Oxygen delivery in anaemia — FRCA Primary MCQ

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EasyPhysiologyOxygen delivery in anaemiaFRCA Primary

A bleeding patient has normal SpO2 but lactate rises with haemoglobin 65 g L-1. What is the most likely explanation?

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Correct answer: D — Reduced haemoglobin lowers arterial oxygen content

Haemoglobin concentration is the dominant determinant of arterial oxygen content. Citrate binds ionised calcium is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Raised PaCO2 lowers alveolar oxygen tension is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Hypocapnia causes cerebral vasoconstriction is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Left ventricular coronary perfusion occurs mainly in diastole is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. In Primary FRCA physiology, the correct answer is usually the variable that best explains the observed change in the anaesthetised patient.

Reference: West's Respiratory Physiology; Ganong Review of Medical Physiology; Primary FRCA textbooks