Fig. 1.
Delivery kinetics of norepinephrine (NE) versus methylene blue (MB). For the conventional infusion, a pump drove the normal saline carrier fluid at the fixed rate of 10 ml/h. To initiate drug delivery by conventional means, flow from the pump driving the drug infusion (fixed rate of 3 ml/h) was allowed to enter the main fluid path by opening the stopcock in the manifold and closing the vent. To initiate an algorithm-controlled infusion, a computer directed the flows of both the carrier pump and the drug pump after opening the stopcock in the manifold and closing the vent. The same diffusion coefficient was used for MB and for NE in the algorithm-driven infusions. Calibration to arrive at the empiric dead volume used in the algorithms involved performing a least-squares fit of the conventional curves against the model-predicted curves by varying the dead volume used in the model calculations. At time 0, the vent was closed and drug entered the main fluid pathway. (A) Conventional (N = 6 for NE and N = 4 for MB); (B) algorithm (N = 3 for NE, N = 4 for MB); data points represent mean ± SD.