Ketamine for Anesthesia

 

Ketamine for Anesthesia Summary

Ketamine is used as a dissociative anesthetic for various medical and surgical procedures. Usually it is used for short-term procedures that don't require full muscle relaxation. It is also sometimes used as an initiator before other agents are introduced. Due to its effectiveness and safety profile it is also a common choice for any anesthesia involving children. What makes Ketamine unique is that it affects the N-methyl-D-aspartate (NMDA) receptor instead of GABA receptors. This means Ketamine preserves airway reflexes and respiratory function, increases heart rate and blood pressure, while providing strong pain relief by disrupting pain signal transmission in the central nervous system.

1) Mechanism of Action

Primary mechanism: Noncompetitive antagonism of NMDA (N-methyl-D-aspartate) glutamate receptors in the CNS.

  • Dissociative anesthesia (patient appears awake but is disconnected from surroundings)
  • Analgesia
  • Amnesia
  • Sympathomimetic stimulation

Similar to other anesthetics, ketamine tends to preserve airway reflexes and spontaneous breathing.

2) Key Clinical Properties

Dissociative anesthesia

  • Cataleptic state with open eyes
  • Nystagmus
  • Often preserved airway reflexes
  • Profound analgesia and amnesia

Cardiovascular effects

  • Sympathetic stimulation creates increased heart rate
  • Increased blood pressure
  • Increased cardiac output

This is helpful for patients who are hemodynamically unstable.

Respiratory effects

  • Minimal respiratory depression
  • Bronchodilation
  • Helps preserve airway reflexes
  • Useful in asthma and emergency airway situations.

3) Common Clinical Uses in Anesthesia

Procedural sedation

  • Emergency department procedures
  • Fracture reduction
  • Laceration repair
  • Burn dressing changes

Induction of anesthesia

  • Rapid sequence induction (RSI), especially in trauma, hypotension, shock

Pediatric anesthesia

  • Common use in pediatrics
  • Emergence reactions tend to be less frequent in children
  • Provides sedation and analgesia together

Adjunct analgesia

  • Low-dose intraoperative ketamine can reduce opioid requirements
  • May help prevent opioid-induced hyperalgesia

4) Advantages Compared With Other Anesthetics

  • Maintains airway reflexes
  • Minimal respiratory depression
  • Strong analgesia
  • Useful in hypotension/trauma
  • Bronchodilator (beneficial in severe asthma)

5) Important Adverse Effects

Emergence phenomena

  • Hallucinations
  • Vivid dreams
  • Delirium
  • Agitation

These effects are often reduced with a benzodiazepine.

Other adverse effects

  • Hypertension
  • Tachycardia
  • Increased intracranial pressure (historically debated)
  • Increased intraocular pressure
  • Hypersalivation
  • Nausea/vomiting

6) Situations Where Ketamine Is Especially Useful

  • Hemodynamic instability
  • Severe asthma
  • Trauma
  • Hypovolemia
  • Need for rapid analgesia and sedation

7) Situations Where Caution Is Needed

  • Severe coronary artery disease
  • Uncontrolled hypertension
  • Psychosis
  • Elevated intracranial pressure