In my third year of medical school, I was discussing my plan for a heart failure patient in the ED and somehow in the course of our discussion, it got brought up that once upon a time “rotating tourniquets” were used in the emergent management of acute heart failure. This method has long since been abandoned in favor of pharmacological methods of Preload reduction, but still a got me thinking on – I was trying to think about the ways in which  the application of a tourniquet affects physiology. One thought crossed my mind was that a patient with acute heart failure or hemorrhagic shock, or any other low flow state might benefit from a theoretical increase in blood perfusion to vital organs if tourniquets were applied to the limbs. The use of rotating tourniquets in the past in patients suffering from decompensated heart failure might suffice as evidence that this, at least in a time-limited fashion, what at least not be harmful (though I understand that the application of a tourniquet is quite painful, and it would  be necessary to ensure that patients were adequately sedated pain-free if we were to do this).

For some reason, this thought crossed my mind again today and I decided to do a literature search. Unsurprisingly it turns out I am not the only person who has had this idea. Last year a group of Chinese researchers published a paper in which they showed an increase in cerebral perfusion pressure and myocardial blood flow in a porcine model of cardiac arrest. Ten pigs (poor pigs, it is such bad luck that their hearts are like ours)  were assigned to receive standard CPR or  CPR augmented with tourniquets wrapped from the distal to the proximal portion of all four limbs.  Ventricular fibrillation was induced with a pacing wire, and  maintained for seven minutes of “down time” before beginning resuscitation. CPR was performed for two minutes before a dose of epinephrine was given, followed by three more minutes of CPR after which defibrillation was attempted.  There were no significant differences between the outcomes in terms of resuscitation success, number of defibrillation attempts, intra-thoracic pressure, duration of CPR, or the use of epinephrine. What did differ between the groups were measures of cerebral perfusion pressure is measured by carotid bloodflow, systolic and diastolic blood pressures during CPR, coronary perfusion pressure, and end-tidal CO2.  Survival was the same in both groups, but alas, it is difficult to measure neurologic outcome in pigs, so some important end-points were not reported. The differences in CPP were almost 10 mmHg, ETCO2 went from ~ 28 mmHg in the standard CPR pigs to ~36 mmHg in the tourniquet group, and CBF had a ~ 10 mL/min difference (this seems much less clinically-significant to me, but I’m not sure how big of an impact that is– we don’t have this monitor in our ED).

This is obviously a long way away from being ready for prime time in humans, and I’m not sure that you could use this to even get the idea past an IRB.  that said, if you really could improve both coronary and cerebral blood flow, and there were no significant harms associated with this technique I don’t really see the downside of trying– do you?  Some important limitations beyond the animal model  of this study include the relatively short “downtime”, the lack of assessment of function after the resuscitation (even if you can’t measure neurologic outcomes, you could look at cardiac function),  and the fact that there model of tourniquet usage doesn’t really match the way that we use tourniquets and human beings. This may be nitpicky, but the tourniquets were applied during fibrillation, not during CPR– it is hard to imagine that this would be an easy feat to accomplish or get buy-in for outside a setting where you have plenty of free hands. Lastly, these were presumably otherwise-healthy pigs– we really need a porcine model of a more typical cardiac arrest patient if we’re going to try to apply this to humans.

Still, I find this very interesting, who think that there may be a future in trying to use a similar technique in humans eventually. I have seen many “survivors” of cardiac arrest who may have achieved ROSC, but ultimately never made it out of the ICU– these represent the majority of those who survive in and out-of-hospital cardiac arrest– and anything that could potentially improve their most important outcomes, survival of head and heart, would be welcomed. The odds of me being able to do this RCT while in residency? Probably low. But you never know!

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