List the causes of high anion gap metabolic acidosis
- Ketoacids
- diabetic
- alcoholic
- starvation
- Lactic
- Type A (impaired perfusion)
- Type B (impaired carbohydrate metabolism)
- Renal failure
- uraemic
- acute
- Toxins
- ethylene glycol
- methanol
- salicylates
List the causes of normal anion gap metabolic acidosis
- Renal
- tubular acidosis (incl. type 4, AKA Addison’s)
- carbonic anhydrase inhibition
- GIT
- diarrhoea
- uretero-enterostomy or obstructed ileal conduit
- drainage of pancreato-biliary fluid
- small bowel fistula
- Iatrogenic
- resolving DKA
- excess Cl- ion administration
What are the causes of Type A hyperlactaemia
- anaerobic muscular activity
- sprinting
- generalised convulsions
- tissue hypoperfusion
- shock
- cardiac arrest
- regional hypoperfusion
- reduced tissue oxygen delivery
- hypoxaemia
- anaemia)
- reduced oxygen utilisation (CO poisoning)
Respiratory effects of metabolic acidosis
Respiratory
- hyperventillation (of Kussmaul)
- right shift of oxyhaemoglobin dissociation curve (hyperacute)
- decreased 2,3 DPG levels in erythrocytes (compensates for above within six hours)
State Winter’s formula. What is it for?
Expected pCO2 = 1.5 x [HCO3] + 8 mmHg
For determining expected maximal respiratory compensation for metabolic acidosis.
How is anion gap calculated? What is a normal anion gap?
Anion gap = Na+ - Cl- - HCO3
Normal 4 to 12
Can include K+
What are the two major unmeasured ions which contribute to the anion gap? What are they otherwise referred to as?
Albumin and phosphate. Weak acids.
How can changes in albumin be accounted for when calculating the anion gap?
Every 1 g/L decrease in albumin will decrease the anion gap by 0.25 mmol
What is the consequence of hypoalbuminaemia in a patient with a metabolic acidosis?
An acidosis which would normally present with a high anion gap may appear as a normal anion gap acidosis.
What are the three independent variables determining pH?
- pCO2
- Strong ion difference (SID)
- Weak acids (ATot)
Causes of Type B lactaemia
B1: associated with underlying diseases
- leukaemia, lymphoma
- TIPS: thiamine deficiency, infection, pancreatitis, short bowel syndrome
- hepatic, renal, diabetic failures
B2: associated with drugs & toxins
- anti-retroviral drugs
- biguanides
- beta-agonists
- cyanide
- ethanol intoxication in chronic alcoholics
- methanol
- nitroprusside infusion
- paracetamol
- salicylates
B3: associated with inborn errors of metabolism
- congenital forms of lactic acidosis with various enzyme defects (e.g. pyruvate carboxylase deficiency, glucose-6-phosphatase and fructose-1,6-bisphosphatase deficiencies, oxidative phosphorylation enzyme defects)
Causes of lactaemia in sepsis
- Circulatory failure due to hypoxia and hypotension (Type A)
- Cytopathic hypoxia – widespread microvascular shunting and mitochondrial failure (Type A)
- Coexistent liver disease (reduced lactate clearance; Type B1)
- Endogenous catecholamine release and use of adrenaline as an inotrope (Type B2)
- Inhibition of pyruvate dehydrogenase (PDH) by endotoxin
Cardiovascular effects of metabolic acidosis
- Negative inotropy
- Sympathetic overactivity (above pH 7.2, compensates for above)
- Catecholamine resistance
- Peripheral arteriolar vasodilatation
- Peripheral venoconstriction
- Pulmonary vasoconstriction
- Effects of hyperkalaemia on heart
