Intravenous Anaesthetic Agents

Question 1

What do IV induction agents do?

Answer 1

They induce loss of consciousness when injected at the start of general anaesthetic.

Question 2

Do IV induction agents allow rapid recovery?

Answer 2

Yes. They allow rapid recovery from unconsciousness as they are rapidly redistributed. Some could be given intermittently or by infusion for maintenance of anaesthesia.

Question 3

General pharmacology of Intravenous anaesthetic agents. What are there general classification?

Answer 3

Either rapid loss of consciousness in one arm-brain circulation time +- 30 seconds and those with a slower onset.

Question 4

Which drugs are true induction agents?

Answer 4

The rapidly acting agents: Propofol, Thiopentone, Ethomidate, Ketamine.

Question 5

Acronym for rapidly acting induction agents?

Answer 5

KEPT: Patients are KEPT induced faster. Ketamine, Ethomiidate, Propofol, Thiopentone.

Question 6

Acronym for slower acting agents?

Answer 6

Benzo-pams
Neuro-dols
Opioids-morphine-nyl/nil

Question 7

What are the advantages of intravenous induction?

Answer 7

1. Rapid onset
2. Smooth muscle induction
3. More pleasant for pt
4. Pollution free
   (fast, smooth m, pleasant, no smoke.. how sex should be)

Question 8

What isn’t so nice about IV induction?

Answer 8

1. Venepuncture required
2. Overdose is easy
3. No removal of drugs (compared to inhalation drugs via the lungs) Once its in its in > recovery requires metabolism, redistribution and excretion.
4. Sudden loss of normal protective mechanisms and often apnoea.
   (the negative of sex: you need to insert something.. may be sore, you could get too much of it, once you get pregnant there’s no way of stopping it have to wait for metabolism and retrisbution and when you climax your protective mechanisms are gone and you can stop breathing.)

Question 9

Sooo how does IV induction agents work?

Answer 9

Not completely understood but just remember GABA GABA. GABA = inhibitory neurotransmitter.
However> Ketamine is an opioid receptor antagonist (NMDA receptor)

Question 10

What are the pharmacokinetics of IV agents?

Answer 10

induction starts to end as the agent is resdistributed from the brain to less perfused tissues. i.e rapid awakening is NOT due to metabolism or excretion of the drug.

Question 11

Why is it not okay to drive after IV induction?

Answer 11

Because subclinical levels of the drug still persists in the brain. so wait 24-48 hours before operating heavy machinery/ making decisions.

Question 12

Metabolism and excretion of IV agents?

Answer 12

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

Question 13

What is TIVA?

Answer 13

Total Intravenous Anaesthesia. No inhalation agents are used during induction or maintenance.

Question 14

What is TCI?

Answer 14

Target controlled Infusion. A microprocessor-controlled syringe pump automatically and variably controls the rate of infusion of a drug to attain the anaesthetic-defined target level in the plasma or an effect site.

Question 15

Propofol = most common IV induction
Describe Propofol. (Physical properties, PK, PD, Organ effects, recommendations)
Key words: 10mg/ml; fatty, rapid emergence, younger pts require more, older patients require less.

Answer 15

Physical properties: insoluble in water, fatty (use within 6hrs of opening otherwise culture medium eew), Ampoule sizes 20ml, 50ml, 100ml (each contain 10mg/ml Propofol)
PK: Unique therefore: good for induction, maintenance and sedation. highly fat soluble.
PD: Induction: children: 2.5-3mg/kg. adults: 1,5 - 2.5 mg/kg. old: 1-1.5mg/kg
Maintenance: TIVA: 6-12mg/kg/hr. Used wiyh N20 and opiods> reduce.
TCI: inductio 4-8ug/ml & maintenance 3-6ug/ml
Sedation: 1.5 mg/kg/hr
Organ effects: CNS:
Recommendations:

Question 16

Sodium thiopentone (STP):

Answer 16

Physical properties: yellow, amorphous powder
PD: adults 3-5 mg/kg children: 5-6mg/kg (-) elderly
Organ effects: CNS: smooth LOC 30 sec (+) anti-convulsant, brain protection. CVS:

Question 17

Etomidate

Answer 17

Physical properties: 10 ml ampoules containing 2mg/ml dissolved in water.
PK: recovery 6-8min. Repeated doses are not cumulative, not used in infusion > adrenal cortical depression
PD: Induction: 0.2 - 0.3 mg/kg
Organ effects: CNS: rapid onset,
CVS: very stable

Question 18

Ketamine

Answer 18

Physical properties: Multi-use vial (use clean vial) Dose dependant on route. Acidic solution suitable for IV, IM and oral admin. 1% (10mg/ml) and 10% (100mg/ml)
PK: when surgical anaesthesia
PD: Induction: 1-2mg/kg IV. Onset 30-60 sec. Lasts 5-15 min. Maintenance: 0.5 mg/kg IV as incremental boluses or 1-4 mg/kg/hr
Organ effects: CNS:
CVS:
Resp:
GIT
Uterus:
Indications: Poor risk surgical patients, paediatric surgery

Question 19

Benzodiazepines:
Diazepam: Insoluble in water. Original preparation contains 5mg/ml
Midazolam: Water soluble, exhibits a pH dependent ring-opening phenomenon.

Answer 19

PK: Diazepam poorly absorbed when administered intra-muscular but rapidly absorbed after oral admission.
Midazolam: rapidly absorbed after oral and IM administration.
PD: Pre-med Diazepam 0.1-0.2 mg/kg orally (1-2hrs pre-op); Induction: 0.1-0.6mg/kg IV
Midazolam 7.5 -15 mg orally in adults; 0.5mg/kg (max 7.5 mg) in children; Induction: 0.1-0.3mg/kg; Sedation: 0.1mg/kg.
Organ effects: CNS:
CVS
Resp:
GIT:
Uterus:

Question 20

Flumazenil (Anexate) = benzodiazepine antagonist which specifically blocks the central effects by competitive inhibition at the benzodiazepine receptor.
What are the indications and PK?
{Benzo can be bad as he lams a lot so to stop the lamming we give him the Flu from his ma zen nil lamming takes place}

Answer 20

Indications: Termination of general anaesthesia induced and maintained with bezo’s, Reversal of benzo sedation in short procedures, reversal of benzo overdose, Diagnostic measure in unconscious of unknown origin.
PK: IV onset of action = rapid (within 5 mins) but the duration of effect is relatively short about 1-3.5 hours.
0.2mg IV after 60 sec a 2nd dose of 0.1mg may be injected and repeated every 60 sec up to a dose of 1mg.

Question 21

Practical points in using IV induction agents? (Titration techniques? , dosing children vs adults, what influences rapidity of onset?,
Which induction agent has the rapidist recovery (from rapid to slowest)

Answer 21

1. Titrate induction agents to effect, except in rapid sequence inductions.
2. Doses per kg are generally higher for children and lower for elderly and neonates
3. Rapidity of onset determines on nature of drug, speed of injection, central Vd and cardiac output
4. assuming that equivalent doses of the IV agents are given, time to recovery from most rapid to slowest: propofol, etomidate, thiopentone, midazolam, ketamine and diazepam. PET MKD