SCALING OF HEMOLYSIS IN NEEDLES AND CATHETERS

Hemolysis in clinical blood samples leads to inaccurate assay results and often to the need for repeated blood draws. In vitro experiments w ere conducted to determine the influence on hemolysis in phlebotomy ne edles and catheters of pressure difference, cannula diameter, and cann ula material. Fresh blood from five human volunteers was forced from a syringe inside a pressurized chamber through 14, 18, and 27 gauge 304 stainless steel needles and polyurethane and Teflon(R) catheters, all 40 mm long. Hemolysis was measured in the samples by a spectrophotome ter. It was found that hemolysis increased with increases in pressure difference and cannula diameter and no consistent trend could be ident ified with regard to cannula material. The pressure differences requir ed for significant hemolysis were above those typical of clinical veni puncture blood draws. While there was substantial variability among in dividuals, the hemolysis values scaled with exponent S=(t/t(0))[(tau/t au(0)) - 1](2), where t is the characteristic duration of shear, t(0) is a time constant, tau is the wall shear stress, and tau(0) is the wa ll shear stress threshold below which no hemolysis occurs. A hemolysis threshold including both time and shear stress was also defined for S = constant. The threshold implies that a threshold shear stress exists below which erythrocytes are not damaged for any length of exposure t ime, but that red cells may be damaged by an arbitrarily short period of exposure to sufficiently large shear stress. (C) 1998 Biomedical En gineering Society. [S0090-6964(98)02805-7].