AcidBasePathoFall2012

Acid base homeostasis acids produced by co 2 is the

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Acid-Base Homeostasis Acids produced by CO 2 is the main source of acid CO 2 production due to dietary carbohydrate, protein and fat catabolism Tissue metabolism Alkali is introduced through the diet
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Acid-Base Homeostasis Regulated by: Extracellular Buffering Respiratory Tract Kidneys
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Extracellular Buffering Rapidly responds to changes in H+ concentration Primary extracellular buffering system is carbonic acid/bicarbonate Phosphate and proteins are more abundant intracellularly Cannot effectively maintain homeostasis alone
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Respiratory Regulation 2nd line of defense Responds within minutes Chemoreceptors in brainstem respond to changes in pCO 2 and pH ∆ rate or depth of ventilation  ∆ CO 2 excretion  ∆ pH CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+
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Renal Regulation Occurs over several days Kidneys regulate acid-base homeostasis by altering: Proximal tubular HCO3- reabsorption Renal ammoniagenesis For each NH4+ that is excreted, one HCO3- is returned to circulation Distal tubular H + excretion For each H+ that is secreted, one bicarbonate ion is returned to circulation
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Assessing a Patient’s Acid-Base Balance
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Steps in assessing a patient’s acid-base status 1. Collect pertinent labs 2. Answer the following questions: a. Is acidemia or alkalemia present? b. Is the primary abnormality respiratory or metabolic? c. Is there compensation? d. Was the compensatory response appropriate? e. Is there an anion gap?
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Assessing Acid-Base Status Collect Pertinent Labs: Arterial Blood Gas (ABG) Use arterial blood Reflects degree of oxygenation by lungs Electrolyte panel Use venous blood Reflects oxygen use by tissues
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Assessing Acid-Base Status ABG Oxygenation PaO2 SaO2 Acid-base status pH (directly measured) PaCO2 (directly measured) HCO3- (calculated) Normal ABG Values pH 7.4 (7.35-7.45) PaO 2 80-105 mmHg SaO 2 95% PaCO 2 35-45 mmHg HCO 3 - 22-26 mmHg
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Assessing Acid-Base Status Electrolytes Compare HCO3- from ABG and electrolyte panel ABG and electrolyte panel should be drawn at approximately the same time Levels should be similar We’ll use this later to calculate an anion gap
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Assessing Acid-Base Status 1. Is acidemia or alkalemia present? Look at pH: is it acidic or basic? pH = 7.3 pH = 7.52 pH = 7.37 pH = 7.11
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Assessing Acid-Base Status 2. Is the primary abnormality respiratory or metabolic? Look at PaCO2 Identify whether it is acidic, basic or normal 26mmHg 51mmHg Look at HCO3- Identify whether it is acidic, basic or normal 16mmHg 32mmHg
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Assessing Acid-Base Status 2. Is the primary abnormality respiratory or metabolic? If the pH is acidic, identify which parameter (PaCO2 or
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Acid Base Homeostasis Acids produced by CO 2 is the main...

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