Randomized controlled trial of effects of the airflow through the upper respiratory tract of intubated brain-injured patients on brain temperature and selective brain cooling

Efficacy and Safety of Transnasal CoolStat Cooling Device to Induce and Maintain Hypothermia

Targeted temperature management (TTM) is recommended as a standard of care for postcardiac arrest patients. Current TTM methods have significant limitations to be used in an ambulatory setting. We investigated the efficacy and safety of a novel noninvasive transnasal evaporative cooling device (CoolStat™). Eleven Yorkshire pigs underwent hypothermia therapy using the CoolStat device. CoolStat induces evaporative cooling by blowing dehumidified ambient air over the nasal turbinates in a unidirectional fashion. CoolStat's efficacy and safety were assessed by applying different cooling strategies (groups A, B and C). In group A (efficacy study; n = 5, TTM for 8 hours), time to achieve brain target temperature (2°C reduction from baseline), and the percentage of time in which the temperature ranged within ±0.5°C after reaching the target temperature were investigated. In the safety assessment (groups B and C), two worst-case therapy situations were reproduced: in group B (n = 3), continuous maximum air flow (65 L/min) was applied without temperature control and, in group C (n = 3), subjects underwent 24-hour TTM (prolonged therapy). Hemodynamic and respiratory parameters, nasal mucosa integrity (endoscopic assessment), and other therapy-related adverse effects were evaluated. Efficacy study: CoolStat cooling therapy successfully induced and sustained managed hypothermia in all subjects. Brain target temperature was achieved in 0.5 ± 0.6 hours and kept within a ±0.5°C range for the therapy duration (99.9% ± 0.1%). All animals completed the safety studies. Maximum air flow (group B) and 24-hour (group C) therapies were well tolerated and no significant damage was observed on nasal mucosa for neither of the groups. CoolStat was able to efficiently induce and maintain hypothermia using unidirectional high flow of dry air into the nostrils of porcine models. CoolStat therapy was well tolerated and no damage to nasal mucosa was observed under either maximum air flow or prolonged therapy.

Hypothermia Used in Medical Applications for Brain and Spinal Cord Injury Patients

Despite more than 80 years of animal experiments and clinical practice, efficacy of hypothermia in improving treatment outcomes in patients suffering from cell and tissue damage caused by ischemia is still ongoing. This review will first describe the history of utilizing cooling in medical treatment, followed by chemical and biochemical mechanisms of cooling that can lead to neuroprotection often observed in animal studies and some clinical studies. The next sections will be focused on current cooling approaches/devices, as well as cooling parameters recommended by researchers and clinicians. Animal and clinical studies of implementing hypothermia to spinal cord and brain tissue injury patients are presented next. This section will review the latest outcomes of hypothermia in treating patients suffering from traumatic brain injury (TBI), spinal cord injury (SCI), stroke, cardiopulmonary surgery, and cardiac arrest, followed by a summary of available evidence regarding both demonstrated neuroprotection and potential risks of hypothermia. Contributions from bioengineers to the field of hypothermia in medical treatment will be discussed in the last section of this review. Overall, an accumulating body of clinical evidence along with several decades of animal research and mathematical simulations has documented that the efficacy of hypothermia is dependent on achieving a reduced temperature in the target tissue before or soon after the injury-precipitating event. Mild hypothermia with temperature reduction of several degrees Celsius is as effective as modest or deep hypothermia in providing therapeutic benefit without introducing collateral/systemic complications. It is widely demonstrated that the rewarming rate must be controlled to be lower than 0.5 °C/h to avoid mismatch between local blood perfusion and metabolism. In the past several decades, many different cooling methods and devices have been designed, tested, and used in medical treatments with mixed results. Accurately designing treatment protocols to achieve specific cooling outcomes requires collaboration among engineers, researchers, and clinicians. Although this problem is quite challenging, it presents a major opportunity for bioengineers to create methods and devices that quickly and safely produce hypothermia in targeted tissue regions without interfering with routine medical treatment.

Therapeutic hypothermia for stroke: Where to go?

Ischemic stroke is a major cause of death and long-term disability worldwide. Thrombolysis with recombinant tissue plasminogen activator is the only proven and effective treatment for acute ischemic stroke; however, therapeutic hypothermia is increasingly recognized as having a tissue-protective function and positively influencing neurological outcome, especially in cases of ischemia caused by cardiac arrest or hypoxic-ischemic encephalopathy in newborns. Yet, many aspects of hypothermia as a treatment for ischemic stroke remain unknown. Large-scale studies examining the effects of hypothermia on stroke are currently underway. This review discusses the mechanisms underlying the effect of hypothermia, as well as trends in hypothermia induction methods, methods for achieving optimal protection, side effects, and therapeutic strategies combining hypothermia with other neuroprotective treatments. Finally, outstanding issues that must be addressed before hypothermia treatment is implemented at a clinical level are also presented.

Modest cooling therapies (35ºC to 37.5ºC) for traumatic brain injury

BACKGROUND

Animal models of traumatic brain injury suggest that induced normothermia (36.5 or 37 ºC), compared to induced hyperthermia (39 ºC), improves histopathological and neurobehavioural outcomes. Observational clinical studies of patients with TBI suggest an association between raised body temperature and unfavourable outcome, although this relationship is inconsistent.

OBJECTIVES

To assess the effects of modest cooling therapies (defined as any drug or physical therapy aimed at maintaining body temperature between 35 ºC and 37.5 ºC) when applied to patients in the first week after traumatic brain injury.

SEARCH METHODS

The most recent search was run on 23(rd) September 2013. We searched the Cochrane Injuries Group's Specialised Register, The Cochrane Library (CENTRAL), MEDLINE (OvidSP), Embase (OvidSP), ISI WOS: SCI-EXPANDED (1970) & CPCI-S (1990), PubMed and trials registries together with reference checking.

SELECTION CRITERIA

All completed randomised, controlled and placebo-controlled trials published or unpublished, where modest cooling therapies were applied in the first week after traumatic brain injury.

DATA COLLECTION AND ANALYSIS

Two authors independently applied the selection criteria to relevant trials.

MAIN RESULTS

We were unable to find any randomised controlled trials of modest cooling therapies after traumatic brain injury.

AUTHORS' CONCLUSIONS

In order to further explore the preliminary findings provided by animal models and observational clinical studies that suggests there may be a beneficial effect of modest cooling for TBI, randomised trials designed to explore the effect of these interventions on patient-centred outcomes are needed.

In cold blood: intraarteral cold infusions for selective brain cooling in stroke

Hypothermia is a promising therapeutic option for stroke patients and an established neuroprotective treatment for global cerebral ischemia after cardiac arrest. While whole body cooling is a feasible approach in intubated and sedated patients, its application in awake stroke patients is limited by severe side effects: Strong shivering rewarms the body and potentially worsens ischemic conditions because of increased O2 consumption. Drugs used for shivering control frequently cause sedation that increases the risk of aspiration and pneumonia. Selective brain cooling by intraarterial cold infusions (IACIs) has been proposed as an alternative strategy for patients suffering from acute ischemic stroke. Preclinical studies and early clinical experience indicate that IACI induce a highly selective brain temperature decrease within minutes and reach targeted hypothermia 10 to 30 times faster than conventional cooling methods. At the same time, body core temperature remains largely unaffected, thus systemic side effects are potentially diminished. This review critically discusses the limitations and side effects of current cooling techniques for neuroprotection from ischemic brain damage and summarizes the available evidence regarding advantages and potential risks of IACI.

Selective therapeutic hypothermia: A review of invasive and noninvasive techniques

OBJECTIVE: Therapeutic hypothermia is a promising treatment to prevent secondary neurologic injury. Clinical utility is limited by systemic complications of global hypothermia. Selective brain cooling remains a largely uninvestigated application. We review techniques of inducing selective brain cooling. METHOD: Literature review. RESULTS: Strategies of inducing selective brain cooling were divided between non-invasive and invasive techniques. Non-invasive techniques were surface cooling and cooling via the upper airway. Invasive cooling methods include transvascular and compartmental (epidural, subdural, subarachnoid and intraventricular) cooling methods to remove heat from the brain. CONCLUSION: Selective brain cooling may offer the best strategy for achieving hypothermic neuroprotection. Non-invasive strategies have proven disappointing in human trials. There is a paucity of human experiments using invasive methods of selective brain cooling. Further application of invasive cooling strategies is needed.

A review of selective hypothermia in the management of traumatic brain injury

Object

Traumatic brain injury (TBI) remains a significant cause of morbidity and death in the US and worldwide. Resuscitative systemic hypothermia following TBI has been established as an effective neuroprotective treatment in multiple studies in animals and humans, although this intervention carries with it a significant risk profile as well. Selective, or preferential, methods of inducing cerebral hypothermia have taken precedence over the past few years in order to minimize systemic adverse effects. In this report, the authors explore the current methods available for inducing selective cerebral hypothermia following TBI and review the literature regarding the results of animal and human trials in which these methods have been implemented.

Methods

A search of the PubMed archive (National Library of Medicine) and the reference lists of all relevant articles was conducted to identify all animal and human studies pertaining to the use of selective brain cooling, selective hypothermia, preferential hypothermia, or regional hypothermia following TBI.

Results

Multiple methods of inducing selective cerebral hypothermia are currently in the experimental phases, including surface cooling, intranasal selective hypothermia, transarterial or transvenous endovascular cooling, extraluminal vascular cooling, and epidural cerebral cooling.

Conclusions

Several methods of conferring preferential neuroprotection via selective hypothermia currently are being tested. Class I prospective clinical trials are required to assess the safety and efficacy of these methods.

Induced hypothermia in acute ischemic stroke

BACKGROUND

Induced hypothermia is a promising neuroprotective treatment for acute ischemic stroke. Data from both global and focal ischemia animal models have been encouraging. However, only a few small clinical studies have investigated its use in humans.

OBJECTIVE

To review the background, possible mechanisms of action, and the preclinical and clinical data supporting the neuroprotective role of induced hypothermia following acute ischemic stroke.

METHODS

A literature search was performed using the PubMed database. Only papers in English were reviewed.

RESULTS/CONCLUSIONS

Induced hypothermia is effective as a neuroprotectant in animal models of acute ischemic stroke. Its multimodal mechanism of action makes it a very attractive method of neuroprotection. Although human studies suggest it is safe and feasible, larger randomized controlled trials are necessary to address clinical efficacy and to refine the methods and parameters of induced hypothermia protocols.

Modest cooling therapies (35 degrees C to 37.5 degrees C) for traumatic brain injury

BACKGROUND

A recent retrospective study suggested that after traumatic brain injury, patients with a raised body temperature have an unfavourable outcome compared to patients that have a normal body temperature.

OBJECTIVES

To assess the effects of modest cooling therapies (defined as any drug or physical therapy aimed at maintaining body temperature between 35 degrees C and 37.5 degrees C) when applied to patients in the first week after traumatic brain injury.

SEARCH STRATEGY

We searched the Cochrane Injuries Group's Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2007, Issue 3), MEDLINE (1950 to 2008), EMBASE (1980 to 2008), the National Research Register, Zetoc and the Current Controlled Trials MetaRegister of controlled trials. We also contacted investigators, pharmaceutical companies and the manufacturers of cooling equipment. The searches were conducted August to September 2007 and updated in April 2008.

SELECTION CRITERIA

All completed randomised, controlled or placebo-controlled trials published or unpublished, where modest cooling therapies were applied in the first week after traumatic brain injury.

DATA COLLECTION AND ANALYSIS

Two authors independently searched for relevant trials.

MAIN RESULTS

We were unable to find any randomised, placebo-controlled trials of modest cooling therapies after traumatic brain injury.

AUTHORS' CONCLUSIONS

There is no evidence that interventions aimed at reducing body temperature to between 35 degrees C and 37.5 degrees C in the first week after TBI improves patient outcomes. Trials designed to explore the effect of these interventions on patient-centred outcomes are needed.

Design and validation of a critical pathway for hospital management of patients with severe traumatic brain injury

BACKGROUND

Critical pathways for the management of patients with severe traumatic brain injury (STBI) may contribute to reducing the incidence of hospital complications, length of hospitalization stay, and cost of care. Such pathways have previously been developed for departments with significant resource availability. In Mexico, STBI is the most important cause of complications and length of stay in neurotrauma services at public hospitals. Although current treatment is designed basically in accordance with the Brain Trauma Foundation guidelines, shortfalls in the availability of local resources make it difficult to comply with these standards, and no critical pathway is available that accords with the resources of public hospitals. The purpose of the present study was to design and to validate a critical pathway for managing STBI patients that would be suitable for implementation in neurotrauma departments of middle-income level countries.

METHODS

The study comprised two phases: design (through literature review and design plan) and validation (content, construct, and appearance) of the critical pathway.

RESULTS

The validated critical pathway for managing STBI patients entails four sequential subprocesses summarizing the hospital's care procedures, and includes three components: (1) nodes and criteria (in some cases, indicators are also included); (2) health team members in charge of the patient; (3) maximum estimated time for compliance with recommendations.

CONCLUSIONS

This validated critical pathway is based on the current scientific evidence and accords with the availability of resources of middle-income countries.

Fever management practices of neuroscience nurses: national and regional perspectives

Neuroscience patients with fever may have worse outcomes than those who are afebrile. However, neuroscience nurses who encounter this common problem face a translational gap between patient-outcomes research and bedside practice because there is no current evidence-based standard of care for fever management of the neurologically vulnerable patient. The aim of this study was to determine if there are trends in national practices for fever and hyperthermia management of the neurologically vulnerable patient. A 15-item mailed questionnaire was used to determine national and regional trends in fever and hyperthermia management and decision making by neuroscience nurses. Members of the American Association of Neuroscience Nurses were surveyed (N = 1,225) and returned 328 usable surveys. Fewer than 20% of respondents reported having an explicit fever management protocol in place for neurologic patients, and 12.5% reported having a nonspecific patient protocol available for fever management. Several clear and consistent patterns in interventions for fever and hyperthermia management were seen nationally, including acetaminophen administration at a dose of 650 mg every 4 hours, ice packs, water cooling blankets, and tepid bathing. However, regional differences were seen in intervention choices and initial temperature to treat.

Absence of selective brain cooling in unrestrained baboons exposed to heat

To test whether baboons are capable of implementing selective brain cooling, we measured, every 5 min, the temperature in their hypothalamus, carotid arterial bloodstream, and abdominal cavity. The baboons were unrestrained and exposed to 22°C for 7 days and then to a cyclic environment with 15°C at night and 35°C during the day for a further 7 days. During the latter 7 days some of the baboons also were exposed to radiant heat during the day. For three days, during heat exposure, water was withheld. At no time was the hypothalamus cooler than carotid arterial blood, despite brain temperatures above 40°C. With little variation, the hypothalamus was consistently 0.5°C warmer than arterial blood. At high body temperatures, the hypothalamus was sometimes cooler than the abdomen. Abdominal temperature was more variable than arterial blood and tended to exceed arterial blood temperature at higher body temperatures. Hypothalamic temperature cooler than a warm abdomen is not evidence for selective brain cooling. In species that can implement selective brain cooling, the brain is most likely to be cooler than carotid arterial blood when an animal is hyperthermic, during heat exposure, and also dehydrated and undisturbed by human presence. When we exposed baboons to high ambient temperatures while they were water deprived and undisturbed, they never implemented selective brain cooling. We conclude that baboons cannot implement selective brain cooling and can find no convincing evidence that any primate species can do so.

Noninvasive selective brain cooling by head and neck cooling is protective in severe traumatic brain injury

Therapeutic hypothermia is a promising treatment for patients with severe traumatic brain injury (TBI). We present here the results of a study in which noninvasive selective brain cooling (SBC) was achieved using a head cap and neckband. Ninety patients with severe TBI were divided into a normothermia control group (n=45) and a SBC group (n=45), whose brain temperature was maintained at 33-35 degrees C for 3 days using a combination of head and neck cooling. At 24, 48 and 72h after injury, the mean intracranial pressure (ICP) values of the patients who underwent SBC were lower than those of the normothermia controls (19.14+/-2.33, 19.72+/-1.73 and 17.29+/-2.07 mmHg, versus 23.41+/-2.51, 20.97+/-1.86, and 20.13+/-1.87 mmHg, respectively, P<0.01). There was a significant difference in the neurological recovery of the two groups at the 6-month follow-up after TBI. Good neurological outcome (Glasgow Outcome Scale score of 4 to 5) rates 6 months after injury were 68.9% for the SBC group, and 46.7% for the control group (P<0.05). There were no complications resulting in severe sequelae. In conclusion, the noninvasive SBC described here is a safe method of administering therapeutic hypothermia, which can reduce ICP and improve prognosis without severe complications in patients with severe TBI.

Enhanced upper respiratory tract airflow and head fanning reduce brain temperature in brain-injured, mechanically ventilated patients: a randomized, crossover, factorial trial

BACKGROUND

Heat loss from the upper airways and through the skull are physiological mechanisms of brain cooling which have not been fully explored clinically.

METHODS

This randomized, crossover, factorial trial in 12 brain-injured, orally intubated patients investigated the effect of enhanced nasal airflow (high flow unhumidified air with 20 p.p.m. nitric oxide gas) and bilateral head fanning on frontal lobe brain temperature and selective brain cooling. After a 30 min baseline, each patient received the four possible combinations of the interventions--airflow, fanning, both together, no intervention--in randomized order. Each combination was delivered for 30 min and followed by a 30 min washout, the last 5 min of which provided the baseline for the next intervention.

RESULTS

The difference in mean brain temperature over the last 5 min of the preceding washout minus the mean over the last 5 min of intervention, was 0.15 degrees C with nasal airflow (P=0.001, 95% CI 0.06-0.23 degrees C) and 0.26 degrees C with head fanning (P<0.001, 95% CI 0.17-0.34 degrees C). The estimate of the combined effect of airflow and fanning on brain temperature was 0.41 degrees C. Selective brain cooling did not occur.

CONCLUSION

Physiologically, this study demonstrates that heat loss through the upper airways and through the skull can reduce parenchymal brain temperature in brain-injured humans and the onset of temperature reduction is rapid. Clinically, in ischaemic stroke, a temperature decrease of 0.27 degrees C may reduce the relative risk of poor outcome by 10-20%. Head fanning may have the potential to achieve a temperature decrease of this order.

Positive selective brain cooling method: a novel, simple, and selective nasopharyngeal brain cooling method

Brain damage is worsened by hyperthermia and prevented by hypothermia. Conventional hypothermia is a non-selective brain cooling method that employs cooling blankets to achieve surface cooling. This complicated method sometimes induces unfavorable systemic complications. We have developed a positive selective brain cooling (PSBC) method to control brain temperature quickly and safely following brain injury. Brain temperature was measured in patients with a ventriculostomy CAMINO catheter. A Foley balloon catheter was inserted to direct chilled air (8 to 12 L/min) into each side of the nasal cavity. The chilled air was exhaled through the oral cavity. In most patients, PSBC maintained normal brain temperature. This new technique provides quick induction of brain temperature control and does not require special facilities.

Controlled normothermia during ischemia is important for the induction of neuronal cell death after global ischemia in mouse

A stable model of neuronal damage after ischemia is needed in mice to enable progression of transgenic strategies. We performed transient global ischemia induced by common carotid artery occlusions with and without maintaining normal rectal temperature (Trec) in order to determine the importance of body temperature control during ischemia. We measured brain temperature (Tb) during ischemia/reperfusion. Mice with normothermia (Trec within +/- 1 degrees C) had increased mortality and neuronal cell death in the CA1 region of hippocampus, which did not occur in hypothermic animals. If the Trec was kept within +/- 1 degrees C, the Tb decreased during ischemia. After reperfusion, Tb in the normothermia group developed hyperthermia, which reached > 40 degrees C and was > 2 degrees C higher than Trec. We suggest that tightly controlled normothermia and prevention of hypothermia (Trec) during ischemia are important factors in the development of a stable neuronal damage model in mice.

Thermal reactions of blood vessels in vascular stroke and heatstroke

Research on the pathophysiology and treatment of brain damage with special focus on thermal vascular responses is the subject of this minireview. Interruption of cerebral blood supply by vascular obstruction, temporary cardiac arrest or hyperthermia causes a sudden attack of vascular stroke or heatstroke with serious consequences. It may not induce immediate cell death, but can precipitate a complex biochemical cascade leading to a delayed neuronal loss. When testing thermal vasomotor responses by stepwise cooling of isolated carotid arteries, a temperature-proportional dilatation was observed while heating induced the opposite response: a marked vasoconstriction. General hyperthermia with an increased oxygen demand combined with a reduction of blood supply therefore is a serious consequence. At the cellular level an important mechanism involving hyperthermia is the temperature-dependent regulation of K(+) channel tone of vascular smooth muscle. Further, their inhibition through temperature elevation causes vasoconstriction. In heatstroke, which can induce platelet aggregation and the release of the vasoconstrictor serotonin, arterial cooling attenuates this response. General hypothermia is induced to prevent or attenuate neurological damage in stroke. The procedure is not without serious side effects. Therefore, rapid institution of selective brain cooling has been considered in adults and in infants with postpartum encephalopathy.