IV Anaesthetic Agents Flashcards
Define what are Intravenous Anaesthetic Drugs
These drugs induce anaesthesia by means of a single dose given at the beginning of anaesthesia, putting the patient “to sleep.”
IV Anaesthetic Drugs 4x
Thiopentone
Etomidate
Propofol
Ketamine
Factors Influencing Choice of Drug
Fast Induction
Safety
Porphyria
Volume of Distribution (VD)
Reliable
Histamine Release
Metabolism
Side Effects
Effects on Organs: Cardiovascular System (CVS), Brain, Respiratory System, Adrenal Glands
Airway Reflexes: Swallowing / gag reflex, Intubation / Laryngeal Mask Airway (LMA)
Mechanism of Action of Intravenous Anaesthetic Drugs
Thiopentone, Etomidate, Propofol
- Increase/stimulate GABAA receptors (main inhibitory receptors in CNS)
Ketamine
- Inhibits NMDA receptors (main stimulatory receptors in CNS)
Blood Pressure Formulas:
BP = CO x SVR
CO = HR x SV
MOA of IV Anaes drugs name all 4 drugs
- Stimulates GABA receptors inhibitory receptors in CNS
- Thiopentone
- Etomidate
- Propofol - Inhibits NMDA receptors the stimulatory receptors in CNS
- Ketamine
Thiopentone Effects
Cardiovascular: ↓CO, ↓SVR (↓ preload, ↓ afterload, ↓ contractility), ↑HR (tachycardia)
Respiratory: Dose-dependent histamine release, may trigger bronchospasm, does not suppress airway reflexes, decreases respiratory rate.
CNS: “Truth serum” (impairs cognition), good anticonvulsant, decreases brain oxygen demand (useful in brain injury patients)
Thiopentone form, dose
Form: Powder, mixed with water.
very pungent smell
Dose: 3–5 mg/kg
Thiopentone C/I
Porphyria (it is a barbiturate)
asthma (bronchospasm)
airway obstruction
severe cardiac or liver disease
Addison’s disease
severe hypotension
Thiopentone warnings
Do not inject into an arterial line (causes severe vasospasm, may require amputation).
Ensure proper IV placement (extravasation/subcutaneous injection causes tissue vasoconstriction and necrosis)
Propofol Effects
Cardiovascular: ↓BP (due to ↓contractility & ↓SVR), mild tachycardia.
Respiratory: ↓Respiratory drive, inhibits airway reflexes (drug of choice for LMA use).
Other: Anti-emetic, anxiolytic, amnesic, antipruritic, no hangover effect.
Best for porphyria patients P for Prop and Porph * :)
Propofol form dose
Form: Milky white liquid (“milk of amnesia”).
Burns on injection
Dose: 1–2.5 mg/kg (titrate to effect).
Benefits of Propofol
no hangover / accumulation, anti-emetic, anxiolytic, amnesia, antipruritic, “Viagra-in-a-vial” (due to vasodilation)
Propofol complications
Propofol Infusion Syndrome (seen in septic children, leading to metabolic acidosis, neurological issues, and cardiac arrest).
Etomidate Effects
(safest induction agent)
Cardiovascular: Stable, does not decrease contractility, minimal BP drop no tachycardia
Respiratory: No histamine release, less respiratory suppression.
Etomidate form dose
Form: Milky white liquid
(lipid emulsion with egg-yolk phospholipids, soybean oil).
Dose: 0.3 mg/kg.
Etomidate warnings
Use caution in soybean allergy.
Must be used within 6 hours after opening.
Causes adrenal gland suppression.
Etomidate S/E
nausea
vomiting
myoclonus (not epilepsy)
burning on injection (use lignocaine before injection)
adrenal gland suppression
Ketamine Effects
Dissociative anaesthetic may talk & move, but will have amnesia & can’t obey commands
o Patients may hallucinate & this can be traumatic, leading to PTSD combine with a
benzodiazepine e.g. Midazolam or Diazepam (Valium)
Cardiovascular: Increases BP, SVR, HR, CO (useful in hypotensive/shocked patients).
Neurological: Increases cerebral blood flow, intracranial pressure, intraocular pressure (avoid in intracranial disease patients).
Respiratory: Maintains functional residual capacity, bronchodilator, maintains airway reflexes but increases secretions (use anticholinergics before administration).
Because it works on NMDA receptor, it has profound analgesic properties
Dissociative anaesthetic .. patient may talk/move but has amnesia, can cause hallucinations and PTSD—use benzodiazepines to counteract this Midazolam or Diazepam (Valium)
Best for: Shocked patients, status asthmaticus, burn patients
Ketamine dose, form
Form: Water-soluble, stable, non-irritating (no burn) maintains reflexes
Dose:
- IV: 2 mg/kg (works in seconds)
- IMI: 5 mg/kg (works in minutes, only IV anaesthetic usable IMI)
- Oral/Rectal: 10 mg/kg (works in ~30 min)
Often used in ophthalmologic surgery as gas inductions can affect intraocular pressure
Best IVA in shocked patients
Ketamine
NOT Thiopentone
Best IVA in hypertrophic cardiomyopathy
Etomidate
NOT Ketamine
Best IVA in Porphyria
Propofol
NOT Thiopentone
Best IVA in asthma attack
Ketamine
NOT Thiopentone
