Anaesthetics Flashcards
What is the name for assessing fitness for surgery?
ASA grading
What are the stages of ASA grading?
- Normal healthy patient
- Mild systemic disease/ >80
- Systemic disease that causes definite functional limit to life
- Severe systemic disease that’s a constant threat to life.
- Moribund patient unlikely to survive 24hours without surgery
What are the grades of surgery?
- MINOR, excision of skin lesion, drainage of abscess
- INTERMEDIATE, inguinal hernia, tonsillectomy
- MAJOR, thyroidectomy, total abdo hysterectomy
- MAJOR+, colonic resection, total joint replacement
What are the fasting times for surgery?
8hours: Heavy meal
6hours: Non-human milk, formula, light meal
4hours: Breast milk
2hours: Clear liquids (no limit)
Alcohol: At least 24hours before surgery
What delays gastric emptying?
Metabolic: DM, ESKD Anatomical: Pyloric stenosis Trauma Mechanical: Pregnancy, obesity High fat content Anxiety
How is the airway assessed before surgery?
- Hx & Ex
- Mallampatti
- Teeth
- Thyromental & sternomental distance
- Neck movement
- 1-2-3
- Cormack & Lehane
What are METs?
Metabolic Equivalents 1= eating & dressing 3= light household activity/ walk 100m @ 2-3mph 4= climb stairs 6-7= short run
What components make up a general anaesthetic?
Amnesia
Analgesia
Akinesis
What are the most common inducing agents
Propofol
Thiopentone
Ketamine
Etomidate
Propofol:
- Properties
- Reason for use
- Side effects
- MOST COMMON
- Lipid based
- Excellent suppression of airway reflexes & dec PONV (anti-emetic properties)
- SE: drop in HR & BP, pain on inj, involuntary movements
Thiopentone:
- Properties
- Reason for use
- Side effects
- Example
-Barbituate
-Faster acting than propofol
-RSI
Antiepileptic properties & protects the brain
-SE: drops BP, rise HR, rash & bronchospasm, intraA injection
-CI in porphyria
-Pt w/GI perf
Ketamine:
- Properties
- Reason for use
- Side effects
- Example
- Dissociative
- Anterograde amnesia
- Slow onset (90secs)
- Activates sympathetic system
- Bronchodilation
- Moderate-strong analgesic properties
- SE: Rise in BP & HR, N&V, emergence phenomenon
- Change dressings for burns patients
Etomidate:
- Properties
- Reason for use
- Side effects
- Example
- Rapid onset
- Haemodynamically stable
- Lowest incidence of hyperS
- SE: pain on inj, spont movements, adreno-cortical suppression, PONV
- HF patient
What is adreno-cortical suppression & what is it associated with?
Etomidate
Cortisol level suppressed >72hours after bolus. Not used in critically ill/septic patients
What is the problem with intra-arterial injection & what is this associated with?
Thiopentone
Blockage of capillaries due to large crystals can lead to thrombosis & gangrene
When are inhaled agents used?
After inducing agent to maintain amnesia and continued till the end of the operation
Name the most common inhaled agents
Isoflurane Sevoflurane Desflurane Enflurane NO
What is MAC?
Minimum alveolar concentration
Concentration of inhaled agents
Isoflurane:
- MAC
- Properties
- Example
- 1.15%
- Can be used as inhaled amnesic
- Least effect on organs
- Donor-recipient operations
Sevoflurane:
- MAC
- Properties
- Example
- 2%
- Sweet smelling, inhalation induction
- Chubby kid w/ no IV access
Desflurane:
- MAC
- Properties
- Example
- 6%
- Can be used as inhaled amnesic
- Low lipid solubility, rapid on/offset, long operations
- 7hr op for finger re-implant
MAC for NO & Enflurane
NO: 104%- cannot give 1 MAC of NO
En: 1.6%
Name the short-acting opioids & when they would be used?
Fentanyl Alfentanil Remifentanil Used: Intra-operatively Suppress response to laryngoscope Surgical pain
Name the long-acting opioids and when they would be used?
Morphine
Oxycodone
Used: Intra-operatively
Post-operatively
What type of pain is tramadol used for?
Nociceptive
Neuropathic
What type of pain is morphine used for?
Nociceptive
Acute
Severe
Cancer pain
How do GAs stop movement?
As action potential arrives at NM junction, Acetylcholine is released which causes depolarisation of Nicotinic receptors leading to muscle contraction.
What is the pathophysiology of the 2 types of akinesic agents?
Depolarising: Similar to acetylcholine on nicotinic receptors slowly hydrolysed by acetylcoA. Muscle contraction then fatigues
Non-depolarising: Block nicotinic receptors so muscle relaxes
Name the main types of akinesic agents
Suxamethonium- RSI Atracurium Mivacurium Rocuronium Vercuronium Pancuronium
Name the depolarising agents
Suxamethonium
Succinylcholine
Name the non-depolarising agents & describe some of their characteristics
Less SE, slow onset & variable duration, compete with Ach for nicotinic receptors
Atracurium- Short acting Mivacurium- Short acting Rocuronium- Intermediate Vercuronium- Intermediate Pancuronium- Long acting
How are muscle relaxants reversed?
Neostigmine: Anti-cholinesterase prevents breakdown of acetylcholine (SE= brady)
Glycopyrrolate: Antimuscarinic (SE= N&V)
What anti-emetics can be used post-op?
5HT3: Ondansetron Anti-Histamine: Cyclizine Steroid: Dexamethasone Phenothiazine: Prochlorperazine Anti-dopaminergic: Metoclopramide
What is the definition of a local anaesthetic
Reversibly prevents transmission of the nerve impulse in the region to which it is applied without affecting consciousness.
What is the composition of a LA?
Ester
Amide
Describe esters
Less stable in sol Metabolised by PABA associated w/allergies S-A: Procaine, Cocaine, Benzocaine M-A: Prilocaine L-A: Amethocaine
Describe amides
Heat stable (autoclaved)
Rare for allergies
M-A: Lidocaine/lignocaine, Mepivacaine
L-A: Bupivacaine, Levobupivacaine
What is the safe dosage of LA?
Lignocaine: 3mg/kg
(levo)Bupivacaine: 2mg/kg
Prilocaine: 6mg/kg
What is the safe dose of LA with adrenaline?
Lignocaine: 7mg/kg
(levo)bupivacaine: 2mg/kg
Prilocaine: 9mg/kg
What is the MOA of LA?
- Inhibition of voltage sensitive Na channel in axon preventing action potential
- Membrane stabilisation effect
- Prevent pain by causing reversible block of conduction along nerve fibres
- Exert toxicity by blocking Na channels found in the brain or heart:
a. If plasma levels rise SLOWLY CNS is affected first (excitatory symptoms due to inhibition of GABA receptors- metallic taste, dizziness, slurred speech, diplopia, tinnitus, muscle twitching, confusion, convulsions)
b. At high concentrations there is widespread Na channel blockade with generalised neuronal depression leading to coma, respiratory & cardiac arrest
How is LA toxicity treated?
Stop inj & call for help Maintain airway, give 100% O2 Establish IV access Control seizure (benzo/propofol/thiopental) ARREST=CPR IV intralipid (lipid emulsion)
Where is a spinal block & an epidural placed?
BOTH: Skin, Subcut fat, Supraspinus lies, Spinal logs, Ligamentum flavum
S: Through dura & arachnoid to CSF space: L2-S2
E: Space between ligamentum flavum & dura below L1
When is a spinal & epidural used?
S: Ops on lower half of the body
E: Intra-op analgesia & <72hours post-op
How is a spinal & epidural given & onset?
S: Small amount Single injection, rapid onset (5-10mins)
E: Epidural catheter, onset 15-30mins, reliant on catheter placement
Risk factors for PONV?
Female
Previous episodes
Non-smoker
What factors make up the anaesthetic safety checklist?
- Experienced & trained assistant to help with induction
- Fasted appropriately
- IV access that is functional
- On a table that can be rapidly tilted
What is the NCEPOD classification?
Classification of intervention
- Immediate
- Urgent
- Elective
- Expedited
What are the anaesthetic emergencies?
LA toxicity
Airway: Laryngospasm, can’t intubate/can’t ventilate
Anaphylaxis
Malignant hyperthermia
What are the SE of depolarising agents?
Muscle pains Fasciculations HyperK Malignant hyperthermia Rise in ICP, IOP, gastric pressure
What is the pathway of identifying a potential organ donor patient?
1) Inform SNOD of potential donors
2) Speak to family
Can you smoke before an operation?
No-ideally stop 48-72hours
Smoking makes airway more irritable
Raised Hb levels