Acid-base blitz Flashcards
Carbonic acid buffering system
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)
osis (ie acidosis)
‘osis’ = process
emia (ie acidemia)
‘emia’ = state of being
pH less than 7.35 = acidemia
pH greater than 7.45 = alkalemia
pH formula
pH = -log [H+]
as H+ increases, pH decreases and vice versa
acid-base formula
CO2+H2O <–> H2CO3 <–> H+ + HCO3-
water +CO2. carbonic acid. H+ + bicarb
bicarb is the body’s buffer against H+
Henderson Hasselbach equation
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
carbonic acid
H2CO3
volatile acid - wants to dissipate
…into H+ + HCO3 (bicarb)
…or ito CO2 + H2O
bicarb
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.
paCO2
partial pressure of CO2. Normal 35-45
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
compensated vs uncompensated
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.
mixed disturbances
HCO3 and PaCO2 should move in opposite directions with normal compensation
HCO3 and PaCO2 moving in the same direction (ie both acidotic or both alkalotic) indicates a mixed disturbance
ABG Golden rules
for every 10 mmHg change in PaCO2, pH will change 0.08 mmHg in the opposite direction
for every 10 mEq/L change in HCO3-, pH will change 0.15 in the same direction
For every 0.10 change in pH, K+ will change by 0.6 in the opposite direction
what do you treat first? Treat the underlying cause.
causes of respiratory acidosis
Anything that reduces respiratory drive
CO2 retention
COPD, Asthma
Pulmonary edema - less minute ventilation
low pH
elevated HCO3 (acute vs chronic)
high pCO2
causes of metabolic acidosis
GOLD MARK
G: glycols - ethylene and propylene glycol
…ie antifreeze, benzos, dilatin, etomidate
Oxyproline - acetaminophen overdose
L-lactate - excess production -metformin od
D-lactate - short bowel syndrome, Crohn’s
M-methaol - solvents, window washer or de-icer fluid
A-acetylsalicylic acid-aspirin OD. >150mg/kg
R-Renal failure- acute vs chronic. pre, intra, post-renal
K-ketoacidosis - DKA, alcoholics, starvation
Likely to cause partial compensation:
glycols, acetylsalicylic acid, ketoacidosis.
Is pt tachypneic??
low pH
low HCO3
low pCO2
Corrected anion gap calculation
[Na+ - (Cl- + HCO3-)] + K+
Normal anion gap = 12
GAP > 20 = metabolic acidosis
