Lecture 46: Acid Base Pathophysiology

Question 1

what is the biggest source of acid in the body and how is it excreted

Answer 1

• carbonic acid from cell resp

- excreted by lungs

Question 2

what is another source of acid in body and how is it excreted

Answer 2

• non-carbonic in volatile acid from cell metabolism

- excreted by kidneys

Question 3

what is the pH buffer equation

Answer 3

CO2 + H20 H2CO3 H+ + HCO3-

Question 4

outline how asthma an cause acute respiratory alkalosis

Answer 4

• acute asthma
• irregular bronchoconstriction
• ventilation/perfusion mismatch –> hypoxia and hypocapnia
• acute resp alkalosis

Question 5

how is acute resp alkalosis as a result of asthma treated

Answer 5

use bronchodilators

Question 6

outline how asthma can cause acute respiratory acidosis

Answer 6

• asthma deterioration
• fatigue
• -> hypoventilation
• -> hypoxia and normocapnia
• -> hypercapnia
• acute resp acidosis

Question 7

hos is acute resp acidosis as a result of asthma treated

Answer 7

assisted ventilation

Question 8

outline how hyperventilation can cause acute resp alkalosis and chronic resp alkalosis

Answer 8

• anxiety –> ^ ventilation
• -> hypocapnia, ^ resp exchange ratio, tetany
• acute resp alkalosis
• chronic
• -> hypocapnia, normalisation of resp exchange ratio, renal compensation
• chronic resp alkalosis

Question 9

how would you treat/reverse acute resp alkalosis and chronic resp alkalosis as a result of hyperventilation

Answer 9

• reassure Px and explain
• treat cause 2nd to other disease
• treat underlying disease

Question 10

outline how COPD causes chronic resp acidosis

Answer 10

• normal ventilation –> impaired ventilation and ventilation perfusion mismatch
• hypoxia and hypercapnia
• chronic resp acidosis
• exacerbations –> further hypoventilation
• more hypercapnia
• acute on chronic resp acidosis

Question 11

list the causes of resp alkalosis

Answer 11

• hyperventilation
• -> acute
• -> chronic
• -> anxiety
• -> 2nd to other systemic disease
• hypoxia
• -> altitude
• -> ventilation perfusion mismatch
• -> asthma
• -> pulmonary vascular disease
• liver disease
• heart failure
• intake of resp stimulants
• -> aspirin

Question 12

list causes of resp acidosis

Answer 12

• hypoventilation
• -> acute:
  
  • resp centre
  • resp muscles
  • asthma
  • airway obstruction
• -> chronic:
  
  • COPD
  • restriction
• intake of resp depressants
• -> morphine, barbiturates

Question 13

list causes of metabolic alkalosis

Answer 13

• gastric secretion loss
• -> vomiting
• -> nasogastric suction
• hyperaldosteronism
• hypovolaemia
• post hypercapnia
• alkali ingestion
• -> antacids
• -> bicarbonate
• -> citrate e.g. blood transfusions
• diuretics
• -> inhibition of lumen negativity
• -> aldosterone response
• sweat loss in cystic fibrosis
• hypokalaemia –> movement of H+ into cells

Question 14

list the causes of metabolic acidosis

Answer 14

normal anion gap:

• renal tubular acidosis
• chronic renal disease occasionally
• diarrhoea
• ingestion
• -> ammonium chloride

increased anion gap

• chronic renal disease
• lactic acidosis
• ketoacidosis
• liver disease
• ingestion of acids
• -> aspirin
• -> methanol
• -> ethylene glycol

Question 15

how is chronic resp acidosis as a result of COPD treated

Answer 15

• bronchodilators
• inhaled steroids
• controlled O2 therapy
• assisted ventilation

Question 16

outline how COPD can cause metabolic alkalosis

Answer 16

• too high FIO2
• more hypercapnia
• assisted ventilation
• normocapnia
• post hypercapnic metabolic alkalosis

Question 17

outline how CKD can result in metabolic acidosis

Answer 17

• failure to excrete non-carbonic acids and failure to reabsorb bicarbonate
• high anion gap metabolic acidosis
• failure to excrete K
• hyperkalaemia
• H+ displaced from cells
• further metabolic acidosis

Question 18

how is metabolic acidosis as a result of CKD treated

Answer 18

• give bicarbonate
• treat cause of kidney disease
• alter diet
• fluid balance
• dialysis
• transplant

Question 19

outline how type 1 renal tubular acidosis can result in metabolic acidosis

Answer 19

• failure to secrete H+ (distal tubular)
• normal anion gap metabolic acidosis
• failure to secrete and excrete K+
• hyperkalaemia
• further metabolic acidosis

Question 20

how is metabolic acidosis as a result of type 1 renal tubular acidosis treated

Answer 20

give bicarbonate

Question 21

outline how type 2 renal tubular acidosis can result in metabolic acidosis

Answer 21

• failure to reabsorb bicarbonate (proximal tubular)

- normal anion gap metabolic acidosis

Question 22

how is metabolic acidosis as a result of type 2 renal acidosis

Answer 22

give bicarbonate (requires large doses)

Question 23

what can occur in a Px w/ type 1 and treated type 2 renal tubular acidosis

Answer 23

unusual combination of acidosis and hypokalaemia

Question 24

outline how diarrhoea can result in metabolic acidosis

Answer 24

• loss of fluids and bicarbonate
• normal anion gap metabolic acidosis
• loss of K+
• unusual combination of acidosis w/ hypokalaemia

Question 25

how can metabolic acidosis as a result of diarrhoea be treated

Answer 25

give fluids and electrolytes

Question 26

outline how vomiting can result in metabolic alkalosis

Answer 26

- loss of gastric acid - metabolic alkalosis - loss of K+ - hypokalaemia - further alkalosis - loss of fluids - hypovolaemia - hyperaldosteronism - further metabolic alkalosis - inability of kidneys to excrete bicarbonate - prolongation of alkalosis

Question 27

outline how hyperaldosteronism can result in metabolic alkalosis

Answer 27

- hyperaldosteronism - ^ H+ secretion - metabolic alkalosis - ^ K+ secretion - hypokalaemia

Question 28

how might metabolic alkalosis as a result of hyperaldosteronism be resolved

Answer 28

adrenalectomy

Question 29

outline how hypoaldosteronism can result in metabolic acidosis

Answer 29

- hypoaldosteronism - reduced H+ secretion - normal anion gap metabolic acidosis

Question 30

how might metabolic acidosis as a result of hypoaldosteronism be resolved

Answer 30

give aldosterone

Question 31

outline how diabetic ketoacidosis can result in metabolic acidosis

Answer 31

- low cell glucose - shift to fat metabolism - mitochondria overwhelmed - acetone, acetoacetate and B-hydroxybutarate - high anion gap metabolic acidosis - K+ from cells - loss in diuresis - hyperkalaemia

Question 32

how can metabolic acidosis as a result of diabetic ketoacidosis be treated

Answer 32

- insulin - fluids - bicarbonate - electrolytes

Question 33

outline how hepatocellular dysfunction can cause resp alkalosis and metabolic alkalosis

Answer 33

- abnormal levels of toxins and hormones stimulate resp centre - chronic resp alkalosis - hypoalbunimaemia - further metabolic alkalosis

Question 34

outline how hepatocellular dysfunction can result in metabolic acidosis

Answer 34

- abnormal amino acids and other acids | - metabolic acidosis

Question 35

how might metabolic acidosis as a result of hepatocellular dysfunction be resolved

Answer 35

- treat underlying cause e.g. alcohol abuse | - liver transplant

Question 36

outline how salicylate ingestion can result in metabolic acidosis

Answer 36

- non carbonic acid | - high anion gap metabolic acidosis

Question 37

outline how salicylate ingestion can result in resp alkalosis

Answer 37

- stimulation of ventilation - additional hyperventilation - resp alkalosis

Question 38

how might resp alkalosis as a result of salicylate ingestion be resolved

Answer 38

forced alkaline diuresis

Question 39

outline how IV saline pH 7.0 can result in metabolic acidosis

Answer 39

- dilution of bicarbonate - hyperchloraemia - metabolic acidosis

Question 40

how might metabolic acidosis as a result of IV saline pH 7.0 be resolved

Answer 40

citrate based infusions