Cold Comfort
A history of the Cryonics Portable Ice Bath (PIB)
Rapid cooling of a cryonics patient should begin as soon as possible after legal death is pronounced. This is an elementary imperative; it is widely understood. Still, the rationale for it is not always understood in detail, and making it happen is not a trivial matter. Therefore, my purpose here is to provide some thorough background before narrowing my focus to one fundamental piece of equipment that seems simple but is much more difficult to design than you might expect. I refer to the portable ice bath, of which a detailed reassessment is long overdue.
Beginning with the fundamentals: Brain function requires a constant fuel supply in the form of oxygen and glucose. When the heart stops, the fuel supply is interrupted, and loss of consciousness occurs rapidly. Within a few minutes, a cascade of damaging chemical reactions begins, sometimes known as the “ischemic cascade,” which can be fatal for the neurons on which our mental processes depend.[1]
Fortunately, virtually all chemical reactions occur more slowly at lower temperatures, as described by the Arrhenius Equation, developed by Svante Arrhenius in 1889.[2] Therefore, to prevent the ischemic cascade, we simply need to cool the brain. At the same time, we can apply chest compressions (using the procedure commonly known as CPR) to ventilate the lungs and massage the heart, delivering a supply of oxygenated blood that can maintain metabolism.
Chest compressions are not a significant problem. They can be sustained for up to 45 minutes with a single charge of the battery in the LUCAS device shown in Figure 1. But “simply” cooling the brain is not simple at all. Extracting heat rapidly is a challenge, and even measuring our success is problematic. To explain why, I have to digress to some basics of heat transfer.
Figure 1. A LUCAS chest-compression device with a training mannikin.[3]
The second law of thermodynamics tells us that in an isolated system, conservation of energy will be maintained. In simple terms, this means that the only way to cool a hot object is by transferring its heat energy to another object or substance which is not as hot.
The greater the temperature difference, the faster the cooling process will be; but as the transfer of heat continues, the temperature difference diminishes, and the process becomes slower. Ultimately, if the two locations become equal in temperature, heat transfer ceases completely. In formal terminology, they have reached thermodynamic equilibrium. [4]
The implications are important. To “cool down” an object, we must remove its heat and dump it somewhere else. This can be done in three ways:
Conduction
Convection
Radiation
Conduction occurs when you have physical contact. If you grip a glass containing chilled water, heat from your hand is transferred into the glass. The glass gets warmer, while your hand gets colder.
Convection typically occurs when a gas or liquid circulates around or through an object, and the molecules remove or deliver heat. For example, if you sit in front of an air conditioner, convection transfers some of your body heat into the blast of chilled air. At the same time, conservation of energy is maintained, because the heat from your body makes the air fractionally warmer.
What if you were drifting alone and naked in empty space, without any gas or liquid to enable convection, and no nearby object to enable conduction? The temperature of interstellar space is close to absolute zero, so you would expect your body to lose almost all its heat very rapidly. It would be transferred into the cosmos via thermal radiation, and the cosmos would become warmer by an infinitesimal amount.[5]
The question, now, is which of the three methods of heat transfer can be most effective to cool the human body.
If a naked person experiences cardiac arrest in a room that has a temperature of around 25 degrees Celsius (77 degrees Fahrenheit), initially the body will radiate between 100 and 200 watts.[6] But this process will terminate when body temperature equalizes with room temperature, and it won’t happen very fast. By comparison, merely immersing the hands in cold water can dissipate more than 100 watts, so it’s safe to assume that heat radiation from the body, in a typical indoor environment, will be ineffective compared with conducting heat into a substance that has a much lower temperature.[7]
When conduction occurs, it will be affected by four factors:[8]
Temperature difference.
Area of cross section, through which the heat travels.
Distance through which the heat travels.
Properties of the materials that are involved.
Inside the human body, immediately after the heart stops, the temperature may be fairly uniform. But if we cool the skin, we now have a temperature gradient between the core of the body and its surface. Consequently, thermal conduction will occur outward from the core to the skin, through flesh and bone.
For this process to continue, we have to keep the skin cooled, and we should cool as large an area of the skin as possible. Immersing the body in a chilled gas or liquid seems the obvious answer, and a liquid seems preferable, as liquids tend to have better thermal conductivity than gases.[9]
Since the rate of cooling will be maximized if the temperature difference is as large as possible, we may feel tempted to use the coldest liquid we can find. Liquid nitrogen is widely available as a cheap industrial byproduct, with a boiling point of –196 degrees Celsius, so it should induce very rapid cooling.
Unfortunately, it would also cause catastrophic ice formation inside the body; and when water turns to ice inside human cells, it causes mechanical damage and also biochemical injury, as the crystal structure of ice displaces solutes which form toxic intracellular concentrations.[10]
It’s true that liquid nitrogen is commonly used for long-term preservation of cryonics patients, but before that can happen, a cryonics organization may want to protect the patient by perfusing with cryoprotective compounds that prevent the formation of ice crystals. In this text I am only considering rapid intervention immediately after death is pronounced—and during this sensitive period, cryoprotective perfusion is probably not available. Therefore, freezing is not acceptable, and we cannot use radical methods of cooling. Really, what we want during the initial period after cardiac arrest is to lower the body temperature until it is almost 0 degrees Celsius, but not quite. And the most obvious way to achieve this is with water-ice.
The ice that you obtain from a machine outside a supermarket or gas station is likely to be colder than 0 degrees, but when it warms a little and starts to melt, by definition, it is no longer below the freezing point of water. Therefore, immersing the patient in melting ice is a very safe way to apply surface cooling.
But how effective is it? Jordan Sparks at Oregon Brain Preservation ran some tests on human cadavers in an attempt to answer that question.[11] Three methods were used, each cooling only the head. In figures 2 and 3 you see the temperatures of the surface of the brain (blue), the core of the brain (red), and a middle zone (purple). (If you visit the web site of Oregon Brain Preservation, you will find that I have I have simplified their graphs in the interests of clarity. But the three curves are still the same.)
Figure 2 shows the averaged temperatures from 5 experiments in which the head was buried in unbagged ice. The ice was allowed to melt, with the water draining away.
Figure 2. Averaged temperatures from 5 experiments in which a human head was buried in unbagged ice.
In Figure 3, the head was immersed in ice and water, with the ice being refreshed after about 20 minutes. This method was applied to 13 cases, which were averaged to create the cooling curves.
Figure 3. Averaged temperatures from 13 experiments in which a human brain was immersed in ice and water.
You can see that the second method induced cooling more rapidly than the first. This is probably because water makes better contact with the skin than ice cubes alone. Figure 4 shows ice cubes greatly magnified. Clearly, if they are surrounded by water, this will disperse heat transfer over a wider area of the skin. If crushed ice is used instead of cubed ice, that will be helpful too; but in real-world scenarios, a cryopreservation standby team may not be able to obtain crushed ice locally.
Figure 4. Enlarged and simplified view of ice cubes inducing localized cooling.
Even when water is added, I would speculate that some temperature gradient must occur in the water between points where ice touches the skin. This leads me to believe that slightly better results may be obtained if the water is circulated with a pump. The people at Oregon Brain Preservation did try this, but at the same time, in an effort to achieve the fastest possible cooling rate, they infused ice-cold water into the nostrils, doing nasopharyngeal lavage in addition to external surface cooling. This did achieve a better rate of cooling, but we have no way of knowing if circulating the water induced some of the effect, or if it was entirely the result of the lavage.
What we do know, from looking at the graph in Figure 3, is that a mix of ice and water achieved a peak rate of cooling of about 10 degrees per hour during the first two hours, when the temperature was measured at a point midway between the core of the brain and its surface. That is a cooling rate of about 0.17 degrees per minute.
In most biological systems, each decrease in temperature of 10 degrees Celsius will reduce the metabolic rate by a factor of approximately 2.[12] Therefore, in the tests performed at Oregon Brain Preservation, the metabolic rate was reduced by a factor of approximately 4 during the first 2 hours, in the mid-level region of the brain.
I don’t find this very encouraging. External cooling by conduction is a slow process, because flesh and bone do not conduct heat very efficiently. Body fat is even worse, as it has evolved to protect the body by insulating it.
However, the situation will improve if we add the third mode of heat transfer: Convection. This can be achieved internally by circulating the blood, transferring heat from the core of the body to the capillaries near the skin, where the blood liberates some of its heat before circulating back to the core.
In this way, cardiopulmonary support actually serves two purposes: To prevent brain damage, and to transport heat internally by convection.
Unfortunately, there is a snag. If a standby team has been unable to intervene promptly, and more than 30 minutes have passed since the time of cardiac arrest, ventilation can have bad biochemical consequences. The ischemic cascade has begun, and we would prefer not to hasten it by supplying it with oxygenated blood. After longer periods, blood circulation may not even be possible, as clots will begin to form inside blood vessels.[13] In such cases, we will depend entirely on heat transfer by conduction, with disappointing results.
Still, I will assume now that we have a promising case in which cardiopulmonary support is possible. To what extent will this hasten the cooling process?
This question is difficult to answer, because measuring internal body temperature is not as simple as it sounds. It has been done in cryonics cases rectally, tympanically (by inserting a probe into the ear and sealing it with swimmer’s wax), and by using a nasopharyngeal probe inserted into the sinus cavity. But in each of these methods, there is no easy way to know if the temperature probe is really making good contact with tissue. Moreover, no matter how carefully a probe is seated, there is always some risk of ice-cold water seeping in, creating an artificially low reading. This is especially likely when team members are working hastily under stressful conditions, and accurate data collection is not their most urgent priority.
Fortunately, rapid cooling of the human body is not just of interest to people in the field of cryonics. It can be important in conventional medicine, in which temperature measurement may be more reliable, performed under conditions of less stress.
Surface cooling has been used quite often when athletes experience dangerously elevated body temperature as a result of strenuous exercise during hot weather. In 2009, the Journal of Athletic Training published an assessment of multiple studies in which the athletes were immersed in water, or a mixture of water and ice, or ice in bags. The paper is freely available via the National Library of Medicine.[14]
In these case studies, the peak rate of temperature reduction was 0.35 degrees Celsius per minute, achieved by cold-water immersion to neck level. That is twice the rate achieved at Oregon Brain Preservation without any blood circulation. Of course, temperature measurement in Oregon Brain Preservation was not done with the same the rectal protocol predominantly used by physicians treating athletes, but I would hope that the results are roughly comparable if we use the “mid-level” measurements from Oregon for comparison.
However, several other differences make comparisons more difficult.
1. Different duration. The cooling process for athletes was relatively brief (not exceeding 15 minutes), as the goal was a temperature reduction of just a few degrees. The cooling process in Oregon lasted for eight hours, with a goal of reaching 0 degrees Celsius.
2. Different cooled skin area. In many cases involving athletes, ice-cold water was only applied to the torso, limiting its effectiveness.
3. Different rate of blood flow. The athletes had normal cardiac output, while chest compressions applied to a cryonics patient deliver only about half normal blood flow to the brain, according to manufacturers of the LUCAS device.[15] This would suggest that heat convection via the blood, in a cryonics case, should be only half as effective as can be achieved with normal cardiac output. And yet—
4. Paradoxically, some cryonics case reports have claimed cooling rates that are faster than any achieved by the athletes. The graphs in Figure 5 are excerpted from a training manual written by Michael Darwin in 1990.[16]
Figure 5. Cooling rates reported by Michael Darwin in his 1990 training manual, archived by Alcor Foundation.
The steepest of these graphs suggests an initial cooling rate of about 12 degrees in 30 minutes (that is, 0.4 degrees per minute). However, I believe this case may have involved a patient who had unusually low body weight, and this leads me to another factor:
5. Variations in thermal mass. People who weigh less will tend to cool faster than large people, because they contain less heat, and because the heat travels a shorter distance to reach the skin. Moreover, in a cryonics patient who has lost substantial weight as a result of cancer treatment prior to legal death, the body may be emaciated, and fat will be thin at best, enabling faster heat transfer. Last but by no means least, the ratio of skin area to body weight is higher in a small person.
Naturally, Michael Darwin was aware that body mass would affect the cooling rate. He has concluded: “In practice, the maximum rate at which low-mass emaciated patients can be cooled externally is in the range of 0.25 to 0.35 [degrees Celsius per minute], while the maximum rate for larger mass patients with a significant layer of subcutaneous fat is in the range of 0.12 to 0.15 [degrees Celsius per minute].”[17]
Even if we can come up with conversion factors to enable meaningful comparisons between patients who have differing body weight, skin area, and cardiac output, this is still not the end of our problems when we try to make meaningful comparisons. In the field of cryonics, equipment and procedures have not been standardized.
So far as I know, the optimal volume of water and weight of ice to cool a patient has never been established, relative to human body weight.
Some ice baths are larger than others.
The output of pumps that circulate water in an ice bath has not been standardized.
The orientation of pump flow has varied.
Sometimes, a “SQUID” is used. This is a perforated tube distributing water over the exposed upper skin of the patient. But in other cases, this has not been done.
Where a “SQUID” has been used, its design has varied widely, depending on the ideas of the person who designed it.
Sometimes a perforated mask has been used to apply ice-cold water directly to the face and head. In other cases, this has not been done.
Ice may be replenished on an ad-hoc basis, often when someone just happens to notice that a substantial amount of ice has melted.
Experimental science requires control of variables. This is the only way results from different experiments can be compared meaningfully. I have to say, with regret and chagrin, that cryonics organizations have not pursued this very basic requirement very diligently when it comes to standardizing techniques and equipment used in surface cooling.
There is even some room for disagreement on how cooling data should be interpreted. Human metabolism does not stop at the instant when death is pronounced, which means that most body cells are still metabolically active, and are still generating heat. Consequently there may be some latency in the cooling process—a lag time before the cooling curve achieves its steepest slope. The lag time may vary with body weight and general physical condition of the patient. Should latency be ignored? Should we simply cite the maximum rate of cooling, regardless of where it occurs before the curve becomes asymptotic relative to the zero-degrees baseline?
With financing from Biostasis Technologies, I am hoping to perform repeatable experiments to resolve some of these issues. In the meantime, I can only offer three tentative conclusions:
If chest compressions are applied to restore blood circulation, this should greatly improve the rate of body cooling by convection, compared with cooling by conduction alone.
A peak cooling rate of 0.4 degrees Celsius per minute has been mentioned sometimes as an achievable goal, for cases in which cardiopulmonary support is applied promptly after legal death is pronounced. Personally, I tend to believe that 0.2 degrees may be more realistic if we include cases that are less favorable. This rate is not very different from the averaged rate of 0.17 degrees reported by Oregon Brain Preservation, using only conductive cooling, with no convection from blood circulation at all, when the temperature was measured at a point midway between the center of the brain and its surface.
At least one authority has suggested that internal cooling by conduction through flesh and bone is so inferior to cooling by convection via circulating blood, conduction can be ignored. This may not be relevant, however, because immersion in ice and water seems desirable to me under any circumstances, since it must achieve some improvement in the cooling rate compared with simply leaving the patient exposed to ambient air.
There is still one more factor that I have not mentioned. Water-ice seems ideal as a cooling agent, since it melts at precisely the temperature we want. But is there some other substance, with a similar melting point, that is able to remove heat more rapidly?
Gel packs are sometimes suggested as an alternative, with paraffin products and salt hydrates being proposed. But the need to encapsulate them reduces intimate contact with the skin, and most packs cannot absorb as much heat as water-ice, as explained below.[19]
If we turn to standard reference sources, looking for chemicals that freeze around 0 degrees Celsius, formic acid is one, and nitrobenzene is another. But their expense, toxicity, and lack of easy availability would eliminate them from serious consideration. The fact is, water-ice has unbeatable advantages. Standby teams can obtain it quickly, reliably, and cheaply from almost every convenience store, supermarket, and gas station in the United States. It not only melts at the ideal temperature, but more importantly, absorbs a significant amount of latent heat.[20]
The concept of latent heat is of vital importance.
In its liquid state, water consists of molecules that move in a chaotic fashion; but if we lower the temperature of water to freeze it, the molecules lose their freedom. Ultimately they become locked into a crystalline structure, and this transformation is known as a change of state.
Molecules in motion have kinetic energy. When the molecules stop moving, this energy must be transported away—by conduction, convection, or radiation—before the water can freeze. The important point is that while the change of state is occurring, the temperature of a water-ice mixture does not change. It cannot fall below 0 degrees Celsius until all the latent heat has been given up.[21]
Subsequently, if the ice changes back into water, the process is reversed. Now the molecules must acquire energy, to resume their motion. This energy must be drawn from the environment, and while this is occurring, once again, the temperature doesn’t change.
While ice is melting, it absorbs heat, but a mixture of ice and water remains at a constant temperature of 0 degrees until the melting process is complete.
In this way, melting ice functions as a kind of thermostat.
The numbers are not trivial. Water-ice happens to require more latent hear, to melt it, than most other commonly available substances. In fact, 334 joules of energy are required to melt 1 gram of ice, while only 4 joules of energy are required to raise the temperature of 1 gram of water by 1 degree Celsius. In other words, about 80 times as much body heat can be taken from the patient by melting ice, compared with simply using the body heat to warm an equal volume of cold water.
Now I can finally move to the practical issue: Where does a standby-transport team find an actual piece of equipment for cooling the patient?
We should always avoid reinventing the wheel, so my first step is to see what is available in conventional medicine. A quick search reveals many temperature management systems consisting of jackets or pads containing tubes through which chilled liquid can be pumped from a bedside console. The console is basically a refrigerator, and you can dial in the temperature that you want in your cooling jacket. But none of these devices is designed to achieve the rapid, deep hypothermia which we require for a cryonics patient.
After examining the options, the conclusion is inescapable: Direct contact with ice and water, covering the entire body, is essential to maximize the rate of cooling of a cryonics patient; and this configuration is not found in conventional medicine. Therefore, a cryonics organization must build its own ice bath, and team members will have to bring it with them (somehow) if they receive notice that a patient may be terminal. In my experience, sometimes a hospital may allow an ice bath into their facility, and sometimes they won’t; but a hospice may be receptive, and a home hospice should be the easiest of all.
The ice bath will have to satisfy some demanding requirements:
Able to accommodate a relatively large person—say, 200 lbs.
Able to carry the significant additional weight of ice, water, a chest compression device, and probably some other equipment.
Collapsible for transport—by scheduled airline, if possible.
While it is collapsed, one person should be able to carry it.
Easy to unfold under stressful conditions where time is of the essence.
Professional in appearance, to avoid rousing skepticism or hostility from medical personnel.
Legs should bring the ice bath up to a convenient height for administering procedures.
Legs should be removable, so that the bath can be transported in an SUV with limited head room.
Wheels should be large enough for moving over rough surfaces, but not so large that they are unreasonably heavy.
So far as I know, no one has ever satisfied all of these requirements, and this is why I find the challenge of building an ice bath so intriguing. In fact, I have been intermittently interested in developing an “ideal” ice bath for more than 30 years.
My experience began in January, 1992, when I visited a cryonics pioneer named Curtis Henderson at his home in Sayville, Long Island, and found that he kept an ice bath in his living room. He referred to it as a “Pizer tank,” as its design had originated with a cryonics activist named David Pizer, who ran a successful business selling aftermarket automobile seat covers in Phoenix, Arizona.
A diagram illustrating the Pizer tank is shown in Figure 6, excerpted from Michael Darwin’s transport manual, cited previously. It consisted of a slab of 3/4” plywood on which was mounted a frame fabricated from PVC water pipe. Inside the frame was a vinyl liner, and inside the liner was the patient, immersed in a mixture of water and ice. A gap in the frame allowed the use a Michigan Instruments “Thumper,” which required side access and was the only device available to administer mechanical chest compressions at that time.
Figure 6. Michael Darwin’s drawing of the ice bath originated by David Pizer.
The Pizer tank didn’t begin to satisfy many of the features that I have listed above. It was not collapsible, could not be transported (empty) by one person without some difficulty, had no legs, and was embarrassingly unprofessional in appearance. Its big advantage was that almost anyone could build it cheaply, using materials from the nearest lumber yard and hardware store.
Subsequently a Pizer tank was mounted on a wheeled metal frame containing perfusion equipment. I believe Hugh Hixon and Jerry Leaf of Alcor Foundation developed this version, which was named the MALSS, an acronym for Mobile Advanced Life Support System. In Figure 7, you can see the MALSS being unloaded from a lift gate mounted on the ambulance that Alcor used at that time. Hixon is at far left; next to him is Ralph Whelan.
Figure 7. Hugh Hixon, far left, with Ralph Whelan, helping to unload the MALSS ice bath for Alcor Foundation.
Michael Darwin stopped providing service for Alcor in 1993, and started his own company, named BioPreservation. Alcor was understandably reluctant to allow him to take their ice bath with him, so one of Darwin’s colleagues asked me if I could design something more portable. I was living in New York City, in a tiny apartment with no space for a workshop, so I went to a talented artist and sculptor named Julian La Verdiere, who was interested in cryonics and had an industrial loft in which he could fabricate large art objects. I made a wooden scale model, shown in Figure 8, and he built the full-size version from one-inch square aluminum tube, shown in Figure 9.
Figure 8. A scale model of the first Platt design.
Figure 9. The bath built by Julian La Verdiere.
The La Verdiere version was lightweight, and looked a bit more plausibly professional than the Pizer tank, but I lacked practical experience and had been given an incomplete specification. I was unaware, for example, of the need for an IV pole and a side-mounted chest-compression device. Also, La Verdiere underestimated the weight that the bath would carry. The first time the bath was used, the plastic base-plate fractured, with unpleasant consequences.
Meanwhile, Hugh Hixon built a much more sophisticated version of the MALSS which he called the MARC, or Mobile Advanced Rescue Cart. This impressive beast was fabricated from welded steel tube, with two oxygen cylinders to power the “Thumper.”
The MARC is shown in Figure 10. Its craftsmanship was impeccable, but it was so heavy, maneuvering it was a challenge, and lifting it over an obstacle such as a curb was almost impossible. Still, one feature made an enduring impression on me: one end of the bath would telescope inward, so that the beast might fit into an elevator or maneuver around corners in a hallway.
Figure 10. Hugh Hixon built this heavy-duty configuration for Alcor Foundation.
Toward the end of the 1990s, Fred and Linda Chamberlain, who had become the primary administrators at Alcor, came up with an ice bath design that they hoped would be adopted by the regional groups that existed at that time. It would be as cheap and simple as a Pizer tank, but much more portable. It consisted of a minimal frame of thin aluminum tube, with a vinyl liner draped over it, while a pump circulated ice-cold water through spray heads above the body. Unfortunately it could only be used if there was a large, flat surface to rest it on, and if it was not handled carefully, it could fold up unexpectedly. Also, the spray heads created a possible infection hazard from splashing and vapor, if the patient suffered from a communicable disease.
Meanwhile, since I felt embarrassed by the failure of my first design, I started thinking of alternatives. A 3D rendering of one of them is shown in Figure 11. My idea was to have a folding shell containing sections that could be quickly assembled to form the walls of the bath. Two pairs of wheels could also be attached to the underside.
Figure 11. The second Platt design.
Julian La Verdiere was no longer interested in cryonics fabrication projects, and I was still living in my tiny New York apartment, with a very limited set of tools. This meant that anything I fabricated would have to be made of plywood. No one liked the idea of this, partly because wood is not considered an acceptable material for medical equipment, even if you cover it with Formica. So, I never built it.
A few years later, in 2002, a company named Suspended Animation was created by David Hayes and David Shumaker in Florida, specifically to improve standby-transport procedures in cryonics. They employed a paramedic named Mike Quinn who had handyman skills, and he came up with the design shown in Figure 12, with a Thumper attached to the side.
Figure 12. The ice bath created by Mike Quinn for Suspended Animation, Inc.
Quinn’s bath was supported on a framework of steel tubes plugged into T-shaped connectors. This frame was disassembled for transportation, and all the pieces could be stored inside the baseplate, which was hinged in the center. This is shown in Figure 13.
Figure 13. Mike Quinn’s ice bath, disassembled, with all the pieces stowed in one-half of the clamshell baseplate.
Reassembling the bath was a significant challenge. Not only was it complex, but the welding company that Quinn employed was unaccustomed to working with precision. Nothing would fit together easily, so Quinn had to supply a rubber mallet as standard equipment. The president of Cryonics Institute at that time complained that when he took delivery of his Quinn-designed bath, he spent hours trying to assemble it, and finally gave up.
Still, there were aspects of it that I liked. In particular, it had generous proportions. Hayes and Shumaker were relatively heavy people, and naturally they wanted an ice bath which would be big enough for them. Its interior dimensions were 82 inches long, 24 inches wide, and 12 inches deep.
When I took over as general manager of Suspended Animation, Inc., one of my first priorities was to design a bath which would fold and unfold more easily, with no loose parts that could get lost, and no rubber mallet required to make everything fit. I retained the same dimensions as Quinn’s bath, as a small step toward standardization.
By this time, in 2004, I was fortunate to have a highly skilled welder on staff. I could create a 3D rendering of a small component in the morning, and he could give me a welded version by the end of the day, to provide an instant sanity check on my designs. The sequence of photographs in figures 14 through 17 shows the bath that he built being removed from its nylon bag and unfolded by Kelly Kingston, a member of our standby team.
Figure 14. My first serious attempt to create a collapsible ice bath was transportable in a zippered black nylon bag.
Figure 15. The ice bath unfolded without any loose parts, other than the wheels, which plugged in.
Figure 16. The unfolding process was nonintuitive, but reasonably easy to learn.
Figure 17. The floor of the bath was made of expanded stainless steel. A layer of soft plastic protected the vinyl liner from being scratched.
The bath was heavy, but I was able to get it to the airport (despite being 60 years old and not exercising regularly), and it survived airline baggage handling without incident.
I developed a separate set of folding legs, shown in figures 18 through 21, but these were never used while I was working at Suspended Animation, and I don’t know what became of them. They required too many cotter pins to hold them together easily.
Figure 18. Legs for the ice bath were extremely compact but not easy to open.
Figure 19. Bands of Velcro held the legs together while they were being unfolded.
Figure 20. Cotter pins were required to stabilize the legs.
Figure 21. The legs plugged into the frame of the ice bath.
Variants of my ice-bath design were created for permanent installation in a couple of cryonics vehicles. These variants were not collapsible, but still had ends that could be hinged upward to fit into elevators or get around corners.
Figure 22 shows a bath that was commissioned by Cryonics Institute, where they wanted the legs to hinge upward automatically while it was being pushed into the load area on a Chevy Suburban.
Figure 22. The “mortuary style” ice bath emulated the folding legs that are commonly found in mortuary equipment.
The big disadvantage of all these designs was that only a welder could build them, and he had to be highly skilled to make everything fit properly. Tight tolerances are a problem in a welded design, as the heat of welding tends to make metal bend, preventing articulated joints from moving freely.
At Alcor, CEO Steve van Sickle believed that my designs were too expensive and complex, and he felt he should be able to adapt something that already existed. He learned that injured mountain climbers were rescued on a stretcher that disassembled into three pieces, consisting of an aluminum frame with wire mesh, so why not use that? His version is shown in figures 23 and 24. The sections were so compact, they could fit into an oversize backpack. Unfortunately, they would barely accommodate a large patient, and allowed very little room for ice and water.
Figure 23. The Van Sickle ice bath with a dummy, chest-compression device, and medical supplies on a tray.
Figure 24. The Van Sickle design could be transported in a large backpack. Detachable wheels were also provided.
Subsequently, at Alcor, Steve Graber came up with an elegant design using round steel tubing. Graber had prior experience customizing cars, and knew how to do welding and tube bending. He used plain steel (cheaper than stainless steel) and spray-painted it. Because the bath disassembled into small sections, it was very compact, but assembling it did take some time.
In 2022, when Aschwin de Wolf was establishing standby-transport capability for Biostasis Technologies in New York City, he asked me if I could design a new ice bath for him. I saw this as an opportunity to profit from all past experience in this area.
I was living now in Arizona, where I had a very well equipped workshop. I didn’t do welding, and would have to use bolts and rivets to hold everything together—but this limitation had a positive aspect, as I wanted anyone with basic crafts skills to be able to build their own copy.
Initially I made a quarter-scale model. After this was approved, I built the ice bath in collaboration with a friend named Billy Blohm. The bath and its detachable legs are shown in my workshop folded, in Figure 25, and unfolded in Figure 26. Building it took five times as long as we expected, partly because I underestimated the need for precision in parts that had to fit in two different orientations, when folded and unfolded. Still, I was happy with the result.
Figure 25. My first ice bath and separate legs, designed for Biostasis Technologies.
Figure 26. The ice bath in Figure 25, unfolded.
Aschwin de Wolf now wanted something that would be a bit smaller and lighter, and would be easily air-transportable as passenger baggage. I came up with a concept to use thin cables, properly known as wire rope, to brace the rectangular sections of the bath. Instead of square aluminum tube, I used U-shaped aluminum channels which would accommodate the wire rope when the bath was folded up. I made cases from ABS plastic, and the ice bath and its legs were transported as checked baggage without any problems.
This might be the end of the story, except that my client felt that the new design looked less robust than the previous one. Something about wire rope simply didn’t instill confidence. I had chosen US-made wire with a certificate promising that it would hold a 900lb weight, but still, as de Wolf put it, “optics are important.”
I could see the truth in that, so I came up with yet another design, still using aluminum channels but managing to fit 5/8” aluminum tubes into them when the bath was folded, thus retaining the compact dimensions of the previous design while getting rid of the wire rope. At the time of writing, this is a work in progress.
While exploring the challenge of building ice baths, I started to consider accessories that would optimize the process of using them.
In his 1990 transport manual, Michael Darwin stated that placing bags of ice under a patient was “virtually impossible.” Apparently he did not consider fabricating some kind of platform with channels in it to distribute ice-cold water.
Normally, a patient is placed in direct contact with the ice-bath liner, which allows conductive heat incursion from the environment. Therefore, Aschwin de Wolf felt that a cooling platform would be highly desirable.
With this in mind, I built a prototype consisting of longitudinal 1” x 2” aluminum tubes, with walls 1/16” thick, and an input manifold at one end to distribute water through the tubes. Aluminum is an excellent conductor of heat, so the temperature gradient in an aluminum shell that is only 1/16” thick should be negligible. This led me to believe that thin tubes would be almost as effective as direct contact with water itself.
The first prototype platform is shown unfolded in Figure 27, with a submersible pump. The same platform is shown partially folded in Figure 28.
Figure 27. A cooling platform to be placed in the bottom of an ice bath.
Figure 28. The cooling platform, partially folded. While the tube ends were not sealed where they butted together, a small amount of leakage was considered tolerable.
A pump must be used to circulate chilled water through the platform, and an additional pump is necessary to circulate water around and over the patient, via a SQUID. I have not yet reviewed all the previous tubing configurations for upper-surface cooling, but I have addressed the need for a pair of pumps.
After the patient has been pronounced, the bath is likely to move the patient through hallways, out of a building, and into a vehicle. The vehicle will typically transport the patient to a mortuary, where surgical procedures may perfuse the body with a chilled organ preservation solution. During all of these transitions, up until the moment when surgery begins, we would like water circulation to continue without any interruption.
Evidently, battery-powered pumps are necessary. Fortunately 12-volt submersible marine bilge pumps are very affordable, rated to deliver 1,000 gallons per hour, and together they draw about 7.5 amps. This seemed ideal, but now I needed some serious batteries to run the pumps. Small, sealed, 12V lead-acid alarm batteries are available, but they are heavy. High-capacity lithium-ion battery packs are prohibited in checked airline baggage, so—what’s left?
Nickel-metal-hydride (NiMH) battery packs still exist, although they are becoming scarce. They are lighter than lead-acid, they don’t suffer from the memory effect that used to be a problem with NiCads, and if they are properly wired and fused, they won’t start fires. For slightly more than $100 an eight-cell NiMH battery pack rated for 10 amp-hours can be custom-built. This means, theoretically, it can supply 10 amps for 1 hour, or 1 amp for 10 hours—or, in the case of the pumps that I suggested above, 7.5 amps for 1 hour and 20 minutes. I am a little skeptical, however, about battery ratings, and I know that the voltage supplied by a battery pack will diminish as time passes. Therefore it seems wise to rely on the battery pack to run the pumps effectively for up to an hour.
In addition, just in case the battery pack fails or someone forgets to recharge it, an AC-DC converter must be added. These are widely available for only about $20.
Lastly a battery charger is needed, compatible with NiMH batteries. So, the weight penalty was adding up, as it always does: Two pumps, a battery pack, an AC-DC converter, a charger, a cooling fan for the charger, and a high-amperage switch to choose between the various options.
I decided that all this stuff had to be built into its own plastic box, transportable separately from the ice bath, because a bored TSA employee, looking at an x-ray, might see a battery pack and assume that it contained lithium-ion batteries. Even if I included a notice explaining that the batteries are NiMH, a TSA employee might not read it. I wanted the ice bath to get through the baggage-handling system even if the power supply was embargoed, and therefore the power supply has to travel separately.
At the present time, I am planning to test another cooling-platform option and some water-circulation options. I am also thinking about ways to protect temperature probes from ice-cold water incursion.
Lastly, I want to resolve some of the unknowns regarding issues such as the ideal quantity of ice and water, and the best ratio between the two. I am guessing that a 50-50 ratio (by weight) may be desirable. I certainly don’t want too much ice, as it will interfere with water circulation. On the other hand, too little ice will just float, and will allow a temperature gradient in the water below it.
The reader may feel surprised that three or four decades have passed without definitive answers to fundamental unknowns regarding rapid surface cooling. Surely, cryonics organizations have had enough money to pay an engineering company to do the job properly?
In fact, cryonics organizations have never had money to spend on innovative designs by professional engineering consultants, especially when the problem seems to have a relatively low priority. Placing a patient in a bath containing ice and water is considered important, but no one has had much enthusiasm for optimizing it. In fact, for several decades, only one organization bothered to do standby-transport intervention at all.
Long-term patient storage has traditionally been better funded than rapid initial cooling, and protection from ice damage has been the highest financial priority.
Since there’s not enough money for R&D, you might wonder why an organization doesn’t simply adapt one of the stretcher designs used by paramedics. Why not copy them instead of reinventing the wheel?
The answer is that paramedic stretchers don’t have to fold up to comply with airline size restrictions, don’t have to be light enough to comply with weight restrictions, and don’t have to support large quantities of ice and water in addition to a patient. They may seem similar, but their purpose is quite different.
Personally I don’t imagine that any of my ice-bath designs is the end of the story, and I may never know the absolutely ideal way to circulate ice-cold water around the patient. Therefore, if anyone reading this is thinking, “I’m sure I could solve these problems easily enough,” I encourage them to make some suggestions.
Contact the author at (charles.arizona@gmail.com)
(All illustrations are by the author, except where otherwise noted.)
Sources, all accessed on January 10, 2025
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Charles, thank you for this extremely informative essay. It both documents important cryonics history and shows the hard work, focus, and persistence needed to make real progress. I know you have no illusions about the current state of cryonics. That makes me appreciate your dedicated work all the more.