title: Continuous intrathecal infusion of a solution containing two drugs: calculation methods.
abstract: The calculation of the parameters of the pump is complicated for a mixture of two drugs in continuous intrathecal therapy with implantable and programmable pumps. It is important to determine the best proportion of drug solutions to obtain the desired clinical results and also to adapt their proportion to obtain the maximal volume of solution so that the time between two fillings is maximized. This paper proposes mathematical formulas that make easier and faster the calculation of the flow of the pump, the volume of each drug solution to be added to the pump, the concentration of each drug in the mixture, and the duration of the infusion. These values are determined from the desired quantity of each drug to be infused in 24 h, the concentration of each drug solution, and the volume of the reservoir. The calculated values cannot be directly applied because the syringes used to measure the volume of each drug solution have limited accuracy. It is necessary to round the volume of each drug solution and to hold their sum equal to the total volume of the reservoir. All the parameters are then recalculated, and the physician has to choose between several combinations of volumes.
authors.affiliation: Department of Neurosurgery, Centre Hospitalier Universitaire de Charleroi: Charleroi, Belgium, and              Department of Neurology, Centre Hospitalier Universitaire de Charleroi: Charleroi, Belgium in collaboration with the Boston University Neuromuscular Research Center, Boston, Massachusetts.
authors.forename: Yves
authors.initials: Y
authors.lastname: Nubourgh
authors.forename: John
authors.initials: J
authors.lastname: Moore