How do we assess the surface area?
There’s lots of different ways of doing it.
One commonly used one is the rule of nines which is really only valid for adults
and that basically says that the head is 9%,
the front of the torso is 9, the back of the torso’s another 9.
The front of the abdomen’s 9, the back of the lower back is another 9.
Each leg is 18, each arm is 9, it all adds up to a hundred
but it’s actually not terribly reliable even though it is easy to remember
especially at extremes of weight.
So very thin patients or very obese patients,
this doesn’t really give you a good accurate assessment
and there is a pediatric version available
but because these proportions are so growth dependent,
it’s not actually as accurate as we might hope.
So a little bit more sophisticated approach is the Lund-Browder Chart.
This is not one that you’re gonna be able to memorize.
So you would definitely have to pull this up
and refer to it while you’re calculating surface area.
It’s definitely more complex than the rule of nines
but it does address issues of relative growth for pediatric patients.
So it shows you visually how the body is broken down
and then, it actually provides you with a chart based on the patient’s age that tells you,
yeah, if you’ve got half the head involved and it’s a baby, it’s gonna be 9.5%,
whereas if it’s a 15 year old, it’s gonna be 4.5%.
So it addresses the relative sizes of different body parts and different age ranges,
and allows you to more accurately calculate the total percent burned.
The most commonly used one is the Parkland formula.
It’s based on lactated ringers and the calculation is 4cc per kilo per percent surface area burned.
You give half of that in the first 8 hours,
and then, the other half over the next 16 hours.
Now, there have been a lot of studies looking at the Parkland formula
and it actually results in over-resuscitation in a significant percentage of patients.
So you wanna be a little bit careful and make sure that you’re monitoring
and titrating the patient’s fluid intake to their urine output.
A lot of times, people use the Modified Brooke formula
which as you can see, is a little bit less aggressive.
It’s 2cc per kilo per percent burned for adults and 3% for children.
So it’s a little bit less than what Parkland gives
but in either case again, you wanna make sure that you’re carefully monitoring urine output.
We expect half a cc per kilo per hour for adults
and between half a cc and one cc per kilo per hour for children.
If you’re getting significantly more urine output than that,
you’re probably over resuscitating and wanna back off on your fluids a little bit.
So just adjust it so that you maintain the expected urine output over time.
So here’s an example just to go through the calculations for you.
We’ve got a 29-year-old man who got drunk and fell into a campfire.
He’s got burns over his entire anterior chest and abdomen,
as well as his bilateral thighs, which gives us a roughly 27% total body surface area burn.
His weight is 80 kilos.
So by the Parkland formula, 4 cc per kilo times 80 kilos, times 27% burned
gives us 8640 cc of lactated ringers.
Now, Parkland tells us to divide that in half.
We’re gonna give half of that in the first 8 hours.
So 4320 cc over 8 hours which is 540 cc an hour.
That’s a lot of fluid, right?
That’s more than half a liter of fluid per hour.
So it’s a pretty significant volume.
The remainder, we’re gonna give in the next 16 hours
and that’s gonna take us down to 270 cc per hour after the first 8 hours of resuscitation.
So let’s say our patient has 300 cc of urine output in a 2-hour period.
Well, he’s an 80 kilo guy, so we expect him to have half a cc per kilo per hour,
or about 40 cc an hour.
He’s had 300 cc in 2 hours which is more than three times what we’d expect for him.
So this is a situation where we would wanna say,
okay, we’ve gotten a little bit overzealous with our fluid.
Let’s back it down.
Let’s maybe cut it in half and reassess the urine output in a couple of hours
to keep ourselves on track.