Exam 1 Flashcards
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
When to use 5% albumin?
Hypoalbuminemia and/or sepsis
Balanced crystalloids vs Normal saline
- Balanced crystalloid is closer to neutral pH, has contents closer to physiologic levels, showed decreased risk of death, need for renal replacement therapy, and persistent renal dysfunction
Oral Fluid Solutions (Gatorade, Powerade, Pedialyte) Tonicity
Hypotonic because most of the osmolality is derived from dextrose content which is rapidly metabolized in blood stream
*If a patient is really dehydrated and needs oral fluid supplement, Pedialyte is the best option because it is the only one that has reasonable electrolyte content
Normal maintenance fluid infusion rate
100 - 125 ml/hr
How to calculate maintenance fluid infusion rate
1500 + [20/every kg above 20 kg]
Divide by 24 hours to get ml/hour
When to use what type of IV fluid?
Replace fluid losses with the same type of fluid
- Hypotonic loss should be replaced with hypotonic fluids
What to do when patient is hemodynamically instable (low BP and high HR)
Bolus isotonic crystalloids or bolus iso-oncotic colloids until improvement in hemodynamics (to expand intravascular volume as quick as possible)
Once BP and HR are normal, go back to replacing fluid losses with the same type of fluids
Effects of different tonicity fluids in the body
- Isotonic = stays in extracellular fluid
- Hypotonic = shifts water into intracellular space
- Hypertonic = shifts water out of intracellular space
When to give maintenance fluid rate?
- Patient is NPO for procedure
- CKD with mild dehydration
- ESRD with severe dehydration
- HF with moderate dehydration
When to give less than maintenance fluid rate
- 0.75 x = CKD, chronic liver disease, mild heart failure
- 0.5 x = severe heart failure, end-stage renal disease
When to give more than maintenance fluid rate
- 1.25 x = mild dehydration
- 1.5 x = moderate dehydration
- 2 x = severe dehydration
- large volume boluses = hemodynamic shock
Hyponatremia Clinical Presentation
- Low Na
- Symptoms dependent on Na concentration and the rate of change of Na
- Chronic and/or mild hyponatremia → asymptomatic
- Acute hyponatremia → more severe presentation of symptoms
- Neurologic changes (Headache → Confusion → Lethargy → Seizures → Coma)
- May be associated with increased/decreased/normal ECF volume
Drugs that cause SIADH
- SSRIs
- Carbamazepine
- Opiates
Corrected Na equation
Measure Na + 1.6 x (every 100 mg/dl glucose above 100)
How to correct hyponatremia
- Stop symptoms and prevent seizures
- Get corrected Na to > 120
- Correct Na to normal range (135 - 145)
Maximum correction = 6 - 12 per day or 0.25 - 0.5 per hour
What happens when you rapidly correct hyponatremia?
Leads to osmotic demyelination syndrome (central pontine myelinolysis)
What is isotonic hyponatremia
Decreased serum Na, normal measured serum osmolality
Causes of isotonic hyponatremia
Lab error
What is hypertonic hyponatremia
Decreased serum Na, increased measured serum osmolality
Causes of hypertonic hyponatremia
Hyperglycemia
- Elevated glucose in intravascular space pulls water out of the intracellular space which lowers Na in the extracellular space
Treatment of hypertonic hyponatremia
Reduce serum glucose (treat hyperglycemia with insulin) and recheck sodium
What is Hypotonic Euvolemic Hyponatremia
Increased TBW, no change in Na
Causes of Hypotonic Euvolemic Hyponatremia
- SIADH (Overactivity of ADH → water from urine is reabsorbed → concentrated urine and excess free water in ECF)
- Drug-induced SIADH
- Psychogenic Polydipsia (Psychiatric disorder where patient drinks too much water (>20L/day))
Treatment of Hypotonic Euvolemic Hyponatremia
- Treat underlying disorder
- Water restriction 1000-1200 mL/day
- Vasopressin receptor antagonist (rarely used)
- Sodium chloride + loop diuretic
What is Hypotonic Hypervolemic Hyponatremia
Big increase in TBW, increase Na
Causes of Hypotonic Hypervolemic Hyponatremia
- Cirrhosis
- HF
- Nephrotic syndrome
Treatment of Hypotonic Hypervolemic Hyponatremia
- Treat underlying disorder
- Slow progression of disorder
- Water restriction 1000 - 1200 mL/day and salt restriction 2000 mg/day
- Loop diuretics
- V2 receptor antagonist (rarely used)
What is Hypotonic Hypovolemic Hyponatremia
Decrease TBW, big decrease in Na
Causes of Hypotonic Hypovolemic Hyponatremia
GI Losses (Diarrhea/Vomiting):
- Isotonic or hypotonic fluid loss → stimulation of thirst (AVP) → administration of hypotonic fluid with continuing fluid loss → decline in sodium concentration
- Urinary Na < 20 mEq/L
Thiazide Diuretics:
- Urinary Na > 20 mEq/L
- High urine Na because thiazide is stimulating the kidneys to secrete sodium
Treatment of Hypotonic Hypovolemic Hyponatremia
0.9% sodium chloride (replace fluid and sodium)
What is Acute Severe Hypotonic Hypovolemic Hyponatremia
Rapid decline in serum Na < 110 mEq/L
Severe symptom = seizure
Treatment of Acute Severe Hypotonic Hypovolemic Hyponatremia
- Hypertonic saline (3% or 23.4% NaCl) can be used to initially manage
- Desired Na = 125 - 130 mEq/L to avoid rapid overcorrection
- May combine with loop diuretic to enhance free water clearance (not recommended)
- Stop once serum Na > 120 mEq/L or severe symptoms resolve
Demeclocycline dosing
300 mg PO BID-QID
Risks of Demeclocycline
- Risk of renal tubular damage and AKI (this drug is not used anymore because of these risks)
- Avoid in children < 8 years and pregnancy (changes in tooth development)
Use of Conivaptan
V1, V2 receptor antagonist (IV only)
Used for acute euvolemic hyponatremia (FDA indication)
Tolvaptan dosing
15 - 60 mg PO QD
Uses of Tolvaptan
Hyper and euvolemic hyponatremia due to HF, cirrhosis, or SIADH
Autosomal dominant polycystic kidney disease
Tolvaptan AE
- Thirst
- Polyuria (this drug prevents you from responding to ADH and water is not reabsorbed and is eliminated in urine → polyuria)
- Constipation
BBW = hepatotoxicity
What is hypovolemic hypernatremia
Water loss»_space; sodium loss
Decrease Na/Big decrease TBW
Causes of hypovolemic hypernatremia
Over-diuresis
Clinical Presentation of hypovolemic hypernatremia
- Orthostasis
- Hypotension
- Tachycardia
- Dry mucous membranes
Treatment of hypovolemic hypernatremia
- Normal saline IV until BP/HR stable
- Then free water replacement
What is Euvolemic Hypernatremia
Water loss
Neutral Na/decrease TBW
Causes of Euvolemic Hypernatremia
Diabetes insipidus
Clinical Presentation of Euvolemic Hypernatremia
- Polyuria
- Polydipsia
- Lethargy
- Seizures
Treatment of Euvolemic Hypernatremia
- Free water replacement
- Vasopressin (DDAVP)
What is Hypervolemic Hypernatremia
Sodium gain > water gain
Big increase Na/Increase TBW
Causes of Hypervolemic Hypernatremia
Sodium overload
Clinical Presentation of Hypervolemic Hypernatremia
Peripheral and pulmonary edema
Treatment of Hypervolemic Hypernatremia
Free water + loop diuretic
Free Water Deficit Equation
[0.6/kg] x [(Na absorbed/140) - 1]
How to administer free water replacement for hypernatremia
- Administer 50% of free water deficit in first 24 hours, then administer 50% over 2 - 3 days
Close monitoring of serum sodium is necessary
Don’t exceed a sodium correction greater than 6 - 12 mEq/L/day (risk of cerebral edema)
How does renal disease, cardiac dysfunction, liver disease, and excessive salt intake cause edema?
They decrease effective circulatory volume which stimulates RAAS –> increases sodium and water reabsorption at kidneys
- Increases capillary hydrostatic pressure
- Decreases protein production (liver disease) or excessive albumin excretion (renal disease) –> decreased oncotic pressure
Treatment of edema
- Salt restriction = 1,000 - 2,000 mg/day
- Optimize cardiac function
- Pharmacologic diuresis
How does diuresis help treat edema?
Edema causes ECF to expand
Diuresis removes fluid from intravascular compartment and over time, equilibrium between intravascular and interstitial compartments occur
Types of Diuretics
1) Carbonic anhydrase inhibitors (acts in proximal convolutes tubule and blocks the reabsorption of sodium and bicarb)
2) Loop diuretics (in ascending loop of henle and blocks NKCC channel)
3) Thiazides (in distal convoluted tubule and stops reabsorption of Na)
4) K Sparing Diuretics (in collecting duct and blocks aldosterone –> inhibits sodium reabsorption)
Where do loop diuretics act?
Luminal membrane of ascending loop of henle
Types of Loop Diuretics (with IV and PO dosing)
Furosemide (Lasix) = 20 mg IV, 40 mg PO
Bumetanide (Bumex) = 1 mg IV, 1 mg PO
Torsemide (Demadex) = 20 mg IV, 20 mg PO
Ethacrynic Acid (Edecrin) = 50 mg IV, 50 mg PO
AE of Loop Diuretics
Hypokalemia, metabolic alkalosis, renal injury due to dehydration, ototoxicity at high doses, sulfa reactions (use ethacrynic acid if sulfa allergy)
