Chapter 10: Pain Medicine 2026

Published: 24/04/2026

10.7 Low dose ketamine for the management of acute complex pain

Dr Gillian Chumbley, Dr Nicola Stranix

Why do this Quality Improvement Project?

Most patients respond well to conventional pain relief; however, patients who have complex needs may experience an increased incidence of moderate or severe pain in the first 24-48 hours after surgery, putting them at high risk of developing persistent post-surgical pain (PPSP) 1,2,3. This quality improvement project will support the introduction of ketamine for the management of complex pain after surgery. 

Background

Five systematic reviews support the use of ketamine for the management of pain after surgery .4,5,6,7,8 Low-dose ketamine is used to safely manage pain in complex patients and works by blocking the NMDA receptor, antagonising the effects of the excitatory neurotransmitter glutamate.   Ketamine also reduces opioid consumption. The main role of ketamine is seen as an adjuvant in the treatment of pain associated with central sensitisation, such as severe acute pain, acute neuropathic pain and opioid resistant pain.9 

Patients should receive a trial of intravenous (IV) ketamine to establish whether they have an activated NMDA receptor.  If the NMDA receptor is active, pain can be controlled in a matter of minutes by doing the trial.  Ketamine treatment can then be continued by IV, SC or oral route. 

Best practice

  • Hospital Trusts should have an evidence-based guideline for the use of ketamine to rescue patients with uncontrolled, complex post-operative pain.
  • Ketamine should only be started by the anaesthetic team or pain service.
  • An intravenous trial of ketamine should be performed to establish a positive response and to manage severe pain in a timely fashion.
  • Ketamine can be given safely in wards trained to manage patient-controlled analgesia. No additional monitoring is required.
  • Ketamine can be discontinued once opioid consumption has reduced; weaning is not necessary but is often preferred by the patient.
  • Ketamine must be discontinued prior to discharge. 

Suggested data to collect 

  1. Indications for starting ketamine
    • Neuropathic pain, including phantom limb pain
    • Patient with hyperalgesia or allodynia
    • Patients who respond poorly to opioids
    • Patients with a history of high opioid consumption preceding injury or surgery
  2. Trial data
    • Pain score prior to starting the trial
    • Pain score at the end of the trial
    • Loading dose required in IV trial
    • Whether the trial was successful in reducing functional pain scores to the level aimed for
    • Any adverse effect experienced by the patient during the trial
    • The amount of analgesia in oral morphine equivalents (OME) consumed in the 24 hours prior to starting the trial
  3. Starting dose of oral or IV ketamine
  4. Final dose of oral ketamine prior to stopping
  5. Whether the dose needs to be titrated
  6. Number of days taking ketamine
  7. Opioid analgesia in oral morphine equivalent for the previous 24 hours, when the ketamine was stopped
  8. Any adverse effects of taking ketamine in the post-operative phase
  9. Whether the patient needed to start a gabapentinoid

QI methodology

  • Gather stakeholders. These should include members of the acute pain service, anaesthetic department, and you should also consider including surgical teams, ward teams, recovery staff, nursing management, pharmacy representation, and local quality improvement support.  Consider the use of a stakeholder matrix.
  • Consider process mapping the areas being worked on for improvement, for example, if patients are not being identified as struggling with pain postoperatively, identify the reasons for this and work with the inpatient pain team and anaesthetists to understand what changes need to be made in the current system. Consider exploring barriers to introducing low-dose ketamine for post-operative pain by interviewing the staff groups that may be involved.
  • Consider creating a driver diagram to build a view of potential areas influencing the process and changes that could be made to influence the system from a wide set of areas. Areas that may need to be addressed include: reviewing or writing local evidence-based guidance; establishing procurement and stocking of necessary equipment and drug formulations, and the education and training of all staff groups involved.
  • Use Plan-Do-Study-Act cycles, reflecting with the multidisciplinary team (MDT), to monitor progress and how changes are impacting the system.  Potential areas to assess are:
    • Outcome measures such as numerical pain scores, functional assessment scores and oral morphine equivalent, patient satisfaction.
    • Process measures such as policy adherence and appropriate indications for undergoing trial of ketamine therapy.
    • Balancing measurement, such as monitoring of potential ketamine side effects such as dissociation, hypertension and sedation.

Use run or statistical process control charts to monitor quantitative data over time, to understand the impact of changes, and whether the change is sustained. Triangulate this with qualitative metrics such as staff and patient feedback.

References 

1.Macrae WA. Chronic pain after surgery. Br J Anaesth 2001; 87(1): 88-98.

2.Crombie IK, Davies HT, Macrae WA. Cut and thrust: antecedent surgery and trauma among patients attending a chronic pain clinic. Pain 1998; 76(1-2): 167-71.

3.Kehlet H, Jensen TS, Woolf CJ.  Persistent postsurgical pain: risk factors and prevention. Lancet 2006; 367(9522): 1618-25.

4.McCartney CJ, Sinha A, Katz J.  A qualitative systematic review of the role of N-methyl-D-aspartate receptor antagonists in preventive analgesia. Anesth Analg 2004; 98(5): 1385-400.

5.Subramaniam K, Subramaniam B, Steinbrook RA.  Ketamine as adjuvant analgesic to opioids: a quantitative and qualitative systematic review. Anesth Analg 2004; 99(2): 482-95.

6.Laskowski K, Stirling A, McKay WP, Lim HJ.  A systematic review of intravenous ketamine for postoperative analgesia.  Can J Anaesth 2011; 58:911-923.

7.Jouguelet-Lacoste J, La Colla L, Schilling D, Chelly JE.  The use of intravenous infusion or single dose of low-dose ketamine for postoperative analgesia: A review of the current literature.  Pain Med 2015; 16:383-403.

8.Brinck EC, Tiippana E, Heesen M., Bell RF, Straube S, Moore RA, et al. Perioperative intravenous ketamine for acute postoperative pain in adults.  Cochrane Database Syst Rev. 2018 Dec 20;12(12):CD012033. doi: 10.1002/14651858.CD012033.pub4. PMID: 30570761 [accessed July 2025]

9.Schug SA, Palmer GM, Scott DA, Alcock M, Halliwell R, Mott JF. APM:SE Working Group of the Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine (2020), Acute Pain Management: Scientific Evidence (5th edition), ANZCA & FPM, Melbourne. https://www.anzca.edu.au/resources/college-publications/acute-pain-management/apmse5.pdf [accessed July 2025].