The Broselow Pediatric Emergency Tape is one of the most recognizable tools in pediatric resuscitation: lay it alongside the child, read the color zone, and it hands you weight-based drug doses and equipment sizes in seconds. But the tape never measures weight — it measures length. That distinction matters the moment you already know the weight.
Length is a stand-in for weight
The tape's color zones are really weight bands. Length is just the fastest proxy for weight when a child can't be put on a scale — the coding toddler, the trauma bay, the field. So the organizing variable underneath every Broselow recommendation is an estimated weight. When you have an actual, measured weight, you can index the same equipment and dosing directly, skipping the estimation error baked into the length-to-weight step.
When you know the weight, use it
For anything driven by mass or tissue depth, a known weight is the better input. Intraosseous needle length is selected by weight and soft-tissue depth, not length — the Arrow EZ-IO uses the 15 mm needle from 3–39 kg and the 25 mm needle at 40 kg and up, in a child or an adult. Drug doses, fluid boluses, and defibrillation energy are all per-kilogram. Give them the real number when you have it.
Where length and weight diverge: body habitus
Length only predicts weight for an average body habitus. In an obese child, length under-estimates true weight, so a length-based tape under-doses — and the actual weight fixes that for resuscitation gear and dosing. But it cuts the other way for the airway: tube size, depth, and blade track age and length, so feeding raw weight to an airway estimate would over-size the tube in that same heavy child. The two error directions are opposite, which is why length-plus-habitus tools like the PAWPER tape were developed.
Weight-driven vs length/age-driven equipment
- Weight / tissue-driven — IO needle, vascular catheters, fluid and drug dosing, defibrillation energy: use the actual weight.
- Length / age-driven — ETT size and depth, laryngoscope blade, supraglottic airway: track age and length; don't oversize them from weight alone.
Where Master Anesthesia comes in
Master Anesthesia's Weight-Based Reference Card puts all of this one tap away: set the patient's weight (or age) and it sizes airway, vitals, access, labs, and body-weight values to that patient, and shows the sourced rationale — including the habitus caveat — behind every number.