Part 9: Post–Cardiac Arrest Care

Therapeutic hypothermia for acute neurological injuries

Therapeutic hypothermia (TH) is the intentional reduction of core body temperature to 32°C to 35°C, and is increasingly applied by intensivists for a variety of acute neurological injuries to achieve neuroprotection and reduction of elevated intracranial pressure. TH improves outcomes in comatose patients after a cardiac arrest with a shockable rhythm, but other off-label applications exist and are likely to increase in the future. This comprehensive review summarizes the physiology and cellular mechanism of action of TH, as well as different means of TH induction and maintenance with potential side effects. Indications of TH are critically reviewed by disease entity, as reported in the most recent literature, and evidence-based recommendations are provided.

Therapeutic hypothermia in adult cardiac arrest because of drowning

BACKGROUND

Therapeutic hypothermia in adult victims who suffer cardiac arrest following drowning has been applied in only a small number of cases. In the last 4 years, we have employed therapeutic hypothermia to decrease hypoxia-induced brain injury in these patients. The purpose of the present study was to report the results of the treatment of these patients.

METHODS

This study investigated the utilisation of therapeutic hypothermia on consecutive patients with cardiac arrest because of drowning between 2005 and 2008. The study was conducted retrospectively, collecting data by reviewing medical records. Hypothermia, with a target temperature of 32-34°C, was induced for 24 h. Neurological outcomes were classified using the cerebral performance categories (CPCs). The primary outcome was neurological function at discharge.

RESULTS

Twenty patients were treated with therapeutic hypothermia. Four patients (20%) exhibited a favourable neurological outcome (CPC 1-2). Two patients (10%) remained in a vegetative state at discharge (CPC 4), and 14 patients (70%) died (CPC 5). The most common complications during therapeutic hypothermia were pancreatitis and rhabdomyolysis. A longer duration of advanced cardiac life support (P = 0.035), an absence of motor response to pain after 3 days (P = 0.003), an abnormal brain imaging (P = 0.005) and a lack of cortical response to somatosensory evoked potential (P = 0.008) were related to an unfavourable outcome (CPC 3-5).

CONCLUSION

The present study did not demonstrate an advantage of therapeutic hypothermia in adult cardiac arrest after drowning compared with previous studies treated with conventional therapy. Further prospective studies are needed to evaluate the effects of therapeutic hypothermia.

Incidence of treated cardiac arrest in hospitalized patients in the United States

OBJECTIVE

The incidence and incidence over time of cardiac arrest in hospitalized patients is unknown. We sought to estimate the event rate and temporal trends of adult inhospital cardiac arrest treated with a resuscitation response.

DESIGN

Three approaches were used to estimate the inhospital cardiac arrest event rate. First approach: calculate the inhospital cardiac arrest event rate at hospitals (n = 433) in the Get With The Guidelines-Resuscitation registry, years 2003-2007, and multiply this by U.S. annual bed days. Second approach: use the Get With The Guidelines-Resuscitation inhospital cardiac arrest event rate to develop a regression model (including hospital demographic, geographic, and organizational factors), and use the model coefficients to calculate predicted event rates for acute care hospitals (n = 5445) responding to the American Hospital Association survey. Third approach: classify acute care hospitals into groups based on academic, urban, and bed size characteristics, and determine the average event rate for Get With The Guidelines-Resuscitation hospitals in each group, and use weighted averages to calculate the national inhospital cardiac arrest rate. Annual event rates were calculated to estimate temporal trends.

SETTING

Get With The Guidelines-Resuscitation registry.

PATIENTS

Adult inhospital cardiac arrest with a resuscitation response.

MEASUREMENTS AND MAIN RESULTS

The mean adult treated inhospital cardiac arrest event rate at Get With The Guidelines-Resuscitation hospitals was 0.92/1000 bed days (interquartile range 0.58 to 1.2/1000). In hospitals (n = 150) contributing data for all years of the study period, the event rate increased from 2003 to 2007. With 2.09 million annual U.S. bed days, we estimated 192,000 inhospital cardiac arrests throughout the United States annually. Based on the regression model, extrapolating Get With The Guidelines-Resuscitation hospitals to hospitals participating in the American Hospital Association survey projected 211,000 annual inhospital cardiac arrests. Using weighted averages projected 209,000 annual U.S. inhospital cardiac arrests.

CONCLUSIONS

There are approximately 200,000 treated cardiac arrests among U.S. hospitalized patients annually, and this rate may be increasing. This is important for understanding the burden of inhospital cardiac arrest and developing strategies to improve care for hospitalized patients.

Short- and long-latency somatosensory neuronal responses reveal selective brain injury and effect of hypothermia in global hypoxic ischemia

Evoked potentials recorded from the somatosensory cortex have been shown to be an electrophysiological marker of brain injury in global hypoxic ischemia (HI). The evoked responses in somatosensory neurons carry information pertaining to signal from the ascending pathway in both the subcortical and cortical areas. In this study, origins of the subcortical and cortical signals are explored by decomposing the evoked neuronal activities into short- and long-latency responses (SLR and LLR), respectively. We evaluated the effect of therapeutic hypothermia on SLR and LLR during early recovery from cardiac arrest (CA)-induced HI in a rodent model. Twelve rats were subjected to CA, after which half of them were treated with hypothermia (32-34°C) and the rest were kept at normal temperature (36-37°C). Evoked neuronal activities from the primary somatosensory cortex, including multiunit activity (MUA) and local field potential (LFP), were continuously recorded during injury and early recovery. Results showed that upon initiation of injury, LLR disappeared first, followed by the disappearance of SLR, and after a period of isoelectric silence SLR reappeared prior to LLR. This suggests that cortical activity, which primarily underlies the LLR, may be more vulnerable to ischemic injury than SLR, which relates to subcortical activity. Hypothermia potentiated the SLR but suppressed the LLR by delaying its recovery after CA (hypothermia: 38.83 ± 5.86 min, normothermia: 23.33 ± 1.15 min; P < 0.05) and attenuating its amplitude, suggesting that hypothermia may selectively downregulate cortical activity as an approach to preserve the cerebral cortex. In summary, our study reveals the vulnerability of the somatosensory neural structures to global HI and the differential effects of hypothermia on these structures.

The induction of mild hypothermia improves systolic function of the resuscitated porcine heart at no further sympathetic activation

AIM

Mild hypothermia (MH) after cardiac arrest attenuates hypoxic brain injury and improves survival. As MH increases contractility in normal hearts, we hypothesized that MH improves cardiovascular function after cardiac arrest.

METHODS

In 16 anaesthetized pigs (64 ± 2 kg), ventricular fibrillation was induced electrically for 5 min. At 10 min after resuscitation and return of spontaneous circulation (ROSC), pigs were assigned to normothermia (NT, 38°C, n = 8) or MH (33°C, n = 8, intravascular cooling).

RESULTS

At ROSC 6 h vs. baseline, heart rate (HR) was unchanged in NT, but decreased in MH. Cardiac output (CO, l min(-1)) decreased in MH (3.5 ± 0.2 vs. 5.5 ± 0.4, P < 0.05) more than in NT (4.8 ± 0.4 vs. 5.7 ± 0.4, P = ns). Mixed venous oxygen saturation decreased in NT (56 ± 2 vs. 66 ± 3%, P < 0.05), but remained constant in MH (64 ± 2 vs. 65 ± 2%) due to a 35% decrease of whole body oxygen consumption. Left ventricular (LV) dP/dt(max) (mmHg s(-1)) decreased in NT (1163 ± 97 vs. 1665 ± 134, P < 0.05), but was preserved in MH (1602 ± 102 vs. 1603 ± 96), whereas LV relaxation was profoundly slowed during MH. Pressure-volume analysis confirmed improved LV systolic function during MH, but also demonstrated decreased LV end-diastolic distensibility, which was further potentiated by right atrial pacing at baseline HR. MH did not increase plasma catecholamine levels. Spectral analysis of heart rate variability revealed reduced sympathetic activation during MH.

CONCLUSION

The induction of MH after cardiac resuscitation improves systolic myocardial function without further sympathetic activation. A reduced metabolism during MH outweighs a decreased CO and thereby acts favourably on systemic oxygen supply/demand balance.

Protective effects of therapeutic hypothermia in post-resuscitation myocardium

AIM OF THE STUDY

Post-resuscitation therapeutic hypothermia has been recommended because of its neuroprotective effects. However, a few studies have reported the effects of therapeutic hypothermia on the heart, especially in ventricular fibrillation cardiac arrest. The aim of this study was to determine whether therapeutic hypothermia attenuates post-resuscitation myocardial injury in a swine cardiac arrest model.

METHODS

A prospective animal study was performed in the university hospital animal research laboratory. Ventricular fibrillation cardiac arrest was induced in domestic pigs weighing 35-40 kg. After 6 min of no flow time, cardiopulmonary resuscitation was provided to pigs, and the restoration of spontaneous circulation (ROSC) was achieved. The subjects were randomly allocated to a normothermic (NT group, n=5) or hypothermic (HT group, n=5) group. In the HT group, therapeutic hypothermia (core temperature 32-34 °C) was maintained for 24h, and rewarming was performed over a period of 8 h. In the NT group, core temperature was maintained at 37 °C throughout the experiments. Sixty hours after ROSC, blood and myocardial tissues were harvested.

RESULTS

Serum troponin I was not significantly different between the groups. However, myocardial histological damage was attenuated in the HT group. Myocardial ATP contents were higher in the HT group than in the NT group. Immunohistochemistry for apoptosis-related protein showed that survivin expression was higher in the HT group, and XAF1 and cleaved caspase-3 expressions were lower in the HT group than in the NT group.

CONCLUSIONS

Therapeutic hypothermia attenuated histological myocardial injury in ventricular fibrillation cardiac arrest model of pigs while preserving more ATP and decreased apoptosis.

Comparison of the durations of mild therapeutic hypothermia on outcome after cardiopulmonary resuscitation in the rat

BACKGROUND

Current studies have demonstrated that applying therapeutic hypothermia for 12 to 24 hours after resuscitation from cardiac arrest improves the outcomes of cardiopulmonary resuscitation. The present study investigated whether a shorter duration of therapeutic hypothermia induced quickly and early after resuscitation would provide an equal improvement in the outcomes of cardiopulmonary resuscitation.

METHODS AND RESULTS

Ventricular fibrillation was induced and untreated for 8 minutes in 24 male Sprague-Dawley rats. Defibrillation was attempted after 8 minutes of cardiopulmonary resuscitation. Seven minutes after resuscitation, animals were randomized into 4 groups (n=6 each): normothermic, hypothermic-2 hours, hypothermic-5 hours, and hypothermic-8 hours. Animals in the hypothermic groups received rapid cooling, which was started 7 minutes after restoration of spontaneous circulation and maintained at 33±0.5°C for 2, 5, or 8 hours. Normothermic animals were maintained at 37±0.2°C. All animals were anesthetized and ventilated for 8 hours after resuscitation. Blood temperature was significantly decreased in the hypothermic groups. Postresuscitation myocardial function, neurological deficit scores, and 72-hour survival were significantly better in animals treated with hypothermia regardless of the duration of cooling. However, significantly better postresuscitation tissue microcirculation, myocardial ejection fraction, and neurological deficit scores were observed in the hypothermic-2 hours animals.

CONCLUSIONS

In a rat model of cardiopulmonary resuscitation, a shorter duration of mild hypothermia induced rapidly and early after restoration of spontaneous circulation improved postresuscitation microcirculation, myocardial and cerebral functions, and survival as well as, or better than, prolonged duration of hypothermia after resuscitation.

Postresuscitation care

Caring in the emergency department for the patient with return of spontaneous circulation after cardiac arrest is challenging. A coordinated and systematic approach to post-cardiac arrest care can improve the mortality and the chance of meaningful neurologic recovery. By achieving appropriate targets for oxygenation, ventilation, and hemodynamic parameters, along with initiating therapeutic hypothermia and arranging early percutaneous coronary intervention, the emergency physician can have the most significant impact on patients who have just been revived from death.

Airway management in cardiac arrest

Airway management has been emphasized as crucial to effective resuscitation of patients in cardiac arrest. However, recent research has shown that coronary and cerebral perfusion should be prioritized rather than airway management. Endotracheal intubation has been deemphasized. This article reviews the current state of the literature regarding airway management of the patient in cardiac arrest. Ventilatory management strategies are also discussed.

Cardiac arrest and the 2010 advanced cardiac life support guidelines--part IV

The chance of a successful outcome with any cardiac arrest is prompt initiation of hands-only compression at a rate of at least 100 per min, to a depth of 2 in.,with full chest recoil, and no more than a 10-s interruption of compressions. The priority, regardless of being in a private clinic or in a facility using a team approach,is to start compressions and maintain effective compressions with minimal interruptions. Most cardiac arrests are related to ventricular fibrillation and the chance of successfully defibrillating this rhythm is highest at the beginning of the arrest. For every minute a patient is in ventricular fibrillation, his or her chance of survival greatly decreases (Traverset al., 2010). This is why it is extremely important to defibrillate immediately. Once a patient has return of spontaneous circulation,postresuscitation care needs to be implemented. The biggest reason for a patient to develop ventricular fibrillation is an acute coronary syndrome, and this is why the new guidelines have outlined transferring a post arrest patient to a cardiac catheterization laboratory to perform an emergency angiogram and angioplasty. Part of this post arrest management also includes therapeutic hypothermia in those patients who remain comatose after return of spontaneous circulation. This article has reviewed a case study of a postoperative patient who developed ventricular fibrillation and the priorities of care according to the 2010 ACLS guidelines. Watch for more ACLS-based case studies in upcoming articles.

Management of postcardiac arrest myocardial dysfunction

PURPOSE OF REVIEW

Recent recognition of the importance of postresuscitation care has stimulated interest and new reports concerning therapies for postcardiac arrest myocardial dysfunction. Such cardiac dysfunction after successful resuscitation can be severe and even lethal; however, it is also transient emphasizing the importance of early supportive therapies.

RECENT FINDINGS

The most important strategies for dealing with postresuscitation myocardial dysfunction include a community-formalized effort by individual communities to shorten the time from arrest to restoration of spontaneous circulation, use of therapeutic hypothermia for myocardial preservation, not just cerebral, and early coronary angiography and intervention for all survivors with a high suspicion of a cardiac cause for their arrest. Exciting specific therapies targeted for one or another of the ischemia/reperfusion myocardial injuries associated with cardiac arrest include manipulation of the nitric oxide production in the myocardium, treatment of myocardial microcirculatory dysfunction post resuscitation, inhibition of Na+/H+ exchange, and treatment of calcium flux abnormalities.

SUMMARY

Every community should be striving to provide more timely restoration of pulse and circulation, whereas every medical center receiving patients resuscitated from out-of-hospital cardiac arrest should be providing therapeutic hypothermia for both central nervous system and myocardial preservation. The ability and commitment to provide '24/7' early coronary angiography and percutaneous intervention for all resuscitated victims of sudden cardiac death with a likely cardiac cause for their arrest is also key.

Surface cooling after cardiac arrest: effectiveness, skin safety, and adverse events in routine clinical practice

BACKGROUND

Effectiveness of cooling and adverse events (AEs) involving skin have not been intensively evaluated in cardiac arrest survivors treated with therapeutic hypothermia (TH) when induced and maintained with a servomechanism-regulated surface cooling system.

METHODS

Retrospective review of sixty-nine cardiac arrest survivor-events admitted from April 2006-September 2008 who underwent TH using the Medivance Arctic Sun Temperature Management System. A TH database and medical records were reviewed, and nursing interviews conducted. Primary endpoint was time from initiation to target temperature (TT; 32-34 °C). Secondary endpoints were cooling rate, percentage of hypothermia maintenance phase at TT, effect of body-mass index (BMI) on rate of cooling, and AEs.

RESULTS

Mean time to the target temperature (TT) was 2.78 h; 80% of patients achieved TT within 4 h; all did within 8 h. Patients were at TT for 96.7% of hypothermia maintenance; 17% of patients had >1 hourly temperature measurement outside TT range. Mean cooling rate during induction phase was 1.1 °C/h, and was not associated with BMI. Minor skin injury occurred in 14 (20%) patients; 4 (6%) were device-related. Skin injuries were associated with shock (P = 0.04), and decubitus ulcers were associated with left ventricular ejection fraction <45% (P = 0.004). AEs included shivering (94%), hypokalemia (81%), hyperglycemia (57%), pneumonia (23%), bleeding (22%), post-cooling fever (17%), and bacteremia (9%).

CONCLUSIONS

The Arctic Sun Temperature Management System was an effective means of performing therapeutic hypothermia after cardiac arrest. Infrequent skin injuries were associated with vasopressor use and low ejection fraction.

Reversible brain death after cardiopulmonary arrest and induced hypothermia

OBJECTIVE

To describe a patient with transient reversal of findings of brain death after cardiopulmonary arrest and attempted therapeutic hypothermia.

DESIGN

Case report.

SETTING

Intensive care unit of an academic tertiary care hospital.

PATIENT

A 55-yr-old man presented with cardiac arrest preceded by respiratory arrest. Cardiopulmonary resuscitation was performed, spontaneous perfusion restored, and therapeutic hypothermia was attempted for neural protection. After rewarming to 36.5°C, neurologic examination showed no eye opening or response to pain, spontaneous myoclonic movements, sluggishly reactive pupils, absent corneal reflexes, and intact gag and spontaneous respirations. Over 24 hrs, remaining cranial nerve function was lost. The neurologic examination was consistent with brain death. Apnea test and repeat clinical examination after a duration of 6 hrs confirmed brain death. Death was pronounced and the family consented to organ donation. Twenty-four hrs after brain death pronouncement, on arrival to the operating room for organ procurement, the patient was found to have regained corneal reflexes, cough reflex, and spontaneous respirations. The care team faced the challenge of offering an adequate explanation to the patient's family and other healthcare professionals involved.

INTERVENTIONS

Induced hypothermia and brain death determination.

MEASUREMENTS AND MAIN RESULTS

This represents the first published report in an adult patient of reversal of a diagnosis of brain death made in full adherence to American Academy of Neurology guidelines. Although the reversal was transient and did not impact the patient's prognosis, it impacted his eligibility for organ donation and cast doubt about the ability to determine irreversibility of brain death findings in patients treated with hypothermia after cardiac arrest.

CONCLUSIONS

We strongly recommend caution in the determination of brain death after cardiac arrest when induced hypothermia is used. Confirmatory testing should be considered and a minimum observation period after rewarming before brain death testing ensues should be established.

Impact of therapeutic hypothermia onset and duration on survival, neurologic function, and neurodegeneration after cardiac arrest

OBJECTIVE

Post-cardiac-arrest therapeutic hypothermia improves outcomes in comatose cardiac arrest survivors. This study tests the hypothesis that the efficacy of post-cardiac-arrest therapeutic hypothermia is dependent on the onset and duration of therapy.

DESIGN

Prospective randomized laboratory investigation.

SETTING

University research laboratory.

SUBJECTS

A total of 268 male Long Evans rats.

INTERVENTIONS

Post-cardiac-arrest therapeutic hypothermia.

MEASUREMENTS AND MAIN RESULTS

Adult male Long Evans rats that achieved return of spontaneous circulation after a 10-min asphyxial cardiac arrest were block randomized to normothermia (37°C ± 1°C) or therapeutic hypothermia (33°C ± 1°C) initiated 0, 1, 4, or 8 hrs after return of spontaneous circulation and maintained for 24 or 48 hrs. Therapeutic hypothermia initiated 0, 1, 4, and 8 hrs after return of spontaneous circulation resulted in 7-day survival rates of 45%*, 36%*, 36%*, and 14%, respectively, compared to 17% for normothermic controls and survival with good neurologic function rates of 24%*, 24%*, 19%*, and 0%, respectively, compared to 2% for normothermic controls (*p < .05 vs. normothermia). These outcomes were not different when therapeutic hypothermia was maintained for 24 vs. 48 hrs. In contrast, hippocampal CA1 pyramidal neuron counts were 53% ± 27%*, 53% ± 19%*, 51% ± 24%*, and 65% ± 16%* of normal, respectively, when therapeutic hypothermia was initiated 0, 1, 4, or 8 hrs after return of spontaneous circulation compared to 9% in normothermic controls (*p < .01 vs. normothermia). Furthermore, surviving neuron counts were greater when therapeutic hypothermia was maintained for 48 hrs compared to 24 hrs (68% ± 15%* vs. 42% ± 22%, *p < .0001).

CONCLUSIONS

In this study, post-cardiac-arrest therapeutic hypothermia resulted in comparable improvement of survival and survival with good neurologic function when initiated within 4 hrs after return of spontaneous circulation. However, histologic assessment of neuronal survival revealed a potentially broader therapeutic window and greater neuroprotection when therapeutic hypothermia was maintained for 48 vs. 24 hrs.

Neurologic and cardiac benefits of therapeutic hypothermia

Numerous studies have shown the favorable effects of lowering the core temperature of the body in various conditions such as acute myocardial infarction, acute cerebrovascular disease, acute lung injury, and acute spinal cord injury. Therapeutic hypothermia (TH) works at different molecular and cellular levels. TH improves oxygen supply to ischemic areas and increases blood flow by decreasing vasoconstriction, as well as oxygen consumption, glucose utilization, lactate concentration, intracranial pressure, heart rate, cardiac output, and plasma insulin levels. TH has been shown to improve neurologic outcome in acute cerebrovascular accidents. Furthermore, recent studies revealed that TH is a useful method of neuroprotection against ischemic neuronal injury after cardiac arrest. TH in out-of-hospital cardiac arrest is becoming a standard practice nationwide. Further studies need to be performed to develop a better understanding of the benefits and detrimental effects of TH, to identify the most efficacious TH strategy, and the candidates most likely to derive benefit from the procedure. Although many animal studies have demonstrated benefit, larger human clinical trials are recommended to investigate the beneficial effect of TH on reducing myocardial infarction size and coronary reperfusion injuries.

A comparison of cooling techniques to treat cardiac arrest patients with hypothermia

Introduction. We sought to compare the performance of endovascular cooling to conventional surface cooling after cardiac arrest. Methods. Patients in coma following cardiopulmonary resuscitation were cooled with an endovascular cooling catheter or with ice bags and cold-water-circulating cooling blankets to a target temperature of 32.0-34.0°C for 24 hours. Performance of cooling techniques was compared by (1) number of hourly recordings in target temperature range, (2) time elapsed from the written order to initiate cooling and target temperature, and (3) adverse events during the first week. Results. Median time in target temperature range was 19 hours (interquartile range (IQR), 16-20) in the endovascular group versus. 10 hours (IQR, 7-15) in the surface group (P = .001). Median time to target temperature was 4 (IQR, 2.8-6.2) and 4.5 (IQR, 3-6.5) hours, respectively (P = .67). Adverse events were similar. Conclusion. Endovascular cooling maintains target temperatures better than conventional surface cooling.

Post-cardiac arrest syndrome: update on brain injury management and prognostication

OPINION STATEMENT

Treatment of cardiac arrest should focus on maximizing neurologic recovery as well as systemic recovery to ensure the best possible functional outcome. This article focuses on the neurologic care of patients after they have been resuscitated from cardiac arrest. Maximizing neurologic outcome after cardiac arrest requires attention to prevention of primary and secondary brain injury. Primary brain injury such as hypoperfusion and hypoxic injury should be avoided by optimizing hemodynamic goals to maximize cerebral perfusion and maintain normoxia and normocarbia. Secondary brain injury mediated by excitotoxicity and the inflammatory cascade may be mitigated by therapeutic hypothermia. Other strategies that may be beneficial include the treatment of seizures and maintaining normoglycemia. Finally, accurate and timely prognostication is crucial because it influences withdrawal of care and overall mortality. With the adoption of therapeutic hypothermia, the classic prognostic paradigm that was previously used needs to be reexamined. The application of our knowledge of risk factors for poor outcome, serial physical examinations, neurophysiological tests, neuroimaging, and biochemical markers may need to be delayed until after rewarming. We emphasize the importance of a shift in physicians' approach to the management of post-cardiac arrest syndrome, not only in prognostication, but also in the early and aggressive therapies that have been shown to improve survival and quality of life.

Protecting the future: neuroprotective strategies in the pediatric intensive care unit

PURPOSE OF REVIEW

Brain injury is the leading cause of death in pediatric intensive care units, and improvements in therapy and in understanding the pathogenesis are urgently needed. This review presents recent advances in the understanding of neuroprotective therapy and brain-specific monitoring for critically ill pediatric patients.

RECENT FINDINGS

Two neuroprotective strategies are becoming increasingly accepted as they are applied to different mechanisms of brain injury. The rapid application of hypothermia and avoidance of hyperoxia after cardiac arrest and other brain injuries are each being more commonly used as both human and animal data advocating for these approaches accumulate. In addition, more advanced and noninvasive technologies are emerging that are designed to serve as surrogates for brain function and may be used to help predict outcome. Near-infrared spectroscopy is one such commonly used technique that has prompted many studies to understand how to incorporate it into practice.

SUMMARY

Protection of the pediatric brain from both a primary insult and the common subsequent secondary injury is essential for improving long-term neurologic outcomes. Whereas monitoring technology is being constantly modified, it must be proven efficacious in order to understand the utility of new and presumed neuroprotective therapies like hypothermia and avoidance of hyperoxia.

Is hypothermia after cardiac arrest effective in both shockable and nonshockable patients?: insights from a large registry

BACKGROUND

Although the level of evidence of improvement is significant in cardiac arrest patients resuscitated from a shockable rhythm (ventricular fibrillation or pulseless ventricular tachycardia [VF/Vt]), the use of therapeutic mild hypothermia (TMH) is more controversial in nonshockable patients (pulseless electric activity or asystole [PEA/asystole]). We therefore assessed the prognostic value of hypothermia for neurological outcome at hospital discharge according to first-recorded cardiac rhythm in a large cohort.

METHODS AND RESULTS

Between January 2000 and December 2009, data from 1145 consecutive out-of-hospital cardiac arrest patients in whom a successful resuscitation had been achieved were prospectively collected. The association of TMH with a good neurological outcome at hospital discharge (cerebral performance categories level 1 or 2) was quantified by logistic regression analysis. TMH was induced in 457/708 patients (65%) in VF/Vt and in 261/437 patients (60%) in PEA/asystole. Overall, 342/1145 patients (30%) reached a favorable outcome (cerebral performance categories level 1 or 2) at hospital discharge, respectively 274/708 (39%) in VF/Vt and 68/437 (16%) in PEA/asystole (P<0.001). After adjustment, in VF/Vt patients, TMH was associated with increased odds of good neurological outcome (adjusted odds ratio, 1.90; 95% confidence interval, 1.18 to 3.06) whereas in PEA/asystole patients, TMH was not significantly associated with good neurological outcome (adjusted odds ratio, 0.71; 95% confidence interval, 0.37 to 1.36).

CONCLUSIONS

In this large cohort of cardiac arrest patients, hypothermia was independently associated with an improved outcome at hospital discharge in patients presenting with VF/Vt. By contrast, TMH was not associated with good outcome in nonshockable patients. Further investigations are needed to clarify this lack of efficiency in PEA/asystole.

Cardiovascular consequences of cooling in critical care

This commentary discusses a paper by Filseth and colleagues in a previous issue of Critical Care. The authors describe the cardiovascular effects of induced hypothermia, focusing particularly on post-hypothermic ventricular function. The findings indicate that the treatment resulted in reduced systolic but unchanged diastolic left ventricular function with compensatory effects on heart rate and systemic vascular resistance. The novel aspects of this study are the registration of ventricular function using sophisticated, load-independent indices in a clinically relevant, large animal model during the entire cooling and re-warming trajectory of hypothermia therapy.