Recent Evidence Challenges Four Inpatient Management Habits
Acute Kidney Injury
Can the fractional excretion of sodium (FENa) or fractional excretion of urea nitrogen (FEUN) help narrow the differential diagnosis in acute kidney disease? Widespread use of these measures began after a 17-person study in 1976 suggested that patients with prerenal azotemia had a FENa of less than 1 and patients with acute tubular necrosis had a FENa greater than 3 (JAMA 1976;236:579-81).
The FENa is not perfect, because many intrinsic kidney disorders can cause low FENa and the FENa can be elevated when diuretic use contributes to prerenal states, so a few studies looked at adding the FEUN to the diagnostic tools. Their results were contradictory.
One study of 102 patients in the ICU found that incorporating FEUN was 85% sensitive and 92% specific in detecting prerenal injury, but the study excluded patients with acute glomerulonephritis and obstructive nephropathy, "so you have to make sure that you exclude those patients if you’re going to use FEUN," Dr. Feldman said (Kidney Int. 2002;62:2223-9).
In a separate study of 99 patients, however, the FENa and FEUN were much less impressive in patients with or without diuretics. In patients on diuretics, FEUN had a sensitivity for distinguishing transient from persistent acute kidney injury of 79% and a specificity of 33%, and in patients not on diuretics the sensitivity was 48% and the specificity was 75% (Am. J. Kidney Dis. 2007;50:568-73).
A recent analysis reviewed the literature to provide some guidance for clinicians, but the end result is confusing, Dr. Feldman said. Under best-case scenarios, these two measures would be likely to make a difference in diagnosing the cause of acute kidney injury, but under worst-case scenarios, "they really stink," he said (Cleve. Clin. J. Med. 2012;79:121-6).
The authors cautioned that a single index calculated at a specific time often is insufficient to properly characterize the pathogenesis of acute kidney injury. "In the end, probably FENa and FEUN really don’t help you very much to decide" the reason behind acute kidney injury, Dr. Feldman said.
Chest X-Rays
Routine chest x-rays in mechanically ventilated patients in ICUs provide, well, too many unneeded x-rays, recent data show.
A crossover study that randomized 21 French ICUs to either routine daily chest x-rays for these patients or x-rays on demand found that the on-demand strategy reduced the number of x-rays by 32% without affecting the number of days on ventilation, length of ICU stay, or mortality. With the daily x-ray strategy, 424 patients got 4,607 x-rays, compared with 3,148 x-rays in 425 patients under the on-demand strategy (Lancet 2009;374:1687-93).
Patients had their ventilators changed more often under the on-demand strategy, probably as clinicians were troubleshooting potential problems, but the number of interventions did not differ significantly by x-ray strategy, Dr. Feldman noted.
A meta-analysis this year of eight trials including 7,078 adult ICU patients concluded that routine daily x-rays can be eliminated without increasing adverse outcomes (Radiology 2012;255:386-95).
Dr. Feldman suggested specific goals for these four scenarios, which he presented at the annual meeting of the Society of Hospitalist Medicine.
"Do not reflexively transfuse cardiac patients to hematocrits of 30%. Do not do routine daily chest x-rays. Do not reflexively NG [nasogastric] lavage our patients. And spend more time doing a really great history and physical and thinking about why your patient has acute renal failure than trying to use indices that don’t actually help us very much," he said.
He added a personal goal: "If I can make the residents at Johns Hopkins change, that will be a real feat, because they love to order tests on everybody."
Dr. Feldman, Dr. Whelan, and Dr. VanderEnde reported having no financial disclosures.
