I needed a litre of saline during a field exercise in heavy gear.

May 23, 2019 2:17 PM

I recently chose to fall out to the medical tent; and was given two 0.5L bags of saline; how badly dehydrated was I (185lbs, male, over 45, regular exercise and fitness)?

I recently chose to fall out to the medical tent; and was given two 0.5L bags of saline.
I'm around 185lbs, over 45; above average health and conditioning; weather was around 85 degrees full sun and at 1,000' altitude.
I was in standard BDUs; also wearing full MOPP gear; helmet, a MTV tactical vest with side and front SAPI plates; wearing a M50 gas mask; and carrying my M4 rifle.
Can't say I crashed hard; or even crashed. I felt a little dizzy; like a person might be during a strenuous uphill bike ride; a long swim; or after climbing several flights of stairs.
My t-shirt was totally soaked through; I think I over exerted more than actually dehydrated.
All turned out well; no harm done. I mean; I could have kept going; but well; honestly; I didn't want to perhaps actually fall down too too far from home base so to speak.

Question is; and I can't find it on the 'net; is how bad off was I? How far dehydrated or into heat exhaustion is a person at to take on a litre of saline? What kind of a recovery time should a person have after needing a litre of saline? (I was benched for 48 hours - as before; I know when to say when).
Thanks!

posted by anonymous to Health & Fitness (6 answers total)

Unless you hadn't had any water in the 24 hours leading up to your exercise, I'd guess you probably weren't that dehydrated. I had a 72 hour bout in the field with dysentery once where I couldn't get fluids to stay in for the full 3 days and ended up on an IV to onboard a liter of saline.

You may have noticed the slight rush of feeling better as you took your saline on - for me it felt like life coursing back into my body. The IV is just a faster way to re-hydrate your entire system than actually drinking the same amount of fluids - but at the end of the day, a liter piped in via esophagus = a liter piped in via hypodermic (the latter being slightly more salty, rough equivalent of sweat or tears).

Regarding recovery time, I assume your medics would error on the side of caution but I'm guessing it would be hours rather than days to be GTG.
posted by allkindsoftime at 2:39 PM on May 23, 2019

A liter of NS is really not that much, assuming your kidneys are in good shape. Baseline insensible water loss (basically breathing) is about 30 mL/kg/day; for you that is about 2.5 L/day.

If you want to do the math, this maintenance fluid calculator recommends ~2.8L maintenance fluids per day, which makes up for the insensible loss as well as peeing and pooping. If you are in a hot environment and exerting yourself, as you describe, I'd about double that, say 5L requirement.

So yeah, you don't have to feel dehydrated, or even be dehydrated in a clinical sense to be able to tank up from a liter, or even two, or NS.
posted by basalganglia at 3:13 PM on May 23, 2019 [5 favorites]

I've had four bags of saline in one night and still not had enough fluid built up to pee.
posted by The Underpants Monster at 5:08 PM on May 23, 2019

+1 for probably not that dehydrated, probably would have been just fine sitting in the shade and sipping from a bottle. Given how much people sweat in MOPP gear, and since it sounds like this was an exercise with good supply, I wouldn't be surprised if the medics gave IV saline freely.
posted by meaty shoe puppet at 6:58 PM on May 23, 2019

A liter is a kilo, or about 1.2 percent of your bodyweight. This article says "The standard rule of thumb is that losing 2 percent of your starting weight signals trouble," but then reviews research that suggests that is overstated, and that in many cases you are fine losing 4-6 percent of your weight, and some people are OK losing 10 percent during prolonged exercise. But the conclusion is to drink when thirsty, and of course pay attention to how you are actually feeling, rather than any specific numbers.
posted by Mr.Know-it-some at 7:22 PM on May 23, 2019

Military doc (albeit OB/gyn) here. Sounds like you had a heat casualty of some sort rather than dehydration. Everyone gets a liter of saline from their medics because that’s what medics are trained to do.

Read Endure:Mind, Body and the curiously elastic limits of human performance by Alex Hutchinson for a great deep dive into the differences as well as other intriguing studies.
posted by eglenner at 10:13 PM on May 23, 2019 [4 favorites]