Perfusion de dopamine par voie veineuse centrale. Variation de la dose lors de la mesure de la pression veineuse centrale

Abstract

The changes in the doses of dopamine administered at a steady rate which occur during central venous pressure (CVP) measurement were studied. A workbench model with a single lumen central venous catheter was devised with which a mathematical model was constructed to calculate the alterations due to changes in different variables : central venous pressure, dopamine dose, collateral infusions. The average time for CVP measurement was 2 min. The volume of 5 % glucose solution filling the manometer was 2.3 ml. The dopamine bolus generated by CVP measurement was equivalent to a dose of 85 μg · kg −1 · min −1. The delay required for a return to the initial dose was 2 h 42 min. Changes in CVP led to inversely proportional changes in dopamine dose. These also depended on the level to which the measuring tube was filled before carrying out the measurement. High initial rates of dopamine infusion required shorter times for a return to initial dopamine doses. The bolus and time for recovery were also inversely proportional to the volume of infusion fluids given at a steady rate on the same venous line. This model was tested in a patient suffering from bacterial pneumonia and septic shock (60 years, 55 kg). CVP measurement resulted in a bolus dose of 17 μg · kg −1 · min −1, leading to a 43 % decrease in aortic flow rate and 60 % in the ejection volume. After about 25 min, heart rate and mean arterial blood pressure had returned to their initial values, although aortic flow rate remained 30 % below initial values. This problem is also met with other drugs, such as heparin. Several solutions are suggested to avoid these abrupt changes in drug doses. Venous access reserved for this is the best way out. As an alternative, a three-way tap may be placed on the CVP line as close as possible to the patient, so as to reduce the volume of fluid within the common tubing, and, therefore, the drug bolus.