Anaesthetics – Pharmacology and Mechanisms Flashcards
What is the definition of anaesthesia?
Provision of insensibility to pain during surgical, obstetric, therapeutic and diagnostic procedures
How do local anaesthetics work?
Block generation and conduction of nerve impulses at local contact site
Consciousness is maintained
EC- uncharged LA, becomes charged binds to voltage gated Na channels, prevent action potentials being generated
Give three examples of local anaesthetics
Lignocaine
Bupivacaine
Ropivacaine
What are three clinical uses of LA
Topical- nasal mucosa and wound margins
Infiltration- vicinity of peripheral nerve endings and nerve trunks in dental practice
Regional- IV injection leading to numbing of a larger area of the body in labour/childbirth
How do general anaesthetics work?
Alter central neural processing
Readily reversible loss of consciousness with decreased response to painful stimuli and muscle tone
Divided into inhalation and intravenous anaesthetics
What are the three main stages of anaesthesia?
Induction- inhalation or IV
Maintenance- volatile agents
Recovery- monitor to assure recovery
List and describe the 4 detailed stages of anaesthesia?
- Analgesia- Reflexes present, higher cortical function lost, smell and pain lost at the end, conscious not lost- just blurred thoughts
- Excitement- Increased muscle tone, vomiting, Temperature control lost, a-rhythm of EEG desynchronised, respiration reduced, irregular. Cortical inhibitory centres depressed
- Surgical- slow synchronised EEG rhythm, reflexes lost, pupils dilated, medullary centres depressed, regular slow breathing
- Medullary paralysis- lost of resp, EEG waves- small, lost–DEATH
List the main types of inhalation GA
Gas- nitrous oxide
Volatile- Halothane, enflurane, isoflurane, sevoflurane, desflurane
List the main types of IV GA
Inducing agents- thiopental, propofol
Benzodiazepines
Dissasociative- ketamine
What are the 6 features of an ideal inhalation anaesthetic
Odorless Anti emetic, analgesic, muscle relaxant Not degraded by light Minimal resp depression and cardio effects Excreted completely by resp system Not metabolised, no active metabolites
What determines the potency of inhalation anaesthetics?
Minimum alveolar concentration
Dose that prevents movement to surgical stimulus in 50% of pts
low MAC- high potency
What is the route of an inhalation anaesthetic?
Inhaled→alveoli→brain by partial pressure
Steady state dependenn of partial pressure of alveoli, blood and brain
1. Equilibrium between gas in FRC and anaesthetic
2. Uptake and distribution- blood gas partition coefficient dependent
3. Cardiac output- high- travels to peripheral tissue, slower uptake to brain
Alveolar to venous partial pressure gradient
4. Distribution to brain- brain highly perfused, rapidly achieves steady state with anaesthetic in blood
5. Elimination and recovery, NO exits faster than halothane
What is the route of an IV anaesthetic?
Once enters bs, some binds to plasma proteins/free
Venous-systemic-cerebral circulation
Partial pressure gradient
Unbound, lipid soluble, unionised molecules cross BBB the quickest
Outline the main features of Propofol (IV)
Not analgesic
+ Excitatory phenomena- yawn, hiccups,
Antiemetic effects post recovery
Outline the main features of Thiopental (IV)
Similar to propofol, rapid acting- 1 min
Cause apnea, cough, chest wall spasm, laryngospasm, bronchospasm
