Similar to patients who undergo cardiac surgery, there is also an association between hemoglobin and the risk of kidney injury in patients undergoing noncardiac surgery. (Image source: Thinkstock)

Similar to patients who undergo cardiac surgery, there is also an association between hemoglobin and the risk of kidney injury in patients undergoing noncardiac surgery. (Image source: Thinkstock)

What are the risk factors for kidney injury after noncardiac surgery? If we know these factors, can the risk be modifiable? It is already known that anemia and transfusions are associated with kidney injury after cardiac surgery. Is the same true for patients who do not undergo cardiac surgery? Dr. Michael Walsh, Departments of Medicine and Clinical Epidemiology and Biostatistics, McMaster University, E Hamilton, ON and co-authors studied whether preoperative hemoglobin and perioperative reduction of hemoglobin were associated with kidney injury in patients who underwent noncardiac surgery. The results of their study were published in this month’s Anesthesia & Analgesia in the article “The Association Between Perioperative Hemoglobin and Acute Kidney Injury in Patients Having Noncardiac Surgery.”

The authors used their electronic medical record database to study the risk of acute kidney injury (AKI) in patients who underwent over 33,000 noncardiac surgeries and who had normal preoperative kidney function. Acute kidney injury occurred in 7.4% of surgeries. Patients who suffered kidney injury were older, more frequently male, had a higher risk of 30-day mortality, more cardiovascular disease, and more often had emergency surgery. As preoperative hemoglobin concentration decreased, the risk of AKI increased. There was also a strong graded association observed between a decrease in postoperative hemoglobin in the first 24 hours after surgery and AKI.

These findings are somewhat similar to studies of patients who undergo cardiac surgery. Preoperative hemoglobin is related to the risk of acute kidney injury after cardiac surgery, though the finding that postoperative hemoglobin is also associated with AKI is new. Also, though the amount of blood lost for noncardiac surgery is less than that lost for cardiac surgery, there is still an association between even small decrements in hemoglobin and AKI.

This was a single-center study. Whether transfusion or methods used to decrease blood loss will decrease the risk of acute kidney injury remains to be seen.

OpenAnesthesia has a summary on acute kidney injury.