A 50-year-old construction worker is evacuated by helicopter to the trauma center followin… — USMLE Step 2 CK

A 50-year-old construction worker is evacuated by helicopter to the trauma center following a localized industrial explosion. The patient weighs $80\text{ kg}$ . Paramedics report the incident occurred exactly $2\text{ hours}$ prior to arrival. Primary survey reveals a patent airway with no signs of inhalation injury, clear breath sounds bilaterally, and a heart rate of $115\text{ beats/min}$ . Secondary survey is notable for deep partial-thickness and full-thickness thermal burns covering the entirety of his posterior trunk (including buttocks), his entire left lower extremity, and his entire right upper extremity. Superficial (first-degree) burns are noted on his face but are not blistering. Large-bore intravenous access is established. The trauma team initiates fluid resuscitation using lactated Ringer solution according to current Advanced Trauma Life Support (ATLS) guidelines ( $2\text{ mL/kg/\%TBSA}$ for adult thermal burns).

What should be the initial rate of the fluid infusion (in $\text{mL/hr}$ ) programmed on the intravenous pump for the time remaining in the first 8-hour post-injury window?

Answer: 600 mL/hr

Answer

600

The correct calculation requires summing the TBSA (

18\%

posterior trunk +

18\%

left leg +

9\%

right arm =

45\%

), multiplying by

80\text{ kg}

and

2\text{ mL}

(totaling

7,200\text{ mL}

for 24 hours), dividing in half for the first 8 hours (

3,600\text{ mL}

), and dividing by the

6

hours remaining in that window (

3,600\text{ mL} / 6\text{ hr} = 600\text{ mL/hr}

Step-by-Step Solution

Calculate affected Total Body Surface Area (TBSA)

45\%

Using the Rule of Nines: Posterior trunk is

18\%

, left leg is

18\%

, and right arm is

9\%

. Superficial burns are not included in TBSA calculations for fluid resuscitation.

Calculate total 24-hour fluid requirement

7,200\text{ mL}

Formula:

2\text{ mL} \times 80\text{ kg} \times 45 = 7,200\text{ mL}

Determine fluid volume for the first 8 hours

3,600\text{ mL}

Half (

50\%

) of the total 24-hour volume is administered during the first 8 hours post-injury.

Calculate infusion rate for the remaining time in the first 8-hour window

600\text{ mL/hr}

The injury occurred

2

hours prior to arrival, leaving

6

hours (

8 - 2 = 6

) in the initial window. Rate =

3,600\text{ mL} / 6\text{ hr} = 600\text{ mL/hr}

Key Concept

Calculation of initial burn fluid resuscitation using the Rule of Nines, the ATLS modified formula (2 mL/kg/%TBSA for adult thermal burns), and adjusting the rate for pre-hospital time elapsed since the injury.

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