Practice Test Geeks(CCP) Certified Clinical Perfusionist Practice Test
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Blood Gas & Acid-Base Interpretation Flashcards

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  1. Which electrolyte abnormality is MOST likely to accompany a metabolic alkalosis in a patient receiving furosemide after cardiac surgery?

    Answer: Hypokalemia and hypochloremia

    Furosemide causes urinary losses of potassium and chloride; hypokalemia and hypochloremia both promote metabolic alkalosis by increasing renal bicarbonate reabsorption.

  2. What does a delta-delta ratio (ΔAG/ΔHCO3-) greater than 2 in a metabolic acidosis indicate?

    Answer: A concurrent metabolic alkalosis superimposed on the high AG acidosis

    A delta-delta ratio >2 means the bicarbonate is higher than expected for the anion gap elevation, implying a concurrent metabolic alkalosis is also present.

  3. During CPB at normothermia, a patient has measured PaO2 of 200 mmHg. Calculated oxygen content (CaO2) depends primarily on:

    Answer: Hemoglobin concentration and SaO2, with a minor contribution from dissolved O2

    CaO2 = (Hb × 1.34 × SaO2) + (0.003 × PaO2); at normal hemoglobin levels, bound oxygen constitutes >98% of total content while dissolved oxygen is minimal.

  4. A perfusionist using alpha-stat management during hypothermic CPB at 28°C corrects blood gases to 37°C before interpretation. If pH reads 7.42 at 37°C, the actual (in vivo) pH at 28°C is:

    Answer: Higher, approximately 7.52

    As temperature decreases, blood pH rises by approximately 0.015 per degree Celsius; at 28°C (9°C below 37°C), the in vivo pH would be approximately 7.42 + 0.135 ≈ 7.55.

  5. A blood gas from the CPB circuit venous line shows PvO2 of 25 mmHg and SvO2 of 45%. This finding MOST likely indicates:

    Answer: Inadequate oxygen delivery relative to metabolic demand (high oxygen extraction)

    Normal SvO2 is 65-75%; an SvO2 of 45% reflects high oxygen extraction, indicating that tissues are consuming more oxygen than is being delivered.

  6. Which of the following BEST describes the relationship between pH and hydrogen ion concentration [H+] that is most useful for rapid bedside estimation?

    Answer: pH 7.40 = [H+] 40 nmol/L; each 0.10 pH unit change doubles or halves [H+]

    At pH 7.40, [H+] is 40 nmol/L, and because pH is a logarithmic scale, each 0.10 unit decrease roughly doubles [H+] while each 0.10 unit increase halves it.

  7. Sodium bicarbonate administration during CPB to correct metabolic acidosis may cause which unintended complication?

    Answer: Metabolic alkalosis, hyperosmolarity, and transient intracellular acidosis from CO2 generation

    NaHCO3 generates CO2 (which freely crosses cell membranes), can cause transient intracellular acidosis, and delivers a large sodium load increasing osmolarity; overcorrection also risks metabolic alkalosis.