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
In addition to amnesics, analgesics and muscle relaxants, which other drugs are given?
- Vaso-active drugs
- Anti-emetics
- Antibiotics (if indicated)
What are the commonly used drugs to treat hypotension? (3)
- Ephedrine
- Phenylephrine
- Metaraminol
Ephedrine - used for low BP and low HR
Other two used for low BP but high HR
What are the commonly used drugs to treat severe hypotension? (3)
- Noradrenaline
2 Adrenaline - Dobutamine
When is ephedrine used?
When there is a low BP and low HR
When is phenylephrine and metaraminol used?
When there is a low BP but a high HR - so causes a rise in BP by vasoconstriction and a drop in HR
Which receptors do phenylephrine and metaraminol act on?
Alpha receptors
Which receptors does ephedrine act on?
Alpha and beta receptors
Which vaso-actiev agent is best used for someone in intensive care with severe sepsis?
Noradrenaline or adrenaline
Which three anti-emetics are most commonly used during surgery?
- Ondansetron
- Cyclizine
- Dexamethasone
How is the general anaesthetic reversed to wake the patient up?
- Give oxygen (as they will be respiratory suppressed due to opioids etc)
What does neostigmine do?
It is an anti-cholinesterase which prevents breakdown of acetylcholine
Which drug is best used to reverse anaesthesia, but is not commonly used due to it being very expensive?
Sugammadex
What happens on the post-anaesthesia care unit?
- Administer O2
- Handover the patient e.g. brief history, any problems anticipated, intraoperative analgesia and PONV anaphylaxis
- Prescribe:
- Rescue analgesia
- Rescue anti-emetics
- Fluids
- Other medications as indicated
What is the sequence of general anaesthesia?
- Oxygenation
- Opioid (fentanyl/alfentanyl)
- Induction agen (propofol)
- Turn on volatile agent (sevoflurane/isoflurane)
- Bag valve mask ventilation
- Inset LMA
What are the sequences of intubation?
- Oxygenation
- Opioid
- Induction agent (propofol)
- Turn on volatile agent (sevoflurane/isoflurane)
- Bag valve mask ventilation
- Muscle relaxant
- Endotracheal intubation
In terms of fasting guidelines before an operation, what are the various time slots for food and fluids?
6 hours fasting for solid foods (light meal) and milk
4 hours fasting for breast milk and fluids with pulp
2 hours fasting for water and clear fluids like black coffee and black tea
If someone needs to take tablets with water 30 minutes before their operation, how much are they allowed?
30ml
What are the metabolic causes of gastric emptying? (2)
- Diabetes mellitus
2. End stage renal failure
What is the anatomical cause of delayed gastric emptying?
Pyloric stenosis
What is the mechanical cause for delayed gastric emptying?
Anything that causes a raised intra-abdominal pressure - pregnancy, obesity
What are the others causes of delayed gastric emptying?
- Head injury
- High fat content
- Anxiety
- GORD
When is rapid sequence induction performed?
Normally in an emergency, when the patient has a full stomach for any reason
What is the initial step of rapid sequence induction?
Pre-oxygenation; three minutes, 5 full vital capacity breaths, EtO2 concentration >90 (rationale for this is to replace FRC with oxygen)
Which drugs are given in rapid sequence induction? - dose, onset and duration of action? (3)
- Thiopentone: 4-5mg/kg, onset 15-30 seconds and duration is 4-8 minutes
- Propofol: 1.5-2.5mg/kg, onset 30 seconds and duration of action is 2-6 minutes
- Suxamethonium: 1-1.5mg/kg, duration of action is 6 minutes
What is the dose of lignocaine without adrenaline in mg/kg?
3mg/kg
What is the dose of lignocaine with adrenaline in mg/kg?
7mg/kg
What is the dose of bupivacaine/levobupivacaine, and why is it different to prilocaine and lignocaine?
Dose is 2mg/kg and this is different as it does not change if it is with or without adrenaline
What is the dose of prilocaine in mg/kg?
6mg/kg
What is the dose of prilocaine with adrenaline?
8mg/kg
What does 1% lignocaine mean in terms of mg/ml?
1% is 1gram/100ml (or 1000mg/100ml) (or 10mg/ml)
So what is 2% lignocaine in terms of mg/ml?
2 x 10 = 20mg/ml
So what is 0.25% lignocaine in terms of mg/ml?
2.5mg/ml
What is a local anaesthetic?
A drug which reversibly prevents transmission of the nerve impulse in the region to which it is applied, without affecting consciousness
What is a local anaesthetic composed of?
Two groups; lipid-soluble hydrophobic aromatic group and a charged hydrophilic amide group
How is a local anaesthetic classified?
According to whether it has an ester or amide link:
- esters
- amides
Which classification of local anaesthetic rarely causes an allergic reaction?
Amides
Which ester local anaesthetics have a short duration of action? (3)
- Procaine
- Benzocaine
- Cocaine
Which ester local anaesthetic have a medium duration of action?
Prilocaine
Which ester local anaesthetic has a long duration of action?
Amethocaine
Which amide local anaesthetic have a medium duration of action?
- Lidocaine (lignocaine)
2. Mepivacaine
Which amide local anaesthetics have a long duration of action?
- Bupivacaine
- Levobupivacaine
- Ropivacaine
Which receptor channels for does local anaesthetic act upon?
Sodium channels
How does blocking the sodium channels work to anaesthetise?
Causes inhibition of voltage sensitive sodium channel in axon, preventing action potential. This prevents pain by causing a reversible block of conduction along nerve fibres
What are the 5 types/techniques of local anaesthetics?
- Topical
- Infiltration
- Conduction
- Extradural
- Spinal
Which type of local anaesthetic is used for infiltration anaesthesia?
This is for minor surgical procedures and commonly amides are used.
What does conduction anaesthesia refer to?
Minor or major nerve blockade e.g. single nerve block like ulnar nerve, or brachial plexus block
What are the signs of local anaesthetic toxicity? (In order of development) (12)
- Tongue paraesthesia
- Metallic taste
- Dizziness
- Slurred speech
- Diplopia
- Tinnitus
- Confusion
- Restlessness
- Muscle twitching/convulsions
- Coma
- Respiratory arrest
- CVS depression
What is the treatment for local anaesthetic toxicity? (8)
- Stop injecting the LA
- Call for help
- A : Maintain the airway and if necessary secure it with a tracheal tube
- B : Give 100% oxygen and ensure adequate lung ventilation
- C : Confirm or establish IV access
- D : Control seizures - benzodiazepine, thiopental or propofol
- Give IV lipid emulsion
- Consider drawing blood for analysis, in circulatory arrest start CPR
What is the safe dose of prilocaine with adrenaline?
8mg/kg
How much 1% lignocaine can a 70kg man have?
Lignocaine safe dose is 3mg/kg
- So 70x3 = 210mg
- 1% lignocaine = 10mg/ml
- 210/10 - 21mls
What is the safe dose of 2% lignocaine with adrenaline for a 60kg woman?
Lignocaine with adrenaline is 7mg/kg
-So 60x7 = 420mg
-2% lignocaine = 20mg/ml
420/20 = 21mls
What is the safe dose of 0.25% bupivacaine for a 60kg woman?
Bupivacaine is 2mg/kg (with or without adrenaline)
- So 60x2 = 120mg
-0.25% = 2.5mg/ml
120/2.5 = 48ml
What is the safe dose of 0.5% bupivacaine with adrenaline for a 60kg woman?
Bupivacaine with adrenaline is still 2mg/kg
- So 60x2 = 120mg
-0.5% x 10 = 5mg/ml
120/5 = 24ml
What is the safe dose in mLs of 1% prilocaine for a 60kg woman?
Prilocaine without adrenaline is 6mg/kg
-So 60x6 = 360mg
-1% x 10 = 10mg/ml
360/10 = 36mls
What is the mechanism of action of paracetamol?
It inhibits prostaglandin production and acts centrally on COX-3. This helps to increase the pain threshold and reduced prostaglandin concentrations in the thermoregulatory region of the hypothalamus, controlling fever.
What is the maximum dose of paracetamol in 24 hours?
Max 4g in 24 hours
How does paracetamol produce toxicity in overdose?
The metabolite of paracetamol is called NAPQI (N-acetyl-p-benzoquinone imine). NAPQI damages hepatocytes. Our body’s contain glutathione which is able to conjugate NAPQI and excrete it, however our glutathione reserves are limited, and excess paracetamol leads to excess NAPQI which inevitable damages the liver.
How long do stores of glutathione in the body normally last? - and why does this matter?
8-10 hours, so the symptoms/signs of toxicity won’t develop until the store of depleted, go after 8 hours.
What is the treatment for paracetamol overdose?
NAC - n-acetylcysteine. NAC is a precursor of glutathione, and thus does the same job by conjugating/binding to the NAPQI to form cysteine which is non-toxic.
Which receptors do opioids act on?
mu receptors
What is clonidine?
Clonidine is an alpha 2 agonist; acting on the brain and dorsal horn causing sedation and analgesia.
What is the concentration of sodium in NaCl?
0.9%
What is the definition of a solute?
a dissolved substance e.g. glucose
What is a solvent?
A liquid which is able to dissolve a solute to form a solution e.g. water
What is a semipermeable membrane?
Freely permeable to the solvent but not the solute
What is the modified mallampati scoring system?
There are 4 groups, and the scoring system predicts how difficult an intubation may be. It is based upon the visibility of the pharyngeal structures with the mouth open as wide as possible.
In 10% of patients an LMA is inserted incorrectly and airway obstruction occurs. What has normally happened when this occurs?
When inserting the LMA the epiglottis is folded back and pushed down by the mask.
What is the average size for tracheal tubes in men and women- and what does the size refer to?
8.0mm tube for females
9.0mm tube for males
Size refers to the internal diameter of the tube
What clinical signs are used to confirm tracheal intubation? (6)
- Direct visualisation of the tracheal tube through vocal cords
- Palpation of tube movements within the trachea
- Chest movements
- Breath sounds
- Reservoir bag compliance and refill
- Condensation of water vapour on clear tracheal tubes
What are the technical tests to confirm intubation?
- End-tidal CO2 monitoring (six breaths)
2. Fibreoptic observation of the trachea
Why is it important to test six breaths for CO2 in expired air after intubation?
Alveolar CO2 may have been ventilated into the upper GI tract before intubation and then will be excreted.
Also if the individual has drank a carbonated drink, this may give false reading
Which muscle relaxant has the fastest onset and shortest duration, and is often used in emergency operations or in patients with full stomachs?
Suxamethonium
Which new drug is used to reverse the effects of long-acting muscle relaxants?
Sugammadex
What are the two local anaesthetics in EMLA cream?
Lignocaine/Prolicaine
What is the maximum dose of 0.5% lignocaine with adrenaline for a 75kg patient?
75 x 7 = 525
0.5% = 5
525/5 = 105mls
How do local anaesthetics work?
By blocking voltage-gated Na+ channels, preventing depolarisation
What is the equation for calculating pH of blood? (Henderson-Hasselbach equation)
pH = 6.1 + log10 (conc. HCO3 / 0.0307 x pCO2)
How many litres of oxygen are comfortably delivered in a nasal cannula, and therefore what % of oxygen is being delivered?
2-3 litres at 24-28%
How many litres of oxygen are delivered in a hudson face mask and therefore what % of oxygen?
6 litres, generally about 30-40%
In the non-rebreathe mask, how many litres are delivered, at what % of oxygen?
15L high flow oxygen at close to 100%
How do you measure a guedel/oropharyngeal airway appropriately?
From the corner of the mouth to the tracheal ear, or from the mandible to the centre of the teeth
How do you measure the correct diameter of the nasopharyngeal airway?
Diameter of the patients little finger
When is a nasopharyngeal airway contraindicated?
In patients with a basal skull fracture
What is the normal size of endotracheal tube used for males and females respectively?
Males 8-9mm
Females 7-8mm
How do you check the endotracheal tube has been fitted properly?
- Misting of the tube
- CO2 expiration
- Equal chest rising
- Visually watched the tube enter
- Auscultate lungs and stomach
