Anaesthesia: Conduct of Anaesthesia Flashcards
Define anaesthesia
Partial or complete loss of sensation with or without loss of consciousness
State, and briefly describe, the three main types of anaethesia
- General anaesthesia: state of controlled unconsciousness iin which patient feels nothing and has no memory of what happened whilst anaesthetised.
- Local anaesthesia: loss of sensation in small area of body; patient remains conscious
- Regional anaesthesia: loss of sensation in a larger area of body (compared to in local anaesthesia; drug is injected near to the nerves that supply a larger or deeper area. E.g. spinal & epidural anaesthesia, nerve blocks
State when each of the following types of anaesthesia may be used:
- General
- Local
- Regional
- General: most major operations on the heart, lungs or in the abdomen, and many operations on the brain or the major arteries.
- Local: having teeth removed, common operations on the eye, skin biopsy, mole removal etc…
- Regional: operations on lower body e.g. caesarean section, hip operation, bladder operation
What is meant by conscious sedation in regards to anaesthesia?
- Using small amounts of anaesthetics or benzodiazepines to produce ‘sleepy-like’ state.
- Some people having a local or regional anaesthetic do not want to be fully awake for surgery. They choose to have sedation as well.
- You may remember everything, something or nothing after sedation. However, sedation does not guarantee that you will have no memory of the operation.
- Examples of when it may be used: endoscopy, egg retrieval etc..
Briefly outline the process a patient will go through if they are having anaesthesia
- Pre-anaesthetic care
- Pre-assessment (risk stratification, planning)
- Pre-optimisation (e.g. optimising current conditions such as diabetic control, correcting any electrolyte or fluid imbalances etc..)
- Anaesthesia
- Post-anaesthetic care
- Enhanced care, standard care, higher level of care
- Follow up
Safety culture is a vital part of anaesthetics and surgery; discuss what is included in the WHO Anesthesia Safety Checklist
Comprehensive guide that prompts you to check:
- Numerous things prior to induction of anaesthesia (see image)
- Suitability of OR e.g. good lighting, correct equipment both for procedure & to monitor pt, drugs & consumables for routine & emergency use
- Sponge & instrument counts
When, during a procedure, should sponge & instrument counts be done?
It is standard practice to count supplies (instruments, needles and sponges):
- Before beginning a case
- Before final closure
- On completing the procedure
The aim is to ensure that materials are not left
Safety culture is a vital part of anaesthetics & surgery; discuss what is included in the WHO surgical safety checklist
State the anaesthetic triad
Anaesthetic triad:
- Hypnosis
- Muscle relaxation
- Analgesia
… or more informally “Asleep, immobile, comfortable”
What is meant by balanced anaesthesia?
When a combination of different techniques/drugs are used to acheive anaesthetic triad e.g.
- Hypnosis= general anaesthetic*
- Muscle relaxation= muscle relaxants*
- Analgesia= opiates, local anaesthetics*
General anaesthesia can given via two methods, for each method describe:
- What drugs are used
- When commonly used
General anaesthesia can be given intravenously or via inhalation (volatile):
Intravenous
- Propofol (most common- rapid), barbituates (rapid), ketamine (slower), etomidate
- Induction usually with intravenous GA, maintenance usually with inhalational however if doint surgery to e.g. face may continue to use intravenous GA
Inhalational/volatile
- Sevoflurane, chloroform, halothane, xenon
- Usually used as maintenance or induction in paediatrics
Describe the different phases/outline general conduct of general anaesthesia
- Pre-assessment
- Preparation e.g. may include premedication (e.g. pt may need benzodiazepines if anxious)
- Induction (usually IV but may be inhalational)
- Intraoperative analgesia (usually opiod)
- Muscle paralysis
- Maintenance (typically inhalational but may be IV)
- Reversal of muscle paralysis
- Emergence i.e. waking them up
- Recovery (managing them until ward ready)
- Follow up
What is an arm-brain circulation time?
How long does it take for IV induction agents to cause sleep?
- Time taken for the drug to travel from the site of injection (usually the arm) to the brain where the drugs have their effect
- IV induction agents usually cause sleep in one arm-brain ciruclation time
State some muscle relaxations used to achieve the anaesthetic triad
- Atracurium (non-depolarising)
- Rocuronium (non-depolarising)
- Suxamethonium/succinylcholine (depolarising. Used in rapid sequence)
Remind yourself of the difference between a depolarising and non-depolarising muscle relaxant
- Depolarising: these are ACh agonists, bind to ACh receptors and generate action potential however because the drugs are not metabolised by acetylcholinesterase the binding of the drug to ACh receptors is prolonged resulting in extended depolarisation of end plate. As a result, end plate cannot repolarise
- Non-depolarising: these are competitive antagonists; bind to ACh receptors but do not initiate action potential but prevent ACh from binding and initiating action potential
What can be used to ensure pt is ‘comfortable’/’analgesia’ as part of anaesthetic triad
- Opiates
- Local anaesthetics
Describe the mechanism of action of all anaesthetics except Xe, N2O and ketamine
- Bind to GABAA receptors in brain
- GABA is main inhibitory neurotransmitter in brain
- GABA are ligand Cl- gated channels
- By binding to GABAA they potentiate the opening of the Cl- channels
- Increse Cl- influx
- Hyperpolarisation
- Decrase action potential firing as threshold not reached
Describe the mechanism of action of Xe, N2O and ketamine
Act via NMDA receptors
NMDA receptors are excitatory
Therefore most likley inhibit NMDA receptors
How do we measure volatile anaesthetic potency?
- Minimum alveolar concentration
- Alveolar concentration (at 1atm) at which 50% of sujects fail to move in response to surgical stimulus
- At equilibrium: [alveolar] = [spinal cord]
State how the following affect MAC:
- Age
- Hyperthermia
- Hypothermia
- Pregnancy
- Alcoholism
- Acute alcohol intake
- Central stimulants
- Other anaesthetics and sedatives
- Acute opiod intake
- Chronic opiod intake
- Age: decrease
- Hyperthermia: increases
- Hypothermia: decrease
- Pregnancy: decreases
- Alcoholism: increases
- Acute alcohol intake: decrease
- Central stimulants: increases
- Other anaesthetics and sedatives: decreases
- Acute opiod intake: decreases
- Chronic opiod intake: increases
What is often added to volatile general anaesthetics to reduce dosing?
Nitrous oxide
How do we measure intravenos anaesthetic potency?
Plasma concentration required to achieve a specific end point (e.g. loss of eyelash reflex)
Describe the mechanism of action of local anaesthetics
Block voltage gated Na+ channels tht are responsible for depolarisation and hence generation of action potentials. Most local anaesthetics block these channels by either of the two following mechanisms:
- Hydrophobic route: uncharged form enters the membrane and blocks the channel froma site in the protein-membrane interface
- Hydrophilic route: charged form enters the channel and blocks it
Nerve block occurs when the number of non-inactivated channels (those unaffected by the drug) is insufficient to bring about depolarisation to threshold
State some examples of local anaesthetics
- Lidocaine (rapid)
- Procaine
- Bupivacaine (slow)
Local anaesthetics can have ester or amide link; which is longer acting and why?
- Amide link longer acting as there are lots of esterases in blood
What is adrenaline often used with local anaesthetic and why? (3)
- Adrenaline
- To increase the amount of local anaesthetic that can be used; to increase the duration of action of the anaesthetic and to aid in reduction of bleeding from operation site
- Adrenaline causes vasoconstriction by binding to alpha-1 receptors in blood vessels and causing vasoconstriction
- Vasoconstriction delays the systemic absoprtion of the local anaesthetic and therefore increases duration of action of local anaesthetic
- Furthermore, by delaying systemic absorption of local anaesthetic adrenaline increases the amount of anaesthetic that can be used as risk of toxicity is decreased
- Vasoconstriction decreases blood flow to area to decrease bleeding risk
Although adrenaline is often used in combination with local anaesthetics, when can you not use adrenaline in combination with local anaesthetics?
Areas with an end-arterial supply, such as digits, the pinna, penis, or nose, as the vasoconstriction can cause ischaemia and gangrene of the area
State some side effects of anaesthetics
- Nausea & vomitting
- Confusion & memory loss
- Chills & shivering (related to hypothermia)
- Itching
- Sore throat
- Muscle aches
What must be done when preparing for the induction phase of general anaesthesia?
- Check eqipment
- Draw up and label drugs
- Personnel available checked
- IV fluids, blood, other equipment you may need e.g. ultrasound, cell salvage etc.. checked and readily available
For pre-oxygenation, discuss:
- What it is
- Why it is done
- When it is done
- How it is done
- Pre-oxygenation is the administration of oxygen to a patient prior to intubation and extubation to extend ‘the safe apnoea time’
- FRC of lungs acts as a reservoir to prevent hypoxaemia e.g. during breath holding. However, when someone has been breathing in room air the majority of the FRC is nitrogen. The purpose of pre-oxygenation is to replace nitrogen with oxgyen therefore increasing time for which a pt can be apnoeic as they have greater oxygen reserves
- Useful in situations in which you think intubation may be difficult; however, hard to determine whether intubation will be difficult therefore desirable in all pts? CHECK WITH ANAESTHETIST
- Get pts to breathe 100% oxygen via tighlty fitting facemask for about 3 minutes or until oxygen concentration in expired gas excedes 85%. In emergency, can ask pt to take 4-8 vital capacity breathes of 100% oxygen
Define the period of safe apnoea
Time until pt reaches oxygen saturations of 88-90%; this time allows for placement of definitive airway
Tracheal intubation requires the abolition of laryngeal reflexes and this is achieved by giving neuromuscular blocking agent; true or false?
True
State some risk factors for aspiration during anaesthetic
- Full stomach (e.g. emergency pts who haven’t starved, increased GI contents secondary to bowel obstruction)
- Delayed gastric emptying caused by e.g. drugs (opiates), trauma (head injury), peritoneal irritation
- Obstetric pts
- Other:
- Obesity
- History of GORD
- Hiatus hernia
- Head-down position
- Oesophageal pouch or stricture
What method of induction is used in pts with increased risk of apsiration?
Rapid sequence induction
What is Sellick’s manoeuvre?
- Apply pressure to cricoid cartilage
- Cricoid cartilage is complete ring
- By applying pressure to anterior aspec tyou force whole ring posteriorly
- This consequently compresses oesophagus against C6 occluding oesophagus and preventing aspiration
Explain the difference between normal sequence and rapid sequence anaesthesia?
Idea that muscle relaxant is given is rapid sucession after induction anaesthesia to reduce risk of aspiration. Anaesthesia causes muscle relaxation which could result in regurgitation & aspiration; by giving muscle relaxant in rapid sucession after induction means you can insert endotracheal tube immediately to reduce risk of aspiration.
- Normal sequence: induction anaesthesia, cause muscle relaxation to some degree, check can ventialte via facemask before give muscle relaxant, then give muscle relaxant, whilst wait for muslce relaxant to reach maximial effect (few mins) will require manual ventilation via face mask, once degree of muscle relaxation adequete intubate
- Rapid sequence: assistant applies light cricoid pressure, IV induction given, as consciousness lost cricoid pressure increased, give muscle relaxant e..g suxamethonium, facemask held against pts face but no manual ventilation performed (as oxygen could be forced into stomach, distension, increase regurgitation risk), once fasciculations from suxamethonium stopped laryngoscopy performed and endotracheal tube inserted
What are the minimum monitoring standards/requirements during general anaesthesia?
- Capnography
- Pulse oximetry
- ECG
- BP
- Agent analyser
- Temperature
For capnography, explain:
- What it measures
- How it works
- Measures CO2 concentration in air at end of expiration
How it works
- Shines infrared light on exhaled air
- CO2 absorbs infrared light
- Therefore, lower infrared reading, more infrared absorbed, more CO2 in breath
- In healthy person, CO2 in breath correlates well with PaCO2
- PaCO2 is inversely proportional to alveolar ventilation (think, high PaCO2 alveolar ventilation must be low as CO2 not being removed)
State some uses of capnography
- Indicator of degree of alveolar ventilation ***MAIN
- To indicate tracheal tube is in trachea (i.e. is there CO2 in expired gas, if yes in trachea)
- Indicator of CO (if CO falls, but ventilation is maintained, then end-tidal CO2 falls as CO2 is not delivered to lungs; may be due to hypovolaemia, cardia arrest, massive PE)
Discuss when and when you wouldn’t intubate a pt having general anaesthesia?
General anaesthesia frequently causes the pt’s airway to become obstructed following loss o ftone in the muscles of the tongue & pharynx. Patency can be restored via manoeuvres e.g. jaw thrust & head tilt, chin lift however these are not practical to maintain and intubation is not always required. Therefore supraglottic airway devices are used e.g. nasopharyngeal, oropharyngeal, LMA (larygneal mask airway).
However, sometimes intubation is required such as in:
- Muscle relaxants used to facilitate surgery
- Pts full stomach to prevent aspiration
- Major/long surgery
- Position of pt make difficult to maintain airway
- Operations on head & neck
- Controlled ventilation used to improve surgical acesss e.g. neurosurgery
- During CPR
- Other techniques not satisfactory
During a procedure, alongside maintenace anaesthesia what other medications may be given?
- Fluids
- Abx
- Insulin
- Antiemetics
- etc…
Emergence (also known as waking up) can be done in numerous ways; state and describe 5 ways
- Wears off: metabolised by enzymes in body after one off use e.g. depolarising relaxants such as suxamethonium
- Withdraw: stopping maintenance IV or volatile drugs
- Reverse: usually in relation to using drugs to reverse action of non-depolarising muscle relaxants (e.g. use neostigmine+glycopyrrolate, sugammadex)
- Antagonise: usually in relation to using antagonists to oppose effects of opiates, benzodiazepines etc..
- Stimulate: use respiratory stimulants such as doxapram (rarely done)
For malignant hyperthermia, discuss:
- What it is
- Pathophysiology
- Presentation
- Immediate management (highlight key parts)
- Malignant hyperthermia is an inherited disorder of the skeletal muscle in which patients develop a potentially fatal reaction to certain commonly used anaesthetic drugs
- Exposure to inhalational anaesthetic agents and suxamethonium causes release of abnormally high concentrations of calcium from the sarcomplasmic reticulum causing increased muscle activity and metabolism
- Presentation:
- Progressive rise in body temperature
- Unexplained tachycardia
- Increased end-tidal CO2
- Tachypnoea (in pts breathing spontaneously)
- Muscle rigidity, failuer to relax after suxamethonium
- Falling O2 sats and cyanosis
- Management:
- Stop all volatile anaesthetic drugs
- Hyperventilate with 100% oxygen
- Maintain anaesthesia with TIVA
- Change anaesthesia machine & circuits
- Dantrolene
- Start active coling (cold IV 0.9% saline, expose pt, sruface cooling)
- Treat acidosis with bicarb
- Treat hyperkalaemia
- ITU admission
What can we add to propofol to decrese the amount of propofol required?
Opiods e.g. fentanyl
Compare CPAP and BIPAP
CPAP
- Continous positive airway pressure
- Constant pressure/resistance.
- Has no inspiratory flow unlike BIPAP but helps to stent airways open
- Used in e.g. pulmonary oedema, COPD
BIPAP
- Bilevel positive airway pressure
- Higher positive pressure on inspiration to aid inspiratory flow. Lower pressure on expiration. Has an inspiratory flow unlike CPAP
- Used in e.g. type 1 repsiratory failure
