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What is the best way to measure plasma pH?
Via arterial blood gases (ABG)
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Acidosis
- LOW pH (< 7.35)
- High H+ concentration
- HCO3- BELOW normal
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Alkalosis
- HIGH pH (> 7.45)
- Low H+ concentration
- HCO3- ABOVE normal
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Arterial Blood Gases (ABG) -- 7.40/40/90/26/98%
- pH = 7.35 - 7.45
- paCO2 = 35 - 45 mm Hg
- paO2 = 80 - 100 mm Hg
- HCO3- = 21 - 28 mEq/L
- Oxygen Saturation = 95% - 100%
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Regulation of Acid-Base
- Chemical buffer system: proteins & chemicals (bicarb & phosphate)
- Lungs
- Kidneys
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Acid-Base Ratio
- CO2 + H2O = H2CO3H2CO3 = H+ + HCO3-
- (Bicarbonate 20 parts/Carbonic acid 1 part)
- If ratio is disturbed - imbalance will occur & pH will be changed
- It is the ratio that is important, NOT the absolute values
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Regulation with the Lungs
- Very large surface area from which CO2 can diffuse
- Lungs remove CO2 from the body in response to increases in H+ concentration
- CO2 has the most profound effects on respirations
- Hyperventilation: CO2 is "blown off"
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Regulation with the Kidneys
- Works slowly
- Powerful & efficient
- Major function: HCO3- regulation
- Vital role in pH regulation
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Metabolic Acidosis
- Decrease in pH
- HCO3- deficit OR H+ excess
- Causes: CRF, aspirin OD, ketoacidosis, diarrhea
- Manifestations: H/A, confussion, increased RR, N/V
- Interventions: correct underlying problem, IV HCO3-, observe for hyperkalemia
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Metabolic Acidosis
- High pH
- HCO3- excess OR loss of H+
- Causes: vomitting, gastric suction, antacids
- Manifestations: dizziness, irritability, tingling of the digits, decreased RR
- Intervention: reverse underlying disorder, increase Cl- to absorb Na+ resulting in excretion of HCO3-, observe for hypokalemia
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Respiratory Acidosis
- H2CO3- Excess (CO2 Excess)
- Causes: cardiac/respiratory arrest, COPD, OD of sedatives
- Manifestations: mental changes, H/A, feeling of fullness in head, dizziness, coma
- Interventions: IMPROVE VENTILATION! (bronchodilators, mechanical ventilation, CPT, hydration); administering bicarbonate is questionable
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Respiratory Alkalosis
- H2CO3- deficit (low CO2 levels)
- Causes: hyperventilation, aftermath of severe exercise, anxiety
- Manifestations: "Hyperventiation Syndrome" (palpitations, lightheadedness, sweating, dry mouth, N/V, epigastric pain)
- Interventions: eliminate cause, control breathing, breath into a closed system
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Uncompensated
Normal value in the CO2 or HCO3
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Partially Compensated
No normal values
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Completely Compensated
A normal value in pH with other abnormal values
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ABG Analysis "Arrow Method"
- 1. Look at the pH: if arrow UP = alkalosis; if arrow DOWN = acidosis
- 2. Look at CO2 and HCO3: determine if levels are elevated or down, place up or down arrows
- 3. Determine compensation: partial, complete, or uncompensated
- 4. Determine the type of imbalance: if all arrows (CO2, HCO3, and pH) are in the SAME direction = METABOLIC imbalance.. If CO2 and HCO3 are OPPOSITE the pH = RESPIRATORY imbalance
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