A 70 kg patient undergoing elective colectomy receives 6 units of packed red cells over 4 hours due to intraoperative haemorrhage. The most important physiological effect of transfusing large volumes of stored packed red cells (>14 days storage) is:
- A Hypernatraemia due to sodium-rich preservative solutions
- B Respiratory alkalosis from citrate metabolism
- C Tissue hypoxia despite adequate haemoglobin due to reduced 2,3-DPG and leftward shift of the oxygen-dissociation curve ✓
- D Hypermagnesaemia causing cardiac arrhythmias
Correct answer: C. Tissue hypoxia despite adequate haemoglobin due to reduced 2,3-DPG and leftward shift of the oxygen-dissociation curve
Explanation
Stored packed red cells progressively lose 2,3-diphosphoglycerate (2,3-DPG) over time. Reduced 2,3-DPG increases haemoglobin's oxygen affinity, shifting the oxygen-dissociation curve leftward — haemoglobin binds oxygen tightly and releases less to tissues. This can cause tissue hypoxia despite a normal haemoglobin level. Other storage lesion effects include hyperkalaemia (not hyponatraemia), decreased NO bioavailability, and microaggregate formation. Citrate causes hypocalcaemia (not alkalosis) when metabolised incompletely in massive transfusion.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
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