Induction agents Flashcards
(14 cards)
Tell me about propofol?
Propofol (2-6, di-isopropylphenol)
Phenol derivative, which is used for IV induction and maintenance of anaesthesia and sedation in theatres, ICU, pre-hospital and ED. Also for refractory status epilepticus in certain situations
Physical properties:
- white lipid emulsion with soya leitchin and egg phosphatide for stability
- stored in cupboard
- 1-2 and 2-5 for kids for IV
- pH 7 and pKa 11
PK:
A: 100
D: Vd 4L and PB of 98%
M: liver to inactive, mostly glucuronidation
E: renal excretion - 25ml/min/kg
PD:
- sedation and hypnosis
- ?GABA a potentiation and cannabinoid receptors
A: obtunds
B: increased RR, but VT down and bronchodilation
C: decreased BP and SVR via NO, reduced/normal HR, SV and contractility
D: hypnosis, anxiolysis and jerks. Reduced o2 and CBF
G: antiemetic
Other notable: green hair and urine and PRIS
Tell me about thiopentone?
Thiopentone
Barbiturate, which is used for IV induction
Physical properties:
- pale yellow powder mixed with sodium carbonate and stored under nitrogen to prevent oxidisation
- stored in cupboard
- 3-7 for IV
- solution pH 11 and pKa 7.6
PK:
A: 100
D: Vd 2.5 and PB of 80%
M: hepatic to mainly inactive (phenobarbitone = active). Zero order kinetics with infusion
E: renal excretion - 11ml/min/kg
PD:
- hypnosis
- GABA a potentiation
A: reflexes preserved
B: depression and l/b spasm
C: decreased BP and SVR, normal/increased HR, decreased SV and CO
D: hypnosis, reduced blood flow and O2
E/F: decreased UO via ADH and reduced CO
Other notable: porphyria, arterial necrosis and 1:20k anaphylaxis
Tell me about etomidate?
Etomidate
Imidazole derivative, which is used for IV induction of GA
Physical properties:
- CCS
- stored in cupboard
- 0.3mg/kg IV
- pH 8 and pKa 4
PK:
A: 100
D: Vd 3L and PB of 75%
M: hepatic and plasm esterases
E: 90% renal excretion - 19ml/min/kg
PD:
- hypnosis
- GABA a potentiation
A: normal
B: depressed, no HPV effect
C: slight decreased SVR, rest normal
D: hypnosis, movements and epiletiform. Reduced cerebral
E: inhibits steroid synthesis 11b hydroxylase
G: n&v
Other notable: painful and porphyria
Tell me about ketamine?
Ketamine
Phencyclidine derivative, which is used for IV induction of anaesthesia and sedation in theatres, ICU, pre-hospital and ED. It is also used as an adjunct for pain
Physical properties:
- CCS
- stored in cupboard (CD)
- 1-2 IV and 5-10 IM
- pH 4.5 and pKa 7.5
PK:
A: 100
D: Vd 3L and PB of 12%
M: liver to norketamine (30%) then conjugation to inactive
E: renal excretion - 18ml/min/kg
PD:
- sedation and hypnosis and analgesia via dissociative anaesthesia (strong analgesia and light sleep)
- nc nmda receptor antagonist = decreased reuptake of NA, DA and 5HT3 and maybe opioids
A: maintained
B: increased RR and bronchodilation
C: increased
D: hypnosis, amnesia and increased O2 and BF. Increased IOP. Emergence phenomena and increased tone
G: n+v and salivation
What does Thiopentone do in solution?
Weak acid but mixture forms alkali when mixed with water (high pH = bacteriostatic)
Water = enol form, at physiological pH = keto form which is lipid soluble.
Tautomerism or dynamic isomerism
How do we treat extravasation/arterial injection of thio?
E= ulcers and necrosis. Leave cannula in situ and flush to dilute. Then inject s/c hyaluronidase (enzyme which breaks down hyaluronic acid)
A= precipitation and spasm = ischaemia and thrombosis
Paperverine, lidocaine and brachial plexus block for dilation and pain and heparin for thrombosis.
Tell me about midazolam?
Midazolam
Benzodiazepine, which is occasionally used for IV induction of anaesthesia, but more commonly and sedation and anxiolysis across a broad range of settings e.g. theatres, endoscopy and palliative care. It is a BDZ so could also be used as a drug of abuse
Physical properties:
- CCS
- stored in cupboard
- used as a premed for kids in a dose of 0.5 up to 20mg, high first pass (40%) so oral only 7mg. Titrate in adults
- has a benzene and a di-azepine ring, which at pH below 4 is open and water soluble due to the NH3+ group, but it closes at pH’s over 4 I.e. physiological to become lipid soluble
- pH 4 and pKa 6
PK:
A: 100
D: Vd 1L and PB of 97%
M: liver to inactive, mostly conjugated and excreted. Small amount to oxazepam which is active
E: renal excretion - 7ml/min/kg
PD:
- sedation, anxiolysis, anterograde amnesia and hypnosis
- GABA a potentiation
A: maintained
B: increased RR, but VT down, no change in MV until big doses can cause apnoea. Blunted CO2
C: decreased SVR and increased HR
D: as above and decreased CBF etc. decreases MAC
F: decreased renal blood flow
G: decreased hepatic blood flow
How do BDZ’s work?
Modulate GABA a receptors by binding between the alpha and gamma subunits.
A1 subtype = anxiolysis in cord and cerebellum
A2 = sedative and anticonvulsant cord and cortex
Tell me about diazepam?
Benzodiazepine which can be given orally or IV for sedation, for seizure prophylaxis in alcohol withdrawal and for termination of seizures. Also a drug of abuse
Physical:
- CCS
- stored in cupboard
PK:
A: near 100% OBA
D: 1L with 99% PB
M: liver to active I.e. temazepam and oxaz
E: renal
PD:
A: normal
B: reduced RR and apnoea in high
C: transient hypotension and increased coronary artery vasodilation
D: anxiolysis, sedation, hypnosis, amnesia, anticonvulsant, addiction
Tell me about temazepam?
Benzodiazepine used for sedation and anxiolysis and a common pre-med.
Physical:
- oral or IV
cCS
20mg for pre.
PK:
A: oral BA 100%
D: Vd 1L and 75% PB
M: hepatic to mainly inactive
E: mostly urine, little faces
PD:
Potentiated GABAa
B: blunts CO2 at high
C: minimal
D: hypnosis, sedation and anxiolysis
Tell me about lorazepam?
BDZ most commonly used for termination of seizures (4mg or 0.1mg/kgin kids)
Can be given orally or IV
Highly protein bounds
Hepatic too active
Tell me about flumazenil?
Selective GABAa receptor antagonist used to competitively reverse the effects of BDZ’s. Also sometimes for post op shivering
CCS of 100mcg/ml
Give 200mcg boluses (once a min) to max of 2mg
Takes 2 min for effects and half life is 1h
Hepatic and renal
Caution in mixed OD as can antagonise anticonvulsant effects of other drugs
Tell me about dexmetomidine?
Alpha agonist with far higher selectivity for 2 over 1 (1600:1)
Used for sedative anxiolytic, hypnotic, analgesic and sympatholytic properties. Predominantly used for sedation in ICU, but also in theatres for sedation or as an adjunct to peripheral nerve block. Off label uses include prevention of delirium and treatment of alcohol withdrawal
Can cause: hypotension, brady, hypertension
Tell me about methohexital?
Barbiturate derivative used for induction of GA or sedation. Lowers seizure threshold therefore good for ECT
Physical:
- white powder with sodium carbonate 500mg vial
- cupboard
- 1-2mg/kg
PK:
A: Iv 100 also rectal with variable
D: Large VD. Rapid onset and recovery 3-7mins and full in 30mins
M: Hepatic
E: Cl higher than thio
PD: gABAa
B: apnoea in high
C: stable
D: seizure, sedation and hypnosis
G: hiccups
Other: painful on injection
