Insensible losses from lungs and skin in a 100 kg afebrile person are approximately how many milliliters per day?

• A. 1000 mL/day
• B. 500 mL/day
• C. 800 mL/day
• D. 1200 mL/day

Answer: (A)

Insensible losses are the water lost without being noticed, mainly through the skin by evaporation and through the lungs as water vapor in exhaled air. In a healthy, resting adult around 100 kg, these losses add up to about a liter per day. The skin contributes the larger share, with the lungs adding the rest, giving a standard maintenance estimate of roughly 1000 mL/day. While activity, temperature, humidity, and breathing rate can nudge this up or down, 1 liter per day is the typical figure used in fluid planning. The other options fall outside this common baseline: they are noticeably lower or higher than the expected total.