What is the recommended induction dose for ketamine (intravenous anesthetic)?

Ketamine Induction Dose

For intravenous induction of anesthesia in adults, administer ketamine at 1-4.5 mg/kg IV, with 2 mg/kg being the average dose that produces 5-10 minutes of surgical anesthesia within 30 seconds. 1

Intravenous Administration

• The FDA-approved induction dose range is 1-4.5 mg/kg IV, administered slowly over 60 seconds to avoid respiratory depression and enhanced vasopressor response 1
• The standard induction dose of 2 mg/kg IV produces surgical anesthesia within 30 seconds and lasts 5-10 minutes 1
• Rapid administration must be avoided as it increases risk of respiratory depression and exaggerated cardiovascular responses 1

Alternative Dosing Considerations

• For procedural sedation in the emergency department, lower doses of 1-1.5 mg/kg IV are often effective and may be preferable when full surgical anesthesia is not required 2
• In ASA class III and IV patients who are premedicated, the ED50 for ketamine induction is 0.9 mg/kg for loss of response to verbal commands, with an ED95 of 1.6 mg/kg 3
• For pediatric procedural sedation, 2 mg/kg IV has been shown safe and effective, producing adequate sedation within approximately 1.5 minutes 4

Intramuscular Route

• When IV access is unavailable, administer 6.5-13 mg/kg IM, with 9-13 mg/kg producing surgical anesthesia within 3-4 minutes 1
• The anesthetic effect from IM administration typically lasts 12-25 minutes 1

S-Ketamine Dosing Adjustment

• If using S-ketamine (the more potent enantiomer), reduce the dose to 0.25-0.5 mg/kg because S-ketamine has approximately four times the affinity for NMDA receptors compared to R-ketamine 5

Critical Safety Requirements

• Dilute the 100 mg/mL concentration with an equal volume of sterile water, normal saline, or 5% dextrose before IV administration 1
• Use the diluted solution immediately after preparation 1
• Continuous monitoring of vital signs (ECG, pulse oximetry, blood pressure) is mandatory throughout induction and for at least 15 minutes afterward 5, 6
• Emergency airway equipment must be immediately available, and only physicians experienced in airway management should administer ketamine 1

Cardiovascular Effects

• Ketamine increases systolic blood pressure by approximately 23 mmHg, diastolic pressure by 17 mmHg, and heart rate by 18 beats/min in ASA class III-IV patients 3
• This sympathomimetic response contrasts with the hemodynamic depression seen with thiopental or propofol 3, 7
• Avoid ketamine in patients with uncontrolled cardiovascular disease 6

Adjunctive Medications

• Administer a benzodiazepine (such as midazolam) to prevent emergence reactions and neuropsychological manifestations 1, 7
• The combination of midazolam 0.15 mg/kg with ketamine 0.75 mg/kg effectively attenuates ketamine's cardiostimulatory effects and reduces emergence dysphoria 7
• Give an antisialagogue prior to induction to manage ketamine-induced salivation 1

Common Pitfalls

• Never inject the 100 mg/mL concentration IV without dilution - this is explicitly contraindicated 1
• Avoid using ketamine in patients who have not followed NPO guidelines due to aspiration risk, despite some preservation of airway reflexes 1
• Do not confuse induction dosing with the much lower subanesthetic doses used for perioperative analgesia (0.1-0.5 mg/kg bolus) 6, 2