Validation of the Kidney Disease Improving Global Outcomes Criteria for AKI and Comparison of Three Criteria in Hospitalized Patients

Background and objectives

AKI is a major clinical problem and predictor of outcome in hospitalized patients. In 2013, the Kidney Disease: Improving Global Outcomes (KDIGO) group published the third consensus AKI definition and classification system after the Risk, Injury, Failure, Loss of Kidney Function, and End-Stage Kidney Disease (RIFLE) and the Acute Kidney Injury Network (AKIN) working group systems. It is unclear which system achieves optimal prognostication in hospital patients.

Design, setting, participants, & measurements

A retrospective observational study using hospital laboratory, admission, and discharge databases was performed that included adult patients admitted to a teaching hospital in Tokyo, Japan between April 1, 2008, and October 31, 2011. AKI occurring during each hospital stay was identified, and discriminative ability of each AKI classification system based on serum creatinine for the prediction of hospital mortality was assessed. The receiver operating characteristic curve, a graphical measure of test performance, and the area under the curve were used to evaluate how classifications preformed on the study population.

Results

In total, 49,518 admissions were studied, of which 11.0% were diagnosed with RIFLE criteria and 11.6% were diagnosed with KDIGO criteria, but only 4.8% were diagnosed with AKIN criteria. Overall hospital mortality was 3.0%. AKI staging and hospital mortality were closely correlated in all systems. Discrimination for hospital mortality was similar for RIFLE and KDIGO criteria (area under the curve=0.77 versus 0.78; P=0.02), whereas AKIN discrimination was inferior (area under the curve=0.69 versus RIFLE [P<0.001] versus KDIGO [P<0.001]).

Conclusion

Among hospital patients, KDIGO and RIFLE criteria achieved similar discrimination, but the discrimination of AKIN was inferior.     

Comparison of Diagnostic Criteria for Acute Kidney Injury in Cardiac Surgery

Background

There is considerable controversy regarding the diagnosis of Acute Kidney Injury (AKI), and there are over 30 different definitions.

Objective

To evaluate the incidence and risk factors for the development of AKI following cardiac surgery according to the RIFLE, AKIN and KDIGO criteria, and compare the prognostic power of these criteria.

Methods

Cross-sectional study that included 321 consecutive patients (median age 62 [53-71] years; 140 men) undergoing cardiac surgery between June 2011 and January 2012. The patients were followed for up to 30 days, for a composite outcome (mortality, need for dialysis and extended hospitalization).

Results

The incidence of AKI ranged from 15% - 51%, accordingly to the diagnostic criterion adopted. While age was associated with risk of AKI in the three criteria, there were variations in the remaining risk factors. During follow-up, 89 patients developed the outcome and all criteria were associated with increased risk in the univariate Cox analysis and after adjustment for age, gender, diabetes, and type of surgery. However, after further adjustment for extracorporeal circulation and the presence of low cardiac output, only AKI diagnosed by the KDIGO criterion maintained this significant association (HR= 1.89 [95% CI: 1.18 - 3.06]).

Conclusion

The incidence and risk factors for AKI after cardiac surgery vary significantly according to the diagnostic criteria used. In our analysis, the KDIGO criterion was superior to AKIN and RIFLE with regard its prognostic power.     

Derivation of Urine Output Thresholds That Identify a Very High Risk of AKI in Patients with Septic Shock

Background and objectives

To promote early detection of AKI, recently proposed pretest probability models combine sub–Kidney Disease Improving Global Outcomes (KDIGO) AKI criteria with baseline AKI risk. The primary objective of this study was to determine sub-KDIGO thresholds that identify patients with septic shock at highest risk for AKI.

Design, setting, participants, & measurements

This was a retrospective analysis of 390 adult patients admitted to the medical intensive care unit (ICU) of a tertiary, academic medical center with septic shock between January 2008 and December 2010. Hourly urine output was collected from the time of septic shock recognition (hour 0) to hour 96, urine catheter removal, or ICU discharge (whichever occurred first). All available serum creatinine (SCr) measurements were collected until hour 96. The AKI pretest probability model was assessed during the first 12 hours of resuscitation and included the initial episode of oliguria, increase from baseline to peak SCr level, and Acute Physiology and Chronic Health Evaluation (APACHE) III score in a multivariable receiver-operator characteristic (ROC) analysis. The primary outcome was the incidence of stage II or III (stage II+) AKI defined by KDIGO criteria. Secondary outcomes included the need for RRT and 28-day mortality.

Results

Ninety-eight (25%) patients developed stage II+ AKI after septic shock recognition. APACHE III score and increase in SCr level in the first 12 hours were not statistically associated with stage II+ AKI in multivariable ROC analysis. Consecutive oliguria for 3 hours had fair predictive ability for achieving stage II+ AKI criteria (area under ROC curve, 0.73; 95% confidence interval [95% CI], 0.68 to 0.78), and oliguria for 5 hours demonstrated optimal accuracy (82%; 95% CI, 79% to 86%).

Conclusions

Three to 5 hours of consecutive oliguria in patients with septic shock may provide a valuable measure of AKI risk. Further validation to support this finding is needed.     

Serum Creatinine Back-Estimation in Cardiac Surgery Patients: Misclassification of AKI Using Existing Formulae and a Data-Driven Model

Background and objectives

A knowledge of baseline serum creatinine (bSCr) is mandatory for diagnosing and staging AKI. With often missing values, bSCr is estimated by back-calculation using several equations designed for the estimation of GFR, assuming a “true” GFR of 75 ml/min per 1.73 m². Using a data set from a large cardiac surgery cohort, we tested the appropriateness of such an approach and compared estimated and measured bSCr. Moreover, we designed a novel data-driven model (estimated serum creatinine [eSCr]) for estimating bSCr. Finally, we analyzed the extent of AKI and mortality rate misclassifications.

Design, setting, participants, & measurements

Data for 8024 patients (2833 women) in our cardiac surgery center were included from 1997 to 2008. Measured and estimated bSCr were plotted against age for men and women. Patients were classified to AKI stages defined by the Kidney Disease Improving Global Outcomes (KDIGO) group. Results were compared with data from another cardiac surgery center in Zurich, Switzerland.

Results

The Modification of Diet in Renal Disease and the Chronic Kidney Disease Epidemiology Collaboration formulae describe higher estimated bSCr values in younger patients, but lower values in older patients compared with the measured bSCr values in both centers. The Pittsburgh Linear Three Variables formula correctly describes the increasing bSCr with age, however, it underestimates the overall bSCr level, being in the range of the 25% quantile of the measured values. Our eSCr model estimated measured bSCr best. AKI stage 1 classification using all formulae, including our eSCr model, was incorrect in 53%–80% of patients in Vienna and in 74%–91% in Zurich; AKI severity (according to KDIGO stages) and also mortality were overestimated. Mortality rate was higher among patients falsely classified into higher KDIGO stages by estimated bSCr.

Conclusions

bSCr values back-estimated using currently available eGFR formulae are inaccurate and cannot correctly classify AKI stages. Our model eSCr improves the prediction of AKI but to a still inadequate extent.     

Plasma Catalytic Iron,AKI, and Death among Critically Ill Patients

Background and objectives

Catalytic iron has been hypothesized to be a key mediator of AKI. However, the association between plasma catalytic iron levels and AKI has not been well studied in humans.

Design, settings, participants, & measurements

A single-center, prospective, nonconsecutive cohort study of 121 critically ill patients admitted to intensive care units (ICUs) between 2008 and 2012 was performed. Plasma catalytic iron, free hemoglobin, and other iron markers were measured on ICU days 1 and 4. The primary end point was in-hospital mortality or AKI requiring RRT. Secondary end points included mortality (assessed during hospitalization, at 30 days, and 1 year) and incident AKI, defined by modified Kidney Disease Improving Global Outcomes criteria.

Results

ICU day 1 plasma catalytic iron levels were higher among patients who reached the primary end point (median, 0.74 µmol/l [interquartile range, 0.31–3.65] versus 0.29 µmol/l [0.22–0.46]; P<0.01). ICU day 1 plasma catalytic iron levels were associated with number of packed red blood cell transfusions before ICU arrival (r_s=0.29; P<0.001) and plasma free hemoglobin levels on ICU day 1 (r_s=0.32; P<0.001). Plasma catalytic iron levels on ICU day 1 were significantly associated with in-hospital mortality or AKI requiring RRT, even after adjusting for age, enrollment eGFR, and number of packed red blood cell transfusions before ICU arrival (13 events; adjusted odds ratio per 1-SD higher ln[catalytic iron], 3.33; 95% confidence interval, 1.79 to 6.20). ICU day 1 plasma catalytic iron levels were also significantly associated with incident AKI, RRT, hospital mortality, and 30-day mortality.

Conclusions

Among critically ill patients, elevated plasma catalytic iron levels on arrival to the ICU are associated with a greater risk of incident AKI, RRT, and hospital mortality.     

Performance and Limitations of Administrative Data in the Identification of AKI

Background and objectives

Billing codes are frequently used to identify AKI events in epidemiologic research. The goals of this study were to validate billing code–identified AKI against the current AKI consensus definition and to ascertain whether sensitivity and specificity vary by patient characteristic or over time.

Design, setting, participants, & measurements

The study population included 10,056 Atherosclerosis Risk in Communities study participants hospitalized between 1996 and 2008. Billing code–identified AKI was compared with the 2012 Kidney Disease Improving Global Outcomes (KDIGO) creatinine-based criteria (AKI_cr) and an approximation of the 2012 KDIGO creatinine- and urine output–based criteria (AKI_{cr_uop}) in a subset with available outpatient data. Sensitivity and specificity of billing code–identified AKI were evaluated over time and according to patient age, race, sex, diabetes status, and CKD status in 546 charts selected for review, with estimates adjusted for sampling technique.

Results

A total of 34,179 hospitalizations were identified; 1353 had a billing code for AKI. The sensitivity of billing code–identified AKI was 17.2% (95% confidence interval [95% CI], 13.2% to 21.2%) compared with AKI_cr (n=1970 hospitalizations) and 11.7% (95% CI, 8.8% to 14.5%) compared with AKI_{cr_uop} (n=1839 hospitalizations). Specificity was >98% in both cases. Sensitivity was significantly higher in the more recent time period (2002–2008) and among participants aged 65 years and older. Billing code–identified AKI captured a more severe spectrum of disease than did AKI_cr and AKI_{cr_uop}, with a larger proportion of patients with stage 3 AKI (34.9%, 19.7%, and 11.5%, respectively) and higher in-hospital mortality (41.2%, 18.7%, and 12.8%, respectively).

Conclusions

The use of billing codes to identify AKI has low sensitivity compared with the current KDIGO consensus definition, especially when the urine output criterion is included, and results in the identification of a more severe phenotype. Epidemiologic studies using billing codes may benefit from a high specificity, but the variation in sensitivity may result in bias, particularly when trends over time are the outcome of interest.     

AKI in Low-Risk versus High-Risk Patients in Intensive Care

Background and objectives

AKI in critically ill patients is usually part of multiorgan failure. However, nonrenal organ failure may not always precede AKI and patients without evidence of these organ failures may not be at low risk for AKI. This study examined the risk and outcomes associated with AKI in critically ill patients with and without cardiovascular or respiratory organ failures at presentation to the intensive care unit (ICU).

Design, setting, participants, & measurements

A large, academic medical center database, with records from July 2000 through October 2008, was used and the authors identified a low-risk cohort as patients without cardiovascular and respiratory organ failures defined as not receiving vasopressor support or mechanical ventilation within the first 24 hours of ICU admission. AKI was defined using Kidney Disease Improving Global Outcomes criteria. The primary end points were moderate to severe AKI (stages 2–3) and risk-adjusted hospital mortality.

Results

Of 40,152 critically ill patients, 44.9% received neither vasopressors nor mechanical ventilation on ICU day 1. Stages 2–3 AKI occurred less frequently in the low-risk patients versus high-risk patients within 24 hours (14.3% versus 29.1%) and within 1 week (25.7% versus 51.7%) of ICU admission. Patients developing AKI in both risk groups had higher risk of death before hospital discharge. However, the adjusted odds of hospital mortality were greater (odds ratio, 2.99; 95% confidence interval, 2.62 to 3.41) when AKI occurred in low-risk patients compared with those with respiratory or cardiovascular failures (odds ratio, 1.19; 95% confidence interval, 1.09 to 1.3); interaction P<0.001.

Conclusions

Patients admitted to ICU without respiratory or cardiovascular failure have a substantial likelihood of developing AKI. Although survival for low-risk patients is better than for high-risk patients, the relative increase in mortality associated with AKI is actually greater for low-risk patients. Strategies aimed at preventing AKI should not exclude ICU patients without cardiovascular or respiratory organ failures.     

Urinary Biomarkers and Progression of AKI in Patients with Cirrhosis

Background and objectives

AKI is a common and severe complication in patients with cirrhosis. AKI progression was previously shown to correlate with in-hospital mortality. Therefore, accurately predicting which patients are at highest risk for AKI progression may allow more rapid and targeted treatment. Urinary biomarkers of structural kidney injury associate with AKI progression and mortality in multiple settings of AKI but their prognostic performance in patients with liver cirrhosis is not well known.

Design, setting, participants, & measurements

A multicenter, prospective cohort study was conducted at four tertiary care United States medical centers between 2009 and 2011. The study comprised patients with cirrhosis and AKI defined by the AKI Network criteria evaluating structural (neutrophil gelatinase–associated lipocalin, IL-18, kidney injury molecule-1 [KIM-1], liver-type fatty acid–binding protein [L-FABP], and albuminuria) and functional (fractional excretion of sodium [FENa]) urinary biomarkers as predictors of AKI progression and in-hospital mortality.

Results

Of 188 patients in the study, 44 (23%) experienced AKI progression alone and 39 (21%) suffered both progression and death during their hospitalization. Neutrophil gelatinase–associated lipocalin, IL-18, KIM-1, L-FABP, and albuminuria were significantly higher in patients with AKI progression and death. These biomarkers were independently associated with this outcome after adjusting for key clinical variables including model of end stage liver disease score, IL-18 (relative risk [RR], 4.09; 95% confidence interval [95% CI], 1.56 to 10.70), KIM-1 (RR, 3.13; 95% CI, 1.20 to 8.17), L-FABP (RR, 3.43; 95% CI, 1.54 to 7.64), and albuminuria (RR, 2.07; 95% CI, 1.05–4.10) per log change. No biomarkers were independently associated with progression without mortality. FENa demonstrated no association with worsening of AKI. When added to a robust clinical model, only IL-18 independently improved risk stratification on a net reclassification index.

Conclusions

Multiple structural biomarkers of kidney injury, but not FENa, are independently associated with progression of AKI and mortality in patients with cirrhosis. Injury marker levels were similar between those without progression and those with progression alone.     

Risk factors for acute kidney injury in overweight patients with acute type A aortic dissection: a retrospective study

Background

To identify risk factors for acute kidney injury (AKI) in overweight patients who underwent surgery for acute type A aortic dissection (TAAD).

Methods

A retrospective study including 108 consecutive overweight patients [body mass index (BMI) ≥24] between December 2009 and April 2013 in Beijing Anzhen Hospital has been performed. AKI was defined by Acute Kidney Injury Network (AKIN) criteria, which is based on serum creatinine (sCr) or urine output.

Results

The mean age of the patients was 43.69±9.66 years. Seventy-two patients (66.7%) developed AKI during the postoperative period. A logistic regression analysis was performed to identify two independent risk factors for AKI: elevated preoperative sCr level and 72-h drainage volume. Renal replacement therapy (RRT) was required in 15 patients (13.9%). The overall postoperative mortality rate was 7.4%, 8.3% in AKI group and 5.6% in non-AKI group. There is no statistically significant difference between the two groups (P=0.32).

Conclusions

A higher incidence of AKI (66.7%) in overweight patients with acute TAAD was confirmed. The logistic regression model identified elevated preoperative sCr level and 72-h drainage volume as independent risk factors for AKI in overweight patients. We should pay more attention to prevent AKI in overweight patients with TAAD.     

Epidemiology and Clinical Correlates of AKI in Chinese Hospitalized Adults

Background and objectives

Comprehensive epidemiologic data on AKI are particularly lacking in Asian countries. This study sought to assess the epidemiology and clinical correlates of AKI among hospitalized adults in China.

Design, setting, participants, & measurements

This was a multicenter retrospective cohort study of 659,945 hospitalized adults from a wide range of clinical settings in nine regional central hospitals across China in 2013. AKI was defined and staged according to Kidney Disease Improving Global Outcomes criteria. The incidence of AKI in the cohort was estimated using a novel two-step approach with adjustment for the frequency of serum creatinine tests and other potential confounders. Risk factor profiles for hospital-acquired (HA) and community-acquired (CA) AKI were examined. The in-hospital outcomes of AKI, including mortality, renal recovery, length of stay, and daily cost, were assessed.

Results

The incidence of CA-AKI and HA-AKI was 2.5% and 9.1%, respectively, giving rise to an overall incidence of 11.6%. Although the risk profiles for CA-AKI and HA-AKI differed, preexisting CKD was a major risk factor for both, contributing to 20% of risk in CA-AKI and 12% of risk in HA-AKI. About 40% of AKI cases were possibly drug-related and 16% may have been induced by Chinese traditional medicines or remedies. The in-hospital mortality of AKI was 8.8%. The risk of in-hospital death was higher among patients with more severe AKI. Preexisting CKD and need for intensive care unit admission were associated with higher death risk in patients at any stage of AKI. Transiency of AKI did not modify the risk of in-hospital death. AKI was associated with longer length of stay and higher daily costs, even after adjustment for confounders.

Conclusion

AKI is common in hospitalized adults in China and is associated with significantly higher in-hospital mortality and resource utilization.     

Contrast-Associated AKI and Use of Cardiovascular Medications after Acute Coronary Syndrome

Background and objectives

AKI after coronary angiography is associated with poor long-term outcomes. The relationship between contrast-associated AKI and subsequent use of prognosis-modifying cardiovascular medications is unknown.

Design, setting, participants, & measurements

A cohort study of 5911 participants 66 years of age or older with acute coronary syndrome who received a coronary angiogram in Alberta, Canada was performed between November 1, 2002, and November 30, 2008. AKI was identified according to Kidney Disease Improving Global Outcomes AKI criteria.

Results

In multivariable logistic regression models, compared with participants without AKI, those with stages 1 and 2–3 AKI had lower odds of subsequent use of angiotensin-converting enzyme inhibitors/angiotensin receptor blocker within 120 days of hospital discharge (adjusted odds ratio, 0.65; 95% confidence interval, 0.53 to 0.80 and odds ratio, 0.34; 95% confidence interval, 0.23 to 0.48, respectively). Subsequent statin and β-blockers use within 120 days of hospital discharge was significantly lower among those with stages 2–3 AKI (adjusted odds ratio, 0.44; 95% confidence interval, 0.31 to 0.64 and odds ratio, 0.46; 95% confidence interval, 0.31 to 0.66, respectively). These associations were consistently seen in patients with diabetes mellitus, heart failure, low baseline eGFR, and albuminuria; 952 participants died during subsequent follow-up after hospital discharge (mean=3.1 years). The use of each class of cardiovascular medication was associated with lower mortality, including among those who had experienced AKI.

Conclusions

Strategies to optimize the use of cardiac medications in people with AKI after coronary angiography might improve care.     

Red cell distribution width is associated with hospital mortality in unselected critically ill patients

Background and objectives

Red cell distribution width (RDW) is a variability of red cell sizes and has been associated with outcomes in many clinical settings. Its prognostic value in intensive care unit (ICU) has been reported but requires confirmation. The study aimed to investigate the role of RDW in predicting hospital mortality in critically ill patients.

Methods

This is a retrospective study conducted in a 24-bed ICU of a tertiary teaching hospital. Data on demographic characteristics and laboratory measurements were collected from medical information database. Baseline variables were compared between survivors and nonsurvivors. The primary endpoint was hospital mortality; and ICU length of stays (LOS) were compared between patients with RDW >14.8% and ≤14.8%. The predictive value of RDW was also measured using receiver operating characteristic (ROC) curves. Two-sided P<0.05 was considered to be statistically significant.

Results

A total of 1,539 patients were enrolled during study period, including 1,084 survivors and 455 nonsurvivors. In univariate analysis, variables such as age, sex, primary diagnosis, C-reactive protein (CRP), RDW and albumin were significantly associated with hospital mortality. RDW remained significantly associated with mortality after adjustment for sex, age, Charlson index albumin and CRP, with an odds ratio of 1.1 (95% CI: 1.03-1.16). Diagnostic performance of RDW in predicting mortality appeared to be suboptimal (AU-ROC: 0.62). Changes in RDW during a short follow up period were not associated with mortality.

Conclusions

RDW measured on ICU entry is associated with hospital mortality. Patients with higher RDW will have longer LOS in ICU. Repeated measurements of RDW provide no additional prognostic value in critically ill patients.KEYWORDS : Red cell distribution width (RDW), intensive care unit (ICU), mortality, length of stay (LOS)     

AKI Complications in Critically Ill Patients: Association with Mortality Rates and RRT

Background and objectives

AKI is associated with short- and long-term mortality. However, the exact contribution of AKI complications to the burden of mortality and whether RRT has any beneficial effect on reducing mortality rates in critically ill AKI patients are unknown.

Design, setting, participants, & measurements

This was a retrospective analysis using data from the Multiparameter Intelligent Monitoring in Intensive Care II project. A total of 18,410 adult patients were enrolled from four intensive care units from a university hospital from 2001 to 2008.

Results

Overall, 10,245 patients developed AKI. After adjustments, the odds ratios (ORs) for hospital mortality were 1.73 (95% confidence interval [95% CI], 1.52 to 1.98) for AKI stage 1, 1.88 (95% CI, 1.57 to 2.25) for stage 2, and 2.89 (95% CI, 2.41 to 3.46) for stage 3. Totals of 33%, 59%, and 70% of the excess mortality rates associated with AKI stages 1, 2, and 3, respectively, were attenuated by the inclusion of each AKI-related complication in the model. The main burden of excess hospital mortality associated with AKI was attenuated by metabolic acidosis and cumulative fluid balance. Long-term mortality was not attenuated by any of the associated complications. Next, we used two different approaches to explore the associations between RRT, AKI complications, and hospital mortality: multivariate analysis and propensity score matching. In both approaches, the sensitivity analysis for RRT was associated with a better hospital survival in only the following AKI-related subgroups: hyperkalemia (OR, 0.55; 95% CI, 0.35 to 0.85), metabolic acidosis (OR, 0.70; 95% CI, 0.53 to 0.92), cumulative fluid balance >5% of body weight (OR, 0.60; 95% CI, 0.40 to 0.88), and azotemia (OR, 0.57; 95% CI, 0.40 to 0.81).

Conclusions

A majority of the excess risk of mortality associated with AKI was attenuated by its fluid volume and metabolic complications, particularly in severe AKI. In addition, this study demonstrated that RRT is associated with a better outcome in patients with AKI-related complications.     

Low Systemic Oxygen Delivery and BP and Risk of Progression of Early AKI

Background and objectives

The optimal hemodynamic management of patients with early AKI is unknown. This study aimed to investigate the association between hemodynamic parameters in early AKI and progression to severe AKI and hospital mortality.

Design, setting, participants, & measurements

This study retrospectively analyzed the data of all patients admitted to the adult intensive care unit in a tertiary care center between July 2007 and June 2009 and identified those with stage 1 AKI (AKI I) per the AKI Network classification. In patients in whom hemodynamic monitoring was performed within 12 hours of AKI I, hemodynamic parameters in the first 12 hours of AKI I and on the day of AKI III (if AKI III developed) or 72 hours after AKI I (if AKI III did not develop) were recorded. Risk factors for AKI III and mortality were identified using univariate and multivariate logistic regression analyses.

Results

Among 790 patients with AKI I, 210 (median age 70 years; 138 men) had hemodynamic monitoring within 12 hours of AKI I; 85 patients (41.5%) progressed to AKI III and 91 (43%) died in the hospital. AKI progressors had a significantly higher Sequential Organ Failure Assessment score (8.0 versus 9.6; P<0.001), lower indexed systemic oxygen delivery (DO₂I) (median 325 versus 405 ml/min per m²; P<0.001), higher central venous pressure (16 versus 13; P=0.02), and lower mean arterial blood pressure (MAP) (median 71 versus 74 mmHg; P=0.01) in the first 12 hours of AKI I compared with nonprogressors. Multivariate analysis confirmed that raised lactate, central venous pressure, and Sequential Organ Failure Assessment score as well as mechanical ventilation were independently associated with progression to AKI III; higher DO₂I and MAP were independently associated with a lower risk of AKI III but not survival. The associations were independent of sepsis, heart disease, recent cardiac surgery, or chronic hypertension.

Conclusions

Higher DO₂I and MAP in early AKI were independently associated with a lower risk of progression.     

Recognition and Reporting of AKI in Very Low Birth Weight Infants

Background and objectives

AKI is associated with both increased short-term morbidity and mortality and greater long-term risk for CKD. This study determined the prevalence of AKI among very low birth weight infants using a modern study definition, evaluated the frequency of AKI diagnosis reporting in the discharge summary, and determined whether infants were referred to a pediatric nephrologist for AKI follow-up.

Design, setting, participants, & measurements

Records of very low birth weight infants admitted to a level IV neonatal intensive care unit from 2008 to 2011 were reviewed. AKI was classified using the Kidney Disease: Improving Global Outcomes definition modified to include only serum creatinine.

Results

AKI occurred in 39.8% of 455 infants; 75 (16.5%) infants experienced multiple episodes of AKI, and 8 (2%) infants were discharged with an abnormal last creatinine. Updated clinical risk index for babies score >10 (odds ratio, 12.9; 95% confidence interval, 7.8 to 21.4) and gestational age <28 weeks (odds ratio, 10.6; 95% confidence interval, 6.8 to 16.7) were strongly associated with AKI in univariate analyses. AKI was associated with increased mortality (odds ratio, 4.0; 95% confidence interval, 1.4 to 11.5) and length of stay (11.7 hospital days; 95% confidence interval, 5.1 to 18.4), even after accounting for gestational age, birth weight, and updated clinical risk index for babies score. AKI was recorded in the discharge summary for only 13.5% of AKI survivors. No infants were referred to a nephrologist for AKI follow-up.

Conclusions

AKI occurred in 40% of very low birth weight infants and was concentrated in the most premature and severely ill infants. One in six infants experienced multiple episodes of AKI, and a small number of infants was discharged with an elevated serum creatinine. Reporting a history of AKI in the discharge summary occurred infrequently, and referral to a nephrologist for AKI follow-up did not occur, highlighting areas for quality improvement.     

Renal Outcomes in Critically Ill Patients Receiving Propofol or Midazolam

Background and objectives

Propofol has been shown to provide protection against renal ischemia/reperfusion injury experimentally, but clinical evidence is limited to patients undergoing cardiac surgery. There are no data about its association with oliguria and AKI in critically ill patients.

Design, setting, participants, & measurements

We obtained data from the Multiparameter Intelligent Monitoring in Intensive Care II database (2001–2008). Patient selection criteria included adult patients in their first intensive care unit (ICU) admission, need for mechanical ventilation, and treatment with propofol or midazolam. Propensity score analysis (1:1) was used and renal-related outcomes (AKI, oliguria, cumulative fluid balance, and need for RRT) were evaluated during the first 7 days of ICU stay.

Results

There were 1396 propofol/midazolam-matched patients. AKI in the first 7-day ICU time period was statistically lower in propofol-treated patients compared with midazolam-treated patients (55.0% versus 67.3%, P<0.001). Propofol was associated with lower AKI incidence using both urine output (45.0% versus 55.7%, P<0.001) and serum creatinine criteria (28.8% versus 37.2%, P=0.001). Patients receiving propofol had oliguria (<400 ml/d) less frequently (12.4% versus 19.6%, P=0.001) and had diuretics prescribed less often (8.5% versus 14.3%, P=0.001). In addition, during the first 7 days of ICU stay, patients receiving propofol less frequently achieved cumulative fluid balance >5% of body weight (50.1% versus 58.3%, P=0.01). The need for RRT in the first 7 days of ICU stay was also less frequent in propofol-treated patients (3.4% versus 5.9%, P=0.03). ICU mortality was lower in propofol-treated patients (14.6% versus 29.7%, P<0.001).

Conclusions

In this large, propensity-matched ICU population, patients treated with propofol had a lower risk of AKI, fluid-related complications, and need for RRT.     

Peripheral Edema,Central Venous Pressure,and Risk of AKI in Critical Illness

Background and objectives

Although venous congestion has been linked to renal dysfunction in heart failure, its significance in a broader context has not been investigated.

Design, setting, participants, & measurements

Using an inception cohort of 12,778 critically ill adult patients admitted to an urban tertiary medical center between 2001 and 2008, we examined whether the presence of peripheral edema on admission physical examination was associated with an increased risk of AKI within the first 7 days of critical illness. In addition, in those with admission central venous pressure (CVP) measurements, we examined the association of CVPs with subsequent AKI. AKI was defined using the Kidney Disease Improving Global Outcomes criteria.

Results

Of the 18% (n=2338) of patients with peripheral edema on admission, 27% (n=631) developed AKI, compared with 16% (n=1713) of those without peripheral edema. In a model that included adjustment for comorbidities, severity of illness, and the presence of pulmonary edema, peripheral edema was associated with a 30% higher risk of AKI (95% confidence interval [95% CI], 1.15 to 1.46; P<0.001), whereas pulmonary edema was not significantly related to risk. Peripheral edema was also associated with a 13% higher adjusted risk of a higher AKI stage (95% CI, 1.07 to 1.20; P<0.001). Furthermore, levels of trace, 1+, 2+, and 3+ edema were associated with 34% (95% CI, 1.10 to 1.65), 17% (95% CI, 0.96 to 1.14), 47% (95% CI, 1.18 to 1.83), and 57% (95% CI, 1.07 to 2.31) higher adjusted risk of AKI, respectively, compared with edema-free patients. In the 4761 patients with admission CVP measurements, each 1 cm H₂O higher CVP was associated with a 2% higher adjusted risk of AKI (95% CI, 1.00 to 1.03; P=0.02).

Conclusions

Venous congestion, as manifested as either peripheral edema or increased CVP, is directly associated with AKI in critically ill patients. Whether treatment of venous congestion with diuretics can modify this risk will require further study.     

Acute Respiratory Distress Syndrome and Risk of AKI among Critically Ill Patients

Background and objectives

Increasing experimental evidence suggests that acute respiratory distress syndrome (ARDS) may promote AKI. The primary objective of this study was to assess ARDS as a risk factor for AKI in critically ill patients.

Design, setting, participants, & measurements

This was an observational study on a prospective database fed by 18 intensive care units (ICUs). Patients with ICU stays >24 hours were enrolled over a 14-year period. ARDS was defined using the Berlin criteria and AKI was defined using the Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease criteria. Patients with AKI before ARDS onset were excluded.

Results

This study enrolled 8029 patients, including 1879 patients with ARDS. AKI occurred in 31.3% of patients and was more common in patients with ARDS (44.3% versus 27.4% in patients without ARDS; P<0.001). After adjustment for confounders, both mechanical ventilation without ARDS (odds ratio [OR], 4.34; 95% confidence interval [95% CI], 3.71 to 5.10) and ARDS (OR, 11.01; 95% CI, 6.83 to 17.73) were independently associated with AKI. Hospital mortality was 14.2% (n=1140) and was higher in patients with ARDS (27.9% versus 10.0% in patients without ARDS; P<0.001) and in patients with AKI (27.6% versus 8.1% in those without AKI; P<0.001). AKI was associated with higher mortality in patients with ARDS (42.3% versus 20.2%; P<0.001).

Conclusions

ARDS was independently associated with AKI. This study suggests that ARDS should be considered as a risk factor for AKI in critically ill patients.     

Outcomes After Post-Traumatic AKI Requiring RRT in United States Military Service Members

Background and objectives

Mortality and CKD risk have not been described in military casualties with post-traumatic AKI requiring RRT suffered in the Iraq and Afghanistan wars.

Design, setting, participants, & measurements

This is a retrospective case series of post-traumatic AKI requiring RRT in 51 military health care beneficiaries (October 7, 2001–December 1, 2013), evacuated to the National Capital Region, documenting in-hospital mortality and subsequent CKD. Participants were identified using electronic medical and procedure records.

Results

Age at injury was 26±6 years; of the participants, 50 were men, 16% were black, 67% were white, and 88% of injuries were caused by blast or projectiles. Presumed AKI cause was acute tubular necrosis in 98%, with rhabdomyolysis in 72%. Sixty-day all-cause mortality was 22% (95% confidence interval [95% CI], 12% to 35%), significantly less than the 50% predicted historical mortality (P<0.001). The VA/NIH Acute Renal Failure Trial Network AKI integer score predicted 60-day mortality risk was 33% (range, 6%–96%) (n=49). Of these, nine died (mortality, 18%; 95% CI, 10% to 32%), with predicted risks significantly miscalibrated (P<0.001). The area under the receiver operator characteristic curve for the AKI integer score was 0.72 (95% CI, 0.56 to 0.88), not significantly different than the AKI integer score model cohort (P=0.27). Of the 40 survivors, one had ESRD caused by cortical necrosis. Of the remaining 39, median time to last follow-up serum creatinine was 1158 days (range, 99–3316 days), serum creatinine was 0.85±0.24 mg/dl, and eGFR was 118±23 ml/min per 1.73 m². No eGFR was <60 ml/min per 1.73 m², but it may be overestimated because of large/medium amputations in 54%. Twenty-five percent (n=36) had proteinuria; one was diagnosed with CKD stage 2.

Conclusions

Despite severe injuries, participants had better in-hospital survival than predicted historically and by AKI integer score. No patient who recovered renal function had an eGFR<60 ml/min per 1.73 m² at last follow-up, but 23% had proteinuria, suggesting CKD burden.     

Hospital-acquired Acute Kidney Injury: An Analysis of Nadir-to-Peak Serum Creatinine Increments Stratified by Baseline Estimated GFR

Summary

Background and objectives

Serum creatinine (sCr) increments currently used to define acute kidney injury (AKI) do not take into consideration the baseline level of kidney function. The objective of this study was to establish whether baseline estimated GFR (eGFR) provides additional risk stratification to sCr-based increments for defining AKI.

Design, setting, participants, & measurements

29,645 adults hospitalized at an acute care facility were analyzed. Hospital-acquired AKI was defined by calculating the difference between the nadir and subsequent peak sCr.

Results

Different thresholds of nadir-to-peak sCr were found to be independently associated with increased in-hospital mortality according to baseline eGFR strata. A nadir-to-peak sCr minimum threshold of ≥0.2, ≥0.3, and ≥0.5 mg/dl was required to be independently associated with increased in-hospital mortality among patients with baseline eGFR ≥60 ml/min per 1.73 m² (odds ratio [OR] 1.67; 95% confidence interval [CI] 1.13 to 2.47), 30 to 59 ml/min per 1.73 m² (OR 2.69; 95% CI, 1.82 to 3.97), and <30 ml/min per 1.73 m² (OR 2.15; 95% CI 1.02 to 4.51), respectively. There was a significant interaction between the nadir-to-peak sCr and baseline eGFR for in-hospital mortality (P < 0.001). Using these thresholds, survivors of AKI episodes had an increased hospital length of stay and were more likely to be discharged to a facility rather than home. Sensitivity analyses showed a significant interaction between baseline eGFR strata and relative increases in sCr, as well as absolute and relative decreases in eGFR for in-hospital mortality (P < 0.001).

Conclusions

This study suggests that future sCr-based definitions of AKI should take into consideration baseline eGFR.