Hemodialysis

This process involves movement of solute and water through a semi-permeable membrane. The driving forces behind this movement are the hydrostatic pressure like that of hemoconcentration and the concentration gradient created by the use of dialysate.

Dialysis uses diffusion and hydrostatic pressure to drive solutes across a semipermeable membrane. Concentration gradients are created by flushing dialysate solution counter current to blood flow on the effluent side of the device. Alternating 2000 ml of 0.5% DIANEAL with 1000 ml of normal saline with 50 meq sodium bicarbonate added helps to maintain a normal pH (Fig. 16.2).

By using the recirculation line as the arterial inlet to dialyzer, high volume blood flow can be achieved. The venous side or outlet side is connected to a filtered port of the cardiotomy reservoir (Fig. 16.1).

Indications and Benefits

• Intra-op hemodialysis delays immediate post-op hemodialysis and associated complications at an unstable time.

• Solute levels (i.e., K+) and blood volume can be adjusted to promote cardiac efficiency.

• Also see benefits of hemoconcentration. Perfusion Considerations

• Maintain adequate heparinization and other drug levels.

• Maximize renal function intraoperatively; consider use of low-dose dopamine and/or pulsatile flow during aortic cross-clamp time.

• Maintain a minimum blood flow through the device to avoid stagnation or thrombosis.

• Optimal blood flow through device is 300-500 cc/min.

• Can add suction to the effluent side to promote fluid removal.

Selected Readings

1. Moore RA, Laub GW. Hemofiltration, Dialysis and Blood Salvage Techniques During Cardiopulmonary Bypass. In: Gravlee G, Davis R, Utley J, eds. Cardiopulmonary Bypass-Principals and Practice. Baltimore: Williams and Wilkens, 1993:233-245.

2. David RB. Introduction to Renal Function. Clinical Physiology of Acid Base and Electrolyte Disorders. New York: McGraw-Hill, Inc., 1994:3-19.

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