Module 3b: specific IV anaesthetic agents Flashcards
Give 4 characteristics of propofol?
- 2,6 di-isopropylphenol
- NOT soluble in water-> prepared as emulsion (soya bean oil, egg yolk + glycerol)
- Problems with fat emulsion
- Multiple ampoule sizes: 20ml, 50ml, 100ml OR 1% or 2%
What is the pharmacokinetics of propofol?
extremely lipid soluble
crosses BBB easily
extra hepatic metabolism->rapid plasma clearance->rapid emergence
Versatile agent: induction, maintenance, sedation at lower doses
What are the induction dose for adults, elderly and children in propofol
Adults: 2-2.5mg/kg
Elderly: 1-1.5mg/kg
Children: 2.5-3mg/kg
CNS effects of propofol?
Rapid LOC + recovery
less hangover effect
no excitatory effects
slight analgesic effect
CVS effects of propofol?
dose dependent CVS depression
decreased systemic vasc resistance
Decreased BP
Slight increase in HR
Respiratory effects of propofol?
dose-dependent depression
apnoea on induction close to 100%
inhibits laryngeal reflexes
NO histamine release
Other effects of propofol?
anti-emetic (used in PONV)
What is porpofol infusion syndrome (PRIS)
prolonged high dose infusion which presents with lipaemia, metabolic acidosis and myopathy
In which patients should you be careful with giving propofol?
Elderly
Cardiac failure
hypovolaemia
Fixed cardiac output: AS/MS, HOCM
In what scenario would propofol be ideal?
TIVA Total intravenous anesthesia (TIVA)
Conscious sedation
asthma
porphyria
hx of PONV
hx of malignant hyperthermia
Give the physical properties of thiopentone?
yellow powder(mix with H2O or N/saline)
pH 10.5->precipitates with acides
Strength 2.5% (25mg/ml)
Solution stable 24-48hrs
What is the dosage of thiopentone in adults, children and elderly?
Adults: 3-5mg/kg
Children: 5-6 mg/kg
Elderly: caution
CNS effects of thiopentone?
LOC in 30 sec (used in rapid sequence induction)
Smooth, no reflex movements/coughing
Antanalgesic-> lowers pain threshold
Anti-convulsant
Neuroprotectove: decreased CMRO2 +ICP
CVS effects of thiopentone?
Decreased CO (10-20%) by:
Vasodilation, negative inotropy, decreased central catecholamine release
Compensatory increase in HR
Respiratory effects of thiopentone?
dose-dependent apnoea
no depression of laryngeal reflexes
histamine release
Other effects of thiopentone
irritant to tissues: venous thrombosis with older 5% solutions
Intra-arterial injection precipataes solid crystals-> acute ischemia of limb
What are the contraindication of thiopentone?
Absolute: porphyria, known allergy
Relative: asthma, CVS instability(cardiac failure, fixed CO, hypovoloaemia)
Give the physical properties of etomidate?
10ml ampoules (2mg/ml=20mg in ampoule)
Clear solution with propylene glycol
Opaque with emulsion
What is the dosage in etomidate
0.2-0.3mg/kg (adult 16-20mg)
Pharmacokinetics of etomidate?
rapid recovery: 6-8 min
Repeated doses NOT cumulative
True or false: etomidate can be used for induction only
True: it causes adrenocortical suppression in infused
Etomidate effects on CNS?
rapid LOC
Myoclonus and involuntary movements
Etomidate effects on CVS?
most stable: little change in BP/HR
Etomidate effects of resp?
minimal resp depression, NO HISTAMINE RELEASE
Etomidate effects on GIT?
PONV
Etomidate effects on endocrine
inhibition of steroid synthesis
Physical properties of ketamine
- Solutions of 1%(10mg/ml)
- long shelf half life
- no pain on injection
- NMDA receptor antagonist
4 characteristics of ketamine?
Unusual among induction agents
NMDA receptor antagonist
Causes LOC + analgesic
Given IV, IM or orally
CNS effects of ketamine?
dissociative anaesthetic
Complete analgesia
Increased ICP and IOP
Psychiatric reactions such as hallucinations
CVS effects of ketamine
central sympathetic stimulant:
- Increased HR
- Increased BP
- Increased CO
- Increased SVR
Respiratory effects of ketamine?
minimal respiratory depression
preserved pharyngeal reflexes
maintains airway
bronchodilator (sympathetic stimulation)
Increased salivation
Other considerations with ketamine
PONV
Uterine contraction in 1st trimester
drug of abuse
Indications of ketamine
Sick and unstable adults and children
Burns surgery
Debridement
Change of dressings
Short diagnostic procedures
Analgesia
Battlefield anaesthesia
Status asthmaticus
Contra indication of ketamine
CVS pathology
IHD, hypertension, AAA, CCF
↑ ICP
↑ IOP and “open eye”
Psychiatric patients
Epileptics
Thyrotoxicosis
Early pregnancy
Give the characteristics of benzodiazepines
sedative
act on GABA receptor
given as premedication and intra-operative sedation
What oral premedications form part of benzodiazepines
Lorazepam, temazepam, diazepam, midazolam
What medication forms part of IV sedation
midazolam
Give the physical properties of midazolam
5mg ampoules (1mg/ml) / 15mg ampoules (5mg/ml)
What is the dosage for midazolam
premed: 0.5mg/kg
Adults 7.5-15 mg
Children 0.25-0.5mg/kg PO
Induction: 0.1-0.3 mg/kg
Sedation 0.1mg/kg
CNS effects of midazolam
does not occur in one arm-brain circulation time (55-140sec)
anterograde amnesia
anxiolysis
sedation
CVS, resp, uterus and git effects of midazolam
CVS: stable
resp: little effect
git: low incidence of PONV
Uterus: crosses placenta casuing flopping neonate
what is flumazenil
benzodiazepine antagonist
What is the ideal drug for TIVA
propofol
What are the indications of TIVA
Risk of malignant hyperthermia
– Severe PONV in prior case
– Day-case surgery
– Cheaper than gases
