Prosta metoda przeliczania szybko?ci infuzji na szybko?ć podawania leku

For users whose hospitals do not have enough syringe pumps with automated dose rate calculation, I would like to present a simple method that I have developed for conversion of the infusion rate (ml h^-1) into the dose rate (mg kg^-1 min^-1). The method is based on the use of concentration-dependent constants.

The infusion rate is calculated by multiplying the concentration-dependent constant, the weight factor and the dose rate. The constant equals 1.2 ml h^-1 at a concentration of 5 mg ml^-1 (e.g. 250 mg dobutamine in 50 ml diluent) and 30 ml h^-1 at a concentration of 0.2 mg ml^-1 (e.g. 10 mg adrenaline in 50 ml diluent).

The weight factor is the patient´s weight divided by 100. Hence, the weight factor for a 78 kg patient is 0.8.

Example:

250 mg dobutamine in 50 ml diluent

Concentration: 5 mg ml^-1

Constant: 1.2 ml h^-1

Body weight: 110 kg

Weight factor: 1.1

Dose rate: 5 mg kg^-1 min^-1

Infusion rate = constant x weight factor x dose rate

Infusion rate = 1.2 ml h^-1 x 1.1 x 5 = 6.6 ml h^-1

The concentration-dependent constants for the concentrations used be calculated using the following formula:

1 Constant = 6 mg h^-1 x ----------- concentration (mg ml^-1)

Example:

50 mg nitroglycerin in 50 ml diluent

1 Constant = 6 mg h^-1 x ------- = 6 ml h^-1 1 mg ml^-1

If the dose rate for a running syringe pump is unknown (e.g. when a patient is transferred to any place), it can be calculated by dividing the infusion rate by the product of the constant times the weight factor.