[RPG] Are there any official rules for sharing a held breath

breathingdnd-5e

In many movies, there are dramatic scenes where one victim is trapped underwater and another is responsible for giving them air.

Are there any official rules for those dramatic "rescue breath" moments?

We are writing an adventure where PCs are escaping a collapsing cavern underwater. PCs can get trapped underwater by boulders as they try to escape. PCs can help each other while keeping track of their oxygen reserves.

The challenge we have discovered there is a large gap between characters with high Constitution who can last for dozens of rounds underwater – and the weakest PCs who die in just 6 rounds: an almost 10x difference. Additionally, there seems nothing the long-lasting PCs can do to help the short-lasting PCs. Ideally, we are hoping to find a rules mechanic where one PC can help another PC last longer underwater – such as sharing some of their breath (i.e. like we see in movies) and triaging who they can save while balancing it against their own chances of survival as well.

Here is the table of breath holding we created from the rules:

PCs can hold their breath for a number of minutes equal to 1 + their
Constitution modifier (minimum of 30 seconds). Once choking, a PC
survives a number of rounds equal to their Constitution modifier again
then drop to zero hit points the next round.

$$
\textbf{Breath Holding Table} \\
\begin{array}{r|l|l}
\text{Con modifier} & \text{Seconds of breath} & \text{Rounds of breath until 0 hit points} \\
\hline
\text{-4 to -1} & \text{36 secs} & \text{6} \\
\text{0} & \text{66 secs} & \text{11} \\
\text{+1} & \text{132 secs} & \text{22} \\
\text{+2} & \text{198 secs} & \text{33} \\
\text{+3} & \text{264 secs} & \text{44} \\
\text{+4} & \text{330 secs} & \text{55} \\
\end{array}
$$

From this, it is clear that a PC with high Constitution has substantial extra time from a single breath to survive. Are there any rules for PCs blowing air into the mouth of another PC to prevent them from drowning? For example, could a PC give half of their breath to another PC – thus perhaps extending their time by half again?

Note regarding medical viability from comments: This is, of course, how CPR works as well. The air we breath in is 20% oxygen. The air we breath out is 15% oxygen. Hemoglobin is unusually effective at extracting additional oxygen.

Best Answer

No Official Rules Exist, however...

The answer is probably "No." While D&D Science! doesn't exist in the same way that Real World Science! exists, some things inherently have to stay the same in order for there to be any basis in reality for players to find a foothold in the game.

For example, the maximum time you can hold your breath in D&D without starting to suffocate is 1 + your Constitution modifier, which is capped at +5. This means you can hold your breath for up to 6 minutes.

A creature can hold its breath for a number of minutes equal to 1 + its Constitution modifier (minimum of 30 seconds).

After that, you have a number of rounds equal to your CON modifier, still capped at +5, meaning the maximum time you have remaining (excluding Death Saves) is 30 seconds before it is officially dying.

$$5 rounds * 6 seconds/round = 30 seconds$$

When a creature runs out of breath or is choking, it can survive for a number of rounds equal to its Constitution modifier (minimum of 1 round). At the start of its next turn, it drops to 0 hit points and is dying, and it can't regain hit points or be stabilized until it can breathe again.

This means that, total, one can hold one's breath for 6.5 minutes before dying.

Now, "coincidentally", the longest possible time one can go without oxygen before the brain begins to irreparably damage is ~5-6 minutes. In other words, D&D is actually pretty faithful to science here.

Now, how does this tie-in to the question?

A Typical Breath consumes about 5% of the total oxygen in the volume of air inhaled. This is why one can breath into and out of a bag, even a plastic one, and not immediately die (well, unless one gets the thing lodged in one's throat).

However, when you hold your breath, your body starts using much more oxygen out of that breath simply because the body is attempting to maximize the available oxygen out of that volume.

In fact, a measurable increase in used oxygen is found even when you only slow your breathing down and don't completely hold it. While I can't find any official figures for the amount of oxygen used, that NCBI paper found close-to a 10% increase in blood-oxygenation levels when breathing was slowed to 6 breaths per minute, or one breath every ten seconds. And, since matter can't be created nor destroyed (aside from magic quantum physics, but even then, energy is conserved), that means that that extra 10% Sp02 is coming out of the air being inhaled.

Even without this, two creatures (assuming both of the same, size, stats, and metabolic requirements) sharing a breath does not increase the effective amount of oxygen.

  • At best, the ratio of consumption increases exactly how the volume increases, so twice the air is available, but consumed at twice the rate. Therefore, no change.
  • In the ideal realistic scenario, some air is lost as the two creatures attempt to align their respiratory orifices to each other to share this breath, meaning there is less than twice the oxygen but still twice the consumption.
  • In the worst realistic scenario, one of the pair (or both) loses their hold on their breath and vents pretty-much all of it, meaning that there is roughly the same amount of air (or none) and still twice the consumption, meaning you have about half (or none) of the survival time.

So, overall, no positive change can result.

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