Continuous intravenous infusion flow rate

An intravenous infusion involves a continuous flow of drug into a patient at a rate defined by the infusion rate constant, Rini, with units of mass/time. Discussions of infusion normally present the infusion rate constant as inf, which may be confused with a true reaction rate constant. Therefore, this presentation of infusion uses a less ambiguous variable, Rmi, for the infusion rate constant. 

The flow of pancreatic juice and bile was tested before and after the experiment by means of an intravenous bolus of 5 pmol/kg secretin. Before the experiment the duodenum was continuously perfused at a rate of 2 ml/min for 435 min with isotonic saline containing phenol red (10 mg/1) as a marker. After drug treatment (intravenous infusion of gastrin-releasing peptide or duodenal HC1 perfusion) pancreatic and hepatic secretions were collected in 15-min periods and the volumes determined by weighing. Duodenal effluents were collected in 15-min periods and phenol red concentrations determined spectrophotometrically. Blood sampled were withdrawn for determination of secretin by radioimmunoassay. 

Figure 2.18. Determination of the inuhn clearance. Inuhn is injected intravenously (ideally by way of continuous infusion), and its concentrations in blood and urine are determined. The ratio of these concentrations will be inversely proportional to the urine volume reduction after glomerular filtration multiplied by the urine flow, it thus provides an estimate of the glomerular flltration rate.

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