Intravenous Anaesthetic Agents

Question 1

Name the slower-acting agents

Answer 1

Benzodiazepines
Neuroleptic anaesthetics
Large dose opioids

Question 2

Advantages of intravenous induction?

Answer 2

Rapid onset
Smooth induction, with rapid transfer through stage 2
Pleasant for the patient
Pollution free

Question 3

Disadvantages of intravenous induction

Answer 3

Venepuncture required
Overdose easy
No removal of drug via lungs (once in its in) recovering requires redistribution, metabolism and excretion
Sudden loss of normal protective mechanism and often apnoea

Question 4

Name the Rapidly-acting induction agents

Answer 4

Propofol
Thiopentone
Etomidate
Ketamine

Question 5

Mechanism of action if intravenous induction agents?

Answer 5

Modulates y-aminobutyric acid (GABA), neuronal transmission, interfering with transmembrane electrical activity.

Ketamine is a opioid receptor agonist and antagonises the NMDA receptor

Question 6

What does TIVA stand for?

Answer 6

Total intravenous anaesthetia

Question 7

What’s does TIVA entail?

Answer 7

No inhalation all agents are used during induction or maintenance of GA

Question 8

What does patient still require even with TIVA?

Answer 8

Mixture of air/ N2O and oxygen to be delivered via the breathing circuit.

Question 9

What two agents can be used for TIVA?

Answer 9

Propofol and ketamine

Question 10

How is TIVA administered?

Answer 10

With a syringe at a steady, set rate, to avoid overdose or awareness

Question 11

At what flow rate is TIVA syringe pumps made?

Answer 11

Very low flow rates

Question 12

What do most TIVA’s contain?

Answer 12

A library of frequently used drugs and their usual concentrations

Question 13

What is the simple regime of Propofol TIVA? What is is called?

Answer 13

Initial bolus of 1mg kg-1 follows by an
Infusion of 10mg kg hr for 10mins
                   8mg kg hr for 10mins
                   6mg kg hr thereafter 
The 10-8-6 regimen

Question 14

What is the TIVA Propofol regime in kids?

Answer 14

15-13-11mg kg hr

Question 15

What is the target plasma concentration (Cp)?

Answer 15

3ug ml

Question 16

What is TCI?

Answer 16

Target controlled infusion, an method of delivering TIVA

Question 17

What does a TCI do?

Answer 17

It’s uses a microprocessor controller syringe pump to automatically and variably control the rate of infusion of a drug to attain a defined target level in the plasma or effect site

Question 18

Physical properties of Propofol?

Answer 18

Insoluble in water. Current pre 1% (10mg ml).

Fat emulsion may act as culture medium therefore must be used in 6 hours after opening available in 20ml, 50ml, 100ml

Also 2% (20mg ml) for infusions

Highly lipophilic engraving ability to cross blood brain barrier

Pain on injection (30-40%)

Question 19

Uses of Propofol?

Answer 19

Induction, maintenance or sedation (ICU sedation, regional A, cardioversion)

Question 20

Pharmacodynamics of Propofol

Answer 20

Induction: 1.5-2.5mg kg adults, 2.5-3mg kg in kids

Maintenance: TIVA (6-12mg kg hr) reduce in combination with N2O and or opioid
Plasma concentration for TCI: induction 4-8ugml and maintenance 3-6ugml

Sedation: 1.5-3mg kg hr and Cp 0.1- 2.5ug ml

Question 21

Physical properties of sodium thiopentone

Answer 21

Yellow, amorphous powder, can be dissolved in water or normal saline. It is a barbiturate. Aqueous solution is strongly alkaline pH 10,5, must not be mixed with low pH solutions such as glucose containing fluids–> will cause precipitation of free barbituric acid (also when mixed with mm relaxants (weak bases with higher pH)

Question 22

What is the preferred strength of sodium thiopentone?

Answer 22

2,5% (mix 500mg amp with 20ml= 25mg ml) stable for 24-48hrs

Question 23

Pharmacodynamics of sodium thiopentone?

Answer 23

3-5mg kg in adults and kids 5-6mg mg

Question 24

Is thiopentone used for maintenance and why?

Answer 24

No, because of long elimination half-life with accumulation

Question 25

What happens with intravasculature injection of thiopentone?

Answer 25

Precipitation of solid crystals blocking arterioles and capillaries. Causes intense spasm and thrombosis. Early signs: white hand with cyanosed fingers, skin discoloration and slow onset anesthesia Late sign: ulcers, blisters, oedema and gangrene

Question 26

Treatment of inter-arterial injection of thiopentone?

Answer 26

1- prevention 2- 2,5% solution with test dose 3- treat spasm- leave cannula in artery and inject: Papaverine 40-80mg in 10-20ml saline Procaine 10-20ml of 0,5% solution Phenoxybenzamine 0,5mg 4- brachial plexus or stellar ganglion block: sympathetic block for vasodilation 5- treat thrombosis with heparin bolus 5 000iu 6- analgesia

Question 27

Contraindications to thiopentone?

Answer 27

Absolute: porphyria, known allergy Relative: CVS (HF, hypovol, fixed CO, asthma

Question 28

Etomidate physical properties?

Answer 28

Imidazole In 10ml ampoules with 2mg ml dissolved in water with 35% propylene glycol. pH= 8,1z Can be diluted with 10ml saline or water to make a 1mg ml solution Pain on injection in 25-50%

Question 29

How do you reduce the pain on injection of Etomidate?

Answer 29

Fast injection Use of large vein Addition of 10-20mg of lignocaine

Question 30

What is the induction dose of Etomidate?

Answer 30

0,2-0,3mg kg

Question 31

Physical properties of ketamine?

Answer 31

``` Acidic solution Can use as IV, IM, oral Available as 1% (10mgml), 10% (100mgml) Stable in solution and log shelf life Non-irritant ```

Question 32

Why do you get protracted emergence in ketamine induction?

Answer 32

50-60% still remains in body on active form after surgical anaesthesia terminated. Main metabolite is norketamine, with weak hypnotic properties

Question 33

Pharmacodynamics of ketamine?

Answer 33

Induction: IV: 1-2mg kg (onset 30-60secs, last 5-15mins) IM: 5-10mg kg onset 3-8min lasts 10-30mins Maintenance: IV: 0,5mg kg, as incremental boluses or 1-4mg kg hr by infusion Analgesia: IV: 0,2-0,4mg kg IM: 2-4mg kg Infusion of 0,2-0,3mg kg hr

Question 34

Indications for Ketamine?

Answer 34

Poor risk surgical patients Pediatric surgery Debridement, painful dressings and skin-grafts in patients suffering from burns Short procedures Analgesia Anaesthesia in sub-optimal conditions (trauma, rural) Treat status asthmaticus

Question 35

Contraindications of ketamine?

Answer 35

``` CVS disorders- hypertension, IHD, AA, heart failure Raised ICP, cerebral aneurysm Open eye surgery, increased intraoccular pressure Psychiatric patients Epileptics Thyrotoxicosis Oral cavity or airway surgery Early pregnancy Tricyclic antidepressants ```

Question 36

Why can you give midazolam as an infusion?

Answer 36

It has a high clearance, and a short elimination half-life, therefore shorter duration of action and accumulation is less likely to occur

Question 37

Indications for Flumazenil?

Answer 37

Termination of GA induced and maintained on benzo Reversal of benzo sedation in short diagnosis and therapeutic procedure Reversal of benzo OD Diagnosis of unconsciousness of unknown origin