05.07 - Acid Base (Wall) - PP + Handout, No reading, Not watched Flashcards
Expected HCO3, pCO2 changes for Acute Respiratory Alkalosis
HCO3 decreases 2 mEq for each 10 mm decrease in pCO2
Type 1 (Distal) RTA is caused by __ and causes ___
Defective H-ATPase, decreased acid secretion
Metabolic Acidosis is ___ Bicarb
Decreased
For simple acid-base disorders, pC02 and HCO3 always
change in same direction
Acid Base disorder caused by Hyperaldosteronism
Metabolic Alkalosis
2 disorders with elevated Bicarb (>30)
Metabolic Alkalosis and Chronic Respiratory Acidosis (with kidney compensation)
How does plasma anion gap change with respiratory disorders
Doesn’t
Urine anion gap is an indirect estimate of
Urinary NH4+ excretion
__ % of Bicarb is reabsorbed in PT via __
90% via Na-H antiporter (Na is driving force)
Why is Citrate given in acid base
Metabolized to Bicarb
Normal Urine Anion Gap
Positive, 10 mEq/L
If PAG is normal in Metabolic acidosis
Might be kidney not making NH4+, or Losing Bicarb by Diarrhea
Why can you tell the difference b/t acute and chronic respiratory disorders
Takes kidneys hours to days to compensate
What inhibits Na channel in principal cell of cortical collecting duct?
Amiloride, Triamterene
Isohydric principle
All buffers change in same direction
Metabolic Alkalosis is ___ Bicarb
Increased
What must accompany NH4+ in urine
Chloride
What is synonymous with send a bicarb into blood
Proton pumped into urine that came from intracellular Carbonic Anhydrase
How does renal failure affect acid base balance
Reduced GFR - Decreased Ammonium excretion
What is invariably present in Simple Acid-Base disorders
Compensation
pH and H+ ranges
6.8-7.8; 16-160 neq/L
When A- from HA is excreted into urine
Normal Plasma Anion gap, increased plasma chloride
Anion Gap if you lose Bicarb directly in stool
None b/c there’s no unmeasured anion
Etiology of Metabolic Alkalosis
Loss of H+ into GI or into urine
Respiratory Acidosis is __ CO2
Increased CO2
What must be present in simple acid-base disorders
Secondary physiologic compensation
When will you have lower or negative UAG
If you’ve lost bicarb by diarrhea, ammonium increases in urine, and chloride accompanies it
Major extracellular buffer
Bicarb
If Na concentration stays constant, but Chloride conc. changes, then
an acid base disorder is present
What acid base disorder can dietary protein intake cause
Acidosis
What puts bicarb back into urine
Cl/Bicarb (Pendrin) in beta-intercalated cells
Cl responsive in Metabolic Alkalosis means
Urine Cl
Patient with lower GFR develops more severe acidosis following acid load b/c
can’t secrete NH4+ as well
Expected pH changes for Chronic Respiratory Acidosis
HCO3 increases 4 mEq for each 10 mm increase in pCO2
Timeframe of H+ excretion, Bicarb reabsorption, and Bicarb generation
Hours to days
Expected pH Changes for Acute Respiratory Acidosis
HCO3 increases 1 mEq for each 10 mm increase in pCO2
Type 4 (Hypoaldosteronism) RTA is caused by ___ and causes ___
Impaired proton and K secretion, decreased acid secretion
What drug inhibits sodium bicarb reabsorption in proximal tubule
Acetazolamide (CAi)
Speed and effectiveness of 2 buffering routes in respiratory acidosis
(1) Plasma: rapid but limited, 1-2 mEq/L increase in Bicarb; (2) Kidney excretes NH4, generating new bicarb, delayed 2-3 days
Acid Base disorder caused by Loop or Thiazides
Metabolic Alkalosis
How long does it take kidney to generate new bicarb ions
2-3 days
Bicarb transporter in beta-intercalated cells
Cl/Bicarb (Pendrin)
Normal HCO3-
22-26 (24mEq/L)
Acute Respiratory acid base disorders always have __ change in pH than chronic b/c __
Greater change, b/c kidney is slow in compensating
Changes in HCO3 and pCO2 in Metabolic Alkalosis
Both increase
Changes in HCO3 and pCO2 in Respiratory Acidosis
Both increase
How does CO2 in alpha-intercalated cells affect H secretion/reabsorption
CO2 binds with OH- to form bicarb that is reabsorbed instead of secreted; H+ is the secreted instead of bonding with the OH-
When A- from HA is reabsorbed by kidney or retained in plasma
Unmeasured Anion - Increased Plasma Anion Gap, minimal change in plasma Chloride
HCO3 in Respiratory Alkalosis
Slightly decreased
If PAG increases in metabolic acidosis, it’s
Lactic Acidosis or some other renally conserved acid anion
How does plasma Na change with acid base disorders
Doesn’t
Where is Bicarb primarily reabsorbed
PT and LOH
Cl resistance in Metabolic Alkalosis means
Urine Cl >20 mEq/L (usually >50 mEq/L)
Urine Anion Gap =
Na + K - Cl (in urine)
Primary acid we produce
CO2 from metabolism of fats and carbs
Timeframe of intracellular fluid buffer systems
2-4 hours
Which RTA results from Decreased Acid Excretion?
Type 1 (Distal) and Type 4 (Hypoaldosteronism)
Every proton proton pumped into the urin had to come from
Intracellular Carbonic Anhydrase
Most common form of chronic alkalosis where the kidney compensates
Pregnancy - Alkalemic
2 major buffers of urine
NH4+ and Phosphate
Pregnant women acid base
Slightly Alkalemic
Changes in HCO3 and pCO2 in Respiratory Alkalosis
Both decrease
Decreased Acid excretion is synonymous with
Impaired NH4+ excretion
Trick for converting [H+] to pH
80 - decimal digits of pH
How to distinguish b/t Acute and Chronic
Look at Bicarb: Small change (1-2), then acute; Larger change (4-5) then kidney has compensated and chronic
pKa of Bicarb
6.1
Normal pCO2
36-44 (40mmHg)
Diarrhea results in loss of
Bicarb –> Metabolic Acidosis
Acid Base Disorder caused by Hypokalemia
Metabolic Alkalosis
Final excretion of daily aci load occurs primarily in
CD
Where are non-Carbonic acids eliminated?
Combined with buffers and secreted by kidneys
Indirect estimate of urinary NH4+ excretion
Urine Anion Gap
Why is NH4+ trapped in urinary lumen
Lipid soluble
Expected pH changes for Chronic Respiratory Alkalosis
HCO3 decreases 5 mEq for each 10 mm decrease in pCO2
Compensation for Respiratory disorders occurs by
Alterations in Bicarb concentration
Normal Plasma Bicarb
24 mEq/L
In simple acid-base disorders, the compensatory mechanisms
Must be present, Never fully correct pH
Respiratory Alkalosis is __ CO2
Decreased CO2
Metabolic Disorders are processes that directly alter
Bicarb Concentration
Urine AG becomes less positve/more negative with
Increasing urinary NH4+ –> Cl must accompany NH4+
How to get Bicarb from Total CO2
Subtract 1-1.5
How does plasma Cl change with plasma HCO3
Changes equally and inversely
How much does Total CO2 exceed plasma bicarb?
By 1-1.5 mEq/L
Plasma Cl is altered in which Acid Base Disorders
All except increased Plasma AG Metabolic Acidosis
pH of 7.4 = what [H]
40 nEq/L
Action of Acetazolamide
CA inhibitor - Inhibits Na Bicarb reabsorption in PT
How does low pH alon drive bicarb reabsorption
More CO2 in blood freely enters tubular cell - Meaning more reactant to form H+ that goes into Na-H Antiporter
Changes in HCO3 and pCO2 in Metabolic Acidosis
Decrease in HCO3- and pCO2
[H+] =
24 x pCO2 / [HCO3]
HCO3 in Respiratory Acidosis
Slightly increased
Only caveat to Urine Chloride in Metabolic Alkalosis
If just took Loop diuretic, urine Cl can’t be low b/c block reabsorption
Why is Isohydric principle useful
If we know what Bicarb is doing, we know what others are doing (all change in same direction)
Acid Base Cells in Collecting Duct
Intercalated cells
Where is Carbonic Acid eliminated?
Lungs
Which RTA results from Loss of Bicarb
Type 2 (Proximal) RTA
Respiratory compensation vs Metabolic Compensation
Respiratory compensations is rapid; Metabolic compensation (by kidneys) is slower over 1-2 days
3 Etiology Categories of Metabolic Acidosis
Decreased Renal Acid Excretion; Direct Bicarb Losses; Increased Acid Generation
Total CO2 concentration =
Dissolved CO2 + Bicarbonate concentration in venous sample; 25-26 mEq/L
Normal Chloride
105
