Can there be cryonics without ischemia? To some critics cryonics is destined to fail because of (postmortem) ischemia (“the brain dies after 5 minutes”). This is an unfortunate and persistent misunderstanding because there is nothing inherent in the idea of cryonics that entails ischemia. In fact, if cryonics would be available as an elective medical procedure, it would not need to entail any ischemia at all.
In reality, however, cerebral ischemia is often a part of cryonics as practiced today because of delays and sub-optimal procedures. While there is good reason to believe that meaningful revival is still possible in cryonics patients after significant ischemia, it is obvious that minimizing ischemia is an important mandate for any credible cryonics organization.
Based on earlier work by Dr. Michael Perry and Dr. Steven Harris, Michael Perry and myself developed a metric to estimate the total equivalent normothermic ischemic time sustained in a cryonics case called the S-MIX (Standardized Measure of Ischemic Exposure). Naturally, the ideal S-MIX would be ZERO. In such cases there is no metabolic deficit to injure the brain or other organs. In other words, the only damage sustained during a cryonics procedure would involve things such as cryoprotectant toxicity or mechanical stress (if stored at liquid nitrogen).
So far, the S-MIX has mostly been used to calculate a score for individual cases to evaluate the quality of a specific cryonics case, and to determine what trends can be seen in the delivery of cryonics services over the years. But the S-MIX can also be used pro-actively to understand and model different kinds of scenarios and protocols to improve and plan procedures. This use of the S-MIX enables cryonics organizations to quantify the potential outcomes of new technologies and protocols.
So what type of cryonics case would yield an S-MIX of zero? Most likely, only cryonics cases that are conducted as an elective medical procedure would be able to produce such an outcome. To understand why this is the case requires that we walk through the opportunities in a cryonics case to yield the lowest possible S-MIX.
Induction of Deep Hypothermia under Anesthesia and Metabolic Support
Although it is currently not clear how to apply the S-MIX to a dying, agonal, patient, it is self-evident that if any “pre-mortem” ischemia is prevented, the S-MIX starts at zero at the start of cryonics procedures. At this point the patient transitions to a controlled protocol of induction of deep hypothermia under anesthesia and metabolic support (i.e. oxygenation). Such a procedure will typically entail some kind of cardiopulmonary bypass (CPB). In this protocol, the type of ischemia that is associated with the dying process and cryonics standby and stabilization procedures (mechanical chest compressions and emergency ventilation) will not occur.
Blood Substitution and Cooling to Ultra-Profound Hypothermic Temperatures
At a temperature in the range of 20C to 15C the blood of the patient can be replaced with a universal organ preservation solution (such as MHP-2) to provide further metabolic support and protection against the adverse effects of very low temperatures. Since there are no interruptions in oxygenation, there are no opportunities for an ischemic deficit to accumulate.
Oxygenated Cryoprotectant Perfusion
Cryoprotection of the patient is usually conducted at a temperature between 0c and 5c. At such low temperatures ischemia accumulates at a very slow pace but can conceivably be completely eliminated if the perfusate is oxygenated during perfusion of the lower concentrations of the cryoprotectant (let’s say up to 50% of the concentration necessary to vitrify). At that point, a “reservoir” of energy is available for the patient during the last few hours of “anoxic” cryoprotectant perfusion. After cryoprotectant perfusion is completed at sub-zero temperatures, the patient is then rapidly cooled for long-term metabolic arrest at ultra-low temperatures.
Medical Biostasis
Cryonics as an elective medical procedure is not available in the Western World yet but a detailed medical human biostasis protocol has been drafted by Dr. Ville Salmensuu and myself with support of the Dutch Aeracura Foundation.
Can we approximate such an ideal situation in contemporary cryonics? This is an ambitious R&D project, but cases in which a patient utilizes assisted dying, followed by ultra-rapid external cooling and/or (liquid) ventilation, fast surgery, and oxygenated washout- and cryoprotectant perfusion, should yield an S-MIX score that may not be zero, but low enough to minimize cell damage and related phenomena such as cryoprotectant perfusion impairment.
Currently, the best cryonics case S-MIX scores are close to 1 hour (of equivalent normothermic ischemia) but it should be possible to reduce this number by at least 50% if cryonics organizations have rapid and managed access to the patient and cooling and metabolic support are pushed beyond what is currently the state of the art in the field.
Good article outlining the S-MIX as a standard quantitative measure of ischemic damage in Cryonics, along with protocols to keep this damage as close to zero as possible. The S-MIX quantification helps move Cryonics into the realm of mainstream medicine and provides a metric for cryopreservation quality. Assisted suicide as a legal, ethical, moral necessity will help us keep the S-MIX optimal, and should be supported by our community. Bravo for your work, Aschwin!