Physio - Acid Base

L49-L51

Carnivores have a more ____ diet.

Acidic

Herbivores have a more ____ diet.

alkaline

What’s the difference between simple vs. complex acid base disorders? Which is more common?

Simple: one organ involved → More common (95%)

Complex: multiple organs OR chronic disorder (electrolyte imbalance)

Acids are H+ ______ and bases are H+ ______.

Acids are H+ DONORS and bases are H+ ACCEPTORS.

Bases BUFFER (will take H+ from acids)

Strong vs. Weak Acids (and examples of each)

Strong: dissociate completely (HCl-, NaOH)

Weak: dissociate partially (carbonic acid: H2CO3)

How can a pH change disturb physiology?

1. Changes enzyme function

2. Changes membrane potential → depolarizes

3. Hormones less effective

What’s the pH of ECF?

± 7.4

What’s the pH of blood?

7.35-7.45

At what point is pH considered acidemic or alkaline?

< 7.35 → acidemic

>7.45 → alkaline

At what point can the pH cause death? What factors determine if the animal will die?

Greater than 8.0 or less than 6.8

Severity and duration that the pH has been out of range

What condition in calves can cause serious acid-base imbalances?

Scours (diarrhea)

Does the body produce more acids or bases?

Acids

Where do acids come from in the body?

1. Food

2. Metabolism of lipids and proteins

3. Cellular

What is Michaelis-Menten Kinetics and how is it relevant to acid-base balance?

If there’s too much H+, body will move equation towards production of CO2 + H2O side

If there’s too much CO2, body will move equation towards bicarb and H+ side

What enzyme helps convert CO2 and H2O into carbonic acid?

Carbonic Anhydrase

What molecule does the lung regulate?

CO2

What molecule does the kidney regulate?

Bicarbonate

What is the CO2 Hydration Equation?

CO2 + H2O → H2CO3 → H + HCO3

How can acute diarrhea and vomiting change pH?

Acute d → losing bicarb! → acidosis (low pH)

Acute v → losing HCl (acid) → alkalosis (high pH)

What is the pKa ratio? What’s the normal ratio?

Conjugate base to Acid ratio

6:1

What is the normal Bicarb to carbonic acid ratio?

20:1

What is the relevance of hemoglobin in pH balance?

Major H+ buffer

What is the relevance of plasma proteins in pH balance?

H+ buffer

What’s the difference between volatile and fixed acids?

Volatile → can go into gas form

Fixed → can’t become gas

Where are volatile acids usually found in the body and what form(s) do they take?

Lungs → CO2

Where are fixed acids usually found in the body and what form(s) do they take?

WHERE: Kidney

FORMS:

1. Phosphoric Acid → membrane lipid breakdown

2. Sulfuric Acid → protein breakdown

3. Lactic Acid → ischemia (lack of blood supply to organ), hypoxia (think exercise)

4. Keto-acids → dz (think diabetic ketoacidosis)

What do fixed acids react with to form CO2 and salt?

NaHCO3 → sodium bicarbonate

Do you need a specific concentration of both CO2 and HCO3 for a pH of 7.4?

No, there’s a variety of ranges of each you can have. But if you have a certain concentration of CO2, then you have to have a very specific [HCO3-] for the pH to be 7.4

How do buffers resistant pH changes?

Take up H or release H as conditions change

What does a buffer pair compose of?

Weak Acid + Base

(weak acid can combine or dissociate to either take up/give off H+ based on conditions)

What is the average pKa value of an effective buffer?

Between ± 1.0-1.5 from 7.4

What type of buffers have an immediate response?

Chemical Buffers

What type of buffers have a long lasting response?

Physiological Buffers

What systems are a part of the chemical buffer system?

1. Bicarb Buffer

2. Phosphate Buffer

3. Protein Buffer

What systems are physiological buffers?

1. Respiratory Mechanism

2. Renal Mechanism

What does the renal buffering system do to H+? How long does it take?

Excretes H+ (renal failure = H+ build-up)

Hours to Days

How long does Intracellular Buffering take?

Up to 4 hours

How long does respiratory buffering take?

Minutes! Very fast!

How long does extracellular buffering by bicarb take? What are some examples?

Immediate → seconds

Carbonic Acid, Dihydrogen Phosphate, sodium bicarbonate

What condition causes the most common loss of base?

Diarrhea → lose bicarb

What are some examples of intracellular buffers?

1. Bicarbonate-carbonic acid

2. Hemoglobin

3. Proteins → imidazole of histidine and a-amino acids

4. Organic Phosphates (eg. ATP)

What do intracellular buffers do to H in body?

Decrease H activity

How can respiratory buffering mechanisms change body pH?

Rate and depth of breathing can cause changes in CO2 exhalation

more CO2 exhalation → less pCO2 → less H+

less CO2 exhalation → more pCO2 → more H+

Respiratory buffering mechanisms only work for ____ acids

Volatile

If the animal has metabolic acidosis, what is the compensatory response?

Lungs still get rid of CO2 → Respiratory Alkalosis

What happens to pH if the kidneys fail?

Acidosis (build up of acid)

How does the renal bufferin

What 3 mechanisms does the renal buffering system use to maintain pH?

1. Reabsorbs Bicarb

2. Excretion of Titratable Acid (ie. inorganic phosphates, dihydrogen phosphate)

3. Excretion of Ammonium (NH4+)

What occurs to bicarb reabsorption if more acid is being produced?

Increase in bicarb reabsorption → need more buffer for the acid!

How does antifreeze/ethlene glycol toxicity change H+ production and pH? What imbalance does it cause?

Causes H+ production → decreases pH → metabolic acidosis

How does H+ production and excretion as titratable acid/ammonium in diabetic ketoacidosis compare to normal animals?

Production: Increases of H+

Titratable Acid: Increases

Ammonium: MAJOR increase! → due to glutamine protein breakdown

How does H+ production and excretion as titratable acid/ammonium compare in chronic renal failure compare to normal animals?

Production H: Stays Same

Titratable Acid: Decreases

Ammonium: Decreases

What does the Stewart approach to acid base abnormalities say the pH is influenced by?

pH is the dependent variable and is influenced by…

1. PCO2

2. Strong Ion Differences (SID) between cations and anions

3. Total Weak Acid Concentration (Atct)

What does an increase in cations cause based on the Stewart approach?

Acidosis

What does an increase in anions cause based on the Stewart approach?

Alkalosis

What are some examples of strong cations?

Na, K, Ca and Mg

What are some examples of strong anions?

Cl, lactate, ketoacids

What does the anion gap measure?

The difference between the concentration of cations (Na+) and anions (Cl- and HCO3-)

What’s the typical difference in concentration between Na and Cl?

40 mEq/L

What’s the typical concentration of Na and Cl?

[Na] = 150 mEq/L

[Cl] = 110 mEq/L

What’s the difference between partial and complete compensation?

Partial: pH range will still be outside normal limits

Complete: pH returns to normal range

How does the respiratory system compensate for imbalances?

Hyperventilation or hypoventilation

How does hyperventilation change PCO2 and [H+]?

Hyperventilation = decrease PCO2 = less H+ → alkalosis

How does hypoventilation change PCO2 and [H+]?

Hypoventilation = increase PCO2 and H+ → acidosis

What is the primary disorder and compensatory response if the pH is low and there’s low bicarbonate levels?

Low pH = Acidemia

Low HCO3 = Metabolic → Metabolic Acidemia

Compensate: Respiratory Alkalosis → decrease CO2 (decrease H+) → Hyperventilation

What is the primary disorder and compensatory response if the pH is low and there’s high CO2 levels?

Low pH = Acidemia

High PCO2 = Respiratory → Respiratory Acidemia

Compensation: Metabolic Alkalosis → increase buffer → increase HCO3- reabsorption

What is the primary disorder and compensatory response if the pH is high and there’s high bicarbonate levels?

High pH = Alkalosis

High Bicarbonate = Metabolic → Metabolic Alkalemia

Compensation: Respiratory Acidemia → Increase CO2/H+ → Hypoventilation

What is the primary disorder and compensatory response if the pH is high and there’s low PCO2?

High pH = Alkalemia

Low PCO2 = Respiratory → Respiratory Alkalemia

Compensation: Metabolic Acidemia → decrease buffer → Decrease HCO3- reabsorption

What are the steps to acid-base interpretation?

1. Determine pH (acidosis vs. alkalosis?)

2. Determine PCO2 and HCO3- values

3. Based off values, determine primary and compensatory shift

4. Determine respiratory component of shift

5. Calculate PaO2/FiO2 ratio

What is the normal PCO2 range?

35-45 mmHg

What is the normal HCO3- range?

20-25 mmHg

What is the normal PaO2 value?

100 mmHg

What is the normal PaO2/FiO2 ratio?

> or = 400 mmHg

How much does pH decrease for every 10 mmHg increase in PaCo2 above 40 mmHg?

0.05 units (ie. if PaCO2 is 60 mmHg → pH decreases by 0.10 = 7.3)

What is the normal percent of O2 in air?

20%

At what value of the PaO2/FiO2 ratio is there considered to be severe pulmonary disease or respiratory failure?

< 200 mm Hg

What can red colored gums indicate?

Increase in CO2 (which is a vasodilator) → causes gums to look more red

Check ETCO2 → might be high and indicate respiratory acidosis

What values of PO2, SaO2 and PCO2 indicate respiratory failure?

PO2 (arterial): < 60 mmHg → animal not breathing so less O2 in blood

SaO2: < 90% → pulse ox

PCO2 (venous/arterial): > 55 mmHg → animal not breathing so CO2 is building up in blood