PH3113 - Pain and Analgesia 6 Flashcards
What are the properties of thiopentone?
Barbiturate
Sodium salt
- pale yellow powder
Formulation contains calcium carbonate
- 6% by weight
Nitrogen in place of air
Gives alkaline solution with pH 10.5
Induction dose 3 - 7 mg/kg
What effect does thiopentone have?
Cardiovascular system
- dose dependent reduction in
- cardiac output
- stroke volume
- systemic vascular resistance
- compensatory tachycardia
Central nervous system
- reduction in cerebral oxygen consumption
- reduction in cerebral blood flow
- reduction in CSF pressure
- rapid general anaesthesia lasting 5 - 10 mins
Respiratory system
- dose dependent respiratory depression
- can cause laryngospasm
- can cause bronchospasm
What effect does propofol have?
Cardiovascular disease
- dose dependent systemic vascular resistance
- drop in blood pressure
- reduction in myocardial contractility
- compensatory tachycardia rare
Central nervous system
- excitatory effects seen in 10% patients
- some patients demonstrate choreiform movements
Respiratory system
- respiratory depression leading to apnoea
- cough and laryngospasm
Pain on injection
May turn hair and urine green
Antiemetic effect
What are the properties of ketamine?
Three concentrations available
- 10 mg/ml
- 50 mg/ml
- 100 mg/ml
Water soluble
- forms acidic solution
- 3.5 - 5.5
Intravenous
- 1.2 mg/kg
Intramuscular
- 5 - 10 mg/kg
General anaesthesia and sedation
Chronic pain
What effect does ketamine have?
Cardiovascular system
- sympathetic nervous system stimulation
- increase in
- heart rate
- cardiac output
- blood pressure
Central nervous system
- dissociative anaesthesia
- analgesia
- unpleasant dreams
- hallucinations
- emergence phenomena
- increases
- cerebral blood flow
- intracranial pressure
Respiratory system
- patent airway
- bronchodilation
What are the properties of etomidate?
0.2 % solution
pH 4.1
Induction dose 0.3 mg/kg
Produces least cardiovascular system disturbance
- but
Suppression of adrenocortical function
What is the minimum alveolar concentration (MAC)?
Minimum alveolar concentration at steady state that prevents reaction to a standard surgical stimulus in 50% of patients
What is the minimum alveolar concentration influenced by?
Increasing MAC
- infancy
- hyperthermia
- hyperthyroidism
- sympathomimetics
- chronic opioid use
- chronic alcohol intake
- acute amphetamine
- hypernatraemia
Decreasing MAC
- neonates
- increased age
- pregnancy
- hypotension
- hypothermia
- hypothyroidism
- sedatives
- acute opioid use
- acute alcohol intake
- chronic amphetamine intake
- lithium
What are the ideal properties of an inhaled anaesthetic?
Physical
- not flammable
- preservative free
- stable to heat and light
- cheap
- pleasant odour
- inert when in contact with metal, rubber and soda lime
- atmospherically friendly
Biochemical
- low MAC
- high oil:gas partition coefficient
- only affects the CNS
- not metabolised
- some analgesic properties
- non-toxic
- not epileptogenic
What is the blood/gas partition coefficient?
How the anaesthetic partitions itself between these two phases at equilibrium
What is an inhaled anaesthetic uptake dictated by?
Blood/gas partition coefficient
- low blood/gas partition coefficient
- more soluble in gas
- more rapid onset/offset of anaesthesia
- high blood/gas partition coefficient
- more soluble in blood
- slower onset/offset of anaesthesia
What is the purpose of nitrous oxide?
Used alongside volatile anaesthetics and in combination with oxygen
- entonox
High MAC
Manufactured by heating ammonium nitrate to 250 degrees
Stored in blue cylinders
What effect does nitrous oxide have?
Cardiovascular system
- mild cardiac depressant
- increases sympathetic activity
Central nervous system
- increases cerebral blood flow
- high MAC but may well cause anaesthesia in certain patients
Respiratory system
- causes small fall in thoracic volume
- offset by increase in respiratory rate
What is the role of muscle relaxants?
Effectively paralyse the patient
Not always needed with a general anaesthetic
Anaesthetic reason for muscle relaxation
Surgical reason for muscle relaxation
What is the neuromuscular junction?
Point of contact between a motor neurone and a skeletal muscle cell
