Explanation:

The definition of paediatric massive transfusion (PMT) differs from adult standards due to variations in total blood volume (TBV) across different paediatric age groups and weights. Because a fixed volume threshold is clinically inappropriate for children and neonates, current literature establishes weight-relative and dynamic definitions to guide timely clinical intervention.
In their comprehensive review, Diab, Wong, and Luban (2013) address the lack of a universally accepted paediatric standard and propose a highly influential dynamic definition. They recommend defining PMT as the transfusion of greater than 50% of a patient's TBV within 3 hours, a total transfusion exceeding 100% of TBV within 24 hours, or active transfusion support to address an ongoing blood loss rate of more than 10% of TBV per minute. This approach shifts the focus toward the physiological rate of haemorrhage and immediate resuscitation needs rather than delayed, static retrospective volumes.
Aligning with this dynamic framework, Blain and Paterson emphasize the clinical importance of monitoring blood loss relative to individual patient size. They reiterate that PMT is most effectively defined by red blood cell administration mirroring these precise thresholds: 50% TBV over 3 hours, 100% TBV over 24 hours, or ongoing replacement matching rapid exsanguination at 10% TBV per minute.
Conversely, newer retrospective trauma registries offer simplified, weight-based triggers. As explored by Neff et al. (2021), a static threshold of 40 mL/kg of total blood products administered within the first 24 hours serves as a reliable marker to identify severely injured paediatric patients at high risk for early mortality.

References
Blain S, Paterson N Paediatric massive transfusion BJA Education, 16, 269-275
Lucas P. Neff, Michael Aaron Beckwith, Robert T. Russell, Jeremy W. Cannon, A; Philip C. Spinella, Clinics in Laboratory Medicine, March 01, 2021, Volume 41, Issue 1, Pages 35-49
Diab YA, Wong EC, Luban NL. Massive transfusion in children and neonates. British journal of haematology. 2013 Apr;161(1):15-26.