9/8- Intro to Acid Base Disturbances Flashcards Preview

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

Flashcards in 9/8- Intro to Acid Base Disturbances Deck (33)

Normal values for arterial blood: 


Normal values for venous blood:


What are the main sources for acid in the body?

- Diet (20 mmol H/day)

- Metabolism (H as nonvolatile acids 40 mmol/day)


How much acid is excreted per day?

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


How is pH regulated (constantly)?


- Absorb hydrogen ions when in excess and can release if depleted


What is the largest buffering system? Others?

Largest = bicarbonate

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

Others: phosphates, proteins, hemoglobin...


Bicarbonate buffer system equation


Addition of acid leads to low levels of what?



What is the Henderson Hasselbach equation for bicarbonate buffer system?

- Typically pH and pCO2 are measured from arterial stick and then HCO3- is calculated


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

- 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)


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)



How does the kidney compensate for accumulated PCO2?

Increased bicarbonate (HCO3) retention


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

- Arterial pH = 7.20

- HCO3- = 14 meq/L

- pCO2 = 30 mmHg

Metabolic acidosis (plug into H-H)


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

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


How does the kidney handle H and HCO3?

- Proximal acidification

- Titrable acids and ammonia

- Distal acidification

Proximal acidification:

- Bicarbonate reabsorption

- No acid excretion

Titrable acids and ammonia:

- Acid excreted

Distal acidification:

- Acid excreted


What defects may lead to proximal renal tubular acidosis?

- 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


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

Bicarbonate reabsorption

- No acid excretion in this process


Proximal tubular damage leads to what?

- Bicarbonaturia

- Glycosuria

- Aminoaciduria

- Phosphaturia (Fanconi's)


What are some causes of proximal RTA?


What is fractional excretion (FE)?

Amt excreted / amt filtered


Where does ammoniagenesis happen?

Mostly in proximal tubule, but other places as well


What is the main titratable acid?

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


How does the kidney account for acid overload?

- Titrable acid excretion

- Ammoniagenesis


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

- 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


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


____ is a natural inhibitor of stone formation

Citrate is a natural inhibitor of stone formation


Causes of distal RTA

Idiopathic Familial

- Autosomal dominant and recessive


- Rheumatologic (RA, Sjogren’s, SLE)

- Drugs (Amphotericin B, Ifosfamide, Lithium)

- Renal transplantation

- Others: cirrhosis, sickle cell anemia etc


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


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)


Summary slide


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 



- 60 yo male present with new onset of glucose in the urine

- Tired and his bones "hurt"


- 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



- 24 yo female

- Referred for abnormal lab values

- She also has a rheumatologic disease


- 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