Resuscitation of rodents from hypothermic circulatory arrest
This is the first entry in a series about resuscitation of non-hibernating rodents from circulatory arrest at ultraprofound hypothermic and high subzero temperatures. Prior work in hypothermia began in the early 1900s, but because cardiac and respiratory arrest were observed in the animals around 15 degrees C, researchers assumed they were irreversibly dead and made few attempts to resuscitate them from temperatures below this point.
But there was a thermophysiologist named Radoslav K. Andjus working in the Physiology Department at the University of Belgrade after World War II. Since the university’s library had been destroyed in an air raid, he was unaware of the “conventional wisdom” that the lethal body temperature of rats was 15 degrees, and quickly developed a method of reviving animals from temperatures between 0 and 2 degrees C.
His technique, published in 1951, was surprisingly simple. First, he lowered the core body temperatures of rats from physiological (37 degrees C) to around 20 degrees C by enclosing them in glass jars which were then placed in a refrigerator (with the rats re-breathing their own expired air). To further cool the rats, they were packed in crushed ice until colonic temperatures reached about 1 degree C. They were held at this temperature for 40-50 minutes before resuscitation was attempted.
Andjus first attempted to rewarm the entire body at once in a hot bath, but these animals failed to revive. He quickly determined that the circulation must first be re-established by applying heat locally to the cardiac area before rewarming the whole body. He did so by heating a spatula in the flame of a Bunsen burner and applying it to the chest wall over the heart. Artificial respirations were also given throughout the resuscitation attempt.
While this method was successful, the rate of success (only 20 percent of rats lived more than 24 hours) left something to be desired. When Andjus began working with Audrey U. Smith in 1955, they found that the even easier technique of focusing a powerful beam of light from a projection lamp was even better — 76 percent of these rats survived more than 24 hours, and 68 percent survived more than 66 days.
Thus began a steady stream of experiments in hypothermic resuscitation, primarily as a means of determining the best method for resuscitating victims of accidental cooling or freezing and to facilitate the use of hypothermia in cardiac surgery. We will outline several of those ground-breaking experiments over the coming weeks.
