Constant Rate Infusions

Constant rate infusions (CRIs) are an incredibly useful addition to any analgesia plan but can be something that lots of nurses and vets struggle with and can feel a little overwhelmed by. They require calculations and monitoring so can be forgotten about or underutilised as there is a little extra work involved, but once you get the hang of them, they aren't so scary!

A CRI can hugely improve a painful anaesthetic as well as help create a much smoother and pain-free recovery for the patients. Often when using a CRI during an anaesthetic, the analgesia can help to reduce the anaesthetic requirement and therefore they can help to save on costs within practices as well as reduce carbon footprints from the anaesthetic gases.

This page has some general information on CRIs and you can find an interactive CRI calculator here to get doses for your patient.

Ketamine

Ketamine is a potent analgesic drug with some anaesthetic properties. It is classed as a NMDA antagonist and works really well as a rescue analgesia during painful procedures.

Works effectively for patients with chronic pain
Care in recovery as can cause dysphoria (especially in felines "triples" when sedative is reversed soon after ketamine administration)
Avoid in patients with shock as it can cause hypotension
Extended use can cause cumulative build-up in patients, so care with long-term use
Can cause respiratory depression and apnoea if given rapidly

Loading dose of 0.5mg/kg IM or slow IV

CRI of 10-30ug/kg/min during anaesthesia.

Post operative, reduce to 2ug-10ug/kg/min

Fentanyl

Fentanyl is a very potent μ-opioid receptor agonist that works very well for controlling intra-operative pain. It has a rapid onset of action, making it a very effective rescue analgesic.

It works within 1-2 minutes of adminstration and has a half-life of around 10 minutes.
Short term, repeated boluses (max 5ug/kg) can be given q20min.
It can cause apnoea so IPPV is often required
May cause bradycardia so use of anticholinergics such as atropine or glycopyrollate may be needed alongside

Loading dose of 2.5ug-10ug/kg slow IV

CRI of 2.5ug-10ug/kg/hr during anaesthesia.

Post operative, reduce to 1ug-5ug/kg/hr

Disclaimer:

The information on this website is for reference and education, and any medications and doses should be prescribed by your veterinary surgeon before giving. All patients should be assessed individually and treated as such.