Acid-Base Disorders Flashcards
1
Q
Major types of acid-base disorders
A
- Respiratory alkalosis (decrease in CO2 resulting in a increase in pH)
- Respiratory acidosis (increase in CO2 resulting in a decrease in pH)
- Metabolic alkalosis (increase in HCO3 resulting in an increase in pH)
- Metabolic acidosis (decrease in HCO3 resulting in decrease in pH)
2
Q
Respiratory alkalosis: Definition/differenital dx
A
- respiratory process caues primary decrease in PCO2
- DDx:
- always due to hyperventilation
- pulmonary disease
- hypoxemia
- mechanical ventilation
3
Q
Respiratory alkalosis: compensation
A
- decreased HCO3 due to:
- H+ release from cells (acute)
- renal H+ retention (chronic)
- takes 3-5 days to complete
- compensation rules:
- ##### Acute: ΔHCO3- = ↓ 2 meq/L for every 10 mmHg ↓ in PCO2 [↓(2:10)]
- ##### Chronic (3 to 5 days): ΔHCO3- = ↓4 meqL for every 10 mmHg ↓ in PCO2 [↓(4:10)]
4
Q
Respiratory alkalosis: Signs, Sx, Tx
A
- Lab abnormalities: decreased potassium (small); decreased phosphorus (may be large).
- Symptoms: neurologic (paresthesias, carpopedal spasms).
- Consequences: decreased intracranial pressure, cardiac arrhythmias.
- Tx: treat underlying cause; can depress ventilation w/sedative
5
Q
Respiratory acidosis: definition, DDx
A
- respiratory process causes a primary increase in the PCO2
- DDx:
- always due to inadequate respiration @ 4 steps of respiration: sensing/signaling, muscles, free flow, gas exchange
6
Q
Respiratory acidosis: compensation
A
- increased HCO3 due to:
- cell buffering (acute)
- H+ reabsorbed by intracellular buffers
- renal H+ excretion (chronic)
- 3-5 days
- cell buffering (acute)
- pH should not fall below 7.20 in appropriately compensated chronic respiratory acidosis
- compensation rules:
- Acute: ΔHCO3- = ↑ 1 meq/L for every 10 mmHg ↑ in PCO2 [↑ (1:10)]
- Chronic (3 to 5 days): ΔHCO3- = ↑4 meqL for every 10 mmHg ↑ in PCO2 [↑ (4:10)]
7
Q
Respiratory acidosis: Signs, Sx, Tx
A
- Symptoms: Neurologic: headache, decreased arousal/sleepiness (aka CO2 narcosis)
- Consequences: Increased intracranial pressure, cardiac arrhythmias, hypotension from peripheral vasodilatation
- **Treatment: **
- Treat underlying cause
- Pay attention to PO2
8
Q
Metabolic alkalosis: definition, DDx
A
- metabolic process causes primary increase in HCO3
- DDx:
- generation of bicarb increase
- addition of HCO3
- loss of H+
- loss of fluid w/chloride
- post-hypercapneia
- hypokalemia
- maintenance of met alk is always due to renal inability to excrete excess HCO3
- generation of bicarb increase
9
Q
Main mechanisms that generate metabolic alkalosis
A
- Added HCO3 via:
- direct admin of bicarb
- direct admin of substrate metabolized to bicarb
- Loss of H+ via:
- GI loss: vomiting
- Renal loss: loop, thiazide diuretics, mineralcorticoid excess
- Loss of chloride rich fluid
- loop diuretics
- cystic fibrosis
- post-hypercapnia
- metabolic alkalosis in patient w/chronic respiratory acidosis + mechanical ventilation
- hypokalemia
10
Q
Mechanisms of maintenance of metabolic alkalosis
A
- chloride depletion ==> increased resorption of bicarb (chloride vs. non-chloride responsive met alk)
- potassium depletion
- increased mineralocorticoid activity ==> stimulate H+ ATPase to secrete H+ into tubule ==> bicarb resorption
- hypovolemia ==> release of aldosterone ==> increased Na resorption + bicarb (to maintain electroneurtrality)
11
Q
Definition/causes of chloride responsive metabolic alkalosis
A
- [UCl] < 20 mEq/L => chloride depletion is major maintence factor
- major causes:
- diuretics
- vomiting, gastric drainage
- villous adenomas
- congenital chloride-losing diarrhea
- cystic fibrosis
- post-hypercapnia
12
Q
Definition/causes of chloride resistant metabolic alkalosis
A
- [UCl] > 20 mEq/L
- causes:
- excess mineralocorticoids
- hyperaldosteronism
- cushing’s syndrome
- licorice ingestion
- excess mineralocorticoids
13
Q
Metabolic alkalosis: compensation
A
- rise in pH ==> decrease in ventilation ==> rise in CO2
- compensation rules:
- ΔCO2 (in mmHg) = 0.25 – 1.0 XΔHCO3
14
Q
Metabolic alkalosis: treatment
A
- possible severe consequences:
- cardiac arrhythmias
- hypocalcemia => neuromuscular irrability => tetany
- hypoventilation via mechanical vent
- Chloride responsive = Infusions of NaCl or KCl
- Chloride resistant = block mineralocorticoid effect w/sprionolactone
15
Q
Metabolic acidosis: definition, DDx
A
- metabolic process causes primary decrease in HCO3
- DDx/major mechanisms:
- loss of bicarbonate = normal anion gap
- addition of acid = increased anion gap
- anion gap = [Na] - [Cl] - [HCO3]
- normal = 9 +/- 3