acid-base disorders and compensation

Question 1

respiratory acidosis pH and pCO2 thresholds

Answer 1

pH < 7.35
pCO2 > 45 mmHg

Question 2

respiratory alkalosis of pH and PCO2 thresholds

Answer 2

pH > 7.45
pCO2 < 35 mmHg

Question 3

metabolic acidosis pH and HCO3- thresholds

Answer 3

pH < 7.35
HCO3- < 22 mmol/L

Question 4

metabolic alkalosis pH and HCO3- thresholds

Answer 4

pH > 7.45
HCO3- > 26 mmol/L

Question 5

causes of acute respiratory acidosis

Answer 5

1. drugs that depress CNS (opioids, sedatives)
2. brain trauma
3. chest wall injuries
4. pneumothorax
5. muscle nerve injury (Guillain-Barre syndrome)
6. upper airway obstruction (asthma)
7. cervical cord injury

Question 6

causes of chronic respiratory acidosis

Answer 6

1. restrictive lung disease with V/Q mismatch
2. obstructive lung disease (COPD)
3. neuromuscular disease

Question 7

causes of respiratory alkalosis

Answer 7

1. excessive alveolar ventilation
2. head injury
3. toxins overdose
4. pneumonia, asthma

Question 8

causes of high anion gap metabolic acidosis

Answer 8

LTKR
1. lactate
2. toxins
3. ketones
4. renal failure

Question 9

causes of non-anion gap metabolic acidosis

Answer 9

1. Diarrhoea
2. Acetazolamide (carbonic anhydrase)
3. Renal tubular acidosis
4. Normal saline infusion
5. ingestion of chloride-containing acids
6. failure to eliminate HCl from kidneys

Question 10

causes of metabolic alkalosis

Answer 10

1. hyperkalaemia
2. vomiting
3. impairment of renal excretion of HCO3-
4. diuretics

Question 11

what pH imbalance is expected in vomiting?

Answer 11

metabolic alkalosis

Question 12

what pH imbalance is expected in renal failure?

Answer 12

metabolic acidosis

Question 13

what pH imbalance is expected in student having a panic attack and hyperventilating?

Answer 13

acute respiratory alkalosis

Question 14

what pH imbalance is expected in nerve disease leading to partial paralysis of respiratory muscles?

Answer 14

chronic respiratory acidosis

Question 15

what pH imbalance is expected in anaemia?

Answer 15

chronic respiratory alkalosis

Question 16

what pH imbalance is expected in a patient who has fallen and broken their ribs?

Answer 16

acute respiratory acidosis

Question 17

boston rule 1 for acute respiratory acidosis

Answer 17

1 to 10 rule
Expected [HCO3-] = 24 + 1 [ (Actual pCO2 - 40) / 10 ]

Question 18

boston rule 2 for chronic respiratory acidosis

Answer 18

4 to 10 rule
Expected [HCO3-] = 24 + 4 [ (Actual pCO2) - 40 / 10 ]

Question 19

boston rule 3 for acute respiratory alkalosis

Answer 19

2 to 10 rule
Expected [HCO3-] = 24 + 2 [ 40 - (Actual pCO2) / 10 ]

Question 20

boston rule 4 for chronic respiratory alkalosis

Answer 20

5 to 10 rule
Expected [HCO3-] = 24 + 5 [ 40 - (Actual pCO2) / 10 ]

Question 21

boston rule 5 for metabolic acidosis

Answer 21

Expected pCO2 = 1.5 x [HCO3-] + 8

Question 22

A patient’s blood pH decreases from 7.40 to 7.10. What has happened to [H+] in the blood?

Answer 22

doubled

Remember that doubling [H+] decreases pH by 0.3 and halving [H+] increases pH by 0.3!
log2 = 0.3