Flashcards in IV Agents Deck (56):
1
What are the rapidly acting IV-induction agents?
Propofol
Sodium Thiopentone
Etomidate
Ketamine
2
What are the slower-acting IV inducting agents?
Benzodiazepines (e.g. diazepam, midazolam)
Neuroleptics (e.g. droperidol)
Large-dose opioids (e.g. fentanyl)
3
Advantages of IV induction?
1. Rapid onset of action
2. Smooth induction with rapid transfer through stage II
3. More pleasant for patient
4. "Pollution" free
4
Disadvantages of IV induction?
1. Venepuncture required
2. Easy to overdose
3. No removal of drugs via the lungs (once its in, its in)
4. Sudden loss of normal protective mechanisms and often apnoea
5
MoA of IV induction agents (excluding Ketamine)?
Not fully understood.
Modulate GABA (inhibitory NT) neuronal transmission, thereby interfering with transmembrane electrical activity.
6
MoA of Ketamine?
An opioid receptor agonist
Antagonises NMDA receptor
7
Metabolism and excretion of IV induction agents?
These lipid-soluble drugs are metabolised in the liver to inactive water-soluble metabolites, then excreted in urine.
8
TIVA stands for?
Total Intravenous Anaesthesia
9
The 2 drugs used for TIVA?
Propofol
Ketamine
10
TCI stands for?
Target Controlled Infusion
11
Indications for TIVA?
Risk of hyperthermia
Severe PONV
Day-case surgery
12
TIVA dosing with Propofol?
Initial bolus: 1mg/kg
Infusion:
10mg/kg/hr (10 minutes)
8mg/kg/hr (10minutes)
6mg/kg/hr thereafter
("10-8-6" regimen)
13
Physical properties of Propofol?
1% propofol preparation (10 mg/kg) in a fat emulsion
Fat emulsion can act as a culture medium
Ampoule should be used within 6 hours of opening
Also available as 2% solution for infusion
Often stings on insertion
14
Pharmacokinetics of Propofol?
Clearance > hepatic flow
Highly fat soluble and sequesters in fat following long infusions
Rapid decrease in Propofol concentration upon stopping of infusion (regardless of infusion duration)
15
Dosing of Propofol for induction?
Adults: 1,5-2,5 mg/kg
Infants and young children: 2,5-3,0 mg/kg
Elderly: less than adult
16
Dosing of Propofol for sedation?
1,5-3,0 mg/kg/hr
17
CNS effects of Propofol?
Rapid LOC and rapid recovery
Minimal impairment of psychomotor function
Less hangover effect than other agents
Low incidence of excitatory phenomena
No antanalgesia
Antipruritic
18
CVS effects of Propofol?
Less compensatory tachycardia than other agents
Reduced SVR (systemic vascular resistance)
Greater hypotensive effect than other agents
19
Respiratory effects of Propofol?
Respiratory depression
High incidence apnoea
Depressed laryngeal reflexes (good for LMA insertion)
No histamine release (safe in asthmatics)
20
GIT effects of Propofol?
Anti-emetic properties
21
Metabolic effects of Propofol?
PRIS (Propofol infusion syndrome)
22
Characteristics of PRIS?
Rare
Lipemia, metabolic acidosis, CMO, CF, skeletal myopathy and death
Doses of 5 mg/kg/hr >48 hours
23
Indications for Propofol?
Induction agent of choice for porphyria
Good agent for asthmatics (no histamine release)
Suited for day-case anesthetics
24
Contraindications for Propofol?
Heart failure
Hypovolaemia
Fixed CO (aortic stenosis/ mitral stenosis/HOCM)
(Caution in the elderly)
25
Physical properties of Sodium Thiopentone?
Barbiturate (anti-convulsant)]
Yellow, amorphous powder that can be dissolved in H20/saline
Alkaline solution (pH 10,5)
Must not be mixed with low pH solutions (i.e. glucose, muscle relaxants) as barbiturates will precipitate
Stinky
Mix 500 mg ampoule with 20 ml saline = 25 mg/ml (2,5%)
Solution stable for 24-48 hours
26
Dosing of Thiopentone?
Adults: 3-5 mg/kg
Children: 5-6 mg/kg
27
CNS effects of Thiopentone?
Smooth LOC (within 30s)
Recovery 5-10min
Small doses may cause antanalgesia
Good anti-convulsant
Used in treatment of status epilepticus (brain protection: decreased cerebral metabolic rate of O2 consumption and decreased ICP)
28
CVS effects of Thiopentone?
↓ CO 10-20% (peripheral vaso-dilatation, negative inotropic effect, ↓ central catecholamine release)
Exaggerated in CF, hypovolaemia, fixed CO etc.
29
Respiratory effects of Thiopentone?
POTENT depression of respiratory centre
Laryngeal reflexes NOT depressed until deep (early instrumentation may result in laryngospasm)
Histamine release (not suited for asthmatics)
30
Local effects of Thiopentone?
Extreme irritant to local tissues (beware extra-vascular and intra-arterial injections)
31
Prevention and treatment of an intra-arterial injection of Thiopentone?
Prevent:
Avoid veins next to known arteries
2,5% (NOT 5%) and test dose
Treat spasm:
Leave cannula in artery and inject Papaverine 40-80mg in 10-20ml saline
Sympathetic block (vasodilates)
Anti-coagulation (thrombus)
Analgesia
32
Absolute and relative contraindications to Thiopentone?
Absolute:
Porphyria
Known allergy to Thiopentone
Relative:
CF
Hypovolaemia
Fixed CO
Asthma
33
Physical properties of Etomidate?
Imidazole derivative
pH 8,1 (alkaline)
1 ml ampoules with 2 mg/ml of drug dissolved in water with 35% propylene glycol
May be mixed with saline or water to make 1 mg/ml solution
Also available in fat emulsion (not to be confused with propofol)
Burns on insertion
34
Dosing of Etomidate?
0,2-0,3 mg/kg
35
CNS effects of Etomidate?
Rapid onset
Rapid recovery (6-8min)
High incidence of involuntary movement and myoclonus
36
CVS effects of Etomidate?
Very stable
May cause marked bradycardia with synthetic opioids and suxamethonium
37
Respiratory effects of Etomidate?
Little respiratory depression
No histamine release
38
GIT effects of Etomidate?
High incidence of PONV (“vomidate”)
Anti-emetic recommended
39
Endocrine effects of Etomidate?
Inhibits cortisol and aldosterone synthesis in the adrenal cortex (one dose suppresses adrenal function 5-8h)
40
Physical properties of Ketamine?
Acidic solution
Suitable for IV, IM or oral
1% and 10% solutions available
Stable in solution
Long shelf life
41
Pharmacokinetics of Ketamine?
When surgical anaesthesia terminated, 50-60% drug still remains in body in active form
Main metabolite has weak hypnotic properties
(Causes complete analgesia with superficial sleep)
42
Dosing of Ketamine?
Induction:
IV: 1-2mg/kg (onset 30-60s, lasts 5-15min)
IM: 5-10mg/kg (onset 3-8min, lasts 10-30min)
Maintenance: 0,5mg/kg IV (incremental boluses) OR 1-4mg/kg/hr (infusion)
Analgesia: 0,2-0,4mg/kg IV/2-4mg/kg IM, followed by infusion of 0,2-0,2mg/kg/hr
43
CNS effects of Ketamine?
IV induction 90s
Complete analgesia and amnesia
Involuntary movements not uncommon
Increases ICP and intra-ocular pressure
Psychic reactions during recovery (can be reduced by concurrent administration of benzodiazepines or opioids)
44
CVS effects of Ketamine?
Sympathomimetic effect ↑HR ↑BP ↑CO
Direct stimulation of central catecholamine release
A direct myocardial depressant that may be unmasked if catecholamine stores are depleted
45
Respiratory effects of Ketamine?
Minimal respiratory depression
Pharyngeal reflexes preserved and good airway control (do not need to instrument)
Bronchodilation
No histamine release
Increased bronchial and salivary secretions (administration of a drying agent recommended)
46
GIT effects of Ketamine?
PONV relatively common
47
Uterine effects of Ketamine?
May cause uterine contractions in first trimester
48
Indications for Ketamine?
Poor risk surgical patients
Paediatric surgery
Burns patients
Short procedures
Analgesia
Anaesthesia in sub-optimal conditions (“field work”)
Treatment of status asthmaticus
49
Contraindications for Ketamine?
CVS disorders
Raised ICP
Cerebral aneurysms
Open eye injuries
Increased intraocular pressure
Psyche patients
Epileptics
Thyrotoxicosis
Full stomach
Early pregnancy
Tricylclic antidepressants
50
Pharmacokinetics of Midazolam?
Rapidly absorbed after oral or IM administration
Metabolites have little clinical significance
High clearance
Short elimination half-life
Accumulation less likely to occur than Diazepam, and may be administered as a continuous infusion
51
Dosing of Midazolam?
Premed (30-60 min pre-op): 7,5-15,0 mg orally
Induction: 0,1-0,3 mg/kg IV
52
CNS effects of benzodiazepines?
Slower induction
Good anterograde amnesia
Low incidence of excitatory phenomena
Anticonvulsant
Disorientation after a prolonged period in the elderly
53
CVS effects of benzodiazepines?
Stable
Slight fall in BP
Small transient increased HR
54
What is Flumazenil?
Benzodiazepine antagonist
55
Indications for Flumazenil?
Termination of GA induced/maintained with benzo's
Reversal of benzo sedation
Reversal of benzo OD
Diagnostic measure in unconsciousness of unknown origin
56