation/volatile agents?
Used usually for maintenance of amnesia
What are the 4 induction agents?
- Propofol
- Thiopentone
- Ketamine
- Etomidate
Which induction agent is most commonly used? - and what is the dose per kg?
Propofol, 1.5-2.5 mg/kg (used in more than 95% of patients)
Why is propofol most commonly used as an induction agent?
It has excellent suppression of airway reflexes and decreases the incidence of post-operative nausea and vomiting (PONV)
Why did Michael Jackson call propofol milk?
Because it is lipid-based, hence a white emulsion
What are the side effects/unwanted effects of using propofol? (3)
- Marked drop in HR and BP
- Pain on injection
- Involuntary movements
What type of drug is thiopentone? and what is the usual dose per kg?
A barbiturate, 4-5mg/kg
What are the benefits of using thiopentone?
It is faster acting than propofol, used mainly for rapid sequence induction (want to gain control of airway as quickly as possible as they are at risk of aspiration), it has anti-epileptic properties and protects the brain
What are the unwanted effects of thiopentone? (4)
- Drops BP, but rise in HR
- Rash/bronchospasm
- Intra-arterial injection: thrombosis (it forms crystals)/gangrene
- Contraindicated in porphyria (porphyria is an inherited metabolic disorder that leads to the slow production of haem)
What is the normal dose of ketamine given as an induction agent, per kg?
1-1.5mg/kg
What are the characteristics/uses of ketamine as an induction agent?
It is a dissociative anaesthesia (amnesia prior to operation too - anterograde) causes catatonia, analgesia, amnesia
- Slow onset (90 seconds)
- Rise in HR/BP, bronchodilation
What are the unwanted effects of ketamine as an induction agent? (2)
- Nausea and vomiting
2. Emergence phenomenon: vivid dreams, hallucinations
What are the positives of using Etomidate as an induction agent, and what is the dose per kg? (3)
- Rapid onset (dose 0.3mg/kg)
- Haemodynamic stability
- Lowest incidence of hypersensitivity reactions
What are the unwanted effects of etomidate? (4)
- Pain on injection
- Spontaneous movements
- Adreno-cortical suppression (blood loss, blood pressure continues to decrease)
- High incidence of PONV
Which induction agent is best for a patient requiring a burn dressing change?
Ketamine
Which induction agent is best for a patient undergoing arm operation under GA with an LMA (laryngeal mask airway)?
Propofol
Which induction agent is best for a patient with a history of heart failure and requires a general anaesthetic?
Etomidate (keeps them haemodynamically stable)
Which induction agent is best for a patient which requires an emergency laparotomy for intestinal obstruction?
Thiopentone
Which induction agent is best, and which is contraindicated, for a patient with porphyria coming in for an inguinal hernia repair?
Propofol
thiopentone contraindicated
What are the inhalation agents used to maintain amnesia? (4)
- Isoflurane
- Sevoflurane
- Desflurane
- Enflurane
Which inhalation agent is used for long operations?
Desflurane
Which inhalation agent is best for children with no intravenous access? (and why?)
Sevoflurane as it is sweet smelling and is used for induction too (so no intravenous access required)
Which inhalation agent doesn’t affect organ blood flow, and so it used for organ retrieval from a donor?
Isoflurane
What is needed for general anaesthesia?
- Monitoring
- IV access (to give anaesthetic poisons)
- Start process: induction agents, analgesia, muscle relaxation
- Maintain process:
What are the monitoring standards for anaesthesia? (7)
- ECG
- SpO2
- NIBP
- Airway gases e.g. oxygen, carbon dioxide and vapour
- Airway pressure (how much pressure the machine has to use in order to ventilate the patient)
- if the pressure is high, an obstruction could have occurred, or the patient has aspirated, or anaphylaxis, any cause of bronchospasm) - Nerve stimulator
- Temperature monitoring (if indicated)
What are the sizes of IV access?
14G to 24G
What is the minimum fasting time?
6 hours
Why is IV access important? (2)
- To give induction agent
2. To give fluids (patient will be dehydrated due to fasting)
How are inhalation agents administered?
As vaporisers
What is MAC?
Minimum alveolar concentration of the anaesthetic
What does 1 MAC refer to?
100% of patients will be asleep, 50% will not feel anything
What does 1 MAC refer to in terms of the inhalation agents?
- Sevoflurane is 2%
- Isoflurane is 1.15%
- Desflurane is 6%
- Enflurane is 1.6%
What is analgesia required for during operations/pre/post? (5)
- Insertion of airway
- Laryngeal mask airway
- Intubation
- Intraoperative pain relief
- Postoperative pain relief
Which are the short-acting drugs given as pain relief? (3)
- Fentanyl
- Remifentanil
- Alfentanil
When are short-acting opioids used?
During the induction process, to suppress response to laryngoscopy and surgical pain
What are the long-acting opioids, used during the operation and post-operatively? (2)
- Morphine
2. Oxycodone
Which other analgesic drugs are used?
- Paracetamol (very commonly used)
- NSAIDs; Diclofenac, Parecoxib, Ketorolac
- Weaker opioids; tramadol, dihydrocodeine
*give IV
What are the advantages of using tramadol? (3)
- Safe
- Useful for different pain types
- Can be used with morphine
What are the disadvantages of tramadol? (2)
- Nausea and vomiting
2. Confusion
What are the advantages of using morphine?
- Very effective
- Cheap
- Usually cheap
Which opioid can be given with morphine?
Tramadol
Name the two IV NSAIDs?
- Ketorolac
2. Parecoxib
What are the two mechanisms of action for muscle relaxants?
- Depolarising agents: act similar to acetylcholine on nicotinic receptors but very slowly hydrolysed by acetylcholinesterase. Therefore the muscle contracts then fatigues and relaxes
- Non-depolarising: they block the nicotinic receptors therefore muscle relaxes
What is the depolarising muscle relaxant? and its dose per kg?
Suxamethonium 1-1.5mg/kg
What is the advantage of using suxamethonium?
It has a rapid onset and a rapid offset
What are the adverse effects of using suxamethonium?
- Muscle pains
- Fasciculations
- Hyperkalaemia
- Malignant hyperthermia
- Rise in ICP, IOP (intra-occular pressure) and gastric pressure)
What are the advantages of using non-depolarising muscle relaxants?
- Less side effects
Name two short-acting non-depolarising muscle relaxants?
- Atracurium
2. Mivacurium
Name the two intermediate acting non-depolarising muscle relaxants?
- Vecuronium
2. Rocuronium
Name the long acting non-depolarising muscle relaxant?
- Pancuronium
Which agents can be used to reverse muscle relaxants?
- Neostigmine
2. Glycopyrrolate