What is the recommended dose for a ketamine (intravenous anesthetic) bolus when initiating ketamine infusion therapy in a patient with potential acute or chronic pain, depression, or anxiety, considering their past medical history, including substance abuse, psychiatric conditions, or cardiovascular disease?

Ketamine Bolus Dosing for Infusion Initiation

For adult patients initiating ketamine infusion therapy, administer an intravenous bolus of 0.5 mg/kg over 60 seconds, followed immediately by a continuous infusion of 0.1-0.2 mg/kg/hr (or 1-2 μg/kg/min), with a maximum infusion rate of 0.5 mg/kg/hr. 1, 2

Standard Dosing Protocol

Initial Bolus Administration

• Administer 0.5 mg/kg IV over 60 seconds to avoid respiratory depression and enhanced vasopressor response 1
• For pediatric patients, use the same 0.5 mg/kg bolus dose 3
• The 100 mg/mL concentration must be diluted 1:1 with sterile water, normal saline, or 5% dextrose before IV administration 1

Continuous Infusion Following Bolus

• Start infusion at 0.1-0.2 mg/kg/hr (equivalent to 1-2 μg/kg/min) immediately after the bolus 2, 3
• Maximum infusion rate: 0.4-0.5 mg/kg/hr 3, 2
• For ICU pain management, the American Society of Health-System Pharmacists recommends 0.5-2 mg/kg/hr (maximum 100 mg/hour) 2

Context-Specific Dosing Modifications

Patients with Cardiovascular Compromise or Shock

• Use the same 0.5 mg/kg bolus but start at the lower infusion range (0.1 mg/kg/hr or 1 μg/kg/min) and titrate carefully 4
• Ketamine maintains cardiovascular stability through NMDA blockade and preserved adrenal function, making it superior to propofol or dexmedetomidine in shock states 2, 4
• However, ketamine can suppress myocardial contractility in patients with depleted catecholamine reserves, requiring cautious dosing 4

Patients with Psychiatric History or Substance Abuse

• Maintain standard 0.5 mg/kg bolus dosing as ketamine represents a superior alternative to opioids in patients with addiction risk 2
• Co-administer a benzodiazepine to minimize psychotomimetic effects (dysphoria, nightmares, hallucinations) 2, 5
• Continuous cardiac monitoring and pulse oximetry are mandatory 2, 5

Perioperative Pain Management

• Administer 0.5 mg/kg bolus after induction of anesthesia (not before) to prevent psychodysleptic effects 2
• Follow with infusion of 0.1-0.2 mg/kg/hr intraoperatively 3
• Discontinue infusion 30 minutes before end of surgery and administer a longer-acting opioid to prevent analgesic gap 2
• Do not continue ketamine postoperatively as this increases hallucination risk without significantly improving analgesia 2

Critical Safety Considerations

Absolute Contraindications

• Uncontrolled cardiovascular disease 2, 5
• Pregnancy 2, 5
• Active psychosis 5
• Severe liver dysfunction 5
• High intracranial or ocular pressure 5

Monitoring Requirements

• Continuous cardiac monitoring and pulse oximetry during administration 2, 5
• Regular assessment of sedation level, respiratory status, and hemodynamics 2, 5
• Emergency airway equipment must be immediately available 1
• Practitioners must be able to rescue patients from unintended deep sedation 5

Common Pitfalls to Avoid

• Never administer the 100 mg/mL concentration IV without proper dilution 1
• Avoid rapid bolus administration (<60 seconds) as this causes respiratory depression and enhanced vasopressor response 1
• Do not use in patients who have not followed NPO guidelines due to aspiration risk despite preserved airway reflexes 1
• Administer an antisialagogue prior to induction to manage salivation 1

Alternative Dosing for Specific Indications

Depression/Suicidality (Off-Label)

• Single dose: 0.5 mg/kg IV over 40 minutes 3, 6, 7
• Some patients respond to doses as low as 0.1 mg/kg, while others require up to 0.75 mg/kg 6
• Repeat dosing: typically 2-3 times per week for acute treatment 3

Emergency Department Acute Pain

• Lower dose protocol: 15 mg IV bolus followed by 20 mg/hr infusion for 1 hour 8
• Alternative: 0.3 mg/kg IV over 15 minutes for subdissociative analgesia 2

Breakthrough Pain in PACU

• 0.5 mg/kg IV titrated to effect (no infusion required for single-dose breakthrough management) 3

Expected Outcomes

The 0.5 mg/kg bolus followed by infusion reduces overall opioid requirements by approximately 22 mg morphine equivalents without increasing side effects in patients with acute moderate-to-severe pain 2. This opioid-sparing effect reduces postoperative respiratory impairment and agitation in recovery 2.