Mild hypothermia during prolonged cardiopulmonary cerebral resuscitation increases conscious survival in dogs

The design of the PRINCESS 2 trial: A randomized trial to study the impact of ultrafast hypothermia on complete neurologic recovery after out-of-hospital cardiac arrest with initial shockable rhythm

BACKGROUND

Delayed hypothermia, initiated after hospital arrival, several hours after cardiac arrest with 8-10 hours to reach the target temperature, is likely to have limited impact on overall survival. However, the effect of ultrafast hypothermia, i.e., delivered intra-arrest or immediately after return of spontaneous circulation (ROSC), on functional neurologic outcome after out-of-hospital cardiac arrest (OHCA) is unclear. In two prior trials, prehospital trans-nasal evaporative intra-arrest cooling was safe, feasible and reduced time to target temperature compared to delayed cooling. Both studies showed trends towards improved neurologic recovery in patients with shockable rhythms. The aim of the PRINCESS2-study is to assess whether cooling, initiated either intra-arrest or immediately after ROSC, followed by in-hospital hypothermia, significantly increases survival with complete neurologic recovery as compared to standard normothermia care, in OHCA patients with shockable rhythms.

METHODS/DESIGN

In this investigator-initiated, randomized, controlled trial, the emergency medical services (EMS) will randomize patients at the scene of cardiac arrest to either trans-nasal cooling within 20 minutes from EMS arrival with subsequent hypothermia at 33°C for 24 hours after hospital admission (intervention), or to standard of care with no prehospital or in-hospital cooling (control). Fever (>37,7°C) will be avoided for the first 72 hours in both groups. All patients will receive post resuscitation care and withdrawal of life support procedures according to current guidelines. Primary outcome is survival with complete neurologic recovery at 90 days, defined as modified Rankin scale (mRS) 0-1. Key secondary outcomes include survival to hospital discharge, survival at 90 days and mRS 0-3 at 90 days. In total, 1022 patients are required to detect an absolute difference of 9% (from 45 to 54%) in survival with neurologic recovery (80% power and one-sided α=0,025, β=0,2) and assuming 2,5% lost to follow-up. Recruitment starts in Q1 2024 and we expect maximum enrolment to be achieved during Q4 2024 at 20-25 European and US sites.

DISCUSSION

This trial will assess the impact of ultrafast hypothermia applied on the scene of cardiac arrest, as compared to normothermia, on 90-day survival with complete neurologic recovery in OHCA patients with initial shockable rhythm.

TRIAL REGISTRATION

NCT06025123.

Surgical Science and the Evolution of Critical Care Medicine

Surgical science has driven innovation and inquiry across adult and pediatric disciplines that provide critical care regardless of location. Surgically originated but broadly applicable knowledge has been globally shared within the pages Critical Care Medicine over the last 50 years.

Cryopreservation of Animals and Cryonics: Current Technical Progress, Difficulties and Possible Research Directions

The basis of cryonics or medical cryopreservation is to safely store a legally dead subject until a time in the future when technology and medicine will permit reanimation after eliminating the disease or cause of death. Death has been debunked as an event occurring after cardiac arrest to a process where interjecting its progression can allow for reversal when feasible. Cryonics technology artificially halts further damages and injury by restoring respiration and blood circulation, and rapidly reducing temperature. The body can then be preserved at this extremely low temperature until the need for reanimation. Presently, the area has attracted numerous scientific contributions and advancement but the practice is still flooded with challenges. This paper presents the current progression in cryonics research. We also discuss obstacles to success in the field, and identify the possible solutions and future research directions.

A walk through the progression of resuscitation medicine

Cardiac arrest (CA) is a sudden and devastating disease process resulting in more deaths in the United States than many cancers, metabolic diseases, and even car accidents. Despite such a heavy mortality burden, effective treatments have remained elusive. The past century has been productive in establishing the guidelines for resuscitation, known as cardiopulmonary resuscitation (CPR), as well as developing a scientific field whose aim is to elucidate the underlying mechanisms of CA and develop therapies to save lives. CPR has been successful in reinitiating the heart after arrest, enabling a survival rate of approximately 10% in out-of-hospital CA. Although current advanced resuscitation methods, including hypothermia and extracorporeal membrane oxygenation, have improved survival in some patients, they are unlikely to significantly improve the national survival rate any further without a paradigm shift. Such a change is possible with sustained efforts in the basic and clinical sciences of resuscitation and their implementation. This review seeks to discuss the current landscape in resuscitation medicine-how we got here and where we are going.

Outcomes and Utilization of Therapeutic Hypothermia in Post-Cardiac Arrest Patients in Teaching Versus Non-Teaching Hospitals: Retrospective Study of the Nationwide Inpatient Sample Database (2016)

Background Using therapeutic hypothermia (TH) reduces the core body temperature of survivors of cardiac arrest to minimize the neurological damage caused by severe hypoxia. The TH protocol is initiated following return of spontaneous circulation (ROSC) in non-responsive patients. Clinical trials examining this technique have shown significant improvement in neurological function among survivors of cardiac arrests. Though there is strong evidence to support TH use to improve the neurologic outcomes in shockable and nonshockable rhythms, predictors of TH utilization are not well-characterized. Our study tried to evaluate TH utilization, as well as the effect of the teaching status of hospitals, on outcomes, including mortality, length of stay, and total hospitalization charges. Method We conducted a retrospective analysis of the Healthcare Cost and Utilization Project - Nationwide Inpatient Sample (HCUP-NIS) database. Patients with an admitting diagnosis of cardiac arrest, as identified by the corresponding International Classification of Disease, 10th Revision (ICD-10) code for the year 2016 were analyzed. In addition, we identified TH using the ICD-10 procedure code. A weighted descriptive analysis was performed to generate national estimates. Groups of patients admitted to teaching hospitals were compared to those admitted in non-teaching hospitals. Patients were stratified by age, sex, race, and demographic and clinical data, including the Charlson Comorbidity Index (CCI), for these two groups, and statistical analysis was done for the primary outcome, in-hospital mortality, as well as the secondary outcomes, including length of stay (LOS) and total hospitalization charges. Fisher's exact test was used to compare proportions and student's t-test for continuous variables. Statistical analysis was completed by linear regression analysis. Results A total of 13,780 patients met the inclusion criteria for cardiac arrest admission. The number of patients with cardiac arrest admitted to a teaching hospital was 9285. A total of 670 patients received TH, with 495 admissions to teaching hospitals. The population of females in the hypothermia group was 270. The mean age of patients received TH was 59.4 years. In patients who received TH, 65% were Caucasians followed by Hispanics (16%), with no significant statistical racial differences in groups (p=0.30). The majority of patients with TH in both groups (teaching vs. non-teaching admissions) had Medicare (58.8% vs 49.5%; p=0.75). Hospitals in the southern region had the most admissions in both groups (45.7% and 31.3%), with the northeast region having the least non-teaching hospital admissions (8.5%) and approximately similar teaching hospital admissions in other regions (~22%) (p=0.27). The total number of deaths in this group was 510, out of which 370 were in a teaching hospital. After adjusting for age, sex, race, income, the CCI, hospital location, and bed size, mortality was not significantly different between these two groups (p=0.797). We found increased LOS in patients admitted to teaching hospitals (p=0.021). With a p-value of 0.097, there were no differences in total hospitalization charges in both groups. Conclusion There were no significant differences in mortality or total hospitalization charge between patients admitted with cardiac arrest to a teaching hospital and received TH as compared to a non-teaching hospital although patients admitted to teaching hospitals stayed longer.

Malignant Arrhythmias During Induction of Target Temperature Management After Cardiac Arrest

The aim of this study was to evaluate the incidence and determinants of malignant arrhythmias (MA) in patients with shock following out-of-hospital cardiac arrest (OHCA) treated with targeted temperature management. Risk factors for the development of MA were prospectively analyzed in patients after OHCA. MA were defined as ventricular tachycardia or fibrillation with a duration >30 seconds, which had to be terminated by defibrillation. All patients were treated with therapeutic hypothermia for 24 hours. Demographics, OHCA details, interventions, and intensive care unit (ICU) treatment were recorded. A total of 55 patients were included, 11 (20%) of whom developed MA during the ICU stay. All MA occurred within the first 18 hours after admission. Patients who developed MA showed a stronger decrease in body temperature (Δ -2.4°C ± 0.8°C vs. Δ -1.3°C ± 1.3°C; p = 0.016) and in serum potassium levels (Δ -0.9 ± 1 mmol/L vs. Δ -0.3 ± 0.6 mmol/L; p = 0.037) during the cooling period compared with patients without MA. In the multivariable analysis, fast temperature decline as well as lower potassium levels were associated with MA. In addition, higher number of shocks during resuscitation and higher ICU epinephrine use were independent predictors of MA in patients with OHCA. The use of epinephrine as well as hypokalemia in context with intense cooling may increase the incidence of MA in patients with shock after cardiac arrest. Therefore, these therapeutic strategies should be applied with caution in this vulnerable group of patients.

Translational Models of Arrhythmia Mechanisms and Susceptibility: Success and Challenges of Modeling Human Disease

We discuss large animal translational models of arrhythmia susceptibility and sudden cardiac death, focusing on important considerations when interpreting the data derived before applying them to human trials. The utility of large animal models of arrhythmia and the pros and cons of specific translational large animals used will be discussed, including the necessary tradeoffs between models designed to derive mechanisms vs. those to test therapies. Recent technical advancements which can be applied to large animal models of arrhythmias to better elucidate mechanistic insights will be introduced. Finally, some specific examples of past successes and challenges in translating the results of large animal models of arrhythmias to clinical trials and practice will be examined, and common themes regarding the success and failure of translating studies to therapy in man will be discussed.

Differential effect of mild therapeutic hypothermia depending on the findings of hypoxic encephalopathy on early CT images in patients with post-cardiac arrest syndrome

INTRODUCTION

The aim of this study was to evaluate the differential effects of mild therapeutic hypothermia (MTH) in post-cardiac arrest syndrome (PCAS) patients depending on the presence/absence of hypoxic encephalopathy (HE) in the early brain CT images obtained before the initiation of MTH.

METHODS

We conducted a retrospective review of the data of a total of 129 patients with PCAS who were treated by MTH (34 °C) or normothermia treatment (NT) (35 °C or 36 °C), and had undergone brain CT examination prior to the initiation of these treatments. We divided the subjects into 4 groups, namely, the HE(-)/MTH, HE(-)/NT, HE(+)/MTH, and HE(+)/NT groups, for evaluating the interaction effect between the two variables. Then, we compared the neurological outcomes between the HE(-)/MTH and HE(-)/NT groups by multivariate logistic analysis. Good outcome was defined as a Cerebral Performance Category score of ≤2 at 30 days.

RESULTS

The percentages of subjects with a good outcome in the HE(-)/MTH and HE(-)/NT group were 68.9% (42/61) and 36.1% (13/36), respectively (p = .003), while those in the HE(+)/MTH and HE(+)/NT groups were lower, at 7.4% (2/27) and 20.0% (1/5), respectively (p = .410), suggesting a statistically significant interaction effect between the two variables (p_interaction = 0.002). In the HE(-) group, MTH was associated with a higher odds ratio of a good outcome as compared to NT (OR 6.80, 95% CI 1.19-38.96, p = .031).

CONCLUSIONS

The effect of MTH in patients with PCAS differed depending on the presence/absence of evidence of HE on the early CT images.

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.

Combined intra- and post-cardiac arrest hypothermic-targeted temperature management in a rat model of asphyxial cardiac arrest improves survival and neurologic outcome compared to either strategy alone

AIM

Post-cardiac arrest hypothermic-targeted temperature management (HTTM) improves outcomes in preclinical cardiac arrest studies. However, inadequate understanding of the mechanisms and therapeutic windows remains a barrier to optimization. We tested the hypothesis that combined intra- and post-cardiac arrest HTTM provides a synergistic outcome benefit compared to either strategy alone.

METHODS

Rats subjected to 8-min asphyxial cardiac arrest were block randomized to 4 treatment groups (n=12/group): NTTM) normothermic-targeted temperature management; 1-24 HTTM) HTTM initiated 1h post-ROSC and maintained for 24h; Intra-1 HTTM) HTTM initiated at CPR onset and maintained for 1h; and Intra-24 HTTM) HTTM initiated at CPR onset and maintained for 24h. HTTM was induced by nasopharyngeal cooling and maintained using an automated temperature regulation system. Target temperature range was 36.5-37.5°C for NTTM and 32.0-34.0°C for HTTM. Post-arrest neurologic function score (NFS) was measured daily, and rats surviving 72h were euthanized for histological analysis of neurodegeneration.

RESULTS

Target brain temperature was achieved 7.8±3.3min after initiating intra-arrest cooling. The survival rate was 42%, 50%, 50%, and 92% in the NTTM, 1-24 HTTM, Intra-1 HTTM, and Intra-24 HTTM groups, respectively (p<0.05, Intra-24 group vs. all other groups). The rate of survival with good neurologic function (NFS≥450) was 33% in the Intra-24 HTTM group vs. 0% in all other groups (mid p<0.05). Hippocampal CA1 sector neurodegeneration was significantly reduced in the Intra-24 HTTM group compared to all other groups (p<0.05).

CONCLUSION

Combined intra- and post-cardiac arrest HTTM has greater outcome benefits than either strategy alone.

Variability of Post-Cardiac Arrest Care Practices Among Cardiac Arrest Centers: United States and South Korean Dual Network Survey of Emergency Physician Research Principal Investigators

There is little consensus regarding many post-cardiac arrest care parameters. Variability in such practices could confound the results and generalizability of post-arrest care research. We sought to characterize the variability in post-cardiac arrest care practice in Korea and the United States. A 54-question survey was sent to investigators participating in one of two research groups in South Korea (Korean Hypothermia Network [KORHN]) and the United States (National Post-Arrest Research Consortium [NPARC]). Single investigators from each site were surveyed (N = 40). Participants answered questions based on local institutional protocols and practice. We calculated descriptive statistics for all variables. Forty surveys were completed during the study period with 30 having greater than 50% of questions completed (75% response rate; 24 KORHN and 6 NPARC). Most centers target either 33°C (N = 16) or vary the target based on patient characteristics (N = 13). Both bolus and continuous infusion dosing of sedation are employed. No single indication was unanimous for cardiac catheterization. Only six investigators reported having an institutional protocol for withdrawal of life-sustaining therapy (WLST). US patients with poor neurological prognosis tended to have WLST with subsequent expiration (N = 5), whereas Korean patients are transferred to a secondary care facility (N = 19). Both electroencephalography modality and duration vary between institutions. Serum biomarkers are commonly employed by Korean, but not US centers. We found significant variability in post-cardiac arrest care practices among US and Korean medical centers. These practice variations must be taken into account in future studies of post-arrest care.

Prehospital surface cooling is safe and can reduce time to target temperature after cardiac arrest

PURPOSE

Mild therapeutic hypothermia proved to be beneficial when induced after cardiac arrest in humans. Prehospital cooling with i.v. fluids was associated with adverse side effects. Our primary objective was to compare time to target temperature of out-of hospital cardiac arrest patients cooled non-invasively either in the prehospital setting vs. the in-hospital (IH) setting, to assess surface-cooling safety profile and long term outcome.

METHODS

In this retrospective, single center cohort study, a group of adult patients with restoration of spontaneous circulation (ROSC) after out-of hospital cardiac arrest were cooled with a surface cooling pad beginning either in the prehospital or IH setting for 24h. Time to target temperature (33.9°C), temperature on admission, time to admission after ROSC and outcome were compared. Also, rearrests and pulmonary edema were assessed. Neurologic outcome at 12 months was evaluated (Cerebral Performance Category, CPC 1-2, favorable outcome).

RESULTS

Between September 2005 and February 2010, 56 prehospital cooled patients and 54 IH-cooled patients were treated. Target temperature was reached in 85 (66-117)min (prehospital) and in 135 (102-192)min (IH) after ROSC (p<0.001). After prehospital cooling, hospital admission temperature was 35.2 (34.2-35.8)°C, and in the IH-cooling patients initial temperature was 35.8 (35.2-36.3)°C (p=0.001). No difference in numbers of rearrests and pulmonary edema between groups was observed. In both groups, no skin lesions were observed. Favorable outcome was reached in 26.8% (prehospital) and in 37.0% (IH) of the patients (p=0.17).

CONCLUSIONS

Using a non-invasive prehospital surface cooling method after cardiac arrest, target temperature can be reached faster without any major complications than starting cooling IH. The effect of early non-invasive cooling on long-term outcome remains to be determined in larger studies.

Hypothermia after cardiac arrest as a novel approach to increase survival in cardiopulmonary cerebral resuscitation: a review

Context:

The aim of this review study was to evaluate therapeutic mild hypothermia, its complications and various methods for induced mild hypothermia in patients following resuscitation after out-of-hospital cardiac arrest.

Evidence Acquisition:

Studies conducted on post-cardiac arrest cares, history of induced hypothermia, and therapeutic hypothermia for patients with cardiac arrest were included in this study. We used the valid databases (PubMed and Cochrane library) to collect relevant articles.

Results:

According to the studies reviewed, induction of mild hypothermia in patients after cardiopulmonary resuscitation would lead to increased survival and better neurological outcome; however, studies on the complications of hypothermia or different methods of inducing hypothermia were limited and needed to be studied further.

Conclusions:

This study provides strategic issues concerning the induction of mild hypothermia, its complications, and different ways of performing it on patients; using this method helps to increase patients’ neurological survival rate.

Minocycline attenuates brain tissue levels of TNF-α produced by neurons after prolonged hypothermic cardiac arrest in rats

Neuro-cognitive disabilities are a well-recognized complication of hypothermic circulatory arrest. We and others have reported that prolonged cardiac arrest (CA) produces neuronal death and microglial proliferation and activation that are only partially mitigated by hypothermia. Microglia, and possibly other cells, are suggested to elaborate tumor necrosis factor alpha (TNF-α), which can trigger neuronal death cascades and exacerbate edema after CNS insults. Minocycline is neuroprotective in some brain ischemia models in part by blunting the microglial response. We tested the hypothesis that minocycline would attenuate neuroinflammation as reflected by brain tissue levels of TNF-α after hypothermic CA in rats. Rats were subjected to rapid exsanguination, followed by a 6 min normothermic CA. Hypothermia (30 °C) was then induced by an aortic saline flush. After a total of 20 min CA, resuscitation was achieved via cardiopulmonary bypass (CPB). After 5 min reperfusion, minocycline (90 mg kg−1; n = 6) or vehicle (PBS; n = 6) was given. Hypothermia (34 °C) was maintained for 6 h. Rats were sacrificed at 6 or 24 h. TNF-α was quantified (ELISA) in four brain regions (cerebellum, CEREB; cortex, CTX; hippocampus, HIP; striatum, STRI). Naïve rats (n = 6) and rats subjected to the same anesthesia and CPB but no CA served as controls (n = 6). Immunocytochemistry was used to localize TNF-α. Naïve rats and CPB controls had no detectable TNF-α in any brain region. CA markedly increased brain TNF-α. Regional differences were seen, with the highest TNF-α levels in striatum in CA groups (10-fold higher, P < 0.05 vs. all other brain regions). TNF-α was undetectable at 24 h. Minocycline attenuated TNF-α levels in CTX, HIP and STRI (P < 0.05). TNF-α showed unique co-localization with neurons. In conclusion, we report region-dependent early increases in brain TNF-α levels after prolonged hypothermic CA, with maximal increases in striatum. Surprisingly, TNF-α co-localized in neurons and not microglia. Minocycline attenuated TNF-α by approximately 50% but did not totally ablate its production. That minocycline decreased brain TNF-α levels suggests that it may represent a therapeutic adjunct to hypothermia in CA neuroprotection. University of Pittsburgh IACUC 0809278B-3.

Improved neuroprotective effect of methylene blue with hypothermia after porcine cardiac arrest

BACKGROUND

Induced mild hypothermia and administration of methylene blue (MB) have proved to have neuroprotective effects in cardiopulmonary resuscitation (CPR); however, induction of hypothermia takes time. We set out to determine if MB administered during CPR could add to the histologic neuroprotective effect of hypothermia.

METHODS

A piglet model of extended cardiac arrest (12 min of untreated cardiac arrest and 8 min of CPR) was used to assess possible additional neuroprotective effects of MB when administered during CPR before mild therapeutic hypothermia induced 30 min after restoration of spontaneous circulation (ROSC). Three groups were compared: C group (n = 8) received standard CPR; PH group (n = 8) received standard CPR but 30 min after ROSC these piglets were cooled to 34°C; the PH+MB group (n = 8) received an MB infusion 1 min after commencement of CPR and the same cooling protocol as the PH group. Three hours later, the animals were killed. Immediately after death, the brains were harvested pending histological and immunohistological analysis.

RESULTS

Circulatory variables were similar in the groups except that cardiac output was greater in the PH+MB group 2-3 h after ROSC. Cerebral cortical neuronal injury and blood-brain barrier disruption was greatest in the C group and least in the MB group. The neuroprotective effect of MB and hypothermia was significantly greater than that of delayed hypothermia alone.

CONCLUSION

Administration of MB during CPR added to the short term neuroprotective effects of induced mild hypothermia induced 30 min after ROSC.

Blood pH is a useful indicator for initiation of therapeutic hypothermia in the early phase of resuscitation after comatose cardiac arrest: a retrospective study

BACKGROUND

Therapeutic hypothermia (TH) is one of the key treatments after cardiac arrest (CA). Selection of post-CA patients for TH remains problematic, as there are no clinically validated tools to determine who might benefit from the therapy.

OBJECTIVE

The aim of this study was to investigate retrospectively whether laboratory findings or other patient data obtained during the early phase of hospital admission could be correlated with neurological outcome after TH in comatose survivors of CA.

METHODS

Medical charts of witnessed CA patients admitted between June 2003 and July 2009 who were treated with TH were reviewed retrospectively. The subjects were grouped based on their cerebral performance category (CPC) 6 months after CA, as either good recovery (GR) for CPC 1-2 or non-good recovery (non-GR) for CPC 3-5. The following well-known determinants of outcome obtained during the early phase of hospital admission were evaluated: age, gender, body mass index, cardiac origin, presence of ventricular fibrillation (VF), time from collapse to cardiopulmonary resuscitation, time from collapse to return of spontaneous circulation, body temperature, arterial blood gases, and blood test results.

RESULTS

We analyzed a total of 50 (25 GR and 25 non-GR) patients. Multivariate logistic analysis showed that initial heart rhythm and pH levels were significantly higher in the GR group than in the non-GR group (ventricular tachycardia/VF rate: p = 0.055, 95% confidence interval [CI] 0.768-84.272, odds ratio [OR] 8.047; pH: 7.155 ± 0.139 vs. 6.895 ± 0.100, respectively, p < 0.001, 95% CI 1.838-25.827; OR 6.89).

CONCLUSION

These results imply that in addition to initial heart rhythm, pH level may be a good candidate for neurological outcome predictor even though previous research has found no correlation between initial pH value and neurological outcome.

Updates in small animal cardiopulmonary resuscitation

For dogs and cats that experience cardiopulmonary arrest, rates of survival to discharge are 6% to 7%, as compared with survival rates of 20% for people. The introduction of standardized cardiopulmonary resuscitation guidelines and training in human medicine has led to substantial improvements in outcome. The Reassessment Campaign on Veterinary Resuscitation initiative recently completed an exhaustive literature review and generated a set of evidence-based, consensus cardiopulmonary resuscitation guidelines in 5 domains: preparedness and prevention, basic life support, advanced life support, monitoring, and postcardiac arrest care. This article reviews some of the most important of these new guidelines.

Updates in the American Heart Association guidelines for cardiopulmonary resuscitation and potential applications to veterinary patients

OBJECTIVE

To review the updates in the American Heart Association (AHA) guidelines for cardiopulmonary resuscitation (CPR) and identify potential applications to veterinary patients.

ETIOLOGY

Cardiopulmonary arrest is common in veterinary emergency and critical care, and consensus guidelines are lacking. Human resuscitation guidelines are continually evolving as new clinical and experimental studies support updated recommendations. Synthesis of human, experimental animal model, and veterinary literature support the potential for updates and advancement in veterinary CPR practices.

THERAPY

This review serves to highlight updates in the AHA guidelines for CPR and evaluate their application to small animal veterinary patients. Interventions identified will be evaluated for trans-species potential, raise questions regarding best resuscitation recommendations, and offer opportunities for further research to continue to advance veterinary CPR.

PROGNOSIS

The prognosis for any patient undergoing cardiopulmonary arrest remains guarded.

Core temperature measurement in therapeutic hypothermia according to different phases: comparison of bladder, rectal, and tympanic versus pulmonary artery methods

PURPOSE

Comparisons of bladder, rectal and tympanic temperatures versus pulmonary artery (PA) temperature during different therapeutic hypothermia (TH) phases.

METHODS

Twenty-one patients admitted to our emergency department (ED) after out-of-hospital cardiac arrests were included in this study. For comparison, the temperature of four different sites, urinary bladder (BL), rectal (RE), tympanic membrane (TM) digital thermometers, and a Swan-Ganz catheter were used during TH, which were controlled by a surface cooling method. TH is divided into three phases: induction, maintenance, and rewarming phase.

RESULTS

In the induction phase, the mean differences between PA temperatures and those of the other methods studied were: BL (-0.24 ± 1.30°C), RE (-0.52 ± 1.40°C), and TM (1.11 ± 1.53°C). The mean differences between PA temperatures and those of the other methods in the maintenance phase were BL (0.06 ± 0.79°C), RE (-0.30 ± 1.16°C), and TM (1.12 ± 1.29°C); in the rewarming phase: BL (0.08 ± 0.86°C), RE (-0.03 ± 1.71°C), and TM (0.89 ± 1.62°C); and in the total phase: BL (0.04 ± 0.90°C), RE (-0.22 ± 1.44°C), and TM (1.03 ± 1.47°C).

CONCLUSIONS

The mean difference between BL and PA temperatures is lower than those in other sites during TH. On the contrary, there are larger differences between TM and PA temperatures when compared to other sites. The differences between RE and PA temperatures are comparatively less than those between TM and PA. However, RE temperature tends to be higher than the temperature recorded by a BL thermometer or Swan-Ganz catheter during the rapid induction phase.

RECOVER evidence and knowledge gap analysis on veterinary CPR. Part 7: Clinical guidelines

OBJECTIVE

To present a series of evidence-based, consensus guidelines for veterinary CPR in dogs and cats.

DESIGN

Standardized, systematic evaluation of the literature, categorization of relevant articles according to level of evidence and quality, and development of consensus on conclusions for application of the concepts to clinical practice. Questions in five domains were examined: Preparedness and Prevention, Basic Life Support, Advanced Life Support, Monitoring, and Post-Cardiac Arrest Care. Standardized worksheet templates were used for each question, and the results reviewed by the domain members, by the RECOVER committee, and opened for comments by veterinary professionals for 4 weeks. Clinical guidelines were devised from these findings and again reviewed and commented on by the different entities within RECOVER as well as by veterinary professionals.

SETTING

Academia, referral practice and general practice.

RESULTS

A total of 74 worksheets were prepared to evaluate questions across the five domains. A series of 101 individual clinical guidelines were generated. In addition, a CPR algorithm, resuscitation drug-dosing scheme, and postcardiac arrest care algorithm were developed.

CONCLUSIONS

Although many knowledge gaps were identified, specific clinical guidelines for small animal veterinary CPR were generated from this evidence-based process. Future work is needed to objectively evaluate the effects of these new clinical guidelines on CPR outcome, and to address the knowledge gaps identified through this process.

Therapeutic applications of hypothermia in cerebral ischaemia

There is considerable experimental evidence that hypothermia is neuroprotective and can reduce the severity of brain damage after global or focal cerebral ischaemia. However, despite successful clinical trials for cardiac arrest and perinatal hypoxia-ischaemia and a number of trials demonstrating the safety of moderate and mild hypothermia in stroke, there are still no established guidelines for its use clinically. Based upon a review of the experimental studies we discuss the clinical implications for the use of hypothermia as an adjunctive therapy in global cerebral ischaemia and stroke and make some suggestions for its use in these situations.

Ultrafast and whole-body cooling with total liquid ventilation induces favorable neurological and cardiac outcomes after cardiac arrest in rabbits

BACKGROUND

In animal models of cardiac arrest, the benefit afforded by hypothermia is closely linked to the rapidity of the decrease in body temperature after resuscitation. Because total liquid ventilation (TLV) with temperature-controlled perfluorocarbons induces a very rapid and generalized cooling, we aimed to determine whether this could limit the post-cardiac arrest syndrome in a rabbit model. We especially focused on neurological, cardiac, pulmonary, liver and kidney dysfunctions.

METHODS AND RESULTS

Anesthetized rabbits were submitted to either 5 or 10 minutes of untreated ventricular fibrillation. After cardiopulmonary resuscitation and resumption of a spontaneous circulation, the animals underwent either normothermic life support (control) or therapeutic hypothermia induced by TLV. The latter procedure decreased esophageal and tympanic temperatures to 32°C to 33°C within only 10 minutes. After rewarming, the animals submitted to TLV exhibited an attenuated neurological dysfunction and decreased mortality 7 days later compared with control. The neuroprotective effect of TLV was confirmed by a significant reduction in brain histological damages. We also observed limitation of myocardial necrosis, along with a decrease in troponin I release and a reduced myocardial caspase 3 activity, with TLV. The beneficial effects of TLV were directly related to the rapidity of hypothermia induction because neither conventional cooling (cold saline infusion plus external cooling) nor normothermic TLV elicited a similar protection.

CONCLUSIONS

Ultrafast cooling instituted by TLV exerts potent neurological and cardiac protection in an experimental model of cardiac arrest in rabbits. This could be a relevant approach to provide a global and protective hypothermia against the post-cardiac arrest syndrome.

Protective head-cooling during cardiac arrest and cardiopulmonary resuscitation: the original animal studies

Prolonged standard cardiopulmonary resuscitation (CPR) does not reliably sustain brain viability during cardiac arrest. Pre-hospital adjuncts to standard CPR are needed in order to improve outcomes. A preliminary dog study demonstrated that surface cooling of the head during arrest and CPR can achieve protective levels of brain hypothermia (30°C) within 10 minutes. We hypothesized that protective head-cooling during cardiac arrest and CPR improves neurological outcomes. Twelve dogs under light ketamine-halothane-nitrous oxide anesthesia were arrested by transthoracic fibrillation. The treated group consisted of six dogs whose shaven heads were moistened with saline and packed in ice immediately after confirmation of ventricular fibrillation. Six control dogs remained at room temperature. All 12 dogs were subjected to four minutes of ventricular fibrillation and 20 minutes of standard CPR. Spontaneous circulation was restored with drugs and countershocks. Intensive care was provided for five hours post-arrest and the animals were observed for 24 hours. In both groups, five of the six dogs had spontaneous circulation restored. After three hours, mean neurological deficit was significantly lower in the treated group (P=0.016, with head-cooled dogs averaging 37% and the normothermic dogs 62%). Two of the six head-cooled dogs survived 24 hours with neurological deficits of 9% and 0%, respectively. None of the control group dogs survived 24 hours. We concluded that head-cooling attenuates brain injury during cardiac arrest with prolonged CPR. We review the literature related to the use of hypothermia following cardiac arrest and discuss some promising approaches for the pre-hospital setting.

A comparison between head cooling begun during cardiopulmonary resuscitation and surface cooling after resuscitation in a pig model of cardiac arrest

OBJECTIVE

Employing transnasal head-cooling in a pig model of prolonged ventricular fibrillation, we compared the effects of 4 hrs of head-cooling started during cardiopulmonary resuscitation with those of 8 hrs of surface-cooling started at 2 hrs after resuscitation on 96-hr survival and neurologic outcomes.

DESIGN

Prospective controlled animal study.

SETTING

University-affiliated research laboratory.

SUBJECTS

Domestic pigs.

INTERVENTIONS

Twenty-four male pigs were subjected to 10 min of untreated ventricular fibrillation followed by 5 min of cardiopulmonary resuscitation. In the head-cooling group, hypothermia was started with cardiopulmonary resuscitation and continued for 4 hrs after resuscitation. In the surface-cooling group, systemic hypothermia with a cooling blanket was started, in accord with current clinical practices, at 2 hrs after resuscitation and continued for 8 hrs. Methods in the control animal studies were identical except for temperature interventions.

MEASUREMENTS AND MAIN RESULTS

All animals were resuscitated except for one animal in each of the surface-cooling and control groups. After 5 min of cardiopulmonary resuscitation, jugular vein temperature was significantly decreased in the head-cooled animals. However, there were no differences in pulmonary artery temperatures among the three groups at that time. Nevertheless, both head-cooled and surface-cooled animals had an improved 96-hr survival after resuscitation. Significantly better neurologic outcomes were observed in early head-cooled animals in the first 3 days after resuscitation.

CONCLUSION

Early head-cooling during cardiopulmonary resuscitation continuing for 4 hrs after resuscitation produced favorable survival and neurologic outcomes in comparison with delayed surface-cooling of 8 hrs duration.

Feasibility of intra-arrest hypothermia induction: A novel nasopharyngeal approach achieves preferential brain cooling

AIM

In patients with cardiopulmonary arrest, brain cooling may improve neurological outcome, especially if applied prior to or during early reperfusion. Thus it is important to develop feasible cooling methods for pre-hospital use. This study examines cerebral and compartmental thermokinetic properties of nasopharyngeal cooling during various blood flow states.

METHODS

Ten swine (40+/-4kg) were anesthetized, intubated and monitored. Temperature was determined in the frontal lobe of the brain, in the aorta, and in the rectum. After the preparatory phase the cooling device (RhinoChill system), which produces evaporative cooling in the nasopharyngeal area, was activated for 60min. The thermokinetic response was evaluated during stable anaesthesia (NF, n=3); during untreated cardiopulmonary arrest (ZF, n=3); during CPR (LF, n=4).

RESULTS

Effective brain cooling was achieved in all groups with a median cerebral temperature decrease of -4.7 degrees C for NF, -4.3 degrees C for ZF and -3.4 degrees C for LF after 60min. The initial brain cooling rate however was fastest in NF, followed by LF, and was slowest in ZF; the median brain temperature decrease from baseline after 15min of cooling was -2.48 degrees C for NF, -0.12 degrees C for ZF, and -0.93 degrees C for LF, respectively. A median aortic temperature change of -2.76 degrees C for NF, -0.97 for LF and +1.1 degrees C for ZF after 60min indicated preferential brain cooling in all groups.

CONCLUSION

While nasopharyngeal cooling in swine is effective at producing preferential cerebral hypothermia in various blood flow states, initial brain cooling is most efficient with normal circulation.

Intranasal cooling with or without intravenous cold fluids during and after cardiac arrest in pigs

BACKGROUND

Intranasal balloon catheters circulated with cold saline have previously been used for the induction and maintenance of selective brain cooling in pigs with normal circulation. In the present study, we investigated the feasibility of therapeutic hypothermia initiation, maintenance and rewarming using such intranasal balloon catheters with or without addition of intravenous ice-cold fluids during and after cardiac arrest treatment in pigs.

MATERIAL AND METHODS

Cardiac arrest was induced in 20 anaesthetised pigs. Following 8 min of cardiac arrest and 1 min of cardiopulmonary resuscitation (CPR), cooling was initiated after randomisation with either intranasal cooling (N) or combined with intravenous ice-cold fluids (N+S). Hypothermia was maintained for 180 min, followed by 180 min of rewarming. Brain and oesophageal temperatures, haemodynamic variables and intracranial pressure (ICP) were recorded.

RESULTS

Brain temperatures reductions after cooling did not differ (3.8 +/- 0.7 degrees C in the N group and 4.3 +/- 1.5 degrees C in the N+S group; P=0.47). The corresponding body temperature reductions were 3.6 +/- 1.2 degrees C and 4.6 +/- 1.5 degrees C (P=0.1). The resuscitation outcome was similar in both groups. Mixed venous oxygen saturation was lower in the N group after cooling and rewarming (P=0.024 and 0.002, respectively) as compared with the N+S group. ICP was higher after rewarming in the N group (25.2 +/- 2.9 mmHg; P=0.01) than in the N+S group (15.7 +/- 3.3 mmHg).

CONCLUSIONS

Intranasal balloon catheters can be used for therapeutic hypothermia initiation, maintenance and rewarming during CPR and after successful resuscitation in pigs.

[Effects of induced hypothermia in critically ill children]

OBJECTIVE

To study the efficacy of induced hypothermia (IH) in children, its effect on hemodynamic, hematological, and biochemical parameters and its side effects.

DESIGN

Retrospective, observational study.

SETTING

Pediatric intensive care unit.

PATIENTS

Pediatric patients requiring induced hypothermia.

INTERVENTIONS

None.

DATA COLLECTED

The following variables were recorded prior to the initiation of IH and after 4, 24, 48, 72, and 120 hours: heart rate, systolic blood pressure (SBP), diastolic blood pressure (DBP), diuresis, dose of inotropic, sedative, and muscle relaxant drugs, fluid balance, hematocrit, white cell count, white cell differential percentages, platelet count, blood levels of glucose, sodium, and potassium, C reactive protein, lactate, coagulation times, pressure ulcers, shivering, infections and death.

RESULTS

Thirty-one patients with a mean age of 20 months (SD: 39.8) were included in the study. The mean duration of IH was 3.97 days (range: 1 to 11 days). Among the IH effects, there was a significant fall in heart rate, with no changes in SBP, DBP, or diuresis. The blood tests revealed a progressive and significant fall in platelet count and an increase in C reactive protein levels. The fall in hematocrit and glucose and lactate levels was not significant. Positive cultures were detected in 25.8% of the patients during IH, most commonly from the bronchial aspirate (65%).

CONCLUSIONS

Induced hypothermia can be useful in some critically ill children. Tolerance is generally good and there are usually few side effects, which can be controlled through appropriate monitoring.

Surface vs. aortic flush cooling during cardiac arrest in pigs

BACKGROUND

To investigate the feasibility and efficacy of earlier induction of hypothermia already during the 'no-flow' period of cardiac arrest with non-invasive surface cooling or invasive aortic flush cooling.

METHODS

This was a prospective randomized experimental study that included 14 pigs, Large White breed (30-38 kg), with ventricular fibrillation cardiac arrest plus blanket surface and an invasive cold saline flush cooling. The endpoint was a decline in brain temperature (T(br)) at 35 min after cardiac arrest.

RESULTS

With surface cooling, T(br) decreased from 38.7+/-0.2 degrees C to 37.4+/-0.8 degrees C (P=0.02) and with invasive cooling T(br) decreased from 38.8+/-0.13 degrees C to 19.0+/-2.8 degrees C within 216+/-23 s (P=0.02) and increased back to 33.0+/-0.6 degrees C at 35 min of cardiac arrest (P=0.02 vs. T(br) at 15 min, P=0.002 vs. T(br) at 35 min in the surface cooling groups).

CONCLUSION

Invasive cooling by aortic flush with cold saline rapidly induces deep cerebral hypothermia, whereas non-invasive surface cooling only marginally decreases brain temperature.

Out-of-hospital therapeutic hypothermia in cardiac arrest victims

Despite many years of research, outcome after cardiac arrest is dismal. Since 2005, the European Resuscitation Council recommends in its guidelines the use of mild therapeutic hypothermia (32-34 degrees) for 12 to 24 hours in patients successfully resuscitated from cardiac arrest. The benefit of resuscitative mild hypothermia (induced after resuscitation) is well established, while the benefit of preservative mild to moderate hypothermia (induced during cardiac arrest) needs further investigation before recommending it for clinical routine. Animal data and limited human data suggest that early and fast cooling might be essential for the beneficial effect of resuscitative mild hypothermia. Out-of-hospital cooling has been shown to be feasible and safe by means of intravenous infusion with cold fluids or non-invasively with cooling pads. A combination of these cooling methods might further improve cooling efficacy. If out-of-hospital cooling will further improve functional outcome as compared with in-hospital cooling needs to be determined in a prospective, randomised, sufficiently powered clinical trial.

Prehospital resuscitated cardiac arrest patients: role for induced hypothermia

This article is a support paper for the National Association of EMS Physicians' position paper on induced therapeutic hypothermia in resuscitated cardiac arrest patients. Induced hypothermia is one of the newest treatments aimed at increasing the dismal neurologically intact survival rate for out-of-hospital cardiac arrest patients. Two landmark studies published in 2002 by the New England Journal of Medicine led to the American Heart Association (AHA) Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care IIa recommendation of cooling unconscious adult patients with return of spontaneous circulation after out-of-hospital cardiac arrest due to ventricular fibrillation to 32 degrees C to 34 degrees C for 12 to 24 hours. Despite many limitations of those studies, the AHA also suggests that this therapy may be beneficial for patients with non-ventricular fibrillation arrests. However, the literature is lacking in answers with regard to the best methods to utilize in cooling patients. While avoiding delay in the initiation of cooling seems logical, the literature is also lacking evidence indicating the ideal time at which to implement cooling. Furthermore, it remains unclear as to which patients may benefit from induced hypothermia. Finally, the literature provides no evidence to support mandating induced hypothermia in the prehospital setting. Given limited prehospital resources, sometimes consisting of only two providers, attention first needs to be given to providing the basic care with the utmost skill. Once the basics are being delivered expertly, consideration can be given to the use of prehospital cooling for the resuscitated cardiac arrest patient in the setting of continued cooling in the hospital.

Post-cardiac arrest syndrome: Epidemiology, pathophysiology, treatment, and prognostication: A scientific statement from the International Liaison Committee on Resuscitation; the American Heart Association Emergency Cardiovascular Care Committee; the Council on Cardiovascular Surgery and Anesthesia; the Council on Cardiopulmonary, Perioperative, and Critical Care; the Council on Clinical Cardiology; the Council on Stroke (Part 1)

AIM OF THE REVIEW

To review the epidemiology, pathophysiology, treatment and prognostication in relation to the post-cardiac arrest syndrome.

METHODS

Relevant articles were identified using PubMed, EMBASE and an American Heart Association EndNote master resuscitation reference library, supplemented by hand searches of key papers. Writing groups comprising international experts were assigned to each section. Drafts of the document were circulated to all authors for comment and amendment.

RESULTS

The 4 key components of post-cardiac arrest syndrome were identified as (1) post-cardiac arrest brain injury, (2) post-cardiac arrest myocardial dysfunction, (3) systemic ischaemia/reperfusion response, and (4) persistent precipitating pathology.

CONCLUSIONS

A growing body of knowledge suggests that the individual components of the postcardiac arrest syndrome are potentially treatable.

Anesthetic management of an off-pump open-heart surgery in a dog

OBSERVATIONS

A 9 year-old, 40 kg, female spayed Bouvier des Flandres was anesthetized for surgical removal of an intra-cardiac mass. Pre-anesthetic work-up included thoracic radiographs, which revealed moderate pleural effusion, and cardiac ultrasound, which identified a mass attached to the wall of the right ventricular outflow tract (RVOT). The mass caused dynamic obstruction of the RVOT during systole. The dog was pre-medicated with intravenous (IV) hydromorphone (0.05 mg kg(-1)). Following pre-oxygenation, anesthesia was induced with ketamine (3.75 mg kg(-1), IV) and diazepam (0.18 mg kg(-1), IV). Anesthesia was maintained with isoflurane in oxygen, an intravenous constant rate infusion (CRI) of fentanyl (10-30 microg kg(-1) hour(-1)) and a CRI of lidocaine (50-200 microg kg(-1) minute(-1)). A right lateral thoracotomy was performed. The heart was stopped transiently with a cold cardioplegic solution for 7.83 minutes to allow the removal of the mass through an open-heart procedure. No cardiopulmonary bypass was used. The heart was successfully restarted after cardiopulmonary resuscitation with internal cardiac massage and internal defibrillation. The dog recovered uneventfully from anesthesia without any apparent neurological sequelae. Post-operative analgesia consisted of intercostal nerve blocks with bupivacaine, CRIs of fentanyl (2-5 microg kg(-1) hour(-1)) and lidocaine (40 microg kg(-1) minute(-1)) and with oral meloxicam (0.1 mg kg(-1)). Five days following surgery, the dog was discharged from the hospital. Histopathology and immunohistochemistry of the mass identified an ectopic thyroid carcinoma.

CONCLUSIONS

This case showed the feasibility of whole body hypothermia and using a cold cardioplegic solution to induce cardiac arrest for a short open-heart procedure.

Therapeutic hypothermia: the Safar vision

At the 2(nd) International Brain Hypothermia conference, in Miami, the late Dr. Peter Safar was honored for his many contributions to the field of therapeutic hypothermia. Therapeutic hypothermia played a central role in his overall vision for optimized resuscitation and neurointensive care, across a large number of potential insults. The successful use of therapeutic hypothermia in comatose patients after cardiac arrest, for example, was already included in the historic first "ABCs" of resuscitation, published by Safar in 1964. This review addresses key historical events in the development and implementation of therapeutic hypothermia across a number of central nervous system insults. A discussion of future potential uses of this therapy in a variety of applications as part of the Safar vision is also presented.

Protein nitration and poly-ADP-ribosylation in brain after rapid exsanguination cardiac arrest in a rat model of emergency preservation and resuscitation

BACKGROUND

Emergency preservation and resuscitation (EPR) of 60 min in rats is achievable with favorable outcome, while 75 min is associated with substantial mortality and impaired neurological outcome in survivors. We hypothesized that 75 min but not 60 min of EPR would be associated with activation of two potential secondary injury cascades in brain as reflected by protein nitration and poly (ADP-ribose) polymerase (PARP) activation.

METHODS

Rats were rapidly exsanguinated over 5 min. After 1 min of cardiac arrest (CA), rats were cooled to a target tympanic temperature of 15 degrees C. After either 60 min or 75 min of CA, resuscitation was achieved via cardiopulmonary bypass (CPB). Rats subjected to CPB only served as controls. Overall performance category (OPC) and neurologic deficit score (NDS) were assessed at 24 h. Protein nitration and poly-ADP-ribosylation were assessed by Western blotting and immunohistochemistry for 3-nitrotyrosine and poly-ADP ribose polymers, respectively, in multiple brain regions.

RESULTS

Neurologic outcome was better in the 60 min vs. the 75 min EPR group (OPC, P<0.001; NDS, P=0.001). Densitometric analysis of the major 64 kD band showed that nitration and PARP activation were significantly increased in hippocampus, cortex and striatum in the 75 min EPR group vs. other groups. However, there were no differences in cerebellum. Analysis of the full protein spectrum showed significantly increased PARP activation only in hippocampus in the 75 min EPR group vs. other groups.

CONCLUSIONS

Extending the duration of EPR beyond the limit that can yield favorable recovery in rats was associated with increased nitration and ribosylation of selected proteins in selectively vulnerable brain regions. The impact of these mechanisms on the outcome remains to be determined.

Post-cardiac arrest syndrome: epidemiology, pathophysiology, treatment, and prognostication. A Scientific Statement from the International Liaison Committee on Resuscitation; the American Heart Association Emergency Cardiovascular Care Committee; the Council on Cardiovascular Surgery and Anesthesia; the Council on Cardiopulmonary, Perioperative, and Critical Care; the Council on Clinical Cardiology; the Council on Stroke

AIM OF THE REVIEW

To review the epidemiology, pathophysiology, treatment and prognostication in relation to the post-cardiac arrest syndrome.

METHODS

Relevant articles were identified using PubMed, EMBASE and an American Heart Association EndNote master resuscitation reference library, supplemented by hand searches of key papers. Writing groups comprising international experts were assigned to each section. Drafts of the document were circulated to all authors for comment and amendment.

RESULTS

The 4 key components of post-cardiac arrest syndrome were identified as (1) post-cardiac arrest brain injury, (2) post-cardiac arrest myocardial dysfunction, (3) systemic ischaemia/reperfusion response, and (4) persistent precipitating pathology.

CONCLUSIONS

A growing body of knowledge suggests that the individual components of the post-cardiac arrest syndrome are potentially treatable.

Devices for rapid induction of hypothermia

In industrial countries it is estimated that the incidence of out-of-hospital sudden cardiac arrest lies between 36 and 128 per 100,000 inhabitants per year. Almost 80% of patients who initially survive a cardiac arrest present with coma lasting more than 1 h. Current therapy during cardiac arrest concentrates on the external support of circulation and respiration with additional drug and electrical therapy. Therapeutic hypothermia provides a new and very effective therapy for neuroprotection in patients after cardiac arrest. It is critical that mild hypothermia has to be applied very early after the ischaemic insult to be effective, otherwise the beneficial effects would be diminished or even abrogated. There are numerous methods available for cooling patients after ischaemic states. Surface cooling devices are non-invasive and range from simple ice packs to sophisticated machines with automatic feedback control. Other non-invasive methods include drugs and cold liquid ventilation. The newer devices have cooling rates comparable to invasive catheter techniques. Invasive cooling methods include the administration of ice-cold fluids intravenously, the use of intravascular cooling catheters, body cavity lavage, extra-corporeal circuits and selective brain cooling. Most of these methods are quite invasive and are still in an experimental stage. The optimal timing and technique for the induction of hypothermia after cardiac arrest have not yet been defined, and it is currently a major topic of ongoing research. The induction of hypothermia after cardiac arrest needs to be an integral component of the initial evaluation and stabilization of the patient.

Therapeutic hypothermia following cardiac arrest: a review of the evidence

AIMS AND OBJECTIVES

This paper aims to undertake a review on the current evidence available on therapeutic hypothermia (TH) following cardiac arrest.

BACKGROUND

The use of TH has been associated as a potential treatment for a number of medical conditions including head injury and cerebral vascular accidents. Within the past decade, there have been numerous studies focusing upon the use of hypothermia following cardiac arrest. This paper evaluates the research on the use of TH following cardiac arrest and provides recommendations for clinical practice. Evidence from randomized controlled trials that are reviewed in this paper found that neurological outcome and mortality were significantly improved following inducing hypothermia following cardiac arrest.

SEARCH STRATEGIES

The following databases were accessed: Bandolier, Embase, Medline, Science Direct, CINAHL, Blackwell Synergy, Nursing Collection, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews and the National Electronic Library for Health. The following key words were used to search the databases: 'Therapeutic hypothermia', 'Induced hypothermia', 'cooling post cardiac arrest' and 'post cardiac arrest care'.

INCLUSION AND EXCLUSION CRITERIA

Only evidences published within the past 10 years and written in English were included. Studies on TH for the treatment of raised intracranial pressure were excluded.

CONCLUSIONS

All adult patients who have return of spontaneous circulation and remain unconscious following cardiac arrest should be considered for TH between 32 degrees C and 34 degrees C for at least 12-24 h as this will improve patient mortality and morbidity. Acute hospitals need to devise policies and guidelines on the use of TH following cardiac arrest that include methods on how to achieve effective cooling by cold i.v. infusions, ice packs or purchasing specific cooling mattresses.

Rapidly induced selective cerebral hypothermia using a cold carotid arterial flush during cardiac arrest in a dog model

PURPOSE

The present study was undertaken to determine whether flushing the carotid artery with normal saline at 4 degrees C (hypothermic carotid arterial flush, HCAF) during cardiac arrest can achieve selective cerebral hypothermia rapidly during cardiac arrest and improve cerebral outcome.

METHODS

Ventricular fibrillation (VF) was induced in fourteen dogs and circulatory arrest was maintained for 9 min. Dogs were then resuscitated by cardiopulmonary resuscitation. The dogs were divided into two groups; a control group (n=7), which underwent precisely the same procedure as the experimental group but not HCAF, and an experimental group (HCAF group; n=7), which received HCAF from 8 min after the onset of VF.

RESULTS

Two dogs in the control group and in the HCAF group died within 72 h after the recovery of spontaneous circulation (ROSC) due to extracerebral complications. The remaining 10 dogs survived to final evaluation at 72 h post-ROSC. In the HCAF group, tympanic temperature decreased from 37.7 degrees C (37.5-37.8) to 34 degrees C in 1 min (1-1.5) from the start of HCAF and was maintained below 34 degrees C until 6.5 min (3-12) after the start of HCAF, whereas oesophageal and rectal temperatures were maintained above 35 degrees C. Neurological deficit scores (0-100%) at 72 h post-ROSC were 42.4% (27.0-80.6) in the control group and 18.4% (14.0-36.0) in the HCAF group (p<0.05).

CONCLUSION

HCAF induced selective cerebral hypothermia rapidly during cardiac arrest and improved neurological deficit scores after 9 min of no blood flow in the described canine cardiac arrest model.

Intra-arrest cooling with delayed reperfusion yields higher survival than earlier normothermic resuscitation in a mouse model of cardiac arrest

BACKGROUND

Therapeutic hypothermia (TH) represents an important method to attenuate post-resuscitation injury after cardiac arrest. Laboratory investigations have suggested that induction of hypothermia before return of spontaneous circulation (ROSC) may confer the greatest benefit. We hypothesized that a short delay in resuscitation to induce hypothermia before ROSC, even at the expense of more prolonged ischemia, may yield both physiological and survival advantages.

METHODS

Cardiac arrest was induced in C57BL/6 mice using intravenous potassium chloride; resuscitation was attempted with CPR and fluid administration. Animals were randomized into three groups (n=15 each): a normothermic control group, in which 8 min of arrest at 37 degrees C was followed by resuscitation; an early intra-arrest hypothermia group, in which 6.5 min of 37 degrees C arrest were followed by 90s of cooling, with resuscitation attempted at 30 degrees C (8 min total ischemia); and a delayed intra-arrest hypothermia group, with 90s cooling begun after 8 min of 37 degrees C ischemia, so that animals underwent resuscitation at 9.5 min.

RESULTS

Animals treated with TH demonstrated improved hemodynamic variables and survival compared to normothermic controls. This was the case even when comparing the delayed intra-arrest hypothermia group with prolonged ischemia time against normothermic controls with shorter ischemia time (7-day survival, 4/15 vs. 0/15, p<0.001).

CONCLUSIONS

Short resuscitation delays to allow establishment of hypothermia before ROSC appear beneficial to both cardiac function and survival. This finding supports the concept that post-resuscitation injury processes begin immediately after ROSC, and that intra-arrest cooling may serve as a useful therapeutic approach to improve survival.

Rapid non-invasive external cooling to induce mild therapeutic hypothermia in adult human-sized swine

AIM OF THE STUDY

Mild therapeutic hypothermia is a promising new therapy for patients resuscitated from cardiac arrest. Early and fast induction of hypothermia seems to be crucial for best results. The aim of the study was to investigate the feasibility and safety of a new surface cooling method using cold metal plates.

SUBJECTS AND METHODS

Twelve adult human-sized swine (79+/-9 kg) were cooled from 38 to 33 degrees C brain temperature. The skin surface was covered with -20 degrees C metal plates (M), as compared to ice packs, alcohol rubs, and fans used in a control group (C). Each method was tested during spontaneous circulation and, after re-warming, during cardiac arrest. Temperatures were recorded continuously. Data are given as mean+/-standard deviation or as median (interquartile range), if not normally distributed. Comparisons between the treatment groups were performed with the independent samples t-test, or the Mann-Whitney rank-sum test.

RESULTS

During spontaneous circulation, cooling rates were 9.3+/-1.4 degrees C/h (M), and 6.1+/-1.4 degrees C/h (C) (p=0.003); no skin lesions were observed. During cardiac arrest, cooling rates were 4.1 degrees C/h (1.8-4.8) (M), and 3.7 degrees C/h (3.1-5.3) (C) (p=0.9); no skin lesions were observed.

CONCLUSION

Cooling with cold metal plates was an effective method for rapid induction of mild therapeutic hypothermia in adult human-sized swine during spontaneous circulation, without any signs of skin damage. This new surface-cooling device, independent of energy supply during use, should be further investigated.

Intranasal selective brain cooling in pigs

BACKGROUND

Special clinical situations where general hypothermia cannot be recommended but can be a useful treatment demand a new approach, selective brain cooling. The purpose of this study was to selectively cool the brain with cold saline circulating in balloon catheters introduced into the nasal cavity in pigs.

MATERIAL AND METHODS

Twelve anaesthetised pigs were subjected to selective cerebral cooling for a period of 6 h. Cerebral temperature was lowered by means of bilaterally introduced nasal balloon catheters perfused with saline cooled by a heat exchanger to 8-10 degrees C. Brain temperature was measured in both cerebral hemispheres. Body temperature was measured in rectum, oesophagus and the right atrium. The pigs were normoventilated and haemodynamic variables were measured continuously. Acid-base and electrolyte status was measured hourly.

RESULTS

Cerebral hypothermia was induced rapidly and within the first 20 min of cooling cerebral temperature was lowered from 38.1+/-0.6 degrees C by a mean of 2.8+/-0.6 to 35.3+/-0.6 degrees C. Cooling was maintained for 6 h and the final brain temperature was 34.7+/-0.9 degrees C. Concomitantly, the body temperature, as reflected by oesophageal temperature was decreased from 38.3+/-0.5 to 36.6+/-0.9 degrees C. No circulatory or metabolic disturbances were noted.

CONCLUSIONS

Inducing selective brain hypothermia with cold saline via nasal balloon catheters can effectively be accomplished in pigs, with no major disturbances in systemic circulation or physiological variables. The temperature gradients between brain and body can be maintained for at least 6 h.