Lecture 4: Anesthesia & Renal Physiology: regulation of acid-base balance

Question 1

Normal ECF H+ concentration is:

Answer 1

40nEq/L

Question 2

Normal physiologic pH is:

Answer 2

7.4

Question 3

An acid is defined as a proton (H+) _____.

Answer 3

Donor

Question 4

A base is defined as a proton (H+) _____.

Answer 4

Acceptor

Question 5

the Henderson–Hasselbalch equation describes:

Answer 5

the derivation of pH as a measure of acidity (using pKa, the negative log of the acid dissociation constant) in biological and chemical systems.

Question 6

Buffers are most efficient when _______?

Answer 6

pH=pKa (50/50 mixture)

Question 7

Name the buffers in the body:

Answer 7

• Bicarbonate (#1) H2CO3 or HCO3
• hemoglobin
• intracellular proteins
• phosphate (H2PO4; HPO4)
• Ammonia (NH3; NH4)

Question 8

Bicarbonate buffer:

Hydration of CO2 is catalyzed by ____ ____ in the ____ _____.

Answer 8

-Carbonic anhydrase in the proximal tubule

Question 9

Bicarbonate buffer is effective against _____ acidosis but not _____ acidosis.

Answer 9

Effective against METABOLIC acidosis but not respiratory acidosis.

Question 10

Carbonic Anhydrase inhibitors control BP by:

Answer 10

Increasing excretion of HCO3 (Bicarbonate), sodium, potassium and water. (diuresis)

Question 11

_____% of Bicarbonate is reabsorbed in the proximal tubule and the remaining ____% is reabsorbed in the distal tubule.

Answer 11

80-90% in the proximal tubule

10-20% in the distal tubule

Question 12

H+ secreted in the tubule lumen can combine with HPO4 to form H2PO4 which is not reasorbable and becomes trapped in the urine, this is considered a ____ buffer?

Answer 12

Phosphate buffer.

Question 13

Ammonium is synthesized from _____? What is generated in the synthesis process?

Answer 13

Glutamine; Bicarbonate

Question 14

Ammonia (NH4) is an important tubular fluid butter in the _____, _____, and _____.

Answer 14

Proximal tubule, Thick loop, and Distal Tubule.

Question 15

Renal compensation for Alkalosis:

Large amounts of bicarbonate can be excreted if necessary. Metabolic Alkalosis is mainly possible in 2 situations:

Answer 15

1. Na Depletion (reabsorption)- more sodium is reabsorbed in the proximal tubule, and Cl moves with it to preserve electroneutrality. As Cl in the tubule decreases, HCO3 must be reabsorbed. This is called “contraction alkalosis” that can occur with long-term diuretic use.
2. Increased Aldosterone (mineralocorticoid) activity increases Na reabsorption and H+ secretion in the distal tubule.

Question 16

Base Excess is:

Answer 16

The amount of acid or base that must be added to return blood pH to 7.4

Question 17

A positive base excess indicates _____ _____ and a negative value indicates ____ ____.

Answer 17

Positive= Metabolic Alkalosis

Negative = Metabolic Acidosis

Question 18

Physiologic effects of acidosis:

K increases ____ for each ___ unit increase in pH.

Answer 18

K increases 0.6 mEq/L for each 0.1 unit increase in pH.

Question 19

The oxyhemoglobin dissociation curve shifts to the ___ during acidosis.

Answer 19

Right (decreased affinity for oxygen); gives O2 to tissues.

Question 20

What cardiac effects does acidosis have?

Answer 20

• Decreased responsiveness to catecholamines

- Decreased contractility

Question 21

Anion gap measures what?

Answer 21

The Anion Gap (AG) is a derived variable primarily used for the evaluation of metabolic acidosis to determine the presence of unmeasured anions. The normal anion gap depends on serum phosphate and serum albumin concentrations. An elevated anion gap strongly suggests the presence of a metabolic acidosis.

Question 22

What is a NORMAL anion gap value?

Answer 22

Anion GAP= [Na+] - ([Cl-] + [HCO3-]
Normal values= 140- (104 + 24) = 12 mEq/L

Normal range: 7-14 mEq/L

Question 23

Can you have a NORMAL anion gap and have acidosis?

Answer 23

YES:

Usually seen with hyperchloremia (Cl- takes the place of the bicarbonate anion)

Related conditions:

• Diarrhea
• Renal loss of HCO3-

Question 24

Acidosis with a HIGH anion gap:

Answer 24

-In this case H+ consumes HCO3- and an unmeasured anion accumalates and takes the place of bicarbonate.

Related conditions:

• Uremia
• Diabetic Ketoacidosis
• Lactic acidosis

Question 25

Treatment for Metabolic Acidosis:

Answer 25

-Treat the underlying cause of the acidosis:

(Hypovolemia, anemia (Hgb is a buffer), cardiogenic shock.)

Question 26

Do we treat METABOLIC acidosis with Sodium Bicarbonate (NaHCO3)?

Answer 26

NO!

Rare instances only, like MH when you’re really up shit creek.

Sodium Bicarbonate (NaHCO3) has the effect of increasing the CO2 too much. For a person in respiratory failure or other pulmonary disorders, they cannot expell all the CO2 through respirations.

Question 27

Why do we check ABGs in the OR?

Answer 27

Mainly for H & H changes and secondarily for electrolyte values.

-blood loss is an important indicator of impending acidosis. That’s why EBL is kept track of in OR cases.

Question 28

Treatments of Alkalosis:

Answer 28

• aldosterone antagonist spironolactone or with other potassium-sparing diuretics (eg, amiloride, triamterene)
• HypoKalemia will also augment H+ secretion. (correct K imbalances)

Question 29

ABG interpretation:

What is the normal pH range:

Answer 29

7.35-7.45

Panic Value:
less than 7.25 or greater than 7.55

Question 30

ABG interpretation:

What is the normal pCO2 range:

Answer 30

pCO2 35-45 mmHg

Panic Value: pCO2 >60

Question 31

ABG interpretation:

What is normal pO2?

Answer 31

pO2 >80 mmHg

Panic Value: pO2 <50 mmHg

Remember: pO2 is a measure of oxygenation, not ventilation.

Question 32

ABG interpretation:

Answer 32

22-26 mmol/L

Question 33

Pure respiratory Alkalosis:

Answer 33

pH = HIGH

pCO2 = LOW

HCO3= decreased or normal

Question 34

Pure respiratory Acidosis:

Answer 34

pH = LOW

pCO2 = HIGH

HCO3 = normal or high (compensation)

pO2 = normal or low

Question 35

Pure metabolic Alkalosis:

Answer 35

pH = High

pCO2 = Normal

HCO3 = normal to high

Question 36

Pure Metabolic Acidosis:

Answer 36

pH= LOW

pCO2= NORMAL

HCO3= decreased

Question 37

Metabolic Alkalosis with respiratory compensation:

Answer 37

pH = High

pCO2= High

Question 38

Metabolic Acidosis with respiratory compensation:

Answer 38

pH= low

pCO2= low