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Acute kidney injury after contrast-enhanced examination among elderly1

OBJECTIVES: to assess renal function in elderly patients undergoing contrast-enhanced computed tomography and identify the preventive measures of acute kidney injury in the period before and after the examination. METHOD: longitudinal cohort study conducted at the Federal University of São Paulo Hospital, from March 2011 to March 2013. All hospitalized elderly, of both sexes, aged 60 years and above, who performed the examination, were included (n=93). We collected sociodemographic data, data related to the examination and to the care provided, and creatinine values prior and post exam. RESULTS: an alteration in renal function was observed in 51 patients (54%) with a statistically significant increase of creatinine values (p<0.04), and two patients (4.0%) required hemodialysis. CONCLUSION: There is an urgent need for protocols prior to and post contrast-enhanced examination in the elderly, and other studies to verify the prognosis of this population.


Introduction
after the administration of the contrast agent.
The various contrast media differ in biochemical and physical aspects, and in regard to their properties related to efficacy. The chemical structure, viscosity, osmolality and ionicity are also considered. The nonionic compounds and the ones with low osmolarity were considered less nephrotoxic than the hyperosmolar ones (4,13) . Yet another type of contrast is being developed, characterized by its nonionic dimers that give the molecule a high affinity with the aqueous medium, thereby decreasing the incidence of nephrotoxicity; such compounds are called isosmolar (4) .
Renal lesions caused by the use of contrast are classified into acute tubular necrosis (ATN) and acute tubulointerstitial nephritis (ATIN) (6) . The pathophysiology of ATN is multifactor and involves changes in renal hemodynamics and the renal tubules due to a biphasic response: interspersed vasodilation with vasoconstriction which decreases renal blood flow, causing renal ischemia (8,15) . CIN is characterized by the damage of epithelial cells of the renal tubules causing decreased renal blood flow that leads to hypoxia in the renal medulla, and also by the appearance of granular cylinders, erythrocytes and inflammatory cells in the urine; ATIN can manifest in a milder form (6) .
Examination of renal ultrasound shows that contrast-induced AKI leads to increased renal dimensions. In these cases, scintigraphy with gallium detects inflammatory cells. However, definitive diagnosis is established after renal biopsy (6) . For the prevention of contrast-induced AKI, the use of diuretics is indicated, as well as that of vasodilators, hydration, pharmacological vasoconstrictors, and antioxidants inhibitors (8,16) .
N-acetylcysteine is the most studied compound in the prevention of contrast-induced AKI. It inhibits the action of free radicals thereby protecting renal function.
Prophylaxis is most effective when the medication is administered orally, 24 hours before the procedure (16) .
A study published in Israel, in 2013, showed no benefit in the use of N-acetylcysteine to prevent contrast-induced AKI, but showed a significant association between the solution volumes administered for the prevention of contrast-induced nephropathy (17) .
In elderly subjects, the anatomical and physiological changes in the kidneys, caused by the aging process of the kidney, constitutes an aggravating factor for kidney disease, increasing the susceptibility of renal dysfunction over the years (4)(5) .  (18) .
Hydration, use of medications that reduce renal vasoconstriction and oxidative stress, the use of less nephrotoxic contrast, dose adjustment, and discontinuation of medications with nephrotoxic potential should be considered when contrast-enhanced examinations are requested, especially when it comes to the elderly (19) .
We understand that knowing the frequency of alterations in the renal function of the elderly after contrast-enhanced examinations can target and support the creation and implementation of protocols for AKI prevention among the elderly population.
Facing this scenario, the study objectives were: to assess the impact of changes in renal function in elderly inpatients undergoing computed tomography using contrast medium, and, to identify preventive measures of acute kidney injury in the periods before and after the contrast-enhanced CT examination.

Ethical Considerations
The study was approved by the Board of Ethics in

Population
All elderly hospitalized during the study period and who underwent computerized tomography were included in the study. The sample consisted of 93 elderly patients of both sexes, with a minimum age of 60 years.

Results
Ninety-three elderly who underwent a contrast- were data found on the volume and type of contrast used for the examination (Table 1).   (20) . Aggravating factors that increase this statistic include habits such as: smoking, stress, inactivity, intake of products with high cholesterol, as well as a precarious economic status (21) . In the present study we observed concordance with the findings of the  (19) .
In the present study it was revealed that the institution where the study was conducted followed no standardized protocol for prevention of renal damage, whereas 35.5% of patients who had CT with contrast were not prepared for the exam, and 52.7% of the sampled population did not receive adequate care after the procedure. There was also no standardization in relation to the exam records.
Records relating to the contrast are extremely important, since several studies that evaluated different types and doses of contrasts demonstrated that their toxicity depended on the degree of osmolarity presented by the agents, i.e., osmolar contrasts are considered less nephrotoxic, as well as non-ionic ones (19) . In this study, the number of records that had notes on the type of contrast used in performing the CT examination was 32.2%, and the remaining 67.8% of the analyzed records did not contain records on the type of contrast used. The lack of information may reflect negatively on the decision of possible attitudes related to the prevention of renal damage.
In addition to documenting the type of contrast being of great relevance, studies correlate the amount of contrast administered to the risk of AKI. Other authors also believe that even small dosages could induce renal failure (22) . In this study, 19.4% of the analyzed records did not contain records on the volume used, so this refers to the same issue abovementioned, the lack of documentation can interfere with preventive measures to be adopted.
The vast majority of studies on nephrotoxicity related to contrast recommended that all patients should receive oral or intravenous hydration, but few of them compare the use or non-use of this type of treatment.
A study that compared three types of preparation, normal saline, normal saline and N-acetylcysteine and sodium bicarbonate, showed no differences between the standard method (saline) and other preparations (23) .
Hydration with 0.9% NS for at least 1ml/kg/hour, and if possible 100-150ml/h for 12 hours before and after the procedure, is one of the most appropriate prophylactic measures to prevent alteration of renal function after receiving the contrast. Satisfactory outcomes with the use of normal saline before elective procedures, and even in emergency cases (19) , were also obtained. Studies such as this show the importance of hydration prior to contrast studies, however, in this study, only 49.46% of patients received intravenous hydration as has been advocated in the literature.
A study showed that N-acetylcysteine associated with increased hydration was more effective compared to hydration alone. It is known that N-acetylcysteine has a vasodilatory property, so it increases the expression of the nitric oxide synthase enzyme and may prevent contrast-induced nephropathy (CIN) both by reducing the direct oxidative damage and by improving hemodynamics of the kidney (17) .
A study showed that the N-acetylcysteine dosage that should be administered to someone performing contrast-enhanced exam should be 600mg orally 12/12h a day before the exam and 24 hours after the procedure. In emergency cases, one must consider the use of intravenous n-acetylcysteine 150mg/kg in 500ml of normal saline 30 minutes before the procedure and 50mg/kg four hours after it, as recommended by the Rappid trial (24) .
Despite advances in studies that show the effectiveness of N-acetylcysteine as a protective measure of the renal function before and after contrast examinations, we did not find the use of this prophylactic measure in most patients' record in the present study.  prognostic factor in patients who experience renal disorder is not clear, and there is a tendency in the literature not to consider age as a negative factor in the evolution of these patients (18) .
The alterations in the kidney hemodynamics can collaborate, to some degree, with the renal dysfunction, so that some theories are based on the assumption that the aging process of kidney, the higher frequency of pathological conditions in the elderly, the excessive use of medications by elderly patients, and the increased frequency of interventional and surgical procedures are factors that increase the chances of an individual for developing any change in renal function (18) . The increase in creatinine values, as claimed by some studies (6) , occured within 48 hours; other authors (13) emphasized that this increase may occur 48-72 hours

Conclusions
The current study showed that many elderly had contrast-enhanced examination; however, the protocol on possible preventive measures of renal dysfunction that was implemented in the institution was still not being completed. Despite hospitalization, we did not find clear documentation about the preventive measures that should be used before and after the performance of contrast examinations in this age group.