Continuous Rate Infusions

Continuous Rate Infusions

Wayne E. Wingfield, MS, DVM
Chief, Emergency and Critical Care Medicine
Professor, Department of Clinical Sciences
College of Veterinary Medicine and Biomedical Sciences
Colorado State University
Fort Collins, CO 80523
(970) 221 - 4535 (W)
(970) 491 - 1275 (FAX)
wwingfie@vth.colostate.edu

A continuous rate infusion (CRI) is a precisely calculated amount of drug added to a specific volume and type of fluid. The mixture is then delivered as a continuous intravenous infusion. The efficacy of CRI drugs is increased through maintenance of steady-state concentrations of the drug.

Drugs Administered Via Continuous Rate Infusions

**Drug Formulation CRI Dosage Actions**
Diazepam	5 mg/ml	0.1 - 0.04 mg/kg/hour	Anticonvulsant, ataractic
Diltiazem	5 mg/ml	0.2 - 0.5 mg/kg/hour	Calcium channel blocker
Dobutamine	12.5 mg/ml	2 - 20 ug/kg/minute	Synthetic catecholamine, positive inotrope
Dopamine	40 mg/ml	2 - 20 ug/kg/minute	Dopaminergic, B-agonist, norepinephrine precursor
Epinephrine	1:1000	1 ug/kg/minute	Alpha and beta agonist
Fentanyl	0.05 mg/ml	1 - 5 ug/kg/hour	Narcotic analgesic
Insulin (regular)	100 U/ml	1.1 - 2.2 U/kg/day	Hormone
Isoproterenol	0.2 mg/ml	0.04 ug/kg/hour	Beta-adrenergic agonist
Ketamine	100 mg/ml	1 - 3 ug/kg/minute	Neuroleptoanalgesia
Lidocaine	20 mg/ml (2%)	50 - 100 ug/kg/minute	Ventricular antiarrhythmic
Metoclopramide	5 mg/ml	1 - 2 mg/kg/day	Gastrointestinal stimulant, antiemetic
Nitroprusside	200 ug/ml	1 - 5 ug/kg/minute	Venous and arterial vasodilator
Procainamide	100 or 500 mg/ml	20 - 50 ug/kg/minute	Antiarrhythmic
Propofol	10 mg/ml	0.05 - 0.2 mg/kg/minute	Short-acting hypnotic

Calculations of Continuous Rate Infusions

The objective of CRI dosages is to determine how much drug must be added to a specific volume of intravenous fluid to achieve the required dosage. If the dosage is in ug/kg/minute, then the following equation will apply:

ug X kg X minute = ug required drug

Since ug are given in the dosage orders, and kgs are given for the specific patient, only the number of minutes that a given volume of intravenous fluids will last must be calculated. Simply calculate the number of hours an infusion will last by dividing the volume in the bag by the fluid administration rate per hour. Then, multiply the number of hours by 60 minutes/hour to determine the number of minutes. Next, solve the following equation:

ug X kg X minutes = ug of required drug

Then, divide the number of ug needed by 1000 to convert ugs to mgs.

Example: Give lidocaine CRI at 60 ug/kg/minute to a 15 kg dog. Add the lidocaine to 1000 ml of Normosol-R which is running at a rate of 41 mls/hour. How much lidocaine do you add to the 1000 mls of Normosol-R?

Calculate the number of minutes the 1000 mls of Normosol-R will last:

1000 mls / 41 mls/hour = 24 hours
24 hours X 60 minutes/hour = 1440 minutes

2. Solve the equation:

60 ug X 15 kg X 1440 minutes = 1,296,000 ug

Convert ug to mgs:

1296000 / 1000 = 1296 mgs

Calculate the amount of drug needed per 1000 ml bag by dividing the amount of drug needed by the concentration of drug that you are using (2% lidocaine):

1296 mgs / 20 mg/ml = 64.8 mls of lidocaine

In order to be precise in your dosage, 64.8 mls of Normosol-R should be discarded and then the 64.8 mls of lidocaine added to the bag.

Sample Problems:

"Goldie", a 30 kg Golden Retriever, is in oliguric renal failure. The doctor has ordered a dopamine CRI at 5 ug/kg/minute and a fluid rate of 121 mls per hour. How much dopamine will you add to 1000 ml of 0.9% Sodium Chloride solution?

Answer

"Maggie", a 25 kg Labrador Retriever, was hit by a tractor (HBT). The electrocardiographic monitor is showing a continuous run of multiform ventricular tachycardia. The doctor orders a lidocaine CRI to be given at a rate of 80 ug/kg/minute. The fluid rate is set at 34 mls/hour. How much lidocaine will you add to 1000 mls of Normosol-R?

Answer

"Gretchen", a 7 kg Miniature Schnauzer, has pancreatitis and has been vomiting frequently. The doctor orders a metoclopramide CRI at 2 mg/kg/day. The fluid volume is set at 23 mls/hour. How much metoclopramide will you add to 1000 mls of Normosol-R?

Answer

"Sage, a 42-kg Yellow Labrador Retriever, is in recovery following an abdominal exploratory. The doctor orders a fentanyl CRI at 4 ug/kg/hour. The fluid volume is set at 55 mls/hour. How much fentanyl will you add to 1000 mls of 0.9% Sodium Chloride?

Answers