Simona Detrenis

Facts and fallacies concerning the prevention of contrast medium-induced nephropathy

Objective:The aim of this article is to extract from recent medical literature and nephrologic practice the facts and fallacies concerning the possible prophylaxis of contrast medium–induced nephropathy. Data Sources, Study Selection, and Data Extraction:A MEDLINE/PubMed search (1985 to January 2006) was conducted, including all relevant articles investigating the pathogenesis and prevention of contrast medium–induced nephropathy from a nephrologic critical point of view. Data Synthesis:Considerable efforts have been made to develop pharmacologic therapy for the prevention of contrast medium–induced nephropathy, especially in patients at risk, such as elderly subjects and those with preexisting renal impairment, hypovolemia, or dehydration. There is general consensus that hydration protocols implemented before and after imaging with contrast medium may be effective in preventing contrast medium–induced nephropathy. However, definitive and convincing data related to amounts to be infused, infusion timing, and type of solutions (half-isotonic, isotonic saline solution, or bicarbonate) are lacking. Forced diuresis with furosemide or mannitol and use of dopamine, together with concomitant hydration, have been proved to be ineffective or even more risky in the event of inadequate maintenance of euvolemia. Various direct or indirect vasodilators have been investigated (atrial natriuretic peptide, calcium channel blockers, angiotensin-converting enzyme inhibitors, and endothelin receptor antagonists), yet results have been inconsistent and inconclusive. Recent large meta-analyses concerning the protective role of antioxidant action of N-acetylcysteine have led to the conclusion that the statistical significance of the results is borderline. Preventive hemodialysis has not proved to be useful; on the contrary, it might worsen the clinical conditions by inducing hypotension. Hemofiltration, despite some positive studies, is too complex and cannot be used extensively. Conclusions:It is believed that prevention is actually achieved by correcting hypovolemia, dehydration, or both. Normalization of body fluids is probably the true objective to be achieved by preventive measures in all patients, not only in those at risk. Because limited data have been collected in intensive care units, at present, no firm or specific recommendations can yet be provided for the critically ill. LEARNING OBJECTIVESOn completion of this article, the reader should be able to: Identify risk factors for contrast medium-induced nephropathy (CMIN). Describe effective prophylaxis for CMIN. Use this information in a clinical setting. All authors have disclosed that they have no financial relationships with or interests in any commercial companies pertaining to this educational activity. Lippincott CME Institute, Inc., has identified and resolved all faculty conflicts of interest regarding this educational activity. Visit the Critical Care Medicine Web site (www.ccmjournal.org) for information on obtaining continuing medical education credit.

The Relationship Between Blood Pressure and Pain

The relationship between pain and hypertension is potentially of great pathophysiological and clinical interest, but is poorly understood. The perception of acute pain initially plays an adaptive role, which results in the prevention of tissue damage. The consequence of ascending nociception is the recruitment of segmental spinal reflexes through the physiological neuronal connections. In proportion to the magnitude and duration of the stimulus, these spinal reflexes cause the activation of the sympathetic nervous system, which increases peripheral resistances, heart rate, and stroke volume. The response also involves the neuroendocrine system, and, in particular, the hypothalamic‐pituitary‐adrenal axis, in addition to further activation of the sympathetic system by adrenal glands. However, in proportion to an elevation in resting blood pressure, there is a contemporary and progressive reduction in sensitivity to acute pain, which could result in a tendency to restore arousal levels in the presence of painful stimuli. The pathophysiological pattern is significantly different in the setting of chronic pain, in which the adaptive relationship between blood pressure and pain sensitivity is substantially reversed. The connection between acute or chronic pain and cardiovascular changes is supported observationally, but some of this indirect evidence is confirmed by experimental models and human studies. The pain regulatory process and functional interaction between cardiovascular and pain regulatory systems are briefly reviewed. Various data obtained are described, together with their potential clinical implications.

Ultrafiltration in heart failure

Fluid overload is a key pathophysiologic mechanism underlying both the acute decompensation episodes of heart failure and the progression of the syndrome. Moreover, it represents the most important factor responsible for the high readmission rates observed in these patients and is often associated with renal function worsening, which by itself increases mortality risk. In this clinical context, ultrafiltration (UF) has been proposed as an alternative to diuretics to obtain a quicker relief of pulmonary/systemic congestion. This review illustrates technical issues, mechanisms, efficacy, safety, costs, and indications of UF in heart failure. The available evidence does not support the widespread use of UF as a substitute for diuretic therapy. Owing to its operative characteristics, UF cannot be expected to directly influence serum electrolyte levels, azotemia, and acid-base balance, or to remove high-molecular-weight substances (eg, cytokines) in clinically relevant amounts. Ultrafiltration should be used neither as a quicker way to achieve a sort of mechanical diuresis nor as a remedy for an inadequately prescribed and administered diuretic therapy. Instead, it should be reserved to selected patients with advanced heart failure and true diuretic resistance, as part of a more complex strategy aiming at an adequate control of fluid retention.

Patients at risk for contrast-induced acute kidney injury

Subjects with hypovolemia and/or dehydration and pre-existing renal failure are considered at highest risk for radiocontrast-medium-induced acute kidney injury (RCI-AKI), and this risk increases in the presence of glomerular filtration rate or creatinine clearance rates lower than 60 mL/min (stage 3-5 chronic kidney disease according to the National Kidney Foundation). The authors critically review the evidence-based literature on RCI-AKI, its diagnosis, epidemiological aspects, predisposing conditions, and markers of risk, including advanced age. Procedures requiring the use of iodinated contrast media are increasingly performed in patients over 70 years of age, and there is no definitive consensus regarding the role of advanced age as a marker of risk for RCI-AKI.

[Loop diuretics: facts and fallacies].

Refractory edema is a clinical condition which recognises different etiologies and is characterized by decreased or absent diuretic response before the therapeutic goal is reached. Several pharmacokinetic and pharmacodynamic strategies are used in this setting, and further research is needed in order to optimize drug effectiveness.

Contrast Nephropathy: A Paradigm for Cardiorenal Interactions in Clinical Practice

Contrast-induced nephropathy (CIN) is defined as acute deterioration of renal function after intravascular administration of iodinated contrast agents, in the absence of other causes. Laboratory diagnosis is expressed as an increase in serum creatinine levels of 0.5 mg/dL (or 44 μmol/L) or a 25% or greater relative increase from baseline 48-72 hours after a diagnostic or interventional procedure, even if the clinical significance of this definition in the absence of pre-existing renal failure is questionable (Thomsen & Morcos, 2006).