Normal Physiology Gans.pdf · 5. Evaluate mixed acid-base disorder • Relate delta anion gap to...
Transcript of Normal Physiology Gans.pdf · 5. Evaluate mixed acid-base disorder • Relate delta anion gap to...
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Normal Physiology
Pathophysiological Response to acidemia/alkalemia
Structured Approach
Simple Acid-Base disorders and compensatory responses
Anion Gap
Urinary Anion Gap/Urine Osmolar Gap
Delta-Delta or Delta Ratio
Osmolal Gap
Metabolic AcidosisMetabolic AlkalosisRespiratory AcidosisRespiratory Alkalosis
Arterial-Alveolar Oxygen Tension Difference References
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References and Sources
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versus
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- The major titratable acid buffer is HPO42- (dependent on diet, PTH)
- less important buffers are creatinine and uric acid.
- Ammonium production and excretion
minimum attainable urine pH is 4.0 to 4.5: cannot excrete HCL (requires urine pH of 1.0)
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Physiological Effectsof Metabolic Acidosis
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Structured approach
1. History and Physical Exam: clues to what acid-base disorder might be present2. Look at the pH (If normal consider mixed acid-base disorder)3. Determine primary acid-base disorder and secondary (compensatory) response4. Consider the metabolic component
• Metabolic acidosis: anion gap• High • Normal (urinary anion gap, Na<20mmpl/l: urinary osmol gap, both indirect
measures of ammonium)• Metabolic alkalosis
• Chloride-responsive (Cl <25 mmol/l)• Chloride-resistant (Cl> 40 mmol/l)
• Urinary K <20 or >30 mmol/l)5. Evaluate mixed acid-base disorder
• Relate delta anion gap to the delta bicarbonate6. Evaluate osmolal gap in unexplained high anion gap metabolic acidosis, coma, toxic
ingestions7. Evaluate Respiratory component of acid base disorder
• Relate partial pressure of oxygen to ventilation (alveolar-arterial oxygen tension difference)
8. Verification of diagnosis!
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Anion Gap
[Na+] + [K+] + [Ca2+] + [Mg2+] + [H+] + unmeasured cations=
[Cl−] + [HCO3−] + [CO32−] + [OH−] + albumin + phosphate + sulfate + lactate + unmeasured anions (e.g., inorganic anions)
There is NO GAP: sum of the positive and negative ion chargesin plasma are equal in vivo
reference ranges of 3.0 to 12.0 mmol per liter up to 8.5 to 15.0 mmol/l
A= chloride or unmeasured anion
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G Glycols (ethylene, propylene)O 5-oxoproline (pyroglutamic acid)L L-Lactate, D D-Lactate
M MethanolA AspirinR Renal failure (GFR <20 ml/min)R RhabdomyolysisK Ketoacidosis
High Anion Gap
bicarbonate decreases relative to levels of sodium and chloride
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High Anion Gap (Pitfalls)
• 50% patients with serum lactate between 3.0 and 5.0 mmolper liter have an anion gap within the reference range
• Adjust for albumin (weak acid, up to 75% of the gap):Decrease of 1 g/dl, add 2.3-2.5 mmol/l to the gap
Low or Negative Anion Gap
• high levels of cations: - lithium toxicity- monoclonal IgG gammopathy- high levels of calcium or magnesium.
• pseudohyperchloremia in bromide or iodide intoxication.
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Urinary Anion Gap
Represents excretion of Ammonium NH4+ (as NH4Cl)
Negative in normal anion gap acidosis (Hyperchloremic acidosis should lead to increasedrenal excretion of ammonium)
If positive: consider renal failure, distal renal tubular acidosis, hypoaldosternonism
Unreliable: polyuria, urinary pH >6.5, ammonium excreted with other anion (ketoacid, salicylates, d-lactate, penicilline) or when UNa+< 20 mmol/l
Urinary Osmolal Gap
mmol/l
<40 mmol/l indicates impaired ammonium excretion, except in ketoacidosis
Normally, near zero or positive
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Delta-ratio
-If ratio between 1 and 2, then pure elevated anion gap acidosis
- If < 1, then there is a simultaneous normal anion gap acidosispresent.
- if > 2, then there is a simultaneous metabolic alkalosis present ora compensated chronic respiratory acidosis.
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Delta-ratio
-if <0.4 pure normal anion gap acidosis
- If < 1, then there is a simultaneous normal anion gap acidosis present
-If ratio between 1 and 2, then pure elevated anion gap acidosis
- if > 2, then there is a simultaneous metabolic alkalosis present or a pre-existing chronic respiratory acidosis.
50% of excess acid is buffered intracellularlyand by bone, not by HCO3-Excess anions remain in ECF
Increase in Anions > decrease in HCO3-
Lactic Acidosis: 1.6:1Ketoacidosis 1:1 (loss of ketones with urine)
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Mixed acid base disorders usually produce arterial blood gas results that couldpotentially be explained by other mixed disorders. Oftentimes, the clinical picture will
help to distinguish.
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Osmolal gap
Difference between measured serum osmolality and calculated serum osmolality
Calculated Osmolality: 2 x [Na+] + (Glucose (mg/dl)/18) + (BUN (mg/dl)/2.8)
ethanol (mg/dl)/3.7
Normal: -10-10 mosmol/kg
Increased: toxic alcohols (lactate, ketones)
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Note:Acidic urine!
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Alveolar-arterial Oxygen tension difference
Ventilation-Perfusion mismatch:5-10 mmHg in young15-20 mmHg in elderly
For every decade a person has lived, A-a difference increase by 2 mm Hg;A-a O2 difference = [Age/4] + 4
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Stroomdiagram onderzoek Hypokaliemie