*** Patient Rescue Temperature *** Date sent: Thu, 23 Mar 2000 05:09:47 -0600 To: Cardsurg@aol.com From: Gordon Giesbrecht Subject: Re: Rescue Temperature >I have jsut come back from a meeting in Sweden where there was >discussion about the correct/best temperature to keep in an ambulance >or helicopter when rescuing a victim of hypothermia. the swedish >policy is to keep the interior at 25C in order to keep the vistim >cool and avoid vasodilatation. > >What do you do or advise? Do you think this is important? Does the >length of the trip make a difference, i.e 15 min vs 2 hours? Do you >think that vasodilatation is a likely possibility, and a dangerous >one? > >The Swedish doctors are seeking an opinion and your help would be >valuable. Thanks. Bruce Paton Bruce: Thank you for your inquiry, this is certainly a burning (no pun intended) question that we have discussed at length with Lars Lundberg of the Swedish Military. 1) As a background, I think the idea of not warming the hypothermic victim comes from two areas of thought: a) The original concept of the "metabolic icebox" (a condition where decreased temperature, decreased metabolic rate, respiration and cardiac output is quite compatable with lif), has been described by Dr. Bill Mills. This is OK as long as the temperature doesn't fall further or something else (like rough handling) induces VF. This concept has been misinterpreted such that some (i.e., the swedish military) feel the metabolic icebox is a "safe" condition and that warming the heart may bring it to a warmer range (28-32°C) where the heart is MORE susceptable to VF. This premise seems unfounded as the threshold for VF clearly decreases as heart temperature continues to drop. I would much rather have a heart at 30°C than 25°C. We have demonstrated in a human model for severe hypothermia (mildly hypothermic subjects with shivering inhibited with meperiding/pithidine) that, without active warming, core temperature drops for as much as 2 more °C and can remain at these low levels for 3-4 hours (J. Applied Physiol 83:1630-34, 1997 and 83:11635-40, 1997). b) The other issue is the fear of massive vasodilation and hypotension caused by surface warming. First if someone is mildly hypothermic (Tcore 32-35°C), he/she will surive unless you really try to kill them. Our treatment decisions are much more important at moderate (28-32°C) or severe (<28°C) hypothermia. At these core temperatures, I cannot think of a way that you will induce massive vasodilation with any means available in an ambulance or helicopter. I have tried applying a Thermostat (arm warming device) to a mildly hypothermic subject in my lab, and applied a water perfused blanket at 45°C to the lower arm for 60 minutes. The only response was a 1st degree burn to the entire lower arm. This significant surface warming did not induce vasodilation, such that the heat applied to the arm was not conducted to the core via blood flow. Many other studies and reports indicate that peripheral vasodilation in a severely hypothermic victim is not seen. Leif Vanggard and I have published a paper (Aviat.Space Environ. Med. 1999: 70, 1081-8) where we immersed both lower legs and warms of mildly hypothermic subjects in 45°C water. Only with this massive heat load on the periphery could we induce vasodilation, and in these cases, there was no evidence of hyptension. I suspect that any cardiac problems seen during pre-hospital teatment is due to mechanically-induced reflex effects on the heart or sudden increases in heart work (therefore be very gentle and keep the patient horizontal). 2) I would agree with Ken Zafren and Keith Conover that: rewarming shock is not possible without jostling or verticle positioning, that you should avoid rough handling (to the point of cutting cloths off as a matter of practice). 3) I also feel that warming the vehicle temperature will have little or no effect on vasodilation for another reason. Presumably the patient will be covered, thus insulating from the warm air just as it would be from cold air. 4) I recently hosted a "Cold Injury: Clinical Consensus Meeting" in Winnipeg with several guests including Bruce Paton, Bill Mills, Murray Hamlet, Martin Nemirof, Dan Danzl, Bill Keatings, Leif Vanggard and others. After some discussion we agreed that it was benificial to warm the core of hypothermic patients in a controlled manner (i.e., a target rate of 1-2°C/hr). Once the core temperature reaches 35°C or so, warming could be cut back to prevent overheating and vasodilation. At this point the best way to do this is via torso warming with either forced-air warming (a portable unit has been developed for use in ambulance or helicopters) or the Norweigan charcoal heater (HeatPac). We are just publishing a paper showing that these devices warm non-shivering hypothermic subjects at 1-2 °C/hr. The HeatPac is very easy to use and compact but doesn't warm quite as fast as the more powerful forced-air warming. The choice depends on budget, room, power availability, etc. From our work it also seems that the warming effect requires 20-30 minutes to be apparant. 5) In summary I would recommend that vehicle ambient temperature be kept at a level that provides rescue personnel comfort. Active warming of the patient torso should be initiated especially if the transport time is longer than 20-30 minutes. As usual, continuous monitoring of the patient will allow identification of any untoward effects such as skin burning, drops in blood pressure etc. I trust this is helpful and I would be interested in any feedback on this position. Gord Gordon G. Giesbrecht, Ph.D. Professor Laboratory for Exercise and Environmental Medicine 211 Max Bell Center University of Manitoba Winnipeg, Canada, R3T 2N2 Phone (204) 474-8646; Fax (204) 261-4802; Email ; Lab Web Site http://www.umanitoba.ca/faculties/physed/research/lab1/lab1index.html From: Keith Conover, M.D., FACEP To: Cardsurg@aol.com Subject: Re: Rescue Temperature Copies to: @TEMP2.PML,Jack Grandey Send reply to: kconover+@pitt.edu Date sent: Tue, 14 Mar 2000 12:23:28 -0500 Disclaimer: as the advice below is not evidence-based, you get what you're paying for. >From my review of the literature and the physiology of hypothermia, and experience in both street and wilderness EMS, and as I put into the new U.S. paramedic program as Subject Matter Expert on the topic, I recommend adding as much heat as possible in the prehoospital setting, realizing that until we either have ambulances with hot tubs or usable ambulance-based RF rewarming devices, _rapid_ rewarming and thus major rewarming shock are simply not possible in the back of an ambulance. The only thing that comes close is the HeatPac charcoal-burning rewarming device (see my web page, URL below, for an article about it). I think that raising the ambulance temperature from 25 degrees C (a comfortable room temperature) to, say, 33 degrees C (about as warm as most ambulances could probably get in a cold environment) would (a) not make much difference in rewarming of the patient, and (2) make the ambulance personnel sweat so much that they couldn't see, much less hold onto any equipment. But I really don't think it makes much difference. The temperature of a dry-air ambient environment just isn't going to have much effect on rewarming rate -- even less than warm IV fluids. Hope this helps provoke thought if nothing else. Take care. --Keith Conover, M.D., FACEP http://www.pitt.edu/~kconover