Acid Base & Metabolites

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David.Tripp
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137336
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Acid Base & Metabolites
Updated:
2012-02-24 02:59:02
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Acid Base
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Acid Base
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  1. Acute respiratory acidosis:
    expected [HCO3-] = 24 * 0.1 * (PaCO2 – 40)
  2. Chronic respiratory acidosis:
    expected [HCO3-] = 24 * 0.35 * (PaCO2 – 40)
  3. Acute respiratory acidosis:
    expected [HCO3-] = 24 – 0.2 * (40 – PaCO2)
  4. Chronic respiratory acidosis:
    expected [HCO3-] = 24 – 0.5 * (40 – PaCO2)
  5. Metabolic acidosis:
    expected PaCO2 = 1.5 * [HCO3-] + 8 – short cut: PaCO2 = last 2 digits of pH. For 10 mmol ¯ in HCO3, ¯ PaCO2 by 12.5
  6. Metabolic alkalosis:
    expected PaCO2 = 0.6 * [HCO3-] + 40 - short cut: PaCO2 = last 2 digits of pH. For 10 mmol ­ in HCO3, ­ PaCO2 by 7
  7. Anion gap (mEq/L) =
    Na – Cl – HCO3 Normal 8 - 12
  8. Correct Anion Gap
  9. AGc = AG + 0.25 * (40 – albumin)
  10. Calculated Osmolality
  11. Calculated osm gap = 2* Na + urea + glucose
  12. Approach to acidosis
    • * Is it acidosis or alkalosis
    • * Respiratory or Metabolic
    • * Is compensation appropriate: PaCO2 and HCO3 will move in the same direction
    • * Check Extent of compensation.
    • * Calculate AGc
    • * If High: measure osmolality.
    • * If Normal: measure urinary osmolality.
    • * If Low: lab error, lithium, IgG myeloma
  13. Causes of normal AGc Metabolic Acidosis
    • * Hyperchloraemia
    • * GI losses of SID enteric fluid
    • * Renal tubular acidosis
    • * Acid loads: TPN and NH4Cl administration
    • * Drug induced ­ K with renal insufficiency
    • * Li toxicity
  14. Raised Anion Gap Acidosis
    • * Lactate: L-Lactate acidosis, Short bowel syndrome (D-lactate)
    • * Ketoacidosis
    • * Renal failure: sulphate and other organic anions, ­ PO4
    • * Poisoning: Ethylene glycol, Methanol, Salicylates, Iron
    • * Pyroglutamic acidosis
    • * Myeloma IgA bands
  15. d /d ratio:
    d AG / d HCO3

    Done in high AG disorders to diagnoses and additional acid-base problem
  16. Metabolic Alkalosis
    • * Loop or thiazide diuretics: decr ECF leads to incr­ aldosterone + high distal flow rates of Na leading to K resorption/H loss
    • * Steroid excess: Corticosteroids, Cushing’s * Hypercalcaemia, Milk Alkali syndrome (­ Ca ingestion leads to ­ incr Na excretion + decr PTH leads to HCO3 retention)
    • * Mg deficiency
    • * Loss of H+: vomiting, suctioning
    • * Gain of high SID fluid: NaHCO3, Na citrate (> 8 units stored blood, plasma exchange), renal replacement with high SID fluid
  17. Causes of Respiratory Alkalosis
    • Acute:
    • * Hypoxaemia
    • * Sepsis
    • * PE
    • * Asthma
    • * Drugs: salicylates, SSRIs
    • * Pain, anxiety

    • Chronic:
    • * Pregnancy
    • * Altitude
    • * Chronic lung or liver disease
  18. Causes of Hypertonic Hyponatraemia
    (>285 mOsm/kg):

    • Impermeant solutes:
    • * Glucose
    • * Hypertonic infusions: mannitol, TURP syndrome (absorption of gylcine from irrigation solution)
  19. Causes of Isotonic Hyponatraemia
    (285 – 295 mOsm/kg): ­incr lipids or incr­ protein leading to factitious hyponatraemia (error of measurement)
  20. Hypotonic Hyponatraemia
    and Increased ECF
    (Gain of Na-poor fluid)
    • Urinary sodium > 20:
    • * Acute and chronic renal failure
    • * Hyperaldosteronism from any cause (eg Steroids, Cushings)

    • Urinary sodium < 20:
    • * Liver failure/cirrhosis
    • * CCF (leading to 2ndary hyperaldosteronism)
    • * Nephrotic syndrome
    • * Excess 5% dextrose
  21. Hypotonic Hyponatraemia and Normal ECF (incr ADH)
    • Urinary Na < 20 mEq/L:
    • * Water intoxication
    • * Pain (eg post-operative)

    • Urinary Na > 20 mEq/L:
    • * Renal failure
    • * Hypothyroidism
    • * Adrenal insufficiency
    • * Medications: oxytocin for induced labour, SSRIs in the elderly, thiazides, omeprazole
    • * SIADH (eg pulmonary infections, SCLC)
  22. Hypotonic Hyponatraemia and Low ECF (
    Loss of Na rich fluid)
    • Urinary Na < 20 mEq/L (ie non-urinary loss. Treat with slow resuscitation)
    • * Vomiting
    • * Diarrhoea, fistulas/stomas
    • * Skin losses (sweating, Cystic fibrosis)
    • * Third spacing (eg burns, pancreatitis)

    • Urinary Na > 20 (ie urinary loss - salt wasting states):
    • * Diuretics
    • * Adrenal insufficiency
    • * Renal tubular acidosis
    • * Cerebral salt wasting
  23. Causes of hypokalaemia
    • Decr Intake: anorexia, malabsorption
    • Incr Excretion:
    • * Renal:
    • - Steroids: Conn’s, Cushing’s, Ectopic ACTH
    • - Drugs: diuretics, corticosteroids, carbapenems, gentamicin
    • - RTA
    • * Vomiting: loss of HCl
    • * Diarrhoea, laxatives

    • Redistribution:
    • * Insulin
    • * Alkalosis
    • * b 2 adrenergics
    • * Delayed following blood transfusion
  24. Causes of hyperkalaemia
    • Artifact: haemolysis
    • Incr­ Intake:
    • * Blood transfusion
    • * Exogenous

    • Decr output:
    • * Renal:
    • - Failure
    • - K sparing diuretics
    • - Hypoaldosteronism, including drug induced (ACEI, ARB)

    • Redistribution:
    • * Cell lysis
    • * Acidosis
    • * Digoxin overdose
  25. Causes of Hypocalcaemia giving tetany/cramps
    • Excretion:
    • * Decr Vitamin D
    • * Decr PTH
    • * Loop diuretics

    • Redistribution:
    • * Alkalosis ® ­ protein binding
    • * Citrate from transfusion
    • * decr PTH leading to incr­ bone uptake
  26. Causes of Hypercalcaemia
    • Intake (rare):
    • * Vitamin D intoxication
    • * Milk-alkali syndrome

    • Decr excretion:
    • * Renal failure
    • * Thiazides, Li
    • * Incr Vitamin D

    • Altered redistribution (generally incr resorption from bone):
    • * Any cause of ­ incr Vitamin D (eg granulomatous disease)
    • * Any cause of incr­ PTH: primary hyperparathyroidism, PTH secreting tumours, hyperthyroidism
    • * Bony infiltrates by infection, Paget’s, malignancy
    • * Dehydration
  27. Causes of hypophosphataemia
    • Incr PTH
    • Decr Vitamin D
    • RTA
    • Alkalosis
    • Alcoholism
    • Refeeding Syndrome
  28. Causes of Hyperphosphataemia
    • * Rhabdomyolysis
    • * Renal failure
    • * Vitamin D toxicity
    • * Acidosis
    • * Tumour lysis
    • * Decr PTH

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