Biochemistry

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Author:
timbowles
ID:
167246
Filename:
Biochemistry
Updated:
2012-08-24 07:40:39
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CICM biochemistry data
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Description:
Important data interpretation biochem
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  1. What is the Anion gap?
    Na+ - (HCO3+Cl) normal 6-15 mmol/L

    • Raised vs. normal
    • Reduced: Hypermag, Hypercalc, Lithium, IgG, Hypoalb
  2. How is the anion gap corrected for albumin?
    AGc= AG + 0.25x(44-albumin)
  3. Osmolar gap
    Measured osmolality - calculated

    Calc osm = 2(na+K)+ urea+glucose

    • Increased in:
    • -alcohols
    • -mannitol
    • -glycine(TURP)
    • -radicontrast media
    • -sorbitol/maltose(eg immunoglobulins)
  4. What is the delta gap
    Change in anion gap - change in HCO3

    • Should be 0.
    • If >6 then met alkalosis in conjunction with raised anion gap alkalosis
    • If <-6, both raised and normal anion gap acidoses
  5. Lactate gap
    Bedside lactate - lab lactate

    Present in ethylene glycol toxicity
  6. Oxygen saturation gap
    SpO2-Coox SaO2

    • Occurs in presence of for eg
    • -carboxyhaemoglobin
    • -methaemoglobin
    • -sulfhaemoglobin
  7. Alveolar gas equation?
    PAO2= FiO2(Pb-Ph2o)- PaCO2/R
  8. DKA
    • Raised anion gap (ketoacids, lactate) +normal anion gap - -ve delta gap
    • Serum K+ variable (although whole body low)
    • normally raised ur and cr (cross reactivity between Cr and ketones)
    • Raised glucose- correct Na
  9. HONK
    • Very high glucose
    • Increased osmolality- serum and urine
    • Lactic acidosis
    • Low/absent ketones
    • Increased Ur and Cr
  10. DI
    • Neurogenic- failure of ADH secretion by post pit/hypothalamus (head Ix, Brain Death, nSx/RTx, idiopathic)
    • Nephrogenic- Collecting duct resistance to vasopressin (hereditry, amyloid, Polycystic kidney disease, post-obstructive, myeloma, hypercalcaemia(chronic), chronic hypokalaemia, lithium, amphotericin B, gentamycin, glibenclomide, demeclocycline)
    • -Rule of twos- 200ml/hr for two hours, raised plasma osml, urine osml <200mmol/L
    • - Low urine SG
    • -Desmopressin stimulation test
  11. SIADH
    • From ectopic production
    • (CNS disorders)
    • - SAH
    • -Meningitis
    • -Brain tumour
    • -brain abscess
    • (Pulmonary)
    • -pneumonia
    • -small cell lung Ca
    • -Abscesses
    • (Drugs)
    • -chlorpropramide
    • -clofibrate
    • -Phenothiazine
    • -Cyclophosphamide
    • -SSRIs
    • -Carbamezapine

    • Hypo-osolar hyponatraemia
    • -Increased urinary Na (>20mmol/L) with hypertonic urine relative to serum
  12. Hypoadrenalism
    • Hypo-osmolar hyponatraemia
    • Hyperkalaemia
    • Hypoglycaemia
    • Mild raised urea
    • Mild Met acidosis
    • Hypercalcaemia
    • Eosinophilia
  13. Refeeding
    • When normal caloric intake is resumed
    • Glucose levels estored, insulin secreted
    • Cellular uptake of phos, K and Mag, depletion of ATP
    • Profound deficiency, thiamine def may be revealed
    • Presents as cardioresp failure, paraesthesias, seizures
  14. Pyloric stenosis
    • Presents 2-8 week of life
    • Olive palpable, visible peristalsis, non-bilious vomiting
    • Hypochloraemic, Hypokalaemic met alkalosis
    • Raised Ur and Cr
    • Ketouria
  15. Rhabdomyolysis
    Trauma, compartment, toxin(snake/spider),drugs, seizures, myopathy, burns, sepsis, hypokalaemia

    • -Hyperkalaemia
    • -Hyperphosphataemia, hypocalcaemia
    • Raised Ur and Cr (Reduced Ur:Cr ratio)
    • - Rasied CK, AST, LDH
    • -Myoglobinuria
    • -Met acidosis
  16. Acute pancreatitis
    • Hypocaclcaemia
    • Hyperglycaemia
    • Hypophosphataemia
    • Raised Ur(Cr variable)
    • Raised amylase and lipase
  17. Tumour lysis syndrome
    • Hyperkalaemia
    • Hyperphosphataemia
    • Hypocalcaemia
    • Hyperuricaemia
    • Met acidosis
    • Raised Ur and Cr
  18. Beta-adrenergic stimulation
    • Lactic acidosis
    • Hypokalaemia
  19. Myxoedema
    • Hyponatraemia
    • Hypoglycaemia
    • Hypercholesterolaemia
    • Hypertriglyceridaemia
  20. Plasma Exchange
    • Reduce plasma proteins and enzymes (Globulin, antithrombin, protein C, cholinesterase)
    • Albumin may be normal if albumin has been used as the replacement
  21. Immunoglobulin therapy
    • IgG can caused a lowered anion gap
    • --> Metabolic alkalosis + negative anion gap
  22. Hyponatraemia
    • Hyperosmolar (osm>290mosm/L): Hyperglycaemia, mannitol, ethanol, ethylene glycol
    • Iso-osmolar: Hyperlipidaemia, hyperproteinaemia(eg multiple myeloma)
    • Hypo-osmolar(<270):
    •     -Hypovolaemic: Na + loss> fluid loss- Addisons, polyuric renal failure, diuretics, burns, GI losses
    •    - Normovolaemic: psychogenic polydipsia, sIADH, hypothyrodism, acute adrenal insufficiency
    •    - Hypervolaemic: Excess 5%Dex, CCF, cirrhosis, nephrotic Sx, Renal failure
  23. Hypernatraemia
    • Hypovolaemic(Excess water loss): Diuretics, glycosuria, renal failure, GI loss, fever, burns, thyrotoxicosis
    • Normovolaemic: DI (with replacement)
    • Hypervolaemic(Na gain): saline infusion, bicarb infusion, feed formulae, TPN, mineralocorticoid excess, Conn,s Cushing's

    • Water Deficit:
    • Where TBW = 0.6 x body weight
  24. Hypokalaemia
    • Intracellular shift: Alkalaemia, Catecholamines, salbutamol, insulin, refeeding, hypomagnesaemia
    • Reduced Intake: Starvation
    • Increased loss: Diuretics, mannitol, acetazolamide, steroids, amphotericin, lithium, RTA type 1 and 2, GI losses, ileal conduit, enteric fistulae, skin losses
  25. Hyperkalaemia
    • Artefact: Drip Arm, haemolysis
    • Extracellular shift: acidosis, tissue breakdown, rhabdomyolysis, tumour lysis syndrome, haemolysis, ischaemiareperfusion, leukaemia, sux, DKA, 
    • Increased intake: direct IV/oral, transfusion
    • Reduced clearance: ARF, hypoaldosteronism, T 4 RTA, K sparing diuretics
  26. Hypomagnesaemia
    • Excess loss: Malabsobtion syndromes, GIT fistulae, Short bowel syndrome, diarrhoea, pancreatitis, prolonged NG suction, RTA
    • Reduced intake: EtoH, TPN
    • Redistribution: Hypokalaemia with hypocalcaemia
    • Others: Hyperparathyroidism, hyperthyroidism, DM, hyperaldosteronism, drugs (Aminoglycosides, amphotericin, diuretics, cyclosporin, cisplatinum)
  27. Hypermagnesaeia
    • Excess administration of Mg Salts
    • Laxatives
    • TPN
    • Renal failure
  28. Hypophosphataemia (<0.81 mmol/L)
    • Hyperparathyroidism
    • Osteomalacia
    • Hypomagnesaemia
    • Acute alkalosis
    • Dialysis
    • Ketoacidosis
    • TPN
    • Refeeding syndrome
    • Chronic ETOH
  29. Hyperphosphataemia (1.45 mmol/L)
    • Artifact: haemolysis
    • Increased intake: Excess Vit D replacement
    • Increased release from cells/bone: Rhabdomyolysis, malignancy, starvation, diabetes, tumour lysis syndrome
    • Decreased excretion: hypoparathyroidism, renal failure
  30. Hypocalcaemia (<2.1mmol/L)
    • 40% Albumin bound
    • adjusted Ca= measured +[(40-serum albumin)x 0.02]

    • Decreased parathyroid activity: Hypoparathyroidism
    • Decreased Vit D Activity: Chronic renal failue, Intestinal malabsorbtion, poor diet, liver disease
    • Increased loss: chelating agents
    • Alkalosis
    • Others: hypomagnesaemia, pancreatitis, rhabdomyolysis, hyperphosphataemia
  31. Hypercalcaemia(>2.6mmol/L)
    • Primary or tertiary hyperparathyroidism
    • Malignancy (myeloma or bone mets)
    • Sarcoidosis
    • Vit D intoxication
    • Hyperthyoidism
    • Milk alkali syndrome
    • Immobilisation
    • Thiazides
  32. Hypokalaemic Alkalosis
    • Diuretics (loop or thiazide)
    • Excess mineralocorticoid (Cushing's/Conns)
    • Vomiting, diarrhoea, laxatives
    • Villous adenoma of the recum
  33. Hyponatraemia with hyperkalaemia
    • Hypoadrenalism (Addisons)
    • Potassium sparing diuretics
    • Renal failure (salt losing nephropathy)
    • DKA (pseudohyponatraemia)
  34. Hypocalcaemia with met. acidosis
    • ARF
    • Tumour Lysis Sx
    • Rhabdomyolysis
    • Pancreatitis
    • Ethylene Glycol
    • Hydrofluoric acid
  35. Hypoglycaemia with metabolic acidosis
    • Fulminant hepatic failure
    • Septic Shock
    • Salicylate poisoning
  36. Unconjugated bilirubin
    • Physiological (neonates)
    • Gilbert syndrome(glucuronyl transferase deficiency)
    • Haemolysis
    • Resorption of haematoma
  37. Conjugated Bilirubin
    • Part of multi organ failure
    • Cholestatic drugs: flucloxacillin, chlorpromazine, prochlorperazine
    • TPN
    • Cirrhosis
    • Heart failure inc tamponade
    • Hepatitis
    • Tumour (prim or met)
    • Obstruction: Stones, sludge, Ca, sclerosis cholangitis, lymph nodes, choledochal cyst, biliary atresia, post-op strictures
  38. Transaminases
    • AST: liver, heart, skeletal muscle
    • ALT: Liver and muscle

    • Massive increases with ischaemic and toxic hepatitis
    • Alcoholic: AST normal 1.5-2 x ALT (reversed in most other causes), levels rarely >500U/L GGT/AlkP normally elevated first
    • Transiminases minimally elevated in cirrhosis
  39. GGT
    • Liver(bile), pancreas, kidneys
    • Increased with any liver injury, raised in cholestasis
    • Isolated increase reflects moderate ETOH
  40. AlkP
    • Liver, bone
    • Isolated increase: Late pregnancy, Paget's, bone growth or injury( including mets), primary biliary cirrhosis
  41. LDH
    Elevated reflect ischaemia anywhere
  42. Albumin
    • Reduced: chronic inflam states, nephrotic syndrome, severe malnutrition and liver disease, protein-losing enteropathies and pregnancy (by dilution)
    • If other LFTs normal then likely non-hepatic cause
  43. Blood ammonia
    • Variable increase associated with hep encephalopathy
    • May aid in Dx of altered conc of ?aetiology
    • Increases in urea cycle disorders

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