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Anaesthetics > IV Agents > Flashcards

IV Agents Flashcards

1
Q

What are the rapidly acting IV-induction agents?

A

Propofol
Sodium Thiopentone
Etomidate
Ketamine

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2
Q

What are the slower-acting IV inducting agents?

A

Benzodiazepines (e.g. diazepam, midazolam)
Neuroleptics (e.g. droperidol)
Large-dose opioids (e.g. fentanyl)

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3
Q

Advantages of IV induction?

A
  1. Rapid onset of action
  2. Smooth induction with rapid transfer through stage II
  3. More pleasant for patient
  4. “Pollution” free
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4
Q

Disadvantages of IV induction?

A
  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
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5
Q

MoA of IV induction agents (excluding Ketamine)?

A 
Not fully understood.
Modulate GABA (inhibitory NT) neuronal transmission, thereby interfering with transmembrane electrical activity.
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6
Q

MoA of Ketamine?

A

An opioid receptor agonist

Antagonises NMDA receptor

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7
Q

Metabolism and excretion of IV induction agents?

A

These lipid-soluble drugs are metabolised in the liver to inactive water-soluble metabolites, then excreted in urine.

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8
Q

TIVA stands for?

A

Total Intravenous Anaesthesia

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9
Q

The 2 drugs used for TIVA?

A

Propofol

Ketamine

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10
Q

TCI stands for?

A

Target Controlled Infusion

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11
Q

Indications for TIVA?

A

Risk of hyperthermia
Severe PONV
Day-case surgery

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12
Q

TIVA dosing with Propofol?

A 
Initial bolus: 1mg/kg
Infusion: 
10mg/kg/hr (10 minutes)
8mg/kg/hr (10minutes)
6mg/kg/hr thereafter
("10-8-6" regimen)
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13
Q

Physical properties of Propofol?

A

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

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14
Q

Pharmacokinetics of Propofol?

A

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)

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15
Q

Dosing of Propofol for induction?

A

Adults: 1,5-2,5 mg/kg
Infants and young children: 2,5-3,0 mg/kg
Elderly: less than adult

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16
Q

Dosing of Propofol for sedation?

A

1,5-3,0 mg/kg/hr

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17
Q

CNS effects of Propofol?

A 
Rapid LOC and rapid recovery
Minimal impairment of psychomotor function
Less hangover effect than other agents
Low incidence of excitatory phenomena
No antanalgesia
Antipruritic
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18
Q

CVS effects of Propofol?

A

Less compensatory tachycardia than other agents
Reduced SVR (systemic vascular resistance)
Greater hypotensive effect than other agents

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19
Q

Respiratory effects of Propofol?

A

Respiratory depression
High incidence apnoea
Depressed laryngeal reflexes (good for LMA insertion)
No histamine release (safe in asthmatics)

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20
Q

GIT effects of Propofol?

A

Anti-emetic properties

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21
Q

Metabolic effects of Propofol?

A

PRIS (Propofol infusion syndrome)

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22
Q

Characteristics of PRIS?

A

Rare
Lipemia, metabolic acidosis, CMO, CF, skeletal myopathy and death
Doses of 5 mg/kg/hr >48 hours

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23
Q

Indications for Propofol?

A

Induction agent of choice for porphyria
Good agent for asthmatics (no histamine release)
Suited for day-case anesthetics

24
Q

Contraindications for Propofol?

A

Heart failure
Hypovolaemia
Fixed CO (aortic stenosis/ mitral stenosis/HOCM)
(Caution in the elderly)

25
Q

Physical properties of Sodium Thiopentone?

A

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
Q

Dosing of Thiopentone?

A

Adults: 3-5 mg/kg
Children: 5-6 mg/kg

27
Q

CNS effects of Thiopentone?

A 
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
Q

CVS effects of Thiopentone?

A

↓ CO 10-20% (peripheral vaso-dilatation, negative inotropic effect, ↓ central catecholamine release)

Exaggerated in CF, hypovolaemia, fixed CO etc.

29
Q

Respiratory effects of Thiopentone?

A

POTENT depression of respiratory centre
Laryngeal reflexes NOT depressed until deep (early instrumentation may result in laryngospasm)
Histamine release (not suited for asthmatics)

30
Q

Local effects of Thiopentone?

A

Extreme irritant to local tissues (beware extra-vascular and intra-arterial injections)

31
Q

Prevention and treatment of an intra-arterial injection of Thiopentone?

A

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
Q

Absolute and relative contraindications to Thiopentone?

A

Absolute:
Porphyria
Known allergy to Thiopentone

Relative:
CF
Hypovolaemia
Fixed CO
Asthma
33
Q

Physical properties of Etomidate?

A

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
Q

Dosing of Etomidate?

A

0,2-0,3 mg/kg

35
Q

CNS effects of Etomidate?

A

Rapid onset
Rapid recovery (6-8min)
High incidence of involuntary movement and myoclonus

36
Q

CVS effects of Etomidate?

A

Very stable

May cause marked bradycardia with synthetic opioids and suxamethonium

37
Q

Respiratory effects of Etomidate?

A

Little respiratory depression

No histamine release

38
Q

GIT effects of Etomidate?

A

High incidence of PONV (“vomidate”)

Anti-emetic recommended

39
Q

Endocrine effects of Etomidate?

A

Inhibits cortisol and aldosterone synthesis in the adrenal cortex (one dose suppresses adrenal function 5-8h)

40
Q

Physical properties of Ketamine?

A 
Acidic solution
Suitable for IV, IM or oral
1% and 10% solutions available
Stable in solution
Long shelf life
41
Q

Pharmacokinetics of Ketamine?

A

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
Q

Dosing of Ketamine?

A

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
Q

CNS effects of Ketamine?

A 
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
Q

CVS effects of Ketamine?

A

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
Q

Respiratory effects of Ketamine?

A

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
Q

GIT effects of Ketamine?

A

PONV relatively common

47
Q

Uterine effects of Ketamine?

A

May cause uterine contractions in first trimester

48
Q

Indications for Ketamine?

A 
Poor risk surgical patients
Paediatric surgery
Burns patients
Short procedures
Analgesia
Anaesthesia in sub-optimal conditions (“field work”)
Treatment of status asthmaticus
49
Q

Contraindications for Ketamine?

A 
CVS disorders
Raised ICP
Cerebral aneurysms
Open eye injuries
Increased intraocular pressure
Psyche patients
Epileptics
Thyrotoxicosis
Full stomach
Early pregnancy
Tricylclic antidepressants
50
Q

Pharmacokinetics of Midazolam?

A

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
Q

Dosing of Midazolam?

A

Premed (30-60 min pre-op): 7,5-15,0 mg orally

Induction: 0,1-0,3 mg/kg IV

52
Q

CNS effects of benzodiazepines?

A 
Slower induction
Good anterograde amnesia
Low incidence of excitatory phenomena
Anticonvulsant
Disorientation after a prolonged period in the elderly
53
Q

CVS effects of benzodiazepines?

A

Stable
Slight fall in BP
Small transient increased HR

54
Q

What is Flumazenil?

A

Benzodiazepine antagonist

55
Q

Indications for Flumazenil?

A

Termination of GA induced/maintained with benzo’s
Reversal of benzo sedation
Reversal of benzo OD
Diagnostic measure in unconsciousness of unknown origin

56
Q

Dosing of Flumazenil?

A

0,2 mg IV

A second dose of 0,1 mg may be injected after 60s and repeated every 60s up to a total dosage of 1 mg

Anaesthetics (16 decks)

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