Temperature Control in the Era of Personalized Medicine: Knowledge Gaps, Research Priorities, and Future Directions

Hypoxic-ischemic brain injury (HIBI) is the leading cause of death and disability after cardiac arrest. To date, temperature control is the only intervention shown to improve neurologic outcomes in patients with HIBI. Despite robust preclinical evidence supporting hypothermia as neuroprotective therapy after cardiac arrest, there remains clinical equipoise regarding optimal core temperature, therapeutic window, and duration of therapy. Current guidelines recommend continuous temperature monitoring and active fever prevention for at least 72 h and additionally note insufficient evidence regarding temperature control targeting 32 °C-36 °C. However, population-based thresholds may be inadequate to support the metabolic demands of ischemic, reperfused, and dysregulated tissue. Promoting a more personalized approach with individualized targets has the potential to further improve outcomes. This review will analyze current knowledge and evidence, address research priorities, explore the components of high-quality temperature control, and define critical future steps that are needed to advance patient-centered care for cardiac arrest survivors.

Fluid balance during acute phase extracorporeal cardiopulmonary resuscitation and outcomes in OHCA patients: a retrospective multicenter cohort study

OBJECTIVE

The association between fluid balance and outcomes in patients who underwent out-of-hospital cardiac arrest (OHCA) and received extracorporeal cardiopulmonary resuscitation (ECPR) remains unknown. We aimed to examine the above relationship during the first 24 h following intensive care unit (ICU) admission.

METHODS

We performed a secondary analysis of the SAVE-J II study, a retrospective multicenter study involving OHCA patients aged ≥ 18 years treated with ECPR between 2013 and 2018 and who received fluid therapy following ICU admission. Fluid balance was calculated based on intravenous fluid administration, blood transfusion, and urine output. The primary outcome was in-hospital mortality. The secondary outcomes included unfavorable outcome (cerebral performance category scores of 3-5 at discharge), acute kidney injury (AKI), and need for renal replacement therapy (RRT).

RESULTS

Overall, 959 patients met our inclusion criteria. In-hospital mortality was 63.6%, and the proportion of unfavorable outcome at discharge was 82.0%. The median fluid balance in the first 24 h following ICU admission was 3673 mL. Multivariable analysis revealed that fluid balance was significantly associated with in-hospital mortality (odds ratio (OR), 1.04; 95% confidence interval (CI), 1.02-1.06; p < 0.001), unfavorable outcome (OR, 1.03; 95% CI, 1.01-1.06; p = 0.005), AKI (OR, 1.04; 95% CI, 1.02-1.05; p < 0.001), and RRT (OR, 1.05; 95% CI, 1.03-1.07; p < 0.001).

CONCLUSIONS

Excessive positive fluid balance in the first day following ICU admission was associated with in-hospital mortality, unfavorable outcome, AKI, and RRT in ECPR patients. Further investigation is warranted.

Protein tyrosine phosphatase Shp2 positively regulates cold stress-induced tyrosine phosphorylation of SIRPα in neurons

The membrane protein SIRPα is a cold stress-responsive signaling molecule in neurons. Cold stress directly induces tyrosine phosphorylation of SIRPα in its cytoplasmic region, and phosphorylated SIRPα is involved in regulating experience-dependent behavioral changes in mice. Here, we examined the mechanism of cold stress-induced SIRPα phosphorylation in vitro and in vivo. The levels of activated Src family protein tyrosine kinases (SFKs), which phosphorylate SIRPα, were not increased by lowering the temperature in cultured neurons. Although the SFK inhibitor dasatinib markedly reduced SIRPα phosphorylation, low temperature induced an increase in SIRPα phosphorylation even in the presence of dasatinib, suggesting that SFK activation is not required for low temperature-induced SIRPα phosphorylation. However, in the presence of pervanadate, a potent inhibitor of protein tyrosine phosphatases (PTPases), SIRPα phosphorylation was significantly reduced by lowering the temperature, suggesting that either the inactivation of PTPase(s) that dephosphorylate SIRPα or increased protection of phosphorylated SIRPα from the PTPase activity is important for low temperature-induced SIRPα phosphorylation. Inactivation of PTPase Shp2 by the allosteric Shp2 inhibitor SHP099, but not by the competitive inhibitor NSC-87877, reduced SIRPα phosphorylation in cultured neurons. Shp2 knockout also reduced SIRPα phosphorylation in the mouse brain. Our data suggest that Shp2, but not SFKs, positively regulates cold stress-induced SIRPα phosphorylation in a PTPase activity-independent manner.

Therapeutic Hypothermia: Comparing Surface vs Intravascular Cooling

BACKGROUND

Therapeutic hypothermia (TH) has shown promise for increasing survival and neurological recovery for post-cardiac arrest patients who are not responding neurologically initially after return of spontaneous circulation.

OBJECTIVE

The aim of this study was to explore the differences between surface and intravascular cooling methods of TH related to survival and neurological outcomes in post-cardiac arrest patients.

METHOD

A literature search was conducted from 2008 to 2018 using 4 databases, including PubMed, CINAHL, Web of Science, and Scopus.

RESULTS

Six articles were identified that compared surface and intravascular cooling for TH in post-cardiac arrest patients, with the outcomes being mortality and neurological outcome. The articles included observational retrospective studies, a systematic analysis, and randomized controlled studies. The articles had between 167 and 934 participants from multiple locations, including Europe, Australia, France, Norway, the Netherlands, and South Korea. The analyzed literature did not highlight differences in mortality or neurological outcome when surface cooling or intravascular cooling was used in post-cardiac arrest patients. One study did find that intravascular cooling was superior to surface cooling in mortality and neurological outcome. Three studies showed better survival rates after intravascular cooling even if not statistically significant. Clinically, using either cooling method is acceptable.

DISCUSSION

This review found no difference between intravascular and surface cooling and effects on survival and neurological outcome. More research needs to be performed on the best type of cooling method as well as the best product within each category.

Therapeutic hypothermia and pressure ulcer risk in critically ill intensive care patients: A retrospective study

OBJECTIVE

To examine the role of therapeutic hypothermia in pressure ulcer development in critically ill patients.

RESEARCH METHODOLOGY

Retrospective study in a mixed intensive care unit over 2010-2013. The incidences of pressure ulcers among patients treated with therapeutic hypothermia (n = 148) and the non-hypothermia patient population (n = 6197) were compared.

RESULTS

Patients treated with hypothermia developed more pressure ulcers (25.0%) than the non-hypothermia group 6.3% (p < 0.001). More patients in the hypothermia group were rated as the high pressure ulcer risk group, as defined by the modified Jackson/Cubbin (mJ/C) risk score ≤29 than the rest of the patients. Among the therapeutic hypothermia patients more pressure ulcers tended to emerge in the lower risk group (mJ/C score ≥30) (p = 0.056). Intensive care mortality was higher in the hypothermia (24.3%) than the non-hypothermia group (9.3%, p < 0.0001).

CONCLUSION

Patients treated with therapeutic hypothermia should be considered at high risk for pressure ulcer development and should be managed accordingly. The hypothermia may not as such increase the risk for pressure ulcers, but combined with the severity of the underlying illness, may be more likely. The pressure ulcer risk in this patient group cannot be reliably assessed by the Jackson/Cubbin risk scale.

An observational study of surface versus endovascular cooling techniques in cardiac arrest patients: a propensity-matched analysis

INTRODUCTION

Various methods and devices have been described for cooling after cardiac arrest, but the ideal cooling method remains unclear. The aim of this study was to compare the neurological outcomes, efficacies and adverse events of surface and endovascular cooling techniques in cardiac arrest patients.

METHODS

We performed a multicenter, retrospective, registry-based study of adult cardiac arrest patients treated with therapeutic hypothermia presenting to 24 hospitals across South Korea from 2007 to 2012. We included patients who received therapeutic hypothermia using overall surface or endovascular cooling devices and compared the neurological outcomes, efficacies and adverse events of both cooling techniques. To adjust for differences in the baseline characteristics of each cooling method, we performed one-to-one matching by the propensity score.

RESULTS

In total, 803 patients were included in the analysis. Of these patients, 559 underwent surface cooling, and the remaining 244 patients underwent endovascular cooling. In the unmatched cohort, a greater number of adverse events occurred in the surface cooling group. Surface cooling was significantly associated with a poor neurological outcome (cerebral performance category 3-5) at hospital discharge (p = 0.01). After propensity score matching, surface cooling was not associated with poor neurological outcome and hospital mortality [odds ratio (OR): 1.26, 95% confidence interval (CI): 0.81-1.96, p = 0.31 and OR: 0.85, 95% CI: 0.55-1.30, p = 0.44, respectively]. Although surface cooling was associated with an increased incidence of adverse events (such as overcooling, rebound hyperthermia, rewarming related hypoglycemia and hypotension) compared with endovascular cooling, these complications were not associated with surface cooling using hydrogel pads.

CONCLUSIONS

In the overall matched cohort, no significant difference in neurological outcomes and hospital morality was observed between the surface and endovascular cooling methods.

Evolution of insulin sensitivity and its variability in out-of-hospital cardiac arrest (OHCA) patients treated with hypothermia

INTRODUCTION

Therapeutic hypothermia (TH) is often used to treat out-of-hospital cardiac arrest (OHCA) patients who also often simultaneously receive insulin for stress-induced hyperglycaemia. However, the impact of TH on systemic metabolism and insulin resistance in critical illness is unknown. This study analyses the impact of TH on metabolism, including the evolution of insulin sensitivity (SI) and its variability, in patients with coma after OHCA.

METHODS

This study uses a clinically validated, model-based measure of SI. Insulin sensitivity was identified hourly using retrospective data from 200 post-cardiac arrest patients (8,522 hours) treated with TH, shortly after admission to the intensive care unit (ICU). Blood glucose and body temperature readings were taken every one to two hours. Data were divided into three periods: 1) cool (T <35°C); 2) an idle period of two hours as normothermia was re-established; and 3) warm (T >37°C). A maximum of 24 hours each for the cool and warm periods was considered. The impact of each condition on SI is analysed per cohort and per patient for both level and hour-to-hour variability, between periods and in six-hour blocks.

RESULTS

Cohort and per-patient median SI levels increase consistently by 35% to 70% and 26% to 59% (P <0.001) respectively from cool to warm. Conversely, cohort and per-patient SI variability decreased by 11.1% to 33.6% (P <0.001) for the first 12 hours of treatment. However, SI variability increases between the 18th and 30th hours over the cool to warm transition, before continuing to decrease afterward.

CONCLUSIONS

OCHA patients treated with TH have significantly lower and more variable SI during the cool period, compared to the later warm period. As treatment continues, SI level rises, and variability decreases consistently except for a large, significant increase during the cool to warm transition. These results demonstrate increased resistance to insulin during mild induced hypothermia. Our study might have important implications for glycaemic control during targeted temperature management.

Electroacoustic stimulation: now and into the future

Cochlear implants have provided hearing to hundreds of thousands of profoundly deaf people around the world. Recently, the eligibility criteria for cochlear implantation have been relaxed to include individuals who have some useful residual hearing. These recipients receive inputs from both electric and acoustic stimulation (EAS). Implant recipients who can combine these hearing modalities demonstrate pronounced benefit in speech perception, listening in background noise, and music appreciation over implant recipients that rely on electrical stimulation alone. The mechanisms bestowing this benefit are unknown, but it is likely that interaction of the electric and acoustic signals in the auditory pathway plays a role. Protection of residual hearing both during and following cochlear implantation is critical for EAS. A number of surgical refinements have been implemented to protect residual hearing, and the development of hearing-protective drug and gene therapies is promising for EAS recipients. This review outlines the current field of EAS, with a focus on interactions that are observed between these modalities in animal models. It also outlines current trends in EAS surgery and gives an overview of the drug and gene therapies that are clinically translatable and may one day provide protection of residual hearing for cochlear implant recipients.

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.

Successful treatment of a young woman with acute complicated myocardial infarction

Therapeutic hypothermia is method used to improve the neurological status of patients who are at risk of ischaemia after myocardial infarction. We report a case of a 28-year-old woman who suffered acute myocardial infarction complicated by ventricular fibrillation. The patient was successfully resuscitated. Invasive and non-invasive medical treatment was applied including therapeutic hypothermia. Success was achieved due to adequate public reaction, fast transportation, blood vessel revascularization and application of therapeutic hypothermia. The patient was successfully discharged after one week of treatment, and just minor changes in heart function were present.

State-of-the-art paper: Therapeutic hypothermia in out of hospital cardiac arrest survivors

Out of hospital cardiac arrest (OHCA) is associated with an extremely poor survival rate, with mortality in most cases being related to neurological injury. Among patients who experience return of spontaneous circulation (ROSC), therapeutic hypothermia (TH) is the only proven intervention shown to reduce mortality and improve neurological outcome. First described in 1958, the field of TH has rapidly evolved in recent years. While recent technological advances in TH will likely improve outcomes in OHCA survivors, several fundamental questions remain to be answered including the optimal speed of cooling, which patients benefit from an early invasive strategy, and whether technological advances will facilitate application of TH in the field. An increased awareness and understanding of TH strategies, devices, monitoring, techniques, and complications will allow for a more widespread adoption of this important treatment modality.

An activation-specific platelet inhibitor that can be turned on/off by medically used hypothermia

OBJECTIVE

Therapeutic hypothermia is successfully used, for example, in cardiac surgery to protect organs from ischemia. Cardiosurgical procedures, especially in combination with extracorporeal circulation, and hypothermia itself are potentially prothrombotic. Despite the obvious need, the long half-life of antiplatelet drugs and thus the risk of postoperative bleedings have restricted their use in cardiac surgery. We describe here the design and testing of a unique recombinant hypothermia-controlled antiplatelet fusion protein with the aim of providing increased safety of hypothermia, as well as cardiac surgery.

METHODS AND RESULTS

An elastin-mimetic polypeptide was fused to an activation-specific glycoprotein (GP) IIb/IIIa-blocking single-chain antibody. In silico modeling illustrated the sterical hindrance of a β-spiral conformation of elastin-mimetic polypeptide preventing the single-chain antibody from inhibiting GPIIb/IIIa at 37°C. Circular dichroism spectra demonstrated reverse temperature transition, and flow cytometry showed binding to and blocking of GPIIb/IIIa at hypothermic body temperature (≤32°C) but not at normal body temperature. In vivo thrombosis in mice was selectively inhibited at hypothermia but not at 37°C.

CONCLUSIONS

This is the first description of a broadly applicable pharmacological strategy by which the activity of a potential drug can be controlled by temperature. In particular, this drug steerability may provide substantial benefits for antiplatelet therapy.