INTRA-OP CARE Flashcards
What is anaesthesia and what are its 3 roles?
A drug-induced reversible loss of consciousness which allows for surgery and invasive procedures
The 3 roles are analgesia, hypnosis and muscle relaxation
What are the types of anaesthesia?
General
Local
Regional - indlcudes Spinal and epidural
Sedation
What are the 4 levels of anaesthesia?
Stage 1 = analgesia only
Stage 2 = excitation
Stage 3 = surgical anaesthesia
Stage 4 = medullary depression
What are the signs of the excitation stage of anaesthesia in.e. Stage 2?
Delirium with struggling
Rapid and irregular respirations
Frequent eye movements
Increased pupil diameter
Amnesia
What are the 4 planes of surgical anaesthesia i..e stage 3?
Plane 1 = decrease in eye movements and some pupillary constriction
Plane 2 = loss of corneal reflex
Plane 3 and 4 = loss of pharyngeal reflex and progressive decrease in thoracic breathing and general muscle tone
What is stage 4 anaesthesia i.e. medullary depression?
Loss of spontaneous respiration
Progressive depression of cardiovascular reflexes
No eye movements
Requires respiratory and circulatory support
We dont want to reach this! This occurs when too much Anaesthesia is given
What can be given as pre-medication before a GA?
A H2 receptor antagonists can be used if GORD or emergency surgery - to prevent regurgitation and aspiration of gastric contents
Benzos can be given to reduce anxiety
Analgesia and antiemetics can be given
Antimuscarinics can be given to combat the bronchial and salivary secretions and muscarinic side effects of neostigmine - this is less common now
What are the 4 stages of anaesthesia?
Induction
Maintenance
Emergnce
Recovery
What is induction?
The transition from awake to the anaesthetised state
What is the standard induction regimen?
Quick acting opioid e.g. fentanyl + propofol
When are muscle relaxants required for anaesthetics
If intubation is required
What muscle relaxant agents are used?
Depolarising - suxamethonium
Non-depolarising - rocuronium
What is the additional benefit of giving analgesia in induction of anaesthesia?
It reduces the sympathetic response so stops tachycardia and hypertension to stimuli e.g. laryngoscopy
What are IV drug options for anaesthesia?
Propofol
Ketamine
Thiopental
Etomidate
When should we always choose tracheal intubation over a supraglottic device e.g. LMA?
If there is any risk of airway soiling e..g regurg or anticipated difficulty with ventilation e.g. lung pathology/obesity
When should rapid sequence induction be used?
When pt is considered high risk of airway aspiration
What is rapid sequence induction?
A technique that involves rapid, successive administration of induction and neuromuscular blocking drugs to achieve a state of unconsciousness and paralysis in the shortest time possible to secure the airway
What is the MOA of propofol?
It potentiates GABA A and therefore enhances its inhibitory effects
What are the benefits of propofol?
Rapid induction due to high lipid solubility
Rapid recovery (as half life is 2-4 minutes)
Less hangover effects
Has some anti-emetic effects
Does not accumulate so an continuous infusion can be used
Can also be used for sedation in ICU or for diagnostic procedures
What are the adverse effects of propofol?
Dose-dependant hypotension
May also cause a dose-dependant respiratory depression
Causes pain on IV injection due to activation of the pain receptor TRPA1 (this can be reduced by including IV lidocaine)
Why does propofol cause hypotension?
It inhibits the sympathetic nervous system (causing vasodilation, negative inotropic effect, direct cardiac depression) and impairs the baroreflex regulatory mechanisms
Contraindications for propofol?
Hypotension
Hypersensitivity to the drug, eggs or soy
To prevent hypoxia what should inhalation anaesthetics always contain?
25% oxygen (higher >30% if NO is being used)
What is the Minimum Alveolar Concentration?
A measure of the potency - its the concentration of the anaesthetic when 50% of the population will fail to respond to a single noxious stimuli e.g. first surgical incision
What does it mean that NO has a MAC >100%?
This means that it would take a concentration of NO >100% to achieve its desired effect i.e. it alone cannot put the pt to No has a low oil:gas partition coefficient i..e it is relatively insoluble in blood and tissues and thus is lipid insoluble = low potency
What are examples of volatile liquid anaesthetics?
Sevoflurane, isoflurane and desflurane
What are examples of inhalational anaesthetics?
volatile liquid anaesthetics and NO
What are the possible adverse effects of isoflurane?
HR is generally stable but can rise in younger pt. Systemic arterial pressure and CO can fall causing decreased systemic vascular resistance. It can potentiate the effects of muscle relaxant drugs
When is isoflurane the preferred anaesthetic?
In obstetrics
Why is desflurane not recommended for the induction of anaesthesia?
As it irritates the URT
What are the benefits of desflurane over isoflurane?
Rapid acting. Emergence and recovery are particuarly rapid due to low solubility.
What are the benefits of sevoflurane over the other volatile liquid anaesthetics?
Rapid acting. More potent than desflurane. Emergency and recovery are more rapid than isoflurane (although slower than desflurane). Non-irritant so can be used for induction. Little effect on heart rhythm.
MOA of thiopental sodium?
A barbiturate
Potentiates GABA A
Adverse effects of thiopental sodium?
Dose-related cardiovascular and respiratory depression can occur
Metabolism is slow so sedative effects can persist for up to 24 hours
Can cause laryngospasm
Moa of etomidate?
Potentiates GABA A
Adverse effects of etomidate?
High incidence of myoclonus
Can cause primary adrenal suppression as it reversible inhibits 11 beta hydroxylase
Postoperative nausea and vomiting are more common with etomidate than propofol or barbiturate induction
Benefits of etomidate over propofol and thiopental sodium?
Rapid recovery without a hangover effect
Causes less hypotension
Whats the MOA of ketamine?
Works by blocking NMDA receptors
When is ketamine used as an induction agent?
Paediatrics
Good for trauma as causes less hypotension
Adverse effects of ketamine as an induction agent?
Recovery is slow
High incidence of myoclonus and disorientation
High incidence of transient psychotic effects - hallucinations
Not sure this is a bad thing… Produces dissociative anaesthesia - marked sensory loss, analgesia and amnesia but without complete LOC
What does entonox consist of?
50% NO 50% O2
What is NO used for in anaesthetics?
Maintenance and analgesia
Note: its a weak sedative and muscle relaxant
It cannot be used as a sole anaesthetic as it lacks potency but it is useful as part of a combination of drugs as it allows for a significant reduction in dosage
When should NO not be used?
If there are air-containing spaces e.g. pneumothorax or intracranial air as it can worsen these by increasing the volume of
Why are IV agents better than inhaled anaesthetic agent for induction?
IV agents are infused straight into the blood so can reach an effective concentration very quickly
Inhalational meds need to diffuse across the lung tissue and then into the blood
What is TIVA?
Total IV Anaesthesia - using an IV med for induction and maintenance as a slow continuous infusion
Most commonly done with propofol
Mao of non-depolarising neuromuscular blockade agents?
Competitive antagonists of nicotonic acetylcholine receptors at the NMJ and this decreases skeletal muscle tone
What are the 2 types of neuromuscular blockades?
Depolarising and non-depolarising
Examples of non-depolarising neuromuscular blockers?
Atracurium
Rocuronium
Pancuronium
Cisatracurium
Mivacurium
Examples of depolarising neuromuscular blockers?
Suxamethonium
Why are neuromuscular blockers give in anaesthesia?
They block the transmission of signals between motor nerve endings and skeletal muscles, preventing the affected muscles from contracting and also reducing their resting tone.
Thus they paralyse the jaw and the vocal cords facilitating laryngoscopy and tracheal intubation, and various other muscles whose paralysis may facilitate artificial ventilation and surgery.
How do you reverse the action on non-depolarising neuromuscular blockers?
With neostigmine - an anticholinesterase inhibitor
When trying to reverse the action of rocuronium, why might you give an antimuscarinic e.g. atropine alongside neostigmine?
You may give it to prevent the bradycardia or excessive salivation you may get by stimulation of muscarinic receptors