Biochemistry

Na+ - (HCO3+Cl) normal 6-15 mmol/L

• Raised vs. normal
• Reduced: Hypermag, Hypercalc, Lithium, IgG, Hypoalb

AGc= AG + 0.25x(44-albumin)

Measured osmolality - calculated

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

• Increased in:
• -alcohols
• -mannitol
• -glycine(TURP)
• -radicontrast media
• -sorbitol/maltose(eg immunoglobulins)

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

Bedside lactate - lab lactate

Present in ethylene glycol toxicity

SpO2-Coox SaO2

• Occurs in presence of for eg
• -carboxyhaemoglobin
• -methaemoglobin
• -sulfhaemoglobin

PAO2= FiO2(Pb-Ph2o)- PaCO2/R

• 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

• Very high glucose
• Increased osmolality- serum and urine
• Lactic acidosis
• Low/absent ketones
• Increased Ur and Cr

• 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

• 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

• Hypo-osmolar hyponatraemia
• Hyperkalaemia
• Hypoglycaemia
• Mild raised urea
• Mild Met acidosis
• Hypercalcaemia
• Eosinophilia

• 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

• Presents 2-8 week of life
• Olive palpable, visible peristalsis, non-bilious vomiting
• Hypochloraemic, Hypokalaemic met alkalosis
• Raised Ur and Cr
• Ketouria

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

• Hypocaclcaemia
• Hyperglycaemia
• Hypophosphataemia
• Raised Ur(Cr variable)
• Raised amylase and lipase

• Hyperkalaemia
• Hyperphosphataemia
• Hypocalcaemia
• Hyperuricaemia
• Met acidosis
• Raised Ur and Cr

• Lactic acidosis
• Hypokalaemia

• Hyponatraemia
• Hypoglycaemia
• Hypercholesterolaemia
• Hypertriglyceridaemia

• Reduce plasma proteins and enzymes (Globulin, antithrombin, protein C, cholinesterase)
• Albumin may be normal if albumin has been used as the replacement

• IgG can caused a lowered anion gap
• --> Metabolic alkalosis + negative anion gap

• 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

• 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

• 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

• 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

• 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)

• Excess administration of Mg Salts
• Laxatives
• TPN
• Renal failure

• Hyperparathyroidism
• Osteomalacia
• Hypomagnesaemia
• Acute alkalosis
• Dialysis
• Ketoacidosis
• TPN
• Refeeding syndrome
• Chronic ETOH

• 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

• 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

• Primary or tertiary hyperparathyroidism
• Malignancy (myeloma or bone mets)
• Sarcoidosis
• Vit D intoxication
• Hyperthyoidism
• Milk alkali syndrome
• Immobilisation
• Thiazides

• Diuretics (loop or thiazide)
• Excess mineralocorticoid (Cushing's/Conns)
• Vomiting, diarrhoea, laxatives
• Villous adenoma of the recum

• Hypoadrenalism (Addisons)
• Potassium sparing diuretics
• Renal failure (salt losing nephropathy)
• DKA (pseudohyponatraemia)

• ARF
• Tumour Lysis Sx
• Rhabdomyolysis
• Pancreatitis
• Ethylene Glycol
• Hydrofluoric acid

• Fulminant hepatic failure
• Septic Shock
• Salicylate poisoning

• Physiological (neonates)
• Gilbert syndrome(glucuronyl transferase deficiency)
• Haemolysis
• Resorption of haematoma

• 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

• 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

• Liver(bile), pancreas, kidneys
• Increased with any liver injury, raised in cholestasis
• Isolated increase reflects moderate ETOH

• Liver, bone
• Isolated increase: Late pregnancy, Paget's, bone growth or injury( including mets), primary biliary cirrhosis

Elevated reflect ischaemia anywhere

• 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

• Variable increase associated with hep encephalopathy
• May aid in Dx of altered conc of ?aetiology
• Increases in urea cycle disorders