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The effect of negative pressures used during ultrafiltration on erythrocytes / by Kathleen A. Dryden.

by Dryden, Kathleen A.

Ultrafiltration.

Cardiopulmonary bypass -- Adverse effects

Hemodialysis -- complications.

54 leaves : figures ; 29 cm.

List of figures -- Introduction -- Background: Development and practice of ultrafiltration -- The use of hemoconcentration with cardiopulmonary bypass -- Methods of ultrafiltration -- Blood damage -- Free hemoglobin -- Summary -- Hypothesis -- Methods: Blood preparation -- Circuit description -- Statistical analyses -- Results -- Discussion -- References -- Appendices.

Ultrafiltration is the process of filtering blood through a semi-permeable membrane to selectivly remove water and small molecular weight plasma solutes. Filtration is achieved using the hydrostatic pressure of the inflow solution coupled with a negative pressure created by vacuum suction on the effluent side of the filter. This technique is currently used in cardiothoracic surgery as an effective solution to the continuous challenge of hemodilution and patient volume overload associated with cardiopulmonary bypass and heart surgery. Ultrafiltration, also known as hemoconcentration, has been clinically proven to be a useful tool when incorporated into the circuit of the cardiopulmonary bypass machine to substantially decrease blood volume, increase hematocrit, and decrease the amount of circulating inflammatory mediators. Although ultrafiltration provides several benefits for the patient undergoing CPB, the pressure gradients generated may also be expected to lead to increased stresses on the formed elements of the blood. Therefore, to estaablish the safety of ultrafiltration as an acceptable practice for fluid removal with cardiopulmonary bypass it was necessary to investigate the effects of the pressure gradients used in hemoconcentration on the red blood cells.

Based on the prediction that shear stress will increase when negative pressures are used, and because it is known that increased amounts of shear stress may cause damage to erythrocytes, it is reasonable to predict that hemolysis will occur with ultrafiltration. Therefore the purpose of this investigation was to determine if a vacuum suction applied to the effluent side of the hemoconcentrator would cause erythrocyte damage, as indicated by plasma-free hemoglobin levels (PFHb).

In order to determine if ultrafiltration damaged the erythrocytes, a standard pump circuit was assembled and filled with porcine blood. Included in this pump circuit was an ultrafiltration device connected to a negative pressure source. Five pump runs were performed at each of five different negative pressure settings; 0, -100, -200, -300, and -400 mmHg. The rate of blood flow throughout the investigation was held constant at 400 mL/min for duration of 40 minutes. 3mL blood samples were obtained at 0, 20, and 40 minutes after the start of the pump run to be used for PFHb measurements.

The plasma-free hemoglobin levels and transmembrane pressures at each point were evaluated with a two-way analysis of variance (ANOVA). No significant differences were found to exist between vacuum levels, time, and PFHb levels. A two way ANOVA was used to evaluate the interactions between time and vacuum levels on the transmembrane pressures, and a statistical significance was found to exist among the vacuum levels. Therefore, it is concluded that ultrafiltration at a blood flow rate of 400 mL/min and vacuum up to -400 mmHg applied to the effluent side of the device is a safe practice that does not cause significant hemolysis. Yet, because of the small sample sizes, further studies may be warranted to make sure these results are representative of the population as a whole.

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