Pneumothorax during manned chamber operations: A summary of reported cases.

In-chamber pneumothorax has complicated medically remote professional diving operations, submarine escape training, management of decompression illness, and hospital-based provision of hyperbaric oxygen therapy. Attempts to avoid thoracotomy by combination of high oxygen partial pressure breathing (the concept of inherent unsaturation) and greatly slowed rates of chamber decompression proved successful on several occasions. When this delicate balance designed to prevent the intrapleural gas volume from expanding faster than it contracts proved futile, chest drains were inserted. The presence of pneumothorax was misdiagnosed or missed altogether with disturbing frequency, resulting in wide-ranging clinical consequences. One patient succumbed before the chamber had been fully decompressed. Another was able to ambulate unaided from the chamber before being diagnosed and managed conventionally. In between these two extremes, patients experienced varying degrees of clinical compromise, from respiratory distress to cardiopulmonary arrest, with successful resuscitation. Pneumothorax associated with manned chamber operations is commonly considered to develop while the patient is under pressure and manifests during ascent. However, published reports suggest that many were pre-existing prior to chamber entry. Risk factors included pulmonary barotrauma-induced cerebral arterial gas embolism, cardiopulmonary resuscitation, and medical or surgical procedures usually involving the lung. This latter category is of heightened importance to hyperbaric operations as an iatrogenically induced pneumothorax may take as long as 24 hours to be detected, perhaps long after a patient has been cleared for chamber exposure.

Effect of adjuvant thiamine and ascorbic acid administration on the neurologic outcomes of out-of-hospital cardiac arrest patients: A before-and-after study.

AIM: This study aimed to evaluate the impact of early thiamine and ascorbic acid administration on the neurologic outcome in out-of-hospital cardiac arrest (OHCA) patients treated with targeted temperature management (TTM). METHODS: This before-and-after cohort study used data extracted from two hospitals of the Korean Hypothermia Network prospective registry. The treatment group incorporated patients enrolled from December 2019 to May 2021, that received intravenous thiamine (200 mg) and ascorbic acid (3 g) at 12-hour intervals for a total of six doses. The control group incorporated those enrolled from May 2018 to November 2019. The one-month good neurologic outcome, defined as a Cerebral Performance Category score ≤ 2, between the groups was evaluated using inverse probability of treatment weighting (IPTW). RESULTS: Among the 234 OHCA survivors with TTM, 102 were included in the treatment group and 132 were included in the control group. The one-month (31.4 % vs. 29.5 %, respectively; P = 0.76) good neurologic outcome rates did not differ between the treatment and control groups. After adjusting using the IPTW, vitamin supplementation was not associated with good neurologic outcome (odds ratio [OR], 1.134; 95 % confidence interval [CI], 0.644-1.999; P = 0.66). In subgroup analysis, vitamin administration was significantly associated with a good neurologic outcome in older (≥65 years) patients (adjusted OR, 5.53; 95 % CI, 1.21-25.23; P = 0.03). CONCLUSION: Adjuvant thiamine and ascorbic acid administration in OHCA survivors with TTM did not improve their neurologic outcome after one month. Further clinical trials are warranted.

Comparison of video-assisted education and traditional classroom education in pediatric cardiopulmonary resuscitation education of nursing students.

AIM: This research aimed to compare the effectiveness of traditional classroom education and video-assisted education methods used in Pediatric (CPR) education and determine students' level of satisfaction with the education methods used. METHOD: This research had a randomized, experimental, pretest-posttest design. The research was completed with 98 students (54 in the video-assisted education group and 44 in the traditional classroom education group). The traditional classroom education group received pediatric CPR education through traditional classroom education. On the other hand, the video-assisted education group watched the pediatric CPR education video prepared by the researchers. The level of knowledge of pediatric CPR, the level of pediatric CPR practice skills, and the satisfaction score of each student were evaluated. RESULTS: When the skills levels of the groups were compared, it was determined that there was no statistical difference between the test results. In both groups, the students' mean knowledge and skill scores in the first and second posttests were significantly higher than their pretest knowledge scores. The satisfaction scores of the students in both groups were similar. CONCLUSION: Both methods effectively improve students' pediatric CPR-related knowledge, skills, and satisfaction. IMPLICATIONS FOR PRACTICE: As support for traditional education, using video-assisted visual education materials that nursing students can constantly access when needed is important.

Cardiopulmonary resuscitation during hyperbaric oxygen therapy: a comprehensive review and recommendations for practice.

BACKGROUND: Cardiopulmonary resuscitation (CPR) during hyperbaric oxygen therapy (HBOT) presents unique challenges due to limited access to patients in cardiac arrest (CA) and the distinct physiological conditions present during hyperbaric therapy. Despite these challenges, guidelines specifically addressing CPR during HBOT are lacking. This review aims to consolidate the available evidence and offer recommendations for clinical practice in this context. MATERIALS AND METHODS: A comprehensive literature search was conducted in PubMed, EMBASE, Cochrane Library, and CINAHL using the search string: "(pressure chamber OR decompression OR hyperbaric) AND (cardiac arrest OR cardiopulmonary resuscitation OR advanced life support OR ALS OR life support OR chest compression OR ventricular fibrillation OR heart arrest OR heart massage OR resuscitation)". Additionally, relevant publications and book chapters not identified through this search were included. RESULTS: The search yielded 10,223 publications, with 41 deemed relevant to the topic. Among these, 18 articles (primarily case reports) described CPR or defibrillation in 22 patients undergoing HBOT. The remaining 23 articles provided information or recommendations pertaining to CPR during HBOT. Given the unique physiological factors during HBOT, the limitations of current resuscitation guidelines are discussed. CONCLUSIONS: CPR in the context of HBOT is a rare, yet critical event requiring special considerations. Existing guidelines should be adapted to address these unique circumstances and integrated into regular training for HBOT practitioners. This review serves as a valuable contribution to the literature on "CPR under special circumstances".

High-Dose Insulin for Hyperkalemic Cardiac Arrest.

ABSTRACT: Hyperkalemic cardiac arrest diagnosis can be elusive and management difficult as the cardiac rhythm restoration is often not achieved until the potassium level decreases to a relatively normal level for the patient who suffers the arrest. Current treatment modalities can take hours to achieve this goal. We describe two patients who survived a witnessed hyperkalemic cardiac arrest after being managed with conventional advanced cardiac life support and unconventionally high doses of intravenous insulin.

Comparison of four clinical risk scores in comatose patients after out-of-hospital cardiac arrest.

BACKGROUND AND AIMS: Several different scoring systems for early risk stratification after out-of-hospital cardiac arrest have been developed, but few have been validated in large datasets. The aim of the present study was to compare the well-validated Out-of-hospital Cardiac Arrest (OHCA) and Cardiac Arrest Hospital Prognosis (CAHP)-scores to the less complex MIRACLE2- and Target Temperature Management (TTM)-scores. METHODS: This was a post-hoc analysis of the Targeted Hypothermia versus Targeted Normothermia after Out-of-Hospital Cardiac Arrest (TTM2) trial. Missing data were handled by multiple imputation. The primary outcome was discriminatory performance assessed as the area under the receiver operating characteristics-curve (AUROC), with the outcome of interest being poor functional outcome or death (modified Rankin Scale 4-6) at 6 months after OHCA. RESULTS: Data on functional outcome at 6 months were available for 1829 cases, which constituted the study population. The pooled AUROC for the MIRACLE2-score was 0.810 (95% CI 0.790-0.828), 0.835 (95% CI 0.816-0.852) for the TTM-score, 0.820 (95% CI 0.800-0.839) for the CAHP-score and 0.770 (95% CI 0.748-0.791) for the OHCA-score. At the cut-offs needed to achieve specificities >95%, sensitivities were <40% for all four scoring systems. CONCLUSIONS: The TTM-, MIRACLE2- and CAHP-scores are all capable of providing objective risk estimates accurate enough to be used as part of a holistic patient assessment after OHCA of a suspected cardiac origin. Due to its simplicity, the MIRACLE2-score could be a practical solution for both clinical application and risk stratification within trials.

Thiamine for the Treatment of Cardiac Arrest-Induced Neurological Injury: A Randomized, Blinded, Placebo-Controlled Experimental Study.

Background Thiamine supplementation has demonstrated protective effects in a mouse model of cardiac arrest. The aim of this study was to investigate the neuroprotective effects of thiamine in a clinically relevant large animal cardiac arrest model. The hypothesis was that thiamine reduces neurological injury evaluated by neuron-specific enolase levels. Methods and Results Pigs underwent myocardial infarction and subsequently 9 minutes of untreated cardiac arrest. Twenty minutes after successful resuscitation, the pigs were randomized to treatment with either thiamine or placebo. All pigs underwent 40 hours of intensive care and were awakened for assessment of functional neurological outcome up until 9 days after cardiac arrest. Nine pigs were included in both groups, with 8 in each group surviving the entire intensive care phase. Mean area under the curve for neuron-specific enolase was similar between groups, with 81.5 µg/L per hour (SD, 20.4) in the thiamine group and 80.5 µg/L per hour (SD, 18.3) in the placebo group, with an absolute difference of 1.0 (95% CI, -57.8 to 59.8; P=0.97). Likewise, there were no absolute difference in neurological deficit score at the end of the protocol (2 [95% CI, -38 to 42]; P=0.93). There was no absolute mean group difference in lactate during the intensive care period (1.1 mmol/L [95% CI, -0.5 to 2.7]; P=0.16). Conclusions In this randomized, blinded, placebo-controlled trial using a pig cardiac arrest model with myocardial infarction and long intensive care and observation for 9 days, thiamine showed no effect in changes to functional neurological outcome or serum levels of neuron-specific enolase. Thiamine treatment had no effect on lactate levels after successful resuscitation.

Effects of temperature control on hyperthermia-related cardiac dysfunction in a porcine model of cardiac arrest.

The outcome of cardiac arrest is worse when there is fever after spontaneous circulation is restored (ROSC). The purpose of this study was to investigate the mechanism of post-ROSC cardiac dysfunction after hyperthermia treatment and the effects of temperature control. Twenty-four male Bama minipigs were randomized into 3 groups (8 per group): CPR + controlled normothermia (CN), CPR + hyperthermia (HT), and CPR + therapeutic mild hypothermia (TMH). Defibrillation was given to pigs with ventricular fibrillation after 8 min of untreated fibrillation. Subsequently, these animals received the post-ROSC treatments of hyperthermia (38 °C), controlled normothermia (37 °C) or hypothermia (33 °C) according to the groups. Hemodynamic parameters, left ventricular ejection fraction, blood samples and myocardial tissues were assessed. At 24 h after the post-ROSC treatments, the pigs treated with hyperthermia showed increments in heart rate and plasma cardiac troponin I, and decreases in mean arterial pressure, cardiac index, and left ventricular ejection fraction, compared to those with the controlled normothermia pigs. However, the deterioration of the above parameters can be attenuated by TMH. The pigs in the TMH group also had a reduced percentage of apoptotic cardiomyocytes, an increased anti-apoptotic Bcl-2/Bax ratio and a decreased caspase-3 activity in myocardium, as compared with both controlled normothermia and hyperthermia pigs. In conclusion, hyperthermia is associated with a worse myocardial dysfunction. TMH improves hyperthermia-induced myocardial dysfunction by attenuating apoptosis in a porcine model of cardiac arrest.

Systemic toxic effects of Mesocain® in routine surgical practice upon iatrogenic overdose requiring cardiopulmonary resuscitation - case report.

This case report of a patient with a traumatic head injury provides an example of a systemic toxic reaction to a local anesthetic. Clinical signs of a systemic toxic reaction and hemorrhagic shock may initially be similar: tachycardia, hypotension and unconsciousness. The purpose is thus to remind that even the treatment of a minor injury can develop into a life-threatening condition. When a skin wound is treated using suture under local or regional anesthesia, the annual incidence rate of systemic toxic reactions is 1:3,000 and that of death is 1:30,000.

[Effect of electroacupuncture at Baihui ameliorated neurologic deficit and hemodynamic stability in rat model of post-cardiac arrest syndrome].

OBJECTIVE: To observe the results of electroacupuncture (EA) on the resuscitation of a rat model of asphyxia cardiac arrest (CA). And to explore its effect on the neurologic deficits and hemodynamic instability of post-cardiac arrest syndrome (PCAS). METHODS: A total of 107 male SD rats were randomly divided into sham, CA, and EA groups. Each group received arterial catheterization and tracheal intubation. The sham group was not induced asphyxia. Asphyxial cardiac arrest was established by endotracheal tube clamping. Rats in the CA group received basic respiratory support and fluid resuscitation in return of spontaneous circulation (ROSC) and rats in the EA group received EA at Baihui based on the treatment of CA group after ROSC, with a dense-dispersed wave at frequencies of 4-20 Hz, while the current intensity was adjusted minimum to induce a twitch of the scalp, the course of treatment was 30 minutes. The baseline data, hemodynamics after ROSC, neurological deficit score (NDS), pathological changes of brain tissue, and levels of serum biomarker were recorded and compared among the three groups. The 72-hour survival of rats was analyzed by Kaplan-Meier survival curve. Hematoxylin-eosin (HE) staining was used to observe the pathological changes of necrotic neurons in the hippocampal CA1 region of rat brain. Meanwhile, Nissl staining and TdT-mediated dUTP nick-end labeling (TUNEL) were used to detect cell apoptosis and injury. RESULTS: Compared with the CA group, the mean arterial pressure (MAP) in the EA group increased significantly at 15 minutes after ROSC [mmHg (1 mmHg ≈ 0.133 kPa): 125.00 (94.00, 136.25) vs. 92.00 (72.00, 122.50), P < 0.05]. There was no significant difference in the NDS score between the EA group and the sham group. Still, the NDS score of the rats in the CA group at 6 hours after ROSC were significantly lower than that in the sham group (46.00±10.61 vs. 80.00±0.00, P < 0.05). Kaplan-Meier survival curve analysis showed that EA did not improve the 72-hour survival rate of rats (100% in the sham group, 25% in the CA group, and 30% in the EA group, P > 0.05). The analysis by TUNEL showed that the apoptosis rate of neurons in CA1 region of the hippocampus in EA group at 6 hours after ROSC was significantly lower than that in CA group [(62.84±2.67)% vs. (71.29±3.70)%, P < 0.05]. Compared with the CA group, the level of serum S100 calcium binding protein B (S100B) in the EA group at 6 hours after ROSC was significantly lower (ng/L: 19.30±13.87 vs. 132.28±31.67, P < 0.05), but there were no significant differences in the levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) between these two groups. CONCLUSIONS: In the present study, EA at Baihui can stabilize the hemodynamic, moreover, it has a particular neuroprotective effect on PCAS rats. Still, EA at Baihui does not reduce the systemic inflammatory response and improve the survival rate of rats, and its mechanism remains to be verified in further research.

DNACPR Decisions: Aligning Law, Guidance, and Practice.

Do not attempt cardiopulmonary resuscitation (DNACPR) decisions are a means to consider in advance the appropriateness of CPR measures if an acute crisis arises. During the COVID-19 pandemic, problems with such decisions, for example the putting in place of DNACPR decisions for all residents of certain care homes, received a lot of attention, prompting a Care Quality Commission (CQC) report with recommendations for improvement. Building on the CQC report, our article addresses a cluster of legal uncertainties surrounding DNACPR decisions, in particular about the grounds for such decisions and the correct procedures for the legally required consultation, including with whom to consult. This article will also analyse commonly used DNACPR forms, as well as the Recommended Summary Plan for Emergency Care and Treatment (ReSPECT) form, which aims to incorporate DNACPR decisions as part of more holistic end-of-life care planning. The analysis shows that all forms exhibit shortcomings in reflecting the legal requirements for DNACPR decisions. We recommend a number of changes to the forms aimed at rendering DNACPR practice compliant with the law and more protective of the person's human rights.

Perlite is a suitable model material for experiments investigating breathing in high density snow.

Outdoor breathing trials with simulated avalanche snow are fundamental for the research of the gas exchange under avalanche snow, which supports the development of the international resuscitation guidelines. However, these studies have to face numerous problems, including unstable weather and variable snow properties. This pilot study examines a mineral material perlite as a potential snow model for studies of ventilation and gas exchange parameters. Thirteen male subjects underwent three breathing phases-into snow, wet perlite and dry perlite. The resulting trends of gas exchange parameters in all tested materials were similar and when there was a significant difference observed, the trends in the parameters for high density snow used in the study lay in between the trends in dry and wet perlite. These findings, together with its stability and accessibility year-round, make perlite a potential avalanche snow model material. Perlite seems suitable especially for simulation and preparation of breathing trials assessing gas exchange under avalanche snow, and potentially for testing of new avalanche safety equipment before their validation in real snow.The study was registered in ClinicalTrials.gov on January 22, 2018; the registration number is NCT03413878.

The evolution of cardiopulmonary resuscitation: Global productivity and publication trends.

BACKGROUND/OBJECTIVE: There is still no comprehensive bibliometric study in the literature on cardiopulmonary resuscitation (CPR), an important topic in emergency medicine, the number of global studies on which is increasing day by day. In this study, it was aimed to analyze the scientific articles on CPR published between 1980 and 2020 by statistical methods and to evaluate the subject holistically. METHODS: Articles on CPR published between 1980 and 2020 were downloaded from the Web of Science (WoS) database and analyzed using statistical methods. Network visualization maps were used to identify trending topics. Nonlinear regression analysis (exponential model) was used to estimate the number of articles in the coming years. Correlation studies were conducted using the Spearman correlation coefficient. RESULTS: A total of 21,623 publications were found. Of these publications, 14,818 (68.5%) were articles. The top 3 contributing countries to the literature were the United States (5281, 35.6%), Germany (1458, 9.8%), and the United Kingdom (1152, 7.7%). The 3 most active institutions were the University of Washington (417), University of Pittsburgh (361), and University of Arizona (240). The 3 journals with the most publications were Resuscitation (2822), Critical Care Medicine (522), and the American Journal of Emergency Medicine (421). CONCLUSION: In this comprehensive study, a summary of 14,818 articles was presented. The trending topics in CPR research in recent years are out-of-hospital cardiac arrest, extracorporeal membrane oxygenation, cardio, simulation, in-hospital cardiac arrest, extracorporeal life support, extracorporeal cardiopulmonary resuscitation, targeted management temperature, and outcome. This article may be a useful resource on CPR global outcomes for clinicians and scientists.

A Descriptive Study of Chaplains' Code Blue Responses.

BACKGROUND: Family presence during resuscitation is the compassionate practice of allowing a patient's family to witness treatment for cardiac or respiratory arrest (code blue event) when appropriate. Offering family presence during resuscitation as an interprofessional practice is consistent with patient- and family-centered care. In many institutions, the role of family facilitator is not formalized and may be performed by various staff members. At the large academic institution of this study, the family facilitator is a member of the chaplain staff. OBJECTIVES: To examine the frequency of family presence during code blue events and describe the role of chaplains as family facilitators. METHODS: Chaplain staff documented information about their code responses daily from January 2012 through April 2020. They documented their response time, occurrence of patient death, presence of family at the event, and services they provided. A retrospective data review was performed. RESULTS: Chaplains responded to 1971 code blue pages during this time frame. Family members were present at 53% of code blue events. Chaplains provided multiple services, including crisis support, compassionate presence, spiritual care, bereavement support, staff debriefing, and prayer with and for patients, families, and staff. CONCLUSIONS: Family members are frequently present during code blue events. Chaplains are available to respond to all such events and provide a variety of immediate and longitudinal services to patients, families, and members of the health care team. Their experience in crisis management, spiritual care, and bereavement support makes them ideally suited to serve as family facilitators during resuscitation events.

Being an end-of-life doula.

This article describes what an end-of-life doula is, the training involved and how these individuals can help someone achieve the death they want, reflecting on a role that has existed traditionally in communities for centuries without formal recognition. How end-of-life doulas work holistically but also practically will be considered, outlining how keeping the dying person's preferences and wishes at the heart of their care is the primary aim. Recent issues such as advance care planning, digital legacy and Do Not Attempt Cardiopulmonary Resuscitation (DNACPR) will be reflected on through the lens of the end-of-life doula, with the aim of encouraging open discussion and death oracy as a life skill and creating a space to make choices about the end of life. Also explored is how an end-of-life doula works within an integrative model of healthcare, working in partnership with health professionals.

Advance care planning for patients with COVID-19: a communication guide.

In view of the high morbidity and mortality associated with COVID-19, early and honest conversations with patients about goals of care are vital. Advance care planning in its traditional manner may be difficult to achieve given the unpredictability of the disease trajectory. Despite this, it is crucial that patients' care wishes are explored as this will help prevent inappropriate admissions to hospital and to critical care, improve symptom control and advocate for patient choice. This article provides practical tips on how to translate decisions around treatment escalation plans into conversations, both face-to-face and over the phone, in a sensitive and compassionate manner. Care planning conversations for patients with COVID-19 should be individualised and actively involve the patient. Focusing on goals of care rather than ceilings of treatment can help to alleviate anxiety around these conversations and will remind patients that their care will never cease. Using a framework such as the 'SPIKES' mnemonic can help to structure this conversation. Verbally conveying empathy will be key, particularly when wearing personal protective equipment or speaking to relatives over the phone. It is also important to make time to recognise your own emotions during and/or after these conversations.

Automated mechanical cardiopulmonary resuscitation devices versus manual chest compressions in the treatment of cardiac arrest: protocol of a systematic review and meta-analysis comparing machine to human.

INTRODUCTION: Cardiac arrest is a leading cause of death in industrialised countries. Cardiopulmonary resuscitation (CPR) guidelines follow the principles of closed chest compression as described for the first time in 1960. Mechanical CPR devices are designed to improve chest compression quality, thus considering the improvement of resuscitation outcomes. This protocol outlines a systematic review and meta-analysis methodology to assess trials investigating the therapeutic effect of automated mechanical CPR devices at the rate of return of spontaneous circulation, neurological state and secondary endpoints (including short-term and long-term survival, injuries and surrogate parameters for CPR quality) in comparison with manual chest compressions in adults with cardiac arrest. METHODS AND ANALYSIS: A sensitive search strategy will be employed in established bibliographic databases from inception until the date of search, followed by forward and backward reference searching. We will include randomised and quasi-randomised trials in qualitative analysis thus comparing mechanical to manual CPR. Studies reporting survival outcomes will be included in quantitative analysis. Two reviewers will assess independently publications using a predefined data collection form. Standardised tools will be used for data extraction, risks of bias and quality of evidence. If enough studies are identified for meta-analysis, the measures of association will be calculated by dint of bivariate random-effects models. Statistical heterogeneity will be evaluated by I2-statistics and explored through sensitivity analysis. By comprehensive subgroup analysis we intend to identify subpopulations who may benefit from mechanical or manual CPR techniques. The reporting follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. ETHICS AND DISSEMINATION: No ethical approval will be needed because data from previous studies will be retrieved and analysed. Most resuscitation studies are conducted under an emergency exception for informed consent. This publication contains data deriving from a dissertation project. We will disseminate the results through publication in a peer-reviewed journal and at scientific conferences. PROSPERO REGISTRATION NUMBER: CRD42017051633.

Effects of Shenfu Injection () on Inflammatory Response during Post-Resuscitation Myocardial Dysfunction after Cardiac Arrest in Swine.

OBJECTIVE: To investigate whether Shenfu Injection (SFI, ) can alleviate post-resuscitation myocardial dysfunction by inhibiting the inflammatory response. METHODS: After 8 min of ventricular fibrillation and 2 min of basic life support, 24 pigs were randomly divided into 3 groups (n=8), which were given intravenous bolus injections of SFI (1.0 mL/kg), epinephrine (EP, 0.02 mg/kg) and normal saline (SA), respectively. The animals were sacrificed at 24 h after restoration of spontaneous circulation (ROSC), and serum interleuking-6 (IL-6) and tumor necrosis factor-α (TNF-α) levels were measured by enzyme-linked immunosorbent assay (ELISA); expressions of Toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) mRNAs and proteins were determined by RT-PCR and Western blot, respectively. RESULTS: Compared with the EP and the SA groups, the ultrastructure of myocardial cells were slightly damaged and the systolic function of the left ventricle was markedly improved in the SFI group at 24 h after ROSC (P<0.05). In addition, compared with the EP and SA groups, the SFI group also showed significantly reduced levels of serum IL-6 and TNF-α, protein and mRNA levels of myocardial NF- κB and TLR4 (P<0.05). CONCLUSIONS: Activation of TLR4/NF-κB signaling pathway may be involved in the pathological mechanisms of post-resuscitation myocardial dysfunction. SFI may block NF-κB-mediated inflammatory response by reducing the activity of NF- κB and the level of TNF-α, thus playing a protective role in post-resuscitation myocardial dysfunction.