Acid-Base Physiology

Question 1

Metabolic Alkalosis CO2 Calculation

Describe the significance of the ranges.

Answer 1

“0.7 plus 20”
PCO2 = 0.7 * [HCO3] + 20 (+/-) 5
1. Normal range: >40 mm Hg in order to compensate for the low H+ protons

Question 2

What is the main indicator for a Respiratory Acidosis? What should we expect for acute vs. chronic?

Answer 2

Abnormally HIGH pCO2 > 40 mm Hg.
Acute: +1 mM HCO3 for every +10 mm Hg increase in pCO2
Chronic: +4 mM HCO3 for every +10 mm Hg pCO2 increase

Question 3

What is the indicator for Metabolic Acidosis.

Answer 3

The amount of HCO3 present is lower than 24. Also, the AG can be within range of 7-16 mmol/L. If above, then we indicate “…with elevated AG”

Question 4

What are the baseline concentrations for important blood gases?

Answer 4

HCO3 = 24 meq/ L
PCO2 = 40 mm Hg

Question 5

Acute Respiratory Acidosis

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Answer 5

“Up 1 for 10”

Increase in meq/L HCO3 by 1 for every 10 mm Hg pCO2

Question 6

Chronic Respiratory Acidosis

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Answer 6

“Up 4 for 10”

Increase 4 meq/L HCO3 for every 10 mm Hg

Question 7

Acute Respiratory Alkalosis.

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Answer 7

“Down 2 for 10”

For every 2 meq/L drop in HCO3, there is a 10 mm Hg decrease in pCO2

Question 8

Chronic Respiratory Alkalosis.

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Answer 8

“Down 5 for 10”

For every 5 meq/L drop in HCO3-, there is a 10 mm Hg decrease in pCO2

Question 9

Metabolic Acidosis.

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Answer 9

“One and a half plus 8”

PCO2 = 1.5*(HCO3) + 8 (+/-) 2

Question 9

Metabolic Alkalosis.

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Answer 9

“Zero Point Seven plus 20”

PCO2 = 0.7*(HCO3) + 20 (+/-) 5

Question 10

What is the Formula for the Plasma anion gap (AG)? Define the normal range and abnormal ranges.

Answer 10

AG = Na - (Cl + HCO3)

1. Normal Range: 7-16 mmol/L
2. Elevated AG = Metabolic Acidosis

Question 12

When should we use Delta-Delta? Describe what’s being calculated.

Answer 12

1. Delta-Delta is used when we have an ABNORMAL Anion Gap. This can indicate an underlying/co-existing ion imbalance disorder.
2. DeltaAG = (AG - 12)
   DeltaHCO3 = (24 - HCO3)

Question 13

Describe what happens and how the body compensates for METABOLIC ACIDOSIS.

Answer 13

1. PH decreases,
2. HCO3 decreases
3. pCO2 decreases to compensate
   * Metabolic acidosis is associated with Ketoacidosis, Lactic Acidosis, Alcoholism and Ingestion of Strong Acids (Salicylic Acid, Methanol, Ethylene Glycol)

Question 14

Describe what happens and how the body compensates for METABOLIC ALKALOSIS.

Answer 14

1. pH Inc
2. HCO3 Increases
3. pCO2 increases to compensate for alkalinity

Question 15

Describe what happens and how the body compensates for RESPIRATORY ACIDOSIS.

Answer 15

1. PH decreases
2. PCO2 increases
3. HCO3 increases to compensate (work against the acidity of the raised CO2 levels)

Question 16

Describe what happens and how the body compensates for RESPIRATORY ALKALOSIS.

Answer 16

1. PH increases
2. PCO2 decreases
3. HCO3 decreases to compensate for the alkaline blood levels.

Question 17

Describe the symptoms of Lactic Acidosis.

Answer 17

Low pH and High Lactate levels can lead to K+ channels open more often.
This can present as arrhythmias or Hypotension
Less binding of insulin and reduced catecholamines also contribute to above symptoms [Slide 59]

Question 18

What is the Winter’s Formula (for acidemia) when should it be used and what are its implications?

Answer 18

1. pCO2 = 1.5 * (HCO3) + 8 (+/-) 2
2. This should be used in the scenario of “Metabolic Acidosis”, to see if it’s being compensated for. PCO2 is expected to decrease
3. If calculated levels are above, Respiratory Acidosis is superimposed. If below, there is a superimposed respiratory alkalosis.

Question 19

Name at least 3 lung pathologies that can lead to respiratory acidosis.

Answer 19

1. COPD
2. Severe Asthma
3. Pneumonia
   * Any disorder that affects gas exchange and increases resistance of the diffusion barrier.

Question 20

Name 5 pathologies that can be associated with AG-Elevated Metabolic Acidosis.

Answer 20

1. Diabetes (Ketoacidosis), Alcoholism
2. Lactic acidosis
3. Renal Failure
4. GI excretion of HCO3-
5. Ingestion of strong metabolized acids (salicylic acid, glycolic acid, formic acid, ketoacids, lactic acid)

Question 21

What is the equation for Urine Anion Gap (UAG) and what are the indications?

Answer 21

AG = UNa + UK - UCl

• ”U” is concentration in urine
  1. Urine AG should = 0 normally
  2. If UAG <0, then Metabolic Acidosis occurs with intact Kidneys
  
  • Cl- is excreted
    3. If UAG >0, then Impaired Distal (Urine) Acidication
• NH4-Cl is excreted; kidneys can’t acidify urine

Question 22

Name at least 3 common causes of Metabolic Alkalosis.

Answer 22

1. Diarrhea
2. Vomiting
3. Hypovolemia

Question 23

What 2 channels are activated in the kidneys due to metabolic alkalosis (linked to water loss).

Answer 23

1. Na/H exchanger
   - Na is reabsorbed at the expense of H+ (acidify urine in the process)
2. Na/HCO3 symporter
   - HCO3 is reabsorbed with Na and can compensate for metabolic alkalosis.

Question 24

What is the Delta-Delta difference and how is it calculated?

Answer 24

1. D-D difference indicates the one:one relationship of unmeasured anions and HCO3. Abnormal is when D-D is not =0
2. D-D = (delta-AG) - (delta-HCO3)
   * Delta-AG = AG -12
   * Delta-HCO3 = 24 - HCO3

Question 25

What are the ranges of Delta-Delta values and what do they indicate?

Answer 25

1. Normal range: (-5 to +5) indicates metabolic acidosis alone
2. If Large +: (>+5) then AG Metabolic Acidosis and Metabolic Alkalosis co-exist.
3. If Large - : (

Question 26

Name 2 types of ionic imbalances that can be associated with Metabolic Acidosis.

Answer 26

1. Hyperkalemia: to maintain electroneutrality, most cells dump out intracellular K+ in exchange for picking up extracellular H+
2. Hyperchloremia: too much chloride in the kidneys is being reabsorbed back into blood plasma along with HCO3 to offset acidosis AND add more negative charge to plasma [maintain electroneutrality]

Question 27

Describe associated acid-base disorders of the following clinical symptoms:

1. Vomiting
2. Diarrhea
3. Tachypnea

Answer 27

1. Metabolic Alkalosis - vomiting
2. Non-AG Metabolic Acidosis- diarrhea
3. Respiratory Alkalosis - hyperventilation

Question 28

Describe the important buffers for regulating blood pH (in RBCs and kidneys, respectively).

Answer 28

1. HCO3-: made in RBCs from CO2 and H2O. This offsets H+ in the blood plasma to control impending acidosis.
2. HPO4 - excreted as H2PO4

Question 29

What is the Henderson-Hasselbach equation for calculating pH from HCO3 and CO2?

Answer 29

pH = 6.1 * log [(HCO3-)/(0.03*pCO2)]

Question 30

What are some symptoms associated with a metabolic acidosis/alkalosis without AG elevation (non-AG)

Answer 30

Chronic Diarrhea or Chronic Vomiting DO NOT raise the Anion Gap!
Ex:) We would expect a non-AG metabolic acidosis for diarrhea

Question 31

Describe how these ionic imbalances are associated with Metabolic Acidosis.

1. Hyperkalemia
2. Hyperchloremia

Answer 31

1. K+/H+ swap occurs after several hours of metabolic acidosis. Many cells release intracellular K+ and buffers into the blood while removing H+, hence high K+ levels in the blood.
2. Cl- replaces lost HCO3- to maintain Electroneutrality in the blood. HCl is buffered by HCO3- and fluid loss altogether has the kidneys retain more NaCl > Non-AG Metabolic Acidosis.