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MBBS 3: Internal Medicine > Respiratory acidosis and alkalosis > Flashcards

Respiratory acidosis and alkalosis Flashcards

1
Q

What maintains acid-base balance in the body?

A
  1. lungs
  2. kidneys
  3. buffers
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2
Q

What disrupts acid-base balance in the body?

A
  1. vomiting
  2. diarrhea
  3. respiratory failure
  4. kidney failure
  5. infections and ingestions
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3
Q

What is the normal serum pH?

A

7.35 - 7.45

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4
Q

Blood pH is determined by?

A

the ratio of serum bicarbonate concentration
1. ([HCO3-]) – normal 22 to 26 and
2. partial pressure of CO2 (PaCO2) – normal 38 to 42mmHg

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5
Q

Principles of acid-base diroders?

A
  1. Metabolic acid-base disorders and secondary metabolic compensation alter [HCO3-]
  2. Respiratory acid-base disorders and secondary respiratory compensation alter (PaCO2)
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6
Q

Why is pH so important?

A
  1. Subtle changes in pH cause large shifts in acid-base pair
  2. Determines how drugs disperse and bind and how enzymes react
  3. Proteins function within narrow spectrum of pH
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7
Q

Acidemia and Alkalemia?

A
  1. Acidemia: serum pH < 7.36
  2. Alkalemia: serum pH > 7.44
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8
Q

Acidosis and Alkalosis?

A
  1. Acidosis: pathologic process that lowers [HCO3-] or raises PaCO2
  2. Alkalosis: pathologic process that raises [HCO3-] or lowers PaCO2
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9
Q

What are physiologic buffers?

A

Oppose significant changes in pH

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10
Q

Name the physiologic buffers?

A
  1. Bicarbonate/Carbonic acid system
    - Located primarily in RBCs
    - H+ + HCO3- <> H2CO3 <> H2O + CO2
  2. Intracellular protein buffers
  3. Phosphate buffers
    - Located within bone
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11
Q

What is pulmonary compensation?

A

Peripheral chemoreceptors in the carotid bodies and central chemoreceptors in the medulla change minute ventilation
- Decreased pH > increased minute ventilation > decreased PaCO2
Note; does not fully correct pH but returns it toward normal over many hours

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12
Q

What is the anion gap?

A
  • Estimates unmeasured anions in plasma
    e.g. albumin, sulfates, proteins, ketoacids
  • Used to define or characterize metabolic acidosis
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13
Q

What is the anion gap equation?

A

AG = Na+ - (Cl- + HCO3-)
Normal = 12 +/- 3 mEq/L
∆G will be used in mixed disorders

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14
Q

What is respiratory acidosis?

A
  • Decreased pH due to pulmonary CO2 retention
  • Excess H2CO3 production leads to acidemia
  • H+ + HCO3- <> H2CO3 <> H2O + CO2
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15
Q

Acute vs chronic respiratory acidosis?

A
  1. Acute respiratory acidosis has normal HCO3-
  2. Chronic respiratory acidosis has elevated HCO3- due to renal retention
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16
Q

Causes of respiratory acidosis?

A

anything that causes your minute ventilation to decrease - decrease in respiratory rate and or volume
1. impaired respiratory drive
- drugs, alcohol, medications e.g. opioids, amphetamines, CNS disease
2. airway obstruction
- asthma, COPD, sleep apnea, airway edema

17
Q

Causes of respiratory acidosis?

A
  1. Airway
    - Obstruction, aspiration
  2. Drug-induced CNS depression
    - Alcohol, narcotics, IV sedation
  3. CNS origin
    - Myasthenia gravis, CNS injury, Guillain-Barré
  4. Pulmonary disease
    - Pneumonia, edema, COPD/emphysema
  5. Thoracic cage
    - Pneumothorax, flail chest
18
Q

Would you expect the [HCO3-] to increase or decrease when PaCO2 increases?

19
Q

Acute respiratory acidosis compensation?

A

HCO3- production from intracellular proteins
- [HCO3-] increases 1mEq/L for every 10mm Hg rise in PaCO2

20
Q

Chronic respiratory acidosis compensation?

A
  • Renal retention of HCO3-
  • [HCO3-] increases 3.5mEq/L for every 10mm Hg rise in PaCO2
  • Takes 12 hours to many days for renal retention of HCO3-
  • Nearly normalizes pH
21
Q

Management of respiratory acidosis?

A

correct the minute ventilation
1. Establish airway
2. Re-expand the lung
3. Correct the CNS disease
4. Bronchodilators
5. Antibiotics

22
Q

Management of chronic respiratory acidosis?

A

cautious use of oxygen
- there is progressive decrease in sensitivity to CO2 by respiratory centers so you may lose the hypoxic respiratory drive and develop CO2 narcosis

23
Q

What is respiratory alkalosis?

A

Increased minute ventilation leads to decreased PaCO2 and alkalosis

24
Q

Acute vs chronic respiratory alkalosis?

A
  1. Acute respiratory alkalosis has normal HCO3-
  2. Chronic respiratory alkalosis has decreased HCO3- due to renal compensation
25
Q

What causes respiratory alkalosis?

A

anything that increases minute ventilation

26
Q

Causes of respiratory alkalosis?

A
  1. Hypoxia-mediated hyperventilation
    - High altitude, severe anemia, ventilation-perfusion mismatch
  2. CNS mediated
    - Psychogenic, CVA, increased ICP (tumor/trauma)
  3. Pharmacologic
    - Salicylates, caffeine, vasopressors, thyroxine
  4. Pulmonary
    - Pneumonia, PE, mechanical hyperventilation, atelectasis
  5. Hepatic
    - Encephalopathy
27
Q

Would you expect the [HCO3-] to increase or decrease when PaCO2 decreases?

28
Q

Acute respiratory alkalosis compensation?

A

Plasma [HCO3-] is lowered by 2mEq/L for every 10-mm Hg decrease in PaCO2

29
Q

Chronic respiratory alkalosis compensation?

A

Plasma [HCO3-] is lowered by 5mEq/L for every 10-mm Hg decrease in PaCO2

MBBS 3: Internal Medicine (72 decks)

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