SCOTTSDALE, ARIZ. – Optimal management of patients with chronic kidney disease involves knowing what can be modified, understanding that much is uncertain, and having the wisdom to know the difference, suggested an anesthesiologist at a meeting on perioperative medicine sponsored by the University of Miami.
"There is a lot to be done in terms of evaluation of chronic kidney disease and also defining interventions," said Dr. Claus U. Niemann, professor of anesthesia and surgery at the University of California, San Francisco.
Kidney disease is identified either by markers of function such as glomerular filtration rate (GFR), markers of damage such as proteinuria, and markers of volume sense, such as edema, ascites, and urinary sodium excretion.
None of these measures is particularly accurate at measuring disease, however. For example, GFR is not observed directly but estimated from creatinine clearance, which is produced by the body in varying amounts daily and which depends on muscle mass, so that values for a young, muscular man will be higher than those of a small, older woman, Dr. Niemann noted.
In addition, even in people without kidney disease, GFR declines gradually with age, from about 116 mL/min per 1.73 m2 for people in their 20s, to about 75 mL/min per 1.73 m2 in those aged 70 years and older.
In 2002, the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) developed a five-stage classification for chronic kidney disease (CKD), based on GFR, with CKD defined as either a GFR of less than 60 mL/min per 1.73 m2 for more than 3 months or evidence of kidney damage for more than 3 months, based on the presence of abnormalities such as proteinuria. The classification notes that a combination of GFR less than 60 mL/min per 1.73 m2 and proteinuria is prognostic.
The classification includes moderately and severely reduced GFR, with respective rates of 30-59 and 15-29 mL/min per 1.73 m2, respectively, and end-stage renal disease, with a GFR less than 15 mL/min per 1.73 m2 or a need for dialysis,
The most common cause of CKD is diabetic nephropathy or hypertensive nephrosclerosis, which account for 67% of all cases. About 1 in 5 or 1 in 6 Americans has some form of CKD, and the problem can be lifelong, Dr. Niemann said.
Risk stratification
The goal of perioperative management of patients with CKD is to prevent further renal impairment from acute kidney injury, a rapid reduction in kidney function as measured by a significant rise in serum creatinine levels or reduction in urine output within 48 hours of exposure.
Approximately 5%-7% of all hospitalized patients experience some degree of acute kidney injury and changes in serum creatinine of only 0.3 mg/dL have been associated with greater length of stay and increased morbidity and mortality, Dr. Niemann said.
"What is really necessary is that we do perioperative risk stratification. We want to identify the subset of patients who are at risk, we can do tests potentially, and we want to understand what the procedure is, put it in the context of the patient and his renal disease, and then hopefully define a plan and get him to surgery," Dr. Niemann said.
Defining perioperative renal risk involves determining as best as possible the extent of renal insufficiency or CKD, the etiology of the kidney disease (including severity and complications), and the risk of loss of kidney function from the planned or urgent/emergent surgery. The preop clinical team should also know where the patient will be discharged after surgery (home, ICU, floor).
Risk factors for in-hospital acute renal failure include baseline risks, such as age, diabetes, heart or liver failure, and male sex; acute clinical conditions, such as sepsis, hypotension, shock, volume depletion, or rhabdomyolysis; and use of nephrotoxic agents, such as contrast media, aminoglycosides, chemotherapy drugs, or NSAIDs.
Mixed results
Dr. Niemann noted that in a systematic review of possible interventions for protecting renal function in the perioperative period found little in the way of solid evidence to support the use of various interventions, including dopamine agonists or analogs, loop diuretics, mannitol, calcium inhibitors, angiotensin-converting enzyme (ACE) inhibitors, N-acetylcysteine in contrast studies or surgery, or sodium bicarbonate (Cochrane Database of Syst. Rev. 2013;9:CD003590 [doi:10.1002/14651858.CD003590.pub]).
"The long and the short of it is that no interventions have definitely been shown to make a big difference in randomized trials," he said.
Nonetheless, to prevent further loss of renal function in at-risk patients, clinicians should optimize modifiable variables, such as blood pressure, and discontinue nephrotoxic medications, such as NSAIDs.
In addition, the perioperative team should strive to better control acidosis, anemia, and hyperphosphatemia.