Acid Base

Question 1

Normal anion gap?

Answer 1

14-18 mmol/ L

Question 2

Name the 4 buffering systems of H ions

Answer 2

Principal buffer system in all cells
H + hco3 = h2c03 = h20+c02

Urinary buffers
• hpo4+h = h2p04
• NH3 + h = nh4+

Red blood cell
Hb + h = hhb

Question 3

Name 3 compensatory mechanisms for ph deviations

Answer 3

• Buffering: immediate
• respiratory regulation of paCo2: intermediate 12-24 hours
• renal regulation of h and hc03: slow several days

Question 4

How calculate expected paCo2 compensation in metabolic alkalosis

Answer 4

0,7 x hco3 +20
+/-5

Question 5

How calculate expected hco3 compensation in respiratory acidosis?

Answer 5

Acute: 1 for 10 rule (limit 30 mmol/L) . hco3 increases by 1 mmol/L for every 10 mMHg paco2 increase above 40 mMHg

Chronic: 4 for 10 rule (limit 45)

Take 24 as normal HCO3

Question 6

How calculate expected hco3 compensation in respiratory alkalosis?
Nb

Answer 6

Acute: 2 for 10 rule (limit 18 mmol/l ). Hco3 increases by 2 mmol/l for every 10 mmhg paCo2 decrease below 40 mmhg

Chronic: 5 for 10 rule (limit 12 )

Take 24 as normal HCO3

Question 7

Name 4 causes of metabolic acidosis with high anion gap >18

Answer 7

• Ketoacidosis: DKA (will also have hyperglycaemia and ketones), alcoholic
• lactic acidosis (impained cellular respiration with anaerobic glycolysis), shock, septicaemia, profound hypoxaemia
• ingestion: salicylates, methanol (will also have elevated osmolar gap)
• renal failure

Question 8

How calculate anion gap

Answer 8

(K+na) - (hco3+ cl )

Question 9

Name 4 causes of metabolic acidosis with normal anion gap 14- 18

Answer 9

• Failure to reabsorb bicarbonate by kidney (renal tubular acidosis 2)
• failure to secrete hydrogen ions by kidney (rta1)
. Failure to regenerate bicarbonate
• external loss of bicarbonate eg diarrhoea, ileostomy

Question 10

Name 3 causes metabolic alkalosis

Answer 10

• Volume depletion
-Vomiting, gastric aspiration
-Pyloric stenosis
• chronic alkali intake
• potassium depletion
-Inadequate intake
- mineralocorticoid excess: Conn syndrome, Cushing’s

Question 11

Name 4 causes respiratory acidosis

Answer 11

• Airway obstruction: COPD, bronchospasm eg asthma, aspiration
. Depression of respiratory centre: anaesthetics, cerebral trauma
• neuromuscular disease: guillan barre, MND
• pulmonary disease: pulmonary fibrosis, severe pneumonia

Question 12

Name 3 causes respiratory alkalosis

Answer 12

• Increased respiratory drive: high altitude, severe anaemia, pulmonary disease eg pulmonary embolism/oedema, respiratory stimulants eg salicylates (. early on. Later = metabolic acidosis)
• voluntary hyperventilation: anxiety
• mechanical over ventilation

Question 13

Describe the relationship between pH and paCo2 in respiratory and metabolic acid base disorders

Answer 13

Rome
Respiratory opposite
Metabolic equal

Question 14

In acid base disorders, what does hyperchloraemia usually give a clue to?

Answer 14

Normal anion gap metabolic acidosis

Question 15

In acid base disorders, what does elevated urea and creatinine usually give a clue to?

Answer 15

Uraemic acidosis or hypovolaemia (prerenal kidney fail)