Exam 1 Flashcards
(83 cards)
Limitations of SCr
- Dependent on muscle mass
- Some tubular secretion of creatinine (not accurate measure of glomerular filtration)
Purpose of measuring BUN
When kidneys aren’t working properly (have low perfusion), they reabsorb more urea to increase plasma volume and increase kidney perfusion
BUN/SCr Ratio
Easiest way to look at someone’s volume status in a basic metabolic panel
- Normal = 10:1 to 20:1
- > 20:1 = decreased kidney perfusion
What is CrCl used for?
To estimate GFR
Urinary CrCl equation
(urine creatinine/serum creatinine) x (urine volume/time)
- Used when CrCl is directly measured via 12 or 24 hour urinary collection
Cockcroft-Gault CrCl equation
[(140 - age) x IBW]/[72 x SCr] x 0.85 (if female)
Female IBW = 45.5 + (2.3 x height above 5 ft)
Male IBW = 50 + (2.3 x height above 5 ft)
Limitations of Cockcroft-Gault CrCl
- Value can be different when using total body weight vs ideal body weight
- Lags behind changes in kidney function by at least 1 day (not good for unstable changes in creatinine)
- Overestimates true GFR
- Less reliable for < 30 ml/min b/c more tubular secretion
What is CKD-EPI eGFR used for?
Used for chronic kidney disease staging and drug dosing
Difference between MDRD and CKD-EPI equation
MDRD = included race coefficient which introduced potential disparities in how kidney disease was staged
CKD-EPI = removes race from estimation process and calculates creatinine and cystatin C (decreased inaccuracies in CKD diagnosis and staging)
Limitations of CKD-EPI
- Underestimates true GFR, especially at higher GFR
- SCr must be stable
- Less reliable for > 70 ml/min
Albuminuria Levels
- Normal < 30 mg/day
- Microalbuminuria = 30 - 299 mg/day
- Macroalbuminuria > 300 mg/day
Role of kidney when you are dehydrated
- Preserves as much salt and water as possible
- Decreases urine volume and urine sodium
- Increases urine specific gravity (concentrates urine)
Role of kidney when you have too much fluid in the body
- Eliminates as much salt and water as possible
- Increases urine volume and urine sodium
- Decreases urine specific gravity (dilutes urine)
Obligate water loss
1600 ml/day
Glomerular filtration is reduced by?
- Age
- Renal disease
- Congestive heart failure
- Cirrhosis
- Nephrotic syndromes
- Volume depletion
Delivery of H2O to Loop of Henle is determined by?
- GFR
- Proximal tubule H2O
- Na/Cl reabsorption
Na/Cl reabsorption at thick ascending limb is reduced by?
- Loop diuretics
- Osmotic diuretics
- Interstitial disease
*This is the site of most of Na/Cl and water reabsorption. If you can inhibit this, you can inhibit the vast majority of sodium reabsorption
Na/Cl reabsorption at distal convoluted tubule is reduced by?
Thiazide diuretics
Permeability of Collecting Duct is increased by?
- Vasopressin
- Other drugs
Hypovolemic Physical Characteristics
- Hypotension
- Tachycardia (Lower BP and higher HR because there isn’t enough volume to fill the BV for them to have enough pressure against the BV walls to create normal BP)
- Poor skin turgor
- Slow capillary refill time
- FeNa < 1% (normal = 1-2%)
- FeUrea < 35% if patient is on loop diuretic
Hypervolemic Physical Characteristics
- Hypertension (Blood volume is so large that it is pushing against the walls of the BV → higher BP)
- Edema (peripheral and/or pulmonary) (The higher pressure will push fluids back into the interstitial spaces → edema)
- Weight gain
- Jugular venous distention
Hypotonic IV Fluids
- D5W
- 0.45% NaCl
Isotonic IV Fluids
- 0.9% NaCl
- Lactated Ringers
- 5% albumin
Hypertonic IV Fluids
3% NaCl