Ketamine (Perioperative — Opioid-Sparing Analgesia)

How it works

It is principally an NMDA-receptor antagonist; blockade of these receptors reduces central sensitisation and opioid-induced hyperalgesia, providing analgesia distinct from opioid pathways.

Prescribing in practice

• Use under protocols in a monitored environment, as ketamine can cause psychotomimetic effects, raise blood pressure and heart rate, and should be used cautiously in uncontrolled hypertension, raised intracranial pressure or significant cardiac disease.
• Reserve low-dose analgesic regimens for appropriate cases (major or opioid-tolerant surgery) and prescribe as part of a multimodal plan rather than as sole analgesia.
• Avoid or use cautiously where there is a history of psychosis; emergence reactions can be mitigated by concurrent benzodiazepine and a calm recovery environment.

Monitoring

Monitor conscious level, blood pressure, heart rate and for dissociative or psychotomimetic effects during infusion, with pain scores to titrate the opioid-sparing benefit.

Counselling the patient

• Explain a low-dose infusion may be used to improve pain control and reduce the amount of strong opioid needed.
• Mention that vivid dreams or a floating sensation can occur and to tell staff if these are distressing.

Evidence & guidelines

Low-dose perioperative ketamine for opioid-sparing analgesia is supported by consensus guidelines and trial evidence in major and opioid-tolerant surgery, used off the anaesthetic licence under specialist protocols.