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MS2 Renal > 9/8- Intro to Acid Base Disturbances > Flashcards

9/8- Intro to Acid Base Disturbances Flashcards

1
Q

Normal values for arterial blood:

A
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2
Q

Normal values for venous blood:

A
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3
Q

What are the main sources for acid in the body?

A
  • Diet (20 mmol H/day)
  • Metabolism (H as nonvolatile acids 40 mmol/day)
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4
Q

How much acid is excreted per day?

A

About 70 mmol H+ is excreted in the urine/day

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5
Q

How is pH regulated (constantly)?

A

Buffers

  • Absorb hydrogen ions when in excess and can release if depleted
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6
Q

What is the largest buffering system? Others?

A

Largest = bicarbonate

  • Bicarbonate content can be regulated by the kidney and respiratory drive

Others: phosphates, proteins, hemoglobin…

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7
Q

Bicarbonate buffer system equation

A
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8
Q

Addition of acid leads to low levels of what?

A

Bicarbonate

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9
Q

What is the Henderson Hasselbach equation for bicarbonate buffer system?

A
  • Typically pH and pCO2 are measured from arterial stick and then HCO3- is calculated
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10
Q

What are the cardinal acid base disorders and what can cause them?

A
  • Metabolic acidosis (addition of acid, loss of bicarbonate)
  • Metabolic alkalosis (addition of alkali, loss of acid)
  • Respiratory acidosis (retention of CO2/ventilatory failure)
  • Respiratory alkalosis (loss of CO2/hyperventilation)
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11
Q

Note: PCO2 levels from ventilation/respiratory compensation is always in the same direction as HCO3 (high acid accumulation with low HCO3 levels means PCO2 must be lowered as well, with hyperventilation.. and vice versa)

A

(:

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12
Q

How does the kidney compensate for accumulated PCO2?

A

Increased bicarbonate (HCO3) retention

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13
Q

What is the diagnosis (metabolic/respiratory acidosis/alkalosis) for:

  • Arterial pH = 7.20
  • HCO3- = 14 meq/L
  • pCO2 = 30 mmHg
A

Metabolic acidosis (plug into H-H)

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14
Q

What is the diagnosis for:

  • Arterial pH = 7.42
  • HCO3- = 35 meq/L
  • pCO2 = 60 mmHg

A. Metabolic acidosis

B. No disturbance

C. Metabolic acidosis and respiratory acidosis

D. Metabolic alkalosis and respiratory acidosis

A

Have normal pH but abnormal values (think mixed disorders)

  • Always start with pCO2; it is high, so respiratory acidosis

D. Metabolic alkalosis and respiratory acidosis

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15
Q

How does the kidney handle H and HCO3?

  • Proximal acidification
  • Titrable acids and ammonia
  • Distal acidification
A

Proximal acidification:

  • Bicarbonate reabsorption
  • No acid excretion

Titrable acids and ammonia:

  • Acid excreted

Distal acidification:

  • Acid excreted
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16
Q

What defects may lead to proximal renal tubular acidosis?

A
  • Defect in Na-H exchange (NHE)
  • Defect in carbonic anhydrase enzyme

Threshold of bicarbonate reabsorption reduced

  • Extremely difficult to “normalize” serum bicarbonate level with supplements
17
Q

What is the main goal of the proximal tubule in terms of acid-base equilibrium?

A

Bicarbonate reabsorption

  • No acid excretion in this process
18
Q

Proximal tubular damage leads to what?

A
  • Bicarbonaturia
  • Glycosuria
  • Aminoaciduria
  • Phosphaturia (Fanconi’s)
19
Q

What are some causes of proximal RTA?

20
Q

What is fractional excretion (FE)?

A

Amt excreted / amt filtered

21
Q

Where does ammoniagenesis happen?

A

Mostly in proximal tubule, but other places as well

22
Q

What is the main titratable acid?

A

HPO4- (can accept hydrogen and be excreted as H2PO4)

23
Q

How does the kidney account for acid overload?

A
  • Titrable acid excretion
  • Ammoniagenesis
24
Q

Action of the distal nephron with classic or Type I RTA?

A
  • Defective intercalated cell: protons not pumped or they back-leak into blood Effect of Distal RTA:

—Tubule lumen more negative

—Potassium excretion enhanced

—Urine not acid

  • Acid accumulates over time, and very low HCO3 levels can occur
  • Bone buffers acid, causing osteoporosis, hypercalciuria, and kidney stones
  • Very low serum potassium levels
25
Distal RTA and stones
- Acidemia leads to release of calcium phosphate from bone (buffer) - Acidosis leads to retention of citrate in proximal tubule – ↓ citrate in urine - High urine pH: precipitation of calcium phosphate stone
26
\_\_\_\_ is a natural inhibitor of stone formation
**Citrate** is a natural inhibitor of stone formation
27
Causes of distal RTA
**Idiopathic Familial** - Autosomal dominant and recessive **Secondary** - Rheumatologic (RA, Sjogren’s, SLE) - Drugs (Amphotericin B, Ifosfamide, Lithium) - Renal transplantation - Others: cirrhosis, sickle cell anemia etc
28
What can cause Hypo-renin hypo-aldosteroneism (Type 4) RTA?
- Originally described in diabetics _Other causes:_ - Urinary obstruction - Medications (Bactrim, K-sparing diuretics) - Renal interstitial inflammation ----Allergic interstitial nephritis ----Systemic lupus erythematosus Originally though to be due to low aldosterone state
29
What is seen in Hypo-renin hypo-aldosteroneism (Type 4) RTA?
Principal cell sodium channel defect: - Tubule lumen not negative - Hyperkalemia ensues Hyperkalemia inhibits proximal NH4+ production and bicarbonate generation falls Thus patients appear to have hypoaldosteronism (one of many etiologies Type IV RTA)
30
Summary slide
31
What is the urine "anion gap"? What causes a negative or positive gap?
Urinary (Na + K) should = urinary Cl - Urine NH4 is not directly measured **"Negative urine gap": Cl \> (Na + K)** - NH4 production increased in response to acidosis (e.g. diarrhea) **"Positive" gap:** - NH4 absent (e.g. failure of kidney to make ammonium); RTA
32
Case) - 60 yo male present with new onset of glucose in the urine - Tired and his bones "hurt" _Labs:_ - Arterial pH = 7.29 - HCO3- = 16 meq/L - Anion gap = 10 (normal 10-12) - Urinalysis = 3+ glucose _What is his diagnosis?_ A. Distal RTA (type I) B. Proximal RTA (type 2) C. Hyperkalemic RTA (type 4)
A. Distal RTA (type I) **B. Proximal RTA (type 2)** C. Hyperkalemic RTA (type 4) - Acidemia - Low HCO3, so possibly metabolic acidosis - Proximal RTA affected (glucose in urine) - Giving this pts bicarbonate will not increase levels significantly
33
Case) - 24 yo female - Referred for abnormal lab values - She also has a rheumatologic disease _Labs:_ - Urine pH = 6.5 - HCO3- = 8 meq/L - Anion gap = 10 (normal) - Potassium (2.9 meq/L) _What is her diagnosis?_ A. Distal RTA (type 1) B. Proximal RTA (type 2) C. Hyperkalemic RTA (type 4)
**A. Distal RTA (type 1)** B. Proximal RTA (type 2) C. Hyperkalemic RTA (type 4) - Urine pH can vary from 4.5 - 7 based on diet - Serum bicarb is VERY low... so urine pH should be very low (instead it is high) - Inability to acidify the urine

MS2 Renal (25 decks)

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