EM Cases: Acute Kidney Injury – A Simple Emergency Approach to AKI
- Jan 21st, 2022
- Anton Helman
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How comfortable are we in the ED charting anything but ‘pre-renal AKI’ in the patient who’s creatinine surprisingly comes back sky high? Since when did the term ‘multifactorial AKI’ become synonymous with ‘I don’t know why the creatinine is up’? Turns out those brilliant, well-rested nephrologists have been onto something all along. In this first part of our 2 part series on AKI, with the help of Dr. Edward Etchells and Dr. Bourke Tillmann (plus a bonus POCUS section with Rob Simard), we give you a simple stepwise approach to the ED assessment and management of AKI, as well as give you all the tools you need to pick up and manage rhabdomyolysis. We answer questions such as: Is there any value in the BUN:Cr ratio in distinguishing prerenal from intrarenal disease? Why is nephritic syndrome one of the most important intrarenal causes to pick up in the ED? Is there any value in urine electrolytes for the ED workup of AKI? Is there a role for bicarb in patients with severe AKI? How can we choose wisely when it comes to imaging for patients with AKI? How can we utilize POCUS best in working up the patient with AKI? What are the indications for ordering a CK to look for rhabdomyolysis? At what CK level do patients typically develop AKI? How can the McMahon score help us manage rhabdomyolysis? What is the value of urine myoglobin in the workup of rhabdomyolysis? What are indications for dialysis in patients with rhabdomyolysis? What are safe discharge criteria for patients with rhabdomyolysis? and many more…
Podcast production, sound design & editing by Anton Helman; Voice editing by Sheza Qayyum
Written Summary and blog post by Winny Li, edited by Anton Helman December, 2020.
Cite this podcast as: Helman, A. Etchells, E. Tillmann, B. Episode 150 Acute Kidney Injury – A Simple Emergency Approach to AKI. Emergency Medicine Cases. December, 2020. https://emergencymedicinecases.com/acute-kidney-injury-simple-emergency-approach-aki. Accessed [date]
The 2012 Kidney Disease – Improving Global Outcomes (KDIGO) Clinical Practice Guideline for Acute Kidney Injury (AKI)  defines AKI by any of the following:
- Increase in serum creatinine by ≥0.3 mg/dL (>26.5 μmol/L) within 48 hours; or
- Increase in serum creatinine to ≥1.5 times baseline, which is known or presumed to have occurred within prior 7 days; or
- Urine volume <0.5 mL/kg/h for 6 hours
5 step approach to AKI in the ED
Step 1: Rule out the 2 immediate life-threats
- Hyperkalemia – get ECG, electrolytes off the blood gas
- Severe acidosis – get blood gas
Step 2: Assess for adequate perfusion – are they in shock?
Use your history, physical examination and POCUS to assess for perfusion and treat shock (hemorrhagic, vasodilatory, cardiogenic shock etc.) accordingly.
Step 3: Assess for both pulmonary and peripheral edema
Assess JVP and lungs with POCUS for pulmonary edema, look and palpate for peripheral edema (including pre-tibial edema, sacral edema)
If there is no evidence of pulmonary or peripheral edema, give a fluid challenge.
AKI with adequate perfusion, with pulmonary edema (with or without peripheral edema)
- Give furosemide 1 mg/kg IV (or 1.5 mg/kg IV if on furosemide already)
- Think about pulmonary renal syndromes other than CHF (such as anti-GBM disease, ANCA associated vasculitis, circulating immune complex syndromes like lupus), and look for clinical clues (inflammatory arthritis, purpura, Raynaud’s, mononeuritis multiplex, uveitis or Sicca syndrome?)
AKI with adequate perfusion, with peripheral edema but not pulmonary edema
- Give furosemide 1 mg/kg IV (or 1.5 mg/kg IV if on furosemide already)
- If no improvement in renal function think about hypovolemia (“pre renal”) despite peripheral edema
o Low serum albumin – treat underlying cause, and consider hepatorenal syndrome which may require IV albumin
o Venous insufficiency and/or lymphedema – give crystalloid, consider compression therapy
o Drug induced edema – give crystalloid, reassess offending drug
o Severe myxedema – give L-thyroxine and monitor
Step 4: The golden rules of AKI workup
- Measure a post-void residual (PVR) with bladder scan or urethral catheter
- Get a urine dip to look for blood and protein suggestive of nephritic syndrome
- Monitor urine output ideally with a urethral catheter
- Avoid nephrotoxins (NSAIDs, ACEi, ARBs, gentamicin etc)
Step 5: Consider imaging for a small subset of post-renal AKI
Radiology department imaging should be reserved for those patients who:
- Do not improve with fluid challenge (making pre-renal less likely),
- Have a normal urine dip (making intra-renal less likely),
- Have a post-void residual <100mL (making BPH less likely)
- Have obvious bilateral hydronephrosis on POCUS
These patients warrant further imaging as they might have a rare post-renal bilateral ureteric obstruction cause of AKI such as obstructive metastatic cancer, lymphoma or a kidney stone with a solitary kidney.
AKI pearls and pitfalls
- BUN:Cr ratio >1 is not reliable at distinguishing pre-renal from renal causes. 
- Hematuria and proteinuria are often overlooked or ignored in the ED and should trigger the consideration of nephritic syndrome as an intrarenal cause of AKI, especially in those patients presenting with acute uncontrolled hypertension
- Urine electrolytes and fractional excretion of sodium are rarely required in the ED as they are nonspecific, very difficult to interpret without further inpatient workup and may be misleading; [3,4] They should be considered, however in patients suspected of hepatorenal syndrome.
- The fluid of choice for most patients with pre-renal AKI is Ringer’s Lactate 
- Sodium bicarb should be considered in patients with uremic acidosis, however this is usually best suited for the ICU setting 
- The most common causes of post-renal AKI are BPH and urethral catheter obstruction; radiology department imaging to rule out a pelvic mass causing bilateral ureteral obstruction should be reserved for those with obvious hydronephrosis on POCUS but little or no post-void residual
- A common pitfall is to attribute AKI to obstructive nephrolithiasis; unless the patient has a solitary kidney, nephrolithiasis rarely causes AKI; look for other causes of AKI instead
Prerenal AKI, caused by decreased renal perfusion, is the most common cause of all AKIs (90%) . Prerenal causes occur in the setting of recent volume losses, such as hemorrhage, gastrointestinal or urinary fluid losses, sepsis, and recent postoperative courses during which the patient was hypotensive.
Common causes of pre-renal AKI include:
- Volume depletion (renal losses – ie. Diuretics, and extra-renal losses – GI losses, third spacing, hemorrhage)
- Shock of any etiology
- Cardiorenal syndrome
Additional pre-renal causes of AKI to consider include:
- Hepatorenal syndrome
- Abdominal compartment syndrome
- Hypertensive emergency
- Thrombotic thrombocytopenic purpura & hemolytic uremic syndrome
Fluid of choice in AKI
Our experts recommend Ringers Lactate (RL) as the fluid of choice as it has relatively neutral effect on acid-base status and may reduce the risk of further AKI compared to Normal Saline. Consider 1L bolus up front followed by 150mL/hr and aim for a urine output of ≥50mL/hr (≥200mL/hr in rhabdomyolysis).
Bicarb should be considered in patients with uremic acidosis based on the BICAR-ICU trial but probably best reserved for the ICU.
Intrinsic renal AKI
Intrinsic renal AKI is caused by direct injury to the kidney parenchyma. Intrarenal causes of AKI are usually considered only after pre-renal and post-renal causes have been ruled out. The “can’t miss” diagnosis for emergency physicians in a patient with AKI is nephritic syndrome. Thus it is important to get a urine dip to look for protein and blood in all patients with AKI.
Nephritic syndrome presents as: acutely elevated Cr with hypertension, hematuria, proteinuria and no obvious pre-renal or post-renal cause.
Other important causes of renal AKI to consider in the ED include:
- Nephrotoxic medications (ACEi, NSAIDs, Gentamicin etc.)
- Acute Tubular Necrosis (ATN) (rhabdomyolysis, hemolysis, tumor lysis syndrome)
- Renal thrombosis
Other lab test to differentiate pre-renal vs. renal AKI:
Other than ordering a urine dip to assess for intrinsic renal cause of AKI, there little role for measuring BUN in the ED. BUN:Cr ratio is not reliable at distinguishing pre-renal from renal causes . Similarly, there is a limited role for urine electrolytes in the ED except in suspected of hepatorenal syndrome.
Pearl: Nephritic syndrome presents with acutely elevated Cr, hypertension, hematuria, proteinuria and no obvious pre-renal or post-renal cause.
Post-renal AKI is caused urologic obstruction to urine flow. It’s important to measure a post-void residual in all patients with an AKI. The most common causes are BPH and urethral catheter obstruction.
Imaging to rule out an obstructive cause should not be performed in every patient with AKI NYD. Imaging should be considered in patients with obvious bilateral hydronephrosis on POCUS but little or no post void residual. These patients warrant further imaging as they might have a rare post-renal bilateral ureteric obstruction cause of AKI such as obstructive metastatic cancer, lymphoma or a kidney stone with a solitary kidney.
Pitfall: A common pitfall is to attribute AKI to obstructive nephrolithiasis. Unless the patient has a solitary kidney, nephrolithiasis rarely causes AKI. Look for other causes of AKI instead.
Role of POCUS in AKI
POCUS can provide valuable information about the overall volume status of a patient by via assessment of the JVP, IVC and signs of pulmonary edema.
POCUS can often obviate the need for further advanced renal imaging, as it can also provide important sources information pertaining to post-renal/obstructive causes including assessing a post-void residual, hydronephrosis and absence of ureteric jets. The absence of ureteral jets entering the bladder has a 90% positive predictive value for acute urinary tract obstruction .
However, the accuracy of POCUS by ED docs is provider dependent. Using the consensus radiology interpretation of POCUS as the reference standard, emergency physicians had an overall sensitivity of 85.7%, specificity of 65.9%  The sensitivity of POCUS for the detection of hydronephrosis was 77.1% and the specificity was 71.8% in a 2020 study of patients with nephrolithiasis . The sensitivity of POCUS improved with worsening degrees of hydronephrosis.
Despite the above limitations, our experts recommend using POCUS to assess for hydronephrosis when the pre-test probability for obstruction gathered from history and physical exam is high.
Rhabdomyolysis and AKI
Studies have shown a correlation of CK levels greater than 5000 IU/L and 50% chance of progression to AKI .
When to order CK and other blood tests for rhabdomyolysis
- Any one risk factor for rhabdomyolysis: trauma/compartment syndrome/crush, extreme exertion, hyperthermia, found down
- Any one symptom of rhabdomyolysis: muscle pain, muscle weakness, vomiting, dark urine
Note that CK peaks at 24-72hr after the initial insult, so serial CKs are important to consider, especially if the insult was recent.
If the CK is >1000, consider calcium, phosphate and VBG to estimate severity of rhabdomyolysis and their risk for requiring dialysis.
Management of rhabdomyolysis based on CK levels
- CK<1000 – oral fluids usually adequate as long as CK is not trending upwards and McMahon score is low
- CK 1000-5000 – usually requires IV RL and trending of CK and Cr are especially important to determine disposition
- CK>5000 – usually needs IV RL and admission +/- dialysis if McMahon >6
The McMahon score estimates severity and requirement for dialysis in rhabdomyolysis patients, which includes age, sex, Cr, Ca, CK, phosphate and bicarb as the score parameters .
Urine myoglobin has little role in the ED diagnosis of rhabdomyolysis
There is a limited role for urine myoglobin because the half-life is only 2-3hrs, so a negative result after 4-6 hrs post insult may be misleading [13,14]. In contrast, CK peaks at 24-72 hrs after the initial insult, so may be low or normal in the first few hours.
The indications for dialysis for rhabdomyolysis are the same as for any patient with AKI
Indications for dialysis in rhabdomyolysis are the same as those for any AKI patient; use the mnemonic AEIOU :
Acidemia – pH<7.1 despite medical management
Electrolyte abnormalities – hyperkalemia refractory to medical management
Ingestion – nephrotoxic drug ingestion amenable to dialysis
Overload – volume overload resulting in respiratory failure
Uremia with bleeding, pericarditis or encephalopathy
Safe discharge considerations for patients with rhabdomyolysis
Patients are likely safe to be discharged home according to our experts if the underlying cause is identified and reversed, their CK is <1000 and down-trending, their creatinine has normalized and the patient is reliable to continue fluids orally at home.
Visit EM Cases on instagram for more infographics
Other FOAMed Resources on AKI
For part 2 of this series on AKI go to Episode 151 AKI Part 2- ED Management
References for AKI – A Simple ED Approach
- KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. (2013). Kidney International Supplements. 3(1).
- Manoeuvrier, G., Bach-Ngohou, K., Batard, E., Masson, D., & Trewick, D. (2017). Diagnostic performance of serum blood urea nitrogen to creatinine ratio for distinguishing prerenal from intrinsic acute kidney injury in the emergency department. BMC Nephrology, 18(1).
- Legrand M, Le C, Perbet S, et al. Urine sodium concentration to predict fluid responsiveness in oliguric ICU patients: a prospective multicenter observational study. Crit Care. 2016;20(1):165.
- Ostermann M, Joannidis M. Acute kidney injury 2016: diagnosis and diagnostic workup. Crit Care. 2016;20(1):299.
- Balanced crystalloids versus saline in critically ill adults. (2018). New England Journal of Medicine, 378(20), 1949-1951.
- Kelly, N. (2018). Sodium bicarbonate therapy for patients with severe metabolic Acidaemia in the intensive care unit (BICAR-ICU): A multicentre, open-label, randomised controlled, phase 3 trial. The Journal of Emergency Medicine, 55(5), 733.
- Gaibi T, Ghatak-roy A. Approach to Acute Kidney Injuries in the Emergency Department. Emerg Med Clin North Am. 2019;37(4):661-677.
- Jandaghi AB, Falahatkar S, Alizadeh A, Kanafi AR, Pourghorban R, Shekarchi B, Zirak AK, Esmaeili S. Assessment of ureterovesical jet dynamics in obstructed ureter by urinary stone with color Doppler and duplex Doppler examinations. (2013) Urolithiasis. 41 (2): 159-63.
- Pathan, S. A., Mitra, B., Mirza, S., Momin, U., Ahmed, Z., Andraous, L. G., Shukla, D., Shariff, M. Y., Makki, M. M., George, T. T., Khan, S. S., Thomas, S. H., & Cameron, P. A. (2018). Emergency physician interpretation of point‐of‐care ultrasound for identifying and grading of hydronephrosis in renal colic compared with consensus interpretation by emergency radiologists. Academic Emergency Medicine, 25(10), 1129-1137.
- Sibley, S., Roth, N., Scott, C., Rang, L., White, H., Sivilotti, M. L., & Bruder, E. (2020). Point-of-care ultrasound for the detection of hydronephrosis in emergency department patients with suspected renal colic. The Ultrasound Journal, 12(1).
- Rodríguez, E., Soler, M. J., Rap, O., Barrios, C., Orfila, M. A., & Pascual, J. (2013). Risk factors for acute kidney injury in severe Rhabdomyolysis. PLoS ONE, 8(12), e82992.
Simpson JP, Taylor A, Sudhan N, Menon DK, Lavinio A. Rhabdomyolysis and acute kidney injury: creatine kinase as a prognostic marker and validation of the McMahon Score in a 10-year cohort: A retrospective observational evaluation. Eur J Anaesthesiol. 2016 Dec;33(12):906-912.
- Torres PA, Helmstetter JA, Kaye AM, Kaye AD. Rhabdomyolysis: pathogenesis, diagnosis, and treatment. Ochsner J. 2015;15(1):58-69.
- Petejova, N., & Martinek, A. (2014). Acute kidney injury due to rhabdomyolysis and renal replacement therapy: A critical review. Critical Care, 18(3), 224.
- Nee PA, Bailey DJ, Todd V, Lewington AJ, Wootten AE, Sim KJ. Critical care in the emergency department: acute kidney injury. Emerg Med J. 2016 May;33(5):361-5.
Drs. Helman, Simard, Tillmann and Etchells have no conflicts of interest to declare