title: "Ketamine"
Ketamine
Ketamine is a dissociative anaesthetic with analgesic, amnestic, and bronchodilator properties. It maintains airway reflexes and haemodynamic stability.
Mechanism of Action
- NMDA receptor antagonist - primary mechanism
- Interacts with opioid, muscarinic, and monoamine receptors
- Produces "dissociative anaesthesia" - cataleptic state with eyes open, nystagmus
Pharmacology
| Property | Value |
|---|---|
| Onset (IV) | 30-60 seconds |
| Onset (IM) | 3-4 minutes |
| Duration | 10-20 minutes |
| Metabolism | Hepatic (CYP3A4) |
| Active metabolite | Norketamine (1/3 potency) |
Indications
1. RSI Induction
- Dose: 1-2 mg/kg IV
- Ideal for: Hypotension, asthma, haemodynamic instability
- Maintains BP via sympathomimetic effects
2. Procedural Sedation
- Dose: 1-1.5 mg/kg IV or 4-5 mg/kg IM
- Excellent for: Fracture reduction, wound care, paediatrics
- Maintains airway reflexes and spontaneous ventilation
3. Analgesia
- Dose: 0.1-0.3 mg/kg IV (sub-dissociative)
- Useful adjunct to opioids
- Reduces opioid requirements
4. Bronchospasm
- Bronchodilator properties
- Consider in severe asthma unresponsive to standard therapy
Dosing Summary
| Indication | Route | Dose |
|---|---|---|
| RSI induction | IV | 1-2 mg/kg |
| Procedural sedation | IV | 1-1.5 mg/kg |
| Procedural sedation | IM | 4-5 mg/kg |
| Analgesia | IV | 0.1-0.3 mg/kg |
| Infusion | IV | 0.1-0.5 mg/kg/hr |
Advantages
Clinical Pearl
Ketamine is the induction agent of choice in:
- Hypotension/shock (maintains BP)
- Severe asthma (bronchodilator)
- Burns (analgesic + haemodynamic stability)
- Maintains spontaneous ventilation
- Preserves airway reflexes (not absolute protection)
- Bronchodilation
- Sympathomimetic (↑ HR, ↑ BP)
- Potent analgesia
- Amnestic
Adverse Effects
| Effect | Notes |
|---|---|
| Emergence phenomena | Vivid dreams, hallucinations, dysphoria (20-30%) |
| Hypersalivation | Consider glycopyrrolate/atropine |
| ↑ ICP | Traditional concern, likely not clinically significant |
| ↑ IOP | Avoid in penetrating eye injury |
| Nausea/vomiting | Less than other agents |
| Laryngospasm | Rare, maintain gentle airway support |
Clinical Pearl
Benzodiazepines (midazolam 0.05 mg/kg) can reduce emergence phenomena but may prolong recovery. Routinely used in some centres.
Source: Therapeutic Guidelines (eTG) Acute Pain / local procedural sedation guideline.
Contraindications (Relative)
- Uncontrolled hypertension
- Pre-eclampsia/eclampsia
- Ischaemic heart disease (↑ myocardial O₂ demand)
- Psychosis (may exacerbate)
- Previous adverse reaction
Test Your Knowledge
SBAmediumwikiketamine
28y
BP
85/50↓
Press 1-4 to answer • Sign in for personalized questions & progress tracking