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Journal October 2009 (Vol 31, No 10)

NOTE: You have already passed this course.
NOTE: This course is no longer valid for accreditation purposes.

Arterial and Venous Blood Gases: Indications, Interpretations, and Clinical Applications

1. A pH of 7.40 means the
2. A simple metabolic acidosis is characterized by a low pH and a
3. Hypoventilation (↑Pco2) is potentially dangerous because it
4. The BEecf is the most effective parameter to measure the metabolic component of acid-base disorders because
5. Simple acid-base disturbances are typically characterized by which of the following?
6. Consider the following:
Jack, an adult Labrador retriever, presented with a 2-day history of weakness, excessive thirst, and urination. On examination, he was found to be 8% to 10% dehydrated. Please explain Jack's acid-base status from his initial venous blood gas results:

The expected respiratory compensation for this metabolic acidosis (within a margin of variance of ±3 mm Hg) can be calculated as follows:

Expected Pco2 decrease from midpoint reference value = ∆ HCO3- (decrease in HCO3- concentration from a midpoint reference value associated with the metabolic acidosis) × 0.7 (expected mm Hg decrease in Pco2 for each 1.0 mEq/L decrement in HCO3-)

In this case: (22 - 5.4) × 0.7
16.6 × 0.7 = 11.6 mm Hg

Expected Pco2 = Pco2 midpoint reference range - Expected change in Pco2

In this case:
38 mm Hg - 11.6 = 26.4 mm Hg

Therefore, Jack's expected Pco2 is 26.4 mm Hg, and his measured Pco2 is 24.2 mm Hg.

After reviewing Jack's measured and expected Pco2 values, we can conclude that Jack's respiratory compensation for his metabolic acidosis is
7. Consider the following:
Bonbon, a shih tzu puppy, presented with a 2-day history of vomiting and anorexia. On physical examination, a foreign body was palpated in the cranial abdomen. Please explain Bonbon's acid-base status from her initial venous blood gas results:

Bonbon's metabolic alkalosis could be explained by
8. Consider the following:
Please explain the acid-base status of Lucy, a geriatric dog with a 3-day history of progressive increased respiratory effort. On presentation, Lucy's temperature was 103.6°F (39.8°C), her respiratory rate was 42 breaths/min, and her heart rate was 140 bpm. Her physical examination revealed inspiratory stridor on auscultation.

The expected metabolic compensation for this chronic respiratory acidosis (within a margin of variance of ± 2 mEq/L) can be calculated as follows:

Expected HCO3- increase from midpoint reference value = ∆ Pco2 (increase in Pco2 from midpoint reference range associated with the respiratory acidosis) × 0.35 (expected mEq/L increase in HCO3- for each 1.0 mm Hg increment in Pco2):

In this case: (67.6 - 38) × 0.35
29.6 × 0.35 = 10.4 mEq/L

Expected HCO3- = HCO3- midpoint reference range + Expected increase in HCO3-

In this case:
22 + 10.4 = 32.4 mEq/L

Therefore, Lucy's expected HCO3- is 32.4 mEq/L, and her measured HCO3- is 30.4 mEq/L.

Lucy's acid-base status can be described as
9. Consider the following:
Please explain Lucy's oxygenation status from her arterial blood gas results. The sample was collected before oxygen supplementation was instituted.

The a-a gradient calculation is:
Pao2 = 150 - 1.2 (Paco2)
Pao2 = 150 - 1.2 (67.6)
Pao2 = 68.9

a-a = Pao2 - Pao2
a-a = 68.9 - 62.1 = 6.8

Lucy's respiratory evaluation reveals
10. Consider the following:
Bob is a young adult mixed-breed dog that presented after being hit by a car. Physical examination revealed extensive abrasions on his thorax. His temperature was 102.8°F (39.4°C), his respiratory rate was 62 breaths/min, and his heart rate was 140 bpm. Please explain Bob's oxygenation status from the arterial gas data collected on presentation:

The a-a gradient is:
Pao2 = 150 - 1.2 (Paco2)
Pao2 = 150 - 1.2 (25.9)
Pao2 = 119

a-a = Pao2 - Pao2
a-a = 119 - 63 = 56

Bob's respiratory evaluation reveals
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