Intra- and Post-Operative Ketamine Use

Andrew W. Gorlin, Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine

Ketamine is an NMDA antagonist which, when administered intravenously at sub-anesthetic doses (≤0.3mg/kg bolus or ≤0.3mg/kg/hr infusion), provides analgesia and has a significant opioid sparing effect in the perioperative setting.  There is also evidence that ketamine is useful in treating acute pain in patients who are opioid tolerant.  Sub-anesthetic infusions of ketamine can be safely administered on standard medical-surgical units.

Perioperative indications for ketamine infusion:

• Very painful procedures
• Intractable opioid-resistant pain
• Highly opioid tolerant patients
• Clinical need to minimize opioids
• High risk for persistent post-surgical pain (eg amputation, thoracotomy, etc)

Ketamine Pros:

• Non-opioid analgesic which reduces perioperative opioid consumption
• At sub-anesthetic doses has minimal hemodynamic effects
• At sub-anesthetic doses has no effect on respiratory drive or airway patency

Ketamine Cons:

• Low-moderate incidence (7-16%) of psychomimetic effects such as hallucinations and dysphoria
• Low incidence of diplopia (4-9%)
• Especially when administered in combination with other CNS depressants may contribute to sedation

Ketamine contraindications

• History of psychosis
• Unstable cardiovascular disease
• Liver or renal failure

How to administer ketamine:

Intraoperatively: Anesthesia team can give single bolus with induction and/or serial boluses (every 30-60 minutes) in the operating room (initial 0.3mg/kg and then subsequent 0.1-0.3mg/kg boluses every 30-60 minutes)

• Post-operative infusion requires coordination with the OR, PACU, med-surg unit
  • Ketamine is a controlled substance and should be prepared in a secure storage system (such as a PCA cartridge) by pharmacy and administered by an infusion pump
  • Dose should be ≤0.3mg/kg/hr based on Ideal Body Weight; a good starting point for most patients is 10mg/hr
  • A separate IV is preferable though it can be safely “piggy-backed” onto another line as long as it is on a distal port (ie, close to the patient)
  • Side effects can be managed on a case by case basis but typically hallucinations and other complains will stop within an hour of stopping the infusion
  • Use of benzodiazepines to reduce psychomimetic effects is controversial and may cause more problems with sedation and delirium
  • AZ Board of Nursing required EKG monitoring for the duration of infusion, based on an “increase in scope” of nursing practice.