Blinded Enlightened by Science!
In the post, Reading a Map, we found our hero DTs attempting to yet again simplify EMS math, as he has done so successfully in the past. And lo! it seemed he had again succeeded!
Indeed. Behold the hideous formula for mean arterial pressure,
((Diastolic BP * 2) + Systolic BP) / 3
Too horrible for words! Too grotesque for thought! And too much damned work for 2 am. With parry and jab, the plucky DTs vanquished the offending formula with a simple,
(Systolic / 10) + Diastolic
Yes, as flash bulbs popped, our hero stood proudly upon the podium and explained his conquest, with concrete examples – and even a table! Yet even as he spoke, the silhouette of the beastly equation (quite undead) rose stealthily in the background to the horrified gasps of the press…
In other words, it seems that simplistic equation don’t work so well.
The two methods agree completely when (Systolic / Diastolic) = 1.43. For instance, 120/84 results in MAP=96 using either formula. 80/56 results in MAP=64, again using either formula.
The examples in the original post, plucked randomly from mine own head, all just happened to work out to within a few mmHg, making it an attractive theory. Without peer review, my team published (I count my hands as two separate co-workers, while typing, to help spread the blame).
Further field research blew the thing apart. A simple 120/61 provides traditional MAP=81, DTsMAP=73 – too much error to ignore. As did 137/76, MAP=96 and DTsMAP=90.
A random number generator was quickly pressed into service – with rules (eg Systolic must always be greater than diastolic, etc.) The results did not bear out the usefulness of the formula.
And THIS, folks, is why we have to relearn CPR every couple of years, always with new rules; and why ET tubes in the field are losing support, and a host of other data-driven changes we see all the time in the field.
Cuz it’s Science!