Continuous Rate Infusions (CRI)
Oral surgery in canine and feline patients often requires extended periods of anesthesia necessitating optimal anesthetic
management. A safe and effective mode of pain management for the oral surgery patient is intravenous continuous rate infusion
utilizing a multimodal approach to affect various levels of the nociceptive pathway.
The administration of opiates in various veterinary species has been studied and has been shown to be both safe and effective
in decreasing MAC.1,2,3 Lidocainea acts to decrease central hypersensitivity in significant pain states and when given with opiates has a sparing effect on
those agents.4 In a recent study dogs undergoing limb amputation that received ketamineb infusions had significantly lower pain scores 12 and 18 hours after surgery and were significantly more active on postoperative
day 3 than dogs that did not.5 Furthermore the combination of morphinec , lidocainea and ketamineb delivered as a low dose CRI provides significant decreases in required isoflurane MAC in dogs.6 No adverse hemodynamic effects were experienced. Medetomidined has been used as a CRI in veterinary patients however a recent study warned of adverse hemodynamic effects of this drug
when used in this manner noting that further investigation needs to be done before its use is advocated.7
IV FLUID BAG BASED CRI INFUSIONS
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Detailed spreadsheets are available for calculation of rates, volumes and loading doses for CRI in dogs and cats utilizing
morphinec , lidocainea and ketamineb (Table 1) (1) (2). Weight/volume calculations for commonly used analgesics are particularly convenient resources and can
be found at the Veterinary Anesthesia Support Group website.(2)
Drug CRI Dose Range
MORPHINE - 0.12 to 0.36 mg/kg/hr (2 to 6 ug/kg/min).
LIDOCAINE - 0.6 to 1.5 mg/kg/hr (10 to 25 ug/kg/minute).
Dogs can be given a max. dose of 3.0 mg/kg/hr (50 mcg/kg/min)
Cats should be limited to a max. dose of 1.5 mg/kg/hr (25 mcg/kg/min)
KETAMINE - 0.12 to 1.2 mg/kg/hr (2 to 20 ug/kg/minute).
Loading Doses
MORPHINE - 0.5 mg/kg IM (or very slowly IV)
At 0.5 mg/kg this patients needs a loading dose of: 0.17 ml
LIDOCAINE - 0.5 to 1 mg/kg IV
At 0.25 mg/kg this patients needs a loading dose of: 0.06 ml
At 1.0 mg/kg this patients needs a loading dose of: 0.25 ml
CATS - Limit cats to 0.25 mg/kg loading dose
DOGS - 1.0 mg/kg is the normal loading dose
KETAMINE - 0.25 to 0.50 mg/kg IV bolus
At 0.25 mg/kg this patients needs a loading dose of: 0.01 ml
Drug Concentrations
MORPHINE - 15 mg/ml
LIDOCAINE - 20 mg/ml
KETAMINE - 100 mg/ml
