Anaesthetic Drugs Flashcards
What is the triad of anaesthesia?
Hypnosis (unconscious)
Relaxation
Analgesia (pain-free)
What agents are used for hypnosis?
Anaesthetic agents (IV or Inhaled)
What agents are used for relaxation?
Muscle relaxants (depolarising or non-depolarising)
What agents are used for analgesia?
Analgesia (fentanyl or morphine)
What are the commonly used IV anaesthetic (hypnosis) agents?
Propofol - most common UK
Thiopentone
Ketamine
Etomidate
What is propofol?
An IV anaesthetic agent - ‘milk of anaesthesia’
Used for induction and maintenance
What is the dose of propofol for induction?
1.5-2.5 mg/kg
Less in elderly, more in children
When TICA is used for anaesthesia what does this refer to?
When an IV agent e.g. Propofol is used as a bolus for induction and then as an infusion for maintenance during the surgery
Total IV anaesthesia
CANULA MUST ALWAYS BE VISIBLE
What are the respiratory effects of Propofol?
Respiratory - short period of apnoea and suppression of larygeal reflex
Allows insertion of I-gel without muscle relaxant
What are the cardiovascular effects of Propofol?
Reduction in SVR (systemic vascular resistance), CO and BP
*risk in elderly
What are the CNS effects of Propofol?
Reduced intracranial pressure and cerebral oxygen concentration
What are the other effects of Propofol?
Anti-emetic effects
What is Thiopentone?
IV anaesthetic agent - Thiobarbiturate
In what situation is Thiopentone commonly used?
RSI - Rapid sequence induction
often in maternity unit
What is the dose of Thiopentone?
4-6 mg/kg
What is another use for Thiopentone?
Used in status epilepticus
What are the CNS effects of thiopentone?
Reduced intracranial pressure and metabolic rate of oxygen.
What are the CVS effects of thiopentone?
Reduction in SVR, CO and BP
Causes compensatory tachycardia
What are the respiratory effects of thiopentone?
Respiratory depression
Unlike propofol the reflexes are preserved so not suitable for use alone with laryngeal mask airway
What are the other effects of thiopentone?
Extravasation can cause pain and tissue damage due to high pH
Always flush with saline and avoid in porphyria
What is Ketamine?
IV anaesthetic agent - Antagonist of NMDA receptor
What is the dose of Ketamine?
1-2 mg/kg
What routes can ketamine be used by?
IV, IM, Rectally, Nasally, Epidurally
What patients is Ketamine commonly used in?
Shocked, burned or paediatric patients (haemodynamically compromised)
‘Field anaesthesia’
Also potent analgesic
What are the CNS effects of ketamine?
Analgesia, raised ICP, hallucinations, dissociative anaesthetic
What are the CVS effects of ketamine?
Increases BP and HR, increased CO
Why useful in haemodynamically unstable patient
What are the respiratory effects of ketamine?
Preserved laryngeal reflexes (may cause laryngospasm), bronchodilator, minimal effect on central respiratory drive.
What is etomidate?
IV anaesthetic agent - agonist activation of GABA receptors
What is the dose of etomidate?
0.3 mg/kg
What are the benefits of etomidate?
Patients who require highly cardiovascular stability profile.
What is the downside of etomidate?
Inhibits adrenocortical steroid synthesis, observed endocrine effects.
Reduction in cortisol and aldosterone.
Increased N&V
What are the CVS effects of etomidate?
Stable CV profile (benefit)
Minimal effect on myocardial contractility
What are the CNS effects of etomidate?
Cerebral vasoconstriction, may cause involuntary muscle movements and tremor
What are the respiratory effects of etomidate?
Transient apnoea,
Coughing and hiccupping are common during induction
What are the other effects of etomidate?
Increased incidence of post-op N&V
Pain on injection
Potent inhibitor of steroidogenesis in adrenal cortex
Unsuitable in porphyria
Not commonly used anymore
What are the three major volatile inhalation anaesthetic agents?
Sevoflurane
Isoflurane
Desflurane
What is sevoflurane?
Volatile inhalation anaesthetic agent
Can be used in gaseous induction or maintenance
Good in young children who won’t tolerate canula
What is MAC?
Minimum alveolar concentration - alveolar concentration of gaseous agent required to ensure 50% of test population don’t respond to surgical incision
What is isoflurane?
Volatile inhalation anaesthetic agent
Cheaper and more potent than sevoflurane but irritant with a pungent smell - cannot be used for gaseous induction
What is desflurane?
Volatile inhalation anaesthetic agent
Pungent - not suitable for gaseous induction
Must be shielded from light and have Tec 6 vaporiser
What is a risk of all volatile inhalation agents?
Malignant hyperthermia
What are the two types of muscle relaxants?
Depolarising and non depolarising
What is the only depolarising muscle relaxant used in clinical practice?
Suxamethonium (Sux)
What is the function of Suxamethonium?
(Similar to ACh)
Agonist at post junctional NAChR (Nicoticic ACh receptor)
What are the uses of Suxamethonium?
Rapid and short periods of muscle relaxation (Rapid Sequence Induction), ECT
Muscle function returns within 5 mins.
What is the dose of Suxamethonium?
1-1.5 mg/kg
What is the onset of Suxamethonium?
Rapid onset - 90% laryngeal muscle block in 50 seconds
Recovery begins after 3-5 minutes, complete within 12-15 min
What are the downsides to Suxamethonium?
Myalgia
Elevation of serum potassium (wouldn’t use if already raised)
What are the potential complications of suxamethonium?
Bradycardia
Anaphylaxis
Malignant hyperthermia (rigidity, high temp)
Prolonged block - sux apnoea
What is the treatment of malignant hyperthermia?
Dantrolene
What is malignant hyperthermia?
Autosomal dominant condition in which certain drugs induce increased muscle metabolism and dangerous hyperthermia
What are the non-depolarising muscle relaxants?
Rocuronium - Aminosteroid Vecuronium - " Pancuronium - " Atracurium - Bis-benzylisoquinolinium Cisatracurium - " Mivacurium - "
What are the two groups of non-depolarising muscle relaxants?
Animosteroids - CURONIUM
Bis-benzylisoquinoliums - CURIUM
How do non-depolarising muscle relaxants work?
Compete for the same binding site as ACh
Reducing potential number of interations - reducing in liklihood of action potential being reached
What side effects are reduced with non-depolarising muscle relaxants?
No fasiculations
No myalgia
No potassium released
No malignant hyperthermia
What is Rocuronium?
Non-depolarising muscle relaxant - Aminosteroid
What is the intubating dose of Rocuronium?
0.6 mg/kg
What is the onset of rocuronium?
Rapid 75s duration 33m
Rapid onset, low potency
Can be used as an alternative to Sux for RSI
How can rocuronium be reversed?
Sugammadex
What do the aminosteroid non-polarising muscle relaxants (NMBA’s) rely on for elimination?
Renal and hepatic function
What is Atracurium?
Non-depolarising muscle relaxant - Bis-benzylisoquinoliniums
What is the intubating dose of Atracurium?
0.5 mg/kg
What is the onset of Atracurium?
Slow onset time 110 seconds, not suitable for RSI
What population is Atracurium suitable in?
Elimination independent of liver and kidney function so suitable for use in critically ill patients.
What are the two main options for analgesia?
Fentanyl and Morphine
What is Fentanyl?
Synthetic morphine, potent agonist at mu opioid receptor
What is the potency of fentanyl?
100 x more potent than morphine, short acting
What dose of morphine is given at induction?
1-3 ug/kg often given at induction before IV induction agent
What function aside from analgisia does Fentanyl have?
Reduced response to laryngoscopy
What are the downsides to fentanyl?
Metabolised in the liver Bradycardia and low BP common Can cause respiratory depression N&V post-op Urinary retention Constipation and itching Chest wall rigidity
When are fentanyl and morphine usually used?
Fentanyl for induction (5m before)
Morphine during the operation
What is morphine?
Naturally occurring opiate
What is the potency and onset of morphine?
Less potent, slower onset than fentanyl
What are the downsides to morphine?
Metabolism occurs in the liver May reduce BP and HR Respiratory depression N&V post op Urinary retention Constipation Itching Histamine release - asthmatic bronchospasm
