Blowing hot and cold? Skin counter warming to prevent shivering during therapeutic cooling*:

Characterization of the Effect of Prolonged Therapeutic Hypothermia on Serum Magnesium and Potassium Following Neurological Injury

Current American Heart Association/American Stroke Association guidelines for the management of spontaneous intracerebral hemorrhage suggest therapeutic hypothermia (TH) as a salvage therapy in patients with elevated intracranial pressure. Electrolyte disorders may develop at any stage of the cooling process. Such deregulation can place patients at an increased risk for arrhythmias and worsened neurologic outcomes. The impact of TH on serum electrolyte concentration has been described, but electrolyte changes and repletions are yet to be quantified. The primary objective of this study was to quantify the trends in serum potassium and magnesium concentrations during TH and determine the median amount of electrolyte repletions administered. This study was a single-center retrospective cohort conducted at Virginia Commonwealth University Health. Data were collected from neurosurgical patients with intracranial hypertension who underwent TH (<36°C) for ≥48 hours. Patients with a primary neurological insult cooled with the Arctic Sun^® 5000 Temperature Management System, who were ≥13 years of age at the time of therapy with a core body temperature of ≥36°C before therapeutic hypothermia, were eligible for inclusion. Forty-three patients meeting the inclusion criteria were analyzed. A total of 42 patients (98%) experienced hypokalemia (<3.5 mEq/L) during TH. A median of 45 mEq per day of potassium repletion was administered during the maintenance phase of cooling. Despite those repletions, patients remained hypokalemic 30% of the time. Median serum magnesium concentrations during the maintenance phase of TH remained consistently within goal range of 1.8-2.5 mg/dL. Five patients (12%) experienced at least one episode of cardiac dysrhythmia during the cooling period. Standard potassium electrolyte repletion protocols did not adequately maintain serum potassium concentrations above our target of 3.5 mEq/L in neurosurgical patients undergoing TH. Standard magnesium repletion protocols were sufficient to maintain a normal serum concentration in this patient population when magnesium sulfate was not used for other indications.

Emergency Neurological Life Support: Resuscitation Following Cardiac Arrest

Cardiac arrest is the most common cause of death in North America. An organized bundle of neurocritical care interventions can improve chances of survival and neurological recovery in patients who are successfully resuscitated from cardiac arrest. Therefore, resuscitation following cardiac arrest was chosen as an Emergency Neurological Life Support protocol. Key aspects of successful early post-arrest management include: prevention of secondary brain injury; identification of treatable causes of arrest in need of emergent intervention; and, delayed neurological prognostication. Secondary brain injury can be attenuated through targeted temperature management (TTM), avoidance of hypoxia and hypotension, avoidance of hyperoxia, hyperventilation or hypoventilation, and treatment of seizures. Most patients remaining comatose after resuscitation from cardiac arrest should undergo TTM. Treatable precipitants of arrest that require emergent intervention include, but are not limited to, acute coronary syndrome, intracranial hemorrhage, pulmonary embolism and major trauma. Accurate neurological prognostication is generally not appropriate for several days after cardiac arrest, so early aggressive care should never be limited based on perceived poor neurological prognosis.

Shivering Treatments for Targeted Temperature Management: A Review

BACKGROUND

Shivering is common during targeted temperature management, and control of shivering can be challenging if clinicians are not familiar with the available options and recommended approaches.

PURPOSE

The purpose of this review was to summarize the most relevant literature regarding various treatments available for control of shivering and suggest a recommended approach based on latest data.

METHODS

The electronic databases PubMed/MEDLINE and Google Scholar were used to identify studies for the literature review using the following keywords alone or in combination: "shivering treatment," "therapeutic hypothermia," "core temperature modulation devices," and "targeted temperature management."

RESULTS

Nonpharmacologic methods were found to have a very low adverse effect profile and ease of use but some limitations in complete control of shivering. Pharmacologic methods can effectively control shivering, but some have adverse effects, such that risks and benefits to the patient have to be balanced.

CONCLUSION

An approach is provided which suggests that treatment for shivering control in targeted temperature management should be initiated before the onset of therapeutic hypothermia or prior to any attempt at lowering patient core temperature, with medications including acetaminophen, buspirone, and magnesium sulfate, ideally with the addition of skin counterwarming. After that, shivering intervention should be determined with the help of a shivering scale, and stepwise escalation can be implemented that balances shivering treatment with sedation, aiming to provide the most shivering reduction with the least sedating medications and reserving paralytics for the last line of treatment.

Esophageal Heat Transfer for Patient Temperature Control and Targeted Temperature Management

Controlling patient temperature is important for a wide variety of clinical conditions. Cooling to normal or below normal body temperature is often performed for neuroprotection after ischemic insult (e.g. hemorrhagic stroke, subarachnoid hemorrhage, cardiac arrest, or other hypoxic injury). Cooling from febrile states treats fever and reduces the negative effects of hyperthermia on injured neurons. Patients are warmed in the operating room to prevent inadvertent perioperative hypothermia, which is known to cause increased blood loss, wound infections, and myocardial injury, while also prolonging recovery time. There are many reported approaches for temperature management, including improvised methods that repurpose standard supplies (e.g., ice, chilled saline, fans, blankets) but more sophisticated technologies designed for temperature management are typically more successful in delivering an optimized protocol. Over the last decade, advanced technologies have developed around two heat transfer methods: surface devices (water blankets, forced-air warmers) or intravascular devices (sterile catheters requiring vascular placement). Recently, a novel device became available that is placed in the esophagus, analogous to a standard orogastric tube, that provides efficient heat transfer through the patient's core. The device connects to existing heat exchange units to allow automatic patient temperature management via a servo mechanism, using patient temperature from standard temperature sensors (rectal, Foley, or other core temperature sensors) as the input variable. This approach eliminates vascular placement complications (deep venous thrombosis, central line associated bloodstream infection), reduces obstruction to patient access, and causes less shivering when compared to surface approaches. Published data have also shown a high degree of accuracy and maintenance of target temperature using the esophageal approach to temperature management. Therefore, the purpose of this method is to provide a low-risk alternative method for controlling patient temperature in critical care settings.

Critical Care Management Focused on Optimizing Brain Function After Cardiac Arrest

The discussion of neurocritical care management in post-cardiac arrest syndrome (PCAS) has generally focused on target values used for targeted temperature management (TTM). There has been less attention paid to target values for systemic and cerebral parameters to minimize secondary brain damage in PCAS. And the neurologic indications for TTM to produce a favorable neurologic outcome remain to be determined. Critical care management of PCAS patients is fundamental and essential for both cardiologists and general intensivists to improve neurologic outcome, because definitive therapy of PCAS includes both special management of the cause of cardiac arrest, such as coronary intervention to ischemic heart disease, and intensive management of the results of cardiac arrest, such as ventilation strategies to avoid brain ischemia. We reviewed the literature and the latest research about the following issues and propose practical care recommendations. Issues are (1) prediction of TTM candidate on admission, (2) cerebral blood flow and metabolism and target value of them, (3) seizure management using continuous electroencephalography, (4) target value of hemodynamic stabilization and its method, (5) management and analysis of respiration, (6) sedation and its monitoring, (7) shivering control and its monitoring, and (8) glucose management. We hope to establish standards of neurocritical care to optimize brain function and produce a favorable neurologic outcome.

Emergency Neurological Life Support: Resuscitation Following Cardiac Arrest

Cardiac arrest is the most common cause of death in North America. Neurocritical care interventions, including targeted temperature management (TTM), have significantly improved neurological outcomes in patients successfully resuscitated from cardiac arrest. Therefore, resuscitation following cardiac arrest was chosen as an emergency neurological life support protocol. Patients remaining comatose following resuscitation from cardiac arrest should be considered for TTM. This protocol will review induction, maintenance, and re-warming phases of TTM, along with management of TTM side effects. Aggressive shivering suppression is necessary with this treatment to ensure the maintenance of a target temperature. Ancillary testing, including electrocardiography, computed tomography and/or magnetic resonance imaging of the brain, continuous electroencephalography monitoring, and correction of electrolyte, blood gas, and hematocrit changes, are also necessary to optimize outcomes.

Ultrarapid Induction of Hypothermia Using Continuous Automated Peritoneal Lavage With Ice-Cold Fluids: Final Results of the Cooling for Cardiac Arrest or Acute ST-Elevation Myocardial Infarction Trial

OBJECTIVES

Hypothermia (32-34 °C) can mitigate ischemic brain injury, and some evidence suggests that it can reduce infarct size in acute myocardial infarction and acute ischemic stroke. For some indications, speed of cooling may be crucial in determining efficacy. We performed a multicenter prospective intervention study to test an ultrarapid cooling technology, the Velomedix Automated Peritoneal Lavage System using ice-cold fluids continuously circulating through the peritoneal cavity to rapidly induce and maintain hypothermia in comatose patients after cardiac arrest and a small number of awake patients with acute myocardial infarction.

DESIGN

Multicenter prospective intervention study.

SETTING

Intensive care- and coronary care units of multiple tertiary referral centers.

MEASUREMENTS AND MAIN RESULTS

Access to the peritoneal cavity was gained using a modified blunt dilating instrument, followed by catheter placement. Patients were cooled to a temperature of 32.5 °C, maintained for 24 hours (cardiac arrest) or 3 hours (acute myocardial infarction) followed by controlled rewarming. Forty-nine patients were enrolled, and 46 patients completed treatment. One placement was unsuccessful (abdominal wall not breached), two patients were ultimately not cooled, and only safety data are reported. Average catheter insertion time was 2.3 minutes. Mean time to temperature less than 33 °C was 10.4 minutes (average cooling rate, 14 °C/hr). Median infarct size in patients who had coronary interventions was 16% of LV. No cases of stent thrombosis occurred. Survival in cardiac arrest patients with initial rhythm of ventricular tachycardia/ventricular fibrillation was 56%, of whom 82 had a complete neurologic recovery. This compares favorably to outcomes from previous studies.

CONCLUSION

Automated peritoneal lavage system is a safe and ultrarapid method to induce and maintain hypothermia, which appears feasible in cardiac arrest patients and awake patients with acute myocardial infarction. The shivering response appeared to be delayed and much reduced with this technology, diminishing metabolic disorders associated with cooling and minimizing sedation requirement. Our data suggest that ultrarapid cooling could prevent subtle neurologic damage compared with slower cooling. This will need to be confirmed in direct comparative studies.

Shivering management during therapeutic temperature modulation: nurses' perspective

Therapeutic temperature modulation, which incorporates mild hypothermia and maintenance of normothermia, is being used to manage patients resuscitated after cardiac arrest. Methods of modulating temperature include intravenous infusion of cold fluids and surface or endovascular cooling. During this therapy, the shiver response is activated as a defense mechanism in response to an altered set-point temperature and causes metabolic and hemodynamic stress for patients. Recognition of shivering according to objective and subjective assessments is vital for early detection of the condition. Once shivering is detected, treatment is imperative to avoid deleterious effects. The Bedside Shivering Assessment Scale can be used to determine the efficacy of interventions intended to blunt thermoregulatory defenses and can provide continual evaluation of patients' responses to the interventions. Nurses' knowledge and understanding of the harmful effects of shivering are important to effect care and prevent injury associated with uncontrolled shivering.

Therapeutic hypothermia in acute stroke

Treatment of acute stroke is difficult due to the complexity of events triggered by ischemic insult. Current reperfusion strategies are time limited and, alone, may not be sufficient to achieve maximal neurologic outcomes. Therapeutic hypothermia (TH) appears to be a promising neuroprotective therapy, as it affects a wide range of destructive mechanisms occurring in ischemic brain tissue. Animal research has substantiated the use of TH in acute stroke. Human studies utilizing TH in acute stroke have shown trends toward positive effects; however, there have been a variety of measurements and methods making comparisons difficult. The ideal protocol for the use of TH in stroke has not yet been developed and requires determination of optimal depth, duration, and methods of temperature measurement and cooling for acute stroke. The purposes of this article were to (1) discuss the effects of ischemia and reperfusion in acute stroke, (2) discuss how TH can potentially limit neurological injury, and (3) review current literature on the use of hypothermia as a treatment for acute stroke.

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.

Techniques for therapeutic hypothermia during transport and in hospital for perinatal asphyxial encephalopathy

Over the past 10 years, several randomised clinical trials of therapeutic hypothermia for perinatal asphyxial encephalopathy have demonstrated both safety and efficacy of therapeutic hypothermia in improving neurological outcome. Today cooling is increasingly used in tertiary level units throughout the developed world. Therapeutic hypothermia (cooling to a rectal or core temperature of 33-34 degrees C for 72 h) is easier to achieve in newborn infants than in adults. There is a natural tendency for the core temperature of infants who suffered birth asphyxia to fall and remain lower than non-asphyxiated infants for up to 16 h after birth. A variety of high- and low-tech surface cooling methods have been used in neonates - newer systems are servo-controlled and provide very stable temperature control. It is well accepted that to be most effective, cooling needs to be initiated as soon as possible after birth and, thus, needs to be commenced prior to the transfer of infants to cooling centres. We describe our experience of passive cooling before and during the transfer of infants with encephalopathy to cooling centres in a major city in the UK.

Mechanisms of action, physiological effects, and complications of hypothermia

BACKGROUND

Mild to moderate hypothermia (32-35 degrees C) is the first treatment with proven efficacy for postischemic neurological injury. In recent years important insights have been gained into the mechanisms underlying hypothermia's protective effects; in addition, physiological and pathophysiological changes associated with cooling have become better understood.

OBJECTIVE

To discuss hypothermia's mechanisms of action, to review (patho)physiological changes associated with cooling, and to discuss potential side effects.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

A myriad of destructive processes unfold in injured tissue following ischemia-reperfusion. These include excitotoxicty, neuroinflammation, apoptosis, free radical production, seizure activity, blood-brain barrier disruption, blood vessel leakage, cerebral thermopooling, and numerous others. The severity of this destructive cascade determines whether injured cells will survive or die. Hypothermia can inhibit or mitigate all of these mechanisms, while stimulating protective systems such as early gene activation. Hypothermia is also effective in mitigating intracranial hypertension and reducing brain edema. Side effects include immunosuppression with increased infection risk, cold diuresis and hypovolemia, electrolyte disorders, insulin resistance, impaired drug clearance, and mild coagulopathy. Targeted interventions are required to effectively manage these side effects. Hypothermia does not decrease myocardial contractility or induce hypotension if hypovolemia is corrected, and preliminary evidence suggests that it can be safely used in patients with cardiac shock. Cardiac output will decrease due to hypothermia-induced bradycardia, but given that metabolic rate also decreases the balance between supply and demand, is usually maintained or improved. In contrast to deep hypothermia (<or=30 degrees C), moderate hypothermia does not induce arrhythmias; indeed, the evidence suggests that arrhythmias can be prevented and/or more easily treated under hypothermic conditions.

CONCLUSIONS

Therapeutic hypothermia is a highly promising treatment, but the potential side effects need to be properly managed particularly if prolonged treatment periods are required. Understanding the underlying mechanisms, awareness of physiological changes associated with cooling, and prevention of potential side effects are all key factors for its effective clinical usage.