What is the recommended dose of ketamine (intravenous anesthetic) for general anesthesia?

Ketamine Dosing for General Anesthesia

For general anesthesia, ketamine should be administered intravenously at an initial dose of 1-4.5 mg/kg (average 2 mg/kg) for induction, followed by maintenance doses of 0.5 mg/kg as needed or a continuous infusion of 0.1-0.5 mg/minute. 1

Induction Dosing

Intravenous Route (Preferred for General Anesthesia)

• Initial dose: 1-4.5 mg/kg IV
• Average effective dose: 2 mg/kg IV (produces 5-10 minutes of surgical anesthesia)
• Administration technique: Administer slowly over 60 seconds to prevent respiratory depression and enhanced vasopressor response
• Alternative administration: Can be given as an IV infusion at 0.5 mg/kg/min for induction 1

Intramuscular Route (Alternative)

• Initial dose: 6.5-13 mg/kg IM
• Average effective dose: 9-13 mg/kg IM
• Onset: Surgical anesthesia within 3-4 minutes
• Duration: Anesthetic effect typically lasts 12-25 minutes 1

Maintenance of Anesthesia

Intermittent Bolus Method

• Repeat increments of one-half to full induction dose as needed 1

Continuous Infusion Method

• Rate: 0.1-0.5 mg/minute via microdrip infusion technique
• Alternative dosing: 0.125-0.25 mg/kg/h continuous infusion 2
• Maximum dose: 0.5 mg/kg/h 2
• Timing: Stop infusion 30 minutes before the end of surgery 2

Special Considerations

Specific Indications for Low-Dose Ketamine

Ketamine at lower doses is specifically recommended for:

1. Surgery with high risk of acute or chronic postoperative pain
2. Patients with vulnerability to pain (particularly those taking long-term opioids or with opioid addiction) 2

Preparation for Administration

• For IV induction: The 100 mg/mL concentration must be diluted with an equal volume of either:
  • Sterile Water for injection
  • 0.9% Sodium Chloride Injection (Normal Saline)
  • 5% Dextrose in Water 1
• For maintenance infusion: Dilute to create a 1 mg/mL solution by adding 10 mL from a 50 mg/mL vial (or 5 mL from a 100 mg/mL vial) to 500 mL of 5% Dextrose or Normal Saline 1

Adjunctive Medications

• Administer a benzodiazepine to prevent neuropsychological manifestations during emergence 1
• Consider an antisialagogue prior to induction to manage ketamine-induced salivation 1

Safety Considerations

Cardiovascular Effects

• Ketamine causes significant cardiovascular stimulation with increases in:
  • Heart rate (average increase of 22±14 bpm)
  • Systolic blood pressure (average increase of 15±11 mmHg)
  • Diastolic blood pressure (average increase of 19±15 mmHg)
  • Mean arterial pressure (average increase of 12±10 mmHg) 3
• Use with caution in patients with hypertension or coronary artery disease 4

Monitoring Requirements

• Continuous ECG and pulse oximetry
• Regular non-invasive blood pressure (every 5 minutes during initial infusion and for first 15 minutes thereafter)
• Emergency airway equipment must be immediately available 1

Contraindications and Precautions

• Avoid in patients who have not followed nil per os guidelines due to risk of aspiration
• Use caution when combining with epinephrine as serious tachyarrhythmias may occur 5
• Monitor for genitourinary pain in patients with history of chronic ketamine use 1

Practical Administration Tips

• Purposeless and tonic-clonic movements may occur during ketamine anesthesia but do not indicate a light plane of anesthesia or need for additional doses 1
• When used as part of balanced anesthesia with other agents, ketamine doses can be reduced 1
• Ketamine can be safely combined with concurrent administration of ketamine for difficult-to-manage pain 2

By following these dosing guidelines and safety precautions, ketamine can provide effective general anesthesia while minimizing potential adverse effects.