Contributions to nephrology
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Since the early 1990s, experts in the field have thought that a reduction in cytokines in the blood compartment could, in theory, reduce mortality, but this is perhaps too naive as the pharmacodynamics and pharmacokinetics of cytokines throughout the body are not well known and are probably much more complicated than previously thought. This ha now led to three leading theories and concepts. Ronco and Bellomo conceived the peak concentration hypothesis in which clinicians concentrate their efforts to remove mediators and cytokines from the blood compartment at the proinflammatory phase of sepsis. ⋯ This has been demonstrated by several reports and is obviously extremely important. Perhaps this can explain why some very recent studies using high-permeability hemofiltration in sepsis have not been effective in improving hemodynamics and survival in septic acute animal models. In summary various brand new theories will be reviewed here in depth.
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The term pre-renal azotemia (or on occasion 'pre-renal renal failure') is frequently used in textbooks and in the literature to indicate an acute syndrome characterized by the presence of an increase in the blood concentration of nitrogen waste products (urea and creatinine). This syndrome is assumed to be due to loss of glomerular filtration rate but is not considered to be associated with histopathological renal injury. Thus, the term is used to differentiate 'functional' from 'structural' acute kidney injury (AKI) where structural renal injury is taken to indicate the presence of so-called acute tubular necrosis (ATN). ⋯ In such patients, several assumptions associated with the 'pre-renal azotemia paradigm' are violated. In particular, there is no evidence that ATN is the histopathological substrate of septic AKI, there is no evidence that urine tests can discriminate 'functional' from 'structural' AKI, there is no evidence that any proposed differentiation leads or should lead to different treatments, and there is no evidence that relevant experimentation can resolve these uncertainties. Given that septic AKI of critical illness now accounts for close to 50% of cases of severe AKI in developed countries, these observations call into question the validity and usefulness of the 'pre-renal azotemia paradigm' in AKI in general.
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Continuous renal replacement therapies (CRRTs) are increasingly used in order to maintain normal or near-normal acid-base balance in intensive care unit (ICU) patients. Acid-base balance is greatly influenced by the type of dialysis employed and by the administration route of replacement fluids. In continuous veno-venous hemofiltration, buffer balance depends on losses with ultrafiltrate and gain with replacement fluid, while in techniques such as continuous veno-venous hemodiafiltration, clinicians should balance the role of the dialysate. ⋯ However, the dialysate buffer or electrolyte concentration need always to be balanced with that of the replacement fluids employed. Both fluids should contain electrolytes in concentrations aiming for a physiologic level and taking into account preexisting deficits or excess and all input and losses. Clinicians should be aware that in CRRTs the quality control for sterility, physical properties, individualized prescription and balance control are vitally important.
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Sustained low-efficiency dialysis (SLED) is an increasingly popular form of renal replacement therapy for patients with renal failure in the intensive care unit. Advantages of SLED are efficient clearance of small solutes, good hemodynamic tolerability, flexible treatment schedules, and reduced costs. Studies comparing outcomes of SLED with those of other dialysis modalities are being performed.
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Traditionally the epidemiology of acute renal failure was assessed in patients requiring renal replacement therapy. Recent data emphasized the importance of less severe impairment of kidney function, hence the terminology acute kidney injury (AKI) was introduced. ⋯ Small changes in kidney function have an impact on outcomes and this knowledge has led to the introduction of the terminology AKI, encompassing both discrete and severe impairment of kidney function. The RIFLE classification describes the whole range of AKI and has been validated in multiple cohorts. As a consequence of increasing comorbidity, the incidence of AKI is increasing. The incidence of acute renal failure requiring renal replacement therapy even compares to that of acute lung injury, and up to two thirds of general ICU patients meet RIFLE criteria for AKI.