The effect of mild therapeutic hypothermia on renal function after cardiopulmonary resuscitation in men

The hypokalaemia that came from the cold

While electrolyte disorders are common in nephrologists' clinical practice, hypothermia is a condition that nephrologists rarely encounter. Hypothermia can induce several pathophysiological effects on the human body, including hypokalaemia, which is reversible with rewarming. Despite growing evidence from animal research and human studies, the underlying mechanisms of hypothermia-induced hypokalaemia remain unclear. Boubes and colleagues recently presented a case series of hypokalaemia during hypothermia and rewarming, proposing a novel hypothesis for the underlying mechanisms. In this editorial, we review the current knowledge about hypothermia and associated electrolyte changes with insights into the effects of hypothermia on renal physiology.

Changes of antioxidant enzymes in the kidney after cardiac arrest in the rat model

Globally, cardiac arrest (CA) is a leading cause of death and disability. Asphyxial CA (ACA)-induced kidney damage is a crucial factor in reducing the survival rate. The purpose of this study was to investigate the role of antioxidant enzymes in histopathological renal damage in an ACA rat model at different time points. A total of 88 rats were divided into five groups and exposed to ACA except for the sham group. To evaluate glomerular function and oxidative stress, serum levels of blood urea nitrogen (BUN) and creatinine (Crtn) and malondialdehyde (MDA) levels in renal tissues were measured. To determine histopathological damage, hematoxylin and eosin staining, periodic acid-Schiff staining, and Masson's trichrome staining were performed. Expression levels of antioxidant enzymes including superoxide dismutase-1 (SOD-1), superoxide dismutase-2 (SOD-2), catalase (CAT), and glutathione peroxidase (GPx) were measured by immunohistochemistry (IHC). Survival rate of the experimental rats was reduced to 80% at 6 h, 55% at 12 h, 42.9% at 1 day, and 33% at 2 days after return of spontaneous circulation. Levels of BUN, Crtn, and MDA started to increase significantly in the early period of CA induction. Renal histopathological damage increased markedly from 6 h until two days post-CA. Additionally, expression levels of antioxidant enzymes were significantly decreased at 6 h, 12 h, 1 day, and 2 days after CA. CA-induced oxidative stress and decreased levels of antioxidant enzymes (SOD-1, SOD-2, CAT, GPx) from 6 h to two days could be possible mediators of severe renal tissue damage and increased mortality rate.

Kinetics of 2 different high-sensitive troponins during targeted temperature management in out-of-hospital cardiac arrest patients with acute myocardial infarction: a post hoc sub-study of a randomised clinical trial

Introduction

Short term hypothermia has been suggested to have cardio protective properties in acute myocardial infarction (AMI) by reducing infarct size as assessed by troponins. There are limited data on the kinetics of these biomarkers in comatose out-of-hospital cardiac arrest (OHCA) patients, with and without AMI, undergoing targeted temperature management (TTM) in the ICU.

Purpose

The aim of this post hoc analyses was to evaluate and compare the kinetics of two high-sensitivity cardiac troponins in OHCA survivors, with and without acute myocardial infarction (AMI), during TTM of different durations [24 h (standard) vs. 48 h (prolonged)].

Methods

In a sub-cohort (n = 114) of the international, multicentre, randomized controlled study “TTH48” we measured high-sensitive troponin T (hs-cTnT), high-sensitive troponin I (hs-cTnI) and CK-MB at the following time points: Arrival, 24 h, 48 h and 72 h from reaching the target temperature range of 33 ± 1 °C. All patients diagnosed with an AMI at the immediate coronary angiogram (CAG)—18 in the 24-h group and 25 in the 48-h group—underwent PCI with stent implantation. There were no stent thromboses.

Results

Both the hs-cTnT and hs-cTnI changes over time were highly influenced by the cause of OHCA (AMI vs. non-AMI). In contrast to non-AMI patients, both troponins remained elevated at 72 h in AMI patients. There was no difference between the two time-differentiated TTM groups in the kinetics for the two troponins.

Conclusion

In comatose OHCA survivors with an aetiology of AMI levels of both hs-cTnI and hs-cTnT remained elevated for 72 h, which is in contrast to the well-described kinetic profile of troponins in normotherm AMI patients. There was no difference in kinetic profile between the two high sensitive assays. Different duration of TTM did not influence the kinetics of the troponins.

Trial registration: Clinicaltrials.gov Identifier: NCT01689077, 20/09/2012.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-022-02778-4.

Experimental models of acute kidney injury for translational research

Preclinical models of human disease provide powerful tools for therapeutic discovery but have limitations. This problem is especially apparent in the field of acute kidney injury (AKI), in which clinical trial failures have been attributed to inaccurate modelling performed largely in rodents. Multidisciplinary efforts such as the Kidney Precision Medicine Project are now starting to identify molecular subtypes of human AKI. In addition, over the past decade, there have been developments in human pluripotent stem cell-derived kidney organoids as well as zebrafish, rodent and large animal models of AKI. These organoid and AKI models are being deployed at different stages of preclinical therapeutic development. However, the traditionally siloed, preclinical investigator-driven approaches that have been used to evaluate AKI therapeutics to date rarely account for the limitations of the model systems used and have given rise to false expectations of clinical efficacy in patients with different AKI pathophysiologies. To address this problem, there is a need to develop more flexible and integrated approaches, involving teams of investigators with expertise in a range of different model systems, working closely with clinical investigators, to develop robust preclinical evidence to support more focused interventions in patients with AKI.

Effect of therapeutic hypothermia against renal injury in a rat model of asphyxial cardiac arrest: Α focus on the survival rate, pathophysiology and antioxidant enzymes

Although multi-organ dysfunction is associated with the survival rate following cardiac arrest (CA), the majority of studies to date have focused on hearts and brains, and few studies have considered renal failure. The objective of the present study, therefore, was to examine the effects of therapeutic hypothermia on the survival rate, pathophysiology and antioxidant enzymes in rat kidneys following asphyxial CA. Rats were sacrificed one day following CA. The survival rate, which was estimated using Kaplan-Meier analysis, was 42.9% one day following CA. However, hypothermia, which was induced following CA, significantly increased the survival rate (71.4%). In normothermia rats with CA, the serum blood urea nitrogen level was significantly increased one day post-CA. In addition, the serum creatinine level was significantly increased one day post-CA. However, in CA rats exposed to hypothermia, the levels of urea nitrogen and creatinine significantly decreased following CA. Histochemical staining revealed a significant temporal increase in renal injury after the normothermia group was subjected to CA. However, renal injury was significantly decreased in the hypothermia group. Immunohistochemical analysis of the kidney revealed a significant decrease in antioxidant enzymes (copper-zinc superoxide dismutase, manganese superoxide dismutase, glutathione peroxidase and catalase) with time in the normothermia group. However, in the hypothermia group, these enzymes were significantly elevated following CA. Collectively, the results revealed that renal dysfunction following asphyxial CA was strongly associated with the early survival rate and therapeutic hypothermia reduced renal injury via effective antioxidant mechanisms.

Fast hypothermia induced by extracorporeal circuit cooling alleviates renal and intestinal injury after cardiac arrest in swine

BACKGROUND

Continuous renal replacement therapy (CRRT) was currently demonstrated to be an effective way to induce fast hypothermia and had proective effects on cardiac dysfunction and brain damage after cardiac pulmonary resuscitation (CPR). In the present study, we aimed to investigate the influence of extracorporeal circuit cooling using CRRT on renal and intestinal damage after CPR based on a porcine model.

METHODS

32 pigs were subjected to ventricular fibrillation for 8 min, followed by CPR for 5 min before defibrillation. All were randomized to receive extracorporeal circuit cooling using CRRT (CRRT, n = 9), surface cooling (SC, n = 9), normothermia (NT, n = 9) or sham control (n = 5) at 5 min post resuscitation. Pigs in the CRRT group were cooled by 8-h CRRT cooling with the infusion line initially submerged in 4 °C of ice water and 16-h SC, while in the SC group by a 24-h SC. Temperatures were maintained at a normal range in the other two groups. Biomarkers in serum were measured at baseline and 1, 3, 6, 12, 24 and 30 h post resuscitation to assess organ functions. Additionally, tissues of kidney and intestine were harvested, from which the degree of tissue inflammation, oxidative stress, and apoptosis levels were analyzed.

RESULTS

The blood temperature decreased faster by extracorporeal circuit cooling using CRRT than SC (9.8 ± 1.6 vs. 1.5 ± 0.4 °C/h, P < 0.01). Post-resuscitation renal and intestinal injury were significantly improved in the 2 hypothermic groups compared to the NT group. And the improvement was significantly greater in animals received extracorporeal circuit cooling than those received surface cooling, from both the results of biomarkers in serum and pathological evidence.

CONCLUSION

Fast hypothermia induced by extracorporeal circuit cooling was superior to. surface cooling in mitigating renal and intestinal injury post resuscitation.

Hyperoxia After Return of Spontaneous Circulation in Cardiac Arrest Patients

Current guidelines emphasize the use of 100% oxygen during cardiopulmonary resuscitation after cardiac arrest. When patients are ventilated for variable periods after return of spontaneous circulation (ROSC), hyperoxia causes increased morbidity and mortality by overproduction of reactive oxygen species. Various patient, volunteer, and animal studies have shown the harmful effects of hyperoxia. This mini-review article aims to expand the potential clinical spectrum of hyperoxia on individual organ systems leading to organ dysfunction. A framework to achieve and maintain normoxia after ROSC is proposed. Despite the harmful considerations of hyperoxia in critically ill patients, additional safety studies including dose-effect, level and onset of the reactive oxygen species effect, and safe hyperoxia applicability period after ROSC, need to be performed in various animal and human models to further elucidate the role of oxygen therapy after cardiac arrest.

Renal replacement therapy is independently associated with a lower risk of death in patients with severe acute kidney injury treated with targeted temperature management after out-of-hospital cardiac arrest

BACKGROUND

The effect of renal replacement therapy (RRT) on the outcomes of severe acute kidney injury (AKI) after out-of-hospital cardiac arrest (OHCA) is uncertain. This study aimed to evaluate the association of RRT with 6-month mortality in patients with severe AKI treated with targeted temperature management (TTM) after OHCA.

METHODS

This was a retrospective analysis of a prospectively collected multicentre observational cohort study that included adult OHCA patients treated with TTM across 22 hospitals in South Korea between October 2015 and December 2018. AKI was diagnosed using the Kidney Disease: Improving Global Outcomes criteria. The primary outcome was 6-month mortality and the secondary outcome was cerebral performance category (CPC) at 6 months. Multivariate Cox regression analysis was performed to define the role of RRT in stage 3 AKI.

RESULTS

Among 10,426 patients with OHCA, 1373 were treated with TTM. After excluding those who died within 48 h of return of spontaneous circulation (ROSC) and those with pre-arrest chronic kidney disease, our study cohort comprised 1063 patients. AKI developed in 590 (55.5%) patients and 223 (21.0%) had stage 3 AKI. Among them, 115 (51.6%) were treated with RRT. The most common treatment modality among RRT patients was continuous renal replacement therapy (111 [96.5%]), followed by intermittent haemodialysis (4 [3.5%]). The distributions of CPC (1-5) at 6 months for the non-RRT vs. the RRT group were 3/108 (2.8%) vs. 12/115 (10.4%) for CPC 1, 0/108 (0.0%) vs. 1/115 (0.9%) for CPC 2, 1/108 (0.9%) vs. 3/115 (2.6%) for CPC 3, 6/108 (5.6%) vs. 6/115 (5.2%) for CPC 4, and 98/108 (90.7%) vs. 93/115 (80.9%) for CPC 5, respectively (P = 0.01). The RRT group had significantly lower 6-month mortality than the non-RRT group (93/115 [81%] vs. 98/108 [91%], P = 0.04). Multivariate Cox regression analyses showed that RRT was independently associated with a lower risk of death in patients with stage 3 AKI (hazard ratio, 0.569 [95% confidence interval, 0.377-0.857, P = 0.01]).

CONCLUSION

Dialysis interventions were independently associated with a lower risk of death in patients with stage 3 AKI treated with TTM after OHCA.

Renal function after out-of-hospital cardiac arrest; the influence of temperature management and coronary angiography, a post hoc study of the target temperature management trial

Background

To elucidate the incidence of acute kidney injury (AKI) after out-of-hospital cardiac arrest (OHCA) and to examine the impact of target temperature management (TTM) and early coronary angiography on renal function.

Methods

Post hoc analysis of the TTM trial, a multinational randomised controlled trial comparing target temperature of 33 °C versus 36 °C in patients with return of spontaneous circulation after OHCA. The impact of TTM and early angiography (within 6 h of OHCA) versus late or no angiography on the development of AKI during the 7-day period after OHCA was analysed. AKI was defined according to modified KDIGO criteria in patients surviving beyond day 2 after OHCA.

Results

Following exclusions, 853 of 939 patients enrolled in the main trial were analysed. Unadjusted analysis showed that significantly more patients in the 33 °C group had AKI compared to the 36 °C group [211/431 (49%) versus 170/422 (40%) p = 0.01], with a worse severity (p = 0.018). After multivariable adjustment, the difference was not significant (odds ratio 0.75, 95% confidence interval 0.54–1.06, p = 0.10].

Five hundred seventeen patients underwent early coronary angiography. Although the unadjusted analysis showed less AKI and less severe AKI in patients who underwent early angiography compared to patients with late or no angiography, in adjusted analyses, early angiography was not an independent risk factor for AKI (odds ratio 0.73, 95% confidence interval 0.50–1.05, p = 0.09).

Conclusions

In OHCA survivors, TTM at 33 °C compared to management at 36 °C did not show different rates of AKI and early angiography was not associated with an increased risk of AKI.

Trial registration

NCT01020916. Registered on www.ClinicalTrials.gov 26 November 2009 (main trial).

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2390-0) contains supplementary material, which is available to authorized users.

Early withdrawal of life support after resuscitation from cardiac arrest is common and may result in additional deaths

AIM

"Early" withdrawal of life support therapies (eWLST) within the first 3 calendar days after resuscitation from cardiac arrest (CA) is discouraged. We evaluated a prospective multicenter registry of patients admitted to hospitals after resuscitation from CA to determine predictors of eWLST and estimate its impact on outcomes.

METHODS

CA survivors enrolled from 2012-2017 in the International Cardiac Arrest Registry (INTCAR) were included. We developed a propensity score for eWLST and matched a cohort with similar probabilities of eWLST who received ongoing care. The incidence of good outcome (Cerebral Performance Category of 1 or 2) was measured across deciles of eWLST in the matched cohort.

RESULTS

2688 patients from 24 hospitals were included. Median ischemic time was 20 (IQR 11, 30) minutes, and 1148 (43%) had an initial shockable rhythm. Withdrawal of life support occurred in 1162 (43%) cases, with 459 (17%) classified as eWLST. Older age, initial non-shockable rhythm, increased ischemic time, shock on admission, out-of-hospital arrest, and admission in the United States were each independently associated with eWLST. All patients with eWLST died, while the matched cohort, good outcome occurred in 21% of patients. 19% of patients within the eWLST group were predicted to have a good outcome, had eWLST not occurred.

CONCLUSIONS

Early withdrawal of life support occurs frequently after cardiac arrest. Although the mortality of patients matched to those with eWLST was high, these data showed excess mortality with eWLST.

Erythropoietin in traumatic brain injury associated acute kidney injury: A randomized controlled trial

BACKGROUND

Acute kidney injury (AKI) in traumatic brain injury (TBI) is poorly understood and it is unknown if it can be attenuated using erythropoietin (EPO).

METHODS

Pre-planned analysis of patients included in the EPO-TBI (ClinicalTrials.gov NCT00987454) trial who were randomized to weekly EPO (40 000 units) or placebo (0.9% sodium chloride) subcutaneously up to three doses or until intensive care unit (ICU) discharge. Creatinine levels and urinary output (up to 7 days) were categorized according to the Kidney Disease Improving Global Outcome (KDIGO) classification. Severity of TBI was categorized with the International Mission for Prognosis and Analysis of Clinical Trials in TBI.

RESULTS

Of 3348 screened patients, 606 were randomized and 603 were analyzed. Of these, 82 (14%) patients developed AKI according to KDIGO (60 [10%] with KDIGO 1, 11 [2%] patients with KDIGO 2, and 11 [2%] patients with KDIGO 3). Male gender (hazard ratio [HR] 4.0 95% confidence interval [CI] 1.4-11.2, P = 0.008) and severity of TBI (HR 1.3 95% CI 1.1-1.4, P < 0.001 for each 10% increase in risk of poor 6 month outcome) predicted time to AKI. KDIGO stage 1 (HR 8.8 95% CI 4.5-17, P < 0.001), KDIGO stage 2 (HR 13.2 95% CI 3.9-45.2, P < 0.001) and KDIGO stage 3 (HR 11.7 95% CI 3.5-39.7, P < 0.005) predicted time to mortality. EPO did not influence time to AKI (HR 1.08 95% CI 0.7-1.67, P = 0.73) or creatinine levels during ICU stay (P = 0.09).

CONCLUSIONS

Acute kidney injury is more common in male patients and those with severe compared to moderate TBI and appears associated with worse outcome. EPO does not prevent AKI after TBI.

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.

Targeted Temperature Management in Brain Injured Patients

Evidence from animal models indicates that lowering temperature by a few degrees can produce substantial neuroprotection. In humans, hypothermia has been found to be neuroprotective with a significant impact on mortality and long-term functional outcome only in cardiac arrest and neonatal hypoxic-ischemic encephalopathy. Clinical trials have explored the potential role of maintaining normothermia and treating fever in critically ill brain injured patients. This review concentrates on basic concepts to understand the physiologic interactions of thermoregulation, effects of thermal modulation in critically ill patients, proposed mechanisms of action of temperature modulation, and practical aspects of targeted temperature management.

Targeted Temperature Management in Brain Injured Patients

Evidence from animal models indicates that lowering temperature by a few degrees can produce substantial neuroprotection. In humans, hypothermia has been found to be neuroprotective with a significant impact on mortality and long-term functional outcome only in cardiac arrest and neonatal hypoxic-ischemic encephalopathy. Clinical trials have explored the potential role of maintaining normothermia and treating fever in critically ill brain injured patients. This review concentrates on basic concepts to understand the physiologic interactions of thermoregulation, effects of thermal modulation in critically ill patients, proposed mechanisms of action of temperature modulation, and practical aspects of targeted temperature management.

Acute kidney injury and mild therapeutic hypothermia in patients after cardiopulmonary resuscitation - a post hoc analysis of a prospective observational trial

Background

The aim of this study was to investigate the influence of mild therapeutic hypothermia (MTH) on the incidence of and recovery from acute kidney injury (AKI).

Methods

Patients who had undergone successful cardiopulmonary resuscitation (CPR) were included. Serum creatinine and cystatin C were measured at baseline, daily up to 5 days and at ICU discharge. AKI was defined by the Kidney Disease Improving Global Outcomes (KDIGO) criteria. MTH was applied for 24 h targeting a temperature of 33 °C. Neurological outcome was assessed with the Cerebral Performance Categories score at hospital discharge.

Results

126 patients were included in the study; 73 patients (58%) developed AKI. Patients treated with MTH had a significantly lower incidence of AKI as compared to normothermia (NT) (44 vs. 69%; p = 0.004). Patients with less favourable neurological outcomes had a significantly higher rate of AKI, although when treated with MTH the occurrence of AKI was reduced (50 vs. 80%; p = 0.017). Furthermore, MTH treatment was accompanied by significantly lower creatinine levels on day 0–1 and at ICU discharge (day 0: 1.12 (0.90–1.29) vs. 1.29 (1.00–1.52) mg/dl; p = 0.016) and lower cystatin C levels on day 0–3 and at ICU discharge (day 0: 0.88 (0.77–1.10) vs. 1.29 (1.06–2.16) mg/l; p < 0.001).

Conclusions

Mild therapeutic hypothermia seems to have a protective effect against the development of AKI and on renal recovery. This may be less pronounced in patients with a favourable neurological outcome.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2061-6) contains supplementary material, which is available to authorized users.

Clinical Experience of Therapeutic Hypothermia in Cases of Near-Hanging and Recovered from Cardiac Arrest Due to Hanging

Objective

There is no specific treatment for comatose patients after near-hanging or in those who recover from cardiac arrest (CA) caused by hanging. Since 2009, we have used therapeutic hypothermia (TH) to treat all comatose survivors of near-hanging and in patients who recovered from CA caused by hanging. The purpose of this study was to describe the outcomes in comatose patients after near-hanging.

Design

Case series.

Setting

Emergency departments of two regional hospitals.

Methods

We collected patient data from the Samsung Medical Center hypothermia database between November 2009 and November 2011. We included all patients presented with near-hanging or CA caused by hanging; who remained comatose and received TH after resuscitation for analysis. Clinical characteristics and outcome of patients were presented. Results During the study period, 26 patients were admitted to the emergency department after near-hanging or CA caused by hanging; 21 patients were enrolled in this study. Twelve patients with CA and 9 comatose patients without CA were treated with TH. Only 1 patient with CA had a good neurological outcome. By contrast, all near-hanging patients without CA had a good neurological outcome.

Conclusions

TH can be an effective therapeutic modality in cases of near-hanging without CA. However, the effectiveness of TH is questionable in patients who survive from CA caused by hanging. (Hong Kong j.emerg.med. 2014;21:316-321)

Effect of mild hypothermia on renal ischemia/reperfusion injury after cardiopulmonary resuscitation in a swine model

Purpose:

To investigate the effect of intravascular cooling on renal function after resuscitation.

Methods:

Twenty four pigs were randomized into three groups (n=8 in each group): therapeutic hypothermia group (TH group), normothermia group (NH group) and sham operation group (SHAM group). After 6 minutes of untreated VF, CPR was performed. Upon ROSC, the TH group received the intravascular cooling. The NH and SHAM group did not undergo therapeutic hypothermia. Haemodynamic parameters were recorded. The bloods were analyzed for serum creatinine (sCr), CysC and NGAL. The kidney was surgically removed observe pathologic changes under a light microscope.

Results:

The sCr increased in both TH and NH groups after ROSC, compared to baseline. Between two groups, the sCr and creatinine clearance (Cc) showed lower level in the TH group. The urine volume per hour in the TH group were higher during cooling. After resuscitation, NGAL and CysC in the NH group were higher than in the TH group. Under the light microscope, compared with the TH group, the renal injury was prominent in the NH group.

Conclusion:

Mild hypothermia had a protection to renal ischemia reperfusion injury after resuscitation.

A Population Pharmacokinetic Analysis to Study the Effect of Therapeutic Hypothermia on Vancomycin Disposition in Children Resuscitated From Cardiac Arrest

OBJECTIVES

Limited data exist on the effects of therapeutic hypothermia on renal function and pharmacokinetics in pediatric patients after cardiac arrest. The objective was to describe the differences in vancomycin disposition in pediatric patients following cardiac arrest treated with either therapeutic hypothermia or normothermia using population pharmacokinetic modeling.

DESIGN

Single-center, retrospective cohort study.

SETTING

A tertiary care hospital pediatric and cardiac ICU.

PATIENTS

Fifty-two pediatric patients (30 d to 17 yr old) who experienced a cardiac arrest, received vancomycin, and were treated with therapeutic hypothermia (32-34°C) or normothermia (36.3-37.6°C) between January 1, 2010, and September 30, 2014, were reviewed.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A two-compartment model with linear elimination, weight effects on clearance, intercompartmental clearance (Q), central volume of distribution (V1), and peripheral volume of distribution (V2) adequately described the data despite high variability due to the small sample size. The typical value of clearance in this study was 4.48 L/hr (0.19 L/hr/kg) for a normothermic patient weighing 70 kg and a glomerular filtration rate of 90 mL/min/1.73 m. Patients treated with normothermia but with reduced or poor renal function (≤ 90 mL/min/1.73 m) had up to an 80% reduction in vancomycin clearance compared to those with normal renal function (90-140 mL/min/1.73 m). Patients with normal renal function but treated with therapeutic hypothermia versus normothermia experienced up to 25% reduction in vancomycin clearance. Patients treated with therapeutic hypothermia and with poor renal function experienced up to an 84% reduction in vancomycin clearance.

CONCLUSIONS

Patients receiving hypothermia and/or with decreased renal function had lower vancomycin clearances based on a retrospectively fitted two-compartment model in children who experience cardiac arrest.

The Extent of Myocardial Injury During Prolonged Targeted Temperature Management After Out-of-Hospital Cardiac Arrest

AIM

The aim of this study is to evaluate the extent of myocardial injury by cardiac biomarkers during prolonged targeted temperature management of 24 hours vs 48 hours after out-of-hospital cardiac arrest.

METHODS

This randomized Scandinavian multicenter study compares the extent of myocardial injury quantified by area under the curve (AUC) of cardiac biomarkers during prolonged targeted temperature management at 33°C ± 1°C of 24 hours and 48 hours, respectively. Through a period of 2.5 years, 161 comatose out-of-hospital cardiac arrest patients were randomized to targeted temperature management for 24 hours (n = 77) or 48 hours (n = 84). The AUC was calculated using both high-sensitivity cardiac troponin T (hs-cTnT_AUC) and creatine kinase-myocardial band (CK-MB_AUC) that were based upon measurements of these biomarkers every 6 hours upon admission until 96 hours after reaching target temperature.

RESULTS

The median hs-cTnT_AUC of 33,827 ng/L/h (interquartile range [IQR] 11,366-117,690) of targeted temperature management at 24 hours did not differ significantly from that of 28,973 ng/L/h (IQR 10,656-163,655) at 48 hours. In contrast, the median CK-MB_AUC of 1829 μg/L/h (IQR 800-6799) during targeted temperature management at 24 hours was significantly lower than that of 2428 μg/L/h (IQR 1163-10,906) within targeted temperature management at 48 hours, P <.05.

CONCLUSION

This study of comatose out-of-hospital cardiac arrest survivors showed no difference between the extents of myocardial injury estimated by hs-cTnT_AUC of prolonged targeted temperature management of 48 hours vs 24 hours, although the CK-MB_AUC was significantly higher during 48 hours vs 24 hours. Hence, it seems unlikely that the duration of targeted temperature management has a beneficial effect on the extent of myocardial injury after out-of-hospital cardiac arrest, and may even have a worsening effect.

Analgesia, sedation, and neuromuscular blockade during targeted temperature management after cardiac arrest

The approach to sedation, analgesia, and neuromuscular blockade during targeted temperature management (TTM) remains largely unstudied, forcing clinicians to adapt previous research from other patient environments. During TTM, very little data guide drug selection, doses, and specific therapeutic goals. Sedation should be deep enough to prevent awareness during neuromuscular blockade, but titration is complex as metabolism and clearance are delayed for almost all drugs during hypothermia. Deeper sedation is associated with prolonged intensive care unit (ICU) and ventilator therapy, increased delirium and infection, and delayed wakening which can confound early critical neurological assessments, potentially resulting in erroneous prognostication and inappropriate withdrawal of life support. We review the potential therapeutic goals for sedation, analgesia, and neuromuscular blockade during TTM; the adverse events associated with that treatment; data suggesting that TTM and organ dysfunction impair drug metabolism; and controversies and potential benefits of specific monitoring. We also highlight the areas needing better research to guide our therapy.

Vancomycin pharmacokinetic parameters in patients with acute brain injury undergoing controlled normothermia, therapeutic hypothermia, or pentobarbital infusion

BACKGROUND

Therapeutic strategies that cause an alteration in patient temperature, such as controlled normothermia (CN), therapeutic hypothermia (TH), and pentobarbital infusion (PI), are often used to manage complications caused by acute brain injury. The purpose of this study was to evaluate pharmacokinetic (PK) parameters of vancomycin in patients with acute brain injury undergoing temperature modulation.

METHODS

This was a retrospective cohort study of adult patients with acute brain injury admitted between May 2010 and March 2014 who underwent CN, TH, or PI and received vancomycin. Predicted PK parameters based on population data were compared with calculated PK parameters based on serum concentrations.

RESULTS

Seventeen CN patients and 10 TH/PI patients met inclusion criteria. Traumatic brain injury and aneurysmal subarachnoid hemorrhage accounted for the majority of admitting diagnoses. In the CN group, the median dose was 16.7 (15.5-18.4) mg/kg. The median calculated elimination rate constant [0.155 (0.108-0.17) vs. 0.103 (0.08-0.142) hr(-1); p = 0.04] was significantly higher than the predicted value. The median measured trough concentration [8.9 (7.7-11.1) vs. 17.1 (10.8-22.3) υg/mL; p = 0.004] was significantly lower than predicted. In the TH/PI group, the median dose was 15.4 (14.7-17.2) mg/kg. No significant differences were found between the median calculated and predicted elimination rate constant [0.107 (0.097-0.109) vs. 0.112 (0.102-0.127) hr(-1); p = 0.41] and median measured and predicted trough concentration [14.2 (12.7-17.1) vs. 13.1 (11-17.8) υg/mL; p = 0.71].

CONCLUSION

Patients who underwent TH/PI did not exhibit PK alterations when compared to predicted PK parameters based on population data, while patients who underwent CN experienced PK alterations favoring an increased elimination of vancomycin.

Acute kidney injury after cardiac arrest

Introduction

The aim of this study was to evaluate the incidence and determinants of AKI in a large cohort of cardiac arrest patients.

Methods

We reviewed all patients admitted, for at least 48 hours, to our Dept. of Intensive Care after CA between January 2008 and October 2012. AKI was defined as oligo-anuria (daily urine output <0.5 ml/kg/h) and/or an increase in serum creatinine (≥0.3 mg/dl from admission value within 48 hours or a 1.5 time from baseline level). Demographics, comorbidities, CA details, and ICU interventions were recorded. Neurological outcome was assessed at 3 months using the Cerebral Performance Category scale (CPC 1–2 = favorable outcome; 3–5 = poor outcome).

Results

A total of 199 patients were included, 85 (43%) of whom developed AKI during the ICU stay. Independent predictors of AKI development were older age, chronic renal disease, higher dose of epinephrine, in-hospital CA, presence of shock during the ICU stay, a low creatinine clearance (CrCl) on admission and a high cumulative fluid balance at 48 hours. Patients with AKI had higher hospital mortality (55/85 vs. 57/114, p = 0.04), but AKI was not an independent predictor of poor 3-month neurological outcome.

Conclusions

AKI occurred in more than 40% of patients after CA. These patients had more severe hemodynamic impairment and needed more aggressive ICU therapy; however the development of AKI did not influence neurological recovery.

Prolonged induced hypothermia in hemorrhagic shock is associated with decreased muscle metabolism: a nuclear magnetic resonance-based metabolomics study

Hemorrhagic shock is a leading cause of trauma-related death in war and is associated with significant alterations in metabolism. Using archived serum samples from a previous study, the purpose of this work was to identify metabolic changes associated with induced hypothermia in a porcine model of hemorrhagic shock. Twelve Yorkshire pigs underwent a standardized hemorrhagic shock and resuscitation protocol to simulate battlefield injury with prolonged evacuation to definitive care in cold environments. Animals were randomized to receive either hypothermic (33°C) or normothermic (39°C) limited resuscitation for 8 h, followed by standard resuscitation. Proton nuclear magnetic resonance spectroscopy was used to evaluate serum metabolites from these animals at intervals throughout the hypothermic resuscitation period. Animals in the hypothermic group had a significantly higher survival rate (P = 0.02) than normothermic animals. Using random forest analysis, a difference in metabolic response between hypothermic and normothermic animals was identified. Hypothermic resuscitation was characterized by decreased concentrations of several muscle-related metabolites including taurine, creatine, creatinine, and amino acids. This study suggests that a decrease in muscle metabolism as a result of induced hypothermia is associated with improved survival.

Kidney protection by hypothermic total liquid ventilation after cardiac arrest in rabbits

BACKGROUND

Total liquid ventilation (TLV) with perfluorocarbons has been shown to induce rapid protective cooling in animal models of myocardial ischemia and cardiac arrest, with improved neurological and cardiovascular outcomes after resuscitation. In this study, the authors hypothesized that hypothermic TLV can also limit kidney injury after cardiac arrest.

METHODS

Anesthetized rabbits were submitted to 15 min of untreated ventricular fibrillation. After resuscitation, three groups of eight rabbits each were studied such as (1) life support plus hypothermia (32°-33 °C) induced by cold TLV (TLV group), (2) life support without hypothermia (control group), and (3) Sham group (no cardiac arrest). Life support was continued for 6 h before euthanasia and kidney removal.

RESULTS

Time to target esophageal temperature was less than 5 min in the TLV group. Hypothermia was accompanied by preserved renal function in the TLV group as compared with control group regarding numerous markers including creatinine blood levels (12 ± 1 vs. 16 ± 2 mg/l, respectively; mean ± SEM), urinary N-acetyl-β-(D)-glucosaminidase (1.70 ± 0.11 vs. 3.07 ± 0.10 U/mol of creatinine), γ-glutamyltransferase (8.36 ± 0.29 vs. 12.96 ± 0.44 U/mol of creatinine), or β2-microglobulin (0.44 ± 0.01 vs. 1.12 ± 0.04 U/mol of creatinine). Kidney lesions evaluated by electron microscopy and conventional histology were also attenuated in TLV versus control groups. The renal-protective effect of TLV was not related to differences in delayed inflammatory or immune renal responses because transcriptions of, for example, interferon-γ, tumor necrosis factor-α, interleukin-1β, monocyte chemoattractant protein-1, toll-like receptor-2, toll-like receptor-4, and vascular endothelial growth factor were similarly altered in TLV and control versus Sham.

CONCLUSION

Ultrafast cooling with TLV is renal protective after cardiac arrest and resuscitation, which could increase kidney availability for organ donation.

Extracranial hypothermia during cardiac arrest and cardiopulmonary resuscitation is neuroprotective in vivo

There is increasing evidence that ischemic brain injury is modulated by peripheral signaling. Peripheral organ ischemia can induce brain inflammation and injury. We therefore hypothesized that brain injury sustained after cardiac arrest (CA) is influenced by peripheral organ ischemia and that peripheral organ protection can reduce brain injury after CA and cardiopulmonary resuscitation (CPR). Male C57Bl/6 mice were subjected to CA/CPR. Brain temperature was maintained at 37.5°C ± 0.0°C in all animals. Body temperature was maintained at 35.1°C ± 0.1°C (normothermia) or 28.8°C ± 1.5°C (extracranial hypothermia [ExHy]) during CA. Body temperature after resuscitation was maintained at 35°C in all animals. Behavioral testing was performed at 1, 3, 5, and 7 days after CA/CPR. Either 3 or 7 days after CA/CPR, blood was analyzed for serum urea nitrogen, creatinine, alanine aminotransferase, aspartate aminotransferase, and interleukin-1β; mice were euthanized; and brains were sectioned. CA/CPR caused peripheral organ and brain injury. ExHy animals experienced transient reduction in brain temperature after resuscitation (2.1°C ± 0.5°C for 4 minutes). Surprisingly, ExHy did not change peripheral organ damage. In contrast, hippocampal injury was reduced at 3 days after CA/CPR in ExHy animals (22.4% ± 6.2% vs. 45.7% ± 9.1%, p=0.04, n=15/group). This study has two main findings. Hypothermia limited to CA does not reduce peripheral organ injury. This unexpected finding suggests that after brief ischemia, such as during CA/CPR, signaling or events after reperfusion may be more injurious than those during the ischemic period. Second, peripheral organ hypothermia during CA reduces hippocampal injury independent of peripheral organ protection. While it is possible that this protection is due to subtle differences in brain temperature during early reperfusion, we speculate that additional mechanisms may be involved. Our findings add to the growing understanding of brain-body cross-talk by suggesting that peripheral interventions can protect the brain even if peripheral organ injury is not altered.

Urine Output Changes During Postcardiac Arrest Therapeutic Hypothermia

While commonly described, no studies have characterized cold-induced diuresis or rewarm anti-diuresis occurring during the delivery of therapeutic hypothermia (TH). We sought to determine urine output changes during the provision of postcardiac arrest TH. We analyzed clinical data on patients receiving postcardiac arrest TH at an urban tertiary care center. TH measures included cooling by cold intravenous fluid, external ice packs, and a commercial external temperature management system. TH treatment was divided into phases: (1) induction, (2) maintenance, (3) rewarm, and (4) post-rewarm. The primary outcome measure was the mean urine output rate (mL/hour). We compared urine output rates between TH phases using a Generalized Estimating Equations model, defining urine output rate (mL/hour) as the dependent variable and TH phase (induction, maintenance, rewarm, and post-rewarm) as the primary exposure variable. We adjusted for age, sex, initial ECG rhythm, location of arrest, shock, acute kidney injury, rate of intravenous fluid input, and body mass index. Complete urine output data were available on 33 patients. Mean urine output rates during induction, maintenance, rewarm, and post-rewarm phases were 157 mL/hour (95% CI: 104-210), 103 mL/hour (95% CI: 82-125), 70 mL/hour (95% CI: 51-88), and 91 mL/hour (95% CI: 65-117), respectively. Compared with the post-rewarm phase, adjusted urine output was higher during the TH induction phase (output rate difference +51 mL/hour; 95% CI: 3-99). Adjusted urine output during the maintenance and rewarm phases did not differ from the post-rewarm phase. In this preliminary study, we observed modest increases in urine output during TH induction. We did not observe urine output changes during TH maintenance or rewarming.

Hypothermia in neurocritical care

Hypothermia has long been recognized as an effective therapy for acute neurologic injury. Recent advances in bedside technology and greater understanding of thermoregulatory mechanisms have made this therapy readily available at the bedside. Critical care management of the hypothermic patient can be divided into 3 phases: induction, maintenance, and rewarming. Each phase has known complications that require careful monitoring. At present, hypothermia has only been shown to be an effective neuroprotective therapy in cardiac arrest survivors. The primary use of hypothermia in the neurocritical care unit is to treat increased intracranial pressure.

Renal dysfunction is common following resuscitation from out-of-hospital cardiac arrest

BACKGROUND

Cardiac arrest patients often suffer from dysfunction of multiple organ systems after return of spontaneous circulation (ROSC). The incidence of renal dysfunction in patients with out-of-hospital cardiac arrest (OHCA) is not well described. Renal dysfunction has been associated with worse outcomes in critical illness.

HYPOTHESIS

Renal dysfunction is common after OHCA, and renal dysfunction is independently associated with survival.

METHODS

We performed a retrospective review of consecutive adult patients admitted to an intensive care unit after successful resuscitation from OHCA between 01/01/2005 and 12/31/2010. Patients were excluded for death or withdrawal of care within 24h, preexisting end-stage renal disease, or OHCA due to hyperkalemia. The RIFLE criteria were used to classify subjects with renal dysfunction into one of three categories - risk, injury, or failure - based on trending of serum creatinine concentration or glomerular filtration rate. Data were analyzed using descriptive statistics.

RESULTS

Of 364 patients, 38 were excluded due to death or withdrawal of care within 24h, 11 due to end-stage renal disease, and 4 due to OHCA from hyperkalemia, leaving 311 patients in the final analysis. The mean age was 58 (SD 16) years; 174 (59%) were male, VF/VT was the primary rhythm in 156 (50%), and 236 (80%) were comatose at hospital arrival. Among 311 patients, 32 (10.3%) developed acute renal failure (ARF), 27 (8.7%) developed acute kidney injury (AKI), and 56 (18.0%) developed risk of renal dysfunction. Of the 32 subjects that developed ARF, renal replacement therapy (RRT) was initiated on 13 (40.6%). Development of ARF was not associated with survival (OR 0.73; 95% CI 0.26, 2.05) after adjusting for initial rhythm or illness severity.

CONCLUSIONS

More than one-third of patients resuscitated from OHCA developed evidence of renal dysfunction, and 19% of patients meeting criteria for AKI or ARF. In this study, development of renal failure was not independently associated with survival.

Hypothermia for acute brain injury--mechanisms and practical aspects

Hypothermia is widely accepted as the gold-standard method by which the body can protect the brain. Therapeutic cooling--or targeted temperature management (TTM)--is increasingly being used to prevent secondary brain injury in patients admitted to the emergency department and intensive care unit. Rapid cooling to 33 °C for 24 h is considered the standard of care for minimizing neurological injury after cardiac arrest, mild-to-moderate hypothermia (33-35 °C) can be used as an effective component of multimodal therapy for patients with elevated intracranial pressure, and advanced cooling technology can control fever in patients who have experienced trauma, haemorrhagic stroke, or other forms of severe brain injury. However, the practical application of therapeutic hypothermia is not trivial, and the treatment carries risks. Development of clinical management protocols that focus on detection and control of shivering and minimize the risk of other potential complications of TTM will be essential to maximize the benefits of this emerging therapeutic modality. This Review provides an overview of the potential neuroprotective mechanisms of hypothermia, practical considerations for the application of TTM, and disease-specific evidence for the use of this therapy in patients with acute brain injuries.

Therapeutic hypothermia and prevention of acute kidney injury: a meta-analysis of randomized controlled trials

BACKGROUND

Therapeutic hypothermia has been shown to reduce neurological morbidity and mortality in the setting of out-of-hospital cardiac arrest and may be beneficial following brain injury and cardiopulmonary bypass. We conducted a systematic review to ascertain the effect of therapeutic hypothermia on development of acute kidney injury (AKI) and mortality.

METHODS

We searched for randomized controlled trials in MEDLINE through February 2011. We included trials comparing hypothermia to normothermia that reported kidney-related outcomes including, development of AKI, dialysis requirement, changes in serum creatinine, and mortality. We performed Peto fixed-effect and random-effects model meta-analyses, and meta-regressions.

RESULTS

Nineteen trials reporting on 2218 patients were included; in the normothermia group, the weighted rate of AKI was 4.2%, dialysis requirement 3.7%, and mortality 10.8%. By meta-analysis, hypothermia was not associated with a lower odds of AKI (odds ratio [OR] 1.01, 95% confidence interval [CI] 0.68, 1.51; P=0.95) or dialysis requirement (OR 0.81; 95% CI 0.30, 2.19; P=0.68); however, by meta-regression, a lower target cooling temperature was associated with a lower odds of AKI (P=0.01). Hypothermia was associated with lower mortality (OR 0.69; 95% CI 0.51, 0.92; P=0.01).

CONCLUSIONS

In trials that ascertained kidney endpoints, therapeutic hypothermia prevented neither the development of AKI nor dialysis requirement, but was associated with lower mortality. Different definitions and rates of AKI, differences in mortality rates, and concerns about the optimal target cooling temperature preclude definitive conclusions.

Acute kidney injury after cardiac arrest

AIM

Cardiac arrest (CA) in humans causes warm renal ischemia-reperfusion injury, similar to animal models of ischemic acute kidney injury (AKI). We aimed to investigate the incidence and risk associations of AKI after CA, with or without post-resuscitation cardiogenic shock (PRCS).

METHODS

We examined the renal outcomes of adult patients admitted to the intensive care unit (ICU), who survived for more than 48 h following successful resuscitation after CA.

RESULTS

Of 105 patients (median age 65 years; 69% male), 58 (55.2%) had PRCS and were on vasoactive drugs beyond 24h; and 9 (8.6%) (all of whom had PRCS) received renal replacement therapy. Only 3 (6.4%) of 47 patients without PRCS had RIFLE-'I'/'F' AKI, compared to 30 (51.7%) of 58 patients with PRCS (p<0.001). Median peak serum creatinine in the non-PRCS group was 102 μmol/L (interquartile range 85-115), compared to 155 μmol/L (interquartile range 112-267) (p<0.001) in the PRCS group. On multivariate analysis, cumulative noradrenaline dose during the first 24h in ICU, PRCS, and pre-CA renin-angiotensin-aldosterone-system blockade were independently associated with RIFLE-'I'/'F' AKI; while higher serum lactate 12h after CA, baseline creatinine, and PRCS were independently associated with greater rise in creatinine from pre-CA levels. Estimated time without spontaneous circulation, total adrenaline dose and initial cardiac rhythm during CA, had no independent associations with renal outcomes.

CONCLUSIONS

In the absence of PRCS, CA in isolation is uncommonly associated with significant AKI. The human kidney may be more resistant to warm ischemia-reperfusion injury than previously thought.

Therapeutic hypothermia: benefits, mechanisms and potential clinical applications in neurological, cardiac and kidney injury

Therapeutic hypothermia involves the controlled reduction of core temperature to attenuate the secondary organ damage which occurs following a primary injury. Clinicians have been increasingly using therapeutic hypothermia to prevent or ameliorate various types of neurological injury and more recently for some forms of cardiac injury. In addition, some recent evidence suggests that therapeutic hypothermia may also provide benefit following acute kidney injury. In this review we will examine the potential mechanisms of action and current clinical evidence surrounding the use of therapeutic hypothermia. We will discuss the ideal methodological attributes of future studies using hypothermia to optimise outcomes following organ injury, in particular neurological injury. We will assess the importance of target hypothermic temperature, time to achieve target temperature, duration of cooling, and re-warming rate on outcomes following neurological injury to gain insights into important factors which may also influence the success of hypothermia in other organ injuries, such as the heart and the kidney. Finally, we will examine the potential of therapeutic hypothermia as a future kidney protective therapy.

A comparison of intravascular and surface cooling techniques in comatose cardiac arrest survivors

OBJECTIVES

Mild therapeutic hypothermia after out-of-hospital cardiac arrest is usually achieved either by surface cooling or by core cooling via the patient's bloodstream. We compared modern core (Coolgard) and surface (Arctic Sun) cooling devices with a zero hypothesis of equal cooling, complications, and neurologic outcomes.

DESIGN

Single-center observational study.

SETTING

University hospital medical and cardiac intensive care units.

PATIENTS

One hundred sixty-seven consecutive patients comatose after out-of-hospital cardiac arrest of all causes treated with mild therapeutic hypothermia in a 5-yr period.

INTERVENTIONS

Nonrandomized allocation to core or surface cooling depending on availability and physician preference.

MEASUREMENTS AND MAIN RESULTS

All out-of-hospital cardiac arrest patients' records were reviewed for relevant data regarding medical history, cardiac arrest event, prehospital care, in-hospital treatment, and complications. Survivor neurologic function was reassessed at follow-up after 6 to 12 months. Baseline patient and arrest episode characteristics were similar in the treatment groups. There was no significant difference in survival with good neurologic function, either to hospital discharge (surface, 34/90, 38%; core, 34/75, 45%; p=.345) or at follow-up (surface, 34/88, 39%; core, 34/75, 45%; p=.387). Time from cardiac arrest to achieving mild therapeutic hypothermia was equal with both devices (surface, 273 min, interquartile range 158-330; core, 270 min, interquartile range 190-360; p=.479). There were significantly more episodes of sustained hyperglycemia among the surface-cooled patients (surface, 64/92, 70%; core, 36/75, 48%; p=.005) and significantly more hypomagnesaemia among core-cooled patients (surface, 16/87, 18%; core, 27/74, 37%; p=.01).

CONCLUSIONS

In this study, surface and core cooling of out-of-hospital cardiac arrest patients following the same established postresuscitation treatment protocol resulted in similar survival to hospital discharge and comparable neurologic function at follow-up.

The role of hypothermia in post-cardiac arrest patients with return of spontaneous circulation: a systematic review

OBJECTIVES

To update a comprehensive systematic review of the use of therapeutic hypothermia after cardiac arrest that was undertaken initially as part of the 2010 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science. The specific question addressed was: 'in post-cardiac arrest patients with a return of spontaneous circulation, does the induction of mild hypothermia improve morbidity or mortality when compared with usual care?'

METHODS

Pubmed was searched using ("heart arrest" or "cardiopulmonary resuscitation") AND "hypothermia, induced" using 'Clinical Queries' search strategy; EmBASE was searched using (heart arrest) OR (cardiopulmonary resuscitation) AND hypothermia; The Cochrane database of systematic reviews; ECC EndNote Library for "hypothermia" in abstract OR title. Excluded were animal studies, reviews and editorials, surveys of implementation, analytical models, reports of single cases, pre-arrest or during arrest cooling and group where the intervention was not hypothermia alone.

RESULTS

77 studies met the criteria for further review. Of these, four were meta-analyses (LOE 1); seven were randomised controlled trials (LOE 1), although six of these were from the same set of patients; nine were non-randomised, concurrent controls (LOE 2); 15 were trials with retrospective controls (LOE 3); 40 had no controls (LOE 4); and one was extrapolated from a non-cardiac arrest group (LOE 5).

CONCLUSION

There is evidence supporting the use of mild therapeutic hypothermia to improve neurological outcome in patients who remain comatose following the return of spontaneous circulation after a cardiac arrest; however, much of the evidence is from low-level, observational studies. Of seven randomised controlled trials, six use data from the same patients.

Therapeutic hypothermia is associated with a decrease in urine output in acute stroke patients

AIMS

It is unclear what effect therapeutic hypothermia may have on renal function, because its effect has so far been primarily evaluated in settings in which there may be possible confounding perturbations in cardiovascular and renal physiology, such deep intraoperative hypothermia, general anesthesia, and post-cardiac arrest. We sought to determine if therapeutic hypothermia affects renal function in awake patients with normal renal function who were enrolled into a clinical trial of hypothermia plus intravenous thrombolysis for acute ischemic stroke.

METHODS

Eleven patients with normal renal function were cooled to 33°C for 24 h using an endovascular catheter, and then re-warmed over 12 h to 36.5°C, while hourly temperature, blood pressure, and fluid status data was recorded. Blood samples for blood urea nitrogen (BUN), creatinine, and hematocrit were drawn prior to treatment (baseline), immediately after hypothermia and re-warming (day 2), and again at day 7 or discharge, and values compared.

RESULTS

On initiation of cooling, temperatures dropped from a median pre-treatment value of 36.1°C (IQR: 35.8-36.4°C) to 33.1°C (IQR: 33.1-33.4°C). Urine output decreased 5.1 ml/h for every 1°C decrease in body temperature (p-value=0.001), with no associated serious adverse events. There were no statistically significant changes in BUN, creatinine, or hematocrit in the hypothermia patients.

CONCLUSION

Inducing hypothermia in patients with relatively unperturbed renal physiology results in a decrease in urine output that is linearly correlated with the decrease in core temperature. This has important implications for fluid management in patients undergoing therapeutic hypothermia.

The small chill: mild hypothermia for cardioprotection?

Reducing the heart's temperature by 2-5°C is a potent cardioprotective treatment in animal models of coronary artery occlusion. The anti-infarct benefit depends upon the target temperature and the time at which cooling is instituted. Protection primarily results from cooling during the ischaemic period, whereas cooling during reperfusion or beyond offers little protection. In animal studies, protection is proportional to both the depth and duration of cooling. An optimal cooling protocol must appreciably shorten the normothermic ischaemic time to effectively salvage myocardium. Patients presenting with acute myocardial infarction could be candidates for mild hypothermia since the current door-to-balloon time is typically 90 min. But they would have to be cooled quickly shortly after their arrival. Several strategies have been proposed for ultra-fast cooling, but most like liquid ventilation and pericardial perfusion are too invasive. More feasible strategies might include cutaneous cooling, peritoneal lavage with cold solutions, and endovascular cooling with intravenous thermodes. This last option has been investigated clinically, but the results have been disappointing possibly because the devices lacked capacity to cool the patient quickly or cooling was not implemented soon enough. The mechanism of hypothermia's protection has been assumed to be energy conservation. However, whereas deep hypothermia clearly preserves ATP, mild hypothermia has only a modest effect on ATP depletion during ischaemia. Some evidence suggests that intracellular signalling pathways might be responsible for the protection. It is unknown how cooling could trigger these pathways, but, if true, then it might be possible to duplicate cooling's protection pharmacologically.