Acid-base blitz

Question 1

Carbonic acid buffering system

Answer 1

CO2+H2O <–> H2CO3 <–> H+ + HCO3-

[buffer 1] eliminates CO2 (150L/day)
[carbonic acid]
[H+ + bicarb]
Oxygen’s job is to consume H+, byproduct is water (H2O).

hydrogen and bicarb (HCO3-) regulate pH

(acid-base part 1)

Question 2

osis (ie acidosis)

Answer 2

‘osis’ = process

Question 3

emia (ie acidemia)

Answer 3

‘emia’ = state of being
pH less than 7.35 = acidemia
pH greater than 7.45 = alkalemia

Question 4

pH formula

Answer 4

pH = -log [H+]
as H+ increases, pH decreases and vice versa

Question 5

acid-base formula

Answer 5

CO2+H2O <–> H2CO3 <–> H+ + HCO3-
water +CO2. carbonic acid. H+ + bicarb

bicarb is the body’s buffer against H+

Question 6

Henderson Hasselbach equation

Answer 6

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

PCO2 = partial pressure of CO2 in blood
CO2 is acid. only way it’s excreted is through lungs. Everything related pt PCO2 is respiratory.
if PCO2 is going up: respiratory acidosis
if PCO2 is going dow: respiratory alkalosis (ie hyperventilation)

https://www.youtube.com/watch?v=D0haz5rtjnw

Question 7

carbonic acid

Answer 7

H2CO3
volatile acid - wants to dissipate
…into H+ + HCO3 (bicarb)
…or ito CO2 + H2O

Question 8

bicarb

Answer 8

HCO3- Normal 22-26

bicarb is a base (antacid), made in and regulated by kidneys. Kidneys take a few days to adjust bicarb production up or down…if HCO3- is off, pt has been sick for longer and is probably more unstable

anything that happens with bicarb is a ‘metabolic’ process.
Decreasing bicarb = metabolic acidosis.
Increasing bicarb = metabolic alkalosis.

Question 9

paCO2

Answer 9

partial pressure of CO2. Normal 34-45

PaCO2 = partial pressure of CO2 in blood
CO2 is acid.
produced everywhere in body and regulated in lungs
only way it’s excreted is through lungs. Everything related pt PCO2 is respiratory.
if PaCO2 is going up: respiratory acidosis
if PaCO2 is going down: respiratory alkalosis

for every 10 mmHg change I PaCO2, pH will change 0.08 mmHg in the opposite direction

Question 10

compensated vs uncompensated

Answer 10

if pH, PaO2, or HCO3 are within normal range, COMPENSATED
if out of normal range, UNCOMPENSATED

pH: low = acidotic, high = alkalotic
PaCO2: low = alkalotic, high = acidotic
HCO3: low = acidotic, high = alkalotic
PaO2:
BE (base excess): -2 / +2

tricky example (mixed disturbance)
pH: 7.09
PaCO2: 20
HCO3-: 10
= partially compensated metabolic acidosis

for every 10 mmHg change I PaCO2, pH will change 0.08 mmHg in the opposite direction
Pt is tachypneic, which is blowing off extra CO2 (acid), which is keeping pH higher. If this pt is intubated and we don’t match their respiratory rate, could be lethal because pH will tank.

Question 11

mixed disturbances

Answer 11

HCO3 and PaCO2 should move in opposite directions with normal compensation

HCO3 and PaCO2 moving in the same direction indicates mixed disturbance

Question 12

ABG Golden rules

Answer 12

for every 10 mmHg change I PaCO2, pH will change 0.08 mmHg in the opposite direction