Advanced Blood Gas Interpretation Flashcards
M. Brashear IVECCS MDR 2020
What is measured to analyze a patient’s acid-base status?
Hydrogen content of blood
Hydrogen is produced by normal metabolism of protein and is necessary for enzyme function and cell structure.
What does a low pH indicate about hydrogen ion concentration?
Increased level of H+
A low pH indicates an acidic environment.
What is the main extracellular buffer in the body?
Bicarbonate (HCO3)
It is the main metabolic indicator of a patient’s acid-base status.
How does carbon dioxide (CO2) relate to pH?
Elevated CO2 contributes to acidosis, while lower than normal CO2 contributes to alkalosis
CO2 is a main respiratory indicator of acid-base status.
What are the two body systems involved with acid-base regulation?
- Kidneys
- Respiratory system
What is the primary acid-base problem determined from?
Blood gas results
This helps in determining the primary disorder and compensatory mechanisms.
What happens to potassium levels during acidosis?
Hyperkalemia may result
Potassium shifts out of cells in exchange for H+.
What is the most common disorder seen in patient populations?
Metabolic acidosis
Noted in patients with lactic acidosis, kidney failure, DKA, and GI losses.
What is a potential treatment for severe metabolic acidosis?
Sodium bicarbonate
It buffers the acid but must be administered cautiously.
What is a common cause of metabolic alkalosis?
GI outflow obstructions
Can also occur with low chloride levels and poor perfusion.
What occurs during respiratory acidosis?
Hypoventilation and CO2 retention
This leads to a drop in pH.
What indicates respiratory alkalosis?
Hyperventilation leading to excessive CO2 loss
This causes the pH to rise.
What happens to the body’s bicarbonate levels in respiratory acidosis?
Hang on to HCO3, excrete H+
What is the normal range of pH in blood?
7.35–7.45
What does a negative base excess indicate?
Primary metabolic acidosis
A positive BE points to primary metabolic alkalosis.
What is the formula for calculating the A-a gradient?
A = [FiO2 × (Pb − PH2O)] − (PaCO2/0.8)
Pb is barometric pressure and PH2O is saturated water vapor pressure.
What does the PaO2:FiO2 ratio indicate?
If the patient is responding appropriately to oxygen
A normal ratio is 300–500.
What is the expected compensation for metabolic acidosis?
Each 1 mEq/L ↓ HCO3 causes pCO2 ↓ by 0.7 mm Hg
What does a high PaCO2 value indicate?
The lungs’ inability to move air
High PaCO2 can be caused by various conditions such as neurologic disease and upper airway disease.
What does the 120 rule help determine?
Adequate lung function
If PaO2 + PaCO2 ≥ 120, lung function is adequate.
What is the significance of venous blood gas values?
Provide important information, but respiratory component is most accurately measured with an arterial sample.
What is a common effect of alkalosis on potassium levels?
Hypokalemia may result
Potassium shifts into cells in exchange for H+.
What are the normal values for PaCO2?
35–45 mm Hg
What is a key consideration when interpreting blood gas results?
Determine the primary disorder and if the body is compensating
What does a normal A-a gradient indicate?
Hypoxia is not due to significant pulmonary parenchymal disease or heart disease.
What is the expected compensation for acute respiratory acidosis?
Each 1 mm Hg ↑ in pCO2 causes HCO3 ↑ by 0.15 mEq/L
What happens to HCO3 for each 1 mm Hg decrease in PCO2 in chronic respiratory alkalosis?
HCO3 decreases by 0.25 mEq/L
What happens to HCO3 for each 1 mm Hg decrease in PCO2 in acute respiratory alkalosis?
HCO3 decreases by 0.55 mEq/L
What is the first step in assessing a mixed disorder in acid-base balance?
Calculate the compensatory response
In respiratory disorders, which value changes to compensate?
HCO3 changes to compensate for CO2
What is the formula to calculate expected HCO3 in respiratory alkalosis?
Expected HCO3 = (midpoint HCO3) − [(midpoint CO2 − patient CO2) × compensation rate]
What is the formula to calculate expected HCO3 in respiratory acidosis?
Expected HCO3 = (midpoint HCO3) + [(patient CO2 − midpoint CO2) × compensation rate]
What indicates a mixed disorder when comparing actual HCO3 to expected HCO3?
If actual HCO3 is much lower than expected HCO3
What is the normal range for the anion gap?
Less than 20
What does an anion gap greater than 20 indicate?
Primary metabolic acidosis
What is the formula for calculating the anion gap?
Anion gap = (Na + K) − (HCO3 + Cl)
Which conditions commonly present with mixed acid-base disorders?
- DKA
- GDV
- Kidney failure
- Cardiopulmonary arrest
- CHF
- Heatstroke
- Sepsis
- Parvovirus
When treating a mixed acid-base disorder, which change should be addressed first?
Respiratory changes
What does a negative base excess indicate?
Primary acidosis
What does a positive base excess indicate?
Primary alkalosis
What are the measured strong ions in plasma?
- Sodium
- Chloride
- Potassium
- Calcium
- Magnesium
- Lactate
What is the normal strong ion difference (SID)?
∼40 mEq/L
What happens to base excess for every 1 mEq/L change in SID?
Base excess changes in the same direction by 1 mEq/L
What indicates acidosis in relation to SID?
A low SID
What can increased serum sodium cause in terms of SID?
Increase in SID indicating alkalosis
What effect does decreased serum chloride have on SID?
Increases SID indicating alkalosis
What is the effect of hypovolemia on sodium and chloride levels?
Loss of sodium and chloride
How does increased serum lactate affect acid-base status?
Contributes to acidosis
What role do albumin and phosphorus play in acid-base balance?
They serve as buffers in the blood
What happens to acid-base status with hypoalbuminemia?
Can worsen alkalosis
What can elevated phosphorus levels due to kidney failure contribute to?
Worsening acidosis
What is the limitation of the traditional acid-base approach in veterinary medicine?
Fails to consider the effect of electrolytes
What is the strong ion approach primarily used for?
To evaluate acid-base status in critically ill patients
What happens when compensation is not occurring as expected?
Look deeper into electrolyte changes and other factors
What is the effect of hyperalbuminemia on acid-base status?
No change
