Bedside Estimation of Blood-Flow Rate

Abstract

There are two clinical situations which require a rough estimation of the bloodflow rate during continuous arteriovenous hemofiltration (CAVH):

• 1. Differentiation between various causes of low filtration rate: Capillary thrombosis, partial occlusion of the vascular access, low blood pressure, high colloidosmotic pressure, high hematocrit, low blood-flow rate due to inappropriate components of the set and unknown changes of membrane permeability.

• 2. Suction-assisted CAVH [3] requires blood-flow rates > 100 ml/min for the use of the Diafilter-20 (Amicon), otherwise the negative pressure will result in a blocking of capillaries by red cell puree with consequent clotting of the extracorporeal circuit. For the clinically experienced it may be sufficient to fill the arterial tubing with saline after occlusion of the arterial three-way valve and to observe the blood-flow velocity through the tubing to the hemofilter. With an internal diameter of the tubing of 4 mm the front of the blood column should move at least 5 cm/s through the tubing after opening the stop cock.