Anaesthesia lectures Flashcards
WHO surgical checklist
A pre-operative assessment performs multiple functions:
anaesthetic chart components
All types of anaesthesia alter normal body physiology to some degree
This may cause several common effects:
Think about which co-morbidities or acute pathology will cause each of these effects to be much worse. For example:
A – Airway obstruction:Obese, large tonsils, snore regularly, already obstructing e.g. intoxicated
B – Hypoventilation & hypoxia:Pre existing lung disease, current asthma exacerbation, pneumonia
C – Hypotension:Heart failure, hypovolaemic, septic
D – Post operative nausea and vomiting (PONV):Previous history of PONV, female, non smoker
E – Heat loss and hypothermia: low body mass, hypothyroid
G – Loss of airway reflexes and reflux risk: not fasted, pre existing reflux
How does pre-op assessment differ elective vs acute surgeries?
core categories from the pre-operative assessment
anaesthetic history
pre-op presenting complaint questions
pre-op PMH: important things to ask
**renal and liver disease **will affect drug handling
Cardio – as in depth as you need. If you find someone has angina, you want to explore this further. What brings it on, what resolves it, how long, has it been getting worse? Unstable angina and recent myocardial infarction (especially in last 3 months) will significantly increase the risk of an anaesthetic PND – paroxysmal nocturnal dyspnoea
Resp – current respiratory illness, especially in children, puts patients at increased risk of worsening infection/pneumonia and airway complications e.g. bronchospasm, laryngospasm. Recent COVID (< 7 weeks) has been shown to increase postoperative complications
Exercise tolerance – anaesthesia and surgery puts additional stress on the body. Can the body respond appropriately? Quantifying how much a person can do for themselves (e.g. independently can wash/dress/cook/clean) is helpful. Can they manage a flight of stairs? Two flights? How far can they walk on the flat or up a hill? What makes them stop – chest pain? SOB? Joint pain?
pre-op DH: key questions
pre-op SH: key things to ask
how does alcohol affect anaesthesia?
Alcohol – will cause increased metabolism of certain drugs, unless progressed to hepatic impairment. Will affect doses, effect and duration
pre-op fasting rules
2 hours – clear fluids (not fizzy or with sediment)
4 hours – breastmilk
6 hours – solid food
Tablets – take with a small sip of water (preferably < 30 ml) at any time
paediatric fasting rules
Paediatrics – fluids up to 1 hour before
factors to consider that will delay gastric emptying in pre-op period
Trauma / pain will delay gastric emptying: Take the fasting time from the time of injury.
Reflux:if significant reflux, when asleep this could cause an aspiration risk. Questions around timing (e.g. when lying down at night) and whether medication helps can help judge severity
pre-op assessement: examination
Examination
* General appearance
* Brief cardiovascular / respiratory: sensible to check pulse (to rule out new arrhythmias) and brief hydration status assessment. Any cardiac history – would benefit from listening to the heart for valve pathology and lungs for evidence of fluid overload or effusion
* Airway / dental
Observations
* HR, BP, RR, SpO2, Temp, Capillary glucose (if diabetic)
* Weight & height
pre op assessemnt: airway assessement key things to consider
- mouth opening: sclerosis, TMJ, fractured mandible
-
dental: Loose teeth can become dislodged and enter the lungs, causing obstruction and collapse.
Patients may also have very expensive dental work that they will be very upset if gets damaged e.g. caps and crowns - neck: If patients are unable to extend their neck (due to arthritis, damage, muscle tension) then this can make any airway manipulation very difficult
what is mallampati score?
Mallampati score. Simple score which is easy to perform. how hard it is to intubate someone
* Class I – can see hard, soft palate, uvula and tonsillar pillars.
* Class II – pillars disappear.
* Class III – cannot see the whole of the uvula and only a tiny portion of the soft palate.
* Class IV – only hard palate visible.
* Class III and IV associated with difficult laryngoscopy and intubation, however poor positive predictor value.
what is an ASA grade and what are its components?
pre-op investigations
table of investigations for elective surgeries: minor, intermediate and major surgery investigations against their ASA grade
Minor surgery: skin lesion excision, draining abscess
Intermediate surgery: tonsillectomy, knee arthroscopy, inguinal hernia repair
Major surgery: total joint replacements, abdominal hysterectomy, prostatectomy
If at risk refers to
AKI risk: pre existing CKD, diabetes, intraperitoneal surgery, heart failure, > 65 years old, on nephrotoxic medications such as ACEi or ibuprofen, liver disease)
pre-op assessment: optimise for elective surgery
pre op medicine management: essential medications to continue and important medications to continue if able
aspirin rule pre op
continue
Clopidogrel rules preop
Clopidogrel – stop 7 days prior. If recent stroke/MI in past year – seek expert advice
rules preop DOACs
DOACs – stop 24 – 72 hours prior to surgery depending on renal function
rules preop Warfarin
Warfarin – stop 5 days prior.
If high risk of thrombosis (previous VTE or mechanical heart valve) – bridge with LMWH
rules preop LMWH
LMWH – last dose 12 hours prior (24 hours if treatment dose for VTE)
pre-op diabetes management
anticipation of haemorrhage in pre-op
pre-op VTE prophylaxis: factors which increase VTE risk
what is done for VTE prophylaxis pre-op?
pre-op assessment consent
3 main types of anaesthesia
- General anaesthesia
Total loss of sensation - Regional anaesthesia
Loss of sensation to a region or part of body - Local anaesthesia +/- Sedation
Topical, Infiltration
MAC: Monitored Anaesthesia Care
Balanced Anaesthesia: the 3 As
Balanced Anaesthesia
* Amnesia –
lack of response and recall to noxious stimuli – Unconsciousness
* Analgesia –
pain relief
* Akinesis –
immobilisation / paralysis
‘Not harmful to the patient’
sequence of anaesthesia
- Standard Monitoring
- IV Cannulation
- Preoxygenation: done for three minutes or 5 full vital capacity breaths over 30 seconds. Aim to achieve EtO2 concentration > 90. Anaesthetic agents depresses or completely stops breathing so pre-oxygenation is important to build oxygen reserves and prevent hypoxaemia.
- Intravenous or Inhalational Induction
- Standard GA or Rapid Sequence Induction
- Establish airway/Respiratory support: : Definite airway i.e Endotracheal tube or Supraglottic airway i.e LMA or I-gel
- Drugs used for various components of balanced anaesthesia (Amnesia, Analgesia & muscle relaxation)
- Cardiovascular support i.e vasoconstrictors. Anaesthetic agents drops Blood Pressure, so may need vasoconstrictors to maintain BP
- Antiemetics
- Fluids or Blood products (if needed)
examples of IV induction agents
Propofol
Thiopentone
Etomidate
Ketamine
what is an induction agent?
to start the process of anaesthesia (Intravenous/Inhalationa)
inhalational induction agents examples
Isoflurane
Sevoflurane
Desflurane
Enflurane
Most commonly used Induction agent is
propofol
Most commonly used Inhalational agent
Sevoflurane
propofol: MOA, dose and benefits
- GABA receptor agonist
- Rapid onset of anaesthesia
- Most commonly used (1.5 – 2.5 mg/kg) (>95% cases)
- Lipid based (white emulsion);
- Excellent suppression of airway reflexes
- Decreases incidence of PONV
- Rapidly metabolised with little accumulation of metabolites
Widely used especially for maintaining sedation on ITU, total IV anaesthesia and for daycase surgery
propofol SE
- Marked drop in HR and BP
- Pain on injection and Involuntary movements
THIOPENTONE MOA, dose and benefits to use
- Barbiturate (dose 4 – 5 mg/kg);
- Faster than propofol
- Used mainly for rapid sequence induction
- Antiepileptic properties and protects brain
- THIOPENTONE downsides
- Drops BP but rise in HR
- Rash / Bronchospasm
- Intra-arterial injection: thrombosis and gangrene
- Contraindicated in porphyria
- Unsuitable for maintenance infusion
- Little analgesic effects
etomidate upsides and doses
- Rapid onset (Dose 0.3 mg/kg);
- Hemodynamic stability: Mainly used in Cardiac patients Induction
- Lowest incidence of hypersensitivity reaction
etomidate SE and downsides to use
- No analgesic properties
- Unsuitable for maintaining sedation as prolonged (and even brief) use may result in adrenal suppression
- Post operative vomiting is common
- Pain on injection
- Spontaneous movements
Cortisol levels can be suppressed up to 72 hours after a single bolus dose of etomidate. Single dose of etomidate may be considered safe safe for otherwise healthy patient undergoing an uncomplicated surgery
Etomidate should preferably never be used for critically ill patients with septic shock because it could increase mortality due to adrenocortical suppression.
Ketamine: MOA, properties and uses
- NMDA receptor antagonist
- Has moderate to strong analgesic properties
- Sole anaesthetic for short procedures
- Dissociative anaesthesia: whihc can result in nightmares
- Anterograde amnesia and profound analgesia
- Sole anaesthetic for short procedures
- Dose: 1 – 1.5 mg/kg
- Slow onset (90 seconds)
- Rise in HR/BP
- Bronchodilation
ketamine unwanted effects
- Nausea and vomiting;
- Emergence phenomenon
Patients have reported “going into other worlds” or “seeing God” while anesthetised, and these unwanted psychological side-effects have reduced the use of ketamine in human medicine.
maintenance of anaesthesia: what can be used to maintain amnesia and how long do induction agents last
what is MAC?
MAC: It is defined as the minimum alveolar concentration of inhaled anaesthetic at which 50% of people do not move in response to a noxious stimulus.
most common inhalation agents to maintain amnesia
sevoflurane vs desflurane vs isoflurane as inhalation maintenance agents
Sevoflurane
* Sweet smelling: used in paeds
* Inhalational induction
Desflurane
* Rapid onset and offset: so used on obese patients
* Maximum greenhouse effect
Isoflurane
* Least effect on organ blood flow
* Organ donation
muscle relaxants: two types
depolarising and non-depolarising
example of depolarising neuromuscular blocker and MOA
- Suxamethonium: (dose 1 -1.5 mg/kg)
- Rapid Sequence Induction (Rapid onset - Rapid offset): acts within 30-45 seconds
- Depolarising neuromuscular blocker
- Inhibits action of acetylcholine at the neuromuscular junction
difference between depolarising and non-depolarising muscle relaxants
DEPOLARISING = act on nicotinic receptors and are very slowly hydrolysed by acetylcholinesterase, causing muscle to contract, then fatigue and relax
NON-DEPOLARISING = block the nicotinic receptors, causing the muscle to relax
adverse effects of Suxamethonium
- muscle pains
- fasciculations
- Hyperkalaemia
- malignant hyperthermia
- rise in ICP, IOP and gastric pressure
- non-depolarising muscle relaxants: MOA and examples
- reversal agents used
analgesia: opioids. short acting vs long acting examples and uses
most common short acting opioid used during induction to suppress response to laryngoscope
fentanyl
morphine: indications, advantages and disadvatages
paracetamol indications, advantages and disadvantages
Indications
* Mild nociceptive pain
* Moderate to severe nociceptive pain (with other medications)
Advantages
* Cheap, safe
* PO, PR, IV
Disadvantages
* Liver damage in overdose
Most commonly used analgesic
paracetamol
Most commonly used oral opioid in adults
Codeine
Intravenous NSAIDS
Ketorolac, Parecoxib
Opioid that can be used with morphine
tramadol
Fluids, Blood & Blood Products
Transfer to Post Anaesthesia Care Unit: what do you need to do?
Summary - General Anaesthesia (all patients)From arrival into anaesthetic room to recovery
what are central neuraxial blocks?
- Epidural Block
- Subarachnoid Block (Spinal Block)
injection of local anaesthetic into close proximities of the nerves arising from the spine
Central neural block uses
spinal anaesthesia vs epidural anasthesia/analgesia:
- onset
- predictability
- density of block
- duration
What are the three layers of the spinal cord?
Pia mater, arachnoid mater and dura mater from inside outwards
Where is CSF present?
- Between Pia and arachnoid i.e. subarachnoid (below arachnoid) space.
- An injection into this space is called spinal block
What lies between the dura mater and the vertebral canal?
Epidural (outside dura) space. Any injection into this space is called epidural injection.
Where does the spinal cord end in adults?
Lower border of L1
Where does the subarachnoid space end?
S1
Where can you do the spinal block?
- Below L2, down to S2. Sacral vertebrae are fused as one and often the 5th lumbar vertebra is joined with the sacral bone. Therefore, the injection can be made at the L4/5, L3/L4 or L2/L3 levels.
- Chose the lowest level possible to minimise the risk of damage to the spinal cord.
Where does the epidural space end?
Sacrococcygeal hiatus
Where can you do the epidural block?
Epidural block can be done at any level but there is a risk of damage to the cord if it is done above the level of L1. For labour analgesia the block is done at the same level as Spinal. However, for laparotomy the block is done at the thoracic level.
What structures does the needle pass when the needle is inserted for epidural or spinal injection?
epidural: skin - subcutaneous fat - supraspinous ligament - infraspinous ligament - ligamentum flavum - parietal layer of dura mater
spinal: + dura and arachnoid mater
advantages of central neural blocks over opioids
Peripheral nerve blocks options and use
used in limb operations to avoid GA
Local Anaesthetics Systemic toxicity signs and symptoms
Local Anaesthetics Systemic toxicity management
Local anaesthesia & Monitored Anaesthesia Care uses
short acting local anasthetics
Short acting: Prilocaine, lignocaine
Long acting local anaesthetics
Long acting : Bupivacaine, Levobupivacaine, Ropivacaine
Lignocaine without adrenaline safe dose
3mg/kg
Lignocaine with adrenaline safe dose
7mg/kg
Bupivacaine safe dose
2mg/kg
local anaesthetic calculations
- in PACU every patient is monitored for:
Anaesthetic drugs stay in system for
up to 24 hours
altered physiology in the immediate post-op phase A+B
altered physiology in the immediate post-op phase C+D
COMPLICATIONS IN EARLY POST-OPERATIVE RECOVERY
Hypotension
SOB
Low GCS
Pain
PONV
post op hypotension causes and treatment
a VBG which might tell you more about their haemoglobin and fluid deficiency using lactate and base excess
post op SOB causes and treatment
post op low GCS causes and tereatment
management of acute pain post-op pathway
Some physiological hints of pain
Some physiological hints:
Tachycardia and hypertension
Tachypnoea
Sweating
Restlessness or confusion
assessment of acute post-operative pain
treatment of acute pain post-op
PCA: which medication is used for it? how does it work? what else do you need to givwe along side PCA?
rules about opioid prescribing post-op
PONV predisposing factors
PONV management
PONV prescribing: Main comorbidity to consider is
Main comorbidity to consider is Parkinson’s disease: several antiemetics affect symptoms and should be avoided. Check before prescribing! Safe options include: cylclizine and ondansetron. If in doubt check the BNF, with a neurologist or the anaesthetist
Complications of spinal and epidural anaesthesia and their management
Rare and serious Complications of spinal and epidural anaesthesia and their management
