Induced hypothermia in critical care medicine: a review

Hemodynamics of the oral mucosa during cooling: A crossover clinical trial

Objective

Oral cryotherapy is used to prevent the onset of oral mucositis, a common and debilitating adverse effect following cancer chemotherapy. A protective mechanism associated with oral cooling is thought to be mediated through reduced tissue microcirculation. The aim of the present study was to examine the underlying mechanism associated with oral mucosal cooling by measuring oral microcirculation and tissue oxygen saturation after cooling with ice chips (IC) and an intraoral cooling device (ICD).

Study design

In a single-center randomized crossover study, 10 healthy volunteers were assigned (1:1) randomly to the order in which the two intraoral cooling procedures (IC/ICD) were to be commenced. On day 1, half of the study participants started with IC and then crossed over to intraoral cooling with the ICD on day 2, while the other half of the participants undertook the same two procedures in the reverse order. Total and functional capillary density (T/FCD) and tissue oxygen saturation (StO2) measurements were obtained at baseline and 30 min following oral cooling.

Results

Following 30 min of oral cooling, a statistically significant difference was found for FCD between IC and ICD (percentage points; +2 vs. -13; p < 0.05). A statistically significant decrease in StO2 was observed with both IC and ICD (%; 13 vs. 10) after 30 min of cooling as compared to baseline (p < 0.05). As for the participants' preference the ICD was preferred over IC by 9 out of 10 participants (p = 0.021).

Conclusions

Both microcirculation parameters and tissue oxygen saturation are altered in conjunction with oral cooling, indicating their potential mechanistic contribution towards cryoprevention of oral mucositis.

Hypocarbia is associated with adverse outcomes in hypoxic ischaemic encephalopathy (HIE)

AIM

Hypocarbia in the early postnatal period might exacerbate brain injury in babies with hypoxic ischaemic encephalopathy following birth asphyxia. This mini-review summarised studies on pCO2 values that were monitored periodically in term newborns with moderate/severe hypoxic-ischaemic encephalopathy and correlated with short or long-term outcomes.

METHODS

We searched the databases MEDLINE, EMBASE, Cumulative Index to Nursing and Allied Health Literature (CINAHL), web of science and the Cochrane Library and identified nine studies.

RESULTS

Among the nine included studies, therapeutic hypothermia was administered in seven studies. In most studies, blood pCO2 levels were measured from birth till 72 h of life or till the endpoint of therapeutic hypothermia. Eight studies showed that any hypocarbia (moderate or severe, or cumulative) was associated with an increased risk of adverse outcomes in the form of brain injury in MRI, death or neurodevelopmental disability.

CONCLUSION

Hypocarbia could lead to adverse short-term and long-term outcomes despite therapeutic hypothermia in neonates with HIE. Hence, it is vital to monitor pCO2 levels closely in these infants and consider strategies to maintain pCO2 levels in the normal range.

Time Limiting Boundaries of Reversible Clinical Death in Rats Subjected to Ultra-Deep Hypothermia

BACKGROUND

It is well known that body temperature maintenance between 20 and 35°C prevents hypoxic damage. However, data regarding the ideal duration and permissible temperature boundaries for ultra-deep hypothermia below 20°C are rather fragmentary. The aim of the present study was to determine the time limits of reversible clinical death in rats subjected to ultra-deep hypothermia at 1-8°C.

RESULTS

Rat survival rates were directly dependent on the duration of clinical death. If clinical death did not exceed 35 min, animal viability could be restored. Extending the duration of clinical death longer than 45 min led to rat death, and cardiac functioning in these animals was not recovered. The rewarming rate and the lowest temperature of hypothermia experienced did not directly influence survival rates.

CONCLUSIONS

In a rat model, reversible ultra-deep hypothermia as low as 1-8°C could be achieved without the application of hypercapnia or pharmacological support. The survival of animals was dependent on the duration of clinical death, which should not exceed 35 min.

The Use of Neuromuscular Blockers to Prevent Shivering in the Setting of Postcardiac Arrest Targeted Temperature Management: A Narrative Review of an Off-Label Indication

Targeted temperature management (TTM) has become a standard of care over the past two decades for the improvement in neurologic function and mortality in postcardiac arrest patients. There are various mechanisms by which hypothermia helps to improve these outcomes, one of which is by reducing oxygen requirements. Less established is the use of nondepolarizing neuromuscular blockers (NMBs) to prevent shivering during TTM. Shivering can be disadvantageous in this setting as it increases oxygen requirements, which TTM is actively trying to decrease, in an already oxygen-deprived system as well as generates heat making it difficult to maintain hypothermia. Whether NMBs can improve these outcomes is conflicting in the currently available literature and there lacks a consensus on their role in shivering management. The pharmacokinetic and pharmacodynamic responses of these agents may be altered in hypothermic patients, therefore, their standard of monitoring may be unreliable. The accurate dosing and administration of these agents also remain unclear, further complicated by the lack of a standard use protocol. Various studies have been conducted regarding the use of NMBs to prevent shivering in postcardiac arrest patients undergoing TTM; however, it remains an off-label indication requiring further investigation.

Measured energy expenditure in mildly hypothermic critically ill patients with traumatic brain injury: A sub-study of a randomized controlled trial

BACKGROUND & AIMS

Prophylactic hypothermia, often used in critically ill patients with traumatic brain injury, reduces energy expenditure and may affect energy delivered by nutrition therapy. The primary objective of this study was to measure energy expenditure in hypothermic patients over the first 3 days after traumatic brain injury (TBI). Secondary objectives included comparison of measured energy expenditure and nutrition delivery to day 7.

METHODS

A prospective sub-study of a randomized controlled trial conducted in patients with severe TBI, investigating prophylactic hypothermia (33-35 °C) as a neuroprotective therapy. In two centers, indirect calorimetry was initiated within 24 h of randomization and repeated up to twice daily to day 7. Data are presented as n (%), mean (standard deviation (SD)), median [interquartile range (IQR)], and mean difference (95% confidence interval (CI)).

RESULTS

Forty patients were included (20 in each group), with 17 patients in the hypothermic and 16 in the normothermic group having an indirect calorimetry measurement in the first 3 days. Over the first 3 days, the mean temperature in the hypothermic and normothermic groups was 33.5 (0.6) ºC (n = 17) and 37 (0.5) ºC (n = 16), p < 0.0001, and the mean measured energy expenditure, was 21 (5) and 27 (4) kcal/kg, p = 0.002, representing a mean difference of 5 (95% CI: 2-8) kcal/kg. Energy expenditure was 20% (95% CI: 9.5-29%) less in hypothermia patients compared to normothermia patients. Hypothermia patients also had higher gastric residual volumes across the 7 day study period (438 (237) mls vs 184 (103) mls, p < 0.0001) and higher use of metoclopramide and erythromycin as prokinetics. Despite enteral nutrition intolerance, hypothermia patients received 93% of measured energy expenditure over 7 days.

CONCLUSION

In TBI patients, energy expenditure was 20% less when receiving prophylactic hypothermia compared to normothermia. Greater gastric residual volumes, use of prokinetics and energy delivery that approximated measured energy expenditure was also observed in hypothermia patients.

TRIAL REGISTRY NUMBER

POLAR-RCT: clinicaltrials.gov Identifier: NCT00987688; Anzctr.org.au Identifier: ACTRN12609000764235. This sub-study was not registered separately.

Perinatal Infection: A Major Contributor to Efficacy of Cooling in Newborns Following Birth Asphyxia

Neonatal encephalopathy (NE) is a global burden, as more than 90% of NE occurs in low- and middle-income countries (LMICs). Perinatal infection seems to limit the neuroprotective efficacy of therapeutic hypothermia. Efforts made to use therapeutic hypothermia in LMICs treating NE has led to increased neonatal mortality rates. The heat shock and cold shock protein responses are essential for survival against a wide range of stressors during which organisms raise their core body temperature and temporarily subject themselves to thermal and cold stress in the face of infection. The characteristic increase and decrease in core body temperature activates and utilizes elements of the heat shock and cold shock response pathways to modify cytokine and chemokine gene expression, cellular signaling, and immune cell mobilization to sites of inflammation, infection, and injury. Hypothermia stimulates microglia to secret cold-inducible RNA-binding protein (CIRP), which triggers NF-κB, controlling multiple inflammatory pathways, including nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasomes and cyclooxygenase-2 (COX-2) signaling. Brain responses through changes in heat shock protein and cold shock protein transcription and gene-expression following fever range and hyperthermia may be new promising potential therapeutic targets.

Can cryoprevention of oral mucositis be obtained at a higher temperature?

OBJECTIVES

Ice chips (IC) have successfully been used to prevent the development of chemotherapy-induced oral mucositis (OM). Although effective, IC entails several shortcomings and may open avenues for systemic infections as the water used may be contaminated by microorganisms, which may jeopardise the medical rehabilitation of an already immunosuppressed patient. This study aimed to investigate the efficacy and tolerability profile of a novel intraoral cooling device (ICD).

SUBJECTS AND METHODS

In total, 20 healthy volunteers were enrolled in this randomised crossover study. Intraoral temperatures were registered using an IR camera, at baseline and following 30 and 60 min of cooling with the ICD, set to 8 °C or 15 °C. Following each cooling session, tolerability was assessed using a questionnaire.

RESULTS

A statistically significant difference in the intraoral temperature was observed using 8 °C compared with 15 °C, following both 30 (1.87 °C, p < 0.001) and 60 min (2.48 °C, p < 0.001) of cooling. Thus, the difference of the intraoral temperatures was less than the 7 °C difference between 8 °C and 15 °C. Furthermore, 60 min of cooling with 15 °C compared with 8 °C was better tolerated and preferred by 15 out of 20 participants (p < 0.001).

CONCLUSION

Cooling was better tolerated when the ICD was set to 15 °C compared with 8 °C, although the difference in reduction of the intraoral mucosal temperature was marginal and may not affect cryoprevention of oral mucositis.

CLINICAL RELEVANCE

The ICD has the potential to improve the care for patients with cancer at high risk of developing OM.

Effect of sub-hypothermia blood purification technique in cardiac shock after valvular disease surgery

To observe the effect of sub-hypothermia (HT) blood purification technique in the treatment of cardiac shock after heart valve disease.The patients were randomly divided into normothermic (NT) continuous blood purification (CBP) group (NT group) and HT CBP group (HT group). Observe the cardiac index (CI), the oxygen delivery (DO2) and oxygen consumption (VO2) ratio, Acute Physiology and Chronic Health Evaluation III(APACHE III) score, multiple organ dysfunction syndrome (MODS) score, dynamic monitoring of electrocardiograph, blood loss with or without muscle tremors, intensive care unit stay, mechanical ventilation time, CBP time, and the cases of infection and mortality at 0 day, 1 day, 2 day, 3 day; all above indicators were compared between 2 groups.Ninety-five patients were randomly assigned into HT group (48 cases) and NT group (47 cases); there were no significant differences between the 2 groups for age, gender, pre-operative cardiac function, cardiothoracic ratio, and type of valve replacement (P > .05). There were no significant differences among the 1 day, 2 day, 3 day after recruited for CI, DO2/VO2 ratio, APACHE III score, MODS score (P > .05). But in HT group, DO2/VO2 ratio had been significantly improved after treatment for 1 day (2.5 ± 0.7 vs 1.8 ± 0.4, P = .024), and CI (3.0 ± 0.5 vs 1.9 ± 0.7, P = .004), APACHE III score (50.6 ± 6.2 vs 77.5 ± 5.5 P = .022), MODS score (6.0 ± 1.5 vs 9.3 ± 3.4, P = .013) also had been significantly improved after treatment for 3 days. In clinical outcomes, there were no significant differences between 2 groups for blood loss (617.0 ± 60.7 ml vs 550.9 ± 85.2 ml, P = .203), infection ratio (54.17% vs 53.19%, P = .341), the incidence of ventricular arrhythmia (31.25% vs 36.17%, P = .237), and muscle tremors (14.58% vs 8.51%, P = .346), while there were significant differences between 2 groups for intensive care unit stay (6.9 ± 3.4 days vs 12.5 ± 3.5 days, P = .017,), mechanical ventilation time (4.2 ± 1.3 days vs 7.5 ± 2.7 days, P = .034,), CBP time (4.6 ± 1.4 days vs 10.5 ± 4.0 days, P = .019), mortality (12.50% vs 23.40%, P = .024). But the incidence of bradycardia in HT group was much higher than the NT group (29.16% vs 14.89%, P = .029).HT blood purification is a safer and more effective treatment than NT blood purification for patients who suffered from cardiac shock after valve surgery.

Pre-arrest hypothermia improved cardiac function of rats by ameliorating the myocardial mitochondrial injury after cardiac arrest

This study investigated the effects of hypothermia induced before cardiac arrest or after return of spontaneous circulation (ROSC) on cardiac function and myocardial mitochondrial injury after ROSC in a rat cardiac arrest model. Sixty healthy, male Wistar rats were randomly divided into the Normothermia group, pre-arrest hypothermia (Pre-HT) group, and post-resuscitation hypothermia (Post-HT) group. The rats underwent 8 min of untreated ventricular fibrillation followed by cardiopulmonary resuscitation. Twelve rats in each group were used to evaluate the left ventricular ejection fraction before ventricular fibrillation and 4 h after ROSC. Survival was determined at 24 h after ROSC. The remaining eight rats in each group were used to detect for heart malondialdehyde, reduced glutathione, adenosine triphosphate levels and mitochondrial histology. Oxygen consumption rate and mitochondrial membrane potential were evaluated 4 h after ROSC; 10 of 12 rats in Pre-HT group, 5 of 12 in Post-HT group, and 6 of 12 in normothermia group were successfully resuscitated. The survival rate of each group was 66.7%, 33.3%, and 25%, respectively. Rats in the Pre-HT group showed less alteration of the mitochondrial ultrastructure and oxidative stress injury, better maintenance of adenine nucleotides, and more preservation of the mitochondrial membrane potential and respiratory function when compared with rats in the Post-HT and normothermia groups. Transient hypothermia is an effective preconditioning stimulus to induce ischemic tolerance in a cardiac arrest model and worthy of further evaluation for potential clinical use.

Impact statement

In this paper, we investigated the effects of hypothermia induced before ischemia or after ROSC on cardiac function, oxidative stress damage, and myocardial mitochondrial ischemia–reperfusion injury after cardiac arrest in a rat model with VF. We demonstrated that pre-arrest hypothermia conferred greater cardio-protective benefits than delayed post-resuscitation hypothermia, reduced the number of defibrillations required and dosages of epinephrine during CPR, decreased oxidative stress, ameliorated mitochondrial dysfunction, and subsequently improved survival rate.

Current Use of Neuromuscular Blocking Agents in Intensive Care Units

Neuromuscular blocking agents can be used for purposes such as eliminating ventilator-patient dyssynchrony, facilitating gas exchange by reducing intra-abdominal pressure and improving chest wall compliance, reducing risk of lung barotrauma, decreasing contribution of muscles to oxygen consumption by preventing shivering and limiting elevations in intracranial pressure caused by airway stimulation in patients supported with mechanical ventilation in intensive care units. Adult Respiratory Distress Syndrome (ARDS), status asthmaticus, increased intracranial pressure and therapeutic hypothermia following ventricular fibrillation-associated cardiac arrest are some of clinical conditions that can be sustained by neuromuscular blockade. Appropriate indication and clinical practice have gained importance considering side effects such as ICU-acquired weakness, masking seizure activity and longer durations of hospital and ICU stays. We mainly aimed to review the current literature regarding neuromuscular blockade in up-to-date clinical conditions such as improving oxygenation in early ARDS and preventing shivering in the therapeutic hypothermia along with summarising the clinical practice in adult ICU in this report.

Cerebral Tissue Oxidative Ischemia-Reperfusion Injury in Connection with Experimental Cardiac Arrest and Cardiopulmonary Resuscitation: Effect of Mild Hypothermia and Methylene Blue

The present investigation is an expansion of previous studies which all share a basic experimental protocol of a porcine-induced cardiac arrest (CA) of 12 min followed by 8 min of cardiopulmonary resuscitation (CPR), different experimental treatments (immediate as well as postponed induced mild hypothermia and administration of much or less cool intravenous fluids), and a follow-up period of 3 h after which the animals were sacrificed. Another group of animals was studied according to the same protocol after 12-min CA and “standard CPR.” After death (within 1 min), the brains were harvested and frozen in liquid nitrogen awaiting analysis. Control brains of animals were collected in the same way after short periods of untreated CA (0 min, 5 min, and 15–30 min). Previous studies concerning chiefly neuropathological changes were now expanded with analyses of different tissue indicators (glutathione, luminol, leucigenin, malonialdehyde, and myeloperoxidase) of cerebral oxidative injury. The results indicate that a great part of oxidative injury occurs within the first 5 min after CA. Immediate cooling by administration of much intravenous fluid results in less cerebral oxidative injury compared to less intravenous fluid administration. A 30-min postponement of induction of hypothermia results in a cerebral oxidative injury comparable to that of “standard CPR” or the oxidative injury found after 5 min of untreated CA. Intravenous administration of methylene blue (MB) during and immediately after CPR in combination with postponed cooling resulted in no statistical difference in any of the indicators of oxidative injury, except myeloperoxidase, and glutathione, when this treatment was compared with the negative controls, i.e., animals subjected to anesthesia alone.

Clinicopathological prognostic indicators of survival and pathological findings in cold-stressed Florida manatees Trichechus manatus latirostris

Cold-stress syndrome (CSS) is a leading natural cause of mortality in free-ranging Florida manatees Trichechus manatus latirostris, but comprehensive investigations into blood analyte derangements and prognostic indicators in CSS are lacking. The objectives of this study were to (1) compare admission blood analyte data of manatees pre and post rehabilitation for CSS to identify clinicopathological derangements, (2) identify blood analyte prognostic indicators for survival, and (3) correlate post-mortem anatomic pathological changes with clinicopathological findings to improve the understanding of CS pathophysiology. CSS manatees admitted to a rehabilitation facility between 2007 and 2017 were included: 59 manatees with data for clinicopathological analysis (7 non-survivors and 49 survivors) and 14 manatees with necropsy data (7 with and 7 without blood analyte data). Main interpretive clinicopathological findings indicated systemic inflammation, bone marrow damage, diuresis, malnutrition, tissue necrosis, fat mobilization, hepatic impairment, acid-base imbalances, and gastrointestinal ulceration. The best diagnostically performing prognostic indicators for survival included platelet concentration, aspartate aminotransferase, calcium, and blood urea nitrogen. The main anatomic pathological findings were cutaneous lesions (n = 14), lipid depletion (n = 12), upper gastrointestinal ulceration and/or hemorrhage (n = 9), and pneumonia (n = 5). Based on the identified blood prognostic indicators interpreted in the context of anatomic pathological findings, multi-organ tissue injury, gastrointestinal ulceration and/or hemorrhage, and hemodynamic and platelet derangements are the presumptive major factors of CSS manatee mortality. These results contribute to the understanding of the complex CSS pathophysiology and offer the use of blood analyte prognostic indicators as a clinically applicable tool for the medical care of manatees during rehabilitation, thereby contributing to increased rehabilitation success and conservation of the Florida manatee.

Supratherapeutic Vancomycin Concentrations Associated With Hypothermia in a Burn Patient

Hypothermia is a dangerous adverse effect that occurs in burn patients. Hypothermia leads to decreased renal blood flow and may decrease renal clearance of medications. Few human studies examine the effect of hypothermia on drug clearance and no known studies examine its effect on vancomycin clearance in burn patients. This case report describes a 39-year-old female who suffered 60% total body surface area third-degree burns. The patient required vancomycin, empirically, and for definitive treatment of methicillin-resistant Staphylococcus aureus. During three of the vancomycin courses, the patient experienced significant hypothermia. Vancomycin concentrations obtained during normothermia were found to be subtherapeutic or therapeutic. Concentrations obtained during hypothermia were found to be supratherapeutic and rate elimination constants were found to be significantly decreased by 45, 25, and 31%, respectively. These patient data suggest that hypothermia can decrease vancomycin clearance in burn patients as evidenced by supratherapeutic vancomycin concentrations and decreased rate elimination constants. Burn patients should be monitored closely for hypothermia. If hypothermia occurs during treatment, vancomycin concentrations should be obtained frequently, even if renal function appears stable. Dosing based on concentrations may be necessary in order to avoid supratherapeutic vancomycin concentrations and associated adverse drug events.

Effects of Mild Hypothermia on Cardiac and Neurological Function in Piglets Under Pathological and Physiological Stress Conditions

To investigate the different effects of mild hypothermia on pathological and physiological stress conditions in piglets, 30 pigs were randomized into four groups: cardiac arrest and mild hypothermia (CA-MH group), cardiac arrest and normothermia (CA-NH group), non-CA-MH (NCA-MH group), and a sham operation. The same hypothermia intervention was implemented in both CA-MH and NCA-MH groups. The CA-NH group did not undergo therapeutic hypothermia after resuscitation. The hemodynamic parameters were recorded. Cerebral metabolism variables and neurotransmitters in the extracellular fluid were collected through microdialysis tubes. The serum of venous blood was used to detect levels of inflammatory factors. The cerebral function was evaluated. At 24 and 72 hours after resuscitation, the cerebral performance category and neurological deficit score in the CA-NH group had higher values. Heart rate and cardiac output (CO) in the CA-MH group during cooling were lower than that of the CA-NH group, but CO was higher after rewarming. Glucose was higher during cooling, and extracellular lactate and lactate/pyruvate ratio in the CA-MH group were lower than that of the CA-NH group. Noradrenaline and 5-hydroxytryptamine in the CA-MH and NCA-MH groups were lower than that of the CA-NH group and sham group during cooling, respectively. Inflammatory factor levels, including interleukin (IL)-1β, IL-2, IL-4, IL-6, IL-8, and tumor necrosis factor-α, in the CA-MH group were lower than that of the CA-NH group at cooling for 12 hours. These values in the NCA-MH group were higher than that of the sham group. Under a light and an electron microscope, the worse pathological results of heart and brain were observed in the two cardiac arrest groups. Mild hypothermia can provide limited organ protection in the specific pathological condition caused by ischemia-reperfusion, but it may produce a negative effect in a normal physiological state.

Effects of Therapeutic Hypothermia Combined with Other Neuroprotective Strategies on Ischemic Stroke: Review of Evidence

Ischemic stroke is a major cause of death and disability globally, and its incidence is increasing. The only treatment approved by the US Food and Drug Administration for acute ischemic stroke is thrombolytic treatment with recombinant tissue plasminogen activator. As an alternative, therapeutic hypothermia has shown excellent potential in preclinical and small clinical studies, but it has largely failed in large clinical studies. This has led clinicians to explore the combination of therapeutic hypothermia with other neuroprotective strategies. This review examines preclinical and clinical progress towards developing highly effective combination therapy involving hypothermia for stroke patients.

Statistical analysis plan for the POLAR-RCT: The Prophylactic hypOthermia trial to Lessen trAumatic bRain injury-Randomised Controlled Trial

Background

The Prophylactic hypOthermia to Lessen trAumatic bRain injury-Randomised Controlled Trial (POLAR-RCT) will evaluate whether early and sustained prophylactic hypothermia delivered to patients with severe traumatic brain injury improves patient-centred outcomes.

Methods

The POLAR-RCT is a multicentre, randomised, parallel group, phase III trial of early, prophylactic cooling in critically ill patients with severe traumatic brain injury, conducted in Australia, New Zealand, France, Switzerland, Saudi Arabia and Qatar. A total of 511 patients aged 18–60 years have been enrolled with severe acute traumatic brain injury.

The trial intervention of early and sustained prophylactic hypothermia to 33 °C for 72 h will be compared to standard normothermia maintained at a core temperature of 37 °C.

The primary outcome is the proportion of favourable neurological outcomes, comprising good recovery or moderate disability, observed at six months following randomisation utilising a midpoint dichotomisation of the Extended Glasgow Outcome Scale (GOSE). Secondary outcomes, also assessed at six months following randomisation, include the probability of an equal or greater GOSE level, mortality, the proportions of patients with haemorrhage or infection, as well as assessment of quality of life and health economic outcomes. The planned sample size will allow 80% power to detect a 30% relative risk increase from 50% to 65% (equivalent to a 15% absolute risk increase) in favourable neurological outcome at a two-sided alpha of 0.05.

Discussion

Consistent with international guidelines, a detailed and prospective analysis plan has been developed for the POLAR-RCT. This plan specifies the statistical models for evaluation of primary and secondary outcomes, as well as defining covariates for adjusted analyses and methods for exploratory analyses. Application of this statistical analysis plan to the forthcoming POLAR-RCT trial will facilitate unbiased analyses of these important clinical data.

Trial registration

ClinicalTrials.gov, NCT00987688 (first posted 1 October 2009); Australian New Zealand Clinical Trials Registry, ACTRN12609000764235. Registered on 3 September 2009.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-2610-y) contains supplementary material, which is available to authorized users.

Safety and Efficacy of Hypothermia (34°C) after Hemicraniectomy for Malignant MCA Infarction

OBJECTIVE

The beneficial effect of hypothermia after hemicraniectomy in malignant middle cerebral artery (MCA) infarction has been controversial. We aim to investigate the safety and clinical efficacy of hypothermia after hemicraniectomy in malignant MCA infarction.

METHODS

From October 2012 to February 2016, 20 patients underwent hypothermia (Blanketrol III, Cincinnati Sub-Zero, Cincinnati, OH, USA) at 34°C after hemicraniectomy in malignant MCA infarction (hypothermia group). The indication of hypothermia included acute cerebral infarction >2/3 of MCA territory and a Glasgow coma scale (GCS) score <11 with a midline shift >10 mm or transtentorial herniation sign (a fixed and dilated pupil). We retrospectively collected 27 patients, as the control group, who had undergone hemicraniectomy alone and simultaneously met the inclusion criteria of hypothermia between January 2010 and September 2012, before hypothermia was implemented as a treatment strategy in Dong-A University Hospital. We compared the mortality rate between the two groups and investigated hypothermia-related complications, such as postoperative bleeding, pneumonia, sepsis and arrhythmia.

RESULTS

The age, preoperative infarct volume, GCS score, National institutes of Health Stroke Scale score, and degree of midline shift were not significantly different between the two groups. Of the 20 patients in the hypothermia group, 11 patients were induced with hypothermia immediately after hemicraniectomy and hypothermia was initiated in 9 patients after the decision of hypothermia during postoperative care. The duration of hypothermia was 4±2 days (range, 1 to 7 days). The side effects of hypothermia included two patients with arrhythmia, one with sepsis, one with pneumonia, and one with hypotension. Three cases of hypothermia were discontinued due to these side effects (one sepsis, one hypotension, and one bradycardia). The mortality rate of the hypothermia group was 15.0% and that of the control group was 40.7% (p=0.056). On the basis of the logistic regression analysis, hypothermia was considered to contribute to the decrease in mortality rate (odds ratio, 6.21; 95% confidence interval, 1.04 to 37.05; p=0.045).

CONCLUSION

This study suggests that hypothermia after hemicraniectomy is a viable option when the progression of patients with malignant MCA infarction indicate poor prognosis.

A retrospective analysis on the relationship between intraoperative hypothermia and postoperative ileus after laparoscopic colorectal surgery

Postoperative ileus (POI) is an important factor prolonging the length of hospital stay following colorectal surgery. We retrospectively explored whether there is a clinically relevant association between intraoperative hypothermia and POI in patients who underwent laparoscopic colorectal surgery for malignancy within the setting of an enhanced recovery after surgery (ERAS) program between April 2016 and January 2017 at our institution. In total, 637 patients were analyzed, of whom 122 (19.2%) developed clinically and radiologically diagnosed POI. Overall, 530 (83.2%) patients experienced intraoperative hypothermia. Although the mean lowest core temperature was lower in patients with POI than those without POI (35.3 ± 0.5°C vs. 35.5 ± 0.5°C, P = 0.004), the independence of intraoperative hypothermia was not confirmed based on multivariate logistic regression analysis. In addition to three variables (high age-adjusted Charlson comorbidity index score, long duration of surgery, high maximum pain score during the first 3 days postoperatively), cumulative dose of rescue opioids used during the first 3 days postoperatively was identified as an independent risk factor of POI (odds ratio = 1.027 for each 1-morphine equivalent [mg] increase, 95% confidence interval = 1.014–1.040, P <0.001). Patients with hypothermia showed significant delays in both progression to a soft diet and discharge from hospital. In conclusion, intraoperative hypothermia was not independently associated with POI within an ERAS pathway, in which items other than thermal measures might offset its negative impact on POI. However, as it was associated with delayed discharge from the hospital, intraoperative maintenance of normothermia is still needed.

Therapeutic hypothermia in acute traumatic spinal cord injury

Therapeutic hypothermia is already widely acknowledged as an effective neuroprotective intervention, especially within the acute care setting in relation to conditions such as cardiac arrest and neonatal encephalopathy. Its multifactorial mechanisms of action, including lowering metabolic rate and reducing acute inflammatory cellular processes, ultimately provide protection for central nervous tissue from continuing injury following ischaemic or traumatic insult. Its clinical application within acute traumatic spinal cord injury would therefore seem very plausible, it having the potential to combat the pathophysiological secondary injury processes that can develop in the proceeding hours to days following the initial injury. As such it could offer invaluable assistance to lessen subsequent sensory, motor and autonomic dysfunction for an individual affected by this devastating condition. Yet research surrounding this intervention's applicability in this field is somewhat lacking, the majority being experimental. Despite a recent resurgence of interest, which in turn has produced encouraging results, there is a real possibility that this potentially transformational intervention for treating traumatic spinal cord injury could remain an experimental therapy and never reach clinical implementation.

Targeted temperature management in neurological intensive care unit

Targeted temperature management (TTM) shows the most promising neuroprotective therapy against hypoxic/ischemic encephalopathy (HIE). In addition, TTM is also useful for treatment of elevated intracranial pressure (ICP). HIE and elevated ICP are common catastrophic conditions in patients admitted in Neurologic intensive care unit (ICU). The most common cause of HIE is cardiac arrest. Randomized control trials demonstrate clinical benefits of TTM in patients with post-cardiac arrest. Although clinical benefit of ICP control by TTM in some specific critical condition, for an example in traumatic brain injury, is still controversial, efficacy of ICP control by TTM is confirmed by both in vivo and in vitro studies. Several methods of TTM have been reported in the literature. TTM can apply to various clinical conditions associated with hypoxic/ischemic brain injury and elevated ICP in Neurologic ICU.

Therapeutic Whole-body Hypothermia Protects Remote Lung, Liver, and Kidney Injuries after Blast Limb Trauma in Rats

BACKGROUND

Severe blast limb trauma (BLT) induces distant multiple-organ injuries. In the current study, the authors determined whether whole-body hypothermia (WH) and its optimal duration (if any) afford protection to the local limb damage and distant lung, liver, and kidney injuries after BLT in rats.

METHODS

Rats with BLT, created by using chartaceous electricity detonators, were randomly treated with WH for 30 min, 60 min, 3 h, and 6 h (n = 12/group). Rectal temperature and arterial blood pressure were monitored throughout. Blood and lung, liver, and kidney tissue samples were harvested for measuring tumor necrosis factor-α, interleukin-6 and interleukin-10, myeloperoxidase activity, hydrogen sulfide, and biomarkers of oxidative stress at 6 h after BLT. The pathologic lung injury and the water content of the lungs, liver, and kidneys and blast limb tissue were assessed.

RESULTS

Unlike WH for 30 min, WH for 60 min reduced lung water content, lung myeloperoxidase activity, and kidney myeloperoxidase activity by 10, 39, and 28% (all P < 0.05), respectively. WH for 3 h attenuated distant vital organs and local traumatic limb damage and reduced myeloperoxidase activity, hydrogen peroxide and malondialdehyde concentration, and tumor necrosis factor-α and interleukin-6 levels by up to 49% (all P < 0.01). Likewise, WH for 6 h also provided protection to such injured organs but increased blood loss from traumatic limb.

CONCLUSIONS

Results of this study indicated that WH may provide protection for distant organs and local traumatic limb after blast trauma, which warrants further study.

Early enteral nutrition in critically ill patients: ESICM clinical practice guidelines

Purpose

To provide evidence-based guidelines for early enteral nutrition (EEN) during critical illness.

Methods

We aimed to compare EEN vs. early parenteral nutrition (PN) and vs. delayed EN. We defined “early” EN as EN started within 48 h independent of type or amount. We listed, a priori, conditions in which EN is often delayed, and performed systematic reviews in 24 such subtopics. If sufficient evidence was available, we performed meta-analyses; if not, we qualitatively summarized the evidence and based our recommendations on expert opinion. We used the GRADE approach for guideline development. The final recommendations were compiled via Delphi rounds.

Results

We formulated 17 recommendations favouring initiation of EEN and seven recommendations favouring delaying EN. We performed five meta-analyses: in unselected critically ill patients, and specifically in traumatic brain injury, severe acute pancreatitis, gastrointestinal (GI) surgery and abdominal trauma. EEN reduced infectious complications in unselected critically ill patients, in patients with severe acute pancreatitis, and after GI surgery. We did not detect any evidence of superiority for early PN or delayed EN over EEN. All recommendations are weak because of the low quality of evidence, with several based only on expert opinion.

Conclusions

We suggest using EEN in the majority of critically ill under certain precautions. In the absence of evidence, we suggest delaying EN in critically ill patients with uncontrolled shock, uncontrolled hypoxaemia and acidosis, uncontrolled upper GI bleeding, gastric aspirate >500 ml/6 h, bowel ischaemia, bowel obstruction, abdominal compartment syndrome, and high-output fistula without distal feeding access.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-016-4665-0) contains supplementary material, which is available to authorized users.

Aortic Arch Atheroma: Stroke Reduction in Cardiac Surgical Patients

Cardiac surgery is increasingly performed on elderly patients with extensive coronary artery abnormalities who have impaired left ventricular function, decreased physiologic reserve, and multiple comorbid conditions. Considerable numbers of these patients develop perioperative neurologic complications ranging from subtle cognitive dysfunction to more evident postoperative confusion, delirium, and, less commonly, clinically apparent stroke. Magnetic resonance imaging studies have elucidated that a considerable number of patients have new ischemic brain infarcts, particularly after conventional coronary artery bypass graft surgery. Mechanisms of cerebral injury during and after cardiac surgery are discussed. Intraoperative transesophageal echocardiography and epiaortic scanning for detection of atheromatous disease of the proximal thoracic aorta is paramount in identifying patients at high risk from neurologic injury. It is important to recognize that our efforts to minimize neurologic injury should not be limited to the intraoperative period. Particular efforts should be directed to temperature management, glycemia control, and pharmacologic neuroprotection extending into the postoperative period. Preoperative magnetic resonance angiography may be of value for screening patients with significant atheroma of the proximal thoracic aorta. It is likely that for patients with no significant atheromatous disease, conventional coronary artery revascularization is the most effective long-term strategy, whereas patients with atheromatous thoracic aorta may be better managed with beating heart surgery, hybrid techniques, or medical therapy alone. Patient stratification based on the aortic atheromatic burden should be addressed in future trials designed to tailor treatment strategies to improve long-term outcomes of coronary heart disease and reduce the risks of perioperative neurologic injury.

Hypothermia protects brain mitochondrial function from hypoxemia in a murine model of sepsis

Sepsis is commonly associated with brain dysfunction, but the underlying mechanisms remain unclear, although mitochondrial dysfunction and microvascular abnormalities have been implicated. We therefore assessed whether cerebral mitochondrial dysfunction during systemic endotoxemia in mice increased mitochondrial sensitivity to a further bioenergetic insult (hyoxemia), and whether hypothermia could improve outcome. Mice (C57bl/6) were injected intraperitoneally with lipopolysaccharide (LPS) (5 mg/kg; n = 85) or saline (0.01 ml/g; n = 47). Six, 24 and 48 h later, we used confocal imaging in vivo to assess cerebral mitochondrial redox potential and cortical oxygenation in response to changes in inspired oxygen. The fraction of inspired oxygen (FiO₂) at which the cortical redox potential changed was compared between groups. In a subset of animals, spontaneous hypothermia was maintained or controlled hypothermia induced during imaging. Decreasing FiO₂ resulted in a more reduced cerebral redox state around veins, but preserved oxidation around arteries. This pattern appeared at a higher FiO₂ in LPS-injected animals, suggesting an increased sensitivity of cortical mitochondria to hypoxemia. This increased sensitivity was accompanied by a decrease in cortical oxygenation, but was attenuated by hypothermia. These results suggest that systemic endotoxemia influences cortical oxygenation and mitochondrial function, and that therapeutic hypothermia can be protective.

Mild hypothermia attenuate kidney injury in canines with oleic acid-induced acute respiratory distress syndrome

BACKGROUND

Hypothermia may attenuate ventilator induced-lung injury in acute respiratory distress syndrome (ARDS). However, the impact of hypothermia on extra-pulmonary organ injury in ARDS remains unclear. The purpose of this study was to investigate whether hypothermia affects extra-pulmonary organ injury in a canine ARDS model induced by oleic acid.

OBJECTIVES

Twelve anesthetized canines with oleic acid-induced ARDS were randomly divided (n=6 per group) into a hypothermia group (core temperature of 33±1°C, HT group) and a normothermia group (core temperature of 38±1°C, NT group) and treated for four hours. The liver, small intestine and kidney were assessed by evaluating biochemical parameters, plasma and tissue cytokine levels, and tissue histopathological injury scores.

RESULTS

The HT group showed a lower plateau pressure, lung elastance and pulmonary vascular resistance. Hypothermia was associated with lower oxygen consumption (138.4±55.0mlmin(-1)vs. 72.0±11.2mlmin(-1), P<0.05) and higher oxygen saturation of mixed venous blood (62.8%±8.0% vs. 77.5%±10.1%, P<0.05). Both groups had similar levels of tumour necrosis factor-α in the plasma and extra-pulmonary organ, however, plasma interleukin-10 (97.1±25.0pgml(-1)vs. 131.4±27.0pgml(-1), P<0.05) was higher in the HT group. Further, the animals in the HT group had a lower levels of plasma creatinine (54.6±19.1UL(-1)vs. 29.1±8.0UL(-1), P<0.05), and lower renal histopathological injury scores [4.0(3.5;7.0) vs. 1.5(0.8;3.0), P<0.05]. Hypothermia did not affect the histopathological injury of the liver and small intestine.

CONCLUSIONS

Short-term mild hypothermia can reduce lung elastance and pulmonary vascular resistance, increase the systemic anti-inflammatory response and attenuate kidney histopathological injury in a canine ARDS model induced by oleic acid.

Therapeutic hypothermia and ischemic stroke: A literature review

BACKGROUND

Ischemic stroke is the fifth leading cause of death in the US. Clinical techniques aimed at helping to reduce the morbidity associated with stroke have been studied extensively, including therapeutic hypothermia. In this study, the authors review the literature regarding the role of therapeutic hypothermia in ischemic stroke to appreciate the evolution of hypothermia technology over several decades and to critically analyze several early clinical studies to validate its use in ischemic stroke.

METHODS

A comprehensive literature search was performed using PubMed and Google Scholar databases. Search terms included "hypothermia and ischemic stroke" and "therapeutic hypothermia." A comprehensive search of the current clinical trials using clinicaltrials.gov was conducted using the keywords "stroke and hypothermia" to evaluate early and ongoing clinical trials utilizing hypothermia in ischemic stroke.

RESULTS

A comprehensive review of the evolution of hypothermia in stroke and the current status of this treatment was performed. Clinical studies were critically analyzed to appreciate their strengths and pitfalls. Ongoing and future registered clinical studies were highlighted and analyzed compared to the reported results of previous trials.

CONCLUSION

Although hypothermia has been used for various purposes over several decades, its efficacy in the treatment of ischemic stroke is debatable. Several trials have proven its safety and feasibility; however, more robust, randomized clinical trials with large volumes of patients are needed to fully establish its utility in the clinical setting.

Laboratory study on the kinetics of the warming of cold fluids-A hot topic

OBJECTIVES

In case of mild therapeutic hypothermia after an out-of-hospital cardiac arrest, several techniques could limit the cold fluid rewarming during its perfusion. We aimed to evaluate cold fluid temperature evolution and to identify the factors responsible for rewarming in order to suggest a prediction model of temperature evolution.

EQUIPMENT AND METHODS

This was a laboratory experimental study. We measured temperature at the end of the infusion line tubes (ILT). A 500ml saline bag at 4°C was administered at 15 and 30ml/min, with and without cold packs applied to the cold fluid bag or to the ILT. Cold fluid temperature was integrated in a linear mixed model. Then we performed a mathematical modelization of the thermal transfer across the ILT.

RESULTS

The linear mixed model showed that the mean temperature of the cold fluid was 1°C higher (CI 95%: [0.8-1.2]) with an outflow rate of 15 versus 30ml/min (P<0.001). Similarly, the mean temperature of the cold fluid was 0.7°C higher (CI 95%: [0.53-0.9]) without cold pack versus with cold packs (P<0.001). Mathematical modelization of the thermal transfer across the ILT suggested that the cold fluid warming could be reduced by a shorter and a wider ILT. As expected, use of CP has also a noticeable influence on warning reduction. The combination of multiple parameters working against the rewarming of the solution should enable the infusion of a solute with retained caloric properties.

CONCLUSIONS

By limiting this "ILT effect," the volume required for inducing mild therapeutic hypothermia could be reduced, leading to a safer and a more efficient treatment.

Targeted temperature management in traumatic brain injury

Traumatic brain injury (TBI) is recognized as the significant cause of mortality and morbidity in the world. To reduce unfavorable outcome in TBI patients, many researches have made much efforts for the innovation of TBI treatment. With the results from several basic and clinical studies, targeted temperature management (TTM) including therapeutic hypothermia (TH) have been recognized as the candidate of neuroprotective treatment. However, their evidences are not yet proven in larger randomized controlled trials (RCTs). The main aim of this review is thus to clarify specific pathophysiology which TTM will be effective in TBI. Historically, there were several clinical trials which compare TH and normothermia. Recently, two RCTs were able to demonstrate the significant beneficial effects of TTM in one specific pathology, patients with mass evacuated lesions. These suggested that TTM might be effective especially for the ischemic-reperfusional pathophysiology of TBI, like as acute subdural hematoma which needs to be evacuated. Also, the latest preliminary report of European multicenter trial suggested the promising efficacy of reduction of intracranial pressure in TBI. Conclusively, TTM is still in the center of neuroprotective treatments in TBI. This therapy is expected to mitigate ischemic and reperfusional pathophysiology and to reduce intracranial pressure in TBI. Further results from ongoing clinical RCTs are waited.

Endovascular Cooling Method for Hypothermia in Injured Swine

We evaluated an endovascular cooling method to modulate core temperature in trauma swine models with and without fluid support. Anesthetized swine (N = 80) were uninjured (SHAM) or injured through a bone fracture plus soft tissue injury or an uncontrolled hemorrhage and then subdivided to target body temperatures of 38°C (normothermia) or 33°C (hypothermia) by using a Thermogard endovascular cooling device (Zoll Medical). Temperature regulation began simultaneously at onset of injury (T0). Body temperatures were recorded from a rectal probe (Rec Temp) and from a central pulmonary artery catheter (PA Temp). At T15, swine received 500 mL IV Hextend over 30 minutes or no treatment (NONE) with continued monitoring until 3 hours from injury. Hypothermia was attained in 105 ± 39 minutes, at a cooling rate of -0.061°C ± 0.007°C/min for NONE injury groups. Postinjury Hextend administration resulted in faster cooling (-0.080°C ± 0.006°C/min); target temperature was reached in 83 ± 11 minutes (p < 0.05). During active cooling, body temperature measured by the PA Temp was significantly cooler than the Rec Temp due to the probe's closer proximity to the blood-cooling catheter balloons (p < 0.05). This difference was smaller in SHAM and fluid-supported injury groups (1.1°C ± 0.4°C) versus injured NONE groups (2.1°C ± 0.3°C). Target temperatures were correctly maintained thereafter in all groups. In normothermia groups, there was a small initial transient overshoot to maintain 38°C. Despite the noticeable difference between PA Temp and Rec Temp until target temperature was attained, this endovascular method can safely induce moderate hypothermia in anesthetized swine. However, likely due to their compromised hemodynamic state, cooling in hypovolemic and/or injured patients will be different from those without injury or those that also received fluids.

Therapeutic hypothermia applicable to cardiac surgery

OBJECTIVE

To review the beneficial and adverse effects of therapeutic hypothermia (TH) applicable to cardiac surgery with cardiopulmonary bypass (CPB) in the contexts of various temperature levels and techniques for achieving TH.

DATABASES USED

Multiple electronic literature searches were performed using PubMed and Google for articles published from June 2012 to December 2014. Relevant terms (e.g. 'hypothermia', 'cardiopulmonary bypass', 'cardiac surgery', 'neuroprotection') were used to search for original articles, letters and reviews without species limitation. Reviews were included despite potential publication bias. References from the studies identified were also searched to find other potentially relevant citations. Abstracts, case reports, conference presentations, editorials and expert opinions were excluded.

CONCLUSIONS

Therapeutic hypothermia is an essential measure of neuroprotection during cardiac surgery that may be achieved most effectively by intravascular cooling using hypothermic CPB. For most cardiac surgical procedures, mild to modest (32-36 °C) TH will be sufficient to assure neuroprotection and will avoid most of the adverse effects of hypothermia that occur at lower body core temperatures.

Electrocardiographic changes during induced therapeutic hypothermia in comatose survivors after cardiac arrest

AIM: To assess the safety of therapeutic hypothermia (TH) concerning arrhythmias we analyzed serial electrocardiograms (ECG) during TH.

METHODS: All patients recovered from a cardiac arrest with Glasgow < 9 at admission were treated with induced mild TH to 32-34 °C. TH was obtained with cool fluid infusion or a specific intravascular device. Twelve-lead ECG before, during, and after TH, as well as ECG telemetry data was recorded in all patients. From a total of 54 patients admitted with cardiac arrest during the study period, 47 patients had the 3 ECG and telemetry data available. ECG analysis was blinded and performed with manual caliper by two independent cardiologists from blinded copies of original ECG, recorded at 25 mm/s and 10 mm/mV. Coronary care unit staff analyzed ECG telemetry for rhythm disturbances. Variables measured in ECG were rhythm, RR, PR, QT and corrected QT (QTc by Bazett formula, measured in lead v2) intervals, QRS duration, presence of Osborn’s J wave and U wave, as well as ST segment displacement and T wave amplitude in leads II, v2 and v5.

RESULTS: Heart rate went down an average of 19 bpm during hypothermia and increased again 16 bpm with rewarming (P < 0.0005, both). There was a non-significant prolongation of the PR interval during TH and a significant decrease with rewarming (P = 0.041). QRS duration significantly prolonged (P = 0.041) with TH and shortened back (P < 0.005) with rewarming. QTc interval presented a mean prolongation of 58 ms (P < 0.005) during TH and a significant shortening with rewarming of 22.2 ms (P = 0.017). Osborn or J wave was found in 21.3% of the patients. New arrhythmias occurred in 38.3% of the patients. Most frequent arrhythmia was non-sustained ventricular tachycardia (19.1%), followed by severe bradycardia or paced rhythm (10.6%), accelerated nodal rhythm (8.5%) and atrial fibrillation (6.4%). No life threatening arrhythmias (sustained ventricular tachycardia, polymorphic ventricular tachycardia or ventricular fibrillation) occurred during TH.

CONCLUSION: A 38.3% of patients had cardiac arrhythmias during TH but without life-threatening arrhythmias. A concern may rise when inducing TH to patients with long QT syndrome.

Induced Hypothermia Does Not Harm Hemodynamics after Polytrauma: A Porcine Model

BACKGROUND

The deterioration of hemodynamics instantly endangers the patients' life after polytrauma. As accidental hypothermia frequently occurs in polytrauma, therapeutic hypothermia still displays an ambivalent role as the impact on the cardiopulmonary function is not yet fully understood.

METHODS

We have previously established a porcine polytrauma model including blunt chest trauma, penetrating abdominal trauma, and hemorrhagic shock. Therapeutic hypothermia (34°C) was induced for 3 hours. We documented cardiovascular parameters and basic respiratory parameters. Pigs were euthanized after 15.5 hours.

RESULTS

Our polytrauma porcine model displayed sufficient trauma impact. Resuscitation showed adequate restoration of hemodynamics. Induced hypothermia had neither harmful nor major positive effects on the animals' hemodynamics. Though heart rate significantly decreased and mixed venous oxygen saturation significantly increased during therapeutic hypothermia. Mean arterial blood pressure, central venous pressure, pulmonary arterial pressure, and wedge pressure showed no significant differences comparing normothermic trauma and hypothermic trauma pigs during hypothermia.

CONCLUSIONS

Induced hypothermia after polytrauma is feasible. No major harmful effects on hemodynamics were observed. Therapeutic hypothermia revealed hints for tissue protective impact. But the chosen length for therapeutic hypothermia was too short. Nevertheless, therapeutic hypothermia might be a useful tool for intensive care after polytrauma. Future studies should extend therapeutic hypothermia.

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.

Improving neurological outcome after cardiac arrest: Therapeutic hypothermia the best treatment

Cardiac arrest, irrespective of its etiology, has a high mortality. This event is often associated with brain anoxia which frequently causes severe neurological damage and persistent vegetative state. Only one out of every six patients survives to discharge following in-hospital cardiac arrest, whereas only 2-9% of patients who experience out of hospital cardiac arrest survive to go home. Functional outcomes of survival are variable, but poor quality survival is common, with only 3-7% able to return to their previous level of functioning. Therapeutic hypothermia is an important tool for the treatment of post-anoxic coma after cardiopulmonary resuscitation. It has been shown to reduce mortality and has improved neurological outcomes after cardiac arrest. Nevertheless, hypothermia is underused in critical care units. This manuscript aims to review the mechanism of hypothermia in cardiac arrest survivors and to propose a simple protocol, feasible to be implemented in any critical care unit.

Brain cell death is reduced with cooling by 3.5°C to 5°C but increased with cooling by 8.5°C in a piglet asphyxia model

BACKGROUND AND PURPOSE

In infants with moderate to severe neonatal encephalopathy, whole-body cooling at 33°C to 34°C for 72 hours is standard care with a number needed to treat to prevent a adverse outcome of 6 to 7. The precise brain temperature providing optimal neuroprotection is unknown.

METHODS

After a quantified global cerebral hypoxic-ischemic insult, 28 piglets aged <24 hours were randomized (each group, n=7) to (1) normothermia (38.5°C throughout) or whole-body cooling 2 to 26 hours after insult to (2) 35°C, (3) 33.5°C, or (4) 30°C. At 48 hours after hypoxia-ischemia, delayed cell death (terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling and cleaved caspase 3) and microglial ramification (ionized calcium-binding adapter molecule 1) were evaluated.

RESULTS

At 48 hours after hypoxia-ischemia, substantial cerebral injury was found in the normothermia and 30°C hypothermia groups. However, with 35°C and 33.5°C cooling, a clear reduction in delayed cell death and microglial activation was observed in most brain regions (P<0.05), with no differences between 35°C and 33.5°C cooling groups. A protective pattern was observed, with U-shaped temperature dependence in delayed cell death in periventricular white matter, caudate nucleus, putamen, hippocampus, and thalamus. A microglial activation pattern was also seen, with inverted U-shaped temperature dependence in periventricular white matter, caudate nucleus, internal capsule, and hippocampus (all P<0.05).

CONCLUSIONS

Cooling to 35°C (an absolute drop of 3.5°C as in therapeutic hypothermia protocols) or to 33.5°C provided protection in most brain regions after a cerebral hypoxic-ischemic insult in the newborn piglet. Although the relatively wide therapeutic range of a 3.5°C to 5°C drop in temperature reassured, overcooling (an 8.5°C drop) was clearly detrimental in some brain regions.

The effect of controlled mild hypothermia on large scald burns in a resuscitated rat model

OBJECTIVE

Early surface cooling of burns reduces pain, depth of injury and improves healing. We hypothesized that controlled mild hypothermia would also prolong survival in a fluid resuscitated rat model of large scald burns.

METHODS

Forty rats were anesthetized and a single full-thickness scald burn covering 40% of total body surface area was created on each of the rats. The rats were then randomized to hypothermia (n=20) or no hypothermia (n=20). Mild hypothermia (a reduction of 2°C) was induced with intraperitoneal 4°C normal saline and ice packs. After 2 hours of hypothermia, the rats were rewarmed back to their baseline temperature with a heating pad. The control rats received room temperature intraperitoneal saline. The difference in survival between the groups was determined using Kaplan-Meier analysis and the log-rank test.

RESULTS

Hypothermia was induced in all experimental rats within a mean of 22 minutes (95% confidence interval, 17 to 27). The number of normothermic and hypothermic rats that expired at each time interval were: at 1 hour, 4 vs. 0; at 10 hours, 2 from each group; at 24 hours, 0 vs. 1; at 48 hours, 2 vs. 2; at 72 hours, 1 vs. 1; and at 120 hours, 1 vs. 1 respectively. There were no differences in time to survival between the groups.

CONCLUSION

Induction of brief, mild hypothermia does not prolong survival in a resuscitated rat model of large scald burns.

Therapeutic hypothermia after cardiac arrest and return of spontaneous circulation: it's complicated

Providing evidence-based care to patients with return of spontaneous circulation after a cardiac arrest is a recent complex innovation. Once resuscitated patients must be assessed for appropriateness for therapeutic hypothermia, be cooled in a timely manner, maintained while hypothermic, rewarmed within a specified time frame, and then assessed for whether hypothermia was successful for the patient through neuroprognostication. Nurses caring for therapeutic hypothermia patients must be knowledgeable and prepared to provide care to the patient and family. This article provides an overview of the complexity of therapeutic hypothermia for patients with return of spontaneous circulation in the form of a case study.

Neuroprotective effect of epidural hypothermia after spinal cord lesion in rats

OBJECTIVES

To evaluate the neuroprotective effect of epidural hypothermia in rats subjected to experimental spinal cord lesion.

METHODS

Wistar rats (n = 30) weighing 320-360 g were randomized to two groups (hypothermia and control) of 15 rats per group. A spinal cord lesion was induced by the standardized drop of a 10-g weight from a height of 2.5 cm, using the New York University Impactor, after laminectomy at the T9-10 level. Rats in the hypothermia group underwent epidural hypothermia for 20 minutes immediately after spinal cord injury. Motor function was assessed for six weeks using the Basso, Beattie and Bresnahan motor scores and the inclined plane test. At the end of the final week, the rats' neurological status was monitored by the motor evoked potential test and the results for the two groups were compared.

RESULTS

Analysis of the Basso, Beattie and Bresnahan scores obtained during the six-week period indicated that there were no significant differences between the two groups. There was no significant difference between the groups in the inclined plane test scores during the six-week period. Furthermore, at the end of the study, the latency and amplitude values of the motor evoked potential test were not significantly different between the two groups.

CONCLUSION

Hypothermia did not produce a neuroprotective effect when applied at the injury level and in the epidural space immediately after induction of a spinal cord contusion in Wistar rats.

A Head and Neck Support Device for Inducing Local Hypothermia

The present work describes the design of a device/system intended to induce local mild hypothermia by simultaneously cooling a patient's head and neck. The therapeutic goal is to lower the head and neck temperatures to 33-35 °C, while leaving the core body temperature unchanged. The device works by circulating a cold fluid around the exterior of the head and neck. The head surface area is separated into five different cooling zones. Each zone has a cooling coil and can be independently controlled. The cooling coils are tightly wrapped concentric circles of tubing. This design allows for a dense packing of tubes in a limited space, while preventing crimping of the tubing and minimizing the fluid pressure head loss. The design in the neck region also has multiple tubes wrapping around the circumference of the patient's neck in a helix. Preliminary testing indicates that this approach is capable of achieving the design goal of cooling the brain tissue (at a depth of 2.5 cm from the scalp) to 35 °C within 30- 40 min, without any pharmacologic or circulatory manipulation. In a comparison with examples of current technology, the device has shown the potential for improved cooling capability.

How effective is "code freeze" in post-cardiac arrest patients?

The use of therapeutic hypothermia or "code freeze" dates back to over 100 years in attempts to resuscitate injured soldiers, preserve limbs, and to provide analgesia for amputations. The purpose of this study was to determine the effectiveness of code freeze through a retrospective review of 187 charts of patients who had a cardiac arrest while hospitalized in a 1-year period. Data were collected to determine which post-cardiac arrest patients received the induced therapeutic hypothermia intervention and why they were selected for induced therapeutic hypothermia. The data were compared with post-cardiac arrest patients who did not receive the code-freeze intervention and why they were not eligible for the intervention. Mortality rates between the 2 patient populations were also compared. The results from this study are presented in this article.

Hypothermia for acute ischaemic stroke

Ischaemic stroke is one of the leading causes of death and disability worldwide, and intravenous alteplase is the only proven effective treatment in the acute setting. Hypothermia has been shown to improve neurological outcomes after global ischaemia-hypoxia in comatose patients who have had cardiac arrest, and is one of the most extensively studied and powerful therapeutic strategies in acute ischaemic stroke. The protective mechanisms of therapeutic hypothermia affect the ischaemic cascade across several parallel pathways and, when coupled with reperfusion strategies, might yield synergistic benefits for patients who have had a stroke. Technological advances have allowed hypothermia to be induced rapidly, and the treatment has been used safely in acute stroke patients. Conclusive efficacy trials assessing therapeutic hypothermia combined with reperfusion therapies in acute ischaemic stroke are ongoing.

Guidelines for the early management of patients with acute ischemic stroke: a guideline for healthcare professionals from the American Heart Association/American Stroke Association

BACKGROUND AND PURPOSE

The authors present an overview of the current evidence and management recommendations for evaluation and treatment of adults with acute ischemic stroke. The intended audiences are prehospital care providers, physicians, allied health professionals, and hospital administrators responsible for the care of acute ischemic stroke patients within the first 48 hours from stroke onset. These guidelines supersede the prior 2007 guidelines and 2009 updates.

METHODS

Members of the writing committee were appointed by the American Stroke Association Stroke Council's Scientific Statement Oversight Committee, representing various areas of medical expertise. Strict adherence to the American Heart Association conflict of interest policy was maintained throughout the consensus process. Panel members were assigned topics relevant to their areas of expertise, reviewed the stroke literature with emphasis on publications since the prior guidelines, and drafted recommendations in accordance with the American Heart Association Stroke Council's Level of Evidence grading algorithm.

RESULTS

The goal of these guidelines is to limit the morbidity and mortality associated with stroke. The guidelines support the overarching concept of stroke systems of care and detail aspects of stroke care from patient recognition; emergency medical services activation, transport, and triage; through the initial hours in the emergency department and stroke unit. The guideline discusses early stroke evaluation and general medical care, as well as ischemic stroke, specific interventions such as reperfusion strategies, and general physiological optimization for cerebral resuscitation.

CONCLUSIONS

Because many of the recommendations are based on limited data, additional research on treatment of acute ischemic stroke remains urgently needed.