Active Rewarming Research Articles

Radiant heat affects thermoregulation and energy expenditure during rewarming from torpor.

The high expenditure of energy required for endogenous rewarming is one of the widely perceived disadvantages of torpor. However, recent evidence demonstrates that passive rewarming either by the increase of ambient temperature or by basking in the sun appears to be common in heterothermic birds and mammals. As it is presently unknown how radiant heat affects energy expenditure during rewarming from torpor and little is known about how it affects normothermic thermoregulation, we quantified the effects of radiant heat on body temperature and metabolic rate of the small (body mass 25 g) marsupial Sminthopsis macroura in the laboratory. Normothermic resting individuals exposed to radiant heat were able to maintain metabolic rates near basal levels (at 0.91 ml O(2) g(-1) h(-1)) and a constant body temperature down to an ambient temperature of 12 degrees C. In contrast, metabolic rates of individuals without access to radiant heat were 4.5-times higher at an ambient temperature of 12 degrees C and body temperature fell with ambient temperature. During radiant heat-assisted passive rewarming from torpor, animals did not employ shivering but appeared to maximise uptake of radiant heat. Their metabolic rate increased only 3.2-times with a 15- degrees C rise of body temperature (Q(10)=2.2), as predicted by Q(10) effects. In contrast, during active rewarming shivering was intensive and metabolic rates showed an 11.6-times increase. Although body temperature showed a similar absolute change between the beginning and the end of the rewarming process, the overall energetic cost during active rewarming was 6.3-times greater than that during passive, radiant heat-assisted rewarming. Our study demonstrates that energetic models assuming active rewarming from torpor at low ambient temperatures can substantially over-estimate energetic costs. The low energy expenditure during passive arousal provides an alternative explanation as to why daily torpor is common in sunny regions and suggests that the prevalence of torpor in low latitudes may have been under-estimated in the past.

Vasopressor response in a porcine model of hypothermic cardiac arrest is improved with active compression-decompression cardiopulmonary resuscitation using the inspiratory impedance threshold valve.

During normothermic cardiac arrest, a combination of active compression-decompression (ACD) cardiopulmonary resuscitation (CPR) with the inspiratory threshold valve (ITV) significantly improves vital organ blood flow, but this technique has not been studied during hypothermic cardiac arrest. Accordingly, we evaluated the hemodynamic effects of ACD + ITV CPR before, and after, the administration of vasopressin in a porcine model of hypothermic cardiac arrest. Pigs were surface-cooled until their body core temperature was 26 degrees C. After 10 min of untreated ventricular fibrillation, 14 animals were randomly assigned to either ACD CPR with the ITV (n = 7) or to standard (STD) CPR (n = 7). After 8 min of CPR, all animals received 0.4 U/kg vasopressin IV, and CPR was maintained for an additional 10 min in each group; defibrillation was attempted after 28 min of cardiac arrest, including 18 min of CPR. Before the administration of vasopressin, mean +/- SEM common carotid blood flow was significantly higher in the ACD + ITV group compared with STD CPR (67 +/- 13 versus 26 +/- 5 mL/min, respectively; P < 0.025). After vasopressin was given at minute 8 during CPR, mean +/- SEM coronary perfusion pressure was significantly higher in the ACD + ITV group, but did not increase in the STD group (29 +/- 3 versus 15 +/- 2 mm Hg, and 25 +/- 1 versus 14 +/- 1 mm Hg at minute 12 and 18, respectively; P < 0.001); mean +/- SEM common carotid blood flow remained higher at respective time points (33 +/- 8 versus 10 +/- 3 mL/min, and 31 +/- 7 versus 7 +/- 3 mL/min, respectively; P < 0.01). Without active rewarming, spontaneous circulation was restored and maintained for 1 h in three of seven animals in the ACD + ITV group versus none of seven animals in the STD CPR group (not significant). During hypothermic cardiac arrest, ACD CPR with the ITV improved common carotid blood flow compared with STD CPR alone. Moreover, after the administration of vasopressin, coronary perfusion pressure was significantly higher during ACD + ITV CPR, but not during STD CPR. New strategies are needed to improve the efficiency of cardiopulmonary resuscitation (CPR) in hypothermic cardiac arrest. Active compression-decompression CPR with the inspiratory threshold valve improved carotid blood flow (and coronary perfusion pressure with vasopressin) compared with standard CPR.

Management of profound hypothermia in children without the use of extracorporeal life support therapy

Profound hypothermia is managed more and more with extracorporeal life support technology, especially when a patient's circulation is compromised. Many centres do not have rapid access to this service, however, and are still dependent on active internal rewarming techniques--eg, peritoneal and pleural lavage. Such interventions are invasive, and associated with inherent risk. Here, we report our successful experience with an active external rewarming technique in children with profound hypothermia (core temperature <20 degrees C).

A Case Report of Hypothermia in the Wilderness

Accidental hypothermia due to environmental exposure is a common condition encountered in the wilderness setting. I report a case of hypothermia that occurred in New Hampshire to a 42-year-old, poorly prepared mountaineer. He presented with ataxia, impaired judgment, oliguria, and slight confusion, suggestive of mild to moderate hypothermia. He was treated in the field using passive and active external rewarming methods and 1 active internal method. The signs, symptoms, and progression of hypothermia are reviewed, and treatment options are discussed, with an emphasis on management of hypothermia in the wilderness setting. Additionally, more complicated treatment modalities are canvassed, as these are of use to rescue teams and expeditions. Current controversies regarding the treatment of hypothermia, resuscitation efforts, and potential complications are also mentioned.

Accidental hypothermia and active rewarming: the metabolic and inflammatory changes observed above and below 32°C

Objectives: In accidental hypothermia the underlying physiological mechanisms responsible for poor outcome during rewarming through 32°C remain obscure, although possible associations include changes in acid-base balance, divalent cations, and inflammatory...

Hypothermia from prolonged immersion: biophysical parameters of a survivor

We report a case of survival following prolonged immersion and hypothermia. The patient survived for over 9 h in open water, after his vessel capsized and sank in the Pacific Ocean off the coast of Northern California. Water temperature on the day of the sinking was 14.4°C (58.0°F). Although he did have adequate flotation, the patient did not wear a survival suit. On initial physical examination in the Emergency Department (ED), the patient’s rectal temperature was 30.0°C (86.0°F). With active rewarming, his temperature returned to normal (37.0°C {98.6°F}) within 5 h. Body fat of the patient was 19.6%, near the 50th percentile for his age (19.0%). Surface/volume ratio of the patient (.0228 m 2/L) was 19% smaller than a predicted average (.0282 m 2/L). We believe that the patient’s large body habitus contributed to survival and that surface/volume ratio was likely the biophysical variable most closely associated with decreased cooling.

Hypothermia

Accidental hypothermia is defined as an unintentional decline in the core temperature below 35 degrees C. The population of patients at risk is very heterogeneous. Common thermal stressors include both primary exposures and secondary contributory diseases or injuries. As the core temperature progressively declines, the compensatory metabolic, adrenergic, and cardiovascular responses that attempt to maintain thermal homeostasis fail. At this juncture, therapeutic intervention must occur. An understanding of the pathophysiological variables impacting rewarming is critical. For example, the effects of cold on the coagulation system impact both the approach to cardiovascular resuscitation and the choice of rewarming technique. There are no randomized controlled trials that definitively establish the ideal rewarming strategy for each unique presentation. The resuscitative goal is to match the clinical presentation with the threshold temperatures at which various rewarming modalities and pharmacological interventions should occur. Identification of the indications for both noninvasive and invasive active rewarming techniques in patients requiring critical care is key. Poikilothermia, failure to rewarm, endocrinologic insufficiency, cardiovascular instability, traumatic or toxicological induced peripheral vasodilation, or the presence of major predisposing factors mandates active rewarming. The simultaneous or sequential use of the various rewarming techniques permits a versatile approach to therapy. Outcome remains problematic to predict because there may never be a validated prognostic neurological scale. The history, physical examination, and, ironically, the vital signs are routinely misleading. A tachycardia that is not proportionate to the degree of hypothermia suggests hypovolemia, hypoglycemia, or the presence of toxins. Given the decreased carbon dioxide production, persistent hyperventilation implies an underlying organic acidosis or central nervous system abnormality. Finally, toxic or traumatic or infectious impairment of the central nervous system may be obscured by hypothermia.

Clinical Characteristics of Hypothermia with Osborn Wave on ECG Based on the Analysis of 5 Patients

Background and Objectives:The Osborn wave is the name designated to the wave formation produced when there is a large, prominent deviation of the J point from the baseline. The wave has been reported in many countries, but only 2 cases have been reported in Korea. Thus, the purpose of our study was to evaluate the clinical characteristics and therapy of hypothermia employing the Osborn wave with Koreans. Subjects and Methods:Between February 2001 and April 2001, five patients visiting our department with hypothermia were enrolled in this study. We analyzed these patients for their distribution, symptoms and signs, associated disorders, risk factors, electrocardiogram and laboratory findings. Results:All 5 patients were male with an average age was 44.8±12.7 years. Three patients had a semi-comatose mentality and 2 cases had a comatose mentality. Their associated disorders were diabetes (2 cases), psychotic problems (1 case) and nutritional deficiency (1 case). Risk factors were alcohol abuse (3 cases) and drug in toxication (1 case). Laboratory abnormalities were acidosis (4 cases), increased serum glucose levels (all 5 cases) and increased serum potassium levels (3 cases). After active core rewarming by a line heat exchanger, 3 of the 5 patients completely recovered from hypothermia, 1 case immediately expired following admission and 1 case survived for 10 days, but later expired due to acute respiratory distress syndrome. The Osborn wave was persistent in 1 case and disappeared in 3 cases. Conclusion:We experienced 5 cases of hypothermia with an Osborn wave. The mortality of patients displaying an Osborn wave is expected to decrease if this anomaly is immediately found and treated by an appropriate method. (Korean Circulation J 2002;32(8):710-714)

Effects of epinephrine in a pig model of hypothermic cardiac arrest and closed-chest cardiopulmonary resuscitation combined with active rewarming

Objective: The aim of the current study was to assess the effects of epinephrine in a pig model of hypothermic cardiac arrest followed by closed-chest cardiopulmonary resuscitation combined with active rewarming, simulating the clinical management of an arrested hypothermic patient in a hospital without cardiopulmonary bypass facilities. Design: Prospective, randomized animal study. Setting: University research laboratory. Subjects: Twelve 12- to 16-week-old domestic pigs. Interventions: Pigs were surface cooled to a body core temperature of 28°C. After 4 min of untreated cardiac arrest, manual closed-chest CPR and thoracic lavage with 40°C warmed fluid were started. After 3 min of external chest compression animals were randomly assigned to receive epinephrine (45, 45 and 200 μg/kg) or saline placebo in 5-min intervals. Measurements and main results: Coronary perfusion pressure was about 15 mmHg in placebo group pigs. Coronary perfusion pressure was significantly higher after epinephrine, but restoration of spontaneous circulation was not more frequent (one of six epinephrine versus three of six saline placebo pigs, P=0.34). After 45 μg/kg epinephrine the arterial P o 2 was significantly lower when compared to the saline placebo. The third 200 μg/kg epinephrine dose resulted in a significantly enhanced mixed venous hypercarbic acidosis. Conclusions: After a short 4-min period of hypothermic cardiac arrest, epinephrine may not be necessary to maintain coronary perfusion pressure around the threshold usually correlating with successful defibrillation, even during prolonged closed-chest CPR combined with active rewarming. The enhanced mixed venous hypercarbic acidosis in epinephrine-treated animals may support the argument against repeated or high dose epinephrine administration during hypothermic CPR.

Hemodialysis in management of hypothermia

Hypothermia is defined as a core body temperature of less than 35[deg ]C and is divided further into mild, moderate, and severe depending on the temperature level. Several active internal rewarming modalities have been described in the management of moderate-to-severe accidental hypothermia. We report a 73-year-old black man with underlying end-stage renal failure and ischemic cardiomyopathy who was admitted with severe accidental hypothermia (core body temperature, 24.9[deg ]C) secondary to environmental cold exposure. The patient was resuscitated initially with warm intravenous fluids and peritoneal dialysis with warm fluids with an average temperature rise of 1[deg ]C. The patient was switched to hemodialysis that brought his temperature from 30.2[deg ]C to 36.7[deg ]C during a 3.5-hour dialysis with an average rise of 1.9[deg ]C/h. Hemodialysis is a rapid and efficient modality of rapid internal rewarming for moderate-to-severe accidental hypothermia. [copy ] 2001 by the National Kidney Foundation, Inc.

Damage control: collective review.

Damage control: collective review.

Part 8: Advanced Challenges in Resuscitation

Part 8: Advanced Challenges in Resuscitation

Resistive heating is more effective than metallic-foil insulation in an experimental model of accidental hypothermia: A randomized controlled trial

Study objective: We study a resistive-heating blanket in a volunteer model of severe accidental hypothermia to evaluate differences in rates of rewarming, core temperature afterdrop, and body heat content and distribution during active and passive rewarming. Methods: Eight volunteers participated in a crossover design on 2 days. The volunteers were anesthetized and cooled to 33°C (91.4°F); anesthesia was subsequently discontinued, and shivering was prevented with meperidine. On one randomly assigned day, the volunteers were rewarmed passively with reflective foil (passive insulation), whereas on the other they were covered with a carbon fiber–resistive heating blanket set to 42°C (107.6°F; active rewarming). Trunk and head temperature and heat content were calculated from core (tympanic membrane) temperature. Peripheral (arm and leg) tissue temperature and heat content were estimated by using fourth-order regressions and integration over volume from 30 tissue and skin temperatures. Results: Core heat content increased 73±14 kcal (mean±SD) during 3 hours of active warming, but only 31±24 kcal with passive insulation, a difference of 41±20 kcal (95% confidence interval [CI] 27 to 55 kcal; P <.001). Peripheral tissue heat content increased linearly by 111±16 kcal during active warming but only by 38±31 kcal during passive warming, a difference of 74±34 kcal (95% CI 50 to 97; P <.001). Consequently, total body heat increased 183±22 kcal during active warming but only 68±54 kcal with passive insulation, a difference of 115±42 kcal (95% CI 86 to 144 kcal; P <.001). Core temperature increased from 32.9°C±0.2°C to 35.2°C±0.4°C during 3 hours of active warming, a difference of 2.3°C±0.4°C. In contrast, core temperature with foil insulation only increased from 32.9°C±0.2°C to 33.8°C±0.5°C, a difference of only 0.8°C±0.4°C. The difference in the core temperature increase between the two treatments was thus 1.5°C±0.4°C (95% CI 1.2°C to 1.7°C; P <.001 between treatments). Active warming was not associated with an afterdrop, whereas the afterdrop was 0.2°C±0.2°C and lasted a median of 45 minutes (interquartile range, 41 to 64 minutes) with passive insulation. Conclusion: Resistive heating more than doubles the rewarming rate compared with that produced by reflective metal foil and does so without producing an afterdrop. It is therefore likely to be useful in the prehospital setting. [Greif R, Rajek A, Laciny S, Bastanmehr H, Sessler DI. Resistive heating is more effective than metallic-foil insulation in an experimental model of accidental hypothermia: a randomized controlled trial. Ann Emerg Med. April 2000;35:337-345.]

Accidental hypothermia and active rewarming: the metabolic changes observed above and below 32°C

Accidental hypothermia and active rewarming: the metabolic changes observed above and below 32°C

Effects on C3 and CH50 Levels During and Following Extracorporeal Whole Body Hyperthermia

Cardiopulmonary bypass can affect inflammatory reactions and evoke the “postperfusion syndrome,” manifested as multiple organ dysfunction in the recovery period. This syndrome is generated by the activation of complement, macrophages, neutrophils, and inflammatory cytokines. Following the use of hypothermia during cardiac procedures, active hyperthermic rewarming is used to reestablish body temperature. Complement levels and their interactions have been investigated during and following hypothermia. Hyperthermia is being used clinically; however, the effect of markedly elevated temperatures on complement is unknown and, therefore, needs to be investigated. A pilot canine study was designed to begin to explore what role hyperthermia may play on complement levels during and following extracorporeal whole body hyperthermia. Five dogs were heated to a core temperature of approximately 42°C, held at this elevated temperature for 90 minutes, then cooled to normothermia. A decline in C3 levels at the end of warming with further declines through day 4 post treatment was observed. CH50 levels mimicked the C3 level decline; however, there was a trend for rebounding by day 4. The findings involving complement factors following hyperthermia signify that this increase in temperature causes a decrease in both C3 and CH50 levels.

Effects of ethanol on systemic hemodynamics in a swine model of accidental hypothermia

☆ Sources of fundings: This study was supported by Haa Sinai Medical Center (Cleveland, OH) (GL) and a Depar Foundation Grant from the MetroHealth Medical Center ( ☆☆ The authors have no conflicts of interest related to th an investigator-directed research grant from Gilead Scienc to this work. ⁎ Corresponding author at: Heart and Vascular Researc Case Western Reserve University, 2500, MetroHealth D Tel.: +1 216 778 5293; fax: +1 216 778 7342. E-mail address: lwilson@metrohealth.org (L.D. Wilson http://dx.doi.org/10.1016/j.ajem.2015.07.012 0735-6757/© 2015 Elsevier Inc. All rights reserved. Article history: Received 18 May 2015 Received in revised form 14 July 2015 Accepted 14 July 2015 Objectives: Accidental hypothermia is frequently associated with ethanol intoxication. Each has independent effects on systemic hemodynamics, but their combined effects are poorly understood. We aimed to describe the hemodynamic effects of ethanol intoxication in a model of severe hypothermia and rewarming. Methods:Anesthetized pigswas assigned to control (n=8) or ethanol groups (ETOH) (n=7, 3mg/kg of ethanol via an orogastric tube). Subjects were cooled to 25°C using ice packs and then warmed to baseline core temperature with passive external and active core rewarming. Results: In the ETOH group, peak serum ethanol concentration was 202 mg/dL at 25°C. Ethanol had no effect on time of cooling or rewarming. In both the control and ETOH, there were similar maximal decreases in mean arterial pressure (from 94 ± 24 to 50 ± 15 mm Hg and 100 ± 27 to 31 ± 12 mm Hg, respectively), ventricular contractility (rate of maximal left ventricular pressure rise from 5731 ± 1462 to 2610 ± 596 mm Hg/s and 6832 ± 1384 to 1937 ± 437 mm Hg/s, respectively), and cardiac output (from 2.14 ± 0.8 to 0.53 ± 0.3 L/min and 2.93 ± 0.9, to 0.44 ± 0.2 L/min, respectively; all P b .001). After rewarming, only in the ETOH group were persistent decreases in mean arterial pressure (59 ± 14 mmHg), contractility (3982 ± 1573 mmHg/s), and cardiac output (1.6 ± 0.9 L/min, all P b .03) observed. Conclusions:Hypothermia caused significant adverse effects on cardiac function and systemic hemodynamics,which returned to baseline with rewarming. Ethanol intoxication had no additional effects on systemic hemodynamics during cooling; however, it caused more prolonged depression of cardiac function and adverse effects on systemic hemodynamics during rewarming. These data may have implications for resuscitation of ethanol-intoxicated victims of accidental hypothermia. © 2015 Elsevier Inc. All rights reserved.

Effects of short heat exposure on human red and white blood cells.

The infusion of warm intravenous fluid (IVF) is a simple and effective method used to maintain or restore core body temperature. At present, 40 degrees C is believed to be the highest temperature that can be safely administered. There is concern that temperatures greater than 40 degrees C may harm blood cells. The mixing time of IVF infused into a high-flow vein such as the superior vena cava is very short, however, approximately 300 milliseconds. We will determine the maximum temperature and exposure time tolerated by human red and white blood cells without producing injury. Whole blood and isolated neutrophils were exposed to temperatures (40-80 degrees C) for short time intervals (150-1,200 milliseconds). Lethal injury to red and white blood cells was measured by the plasma free hemoglobin and percent viability, respectively. Neutrophil viability was measured by trypan blue staining. Sublethal injury to red and white cells was measured by osmotic fragility and oxidative burst, respectively. Neutrophil oxidative burst was measured by chemiluminescence. Control values were compared with postexposure values using analysis of variance with p < 0.05 indicating significance. Lethal injury to red blood cells did not occur until exposure at 70 degrees C for 300 milliseconds (plasma free hemoglobin, 116.3 +/- 34.7 mg%; p < 0.05). Lethal injury to neutrophils did not occur, even at exposure at 80 degrees C for 1,200 milliseconds. Sublethal injury to red blood cells did not occur until exposure at 60 degrees C for 1,200 milliseconds. Sublethal injury to neutrophils did not occur until exposure at 60 degrees C for 600 milliseconds (percent change in oxidative burst = 28.9 +/- 0.96%; p < 0.05). The exposure of human red blood cells and neutrophils to temperatures up to 60 degrees C for up to 600 milliseconds does not cause lethal or sublethal injury. These findings contribute to the body of evidence supporting the use of centrally infused IVF at temperatures greater than 40 degrees C for active core rewarming.

Which rewarming therapy in hypothermia? A review of the randomised trials

AbstractIntroductionHypothermia may be encountered at some time in most parts of Australasia. There is a need to evaluate the merits of the various practical rewarming therapies available.MethodAn electronic and manual search of databases to identify randomised trials published between 1966 and 1996 inclusive which evaluated rewarming therapies in hypothermia.ResultsThere is a paucity of randomised trials on this subject and many of the rewarming therapies recommended in authoritative texts and reviews have never been evaluated in randomised clinical trials. In published trials core afterdrop is typically &lt;0.5 C and is least with active core rewarming. Passive rewarming alone may be expected to raise core temperature by 0.75 C/hr and the addition of inhalation and/or forced air rewarming can be expected to at least double this.ConclusionsThe choice of rewarming therapy may be largely one of practicality and availability. Future rewarming research should focus on clinical outcomes in patients with moderate to severe hypothermia.

Transcutaneous Pacing in a Hypothermic-Dog Model

Study objective: To evaluate the hemodynamic response to transcutaneous pacing (TCP) during rewarming from hypothermia. Methods: We conducted a prospective, controlled laboratory investigation using 20 mongrel dogs. The animals were anesthetized, intubated, and mechanically ventilated. Arterial pressure, core temperature, and cardiac rhythm were continuously monitored. All dogs were cooled to a core temperature of 27 ° C; experimental animals were then subjected to TCP with active rewarming, and control animals underwent sham trancutaneous pacing and rewarmed in the same manner. Serial hemodynamic measurements, time to rewarming, and cardiac isoenzyme concentrations were analyzed. Results: Rewarming was accomplished significantly faster in the paced group (171.5±31.5 minutes) than in the control group (254±55.9 minutes, P<.05). After rewarming, the mean cardiac index in the paced dogs returned to 84% of baseline, compared with 63% of baseline in the nonpaced group ( P < .05). None of the paced animals demonstrated significant hemodynamic deterioration, potentially lethal arrhythmias, or other evidence of myocardial injury. Conclusion: TCP is safe, effective and easily implemented in dogs. In this small series of dogs, TCP restored and maintained hemodynamic stability and allowed the hypothermic animals to rewarm in half the time required by their nonpaced counterparts. [Dixon RG, Dougherty JM, White LJ, Lombino D, Rusnak RR: Transcutaneous pacing in a hypothermic-dog model. Ann Emerg Med May 1997; 29:602-606.]

偶発性高度低体温症改善後に生じた細菌性腹膜炎にて死亡した１例

We present the case of a patient who suffered accidental hypothermia. The patient's rectal temperature was 25°C on arrival. She showed disturbance of consciousness (JCS III-200) and circulatory shock due to the hypothermia. We attempted treatment by intravenous administration of heated fluids and irrigation of the stomach with warm physiological saline. Although within the next 12 hours her body temperature gradually normalized, she suffered multiple organ failure and developed bacterial peritonitis. She died of adult respiratory distress syndrome, bacterial peritonitis and sepsis caused by Pseudomonas aeruginosa. Prolonged hypothermia accelerated coagulatory system due to hypotension, dehydoration, microscopic circulatory failure, acceleration of blood viscosity and disseminated intravascular coagulation. Several techniques of active core rewarming are reported. Rapid rewarming is the most important of all to prevent thrombosis. Therefore for the non-arrested patient who has a temperature less than 30°C, extracorporeal circulation seems to be the technique of choice, for the arrested patient without trauma, cardiopulmonary bypass seems to be the technique. These treatments prevent complications after recovery from hypothermia.