AKI / Renal Failure / UTI / PN

Question 1

Pre-renal azotemia

Answer 1

A decrease in GFR due to decreases in renal perfusion pressure; caused by:

Hypovolemia
Decreased EABV (CHF, cirrhosis) 

Most common cause of acutely decreased GFR in a hospitalized patient

Question 2

Fractional Excretion of Na+ (FENa)

Answer 2

FENa = (Urine Na / Plasma Na) / (Urine Cr / Plasma Cr)

Low (3%) in intrarenal azotemia

Question 3

Post-renal azotemia

Answer 3

AKA Obstructive Nephropathy; increased tubular hydrostatic pressure decreases the pressure gradient gradient that usually favors filtration

Question 4

Renal azotemia - Pathogenesis

Answer 4

AKA intrinsic renal disease due to direct injury of:

1. Vessels (arteriol emboli, venous thrombosis, vasculitis)
2. Glomeruli (glomerulonephritis)
3. Interstitium (acute interstitial nephritis, infection)
4. Tubules (acute tubular necrosis)

Question 5

Acute Kidney Injury (AKI) - Definition

Answer 5

A rapid decrease in GFR manifested by a rise in plasma creatinine concentration, urea, and other nitrogenous waste products; creates a state of azotemia

Question 6

Uremia

Answer 6

The constellation of signs and symptoms of multiple organ dysfunction caused by retention of uremic toxins and lack of renal hormones due to acute or chronic kidney injury, including:

Nausea
Vomiting
Abdominal Pain
Diarrhea 
Weakness
Fatigue

Question 7

Azotemia

Answer 7

A clinical state characterized by build-up of nitrogenous wastes in the blood - i.e. elevated BUN and SCr

Question 8

Oliguria

Answer 8

Urine volume < 400 mL/24 hours

Question 9

Anuria

Answer 9

Urine volume < 50 mL/24 hours

Question 10

Mechanisms of decreased GFR in ATN

Answer 10

1. Reduction in renal blood flow - causes ischemic injury to proximal tubule epithelial cells, which slough off
2. Epithelial cells clog up the proximal tubule, causing tubular obstruction
3. Tubular “backleak” occurs through bare sections of the basement membrane
4. Ischemic injury produces a failure of autoregulation of renal blood flow, maintaining ATN and allowing recurrent ischemic insults from mild episodes of hypotension

Question 11

Prerenal azotemia - Urine lab findings

Answer 11

High specific gravity (> 1.010)
Low Urine Na (20)
FENa < 1%

Question 12

Lab findings - Intra renal azotemia

Answer 12

1. Vascular etiology: hematuria
2. Glomerulonephritis: + heme, RBCs, RBC casts
3. AIN: + WBC casts
4. ATN: + Granular casts, + renal tubular epithalial cells (RTEs)

Question 13

ATN – Urine Lab findings

Answer 13

Usually isotonic (normal specific gravity)
High Urine Na (>20 mEq/L)
Low Urine Creatinine (UCr/PCr < 20)
FENa > 2%

Question 14

Urine lab findings - post renal AKI

Answer 14

High Urine Na (>40 mEq/L)
Low Urine Creatinine (UCr/PCr < 20)
FENa > 2%
Usually NO blood or protein in urine

Question 15

What is the most common cause of UTI?

Answer 15

Ascending infection from GI/perineal E. coli

Question 16

Urinalysis features of UTI

Answer 16

Many WBCs and WBC casts
Variable RBCs

Bacteruria: always > 10,000 bacteria/ml and usually > 100,000 bacteria/ml