Motivation: Lately, hypothermia has not been good enough for me. There have been too many people who have suffered cardiac arrests at home and ended up severely impaired despite receiving mild hypothermia according to protocol. Can we do better? For instance, if we can quickly institute deep hypothermia, is it any better?
Some of the coldest studies in this field have been performed in dogs. In this amazing study, dogs were tested for neurological recovery after many hours of hypothermia.
Paper: Nozari A, Safar P, Wu X, et. al. "Suspended Animation Can Allow Survival without Brain Damage after Traumatic Exsanguination Cardiac Arrest of 60 Minutes in Dogs." J Trauma (2004); 57: 1266-1275.
Methods: Fourteen dogs were sedated with ketamine and halothane and supported with positive pressure ventilation. The dogs were then exsanguinated over fiver minutes to cardiac arrest. At two minutes, flush of saline at 2 degrees Celsius was administered in femoral artery to achieve tympanic temperature of 10 degrees Celsius. In 6 dogs, reperfusion was performed after 60 minutes of cardiac arrest. In 8 dogs, to simulate trauma, splenic injury was inflicted prior to cardiac arrest. During arrest time of 60 minutes, the spleen was transected. Outcome was determined by overall performance category (1 to 6 with 1 being normal and 6 being death) at 72 hours.
Results:
Resuscitation: All fourteen dogs were successfully resuscitated from cardiac arrest.
Control group: All six dogs in the control group were neurologically normal after 72 hours (they were judged to be identical in behavior to their pre-intervention condition).
Trauma group: Of the eight dogs who underwent splenectomy during the cardiac arrest time, four were normal after resuscitation. One had moderate disability while another dog had severe disability. Two dogs remained in coma.
Discussion: In this remarkable study, dogs could be maintained in suspended animation at 10 degrees Celsius when rapidly cooled after two minutes. The most obvious problem in extending this strategy to the real world is that Emergency Medical response time is certainly greater than two minutes. However, while we know that delayed cooling leads to increased brain injury, trials using suspended animation have not been tried in human beings even in settings in which prompt response is possible (such as hypothermia instituted in the field). One of the other interesting findings in the study is that operative trauma during suspended animation (splenectomy) leads to a worse outcome after reperfusion. The cause is unclear in this case but could be secondary to need for increased recovery times (all dogs were timed at 72 hours and not at best long term performance) or possibly injury from increased systemic inflammation.
Some of the coldest studies in this field have been performed in dogs. In this amazing study, dogs were tested for neurological recovery after many hours of hypothermia.
Paper: Nozari A, Safar P, Wu X, et. al. "Suspended Animation Can Allow Survival without Brain Damage after Traumatic Exsanguination Cardiac Arrest of 60 Minutes in Dogs." J Trauma (2004); 57: 1266-1275.
Methods: Fourteen dogs were sedated with ketamine and halothane and supported with positive pressure ventilation. The dogs were then exsanguinated over fiver minutes to cardiac arrest. At two minutes, flush of saline at 2 degrees Celsius was administered in femoral artery to achieve tympanic temperature of 10 degrees Celsius. In 6 dogs, reperfusion was performed after 60 minutes of cardiac arrest. In 8 dogs, to simulate trauma, splenic injury was inflicted prior to cardiac arrest. During arrest time of 60 minutes, the spleen was transected. Outcome was determined by overall performance category (1 to 6 with 1 being normal and 6 being death) at 72 hours.
Results:
Resuscitation: All fourteen dogs were successfully resuscitated from cardiac arrest.
Control group: All six dogs in the control group were neurologically normal after 72 hours (they were judged to be identical in behavior to their pre-intervention condition).
Trauma group: Of the eight dogs who underwent splenectomy during the cardiac arrest time, four were normal after resuscitation. One had moderate disability while another dog had severe disability. Two dogs remained in coma.
Discussion: In this remarkable study, dogs could be maintained in suspended animation at 10 degrees Celsius when rapidly cooled after two minutes. The most obvious problem in extending this strategy to the real world is that Emergency Medical response time is certainly greater than two minutes. However, while we know that delayed cooling leads to increased brain injury, trials using suspended animation have not been tried in human beings even in settings in which prompt response is possible (such as hypothermia instituted in the field). One of the other interesting findings in the study is that operative trauma during suspended animation (splenectomy) leads to a worse outcome after reperfusion. The cause is unclear in this case but could be secondary to need for increased recovery times (all dogs were timed at 72 hours and not at best long term performance) or possibly injury from increased systemic inflammation.
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