acid base balance (biochem)

Question 1

change in:

1. plasma volume
2. interstitial fluid volume

during pregnancy

Answer 1

1. 3 to 4.5L
2. 11 to 15L

Question 2

what is a buffer?

Answer 2

system that minimises change in pH value in a solution

Question 3

what are the 2 main buffers in the body?

Answer 3

bicarbonate & haemoglobin

Question 4

3 ways in which CO2 is carried through body:

Answer 4

1. in simple solution
2. carbamino compounds with plasma proteins
3. in red blood cells

Question 5

with CO2 in RBCs 1 of the following 3 things happens:

Answer 5

CO2:

1. stays in simple solution
2. forms carbinaminohaemoglobin
3. H2CO3 is formed through reaction catalysed by carbonic anhydrase

Question 6

acid base disturbance in pregnancy

Answer 6

slight respiratory alkalosis

Question 7

if there is base excess what must there be?

what’s the disturbance if:
i) -ve base excess
ii) +ve base excess

Answer 7

metabolic change

i) metabolic acidosis
ii) metabolic alkalosis

Question 8

causes of metabolic acidosis:

Answer 8

increased endogenous acid production:
- ketoacidosis
- lactic acidosis

increased exogenous acids:
- methanol
- ethylane glycol
- aspirin

inability to excrete acid:
- chronic renal F

Question 9

causes of respiratory acidosis:

Answer 9

central depression of respiratory drive:
- drugs inc benzodiazepines
- CNS lesions
- O2 in pts with chronic hypercapnia

neuromuscular disorders causing respiratory muscle weakness
e.g. motor neurone disease, muscular dystrophy, Guillan Barre

chest wall/ thoracic cage abnormality
e.g. obesity hypoventilation syndrome, kyphoscoliosis , flail chest

disorders affecting gas exchange
- COPD
- pneumonia
- severe asthma
- acute pulmonary oedema

airway obstruction
- obstructive sleep apnoea

Question 10

causes of metabolic alkalosis:

Answer 10

hydrogen ion loss
i) GI
- vomiting
- NG suction
ii) renal
- primary mineralocorticiois excess e.g. secondary to Cushing’s or Conns
- loop or thiazide diuretics
- posthyperkalaemia

intracellular shift of hydrogen
- hypokalaemia

contraction alkalosis
- diuretics

Question 11

causes of respiratory alkalosis:

Answer 11

CNS stimulation e.g. pain, anxiety, hyperventilation

hypoxaemia or tissue hypoxaemia
- severe altitude
- anaemia

pulmonary disease
- asthma
- PE
- pneumonia
- ILD

drugs (respiratory stimulants)
- salicylates
- aminophylline
- progesterone