Urinary indices and microscopy in sepsis-related acute renal failure

The Use of Selected Urine Chemistries in the Diagnosis of Kidney Disorders

Urinary chemistries vary widely in both health and disease and are affected by diet, volume status, medications, and disease states. When properly examined, these tests provide important insight into the mechanism and therapy of various clinical disorders that are first detected by abnormalities in plasma chemistries. These tests cannot be interpreted in isolation, but instead require knowledge of key clinical information, such as medications, physical examination, and plasma chemistries, to include kidney function. When used appropriately and with knowledge of limitations, urine chemistries can provide important insight into the pathophysiology and treatment of a wide variety of disorders.

Fluid and Volume Monitoring

Background

Fluid resuscitation is not only used to prevent acute kidney injury (AKI) but fluid management is also a cornerstone of treatment for patients with established AKI and renal failure. Ultrafiltration removes volume initially from the intravascular compartment inducing a relative degree of hypovolemia. Normal reflex mechanisms attempt to sustain blood pressure constant despite marked changes in blood volume and cardiac output. Thus, compensated shock with a normal blood pressure is a major cause of AKI or exacerbations of AKI during ultrafiltration.

Methods

We undertook a systematic review of the literature using MEDLINE, Google Scholar and PubMed searches. We determined a list of key questions and convened a 2-day consensus conference to develop summary statements via a series of alternating breakout and plenary sessions. In these sessions, we identified supporting evidence and generated clinical practice recommendations and/or directions for future research.

Results

We defined three aspects of fluid monitoring: i) normal and pathophysiological cardiovascular mechanisms; ii) measures of volume responsiveness and impending cardiovascular collapse during volume removal, and; iii) measured indices of each using non-invasive and minimally invasive continuous and intermittent monitoring techniques. The evidence documents that AKI can occur in the setting of normotensive hypovolemia and that under-resuscitation represents a major cause of both AKI and mortality ion critically ill patients. Traditional measures of intravascular volume and ventricular filling do not predict volume responsiveness whereas dynamic functional hemodynamic markers, such as pulse pressure or stroke volume variation during positive pressure breathing or mean flow changes with passive leg raising are highly predictive of volume responsiveness. Numerous commercially-available devices exist that can acquire these signals.

Conclusions

Prospective clinical trials using functional hemodynamic markers in the diagnosis and management of AKI and volume status during ultrafiltration need to be performed. More traditional measure of preload be abandoned as marked of volume responsiveness though still useful to assess overall volume status.

Fractional excretion of urea as a diagnostic index in acute kidney injury in intensive care patients

PURPOSE

Acute kidney injury (AKI) is a dynamic process that evolves from an early reversible condition to an established disease. Value of urine indices in the event of AKI is uncertain in critically ill patients. The aim of this study was to evaluate the performance of fractional excretion of urea (FeU) for differentiating persistent from transient AKI in patients admitted to the intensive care unit.

METHODS

This was an observational study. Forty-seven patients with AKI according to the RIFLE classification were included. Transient AKI was defined as AKI resolved within 3 days after inclusion. Persistent AKI was defined as persistent serum creatinine elevation or oliguria.

RESULTS

Fractional excretion of urea was lower in case of transient, 33% (25-39), than persistent AKI, 47% (36-61) (P = .001). Areas under the receiver operating characteristic curve for FeU in case of transient AKI were better than those for other urinary indexes, 0.78 (95% confidence interval, 0.63-0.92). Optimal cutoff point according to the receiver operating characteristic curve was 40%. In patients treated with diuretics, FeU was the only predictive index of transient AKI. Fractional excretion of urea gradually increased from days 1 to 7 in transient AKI, whereas plasma creatinine decreased.

CONCLUSIONS

Fractional excretion of urea less than 40% was found to be a sensitive and specific index in differentiating transient from persistent AKI in intensive care unit patients especially if diuretics had been administered.

Prognostic significance of urine neutrophil gelatinase-associated lipocalin in patients with septic acute kidney injury

Acute kidney injury (AKI) is a common clinical problem which occurs in critically ill patients. Sepsis is now recognized as the most important contributing factor to AKI in this population. In clinical practice, certain studies have explored the urine neutrophil gelatinase-associated lipocalin (uNGAL) and the urine kidney injury molecule-1 (uKIM-1) as diagnostic and prognostic indices of AKI. Yet, it remains unclear whether uNGAL and uKIM-1 are associated with measures of disease severity and with adverse clinical outcomes in patients with established septic AKI of mixed cause and severity. Ninety-two septic patients with AKI were enrolled in a pilot study to test whether uKIM and uNGAL levels predict 180-day mortality. We initially performed univariate Cox proportional hazards analyses incorporating multiple demographic, clinical and laboratory variables. As a result, the APACHE II score (p= 0.014) and uNGAL (p= 0.015) were identified as independent predictors of 180-day mortality. On the other hand, there was no statistical difference in event-free survival between patients with and without higher serum creatinine, creatinine clearance and uKIM-1 (data not shown). In conclusion, uNGAL may be a promising predictor for septic patients with AKI, resulting in a clear increase in 180-day mortality. Further clinical evaluation of uNGAL is underway.

Plasma and urine neutrophil gelatinase-associated lipocalin in septic versus non-septic acute kidney injury in critical illness

OBJECTIVE

Sepsis is the most common trigger for acute kidney injury (AKI) in critically ill patients. We sought to determine whether there are unique patterns to plasma and urine neutrophil gelatinase-associated lipocalin (NGAL) in septic compared with non-septic AKI.

DESIGN

Prospective observational study.

SETTING

Two adult ICUs in Melbourne, Australia.

PATIENTS

Critically ill patients with septic and non-septic AKI.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Blood and urine specimens collected at enrollment, 12, 24 and 48 h to measure plasma and urine NGAL. Eighty-three patients were enrolled (septic n = 43). Septic AKI patients had more co-morbid disease (p = 0.005), emergency surgical admissions (p < 0.001), higher illness severity (p = 0.008), more organ dysfunction (p = 0.008) and higher white blood cell counts (p = 0.01). There were no differences at enrollment between groups in AKI severity. Septic AKI was associated with significantly higher plasma (293 vs. 166 ng/ml) and urine (204 vs. 39 ng/mg creatinine) NGAL at enrollment compared with non-septic AKI (p < 0.001). Urine NGAL remained higher in septic compared with non-septic AKI at 12 h (p < 0.001) and 24 h (p < 0.001). Plasma NGAL showed fair discrimination for AKI progression (area under receiver-operator characteristic curve 0.71) and renal replacement therapy (AuROC 0.78). Although urine NGAL performed less well (AuROC 0.70, 0.70), peak urine NGAL predicted AKI progression better in non-septic AKI (AuROC 0.82).

CONCLUSION

Septic AKI patients have higher detectable plasma and urine NGAL compared with non-septic AKI patients. These differences in NGAL values in septic AKI may have diagnostic and clinical relevance as well as pathogenetic implications.

Hemodynamics and metabolic studies on septic shock in patients with acute liver failure

BACKGROUND

Acute liver failure is often accompanied by hyperdynamic circulation, which is also a characteristic of septic shock. Pre-existing acute liver failure may worsen the hemodynamic impairment and prognosis in sepsis.

AIMS

To evaluate the hemodynamic and metabolic characteristics and clinical outcomes of septic shock in patients with acute liver failure.

METHODS

Twenty patients with acute liver failure and 19 patients without preexisting liver disease were evaluated. Systemic hemodynamics, arterial and mixed vein blood gases, arterial lactate levels, plasma renin activity, and plasma aldosterone levels were checked during the early phase of septic shock.

RESULTS

In acute liver failure group, cardiac index (4.92 +/- 1.13 vs 3.69 +/- 1.06 L/min per square meter, P < .001) and oxygen delivery (604.7 +/- 139.7 vs 485.4 +/- 137.3 mL/min per square meter, P = .011) were significantly higher than those without preexisting liver diseases, while systemic vascular resistance index (1041.2 +/- 503.3 vs 1409 +/- 505.25 dyne.s/cm(5).m(2)), oxygen consumption (119.1 +/- 29.2 vs 162.4 +/- 49.4 mL/min per square meter) and oxygen extraction ratio (20% +/- 6% vs. 32% +/- 8%) were significantly higher in the latter group. Furthermore, the patients with acute liver failure had higher arterial lactate (P = .026), plasma renin activity (P = .03), plasma aldosterone levels (P < .001), and intensive care unit as well as hospital mortality rates (P = .005, and 0.02 respectively).

CONCLUSIONS

In patients with acute liver failure, septic shock was characterized by an accentuated hyperdynamic circulation, hyperlactatemia and an augmented renin-angiotensin-aldosterone system activity. Pre-existing liver failure has a significant impact on the disease severity of septic shock and portends a grave prognosis.

A systematic review of urinary findings in experimental septic acute renal failure

OBJECTIVE

In experimental septic acute renal failure, urinary analysis is used to help diagnose and classify renal injury. However, the scientific basis for such use has not been systematically evaluated. Thus, we appraised the value of common urinary findings for the diagnosis and classification of experimental septic acute renal failure.

DESIGN

Systematic review.

SETTING

Academic medical center and university-based research laboratory.

SUBJECTS

Experimental studies describing urinary biochemistry, derived indexes, and microscopy in septic acute renal failure.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Twenty-seven articles fulfilled all inclusion criteria. Due to heterogeneity, no formal quantitative analysis was possible. The methods for induction of sepsis and models were variable. The urinary sodium, fractional excretion of sodium, and urine osmolality were reported in only four (15%), 21 (78%), and seven (26%) studies, respectively. The fractional excretion of sodium exhibited a decrease, no change, or an increase from baseline in 11 (52%), five (24%), and five (24%) studies, respectively. The urine osmolality decreased from baseline in all endotoxin-induced models but showed an early transient increase in six (22%) studies of cecal-ligation perforation. Proteinuria or urinary enzymuria was reported in only seven (26%) studies. Urinary microscopy was described in one study. Only ten studies (37%) simultaneously reported on histopathology. In all these studies, histology either was normal or showed minor ultrastructural changes on electron microscopy.

CONCLUSIONS

No conclusions are possible on how several urinary tests perform in diagnosing or classifying acute renal failure or in predicting the presence of acute tubular necrosis in experimental sepsis. Additional research is necessary to define the diagnostic and prognostic value of urinalysis in experimental sepsis.