Approach To Acid-Base Disorders DSA Flashcards
Arterial pH: ________
Intracellular pH: _________
- Arterial pH: 7.35 - 7.45
- Intracellular pH: 7.0 - 7.3
Despite constant production of acidic metabolites, our pH is maintained by intracellular and extracullar buffering systems.
What is the most important extracellular buffering system?
Bicarbonate buffer system (HCO3- and CO2)
What is the acid-base equillibrium equation?
CA (present in lung alveoli and renal tubular epithelial cells)
What is the Henderson Hassalbalch Equation?
- ↑ HCO3-; ↑ pH
- ↑ pCO2 (H+); ↓ pH
What are the definitions of:
- Acidosis/alkalosis
- Acidemia/alkalemia
- Acidosis/alkalosis= disorder altering H+ levels
- Acidemia/alkalemia= prescence of high or low pH in blood
Arterial Blood Gas Levels (ABG)
Normal levels:
- pH
- HCO3
- PCO2
- Anion gap
- Osmolality Gap
-
pH: 7.35-744
- Acidosis= pH <7.35
- Alkalosis= pH >7.44
-
HCO3
- 24 mEq/L
-
pCO2
- 40 mmHg
-
Anion gap
- 12
-
Osmolality Gap
- 10 mmol/L
________ regulates pH by altering CO2.
How?
Lungs regulate pH by altering CO2.
- ↑ RR (hyperventilation) = ↑ CO2 blown off = ↑ pH; more basic
- ↓ RR (hypoventilation) = ↓ CO2 blown off = ↓ pH; more acidic
________ regulates pH by altering HCO3-.
How?
Kidneys regulates pH by altering HCO3-.
- To maintain HCO3- as a buffer in the plasma, the kidneys need to do 2 things:
-
Reabsorb all filtered HCO3- and generate new HCO3-.
* If not reabsorbed, makes a alkaline urine.
-
Reabsorb all filtered HCO3- and generate new HCO3-.
-
Excrete H+ protons
* If excreted, excretes an acidic urine.
-
Excrete H+ protons
•Metabolic Acidosis
- Low serum ____
•Metabolic Alkalosis
- High serum ____
•Respiratory Acidosis
- High _____
•Respiratory Alkalosis
- Low ____
•Metabolic Acidosis
- Low serum HCO3-
•Metabolic Alkalosis
- High serum HCO3-
•Respiratory Acidosis
- High pCO2
•Respiratory Alkalosis
- Low pCO2
Types of Metabolic Acidosis
- High anion gap metabolic acidosis (HAGMA)
-
Normal anion gap metabolic acidosis (NAGMA)
- AKA hyperchloremic acidosis
Types of Metabolic Alkalosis
-
Saline-Responsive (hypovolemia)
- AKA contraction alkalosis (or Cl- deficiency alkalosis)
- Saline-Non-responsive (euvolemia)
Types of Respiratory Acidosis and Respiratory Alkalosis
Acute and Chronic
COMPENSATION:
- If the kidney caused acidosis/alkalosis, the _____ compensates
- If the lung caused acidosis/alkalosis, the ______ compensates.
- If the kidney caused acidosis/alkalosis, the lung compensates
- If the lung caused acidosis/alkalosis, the kidney compensates.
How do we compensate for metabolic acidosis?
Induce respiratory alkalosis
- Hyperventilate (↑ RR) = blow out more CO2 = ↓ pCO2 = respiratory alkalosis ( ↑ pH)
How do we compensate for metabolic alkalosis?
Induce respiratory acidosis
Hypoventilate (↓ RR) = retain CO2 = ↑ pCO2 = respiratory acidosis
How do you compensate for respiratory acidosis (↑ pCO2)?
Induce metabolic alkalosis
- Kidney will reclaim and regenerate HCO3- = ↑ HCO3- = ↑ in pH
How do you compensate for respiratory alkalosis (↓ pCO2)?
Induce metabolic acidosis
- Kidney will ↓ reclaim and regeneration of HCO3- = ↓ HCO3- = ↑ in pH
Symptoms in patients with acidosis:
- Hyperventilation (trying to blow out CO2)
- Depression of myocardial contractility
- Cerebral vasodilation (increase cerebral blood flow => increase in ICP)
- If high CO2 levels => CNS depression
- Hyperkalemia (high H+ exchanges with K+)
- Shift in oxyHB dissociation curve (Bohr) effect to the R => decreased pH leads to HB releasing more O2 and it is less saturated
Symptoms in patients with alkalosis:
- Hypoventiliation
- Depression of myocardial contractility
- Cerebral vasoconstriction (Decrease in cerebral blood flow),
- Hypokalemia
- Shift in oxyHb dissociation curve to the left
How do we approach acid-base problems?
- Check pH (<7.35 => acidosis; >7.45= alkalosis) to determine if alkalosis or acidosis
- Check HCO3- and pCO2 to determine if metabolic or respiratory
- Determine acid-base disorder
- Acidosis + low HCO3- = metabolic acidosis
- Acidosis + high pCO2 = respiratory acidosis
- Alkalosis + high HCO3- = metabolic alkalosis
- Alkalosis + low pCO2 = respiratory alkalosis
4.For metabolic acidosis only: calculate anion gap
- If hypoalbunemia, calculate the the corrected anion gap.
- If HAGMA is present:
- calculate the osmolar gap to screen for possible alchol ingestion
- calculate the delta-delta gap to screen for additional NAGMA or metabolic alkalosis.
- Calculate compensation for primary acid-base disorder
- Compensated => only a simple acid-base disorder is present
- Not compensated =>
- Combined respiratory/metabolic
- 2 metabolic disorders
In most acid base disorders, _____ HCO3 and pCO2 are abnormal.
BOTH. One if is the culprit and other is compensatoery change. You have to figure out which is the problem
What 2 pathologic states can both acidotic and akalotic states occur?
- Vomitting (acidotic)
- Diarrhea (alkalotic)
How do we determine if there are 2 disorders present?
Determine the expected response by using renal formulas
- Expected HCO3- for respiratory disorders
- Expected CO2- for metabolic disorders
- If actual does not equal expected => a 2nd disorder is present.
KEY: What is a classic scenario for mixed disorders?
- On its own, a body cannot compensate back to a NL pH.
- Thus, if a patient has a [NL pH with abnormal HCO3- and CO2-], it is a mixed disorder.
How do we determine is the lungs properly compensates for metabolic acidosis?
- Winter’s formula
Tells you the expected CO2 when metabolic acidosis is compensated with respiratory alkalosis
* Actual is not equal to expected = mixed disorder is present
Is this compensated?
Yes.
Perform Winter’s formula:
Expected pCO2= 22 +/- 2
Compensated?
NO. Right away, we know that there are 2 disorders present because pCO2 is NL. In a metabolic acidosis, pCO2 should be compensating.
Use Winters formula.
Expected pCO2 = 26 +/- 2
pCO2 > expected; concomitant respiratory acidosis
How do we determine is the lungs properly compensates for metabolic alkalosis?
How can we determine if the kidney compensate for respiratory acidosis?
-
Acute
-
∆[HCO3-]= ∆pCO2/10
- HCO3- will ↑ by [1 mEq/L] for every [10 mmHg] ↑ in PCO2 from NL (40)
-
∆[HCO3-]= ∆pCO2/10
-
Chronic
-
∆[HCO3-]= 3.5 * ∆pCO2/10
- HCO3- will ↑ by [3.5 mEq/L] for every [10 mmHg] ↑ in PCO2 from NL (40)
-
∆[HCO3-]= 3.5 * ∆pCO2/10
How do we determine if the kidney compensates for respiratory alkalosis?
Acute
- ∆[HCO3-]= 2* ∆pCO2/10
- HCO3- will ↓ by [2 mEq/L] for every [10 mmHg] ↓ in PCO2 from NL (40)
Chronic
- ∆[HCO3-]= 5 * ∆pCO2/10
- HCO3- will ↓ by [5 mEq/L] for every [10 mmHg] ↓ in PCO2 from NL (40)