Shiver suppression using focal hand warming in unanesthetized normal subjects

Focal hand warming for post-anaesthesia shivering control: A simple and safe non-pharmacological approach in resource limited-area

Post-anaesthesia shivering is a common complication and has multiple deleterious effects. Sometimes multiple non-pharmacological interventions applied together may not control post-anaesthesia shivering adequately, necessitating the use of drugs in some cases. Hand warming is commonly used to warm up the body since time immemorial but its role in preventing post-anaesthesia shivering has not been evaluated. This case series describes the application of this simple and safe method of focal hand warming along with other non-pharmacological measures to suppress post-anaesthesia shivering, whereby possible use of drugs could be avoided.

Cheap and simple, could it get even cooler? Mild hypothermia and COVID-19

Purpose

The pathophysiology theories of COVID-19 attach the injury of target organs to faulty immune responses and occasionally hyper-inflammation. The damage frequently extends beyond the respiratory system, accompanying cardiovascular, renal, central nervous system, and/or coagulation derangements. Tumor necrosis factor-α (TNF-α) and interleukins (IL)-1 and − 6 suppression may improve outcomes, as experimentally shown. Targeted therapies have been proposed, but mild therapeutic hypothermia—a more multifaceted approach—could be suitable.

Findings

According to evidence derived from previous applications, therapeutic hypothermia diminishes the release of IL-1, IL-6, and TNF-α in serum and at the tissue level. PaCO2 is reduced and the PaO2/FiO2 ratio is increased, possibly lasting after rewarming. Cooling might mitigate both ventilator and infectious-induced lung injury, and suppress microthrombi development, enhancing V/Q mismatch. Improvements in microhemodynamics and tissue O2 diffusion, along with the ischemia-tolerance heightening of tissues, could be reached. Arrhythmia incidence diminishes. Moreover, hypothermia may address the coagulopathy, promoting normalization of both hypo- and hyper-coagulability patterns, which are apparently sustained after a return to normothermia.

Conclusions

As per prior therapeutic hypothermia literature, the benefits regarding inflammatory response and organic damage might be seen. Following the safety-cornerstones of the technique, the overall infection rate and infection-related mortality are not expected to rise, and increased viral replication does not seem to be a concern. Therefore, the possibility of a low cost and widely available therapy being capable of improving COVID-19 outcomes deserves further study.

Control of Shivering During Targeted Temperature Management

Targeted temperature management (TTM) is used frequently in patients with a variety of diseases, especially those who have experienced brain injury and/or cardiac arrest. Shivering is one of the main adverse effects of TTM that can often limit its implementation and efficacy. Shivering is the body's natural response to hypothermia and its deleterious effects can negate the benefits of TTM. The purpose of this article is to provide an overview of TTM strategies and shivering management.

Induction of therapeutic hypothermia by pharmacological modulation of temperature-sensitive TRP channels: theoretical framework and practical considerations

Therapeutic hypothermia has emerged as a remarkably effective method of neuroprotection from ischemia and is being increasingly used in clinics. Accordingly, it is also a subject of considerable attention from a basic scientific research perspective. One of the fundamental problems, with which current studies are concerned, is the optimal method of inducing hypothermia. This review seeks to provide a broad theoretical framework for approaching this problem, and to discuss how a novel promising strategy of pharmacological modulation of the thermosensitive ion channels fits into this framework. Various physical, anatomical, physiological and molecular aspects of thermoregulation, which provide the foundation for this text, have been comprehensively reviewed and will not be discussed exhaustively here. Instead, the first part of the current review, which may be helpful for a broader readership outside of thermoregulation research, will build on this existing knowledge to outline possible opportunities and research directions aimed at controlling body temperature. The second part, aimed at a more specialist audience, will highlight the conceptual advantages and practical limitations of novel molecular agents targeting thermosensitive Transient Receptor Potential (TRP) channels in achieving this goal. Two particularly promising members of this channel family, namely TRP melastatin 8 (TRPM8) and TRP vanilloid 1 (TRPV1), will be discussed in greater detail.

Fever, immunity, and molecular adaptations

The heat shock response (HSR) is an ancient and highly conserved process that is essential for coping with environmental stresses, including extremes of temperature. Fever is a more recently evolved response, during which organisms temporarily subject themselves to thermal stress in the face of infections. We review the phylogenetically conserved mechanisms that regulate fever and discuss the effects that febrile-range temperatures have on multiple biological processes involved in host defense and cell death and survival, including the HSR and its implications for patients with severe sepsis, trauma, and other acute systemic inflammatory states. Heat shock factor-1, a heat-induced transcriptional enhancer is not only the central regulator of the HSR but also regulates expression of pivotal cytokines and early response genes. Febrile-range temperatures exert additional immunomodulatory effects by activating mitogen-activated protein kinase cascades and accelerating apoptosis in some cell types. This results in accelerated pathogen clearance, but increased collateral tissue injury, thus the net effect of exposure to febrile range temperature depends in part on the site and nature of the pathologic process and the specific treatment provided.

Use of hypothermia in the intensive care unit

Used for over 3600 years, hypothermia, or targeted temperature management (TTM), remains an ill defined medical therapy. Currently, the strongest evidence for TTM in adults are for out-of-hospital ventricular tachycardia/ventricular fibrillation cardiac arrest, intracerebral pressure control, and normothermia in the neurocritical care population. Even in these disease processes, a number of questions exist. Data on disease specific therapeutic markers, therapeutic depth and duration, and prognostication are limited. Despite ample experimental data, clinical evidence for stroke, refractory status epilepticus, hepatic encephalopathy, and intensive care unit is only at the safety and proof-of-concept stage. This review explores the deleterious nature of fever, the theoretical role of TTM in the critically ill, and summarizes the clinical evidence for TTM in adults.

Optimal management of shivering during therapeutic hypothermia after cardiac arrest

Both pharmacological and nonpharmacological methods are used to control shivering in therapeutic hypothermia. An evidence-based protocol based on the most current research has been developed for the management of shivering during therapeutic hypothermia. Meperidine is the drug of choice and provides the greatest reduction in the shivering threshold. Other effective pharmacological agents recommended for reducing the threshold include dexmedetomidine, midazolam, fentanyl, and magnesium sulfate. In addition, skin counterwarming techniques, such as use of an air-circulating blanket, are effective nonpharmacological methods for reducing shivering when used in conjunction with medication. As a last resort, neuromuscular blocking agents are considered appropriate therapy for management of refractory shivering.

Aspects of thermoregulation physiology

PURPOSE OF REVIEW

The review covers the main aspects of thermoregulation physiology and highlights the implications for therapeutic hypothermia trials. Prevention of shivering and other hypothermia side-effects is of key importance because controlling thermoregulatory responses may be essential for demonstrating neuro-protective properties of hypothermia in several pathologic conditions in which its role is still uncertain, such as in traumatic brain injury and stroke.

RECENT FINDINGS

Several recommendations and clinical reviews have been produced in the past 2 years about the application and feasibility of therapeutic hypothermia. Many drugs have been tested in healthy volunteers and anaesthetized patients to abolish shivering but the best protocol for managing side-effects has not yet been defined. A possible strategy might be to simultaneously apply physical methods, such as skin warming, and combination drug therapy. Different drug protocols can be applied, depending on the nature of the care setting.

SUMMARY

During moderate hypothermia treatment, conducted in an intensive care environment, shivering can be treated with sedatives, opioids (meperidine in particular), and α2-agonists, combined with active skin counter-warming. However, new randomized controlled clinical trials in intensive care patients are required to improve our knowledge regarding this treatment.

Induction of therapeutic hypothermia requires modulation of thermoregulatory defenses

Hypothermia has been linked to beneficial neurologic outcomes in different clinical situations and its therapeutic value is considered important. For example, in asphyctic neonates and in patients with out-of-hospital cardiac arrest (with ventricular fibrillation as the initial cardiac rhythm), rapid installation of hypothermia has been reported to add substantial therapeutic benefits over nonthermal standard treatments. Yet, in other groups of patients in which the application of therapeutic hypothermia may be applied with clinical benefits, the optimization of therapy remains less straightforward, as the body possesses vigorous defense mechanisms to protect it from inducing hypothermia, that is, especially in conscious patients and/or in those in which the hypothalamus remains intact, such as stroke patients or patients who suffer a myocardial infarction or spinal cord injury. This overview summarizes the body's primary reactions to hypothermia and the defense mechanisms available or evoked. Then, clinically applicable ways to overcome these forceful cold defenses of the body are described to ensure both an optimal induction process for therapeutic hypothermia and maximal subjective comfort for these conscious patients.

Induction of mild hypothermia by noninvasive body cooling in healthy, unanesthetized subjects

The induction of mild hypothermia has been considered as an important means to provide protection against cerebral ischemia. Yet, to date, the relative clinical efficacies of different noninvasive methods for reducing core body temperature have not been thoroughly studied. The aim of the current investigation was to compare the relative effectiveness of several noninvasive cooling techniques for reducing core temperatures in healthy volunteers. Cooling methods included convective/conductive and evaporative/conductive combinations, as well as evaporative cooling alone. Additionally, focal facial warming was employed as a means to suppress involuntary motor activity and thus better enable noninvasive cooling. Core temperatures were measured so to monitor the relative efficiencies of these induced cooling methodologies. With each employed methodology, rectal temperature reductions were induced, with combined evaporative/conductive (n=4, 1.44°C±0.99°C) and convective/conductive (n=4, 1.51°C±0.89°C) approaches yielding the largest decreases: note, that evaporative cooling alone was not as efficient in lowering core body temperature (n=10, 0.56°C±0.20°C; n=16, 0.58°C±0.27°C). In this study on healthy volunteers, the evaporative/conductive and convective/conductive combination methods were more effective in reducing core temperatures as compared with an evaporative approach alone. These therapeutic approaches for the induction of mild hypothermia (including the use of facial warming) could be employed in warranted clinical cases, importantly without the need for administration of anesthetics or paralytics.

Therapeutic hypothermia for acute ischemic stroke: ready to start large randomized trials?

Therapeutic hypothermia is a means of neuroprotection well established in the management of acute ischemic brain injuries such as anoxic encephalopathy after cardiac arrest and perinatal asphyxia. As such, it is the only neuroprotective strategy for which there is robust evidence for efficacy. Although there is overwhelming evidence from animal studies that cooling also improves outcome after focal cerebral ischemia, this has not been adequately tested in patients with acute ischemic stroke. There are still some uncertainties about crucial factors relating to the delivery of hypothermia, and the resolution of these would allow improvements in the design of phase III studies in these patients and improvements in the prospects for successful translation. In this study, we discuss critical issues relating first to the targets for therapy including the optimal depth and duration of cooling, second to practical issues including the methods of cooling and the management of shivering, and finally, of factors relating to the design of clinical trials. Consideration of these factors should inform the development of strategies to establish beyond doubt the place of hypothermia in the management of acute ischemic stroke.

Defeating normal thermoregulatory defenses: induction of therapeutic hypothermia

Therapeutic hypothermia may be useful in various circumstances including stroke. However, core body temperature is normally tightly regulated. Even mild hypothermia in conscious subjects thus provokes vigorous thermoregulatory defenses which are potentially harmful in fragile patients. Furthermore, thermoregulatory responses are effective, which reduces the rate at which hypothermia can be induced. Drugs are thus often given to blunt normal thermoregulatory defenses. General anesthetics profoundly impair thermoregulatory control, but prolonged general anesthesia is rarely practical or appropriate. A variety of other drugs have therefore been evaluated. Most opioids only slightly impair thermoregulatory defenses, but meperidine is considerably more effective than equipotent doses of other opioids. The central alpha-2 agonists clonidine and dexmedetomidine are also useful. However, the best overall approach to inducing thermal tolerance appears to be a combination of buspirone and meperidine, which reduces the core temperature triggering shivering to about 33.5 degrees C in doses that maintain adequate ventilation.

Thermoregulatory defense mechanisms

Core body temperature is normally tightly regulated by an effective thermoregulatory system. Thermoregulatory control is sometimes impaired by serious illness, but more typically remains intact. The primary autonomic defenses against heat are sweating and active precapillary vasodilation; the primary autonomic defenses against cold are arteriovenous shunt vasoconstriction and shivering. The core temperature triggering each response defines its activation threshold. Temperatures between the sweating and vasoconstriction thresholds define the inter-threshold range. The shivering threshold is usually a full 1 degrees C below the vasoconstriction threshold and is therefore a "last resort" response. Both vasoconstriction and shivering are associated with autonomic and hemodynamic activation; and each response is effective, thus impeding induction of therapeutic hypothermia. It is thus helpful to accompany core cooling with drugs that pharmacologically induce a degree of thermal tolerance. No perfect drug or drug combination has been identified. Anesthetics, for example, induce considerable tolerance, but are rarely suitable. Meperidine-especially in combination with buspirone-is especially effective while provoking only modest toxicity. The combination of buspirone and dexmedetomidine is comparably effective while avoiding the respiratory depression association with opioid administration.

Therapeutic hypothermia and controlled normothermia in the intensive care unit: practical considerations, side effects, and cooling methods

BACKGROUND

Hypothermia is being used with increasing frequency to prevent or mitigate various types of neurologic injury. In addition, symptomatic fever control is becoming an increasingly accepted goal of therapy in patients with neurocritical illness. However, effectively controlling fever and inducing hypothermia poses special challenges to the intensive care unit team and others involved in the care of critically ill patients.

OBJECTIVE

To discuss practical aspects and pitfalls of therapeutic temperature management in critically ill patients, and to review the currently available cooling methods.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

Cooling can be divided into three distinct phases: induction, maintenance, and rewarming. Each has its own risks and management problems. A number of cooling devices that have reached the market in recent years enable reliable maintenance and slow and controlled rewarming. In the induction phase, rapid cooling rates can be achieved by combining cold fluid infusion (1500-3000 mL 4 degrees C saline or Ringer's lactate) with an invasive or surface cooling device. Rapid induction decreases the risks and consequences of short-term side effects, such as shivering and metabolic disorders. Cardiovascular effects include bradycardia and a rise in blood pressure. Hypothermia's effect on myocardial contractility is variable (depending on heart rate and filling pressure); in most patients myocardial contractility will increase, although mild diastolic dysfunction can develop in some patients. A risk of clinically significant arrhythmias occurs only if core temperature decreases below 30 degrees C. The most important long-term side effects of hypothermia are infections (usually of the respiratory tract or wounds) and bedsores.

CONCLUSIONS

Temperature management and hypothermia induction are gaining importance in critical care medicine. Intensive care unit physicians, critical care nurses, and others (emergency physicians, neurologists, and cardiologists) should be familiar with the physiologic effects, current indications, techniques, complications and practical issues of temperature management, and induced hypothermia. In experienced hands the technique is safe and highly effective.

Progress in shivering control

Hypothermia is a potent neuroprotectant and induced hypothermia holds great promise as a therapy for acute neuronal injury. Thermoregulatory responses, most notably shivering, present major obstacles to therapeutic temperature management. A review of thermoregulatory physiology and strategies aimed at controlling physiologic responses to hypothermia is presented.

Physiology and clinical relevance of induced hypothermia

Experimental evidence and clinical experience suggest that mild hypothermia protects numerous tissues from damage during ischemic insult. However, the extent to which hypothermia becomes a valued therapeutic option will depend on the clinician's ability to rapidly reduce core body temperature and safely maintain hypothermia. To date, general anesthesia is the best way to block autonomic defenses during induction of mild-to-moderate hypothermia; unfortunately, general anesthesia is not an option in most patients likely to benefit from therapeutic hypothermia. Induction of hypothermia in awake humans is complicated by both the technical difficulties related to thermal manipulation and the remarkable efficacy of thermoregulatory defenses, especially vasoconstriction and shivering. The most effective thermal manipulation devices are generally invasive and, therefore, more prone to complications than surface methods. In an effort to inhibit thermoregulation in awake humans, several agents have been tested either alone or in combination with each other. For example, the combination of meperidine and buspirone has already been applied to facilitate induction of hypothermia in human trials. However, pharmacological induction of thermoregulatory tolerance to cold without excessive sedation, respiratory depression, or other serious toxicity remains a major focus of current therapeutic hypothermia research.

Clinical trial of a novel surface cooling system for fever control in neurocritical care patients

OBJECTIVE

To compare the efficacy of a novel water-circulating surface cooling system with conventional measures for treating fever in neuro-intensive care unit patients.

DESIGN

Prospective, unblinded, randomized controlled trial.

SETTING

Neurologic intensive care unit in an urban teaching hospital.

PATIENTS

Forty-seven patients, the majority of whom were mechanically ventilated and sedated, with fever > or =38.3 degrees C for >2 consecutive hours after receiving 650 mg of acetaminophen.

INTERVENTIONS

Subjects were randomly assigned to 24 hrs of treatment with a conventional water-circulating cooling blanket placed over the patient (Cincinnati SubZero, Cincinnati OH) or the Arctic Sun Temperature Management System (Medivance, Louisville CO), which employs hydrogel-coated water-circulating energy transfer pads applied directly to the trunk and thighs.

MEASUREMENTS AND MAIN RESULTS

Diagnoses included subarachnoid hemorrhage (60%), cerebral infarction (23%), intracerebral hemorrhage (11%), and traumatic brain injury (4%). The groups were matched in terms of baseline variables, although mean temperature was slightly higher at baseline in the Arctic Sun group (38.8 vs. 38.3 degrees C, p = .046). Compared with patients treated with the SubZero blanket (n = 24), Arctic Sun-treated patients (n = 23) experienced a 75% reduction in fever burden (median 4.1 vs. 16.1 C degrees -hrs, p = .001). Arctic Sun-treated patients also spent less percent time febrile (T > or =38.3 degrees C, 8% vs. 42%, p < .001), spent more percent time normothermic (T < or =37.2 degrees C, 59% vs. 3%, p < .001), and attained normothermia faster than the SubZero group median (2.4 vs. 8.9 hrs, p = .008). Shivering occurred more frequently in the Arctic Sun group (39% vs. 8%, p = .013).

CONCLUSION

The Arctic Sun Temperature Management System is superior to conventional cooling-blanket therapy for controlling fever in critically ill neurologic patients.

Treatment of Refractory Fever in the Neurosciences Critical Care Unit Using a Novel, Water-Circulating Cooling Device

Fever after acute brain injury affects neuronal function and recovery. Standard therapies have proven to be inadequate in treating hyperthermia in this patient population. We report on safety/efficacy pilot data collected using a noninvasive, novel, water-circulating cooling device in febrile acute brain injury patients. We enrolled patients who developed fever (rectal temperature > or =38.0 degrees C) refractory to pharmacological therapy. The treatment device uses an ice water circulating system embedded in hydrogel-coated, energy transfer pads. Its thermoregulatory feedback control uses cold water (4.0 degrees C-42.0 degrees C) and was set at 36.5 degrees C for this study. We analyzed the temperature response during 600 consecutive minutes of treatment. Six consecutive patients were enrolled and seven episodes of fever were recorded; the mean age of the patients was 59.7 years (range 46-71 years; five male, one female). Diagnoses were as follows: subarachnoid hemorrhage (two), severe traumatic brain injury (two), status epilepticus following massive cerebral infarction (one), and intracerebral/intraventricular hemorrhage (one). Hand warming was applied at treatment onset on all patients; shivering only responsive to meperidine occurred in five of them. Fever of 38.4 degrees C (range 38.0 degrees C-38.9 degrees C) was reduced to 36.9 degrees C (range 36.0 degrees C-38.0 degrees C) after 120 minutes (P<0.001). Core temperature remained "locked" during the remainder of the treatment (36.6 degrees C, P=0.5; 36.6 degrees C, P=0.9; and 36.5 degrees C, P=0.9 at 180, 300, and 600 minutes, respectively). Skin integrity under the pads was preserved in all study subjects. Our results indicate that use of this novel technique is safe, rapidly effective, and able to maintain sustained normothermia following fever in a cohort of critically ill neurologic/neurosurgical patients.

Neither arm nor face warming reduces the shivering threshold in unanesthetized humans

BACKGROUND AND PURPOSE

Hand warming and face warming, combined with inhalation of heated air, are reported to suppress shivering. However, hand or face temperature contributes only a few percent to control of shivering. Thus, it seems unlikely that manipulating hand or facial skin temperature alone would be sufficient to permit induction of therapeutic hypothermia. We tested the hypothesis that focal arm (forearm and hand) warming or lower facial warming, combined with inhalation of heated and humidified gas, only minimally reduces the shivering threshold (triggering core temperature).

METHODS

We studied 8 healthy male volunteers (18 to 40 years of age) on 3 days: (1) control (no warming), (2) arm warming with forced air at approximately 43 degrees C, and (3) face warming with 21 L/min of air at approximately 42 degrees C at a relative humidity of 100%. Fluid at approximately 4 degrees C was infused via a central venous catheter to decrease tympanic membrane temperature 1 degrees C/h to 2 degrees C/h; mean skin temperature was maintained at 31 degrees C. A sustained increase in oxygen consumption quantified the shivering threshold.

RESULTS

Shivering thresholds did not differ significantly between the control (36.7+/-0.1 degrees C), arm-warming (36.5+/-0.3 degrees C), or face-warming (36.5+/-0.3 degrees C; analysis of variance, P=0.34) day. The study was powered to have a 95% probability of detecting a difference of 0.5+/-0.5 degrees C (mean+/-SD) between control and either of the 2 treatments at alpha=0.05.

CONCLUSIONS

Focal arm or face warming did not substantially reduce the shivering threshold in unanesthetized volunteers. It thus seems unlikely that these nonpharmacological modalities will substantially facilitate induction of therapeutic hypothermia.