The main character of the story was created by nanites/(micro technology). Because of this trillions of nanites are in her body making her memory more efficient, reasoning skills sharper, and healing very fast (0.2 - 5 minutes) normally. She becomes a police detective because she thinks she is a good fit.

During one arrest she gets shot in the heart by a sniper. making her start bleed out. because the heart was just shot and the fastest way (but not the only way), for the nanites to heal her heart is through going with the blood stream it world take around 10 minutes before the gun hole passing through her to be healed. The nanites know this because they are all through out her body. They want to keep her alive, with the least amount of brain damage as possible. What would be the a beneficial strategy for the nanites to do with her brain while healing her heart?

Things to know are the police around her first detect no pulse at first, the bullet went right through her body damaging the wall behind her, and she seems dead or unconscious for the first 8 minutes.

  • $\begingroup$ Link up and use peristalsis to move blood into the brain bypassing the heart? Though after 8 mins it might be too late? $\endgroup$
    – Richard
    Commented Mar 24, 2022 at 1:05
  • $\begingroup$ @Richard I think that might be a good strategy, she is unconscious and not really dead for the 8 minutes, but she does appear dead because she doesn't have a pulse. $\endgroup$
    – intro
    Commented Mar 24, 2022 at 1:13
  • $\begingroup$ If i remember correctly there is a good scene in Ben Bova's Moonwar that has a good description of nanites desperately trying to save their host, in this case when there is no oxygen, might be worth a read $\endgroup$
    – mgh42
    Commented Mar 24, 2022 at 3:00
  • $\begingroup$ Hello @intro, welcome to Worldbuilding. For future reference, please avoid the use of superlatives like "best" and "worst" because they're hugely dependent on your story (which we don't help with, see the help center). Stick with asking questions like, "What strategy could nanites adopt to protect someone's brain from damage while repairing the heart?" My point is, superlatives are subjective unless you specifically and in great detail explain what conditions represent "best." If you leave those conditions up to respondents, your question is subject to closure. $\endgroup$
    – JBH
    Commented Mar 24, 2022 at 4:28
  • $\begingroup$ @JoinJBHonCodidact I understand I hopeful fixed the wording of my question. If there are any other suggestions I will try to fix them. $\endgroup$
    – intro
    Commented Mar 24, 2022 at 11:17

10 Answers 10


Others have mentioned my first thought, which was to use the nanites to transport oxygen directly to the brain.

Depending on how magical the nanites are another option might be to use partial or complete stasis to ensure that the brain needs less (or no) oxygen. If you get someone cold enough they can be revived after a surprisingly long time. While cold is one option, your nanites might also be able to go in and directly decrease the brain activity, thus reducing the need for oxygen (seeing as how they already seem to finely interact with the brain for memory and reasoning). If we posit that the brain is "just" a bunch of biochemistry and electrical impulses, then sufficiently advanced nanites might be able to reduce it to a lump of inert matter for a while (thus preventing it from hurting itself through lack of oxygen), and then kickstart it once the heart is repaired.

  • $\begingroup$ Indeed, I remember a story in which these sorts of nanites were commonplace, and in case of severe trauma, this is exactly what they did. You could literally lose your head and survive (growing back a new body takes a while). Whether or not that sort of brain-stasis is realistic is another question. (Personally, I do believe in souls, but there's evidence that they can "come back" if the body gets sufficiently fixed, so I wouldn't see that as an issue here even if "consciousness" transcends the mere chemistry of the brain. Your character might have an OOBE though!) $\endgroup$
    – Matthew
    Commented Mar 30, 2022 at 15:45

The nanites have to essentially replace the functions of the cardiovascular system to preserve the brain, ignore everything else in the body.

They would need to keep the blood in the head circulating while not going to the rest of the body, and they would need to find a way to oxygenate the blood.

If they are able to get oxygen directly from the mouth/nose and directly feed that into the red blood cells, or maybe breaking down other elements in the body to produce oxygen whilst creating a pumping effect to keep things circulating then brain-death will not occur and they have a chance to fix the heart a bit slower.

Then after your 10 minutes are up when the nanites are able to restore the heart, then they will be able to undo the emergency measures and restart the heart allowing detection of the heart beat.

The only real limitation this kind of magical nanites has is raw materials, so you could describe them scavenging her fat stores and breaking down the molecules into Carbon, Hydrogen and Oxygen, then when she does wake up she looks like she is close to starvation and her first words are asking for a burger


She's Dead, Jim

Sorry, but even nanites can't help her out of this situation. You specify two conditions:

  • shot in the heart by a sniper --- this means the likelihood of a botched job, wherein the victim survives, is very low
  • making her start bleed out --- "bleeding out" is a quasi technical term that means excessive damage causing massive and rapid loss of blood

Just before the ventricles contract, each of them (2) holds about 100 to 150cc of blood. A typical ejection fraction, the amount of blood expelled with each contraction, is around 55 or 60%.

Worst case scenario: the sniper hits dead center through both ventricles. She's now got two big holes that will drain all the blood into the pericardial sac and the thoracic cavity in general and because of the pressure gradient, will spew blood through the external wounds as well. Very little will actually get into the aorta. Her blood pressure will essentially bottom out.

Her heart rate is elevated from the stress and excitement of the chase plus all the adrenalin she's got sloshing around. She'll drain about 150 to 200 cc of blood with each beat. Officers on the chase (or obstacle course) can reach heart rates of 150 to 180 bpm. 150 cc x 150 beats is 22 litres. She only started with about 5 litres.

The maths are against her when her heart's been essentially shredded.

Best case scenario: the sniper is off form tonight, perhaps having drunk a cup of coffee last month, and sends the bullet through the right ventricle only. In this case, her left ventricle is still sending blood out to the body, and thus the brain. However, nothing of note is getting to the lungs, so no oxygenation is taking place.

Pressure still drops precipitously and blood loss is still massive. Even with the reduced loss of blood, the maths are still against her.

For consideration: If we give her 1 trillion nanites per litre of blood, those nanites will really do her no real good. The vascular system is very high pressure. If you cut a vein, the blood kind of meanders out of the vessel and pools very nicely. If you cut an artery, the blood literally spurts out and can literally be shot 10 feet or more from the body. What this means is that the vast majority of the nanites in her blood will be all over the outside of her body, trapped within her thoracic cavity and, really, just about everywhere except where they need to be. The only nanites that can be of any real help are those located within the cardiac tissues where the injury happens.

Conclusion: I think your scenario is too little too late. I think the best outcome for her will be that she ends up with nicely healed heart after 10 minutes, but no blood for it to pump.

I think you can get around this by specifying a less fatal scenario. First, make the shooter someone other than a sniper. Maybe a hunter or a criminal who is an avid target shooter. This would allow the likelihood of a non-fatal GSW to be the result. Maybe nick her superior vena cava or something like that. The SVC shunts blood from the head to the right heart where it can be sent to the lungs for oxygenation. The key here is that blood from the body, that flows up the IVC will outweigh the blood lost through the SVC. The nanites will have a better chance at making a repair: the pressure is much lower in the venous system and your MC will lose less blood overall and repairing a vein wall is much less difficult than repairing a heart wall!


Nanite Scab

enter image description here

This is called a scab. It is a short-term measure that your body takes when it gets a hole, to stop your insides becoming your outsides. The blood near the entrance to the hole hardens into a lump that plugs the hole.

The scab can form in moments. It stays on until the hole is healed. This might take months. When the hole is fixed the scab drops off, gets reabsorbed, or eaten.

Your nanites know how to make scabs. It might take them 10 minutes to fill up the hole in the heart with healthy heart cells. But it only takes 30 seconds for them to form up like these guys

enter image description here

and make a film of nanites over the hole.

The film knows how to expand and contract as the heart pumps. That means the heart can continue pumping as the nanites get to work on the brain.

Bonus points if the film is made by forming a mesh over the hole and encouraging the blood cells to clot to fill up the mesh.

When the brain is fixed, the nanites redirect to replace the film with healthy cells.


Cybernetic nanotech is just biotech with little robots

In contradiction to nearly every other post, I suggest that they would shut brain cells down and attempt to put the brain into an alternative survival mode rather than rushing oxygen to it.

The brain and nervous system is more sensitive than other tissues, they could safely ignore most of the rest of the body for a few minutes.

They could firstly reduce the rate of metabolism as low as possible to preserve what little oxygen remains in the environment.

Then they could begin extracting oxygen from the body's environment, for example from free range co2, or from other less important more replaceable cells

To facilitate life support the nanites can enter the brain cells and perform cellular functions. I would consider the possibility that they might be able to provide an alternative glycolysis pathway which could fuel brain cells by providing ATP without consuming oxygen. If they are an integrated part of the body then why wouldn't they include some such handy biotech enhancements? You could even breathe underwater with the right nanomachinery.

Then they can block say the Bcl2 / cytochrome c / CASP-9 apoptosis pathway (https://pubmed.ncbi.nlm.nih.gov/12370489/) to prevent cell death by apoptosis. This is the primary mode of cell death from oxygen deprivation and it could be blocked with nanomachinery which inhibits the bcl2 at the top of the chain or anything, anywhere further down the chain. As well as blocking signals by absorbing signalling molecules, they could also manufacture artificial proteins which target the cytochrome-c / CASP-9 / etc gene and prevent it's expression.

Actually why wouldn't cybernetic nanites just have their own transcriptase equivalent, their own ribosome equivalent, and a copy of the host's DNA which they could modify at will? The nanite or multiple nanites could enter a cell and become an artificial organelle, acting like a secondary nucleus or mitochondria - directing cell orchestration. It becomes a question of how clever your nanites are. They might even be able to stave off eventual cell necrosis by blocking necrosis signalling pathways and killing anything like bacteria / macrophages / etc which threatened to destroy the neurons. Without anything to cause decay and with all auto destruct pathways blocked, decay will be very slow. DNA and especially RNA do degrade on their own but as long as the nanite organelle is functional it could repair this damage as well.

Anyway if all of these things are in play then they have until

1: They run out of oxygen for artificially-slowed metabolism

2: They run out of things to extract oxygen from

3: They run out of things to use for anaerobic energy production

4: The cell eventually begins to die of necrosis / the nanites themselves run out of energy for cell life support orchestration.

This could potentially buy hours, maybe even days. Hell maybe the nanites could completely re wire the brain's metabolic pathways and bring it back online using some esoteric method - once you have custom cybernetic nucleotide & protein production then with enough intelligence you can completely re write the code for life.

You'd have to make sure the cells don't self destruct from an overabundance of oxygen species and ATP + whatever damage was sustained during the stasis, once they return to normal metabolism. This could just be a matter of continuing to artificially inhibit cell metabolism and bringing it up slowly, using the energy to power the nanites and gingerly restarting internal cell processes one by one whilst making sure the cell doesn't immediately panic and go into apoptosis mode.

Maybe she stays in a coma for a little while after the heart starts beating again & the nanites activate the brain once the cells are functioning independently again.


Reduce metabolism and bock the arteries

A bullet through the heart gives a great many uncertainties. There's two holes that need to be patched if through and through, or a single hole and a bullet to deal with, which is worse. Target what you can control. First block the arteries to the heart and veins to the rest of the damage. The blood vessels are already known, most smaller than the bullet holes and can be constricted to become even smaller. This requires less nanites to block the flow. Replacing blood is easy, but takes time. Blocking further outflow will make sure there's enough blood left when the holes are fixed. Together with only passing the nanites to repair the body they shiuld be the first measure. There will be plenty of blood visible for onlookers to shock them.

Next is reducing metabolism. Brain cells have great difficulty to survive without this constant supply. Most important is oxygen.

We can see from drowning victims that they have the least damage and most chance to survive if they are in cold water. This slows metabolism and increases the chances to survive. In the most extreme cases a 3 year old girl was resuscitated after 50 minutes and a 32 year old woman after 80 minutes without brain damage (I remember 20 minutes, but google doesn't lie I guess). 'You're not dead until you're warm and dead' is a saying I regularly head in the hospital for this reason.

Finally it can be trained, like David Blain did. 17 minutes of slowing his metabolism to a crawl and stay under water. This shows that decreasing metabolism might be enough under 'normal' circumstances to survive past the 10 minute mark.

The nanites can aggressively decrease metabolism and cool down the body. This can increase the time to survive way past the 10 minute mark. Include the nanites working to stop and reverse damage and there should be little problem to patch the hole and survive.

Slowly increase the temperature and reinstate the heartbeat when the most vital repairs have been done. Again, this van probably be done faster with the magic nanites, but best to follow the protocols of the hospitals. Carefully heating people back up and resuscitate them during to get them back with little to no damage.


Electric respiration

This is sort of my go-to for space-adapted humans, but it works here somewhat in reverse. Instead of sending glucose and oxygen via blood and astrocytes to the neurons, the body simply works as a fuel cell, converting O2 to H2O by adding electrons to the oxygen near the lungs, and converting glucose to CO2 at the intestine by a more complex set of reactions that involve repeated oxidation (removal of electrons). The voltage difference between these electrodes is now used to directly pump protons, maintaining the proton gradient for ATP production in each mitochondrion of the neurons of the brain and other cells. The system can also make NADH as needed and so on; nanotech provides a great deal of response to each cell. There is no metabolic need for circulation, though subjective considerations and endocrine functions might still prefer it to continue. The loss of blood is no great problem.

This set-up is absolutely standard of care for any modern clinic, but it does have certain issues in the near future. Just like ordinary respiration, the system can only maintain function so long without external food. Over time the user's brain may need to reduce some functions while focusing on survival needs such as food acquisition. It has also been noted that the nanites have a tendency to spread from exposed dentine surfaces, these being treated by the system as broken bones. The privacy protections of the system, using hard encryption, and its vulnerability to hostile hacks nonetheless raise some additional issues. In short, there is a certain risk that she'll start a zombie plague if she isn't given treatment promptly. But the odds of that are very remote, aren't they?


Focus as many nanites as necessary towards extracting oxygen to send to the brain. Any spare nanites should be used to stop external bleeding. Once external bleeding has been dealt with, internal repairs are the next priority. Fix the heart to start oxygen flowing naturally again, freeing up the nanites that had that job. Begin fixing other systems. That's the basic strategy I would take given that little time, though who knows? Nanites can think faster than I can, after all.


Around the heart, seal everything up.

They need to stop her going into hypotension. If she doesn't have enough blood she won't be able to maintain bodily functions, and unless they have magic, they won't be able to do much. Nanobots around the skin, arteries, veins and capillaries will need to seal off damaged tissue as quickly as possible to keep as much blood inside as possible.

Begin breaking down fat reserves and muscles to repair damaged tissue and replace water.

You're gonna need a lot of resources and extra fluid to keep blood pressure up and the body well supplied for repair. Start breaking down surplus material to repair the damage.

Minimize metabolism everywhere as much as possible.

They're reliant on what they have to keep them alive. They should slow down metabolism as much as possible, putting her into a hibernation state where cells use less scarce energy and oxygen up. Cut off blood flow to the digestive system, the lungs, the heart, anything non essential. Most is easy to repair, but keep some resources for the nerves since they're more fiddly any anything essential.

Use muscular contractions and arterial squeezing to move blood.

It's not as good as a heart, but muscular contractions is how veins move blood. They can slowly move blood around to the brain. She'll look a bit twitchy, but dead people can twitch.

Purge the blood of toxins, and convert carbon dioxide to oxygen.

This will burn a lot of the fat and muscle reserve energy, but it'll let them keep clotting factors, bacteria, dying tissue, and lack of oxygen kill the brain. They'll need to filter the blood to keep everything around.

Cut blood to non essential brain regions.

She needs her memory and anything that maintains personality. A lot of the brain just keeps the body functional and can be replaced with no loss of intelligence. Cut blood to non essential functions. The nanites can take over, and regrow brain tissue from DNA if needed.


When the brain suffers damage due to "lack of oxygen" it isn't the lack of oxygen that causes the trouble, but when oxygen finally floods back in after being absent for too long. Oxygen itself is a rather caustic chemical, after all, and its presence alongside the other substances oxygen-deprived neurons start making is just a recipe for grief. I'm far from an expert on ischemia, of course, and the medical science of this is still developing, but several experiments these last few decades have shed some light on the process itself.

Particularly with those that tend to be labeled "suspended animation" by fluff science journalists. Some of these have to do with removing a body's blood supply entirely and quickly, and replacing it with a cold saline solution to chill (but not freeze) every tissue simultaneously. Supposedly pigs have had this treatment, been on ice for several hours with no brain damage. The idea being to make it less of a mad dash for surgery, because surgeons can only act so quickly.

Other experiments have to do with using sulfur compounds (hydrogen sulfide?) to induce a sort of hibernation response. Apparently, this works poorly in the largest organisms (basically anything larger than a rat), because they have trouble diffusing it throughout tissues quickly in anything too big. The chemistry of those attempts confuses me, to be honest, but is connected to the same mechanisms we're discussing... disrupting those chemicals the body produces in the absence of oxygen, that when rapidly reintroduced to oxygen causes bad stuff to happen and cells to die.

Your nanites don't have to be particularly sophisticated... it might be enough to mop up those chemicals, or even to slow down the flood of oxygen until the body itself can do so.


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