Perioperative Renal Protection
Tuesday, 11 a.m.-noon
Upper 6B
Michael Hutchens, M.D., M.A.
Acute kidney injury (AKI) is one of the greatest dangers in the perioperative environment. When it occurs on top of another organ failure, mortality is 70 percent, and even a mild AKI without other organ failure increases the risk of death by sixfold to eightfold.
Causes of AKI, steps to prevent it and new research on the condition will be discussed in “Perioperative Renal Protection,” from 11 a.m. to noon tomorrow in Upper 6B.
“The most common cause of AKI is associated with decreased renal perfusion in general, and the second most common cause in hospital patients is associated with major surgery,” said Michael Hutchens, M.D., M.A., who will present the session. “If you look at other kinds of perioperative complications we spend anesthesiologist time and resources on — for example, retained foreign bodies — the excess cost, length of stay and mortality for AKI is five to 10 times higher than for leaving in a sponge. It’s a real problem.
“Part of this is because the definition of AKI has changed. In the last 10 years, our definitions are more disciplined, more research-based and more sensitive.”
The challenge in detecting AKI in the O.R. is that urine output is not a good diagnostic measure. Diagnosis depends on the serum creatinine, which does not rise for 12-24 hours after the insult, and by then it is too late to act, said Dr. Hutchens, Associate Professor of Anesthesiology and Perioperative Medicine, Oregon Health & Science University, Portland.
“There are new tests coming out,” he said. “We are close – probably less than five years from a more sensitive, specific and faster test of perioperative renal injury. The most likely of these is NGAL (neutrophil gelatinase-associated lipocalin), which is elevated within two hours of ischemic acute kidney injury, at least in cardiac surgery patients.
“The ideal thing would be a physiologic monitor, like the oxygen saturation probe, which changed the diagnosis of hypoxia.”
Because there is no quick diagnosis of AKI, the best defense is a good offense – paying attention to fundamentals, such as identifying preoperative risks and mitigating intraoperative factors you can mitigate, Dr. Hutchens said.
“People who are at risk have renal insufficiency at baseline, chronic renal disease or chronic liver disease. They have three times the risk of AKI,” he said. “People who are having emergency surgery or congestive heart failure have two times the risk.”
Steps to take in the O.R. include maintaining blood pressure, considering heart failure in the differential of hypotension, and watching for urinary catheter obstruction, Dr. Hutchens said.
“There are no magic bullets. Because the disease mechanism is not well understood, it is unlikely there will be a magic bullet until the disease mechanism is better understood,” he said. “But there is very interesting recent data for remote ischemic preconditioning.
“It seems like a crazy idea. The way it works is you make part of the body ischemic. The classic way to do this is with a blood pressure cuff on the arm or the leg, and relieve the ischemia. Then you do your operation.”
Still, any steps to prevent or quickly detect AKI are far down the road, so the best steps are to realize the dangers of AKI.
“If you want to prevent perioperative AKI, stick to fundamentals. Watch out for the things that increase risk, maintain the blood pressure, think about the heart and consider an inotrope, and think about obstruction in the Foley catheter,” Dr. Hutchens said.
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