Ketamine (Sub-anaesthetic — Orthopaedic Pain)

How it works

It non-competitively antagonises NMDA glutamate receptors, attenuating central pain sensitisation and wind-up; at sub-anaesthetic doses it provides analgesia without full anaesthesia.

Prescribing in practice

• Administer in a setting with appropriate monitoring because of psychotomimetic effects (dissociation, hallucinations), and use cautiously in uncontrolled hypertension, raised intracranial pressure and ischaemic heart disease as it raises blood pressure and heart rate.
• It can cause emergence reactions, nausea and increased secretions; caution in those with a history of psychosis.
• Effects may be additive with other CNS depressants and opioids; reserve initiation and titration to clinicians experienced in its use.

Monitoring

Monitor blood pressure, heart rate, conscious level and for dissociative or psychotomimetic effects during administration.

Counselling the patient

• You may feel detached, dreamy or experience odd sensations while it is given.
• Tell staff if you feel distressed, nauseated or unwell during treatment.
• It is used to improve pain control and reduce reliance on strong opioids.

Evidence & guidelines

Guidance on acute pain supports low-dose ketamine as an opioid-sparing analgesic adjunct in severe or refractory pain within monitored settings.