Nonoliguric acute renal failure

Urine biochemistry assessment in the sequential evaluation of renal function: Time to think outside the box

Urine biochemistry (UB) remains a controversial tool in acute kidney injury (AKI) monitoring, being considered to be of limited value both in terms of AKI diagnosis and prognosis. However, many criticisms can be made to the studies that have established the so called “pre-renal paradigm” (used for decades as the essential physiological basis for UB assessment in AKI) as well as to more recent studies suggesting that UB has no utility in daily clinical practice. The aim of this article is to describe our hypothesis on how to interpret simple and widely recognized urine biochemical parameters from a novel perspective, propose the rationale for their sequential assessment and demonstrate their usefulness in AKI monitoring, especially in the critical care setting.

Acute Renal Failure in Critically Ill Patients

Acute renal failure is an important cause of morbidity in critically ill patients. Acute renal failure results from pre renal and postrenal causes and, most importantly, acute tubular necrosis (ATN). Although it is known that renal toxins and renal ischemia are the most common causes of ATN in hospitalized patients, the exact pathogenesis of this entity is still not fully understood. Patients in the intensive care unit are at high risk for ATN because of hemodynamic instability, the administration of neph rotoxic antibiotics or chemotherapeutic agents, and ex posure to radiographic contrast agents. The acquired immunodeficiency syndrome is also associated with an increased risk of renal failure development, either from complications of the disease itself or from its treatment. Many consequences of acute renal failure such as vol ume overload, acidosis, hyperkalemia, and serositis can be managed adequately with peritoneal dialysis, hemo dialysis, or a newer technique, continuous arteriove nous hemofiltration. Despite improvements in treat ment, however, the mortality of ATN remains high. In this review, we recommend measures to prevent ATN in certain clinical situations that commonly occur among critically ill patients. We also review therapeutic options for treating patients in whom acute renal failure devel ops and discuss newer developments that may begin to reduce the excessive morbidity associated with ATN.

Etiology and outcomes of anuria in acute kidney injury: a single center study

BACKGROUND

It was previously known that anuric acute kidney injury (AKI) is uncommon and its occurrence suggests complete ureteral obstruction, shock, or a major vascular event. As the epidemiology of AKI has significantly changed over the past decade, it is possible that the incidence, etiology, or clinical characteristics of anuric AKI have also changed.

METHODS

A prospective cohort study was conducted that included all patients undergoing renal replacement therapy (RRT) for AKI during a 2-year period in a tertiary hospital. Patients were classified as having anuric, oliguric, or nonoliguric AKI based on their volume of urine when RRT started using the modified Acute Kidney Injury Network criteria.

RESULTS

Of the 203 patients included in the study, 21.2% met the criteria for anuric AKI. Septic and postoperative AKI were the main causes of anuric AKI, with 60.5% of incidences occurring in hospital. Anuric AKI was associated with a younger age, a lower prevalence of pre-morbid chronic kidney disease and diabetes, more frequent continuous RRT requirement, and multi-organ dysfunction. In addition, patients with anuric AKI had a higher rate of in-hospital mortality and long-term dependence on RRT than patients with nonanuric AKI.

CONCLUSION

Anuric AKI is common, with sepsis as the main etiological insult, and is associated with adverse outcomes among patients with AKI who require RRT.

Adjudication of etiology of acute kidney injury: experience from the TRIBE-AKI multi-center study

Background

Adjudication of patient outcomes is a common practice in medical research and clinical trials. However minimal data exists on the adjudication process in the setting of Acute Kidney Injury (AKI) as well as the ability to judge different etiologies (e.g. Acute Tubular Necrosis (ATN), Pre-renal Azotemia (PRA)).

Methods

We enrolled 475 consecutive patients undergoing cardiac surgery at four sites of the Translational Research Investigating Biomarker Endpoints in AKI (TRIBE-AKI) study. Three expert nephrologists performed independent chart review, utilizing clinical variables and retrospective case report forms with pre intra and post-operative data, and then adjudicated all cases of AKI (n = 67). AKI was defined as a > 50% increase in serum creatinine for baseline (RIFLE Risk). We examined the patterns of AKI diagnoses made by the adjudication panel as well as association of these diagnoses with pre and postoperative kidney injury biomarkers.

Results

There was poor agreement across the panel of reviewers with their adjudicated diagnoses being independent of each other (Fleiss’ Kappa = 0.046). Based on the agreement of the two out of three reviewers, ATN was the adjudicated diagnosis in 41 cases (61%) while PRA occurred in 13 (19%). Neither serum creatinine or any other biomarker of AKI (urine or serum), was associated with an adjudicated diagnosis of ATN within the first 24 post-operative hours.

Conclusion

The etiology of AKI after cardiac surgery is probably multi-factorial and pure forms of AKI etiologies, such as ATN and PRA may not exist. Biomarkers did not appear to correlate with the adjudicated etiology of AKI; however the lack of agreement among the adjudicators impacted these results.

Trial registration

Clinicaltrials.gov: NCT00774137

Early diagnosis of acute kidney injury

There is a considerable lack of data concerning the diagnostic testing for kidney damage after surgical procedures. In this situation the most important variables should be examined with respect to their clinical informative value, the costs associated with their analysis, and their potential use in routine diagnostic testing. Forty patients in the surgical intensive care unit (ICU) with acute kidney injury (AKI) that developed during their stay of 13–18 (median, 16) days in the ICU were examined daily during their entire ICU admission. The bulk of the laboratory research consisted of the measurement of creatinine, urea, and sodium, as well as clearances rates and diuresis. Various tests for diagnosing regional renal damage (enzymes and proteins) were also carried out. The included photometry, nephelometric analysis, and ELISA (enzyme-linked immunosorbent assay). Five days before an AKI became evident, pathologic levels of urinary α1-microglobulin (tubular parameter) could already be confirmed. Serum creatinine values or creatinine clearance indicated the presence of disease only 1 day before the AKI was seen. Our results show that determination of α1-microglobulin and immunoglobulin G (glomerular parameter) levels, in addition to the level of urea in serum, be recommended for patients in surgical intensive care units who are at risk for AKI. Use of these procedures can achieve early recognition and sufficiently precise localization of renal damage.

Serum magnesium in recovering acute renal failure

We studied the manifestations of hypomagnesemia in 50 patients with acute renal failure who had been admitted in our hospital over a period of ten months. All patients with serum creatine ≥ 2 mg/dL and normal baseline levels of serum calcium, magnesium, and potassium as well as normal ECG were included in the study. Patients with multi-organ failure, drug-induced acute renal failure, obstructive uropathy, and alcohol addiction were excluded. The mean age of our study population was 40 ± 15 years, 37 of the patients were male and 13 were female. Hypomagnesemia was observed in 31 patients out of 50 during the recovery period of acute renal failure with symptomatic hypomagnesemia being seen in 23 patients. Serum magnesium levels on the day of admission and during the recovery phase were 2.11 ± 0.38 mg/dL and 1.64 ± 0.41 mg/dL respectively. Paresthesia, irritability, agitation, dysartharia, vertigo, and associated hypokalemia and hypocalcemia were noted in symptomatic hypomagnesemic patients. Treatment of hypomagnesaemia and hypokalemia ameliorated the symptoms. We conclude that these abnormalities produce clinically significant manifestations in recovery phase of acute renal failure and clinicians should pay attention to these.

Management of acute renal failure in the elderly patient: a clinician's guide

Numerous anatomical and functional changes occurring in the aging kidney lead to reduced glomerular filtration rate, lower renal blood flow and impaired renal autoregulation. The elderly are especially vulnerable to the development of renal dysfunction and in this population acute renal failure (ARF) is a common problem. ARF is often iatrogenic and multifactorial; common iatrogenic combinations include pre-existing renal dysfunction and exposure to nephrotoxins such as radiocontrast agents or aminoglycosides, use of NSAIDs in patients with congestive cardiac failure and use of ACE inhibitors and diuretics in patients with underlying atherosclerotic renal artery stenosis. The aetiology of ARF is classically grouped into three categories: prerenal, intrinsic and postrenal. Prerenal ARF is the second most common cause of ARF in the elderly, accounting for nearly one-third of all hospitalized cases. Common causes can be grouped into true volume depletion (e.g. decreased fluid intake), decreased effective blood volume (e.g. systemic vasodilation) and haemodynamic (e.g. renal artery stenosis, NSAID use). Acute tubular necrosis (ATN) is the most common cause of intrinsic ARF and is responsible for over 50% of ARF in hospitalized patients, and up to 76% of cases in patients in intensive care units. ATN usually occurs after an acute ischaemic or toxic event. The pathogenesis of ATN involves an interplay of processes that include endothelial injury, microvascular flow disruption, tubular hypoxia, dysfunction and apoptosis, tubular obstruction and trans-tubular back-leak. Vasculitis causing ARF should not be missed as this condition is potentially life threatening. The likelihood of a postrenal cause for ARF increases with age. Benign prostatic hypertrophy, prostatic carcinoma and pelvic malignancies are all important causes. Early identification of ARF secondary to obstruction with renal imaging is essential, and complete or partial renal recovery usually ensues following relief of the obstruction.A comprehensive medical and drug history and physical examination are all invaluable. Particular attention should be paid to the fluid status of the patient (skin turgor, jugular venous pressure, lying and standing blood pressure, urine output). Urinalysis should be performed to detect evidence of proteinuria and haematuria, which will aid diagnosis. Fractional excretion of sodium and urine osmolality may be measured but the widespread use of diuretics in the elderly gives rise to unreliable results. Renal imaging, usually ultrasound scanning, is routinely performed for assessment of renal size and to exclude urinary obstruction. In some cases, renal biopsy is necessary to provide specific diagnostic information. The general principles of managing ARF include treatment of life-threatening features such as shock, respiratory failure, hyperkalaemia, pulmonary oedema, metabolic acidosis and sepsis; stopping and avoiding administration of nephrotoxins; optimization of haemodynamic and fluid status; adjustment of drug dosage appropriate to glomerular filtration rate; early nutritional support; and early referral to nephrologists for diagnosis of ARF cause, timely initiation of dialysis and initiation of specific treatment. The treatment of prerenal and ATN ARF is largely supportive with little evidence of benefit from current pharmacological therapies. Despite advances in critical care medicine and renal replacement therapy, the mortality of ARF has not changed significantly over the last 40 years, with current mortality rates being up to 75%.

Long-term monitoring of renal function in poly-traumatized intensive care patients

INTRODUCTION

For the long-term monitoring of kidney function, polytraumatized patients were examined and routine as well as specialized parameters were compared.

MATERIALS AND METHODS

30 patients of the Surgical Intensive Care Unit (ICU) were examined daily over the entire period they stayed in the ICU. The patients were retrospectively classified as either survivors or deceased patients. Group 1 consisted of 20 patients who resided in the ICU for 11-15 (Median 14) days before they could be transferred to a normal hospital unit. Group 2 consisted of 10 patients who had passed away after 13-18 (Median 16) days in the ICU. In addition to the routine parameters diuresis, serum creatinine and serum urea, specialized parameters for kidney function including the excretion rates of alpha1-microglobulin (alpha1-MG), N-Acetyl-beta-D-glucosaminidase (NAG), angiotensinase A (ATA) and immunoglobulin G (IgG) were determined.

RESULTS

Similar biometric data were shown by all patients at admission into the ICU, but differences did exist regarding the Revised Trauma Score, Injury Severity Score and the APACHE-II-Score. In the period between the 5th and 8th day of intensive treatment almost all patients showed pathological excretion rates of tubular and glomerular parameters whereby no increased frequency of unusual events could be determined at these time-points.

CONCLUSION

During treatment in the ICU, all examined patients showed at times pathological excretion rates of specialized kidney function parameters. Such transient damage was only apparent in a few of the patients when the standard parameters serum creatinine and serum urea were employed. In 90% of the surviving patients the kidney parameters had normalized until the time they were transferred, indicating that such parameters reflected the general state of health of these patients.

Reversing oliguria in critically ill patients

Oliguria is a common occurrence in the ICU setting. In patients with preserved renal function, fluid challenges or low doses of diuretics are generally successful. In patients with oliguric renal failure, it is still essential to ensure adequate intravascular fluid volume, especially in critically ill patients. Loop diuretics remain the mainstay of treatment. When diuretic resistance is encountered, physicians should consider further optimization of hemodynamics, alternative loop diuretics, and combined drug therapy. In some cases, continuous renal replacement therapy can be very effective. Yet, while these interventions can help reduce the morbidity of severe volume overload, they have not been shown to improve mortality rates.

Effects of atrial natriuretic peptide in clinical acute renal failure

Fifty-three consenting patients meeting clinical and urine composition criteria for established intrinsic ARF were assigned to two treatment groups. Group I patients were treated with human atrial natriuretic peptide (ANP) with or without diuretics. Groups II patients were treated with or without diuretics and with no ANP. Age, sex, etiology of ARF, entry serum creatinines (SCr) (Group I, 5.3 +/- 1.8; Group II, 5.1 +/- 2.1 mg/dl) and creatinine clearances (CCr) (Group I, 9.9 +/- 2.1; Group II, 9.2 +/- 2.1 ml/min) were similar. Thirty patients received ANP [0.20 micrograms/kg/min i.v. x 24 hr (N = 20) or 0.08 micrograms/kg/min i.a. x 8 hr (N = 10)] and furosemide, 0.5 mg/kg/hr x 24 hr or mannitol, 12.5 g every six hours x 4, or no diuretic; 23 Group II patients received diuretics as above or no diuretic in a similar distribution to Group I. CCr (verified with simultaneous inulin clearances x 12, r = 0.93, P < 0.001) increased significantly by eight hours of ANP treatment to 17.1 +/- 3.2 ml/min and by 24 hours after discontinuing ANP to 21.0 +/- 4.4 ml/min (both P < 0.05). There was no corresponding increase in CCr in Group II. Dialysis was required in 23% of Group I and in 52% of Group II patients (different at P < 0.05). Mortality rates of 17% for Group I and 35% for Group II were not significantly different (P = 0.11). It is concluded that parenteral ANP increases CCr and reduces need for dialysis in patients with established intrinsic ARF.

Glomerular and tubular factors in urine flow rates of acute renal failure patients

Distinguishing between oliguric and nonoliguric acute renal failure (ARF) has clinical relevance. However, there is a paucity of data regarding the pathophysiologic basis for variations in urine flow rates in ARF. This study was designed to determine whether differences in residual levels of glomerular filtration rate (GFR) or differences in tubular reabsorption of filtered solutes and H2O accounted for the variations in urine flow rates among ARF patients. Twenty-five patients with ARF of 3 to 6 days duration having ischemic and nephrotoxic etiologies, increasing serum creatinines of more than 0.7 mg/dL/d, urine sodium concentrations and fractional excretions of sodium (FENa) of more than 20 mEq/L and more than 1%, respectively, 12 hours after stopping diuretics and urine sediments consistent with acute tubular necrosis were studied. Urine and serum collections were made over an 8-hour period to determine creatinine clearance (Ccr), filtered osmolar load, urine to serum creatinine ratio (U/Scr), urine to serum creatinine osmolality (U/Sosm), and FENa. These were compared with urine flow rates. Creatinine clearance was validated as an estimate of GFR in ARF with simultaneous inulin clearances x 12 measurements (r = 0.935, P < 0.001). Residual Ccr was strongly correlated with urine flow rate (r = 0.857, P < 0.001), as was filtered osmolar load (r = 0.810, P < 0.001). However, the latter relationship was totally dependent on Ccr. There was no correlation between U/Scr, U/Sosm, or FENa and urine flow rates. It is concluded that the residual level of GFR is the primary determinant of variations in urine flow rate in patients with ARF.

Glomerular alterations in experimental oliguric and nonoliguric acute renal failure

Studies were performed in oliguric and nonoliguric forms of uranyl acetate (UA)-induced and ischemic acute renal failure (ARF) to examine whether a reduction in GFR is correlated with glomerular morphologic alterations. UA-induced nonoliguric and oliguric ARF were induced in rabbits by i.v. injections of 0.9 and 2 mg/kg, respectively. A 60-min renal artery clamping produced nonoliguric ARF in previously uninephrectomized rats, but oliguric ARF in the clamped kidneys of sham-nephrectomized animals. A decline in the whole-kidney CIn rate was more marked in oliguric ARF kidneys of both models than in nonoliguric ARF kidneys. Also, tubular damage was more pronounced in oliguric kidneys when compared with nonoliguric kidneys. Scanning electron microscopic observations revealed glomerular alterations in oliguric and nonoliguric kidneys in both models, evidenced by a flattening and spreading of podocyte cell bodies associated with loss of epithelial foot processes and a reduction in the density and diameter of endothelial fenestrae. There was no significant difference in these glomerular changes between oliguric and nonoliguric kidneys. The findings suggest that less reduction in the whole-kidney GFR in nonoliguric ARF kidneys is ascribed largely to less pronounced tubular damage rather than to less severe glomerular morphologic alterations.

Ischemic acute renal failure

Underperfusion of the kidneys often results in the development of ischemic acute renal failure. This review summarizes the recent developments in the understanding of the pathophysiology, diagnosis, and treatment of this serious and costly disorder that affects almost 5% of hospitalized patients.

Fluid needs in acute renal failure

Derangements of fluid, electrolyte, and acid-base homeostasis are an inevitable part of acute renal failure. Understanding the pathophysiology of these disorders is essential to treating and preventing potentially life-threatening complications. Appropriate nutritional support is also an important part of management in childhood acute renal failure.