Can ketamine be used as anesthesia for Total Knee Replacement (TKR)?

Can Ketamine Be Used as Anesthesia for Total Knee Replacement?

Ketamine should not be used as the sole anesthetic agent for total knee replacement, but it is highly effective and recommended as an adjuvant to general or spinal anesthesia to reduce postoperative pain and opioid consumption. 1, 2

Primary Anesthetic Approach for TKR

The evidence-based standard for TKR anesthesia consists of either:

• General anesthesia combined with femoral nerve block, OR 1, 2
• Spinal anesthesia with local anesthetic plus spinal morphine 1, 2

Ketamine alone is insufficient because it does not provide adequate skeletal muscle relaxation required for major orthopedic surgery like TKR. 3

Ketamine as an Effective Adjuvant

Evidence for Adjunctive Use

High-quality evidence demonstrates that intraoperative ketamine significantly reduces postoperative opioid consumption and pain scores when used as an adjuvant. 4

Specific benefits include:

• Reduced morphine consumption: Studies show 24-48 hour morphine use decreased by approximately 35% (45 mg vs 69 mg) when ketamine was added to multimodal analgesia 5
• Lower pain scores: VAS scores were significantly reduced at 6,12,24, and 48 hours postoperatively 6
• Faster rehabilitation: Patients reached 90 degrees of active knee flexion more rapidly (7 days vs 12 days) 5
• Reduced postoperative nausea and vomiting: Relative risk of 0.68 (95% CI 0.50-0.92) 4

Recommended Dosing Protocol

When using ketamine as an adjuvant in TKR:

• Intraoperative bolus: 0.5 mg/kg followed by continuous infusion of 3 μg/kg/min during surgery 5
• Postoperative infusion: 1.5 μg/kg/min for 48 hours, or alternatively 6 μg/kg/min intraoperatively only 7, 5
• Low-dose approach: Continuous infusion reduces pain without increasing side effects 7

Critical Safety Considerations

Use Caution in Elderly Patients

Ketamine should be used with extreme caution in elderly TKR patients due to significant risk of postoperative confusion and delirium. 1, 8

• The typical TKR patient population is elderly with multiple comorbidities 1
• Postoperative confusion is particularly problematic in this demographic 1, 8
• Consider avoiding ketamine entirely in patients with pre-existing cognitive impairment 8

Contraindications

Do not use ketamine in patients with:

• Significant hypertension or cardiovascular disease where blood pressure elevation would be hazardous 3
• Known hypersensitivity to ketamine 3
• Active psychosis or severe psychiatric conditions (relative contraindication) 3

Managing Adverse Effects

To minimize emergence reactions and confusion:

• Reduce environmental stimulation during recovery (minimize verbal, tactile, and visual stimulation) 8, 3
• Use lowest effective doses in conjunction with other analgesics 8
• Consider co-administration with benzodiazepines if emergence phenomena occur, though this may prolong sedation 8

Integration into Multimodal Analgesia

Ketamine works best as part of a comprehensive pain management strategy:

• Baseline: Paracetamol (acetaminophen) scheduled dosing 2
• NSAIDs/COX-2 inhibitors: Unless contraindicated 1, 2
• Regional anesthesia: Femoral nerve block or continuous catheter 1, 2
• Ketamine adjunct: Low-dose continuous infusion 5, 4
• Rescue opioids: IV morphine for breakthrough pain 5
• Non-pharmacologic: Cooling and compression techniques 2

Common Pitfalls to Avoid

• Do not use ketamine as monotherapy for TKR—it lacks muscle relaxation properties and does not suppress pharyngeal/laryngeal reflexes adequately 3
• Do not use high doses attempting to achieve complete anesthesia—this increases confusion risk without additional benefit 8
• Do not combine with theophylline or aminophylline—may lower seizure threshold 3
• Monitor for increased secretions when combining with other medications, particularly in patients with respiratory disease 1