The benefits of analgesic constant rate infusions (CRIs) include providing effective, constant analgesia and avoiding the peaks and troughs seen with intramuscular techniques. The dose can be quickly altered based on patient needs, and CRIs can reduce the requirement for volatile anesthetics and allow better cardiovascular maintenance during general anesthesia. Controlled dosing at a distance prevents most patient interference, allowing for rest and recuperation.

Disadvantages can include increased set-up time and larger required drug volumes, potentially increasing cost and risk for profound bradycardia and respiratory depression. Infusion pumps or syringe drivers for accurate dosing and skilled and trained personnel for constant monitoring add further cost. Many drugs used for CRI are not licensed for use in animals and are controlled substances (eg, morphine, fentanyl, lidocaine, ketamine). A combination of morphine, lidocaine, and ketamine is often used as a CRI in dogs.

Transdermal analgesia, a different technique, relies on drugs with low molecular weight, high lipid solubility, and high potency (eg, fentanyl, buprenorphine). Practitioners should try newer analgesic techniques, starting with low doses and titrating up to provide optimal analgesia.
 
Commentary
The report provided a clinically relevant review on analgesic CRIs, recipes for combining drug CRIs in clinics with limited equipment, and tables with doses and regimens.

There is, however, some anecdotal information interchanged with referred literature; for instance, the article referred to the “cytoprotective” effect of systemic lidocaine infusion, suggesting this as a therapeutic option for disseminated intravascular coagulation (DIC) and systemic inflammatory response syndrome (SIRS). However, little evidence suggests that lidocaine has any effect to delay or correct DIC/SIRS. Although lidocaine can reduce spontaneous action potential (a main cause of neuropathic or chronic pain) and is useful as a minimum alveolar concentration–sparing drug, its cytoprotective effect needs further evaluation.
 
The article is a quick reference with practical (and important) information, but some fact checking is needed.—Andre C. Shih, DVM, DACVA
 
Source
Analgesic constant rate infusions in dogs and cats. Bromley N. IN PRACT 34:512-516, 2012.

Related Article: Pain Management: Constant-Rate Infusion by Dr. Alonso G. P. Guedes