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Ketamine is a phencyclidine derivative which acts as a dissociative anaesthetic agent with analgesic properties. Sub anaesthetic doses of ketamine, given as low dose infusion prevent central sensitisation associated with the development of chronic pain, reduce post operative opioid requirements and hyperalgesia. Low dose ketamine thus provides safe and effective analgesia, usually as part of a multi-modal approach. Evidence suggests use of ketamine reduces pain scores across different patient groups with a lower requirement for post operative opioids.
Ketamine is a non competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, therefore reducing the action of the excitatory neurotransmitter glutamate in the central nervous system. Evidence from a growing number of trials suggests that ketamine attenuates the “wind-up” phenomenon in early post operative patients, associated with a reduction in the development of chronic pain as well as reducing overall post operative opioid requirements. Post operative nausea and vomiting is generally reduced with ketamine treatment, partly due to the reduction in opioid requirements and partly due to NMDA receptor antagonism. Studies show the greatest reduction in opioid requirements in patients undergoing orthopaedic (both limb and spine), intra-abdominal or lower abdominal surgeries. Ketamine is not efficacious in patients undergoing dental or head and neck surgery.
A 2010 Cochrane Review of perioperative ketamine in acute postoperative pain concluded that in sub anaesthetic dose ketamine:
Respiratory depression is minimal with ketamine but clinical use is limited due to its potential to cause hallucinations and dissociative mental state. Although uncommon these side effects generally limit the use of ketamine to patients who’s pain is likely to be difficult to manage with opioids alone. Ketamine has no role in surgery known to produce only mild pain.
Ketamine prescriptions should only be made following consultation with the acute pain service or the on call anaesthetist out of hours. The infusion should be prepared by two nurses with adequate training and knowledge of infusion pumps. Other prescribed analgesics should continue as prescribed following review by the anaesthetic team. The requirement for ketamine infusion should be reviewed daily by the parent team with input from the acute pain service/on call anaesthetist. Ketamine should be considered for short term use only and require anaesthetic consultant review if exceeding 72 hours.
Ketamine is safe for use in asthmatic patients but care should be taken in patients treated with theophylline due to known drug interactions.
Ketamine has known interactions with
An Asena syringe driver with lock box should be obtained. Use a luer lock 50ml syringe attached to an anti siphon line (which must be labelled as per NHS Highland guidelines) and a dedicated IV cannula. Standard aseptic precautions should be deployed.
A new drug syringe should be prepared and discarded every 24 hours. Ketamine should be prepared to a concentration of 5mg/ml using these instructions:
Loading doses are not recommended.
Ketamine undergoes renal excretion however there is no requirement for dose adjustment in patients with renal dysfunction in the dose ranges suggested in this guideline.
Paracetamol and NSAIDS should be continued unless specifically contraindicated.
Concurrent prescription of adequate antiemetics should be available prior to starting the infusion to ameliorate any side effects.
A dedicated ketamine prescription chart must be used and can be obtained from the acute pain team or the intranet. The prescription is not valid unless signed by the treating anaesthetist or acute pain service.
Ketamine infusions should ideally be commenced before 2pm allowing for close monitoring for side effects and toxicity within day time working hours.
Side effects are minimal at the initial dosages in this guideline but may limit usage at higher doses. These include:
If the patient develops disturbing hallucinations or other concerning symptoms the infusion should be stopped and the acute pain service or on call anaesthetist out of hours should be notified urgently.
Respiratory depression and hypotension are not typical features of ketamine however consider the use of naloxone in compromised patients with concurrent opioid treatment.
|Monitoring parameter||1st hour||During dose titration||Thereafter|
|Respiratory Rate and Oxygen Saturations||15 mins||Half Hourly||Hourly|
|Blood Pressure||15 mins||Half Hourly||Hourly|
|Heart rate||15 mins||Half Hourly||Hourly|
|Pain Score||15 mins||Half Hourly||Hourly|
|Sedation Score||15 mins||Half Hourly||Hourly|
|Dysphoria and hallucinations||15 mins||Half Hourly||Hourly|
Patients should be nursed in a critical care environment such as an HDU or ICU only. Ketamine infusions are not suitable for ward level care. Patients may be mobilised with care.
Patients should have supplemental oxygen prescribed for the duration of the infusion. Increasing oxygen requirements should prompt medical review with particular focus on assessment for concurrent opioid toxicity.
Hypotension is unusual with ketamine due to its positive inotropic effects. Persistent hypotension should prompt urgent medical review and consideration of other potential causes eg sepsis, acute coronary syndromes, haemorrhage/ hypotension, post operative complications.
Respiratory depression is not a typical feature of ketamine however any respiratory depression should prompt an increase in monitoring of vital signs and urgent medical review. In the event of respiratory compromise the on call ward doctor should be contacted immediately if the respiratory rate drops below 9/minute and the infusion should be stopped. Administer high flow oxygen via a reservoir mask. If in doubt summon emergency help by calling 2222.
Naloxone has NO effect on ketamine however should be considered in any patient with significant respiratory depression or excessive sedation who is receiving concurrent opioids.
In the event of suspected opioid toxicity with resulting respiratory depression, respiratory rate of 8 or less and difficult to rouse, observe the following actions:
In the event of excessive sedation with ketamine alone WITHOUT respiratory compromise:
Nausea and vomiting should be treated with regular antiemetics with escalation to the anaesthetic team as detailed below.
Guidance for escalation to the acute pain service / on call anaesthetist in the event of:
Patients treated with ketamine infusion should be reviewed at least daily by the acute pain service or on call anaesthetist out of hours. Discontinuation of the infusion will be guided by clinical response under the direction of the acute pain service/on call anaesthetist. Infusions lasting more than 72 hours require are by anaesthetic consultant discretion only following patient review.
Last reviewed: 30 November 2018
Next review: 30 November 2020
Author(s): Acute pain team
Approved By: TAM Subgroup of ADTC
Reviewer Name(s): Acute Pain Nurse Specialists