DURHAM, N.C. -- When physicians routinely "thin" the blood of patients undergoing coronary artery bypass surgery in order to place them on the heart-lung machine, they may be causing more damage to the kidneys and other organs than previously appreciated, according to a new study by Duke University Medical Center researchers.

For years moderate dilution of the blood has been thought to protect the kidneys from damage, but the Duke researchers found in their study of more than 1,400 bypass patients that dilution to the lower levels of accepted ranges is associated with measurable kidney damage. The Duke team published the results of its study in the September 2003 issue of the Annals of Thoracic Surgery.

In order to safely operate on a non-beating heart, physicians attach the body to a heart-lung machine, which takes over for the stopped heart in circulating oxygen-rich blood throughout the body. To prime the pump, physicians add fluid -- usually a balanced saline solution -- to the circuit to fill the tubing and pumping chambers of the machine.

This additional fluid lowers the percentage of oxygen-carrying red blood cells in the blood, a measurement known as hematocrit. Normal hematocrit ranges from 36 to 40 percent. During bypass surgeries, the hematocrit can range from 22 to 26 percent, with even lower percentages being commonly attained at different points during the operation.

"Using hematocrit as a tool to assess a patient's anemia, we found that the lowest hematocrit achieved during the bypass procedure was significantly associated with acute kidney damage," said Duke anesthesiologist and study leader Mark Stafford-Smith, M.D. "Furthermore, we f
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Contact: Richard Merritt
merri006@mc.duke.edu
919-684-4148
Duke University Medical Center
3-Sep-2003