Quantitative Approach Acid Base. Hopper et al. 2008. JVECC

Question 1

Explain the difference between conventional and quantitative acid base analysis.

Answer 1

Conventional analysis assesses whether there is a respiratory/metabolic acidosis/alkalosis but does not assess what the underlying cause for the metabolic disturbance is.

Question 2

How long does respiratory compensation take to start and to reach its max effect?

Answer 2

respiratory compensation starts immediately but needs several hours to reach maximum effect

Question 3

How long does metabolic compensation take to start and when does it reach its max effect?

Answer 3

takes hours to start and is complete within days (2-5 days)

Question 4

How do you identify whether a secondary change is compensatory or presents a mixed acid base disorder?

Answer 4

calculate expected compensation, if outside of this range expect mixed acid base disorder

Question 5

What is the expected change in pCO2 for a given change in HCO3-

Answer 5

BE x 0.7 = expected change up/down in pCO2

Question 6

What is the expected metabolic compensation to an acute respiratory acidosis?

Answer 6

increasing HCO3 of 0.15 mEq/L per 1 mm Hg increase of PaCO2

Question 7

What is the expected metabolic compensation to a chronic respiratory acidosis?

Answer 7

increase of HCO3 of 0.35 mEq/L per 1 mm Hg increase in PaCO2

Question 8

What is the expected metabolic compensation to an acute respiratory alkalosis?

Answer 8

decrease in HCO3 of 0.25 mEq/L per 1 mm Hg decrease in PaCO2

Question 9

What is the expected metabolic compensation to a chronic respiratory alkalosis?

Answer 9

decrease in HCO3- of 0.55 mEq/L per 1 mm Hg decrease in PaCO2

Question 10

Why could the HCO3- be unreliable to assess metabolic status?

Answer 10

HCO3- will change with
* pCO2 values
* temperature
* Hemoglobin

Question 11

Describe Standard Base Excess (SBE)

Answer 11

reflects the titratable strong acid or base needed to restore plasma pH of 1L EC fluid to pH of 7.4
* at PCO2 of 40 mm Hg
* at temperature of 37C
* with fully oxygenated hemoglobin

Question 12

How does SBE of cats compare to dogs

Answer 12

slightly more negative in cats

Question 13

What is the Anion Gap equation?

Answer 13

AG = (Na + K) - (HCO3- + CL)

Question 14

Why does the accumulation of acids - other than Cl - cause a high anion gap?

Answer 14

accumulation of acids will decrease HCO3- in tha AG equation –> will be more positive/higher

Question 15

Why does hyperchloremic metabolic acidosis not cause a high AG?

Answer 15

HCO3- will decrease however, Cl increases –> AG does not become higher

Question 16

What is the major unmeasured anion in health?

Answer 16

albumin

hypoalbuminemia could obscure an otherwise elevated AG

Question 17

According to the Stewart Approach, what are the 3 independent determinants of acid-base balance?

Answer 17

• pCO2
• difference between strong cations and anions
• total weak acids (Atot)

Question 18

What is the simplified equation for SID?

Answer 18

SID = Na+ - Cl- = OH - H+

Question 19

What does apropte ion mean and what are 2 examples?

Answer 19

Na and Cl are aprote ions, which means they can neither donate or accept H+, and therefore per se do not cause a direct change in pH

Question 20

What are the 5 parameters evaluated in the Fencl-Stewart approach of acid base abnormalities?

Answer 20

1) free water effect
2) changes in Cl concentration
3) albumin effect
4) lactate effect
5) phosphate effect

UA=(1+2+3+4+5)

Question 21

How do you calculate the free water effect on acid base status (in dogs and cats)

Answer 21

Dogs = 0.25 (NaPatient - NaNormal)
Cat = 0.22 (NaPatient - NaNormal

Question 22

How do you calculate the corrected Chloride and chloride effect on the acid base status

Answer 22

corrected Cl = ClPatient x (normal Na/Patient Na
chloride effect = normal Cl - corrected Cl

Question 23

How do you calculate the phosphate effect on the acid base status?

Answer 23

mg/dL P
phosphate effect = 0.58 (normal P - measured P)

Question 24

How do you calculate the albumin effect on the acid base status?

Answer 24

g/dL
albumin effect = 3.7 (3.1 - measured albumin)

Question 25

How do you calculate the lactate effect on the acid base status?

Answer 25

lactate effect = - 1 x lactate

Question 26

How do you calculate the unmeasured anion effect?

Answer 26

UA = standardized base excess - sum of effects in frencl stewart approach

Question 27

How does hyponatremia or hypernatremia affect the acid base status? How are those conditions called?

Answer 27

excess of free water (hyponatremia) –> dilutional acidosis
deficit of free water (hypernatremia) –> contraction alkalosis

Question 28

Explain how hypochloremia or hyperchloremia can indicate alkalosis or acidosis

Answer 28

Cl and HCO3- are reciprocally linked in many processes within the body, e.g., gastric acid secretion, intestinal bicarbonate secretion, renal acid-base handling, transcellular ion exchange
–> when Cl ion is excreted, a bicarbonate ion is retained and vice versa
can use Cl as an estimate –> increased Cl associated with decrease in bicarbonate and vise versa

Question 29

Explain how lactic acidosis leads to acidosis

Answer 29

lactate is produced during anaerobic metabolism –> pyruvate not incorporated in the Kreb’s cycle –> pyruvate converted to lactate instead to regenerate NAD –> allowing for ongoing glycolysis
happens concurrent with equimolar production of H+ as consequence of hydrolysis of ATP (for every mole lactate produced, 1 mole of H+ is produced)

Question 30

Name examples of causes for hyperlactatemia that are not or little associated with acidosis

Answer 30

• cytokine mediated increases in glucose metabolism
• hyperventilation
• beta-adrenergic receptor agonists
• contaminaton of blood sample with lactated Ringer’s solution