Intra-arrest selective brain cooling improves success of resuscitation in a porcine model of prolonged cardiac arrest

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.

Temperature Control After Cardiac Arrest: A Narrative Review

Cardiac arrest (CA) is a critical public health issue affecting more than half a million Americans annually. The main determinant of outcome post-CA is hypoxic-ischemic brain injury (HIBI), and temperature control is currently the only evidence-based, guideline-recommended intervention targeting secondary brain injury. Temperature control is a key component of a post-CA care bundle; however, conflicting evidence challenges its wide implementation across the vastly heterogeneous population of CA survivors. Here, we critically appraise the available literature on temperature control in HIBI, detail how the evidence has been integrated into clinical practice, and highlight the complications associated with its use and the timing of neuroprognostication after CA. Future clinical trials evaluating different temperature targets, rates of rewarming, duration of cooling, and identifying which patient phenotype benefits from different temperature control methods are needed to address these prevailing knowledge gaps.

Targeted Temperature Management in Postresuscitation Care After Incorporating Results of the TTM2 Trial

Cardiac arrest still accounts for a substantial proportion of cardiovascular related deaths and is associated with a tremendous risk of neurological injury and, among the few survivors, poor quality of life. Critical determinants of survival and long‐term functional status after cardiac arrest are timely initiation of cardiopulmonary resuscitation and use of an external defibrillator for patients with a shockable rhythm. Outcomes are still far from satisfactory, despite ongoing efforts to improve cardiac arrest response systems, as well as elaborate postresuscitation algorithms. Targeted temperature management at the wide range between 32 °C and 36 °C has been one of the main therapeutic strategies to improve neurological outcome in postresuscitation care. This recommendation has been mainly based on 2 small randomized trials that were published 20 years ago. Most recent data derived from the TTM2 (Targeted Hypothermia Versus Targeted Normothermia After Out‐of‐Hospital Cardiac Arrest) trial, which included 1861 patients, challenge this strategy. It showed no benefit of targeted hypothermia at 33 °C over normothermia at 36 °C to 37.5 °C with fever prevention. Because temperature management at lower temperatures also correlated with an increased risk of side effects without any benefit in the TTM2 trial, a modification of the guidelines with harmonizing temperature management to normothermia might be necessary.

Computational modeling of targeted temperature management in post-cardiac arrest patients

Our core body temperature is held around [Formula: see text]C by an effective internal thermoregulatory system. However, various clinical scenarios have a more favorable outcome under external temperature regulation. Therapeutic hypothermia, for example, was found beneficial for the outcome of resuscitated cardiac arrest patients due to its protection against cerebral ischemia. Nonetheless, practice shows that outcomes of targeted temperature management vary considerably in dependence on individual tissue damage levels and differences in therapeutic strategies and protocols. Here, we address these differences in detail by means of computational modeling. We develop a multi-segment and multi-node thermoregulatory model that takes into account details related to specific post-cardiac arrest-related conditions, such as thermal imbalances due to sedation and anesthesia, increased metabolic rates induced by inflammatory processes, and various external cooling techniques. In our simulations, we track the evolution of the body temperature in patients subjected to post-resuscitation care, with particular emphasis on temperature regulation via an esophageal heat transfer device, on the examination of the alternative gastric cooling with ice slurry, and on how anesthesia and the level of inflammatory response influence thermal behavior. Our research provides a better understanding of the heat transfer processes and therapies used in post-cardiac arrest patients.

Selective Brain Cooling: A New Horizon of Neuroprotection

Therapeutic hypothermia (TH), which prevents irreversible neuronal necrosis and ischemic brain damage, has been proven effective for preventing ischemia-reperfusion injury in post-cardiac arrest syndrome and neonatal encephalopathy in both animal studies and clinical trials. However, lowering the whole-body temperature below 34°C can lead to severe systemic complications such as cardiac, hematologic, immunologic, and metabolic side effects. Although the brain accounts for only 2% of the total body weight, it consumes 20% of the body's total energy at rest and requires a continuous supply of glucose and oxygen to maintain function and structural integrity. As such, theoretically, temperature-controlled selective brain cooling (SBC) may be more beneficial for brain ischemia than systemic pan-ischemia. Various SBC methods have been introduced to selectively cool the brain while minimizing systemic TH-related complications. However, technical setbacks of conventional SBCs, such as insufficient cooling power and relatively expensive coolant and/or irritating effects on skin or mucosal interfaces, limit its application to various clinical settings. This review aimed to integrate current literature on SBC modalities with promising therapeutic potential. Further, future directions were discussed by exploring studies on interesting coping skills in response to environmental or stress-induced hyperthermia among wild animals, including mammals and birds.

Effect of intra-arrest trans-nasal evaporative cooling in out-of-hospital cardiac arrest: a pooled individual participant data analysis

Background

Randomized trials have shown that trans-nasal evaporative cooling initiated during CPR (i.e. intra-arrest) effectively lower core body temperature in out-of-hospital cardiac arrest patients. However, these trials may have been underpowered to detect significant differences in neurologic outcome, especially in patients with initial shockable rhythm.

Methods

We conducted a post hoc pooled analysis of individual data from two randomized trials including 851 patients who eventually received the allocated intervention and with available outcome (“as-treated” analysis). Primary outcome was survival with favourable neurological outcome at hospital discharge (Cerebral Performance Category [CPC] of 1–2) according to the initial rhythm (shockable vs. non-shockable). Secondary outcomes included complete neurological recovery (CPC 1) at hospital discharge.

Results

Among the 325 patients with initial shockable rhythms, favourable neurological outcome was observed in 54/158 (34.2%) patients in the intervention and 40/167 (24.0%) in the control group (RR 1.43 [confidence intervals, CIs 1.01–2.02]). Complete neurological recovery was observed in 40/158 (25.3%) in the intervention and 27/167 (16.2%) in the control group (RR 1.57 [CIs 1.01–2.42]). Among the 526 patients with initial non-shockable rhythms, favourable neurological outcome was in 10/259 (3.8%) in the intervention and 13/267 (4.9%) in the control group (RR 0.88 [CIs 0.52–1.29]; p = 0.67); survival and complete neurological recovery were also similar between groups. No significant benefit was observed for the intervention in the entire population.

Conclusions

In this pooled analysis of individual data, intra-arrest cooling was associated with a significant increase in favourable neurological outcome in out-of-hospital cardiac arrest patients with initial shockable rhythms. Future studies are needed to confirm the potential benefits of this intervention in this subgroup of patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03583-9.

The impact of intra-arrest hypothermia

PURPOSE OF REVIEW

To address the impact of therapeutic hypothermia induced already during cardiopulmonary resuscitation (i.e. intra-arrest cooling) and its association with neurologic functional outcome.

RECENT FINDINGS

Intra-arrest cooling is superior than post-ROSC cooling to mitigate brain injuries in experimental models of cardiac arrest. The delayed initiation of hypothermia in human studies may not have adequately addressed the underlying pathophysiology of ischemia and reperfusion. The assessment of early initiation of cooling has been complicated by increased rate of hemodynamic adverse events caused by infusion of cold intravenous fluids. These adverse events have been more deleterious in patients with initial shockable rhythms. A recent randomized study shows that an alternative intra-arrest cooling method using trans-nasal evaporative cooling was well tolerated and effective to shorten time to target temperature. However, the neurologic outcomes (CPC 1-2 at 90 days) in favor of intra-arrest cooling compared to hospital cooling (34.8% vs 25.9%, P = 0.11) in patients with initial shockable rhythms did not reach statistical significance.

SUMMARY

Therapeutic intra-arrest hypothermia can be initiated safely at the scene of the arrest using transnasal evaporative cooling. The potential beneficial effect of intra-arrest cooling on neurologic recovery in patients with initial shockable rhythms should be explored further.

Time to intra-arrest therapeutic hypothermia in out-of-hospital cardiac arrest patients and its association with neurologic outcome: a propensity matched sub-analysis of the PRINCESS trial

PURPOSE

To study the association between early initiation of intra-arrest therapeutic hypothermia and neurologic outcome in out-of-hospital cardiac arrest.

METHODS

A prespecified sub-analysis of the PRINCESS trial (NCT01400373) that randomized 677 bystander-witnessed cardiac arrests to transnasal evaporative intra-arrest cooling initiated by emergency medical services or cooling started after hospital arrival. Early cooling (intervention) was defined as intra-arrest cooling initiated < 20 min from collapse (i.e., ≤ median time to cooling in PRINCESS). Propensity score matching established comparable control patients. Primary outcome was favorable neurologic outcome, Cerebral Performance Category (CPC) 1-2 at 90 days. Complete recovery (CPC 1) was among secondary outcomes.

RESULTS

In total, 300 patients were analyzed and the proportion with CPC 1-2 at 90 days was 35/150 (23.3%) in the intervention group versus 24/150 (16%) in the control group, odds ratio (OR) 1.92, 95% confidence interval (CI) 0.95-3.85, p = .07. In patients with shockable rhythm, CPC 1-2 was 29/57 (50.9%) versus 17/57 (29.8%), OR 3.25, 95%, CI 1.06-9.97, p = .04. The proportion with CPC 1 at 90 days was 31/150 (20.7%) in the intervention group and 17/150 (11.3%) in controls, OR 2.27, 95% CI 1.12-4.62, p = .02. In patients with shockable rhythms, the proportion with CPC 1 was 27/57 (47.4%) versus 12/57 (21.1%), OR 5.33, 95% CI 1.55-18.3, p = .008.

CONCLUSIONS

In the whole study population, intra-arrest cooling initiated < 20 min from collapse compared to cooling initiated at hospital was not associated with improved favorable neurologic outcome. In the subgroup with shockable rhythms, early cooling was associated with improved favorable outcome and complete recovery.

Inducing Brain Cooling Without Core Temperature Reduction in Pigs Using a Novel Nasopharyngeal Method: An Effectiveness and Safety Study

BACKGROUND

Acute brain lesions constitute an alarming public health concern. Neuroprotective therapies have been implemented to stabilize, prevent, or reduce brain lesions, thus improving neurological outcomes and survival rates. Hypothermia is the most effective approach, mainly attributed to the reduction in cellular metabolic activity. Whole-body cooling is currently implemented by healthcare professionals; however, adverse events are frequent, limiting the potential benefits of therapeutic hypothermia. Therefore, selective methods have been developed to reduce adverse events while delivering neuroprotection. Nasopharyngeal approaches are the safest and most effective methods currently considered. Our primary objective was to determine the effects of a novel nasopharyngeal catheter on the brain temperature of pigs.

METHODS

In this prospective, non-randomized, interventional experimental trial, 10 crossbred pigs underwent nasopharyngeal cooling for 60 min followed by 15 min of rewarming. Nasopharyngeal catheters were inserted into the left nostril and properly positioned at the nasopharyngeal cavity.

RESULTS

Nasopharyngeal cooling was associated with a decrease in brain temperature, which was more significant in the left cerebral hemisphere (p = 0.01). There was a reduction of 1.47 ± 0.86 °C in the first 5 min (p < 0.001), 2.45 ± 1.03 °C within 10 min (p < 0.001), and 4.45 ± 1.36 °C after 1 h (p < 0.001). The brain-core gradient was 4.57 ± 0.87 °C (p < 0.001). Rectal, esophageal, and pulmonary artery temperatures and brain and systemic hemodynamic parameters, remained stable during the procedure. Following brain cooling, values of oxygen partial pressure in brain tissue significantly decreased. No mucosal lesions were detected during nasal, pharyngeal, or oral inspection after nasopharyngeal catheter removal.

CONCLUSIONS

In this study, a novel nasopharyngeal cooling catheter effectively induced and maintained exclusive brain cooling when combined with effective counter-warming methods. Exclusive brain cooling was safe with no device-related local or systemic complications and may be desired in selected patient populations.

The Effect of Therapeutic Mild Hypothermia on Brain Microvascular Endothelial Cells During Ischemia-Reperfusion Injury

BACKGROUND

To determine the cerebral protective effects of mild hypothermia (MH) on cerebral microcirculation.

METHODS

We established ischemia-reperfusion (I/R) injury and MH treatment models with rat brain microvascular endothelial cells (RBMECs) in vitro and examined the apoptotic changes. The cultured RBMECs were randomly divided into the control group, I/R group, and MH group, which was further divided into two subgroups: intra-ischemia hypothermia (IIH) and post-ischemia hypothermia (PIH). Cell morphological changes were assessed using fluorescence microscopy. Apoptotic rates were obtained by flow cytometry. Expressions of caspase-3, Bax, and Bcl-2 were analyzed by Western blot.

RESULTS

I/R injury in vitro induced apoptosis of RBMECs. The apoptotic rates in the control group, I/R group, and MH group were 0.13, 19.04, and 13.13%, respectively (P < 0.01). Compared with the I/R group, the MH group showed a significant decrease in the number of apoptotic cells, mainly in stage I apoptotic cells (P < 0.0083). The caspase-3 and Bax expressions were significantly enhanced (P < 0.05) in RBMECs after I/R injury, while substantial decreases in Bcl-2 expression were noted (P < 0.05). Following MH intervention, the increase in caspase-3 and Bax expression was suppressed (P < 0.05), while Bcl-2 expression significantly increased. The apoptotic rates or protein expressions between the two subgroups were not different significantly (P > 0.05).

CONCLUSIONS

These results indicate that MH could inhibit RBMEC apoptosis by preventing pro-apoptotic cells and early apoptotic cells from progressing to intermediate and advanced stages. This may be due to the effect of MH on I/R-induced apoptotic gene expression changes.

Efficacy of Selective Brain Cooling Using a Nasopharyngeal Method in Piglets

BACKGROUND

Mild hypothermia is an effective neuroprotective strategy for a variety of acute brain injuries. Cooling the nasopharynx may offer the capability to cool the brain selectively due to anatomic proximity of the internal carotid artery to the cavernous sinus. This study investigated the feasibility and efficiency of nasopharyngeal brain cooling by continuously blowing room temperature or cold air at different flow rates into the nostrils of normal newborn piglets.

METHODS

Experiments were conducted on thirty piglets (n = 30, weight = 2.7 ± 1.5 kg). Piglets were anesthetized with 1–2% isoflurane and were randomized to receive one of four different nasopharyngeal cooling treatments: I. Room temperature at a flow rate of 3–4 L min(−1) (n = 6); II. −1 ± 2 °C at a flow rate of 3–4 L min(−1) (n = 6); III. Room temperature at a flow rate of 14–15 L min(−1) (n = 6); IV. −8 ± 2 °C at a flow rate of 14–15 L min(−1) (n = 6). To control for the normal thermal regulatory response of piglets without nasopharyngeal cooling, a control group of piglets (n = 6) had their brain temperature monitored without nasopharyngeal cooling. The duration of treatment was 60 min, with additional 30 min of observation.

RESULTS

In group I, median cooling rate was 1.7 ± 0.9 °C/h by setting the flow rate of room temperature air to 3–4 L min(−1). Results of comparing different temperatures and flow rates in the nasopharyngeal cooling approach reveal that the brain temperature could be reduced rapidly at a rate of 5.5 ± 1.1 °C/h by blowing −8 ± 2 °C air at a flow rate of 14–15 L min(−1).

CONCLUSIONS

Nasopharyngeal cooling via cooled insufflated air can lower the brain temperature, with higher flows and lower temperatures of insufflated air being more effective.

Development of new equipment for intra-arrest brain cooling that uses cooled oxygen in the lungs: volunteer study

Aims

Many experimental studies have reported that intra-arrest cooling during cardiac arrest is a promising treatment to mitigate brain injury. However, there is no clinically established method for cooling the brain during cardiac arrest. We hypothesized that, as blood flow in the lungs must be very slow during cardiopulmonary resuscitation, the blood could be cooled by ventilating the lungs with cooled oxygen like a radiator, and that this cooled blood would in turn cool the brain. The aim of this study was to develop equipment to cool oxygen for this purpose and to confirm its safety on a group of volunteers.

Methods

We developed new equipment that cools oxygen by running it through a vinyl chloride coil submerged in a bottle of water and frozen at -80°C. Using this equipment, seven volunteers were given oxygen by mask, and their blood pressure, heart rate, and peripheral saturation of oxygen were measured. The temperature in the mask was also measured.

Results

This equipment was able to decrease the temperature in the mask to -5°C at the Jackson Rees circuit for an oxygen flow of 10 L/min. Among the volunteer group, vital signs were unchanged and the temperature in the mask decreased from 30.1 ± 2.6°C (mean ± standard deviation) to 15.9 ± 9.6°C. No adverse effects were observed in the volunteers after experimentation.

Conclusion

We successfully developed new equipment to cool oxygen and established its safety in a volunteer study.

Prehospital therapeutic hypothermia after out-of-hospital cardiac arrest: a systematic review and meta-analysis

BACKGROUND

The effectiveness and safety of the infusion of ice-cold fluids for prehospital hypothermia in cardiac arrest victims are unclear. This study assessed its effects in adult victims of out-of-hospital cardiac arrest.

METHODS

An online search of PubMed and Cochrane Library databases was performed. Cooling methods were limited to ice-cold fluid perfusion. Randomized controlled trials were included in this review. The main outcomes were body temperature at hospital arrival, survival to hospital discharge, neurological recovery, incidence of pulmonary edema, and the rate of rearrest.

RESULTS

Among 1155 citations, 5 studies were included in this meta-analysis. The pooled analysis of these studies revealed no differences in survival to hospital discharge, favorable neurological outcomes, and incidence of pulmonary edema between the treatment group and control group. There were significant differences in body temperature at hospital arrival (I² = 0.0%, χ² = 2.58, MD = -0.760, 95% confidence interval = -0.938 to -0.581, P < .001) and the rate of rearrest (I² = 0.0%, χ² = 0.69, 95% confidence interval = 1.109 to 1.479, P = .031).

CONCLUSIONS

Prehospital therapeutic hypothermia induced by intravenous infusion of ice-cold fluids in patients with out-of-hospital cardiac arrest decreased body temperature at hospital arrival but did not improve survival to hospital discharge and favorable neurological outcomes. Ice-cold fluid infusion did not increase the incidence of pulmonary edema but increased the incidence of rearrests.

Safety and feasibility of the RhinoChill immediate transnasal evaporative cooling device during out-of-hospital cardiopulmonary resuscitation: A single-center, observational study

We investigated feasibility and safety of the RhinoChill (RC) transnasal cooling system initiated before achieving a protected airway during cardiopulmonary resuscitation (CPR) in a prehospital setting.In out-of-hospital cardiac arrest (OHCA), transnasal evaporative cooling was initiated during CPR, before a protected airway was established and continued until either the patient was declared dead, standard institutional systemic cooling methods were implemented or cooling supply was empty. Patients were monitored throughout the hypothermia period until either death or hospital discharge. Clinical assessments and relevant adverse events (AEs) were documented over this period of time.In total 21 patients were included. Four were excluded due to user errors or meeting exclusion criteria. Finally, 17 patients (f = 6; mean age 65.5 years, CI95%: 57.7-73.4) were analyzed. Device-related AEs, like epistaxis or nose whitening, occurred in 2 patients. They were mild and had no consequence on the patient's outcome. According to the field reports of the emergency medical services (EMS) personnel, no severe technical problems occurred by using the RC device that led to a delay or the impairment of quality of the CPR.Early application of the RC device, during OHCA is feasible, safe, easy to handle, and does not delay or hinder CPR, or establishment of a secure intubation. For efficacy and further safety data additional studies will be needed.

Integration of Attributes from Non-Linear Characterization of Cardiovascular Time-Series for Prediction of Defibrillation Outcomes

Objective

The timing of defibrillation is mostly at arbitrary intervals during cardio-pulmonary resuscitation (CPR), rather than during intervals when the out-of-hospital cardiac arrest (OOH-CA) patient is physiologically primed for successful countershock. Interruptions to CPR may negatively impact defibrillation success. Multiple defibrillations can be associated with decreased post-resuscitation myocardial function. We hypothesize that a more complete picture of the cardiovascular system can be gained through non-linear dynamics and integration of multiple physiologic measures from biomedical signals.

Materials and Methods

Retrospective analysis of 153 anonymized OOH-CA patients who received at least one defibrillation for ventricular fibrillation (VF) was undertaken. A machine learning model, termed Multiple Domain Integrative (MDI) model, was developed to predict defibrillation success. We explore the rationale for non-linear dynamics and statistically validate heuristics involved in feature extraction for model development. Performance of MDI is then compared to the amplitude spectrum area (AMSA) technique.

Results

358 defibrillations were evaluated (218 unsuccessful and 140 successful). Non-linear properties (Lyapunov exponent > 0) of the ECG signals indicate a chaotic nature and validate the use of novel non-linear dynamic methods for feature extraction. Classification using MDI yielded ROC-AUC of 83.2% and accuracy of 78.8%, for the model built with ECG data only. Utilizing 10-fold cross-validation, at 80% specificity level, MDI (74% sensitivity) outperformed AMSA (53.6% sensitivity). At 90% specificity level, MDI had 68.4% sensitivity while AMSA had 43.3% sensitivity. Integrating available end-tidal carbon dioxide features into MDI, for the available 48 defibrillations, boosted ROC-AUC to 93.8% and accuracy to 83.3% at 80% sensitivity.

Conclusion

At clinically relevant sensitivity thresholds, the MDI provides improved performance as compared to AMSA, yielding fewer unsuccessful defibrillations. Addition of partial end-tidal carbon dioxide (PetCO₂) signal improves accuracy and sensitivity of the MDI prediction model.

A review of compression, ventilation, defibrillation, drug treatment, and targeted temperature management in cardiopulmonary resuscitation

Objective:

Important studies of cardiopulmonary resuscitation (CPR) techniques influence the development of new guidelines. We systematically reviewed the efficacy of some important studies of CPR.

Data Sources:

The data analyzed in this review are mainly from articles included in PubMed and EMBASE, published from 1964 to 2014.

Study Selection:

Original articles and critical reviews about CPR techniques were selected for review.

Results:

The survival rate after out-of-hospital cardiac arrest (OHCA) is improving. This improvement is associated with the performance of uninterrupted chest compressions and simple airway management procedures during bystander CPR. Real-time feedback devices can be used to improve the quality of CPR. The recommended dose, timing, and indications for adrenaline (epinephrine) use may change. The appropriate target temperature for targeted temperature management is still unclear.

Conclusions:

New studies over the past 5 years have evaluated various aspects of CPR in OHCA. Some of these studies were high-quality randomized controlled trials, which may help to improve the scientific understanding of resuscitation techniques and result in changes to CPR guidelines.

Prearrest hypothermia improved defibrillation and cardiac function in a rabbit ventricular fibrillation model

BACKGROUND

Hypothermia when cardiopulmonary resuscitation begins may help achieve defibrillation and return of spontaneous circulation (ROSC), but few data are available.

OBJECTIVE

The objective of this study was to determine whether prearrest hypothermia improved defibrillation and cardiac function in a rabbit ventricular fibrillation (VF) model.

RESULTS

Thirty-six New Zealand rabbits were randomized equally to receive normothermia (Norm) (~39°C), post-ROSC hypothermia (~33°C), or prearrest hypothermia (~33°C). Ventricular fibrillation was induced by alternating current. After 4 minutes of VF, rabbits were defibrillated and given cardiopulmonary resuscitation until ROSC or no response (≥30 minutes). Hemodynamics and electrocardiogram were monitored; N-terminal pro-brain natriuretic peptideand troponin I were determined by enzyme-linked immunosorbent assay. Myocardial histology and echocardiographic data were evaluated. First-shock achievement of perfusion rhythm was more frequent in prearrest than normothermic animals (7/12 vs 1/12; P=.027). After ROSC, dp/dtmax was higher in prearrest than normothermic animals (P<.001). Left ventricular end-systolic pressure was higher in prearrest than normothermic animals (P=.001). At 240 minutes after ROSC, troponin I and N-terminal pro-brain natriuretic peptide were lower in prearrest than normothermic animals (15.74±2.26 vs 25.09±1.85 ng/mL and 426±23 vs 284±45 pg/mL, respectively), the left ventricular ejection fraction and cardiac output were lower in the Norm group than other 2 groups (P<.01). Myocardial histology was more disturbed in normothermic than post-ROSC and prearrest animals, but was not different in the latter 2 groups.

CONCLUSIONS

Induction of hypothermia before VF led to improved cardiac function in a rabbit VF model through improving achievement of perfusing rhythm by first-shock defibrillation and facilitating resuscitation.

Sodium nitroprusside-enhanced cardiopulmonary resuscitation facilitates intra-arrest therapeutic hypothermia in a porcine model of prolonged ventricular fibrillation

OBJECTIVES

The aim of this study was to assess the effect of sodium nitroprusside-enhanced cardiopulmonary resuscitation on heat exchange during surface cooling. We hypothesized that sodium nitroprusside-enhanced cardiopulmonary resuscitation would decrease the time required to reach brain temperature less than 35°C compared to active compression-decompression plus impedance threshold device cardiopulmonary resuscitation alone, in the setting of intra-cardiopulmonary resuscitation cooling. We further hypothesized that the addition of epinephrine during sodium nitroprusside-enhanced cardiopulmonary resuscitation would mitigate heat exchange.

DESIGN

Prospective randomized animal investigation.

SETTING

Preclinical animal laboratory.

SUBJECTS

Female farm pigs (n=28).

INTERVENTIONS

After 10 minutes of untreated ventricular fibrillation, animals were randomized to three different protocols: sodium nitroprusside-enhanced cardiopulmonary resuscitation (n=8), sodium nitroprusside-enhanced cardiopulmonary resuscitation plus epinephrine (n=10), and active compression-decompression plus impedance threshold device alone (control, n=10). All animals received surface cooling at the initiation of cardiopulmonary resuscitation. Sodium nitroprusside-enhanced cardiopulmonary resuscitation included active compression-decompression plus impedance threshold device plus abdominal binding and 2 mg of sodium nitroprusside at 1, 4, and 8 minutes of cardiopulmonary resuscitation. No epinephrine was used during cardiopulmonary resuscitation in the sodium nitroprusside-enhanced cardiopulmonary resuscitation group. Control and sodium nitroprusside-enhanced cardiopulmonary resuscitation plus epinephrine groups received 0.5 mg of epinephrine at 4.5 and 9 minutes of cardiopulmonary resuscitation. Defibrillation occurred after 10 minutes of cardiopulmonary resuscitation. After return of spontaneous circulation, an Arctic Sun (Medivance, Louiseville, CO) was applied at maximum cooling on all animals. The primary endpoint was the time required to reach brain temperature less than 35°C beginning from the time of cardiopulmonary resuscitation initiation. Data are presented as mean±SEM.

MEASUREMENTS AND MAIN RESULTS

The time required to reach a brain temperature of 35°C was decreased with sodium nitroprusside-enhanced cardiopulmonary resuscitation versus control or sodium nitroprusside-enhanced cardiopulmonary resuscitation plus epinephrine (24±6 min, 63±8 min, and 50±9 min, respectively; p=0.005). Carotid blood flow was higher during cardiopulmonary resuscitation in the sodium nitroprusside-enhanced cardiopulmonary resuscitation group (83±15 mL/min vs 26±7 mL/min and 35±5 mL/min in the control and sodium nitroprusside-enhanced cardiopulmonary resuscitation plus epinephrine groups, respectively; p=0.001).

CONCLUSIONS

This study demonstrates that sodium nitroprusside-enhanced cardiopulmonary resuscitation facilitates intra-cardiopulmonary resuscitation hypothermia. The addition of epinephrine to sodium nitroprusside-enhanced cardiopulmonary resuscitation during cardiopulmonary resuscitation reduced its improvement in heat exchange.

Outcomes of asphyxial cardiac arrest patients who were treated with therapeutic hypothermia: a multicentre retrospective cohort study

INTRODUCTION

While therapeutic hypothermia (TH) is in clinical use, its efficacy in certain patient groups is unclear. This study was designed to describe the characteristics and outcomes of patients with out-of-hospital cardiac-arrest (OHCA) caused by asphyxia, who were treated with TH.

PATIENTS AND METHODS

A multicentre, retrospective, registry-based study was performed using data from the period 2007-2012. Comatose patients who were treated with TH after asphyxial cardiac arrest were included, while those who with cardiac arrest attributed to hanging, drowning or gas intoxication were excluded.

RESULTS

Of a total of 932 OHCA patients in the registry, 111 were enrolled in this study. The mean age was 65.8±16.3 years with individuals who were ≥65 years of age accounted for 61.3% of the cohort. Foreign-body airway obstruction was the most common cause (70.3%) of the cardiac arrest. Eighty patients (72.1%) presented with an initial non-shockable rhythm. In all institutions target TH temperatures were 32-34°C, but TH maintenance times varied. A total of 52 patients (46.8%) survived, of whom six patients (5.4%) showed a good neurologic outcome (cerebral performance category scale 1-2). The pupil light reflex, corneal reflex and time to return of spontaneous circulation (p=0.012, 0.015 and 0.032, respectively) were associated with survival. Witnessed arrest, age, previous lung disease, bystander basic life support and time factors were not associated with survival.

CONCLUSION

About half of patients who underwent TH after asphyxial cardiac arrest survived, but a very small number showed a good neurologic outcome. The TH maintenance times were not uniform in these patients. Additional research regarding both the appropriate TH guidelines for patients with asphyxial cardiac arrest and improvement of their neurologic outcome is needed.

Rapid Induction of COOLing in Stroke Patients (iCOOL1): a randomised pilot study comparing cold infusions with nasopharyngeal cooling

Introduction

Induction methods for therapeutic cooling are under investigated. We compared the effectiveness and safety of cold infusions (CI) and nasopharyngeal cooling (NPC) for cooling induction in stroke patients.

Methods

A prospective, open-label, randomised (1:1), single-centre pilot trial with partially blinded safety endpoint assessment was conducted at the neurointensive care unit of Heidelberg University. Intubated stroke patients with an indication for therapeutic cooling and an intracranial pressure (ICP)/temperature brain probe were randomly assigned to CI (4°C, 2L at 4L/h) or NPC (60L/min for 1 h). Previous data suggested a maximum decrease of tympanic temperature for CI (2.1L within 35 min) after 52 min. Therefore the study period was 1 hour (15 min subperiods I-IV). The brain temperature course was the primary endpoint. Secondary measures included continuous monitoring of neurovital parameters and extracerebral temperatures. Statistical analysis based on repeated-measures analysis of variance.

Results

Of 221 patients screened, 20 were randomized within 5 months. Infusion time of 2L CI was 33 ± 4 min in 10 patients and 10 patients received NPC for 60 min. During active treatment (first 30 min), brain temperature decreased faster with CI than during NPC (I: −0.31 ± 0.2 versus −0.12 ± 0.1°C, P = 0.008; II: −1.0 ± 0.3 versus −0.49 ± 0.3°C, P = 0.001). In the CI-group, after the infusion was finished, the intervention no longer decreased brain temperature, which increased after 3.5 ± 3.3 min. Oesophageal temperature correlated best with brain temperature during CI and NPC. Tympanic temperature reacted similarly to relative changes of brain temperature during CI, but absolute values slightly differed. CI provoked three severe adverse events during subperiods II-IV (two systolic arterial pressure (SAP), one shivering) compared with four in the NPC-group, all during subperiod I (three SAP, one ICP). Classified as possibly intervention-related, two cases of ventilator failure occurred during NPC.

Conclusions

In intubated stroke patients, brain cooling is faster during CI than during NPC. Importantly, contrary to previous expectations, brain cooling stopped soon after CI cessation. Oesophageal but neither bladder nor rectal temperature is suited as surrogate for brain temperature during CI and NPC. Several severe adverse events in CI and in NPC demand further studying of safety.

Trial registration

ClinicalTrials.gov NCT01573117. Registered 31 March 2012

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0582-1) contains supplementary material, which is available to authorized users.

Comparative effect of hypothermia and adrenaline during cardiopulmonary resuscitation in rabbits

BACKGROUND

Therapeutic hypothermia was shown to facilitate resumption of spontaneous circulation when instituted during cardiac arrest. Here, we investigated whether it directly improved the chance of successful resuscitation independently of adrenaline administration in rabbits. We further evaluated the direct effect of hypothermia on vascular function in vitro.

METHODS

In a first set of experiments, four groups of anesthetized rabbits were submitted to 15 min of cardiac arrest and subsequent cardiopulmonary resuscitation (CPR). The "control" group underwent CPR with only cardiac massage and defibrillation attempts. Two other groups received cold or normothermic saline infusion during CPR (20 mL/kg of NaCl 0.9% at 4°C or 38°C, respectively). In a last group, the animals received adrenaline (15 µg/kg intravenously) during CPR. In a second set of experiments, we evaluated at 32°C vs. 38°C the vascular function of aortic rings withdrawn from healthy rabbits or after cardiac arrest.

RESULTS

In the first set of experiments, cardiac massage efficiency was improved by adrenaline but neither by hypothermic nor normothermic saline administration. Resumption of spontaneous circulation was observed in five of eight animals after adrenaline as compared with none of eight in other groups. Defibrillation rates were conversely similar among groups (7/8 or 8/8). In the second set of experiments, in vitro hypothermia (32°C) was not able to prevent the dramatic alteration of vascular function observed after cardiac arrest. It also did not directly modify vasocontractile or the vasodilating functions in healthy conditions.

CONCLUSION

In rabbits, hypothermia did not exert a direct hemodynamic or vascular effect that might explain its beneficial effect during CPR.

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

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

Intra-arrest hypothermia during cardiac arrest: a systematic review

Introduction

Therapeutic hypothermia is largely used to protect the brain following return of spontaneous circulation (ROSC) after cardiac arrest (CA), but it is unclear whether we should start therapeutic hypothermia earlier, that is, before ROSC.

Methods

We performed a systematic search of PubMed, EMBASE, CINAHL, the Cochrane Library and Ovid/Medline databases using "arrest" OR "cardiac arrest" OR "heart arrest" AND "hypothermia" OR "therapeutic hypothermia" OR "cooling" as keywords. Only studies using intra-arrest therapeutic hypothermia (IATH) were selected for this review. Three authors independently assessed the validity of included studies and extracted data regarding characteristics of the studied cohort (animal or human) and the main outcomes related to the use of IATH: Mortality, neurological status and cardiac function (particularly, rate of ROSC).

Results

A total of 23 animal studies (level of evidence (LOE) 5) and five human studies, including one randomized controlled trial (LOE 1), one retrospective and one prospective controlled study (LOE 3), and two prospective studies without a control group (LOE 4), were identified. IATH improved survival and neurological outcomes when compared to normothermia and/or hypothermia after ROSC. IATH was also associated with improved ROSC rates and with improved cardiac function, including better left ventricular function, and reduced myocardial infarct size, when compared to normothermia.

Conclusions

IATH improves survival and neurological outcome when compared to normothermia and/or conventional hypothermia in experimental models of CA. Clinical data on the efficacy of IATH remain limited.

Transnasal cooling: a Pandora's box of transnasal patho-physiology

The innovative concept of transnasal evaporative cooling for therapeutic hypothermia in cardio-pulmonary-cerebro-resuscitation has therapeutic implications with evidence of rapid and selective brain cooling; however, this author wants to elicit that this concept may hold answers for many physiological phenomena which have not been explored or completely understood up till now. To affirm the physiological role of transnasal cooling, the innovative non-invasive brain temperature monitoring can help the investigators to explore and understand the following transnasal pathophysiological phenomena: (1) understanding correlation of brain temperature and sinus headache secondary to nasal blockade, (2) exploring the therapeutic role of nasal oxygen for prevention of delirium in intubated patients, (3) realizing the impact of controlled enclosed environments on the mood and affect of the inhabitants, (4) understanding the etio-pathogenesis of claustrophobia after excluding the confounding factors of morbid obesity, severe cardiopulmonary disease and incapacitating musculoskeletal diseases, (5) exploring the anthropological role of male pattern of moustache, beard and hair loss, and (6) possible development of a coolant moustache as proposed by the author. In summary, transnasal pathophysiology offers many promising lines of fruitful research to explore the non-olfactory physiological functions of nose in human beings.

Early selective trans-nasal cooling during CPR improves success of resuscitation in a porcine model of prolonged pulseless electrical activity cardiac arrest

AIM OF STUDY

In the present study, we investigated trans-nasal cooling in settings of pulseless electrical activity (PEA). We hypothesized that early trans-nasal cooling during CPR improves outcomes when cardiac arrest is associated with PEA.

METHODS

Ventricular fibrillation (VF) was electrically induced in 16 domestic male pigs weighing 40±3 kg. After 14 min of untreated VF, PEA was induced following delivery of one or more electrical shocks. One min after onset of PEA, CPR was started, including chest compression and ventilation. Each animal received 5 min of CPR prior to defibrillation attempt. CPR and resuscitation efforts were discontinued at 15 min unless return to spontaneous circulation was achieved. In 8 animals, selective trans-nasal cooling was begun coincident with start of CPR and 8 randomized controls were identically treated except for trans-nasal cooling. Mean aortic pressure was continuously measured together with aortic and right atrial pressure and nasal, body and right jugular vein temperatures. Coronary perfusion pressure (CPP) was computed from measured data.

RESULTS

Six of eight animals were resuscitated after early trans-nasal cooling, while only one untreated control was resuscitated (p=0.012). Nasal, body and jugular vein temperatures decreased after cooling. At PC (precordial compression) 5 min, the cooled group recorded a higher CPP (25±5 mmHg) than the non-cooled group (15±4 mmHg, p=0.001).

CONCLUSION

When selective trans-nasal cooling was initiated during CPR in the animal model of prolonged cardiac arrest with PEA, CPP was higher and the likelihood of return of spontaneous circulation was improved.

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.