In the previous issue of Critical Care, Vermeulen
Windsant and colleagues demonstrate that transfusion
of packed red cells is associated with a transient
increase in plasma free haemoglobin and scavenging
of nitric oxide in vitro. They also demonstrate that older
units of blood have more free haemoglobin in their
supernatants. Whether the administration of older
stored blood results in adverse clinical outcomes is a
topical clinical question. The present study proposes a
mechanism for transfusion-related harm but also has
implications for patients who have other sources of
free haemoglobin in their circulation.