Renal Acidosis Flashcards
What are buffers?
Weak acids
What organ has the largest buffering capacity?
Bone
What is the most important buffer in the ECF?
Bicarbonate
What is the purpose of buffering?
To prevent major shifts in hydrogen ions
What ions mediates intracellular buffering?
Hemoglobin, phosphate, protein
What is the chronic effect of acidosis on bone?
Osteoporosis
What are the two types of acids contribute to your acid load?
- Carbonic
2. Non-carbonic
What type of acid created by the body will become volatile (i.e. excreted by the lungs)
Carbonic acids
Metabolism of what macro-nutrients creates carbonic acids?
Fat and Carbohydrate metabolism
How are carbonic acids excreted?
Eliminated by the lungs after conversion to CO2
Metabolism of what macronutrients leads to non-carbonic acid formation?
Protein, ingested sulfate, phosphate, inorganic acid
How are non-carbonic acids excreted?
Non-volatile therefore excreted via kidneys
Patient presents with pH 7.25, pCO2 30mmHg, what type of acidosis?
Metabolic acidosis
How do you calculate the anion gap?
Na + K - Cl - HCO3 = 12-14 normally
Why is the anion gap not zero?
Albumin is an anion that is not measured
What is the name of metabolic acidosis with an anion gap of <14?
Carbonic/volatile acid = Non-Anion Gap Metabolic Acidosis (NAGMA)
What is the name of metabolic acidosis with anion gap of >14?
Non-Volatile/Non-Carbonic acid = Wide Anion Gap Metabolic Acidosis (WAGMA)
What do you do with a patient with a wide anion gap?
Look for anions - ingested or intrinsic
What is the differential for a WAGMA?
MUDPILES M - methanol/metformin U - uremia D - DKA P - paraldehyde I - iron, infection, isoniazid, isopropyl alchohol L - lactate E - Ethylene glycol S - salicylates
What do you do with a patient with a normal anion gap acidosis?
Think…
- Bicarbonate loss
- Volatile acid gain
- Unable to make bicarbonate
How is bicarbonate reabsorbed?
90% in proximal tubule, 10% in thick ascending LoH. (follows Na reabsorption
How does the kidney excrete the necessary 50-100 mEq of H+/day?
Energy dependent ATPase and hiding the proton in diet-derived titratable acid
What is the purpose of glutamine metabolism in the context of acid/base balance
Formation of two NH4+ and two HCO3- (bicarb formation for buffering)
What are the non-renal causes of bicarbonate loss?
Diarrhea Post hypocapnea (kidneys overcorrecting) Drugs (acetazolamide=carbonic anhydrase i)
What are the non-renal causes of acid retention/reabsorption?
Urinary diversions (i.e. to colon) Drugs (spironolactone - blocks acid secretion)
What are the non-renal causes of inability to make ammonium or bicarb?
Total parenteral nutrition
Which amino acid is needed to create bicarb?
Glutamine
How can the presence/absence of NH4+ in the urine be diagnostic?
Determines the nature of acid/base problem
- proximal bicarb uptake problem=NH4+ in urine
- distal H+ secretion problem=no NH4+ in urine
- problem making/transporting NH4+ = no NH4+ in urine, corrected with exogenous titratable acid
When would ammonium be present in the urine?
When the body needs to excrete acid
How are urine ammonium levels measured?
Charge balance…
NH4+ = Cl - Na - K
NH4+ = 0 to 40
Define an osmole
Discrete particles in solution that cause water movement to balance gradients. i.e. NaCl - 2 osmoles, CaCl2 - 3 osmoles
How do you measure urine osmolar gap?
Measured Osm - calculated Osm
What is the formula for the calculated urine osmolality?
2Na + 2K + 2(NH4) + glucose + urea
How do you measure NH4+ from the urine osmolar gap?
NH4 = (mOsm - 2Na - 2K - glucose - urea) / 2
When is the osmolar gap inaccurate?
When patient has uncharged osmoles like alcohol in the urine
Which NAGMA presents with urine NH4?
Bicarb loss
Which NAGMAs present with no urine NH4?
H+ retention - urine pH stable giving titratable acid
Can’t make NH4/HCO3 - urine pH drops with titratable acid
