eLFH - Biochemistry Flashcards
Classification of hyponatraemia
Hypovolaemia
Euvolaemia
Hypervolaemia
Causes of Hypovolaemic hyponatraemia
Diarrhoea
Vomiting
Burns
Diuretics
Causes of Euvolaemic hyponatraemia
SIADH
Hypothyroidism
Addison’s
Post-surgical
Causes of Hypervolaemic hyponatraemia
Renal failure
Cardiac failure
Liver failure
Non clinical differentiation between type of hyponatraemia
Hypovolaemia - Urinary Na+ < 20 mmol/L
Hypervolaemia - Urinary Na+ > 20 mmol/L
SIADH - urine osmolality > plasma osmolality
Classification of Hypernatraemia
Reduced water intake
Increased water loss
Sodium excess
Causes of hypernatraemia secondary to reduced water intake
Impaired thirst
Deficient intake
Causes of hypernatraemia secondary to increased water loss
Diabetes insipidus
Osmotic diuresis
Loss from skin / lungs
Causes of hypernatraemia secondary to sodium excess
Iatrogenic
Classification of hypokalaemia
Increased renal excretion
GI losses
Redistribution
Reduced intake
Causes of increased renal excretion hypokalaemia
Diuretics
Hyperaldosteronism
Mineralocorticoids
Renal disease
Causes of GI losses hypokalaemia
Vomiting
Diarrhoea
Ileostomies
Causes of redistribution hypokalaemia
Beta agonists
Alkalosis
Insulin
Causes of reduced intake hypokalaemia
Iatrogenic
Dietary deficiency
Classification of hyperkalamia
Reduced renal excretion
Release from cells
Increased K+ load
Spurious
Causes of reduced renal excretion hyperkalaemia
Renal failure
Drugs - ACEi, aldosterone antagonists, NSAIDs
Addison’s
Causes of release from cells hyperkalaemia
Acidosis
DKA
Rhabdomyolysis
Suxamethonium
Causes of increased K+ load hyperkalaemia
Potassium chloride
Blood transfusions
Causes of spurious hyperkalaemia
Blood sample from same arm as infusion fluid
Haemolysis of sample
Causes of isolated increase in Urea levels (normal creatinine)
High protein diets
Tissue catabolism - trauma, surgery, infection
GI haemorrhage
Chronic kidney disease staging
CKD 1: GFR >90 but evidence of kidney damage
CKD 2: GFR 60 - 90
CKD 3: GFR 30 - 60
CKD 4: GFR 15 - 30
CKD 5: GFR <15 - end stage renal failure
Investigations for renal failure
Urine dip
Urine electrolytes
Bloods - usuals + Ca2+, phosphate, uric acid, electrophoresis, autoantibodies, ANCA
Renal imaging
Renal biopsy
Causes if obstructive LFT picture
Gallstones
Drugs
Pancreatic tumour
PBC
PSC
Causes of hepatic LFT picture
Cirrhosis
Viral hepatitis
Drugs
NASH
Ischaemic liver injury
Causes of raised bilirubin
Haemolysis - bilirubin is breakdown product of haem metabolism
Defective bilirubin metabolism - Gilbert’s, Hepatobiliary disease
Causes of elevated Amino-transferases
Hepatocellular damage
ALT more specific to liver
AST also present in skeletal muscle and heart
Causes of elevated Alkaline phosphatase
Release from cells lining biliary ducts - cholestasis
Also present in bone and placenta
Hence rise in pregnancy, Paget’s and bony metastases
Causes of elevated gamma GT
Liver microsomal enzyme - induced by alcohol and enzyme inducing drugs
Rises with cholestasis too
Causes of low albumin
Reduced with impaired synthetic function
Chronic inflammatory disease
Sepsis
Nephrotic syndrome
How is toxic metabolite of paracetamol usually cleared
Normally inactivated by conjugation in liver
Categories of causes of respiratory failure
Respiratory centre depression
Airway obstruction
Neuromuscular causes
Chest wall abnormalities
Increased small airways resistance
Decreased lung compliance
Causes of respiratory centre depression
Sedative / narcotic drugs
CNS injury
CNS infection
Causes of airway obstruction
OSA
Ludwig’s angina
Tracheal stenosis
Causes of neuromuscular disease
GBS
Myasthenia gravis
Motor neurone disease
Post-polio
Causes of chest wall abnormalities
Burns
Flail segment
Kyphoscoliosis
Causes of increased small airways resistance
COPD
Severe asthma
Bronchiolitis
Causes of decreased lung compliance
ALI
Pneumonia
Pulmonary oedema
Classification of metabolic acidosis
High anion gap metabolic acidosis
Normal anion gap metabolic acidosis
Anion gap calculation
Anion gap = [Na+] + [K+] - [Cl-] - [HCO3-]
Normal range of anion gap
6 to 12 mmol/L
Causes of high anion gap metabolic acidosis
CAT MUD PILES
Carbon monoxide poisoning
Alcoholic / starvation ketoacidosis
Toluene
Methanol / Metformin
Uraemia
DKA
Paracetamol
Isoniazid
Lactic acidosis
Ethylene glycol
Salicylates
Types of lactic acidosis
Type A - tissue hypoxia
Type B - metabolic abnormalities
Causes of type A lactic acidosis
Shock
Hypoxia
CO poisoning
Causes of type B lactic acidosis
Sepsis
Liver failure
Paracetamol poisoning
Metformin
Causes of normal anion gap metabolic acidosis
GI bicarb loss
Renal bicarb loss
Reduced renal H+ excretion
Increased HCl production
Causes of GI bicarbonate loss
Diarrhoea
Ileostomy
Causes of renal bicarbonate loss
Acetazolamide
Type 2 renal tubular acidosis
Hyperparathyroidism
Causes of reduced renal H+ excretion
Type 1 and Type 4 renal tubular acidosis
Causes of increased HCl production
Ammonium chloride ingestion
Causes of respiratory alkalosis
Hyperventilation
In acute setting either a response to hypoxaemia or to compensate for metabolic acidosis
Causes of chronic respiratory alkalosis
Pregnancy
High altitude
Neurotrauma
Categories of metabolic alkalosis
Renal H+ loss / HCO3- gain
GI H+ loss
Exogenous HCO3-
Causes of renal H+ loss / bicarbonate gain
Response to rise in PaCO2
Loop / Thiazide diuretics
Cushing’s syndrome
Hyperaldosteronism
Causes of GI H+ loss
Vomiting
Pyloric stenosis
Villous adenoma
Causes of exogenous bicarbonate
Sodium bicarbonate administration
Sodium citrate
Normal CarboxyHb levels in rural areas
< 1%
Normal COHb levels in urban areas
< 5%
Normal COHb levels in smokers
< 10%
How much higher is Hb affinity for CO compared to O2
CO binds to Hb with 210x the affinity that O2 does
Clinical features of carbon monoxide poisoning
Headache
Confusion
Coma
Seizures
Pulmonary oedema
Arrhythmias
