ChemPath - Acid-Base Flashcards
What are the normal values for pH, CO2, bicarbonate, and O2
pH: 7.35-7.45
CO2: 4.7-6kPa
Bicarbonate: 22-30mmol/l
O2: 10-13kPa
What is the formula for pH
log 1/[H+]
What are the causes of metabolic acidosis with a large anion gap
Ketones
Lactate (shock, ischaemia, sepsis)
EtOH
Aspirin
Biguanides (metformin)
ethylene glycol (anti-freeze)
Uraemia
What are the causes of metabolic acidosis with a normal anion gap
Diarrhoea (small bowel GI loss of HCO3)
Acetazolamide (CA inhibitor)
High output stoma
Pancreatic fistula (loss of bicarb)
Addison’s
Renal tubular acidosis
Ammonium chloride ingestion
What is the compensatory response to metabolic acidosis
Hyperventilation → low CO2 - immediate
What are the causes of metabolic alkalosis
Vomiting (H+ loss)(bulimia)
Loop diuretics (K+ depletion)
Hypokalaemia
Conn’s (hyperaldosteronism, K+ loss)
Antacid use
Burns
What is the compensatory response to metabolic alkalosis
Hypoventilation (raised CO2) - immediate
What are the causes of respiratory acidosis
Hypoventilation (T2 resp failure):
- Acute/chronic lung disease (commonest = COPD)
Opioids
Sedatives
Neuromuscular weakness
Normal/high PaCO2 worrying - ITU RV/vent support
(exhaustion
What is the compensatory response to respiratory acidosis
Increased renal bicarbonate reabsorption (raised HCO3-) - delayed
What are the causes of respiratory alkalosis
Hyperventilation:
- Stroke, SAH, meningitis
- Asthma
- Anxiety
- PE
- Pregnancy
- Altitude (hypoxaemia)
- Salicylates
(early – brainstem stimulation)
What is the compensatory response to respiratory alkalosis
Reduced renal bicarbonate reabsorption (Low HCO3-) - delayed
What is the osmolar gap
Osmolality (measured) – Osmolarity (calculated)
Normal = <10
provides indirect evidence for the presence of an abnormal solute
Increased by extra solutes in the plasma (e.g. alcohols, mannitol, ketones,
lactate)
Raised in advanced CKD (retained small solutes)
