CCP Blood Gas & Acid-Base Interpretation 5

Question 1

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

Accepted Answer

Hypokalemia and hypochloremia

Answer

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

Question 2

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

Accepted Answer

A concurrent metabolic alkalosis superimposed on the high AG acidosis

Answer

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.

Question 3

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

Accepted Answer

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

Answer

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

Question 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:

Accepted Answer

Higher, approximately 7.52

Answer

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.

Question 5

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

Accepted Answer

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

Answer

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

(CCP) Certified Clinical Perfusionist Practice Test

(CCP) Certified Clinical Perfusionist Practice Test

CCP Blood Gas & Acid-Base Interpretation 5