Extreme Hemodilution During CABG Linked to Kidney Damage

NEW YORK (Reuters Health) – Nadir hematocrit caused by hemodilution during coronary artery bypass graft (CABG) surgery appears to be associated with increases in creatinine markers of renal injury, according to physicians at Duke University Medical Center in Durham, North Carolina, who also found that the risk is exacerbated in patients who are overweight.

In the Annals of Thoracic Surgery for September, Dr. Mark Stafford-Smith and colleagues note that hemodilution during CABG has been promoted as a way to protect the kidneys by reducing blood viscosity and enhancing regional blood flow during periods of hypoperfusion and hypothermia.

But because the relationship between extreme hemodilution and renal injury after CABG has not been investigated, they examined data for 1,404 patients who underwent primary elective CABG surgery between 1995 and 1998.

They observed a significant two-way interaction between body weight and nadir hematocrit. After adjusting for the hematocrit-body weight interaction, the association between lowest hematocrit (19.5%) during bypass and peak fractional change in creatinine was significant (p = 0.008). They observed similar results in multivariable analyses accounting for preoperative hematocrit, blood transfusion and use of inotropic agents.

Comparable associations of anemia with peak postoperative creatinine and with postoperative creatinine clearance reinforced their findings, the report indicates. In contrast, low bypass perfusion pressure was not associated with renal dysfunction.

“Minimizing bypass prime volumes should reduce anemia without transfusion and potentially reduce renal risk,” Dr. Stafford-Smith’s group writes. They recommend that hemodilution should be monitored closely and excessive falls in hematocrit be avoided, especially when patients are overweight.

In an invited commentary, Dr. David J. Cook writes that the Duke University team’s methods “are not sufficient to determine if low hematocrit during bypass is an expression of comorbid conditions,” such as blood loss, chronic anemia, or heart failure.

Ann Thorac Surg 2003;76.