Reintroduction of Oxygen May Increase Morbidity Following Cardiac Arrest

When modern medical professionals talk about death, they’re usually speaking in terms of the absence of brain activity. Not so long ago, the conventional signifier of shuffling off the mortal coil was the cessation of the heart beat. Modern CPR and electronic defibrillation make that definition obsolete, but both standards for morbidity deal with a common problem: the lack of oxygen. Until recently, the conceptualization of death on the microscopic level consisted of a cell, choked and suffocated after four or five minutes without oxygen, being irreparably damaged and irrevocably lost. This longstanding convention went largely unquestioned until the last few years, when doctors studying oxygen deprived cells under a microscope realized that it took hours, not minutes, for them to die. They also unearthed a second mystery; following four or five minutes without any O2, the cells actually initiated apoptosis (self-destruction) when oxygen was reintroduced. That suggests that the standard practice of oxygenating patients when they arrive at the hospital after suffering cardiac arrest may significantly increase the risk of death instead of helping to reduce it.

Researchers at the University of California published a study last year which tested an alternative method for treating persons in this plight. Administered across four hospitals with 34 separate participants, doctors placed patients who were in cardiac arrest on heart-lung bypass machines to keep oxygen flowing to the brain but not by way of the heart. This allowed them to keep the heart in stasis through cardioplegic blood infusions and to reintroduce oxygen at the slowest rate possible. Having decreased the metabolism of the heart considerably by putting it in a suspended state, the oxygen consumption of the muscle becomes low. As the safe level of oxygen in the heart gradually increases, the chemical boundaries in place to restrain its activity are decreased. When this process passes a self-sustaining threshold, the heart is defibrillated and the bypass machine removed. Using the conventional procedure for treating cardiac arrest (oxygenation, defibrillation, and ephedrine injections), survival rates range from 7% (occurs out of hospital) to 15% (occurs in hospital). Of the 34 patients in the study treated for cardiac arrest, 80% lived to be discharged.

While the sample size of this study leaves much to be desired, its outcomes are provocative and will surely spur further research. In some ways, it’s baffling that cellular death has gone so long misunderstood. If cells can survive for an hour or more without oxygen free of consequence, this discovery may be the vanguard of medical research that provides an entirely new framework for the way we think about death.

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~ by Wil Finley on April 27, 2010.

3 Responses to “Reintroduction of Oxygen May Increase Morbidity Following Cardiac Arrest”

  1. Extremely interesting write up Will. I admit that I know very little that is medically relevant to this article (being an accountant) but I found it fascinating. It appears that although unresearched for so long this initial study could pave the way forward to some vital changes in reviving and treating patients. I will most certainly be looking at how this develops.

  2. 80% of live discharges just sounds to good to be true.
    BTW the procedure used here not only affects the oxygenation but metabolic rate as well. Similar method is used when active cooling is implemented (Down to 32 Deg C).
    Another thing is that the organ most sensitive to lack of oxygen is brain. I wonder why did this influence the mortality so much.
    Main question. DO you have a source?

    • Maciej – Yeah, I agree, 80% does seem too good to be true, another reason why I would like to see additional studies with larger sample sizes and better controls.

      My main source for this article is from Newsweek: http://www.newsweek.com/id/35045/page/1. It is also the URL under the “tested an alternative method” hyperlink in the article. They also discussed induced hypothermia to decrease metabolic rates as you mentioned.

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