Acid/Base Pathophysiology
Terms
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- Acid
- A substance that can donate H+
- Acidosis
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⬢< 7.35
⬢H+ Excess
⬢HCO3 Deficit - Alkalosis
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⬢> 7.45
⬢H+ Deficit
⬢HCO3 Excess - Base
- A substance that can accept H+
- Bicarbonate-Carbonic Acid Buffering system
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⬢Most important ECF buffering system
⬢HCO3 + H+ => H2CO3 => H20 + CO2 breathe out - Buffering anions
- HCO3 major also hemoglobin, phosphate, and proteins
- Carbonic Acid (H2CO3)
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Unable to measure directly
Dissolves in plasma to form CO2 +H20
eliminated by lungs
Use co2 to measure acid component - Causes of Metabolic Acidosis
- Cardiac Arrest, Shock, Diabetic Ketoacidosis, Fasting/starvation/malnutrition, Ketogenic diet, Aspirin Toxicity, Renal Failure, Severe Diarrhea, Hyperchloremia
- Causes of Metabolic Alkalosis
- Excess NaHCO3 intake, prolonged vomiting/bingeing/purging, GI suction, Diuretics, Hyperaldosteronism, Renal Failure
- Causes of Respiratory Acidosis
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HYPOVENTILATION:
COPD, Drug overdose, Head injury, respiratory muscle disorders - Causes of Respiratory Alkalosis
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HYPERVENTILATION:
Panic attacks, hypoxia, Fever, Saliclate Toxicity, Mechanical Ventilation - Exchange between H+ & K+ Buffering System
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⬢Acidosis => H+ moves into ICF K+ moves into ECF
⬢Alkalosis => H+ moves into ECF K+ moves into ICF - CO2
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used to express Carbonic acid
Although CO2 is not an acid (has no H+ to donate), but because of its relationship with H2CO3, it is referred to as an acid - Kidney Regulation of pH
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Retain or excrete HCO3 or H+ as needed
Kidneys compensate slowly but provide complete compensation
Acidosis (↓ pH)
•Retain HCO3 or Excrete H+
Alkalosis (↑ pH)
•Excrete HCO3 or Retain H+ - Metabolic Acidosis
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↓Bicarbonate (HCO3) <21 mEq/L
↓pH
Resp. Comp: Hyperventalation to ↓ PCO2
Renal Comp: if no renal disease, ↑ H+ excretion and ↑ HCO3 Reabsorption
-BE - Metabolic Alkalosis
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↑HCO3 >28 mEq/L
↑pH
Resp. Comp: Hypoventalation to ↑PCO2
Renal Comp: If no renal disease ↓H+ excretion and ↓ HCO3 reabsorption
+ BE - mild hypoxemia
- 60-80 mm Hg PO2
- Mod. Hypoxemia
- PO2: 45-60 mm Hg
- Noncompensation
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pH is abnormal
PCO2 or HCO3 OR Abnormal - Partial Compensation
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pH is abnormal
both PCO2 AND HCO3 are abnormal - PCO2
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In acid-base terminology, CO2 is expressed as PCO2
P = Partial Pressure
Refers to the pressure / tension exerted by this gas in blood
Partial Pressure = because CO2 is only one of several gases contributing to the total pressure (Oxygen, Nitrogen & Other Gases - pH ratio and what is it determined by?
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⬢Determined by ratio of bicarb & carbonic acid
⬢pH maintained by a ratio of 20:1 (bicarb:CA) -
Primary Disturbance
match between pH and PCO2 - Respiratory system causing primary disturbance
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Primary Disturbance:
Match between pH and HCO3 - Metabolic system causing primary disturbance
- Respiratory Acidosis
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↑ PCO2 (>45mm Hg)
↓pH
Renal Comp:↑H+ excretion and ↑HCO3 reabsorption - Respiratory Alkalosis
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↓PCO2 (<35mm Hg)
↑pH
Renal Comp: ↓H+ excretion and ↓ HCO3 reabsorption - Respiratory Regulation of pH
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Lungs regulate carbonic acid (H2CO3) by ↑ ↓ Respirations
Lungs compensate quickly but incompletely
Acidosis (↓ pH)
•↑ RR => Blow off CO2 + H20
Alkalosis (↑ pH)
•↓ RR => Retain CO2 + H2O - Severe Hypoxemia
- PO2: < 45 mm Hg