Definitions

Pros and Cons of Rule-of-Six vs Fixed Concentrations

[This document was created to facilitate discussions over converting from rule-of-six to fixed concentrations. The most compelling argument was suggested by Dr. M. Apkon from Children's Hospital at Yale: fixed concentrations decreased compounding errors.]

Definitions

Rule-of-six concentration. Medicated infusion concentration based on the patient's weight. (A misnomer of the strictest sense since drugs dosed on an hourly or daily basis are not calculated to any multiple of six.)
Fixed concentration. Medicated infusion concentration is predetermined and does not vary with patient weight. Sometimes premixed.
Standard concentration. Ambiguous term that should be avoided.
Fluid rate. The rate that the solution is infusing, usually in mL/hr.
Dose rate. The rate that the medication is infusing, sometimes in mcg/kg/min, mg/hr, or other units.

Analysis

	Pro	Con
Fixed	Best applied to medications with dosing that varies by no more than 50%. Pharmacy intervention is minimized. Premixed solutions usually readily available. Allows Pharmacy to compound most of the medicated infusions, eliminating compounding at the bedside and thereby decreasing compounding errors.	Determining the dose rate usually requires some calculation at the bedside. (Can be remedied by dosing tables or calculating pumps.) When multiple concentrations are available, it may be easy to pull a bag with the wrong concentration. (May be mitigated by color-coding or other schemes.) May not fulfill specific needs for higher concentrations for fluid restriction or high-dose infusions. May not fulfill specific needs for lower concentrations when fluid rates are too low for pumps to deliver accurately. May require the use of "carrier" fluids that can introduce inconsistencies in drug delivery when fluid rates are changed.
Rule-of-Six	Best applied to medications with dosing that varies by 10-fold or more. Determining the dose rate usually requires little or no calculation at the bedside. (Can still be improved by dosing tables.) Custom mixing allows for the use of different diluents. Custom mixing fulfills specific needs for higher concentrations for fluid restriction or high-dose infusions. Custom mixing fulfills specific needs for lower concentrations when fluid rates are too low for pumps to deliver accurately.	Mixing requires some calculation. (Can be remedied by dosing calculators.) Inconsistently applied across medications. (Can be remedied by dosing calculators with standardized application within particular medications.) Higher concentrations can be unstable solutions. (Can be remedied by smart dosing calculators.) Requires rapid pharmacy response or mixing by bedside nurse.

Data to be collected:

Evidence supporting one method over the other, if it exists.
Tables of dose rates and fluid rates across dosing ranges and patient weights for the various fixed concentrations. The fluid rates should then be compared to pump specifications.
Pump specifications. What is the lowest rate that can be delivered consistently without fluctuation. Does it vary with the pressure against which the pump is working?

Weill Cornell University Medical Center - New York Presbyterian Hospital
Created: March 16, 2004 Revised: December 14, 2004