Blood Gas & Acid-Base Interpretation Flashcards
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Read the first 7 Blood Gas & Acid-Base Interpretation flashcards as text
During rewarming from hypothermic CPB, the perfusionist observes increasing metabolic acidosis. The MOST likely cause is:
Answer: Washout of lactate from previously ischemic peripheral tissues
Rewarming mobilizes lactate accumulated during hypothermic ischemia in peripheral tissues, causing a transient metabolic acidosis as lactate washes into the central circulation.
The Henderson-Hasselbalch equation applied to the bicarbonate system is: pH = 6.1 + log([HCO3-] / 0.03 × PaCO2). If HCO3- is 24 mEq/L and PaCO2 is 40 mmHg, pH equals:
Answer: 7.40
pH = 6.1 + log(24 / 1.2) = 6.1 + log(20) = 6.1 + 1.30 = 7.40, confirming these are normal reference values.
Which acid-base disturbance is MOST commonly associated with post-cardiac surgery patients receiving large volumes of 0.9% normal saline?
Answer: Hyperchloremic metabolic acidosis
Large volumes of 0.9% normal saline (154 mEq/L Cl-) cause hyperchloremic metabolic acidosis by diluting bicarbonate and increasing chloride, narrowing the anion gap.
A perfusionist is managing a neonate on DHCA. Regarding acid-base strategy, the benefit of pH-stat management in neonates and infants is:
Answer: Improved cerebral oxygen delivery through CO2-induced vasodilation and better homogeneous brain cooling
pH-stat causes cerebral vasodilation via hypercapnia, increasing cerebral blood flow and improving homogeneous brain cooling before circulatory arrest in neonates.
A patient's blood gas shows pH 7.25, PaCO2 55 mmHg, HCO3- 23 mEq/L. This is BEST classified as:
Answer: Acute respiratory acidosis without metabolic compensation
Elevated PaCO2 with low pH and normal HCO3- indicates acute respiratory acidosis; the kidney has not yet had time to retain bicarbonate to compensate.
The P50 of hemoglobin is defined as the PaO2 at which hemoglobin is 50% saturated. The normal P50 is approximately:
Answer: 27 mmHg
The normal P50 is approximately 26-27 mmHg; a higher P50 indicates rightward shift (decreased affinity), and a lower P50 indicates leftward shift (increased affinity).
During CPB, a high mixed venous oxygen saturation (SvO2 > 85%) combined with a rising lactate suggests:
Answer: Impaired cellular oxygen utilization (cytopathic hypoxia), such as sepsis or cyanide toxicity
High SvO2 with concurrent lactic acidosis indicates cells cannot extract or use delivered oxygen, a hallmark of cytopathic hypoxia seen in distributive shock, sepsis, or mitochondrial poisoning.