Acute Kidney Disease Flashcards
What is Glomerular Hydrostatic Pressure?
the driving force behind glomerular filtration
How can you control how much gets through the glomerular system?
by squeezing down on afferent/efferent side
What is Acute Kidney Injury (AKI)?
ABRUPT (generally within 48 hrs) reduction in kidney function
What are the 4 results of Acute Kidney Injury (AKI)?
- Loss of excretory function of the kidneys (H2O and waste)
- Accumulation of metabolic waste products (e.g. K+, PO4), and a rapid rise in creatinine and urea
- A decline in urine output MAY occur
- Reduced ability to maintain fluid, electrolyte and acid- base balance
What are the Cellular & Metabolic Waste Products?
Accumulation of metabolic waste products, e.g. creatinine & urea
Skeletal Muscle –> Blood Creatine umol/L (60-100 umol/L) –> Kidney (Creatinine excreted in urine)
Protein Metabolism Blood Kidney
Protein –> AA –> NH3 –> (Liver) –> Urea mmol/L (2-7 mmol/L) –> Urea excreted in urine
Waste –> blood –> If we blood outflow (AKI)…what happens to the concentration of the waste in the bucket?
gets higher
(if kidney function stops working, urea rises)
How can we assess the degree of renal damage in AKI?
o Historically the retention of creatinine in the blood has been the GOLD STANDARD for assessing the degree of glomerular filtration impairment in patients with kidney damage
o Creatinine is a by-product of muscle metabolism and is steadily released into the blood
o Creatinine is freely filtered by the glomerulus and thus is an indicator of renal health. This relationship has been used mathematically to express the underlying degree of glomerular filtration (GFR). We assume in medicine that creatinine clearance ~= GFR !
o However, creatinine undergoes some degree of tubular secretion, as well as GFR; and thus this marker may overestimate GFR a little (but often ignored in clinical practice)
How do we assess the degree of renal damage in patients?
Method for estimating GFR as a CrCl = creatinine clearance
CrCL (ml/min/72kg) = (140-Age) x 80 / creatinine (umol/L) x 85% if female
What does The Cockcroft & Gault Equation for assessing the degree of renal damage in patients tell us?
higher age, poorer the function
Ex q for assessing the degree of renal damage in patients?
65 yo
creatinine = 124 umol/L
CrCL (ml/min/72kg) = (140-65 yo) x 80 / 124 umol/L = 48 mL/min/72 kg
Describe the eGFR (MDRD-4 *)
Modified Diet in Renal Disease formula
Developed for prognostication of renal disease
eGFR (mL/min/1.73 m2) = 175* × (Cr)-1.154 × (Age)-0.203 × (0.742 if female) × (1.212 if African American)
Ex q for eGFR (MDRD-4 *)
Modified Diet in Renal Disease formula
(Developed for prognostication of renal disease)
Cr = 124
Age = 65
eGFR = 175 * (124 umol/L-1.154 ) * (65yo -0.203) = 51 mL/min/1.73m2
What is the eGFR (MDRD-4 *)
Modified Diet in Renal Disease formula
used for?
Some will use this formula to assess the degree of renal damage in AKI or even proper dosing of drugs, however it has only been validated for staging the severity of chronic kidney disease (CKD)!
NEVER DESIGNED FOR DRUG DOSE
What are the limitations of using a creatinine in any renal function assessment for GFR?
- Only for adult patients (>18 years of age)
- Assumes a steady-state serum creatinine value! During AKI the actual creatinine may be rising dramatically ever day! Any calculated CrCl or eGFR value is thus a MOVING TARGET!
- Patients with muscle wasting medical conditions (e.g. muscular dystrophy (MD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS) may have an underproduction of creatinine; and thus the formula will give you erroneous results
- A few drugs may compete with creatinine for tubular secretion and thus may ‘falsely’ elevate serum creatinine in patients (e.g. trimethoprim/ sulfamethoxazole)
- IN PEDIATRICS, WE USE THE SCHWARTZ EQUATION: CrCl(ml/min/1.73m2)= [Length(cm) * k] /creatinine, where k = 0.7 for adolescent males 13 - 18 years old for example (but not used in neonatsology, i.e. < 1 mo of age)
- NOT TESTED ON THIS POINT
GFR averages ________ in young healthy adults 18 - 22 years of age
120 -140 mL/min/72kg
GFR gradually declines with age to _______ at age 65 years of age
~ 50 - 60 mL/min/72kg
We expect a GFR in an otherwise healthy, normal 80 y.o. to be
________
~ 30 - 40 mL/min/72kg
(may explain that: more sensitive to drugs, the older you are)
Pediatrics – GFR is ____ _____ to accurately assess!
very difficult
Explain the Classification of kidney damage
Normal Kidneys
Acute Kidney Injury (AKI) - < 7 days
Acute Kidney Disease (AKD) - < 3 months
GFR <60mL/min/1.73m2
Chronic Kidney Disease (CKD) - >/ 3 months
GFR <60mL/min/1.73m2
and has 5 stages based on
GFR & Albuminuria
What is the duration of creatinine elevation on defining kidney damage!
Evidence of Acute Kidney Injury
rapid rise in creatinine & then goes away after 7 days from renal injury
What is the duration of creatinine elevation on defining kidney damage!
Evidence of Acute Kidney Disease
rapid rise in creatinine & then stays for ~month and then goes away after 3 months from renal injury
What is the duration of creatinine elevation on defining kidney damage!
Evidence of Chronic Kidney Disease
rapid rise in creatinine & then stays constant from renal injury
What is the profile in Acute Kidney Injury?
As reflected by the biomarkers creatinine & urea
Plasma Creatinine rises & Urea rises as well (but not as much)
Definition of Acute Kidney Injury (AKI):
o a rise in creatinine and decline in urine output that has developed within hours to days
o an increase in creatinine by > 27 mmol/L within 48 hours, or e.g. baseline Cr = 100 mmol/L jumps to 130 mmol/L
o an increase >/ 1.5 times in creatinine from their presumed baseline (in last 7 days), or e.g. baseline Cr = 30 mmol/L jumps to 45 mmol/L (dCr=15)
o a decrease in urine output (U.O.) by < 0.5 mL/kg/h over 6 hours
e.g. 80 kg patient with U.O. falls < 40 mL/h over 6
hours or described as less than 240 mL in 6 hours
How common is AKI?
- Community – about 1% of patients presenting to hospital have an AKI
- Hospitalized - occurs in only about 2 – 5 %
- Adult ICU –arises in more than 50% of cases
- Pediatric ICU – arises in 30% of cases (12% develop severe AKI)
- AKI is associated with an increased risk of morbidity and mortality
What are the Risk Factors for AKI?
- Male
- African American
- Pre-existing CKD
- Age>65yrs
- Volume depletion (diarrhea, vomiting or dehydration)
- Sepsis
- Critical Illness
- Nephrotoxic drugs
- Hypotension
- Diabetes mellitus
- Acute heart failure
- Chronic Diseases (heart, liver, lung) * Albuminuria
- Major surgery
- Cardiac surgery
- Trauma
- Cancer