Tuesday, May 15, 2007

Sudden Impact

There was a time when I watched TV occasionally. For some reason, the sight of David Letterman dropping a watermelon from a building made me smile. Plus, it's a great physics lesson --- terminal velocity, force of impact, and all that stuff I once knew quite well, but which has been relegated to a few rarely firing synapses in the recesses of my brain (I need to conserve the other space to remember the words to songs I learned in high school, along with every line from Monty Python and the Holy Grail). It also brings to mind the old saying "The bigger they come, the harder they fall."

Bigger = Harder Fall. Something to think about when part of your job involves taking care of trauma victims.

The overwhelming majority of trauma patients I see have suffered some sort of blunt trauma --- most frequently a motor vehicle accident (MVA). The opportunity to understand the basic principles of physics are always on display in MVAs --- the forces that affect the vehicles and their occupants can always be calculated....
(Impulse of force = Average force x change in time = mass x change in velocity; see, Fr. Deeves did teach me something)

Of course, one important component of these calculations is mass, and how it relates to momentum (momentum = mass x velocity). Any first grade boy can explain it to you, as he understands that dropping a brick his sister hurts more than dropping a Nerf ball. And any redneck knows that an F250 will plow over a Prius on the highway with ease.

But what happens the occupants of the F250 and Prius are a bit heftier than standard crash test dummies? Well, when you look at the mass part of the equation above, their increased mass generates a greater impulse of force ---- resulting in more bodily harm. This is the subject of a study published in this month's JACS : Body Mass Index and Outcomes in Critically Injured Blunt Trauma Patients: Weighing the Impact (gotta love that pun). The authors retrospectively reviewed the course of 1,543 patients with blunt trauma and an ISS (injury severity score) of 16 or greater. Out of that group, 30% were obese or morbidly obese; 24% had a BMI between 30-30.9, and 6% had a BMI of 40 or greater. Their findings included:

[1]A rising BMI is directly related to increases in hospital and ICU lengths of stay
>>morbidly obese patients had an LOS nearly twice that of patients with a normal BMI
>>ICU LOS more than doubled
[2]Pulmonary complications were more severe for those with obesity as well
>>they required longer ventilator support
>>ARDS, acute respiratory failure, and pneumonia were more prevalent in those with a higher BMI
[3]Just to add insult to injury, acute renal failure, MSOF, UTI, DVT, and decubitus ulcer formation were also seen more commonly in the morbidly obese blunt trauma patients.
[4]Interestingly, and seemingly incongruously, morbid obesity was not associated with a statistically significant increase in mortality.

So, what's the upshot? Elementary, my dear Watson! The larger the person, the more complicated their post-traumatic injury course. All of the issues that affect the morbidly obese patient in other emergency settings --- sleep apnea, diabetes, poor pulmonary toilet, increased risk for DVT and cardiac complications, etc. --- come into full bloom when they are impacted with an acute decelerating blunt trauma. And, although this article did not address it specifically, the larger the person, the greater the decelerating force they will experience, resulting in a higher risk for injury.

Just a little food for thought. Chew it over. Ruminate on it. Digest it. Just don't add it to your regular diet -- and skip the Cheetos too!