Global hypothermia for neuroprotection after cardiac arrest

Effect of hypothermia on splenic leukocyte modulation and survival duration in severely septic rats

BACKGROUND

Therapeutic hypothermia (HT) in severe septic shock is associated with prolonged survival. We hypothesized that moderate HT would prolong survival and modulate the inflammatory response in rats with septic shock by exerting its therapeutic effect on splenic leukocytes.

MATERIALS AND METHODS

Severe septic shock was created in rats by cecal ligation and incision (CLI). One hour after CLI or laparotomy, rats were randomized to sham, normothermia (NT), or 4 h of HT followed by 2 h of rewarming. HT (31 ± 1°C) was induced using a cooling blanket and monitored via a rectal temperature probe.

RESULTS

Survival duration was 2.78 ± 1.0 h in NT rats and 8.33 ± 0.32 h in HT rats (n = 8/group, P < 0.0001). In separate groups, 3 h after CLI, the spleen weight was significantly smaller in NT rats (769 ± 100 mg) than in HT rats (947 ± 157 mg, P = 0.04). Fluorescent immunostaining of formyl peptide receptors on leukocytes in spleen tissue showed considerably higher formyl peptide receptor expression in HT rats than in NT rats. Significantly elevated proinflammatory cytokines and myeloperoxidase enzyme in plasma were found in NT rats compared with HT rats. Anti-inflammatory cytokine, interleukin-10, was significantly higher in HT rats. Both proinflammatory cytokines and plasma myeloperoxidase were significantly reduced in splenectomized NT rats.

CONCLUSIONS

Moderate hypothermic therapy significantly prolongs the survival duration of rats with severe septic shock. HT dampens the inflammatory response during septic shock by modulating the spleen to an anti-inflammatory mode and preventing the spleen from releasing activated splenic leukocytes into the blood.

Zero-Heat-Flux Thermometry for Non-Invasive Measurement of Core Body Temperature in Pigs

Hypothermia is a severe, unpleasant side effect during general anesthesia. Thus, temperature surveillance is a prerequisite in general anesthesia settings during experimental surgeries. The gold standard to measure the core body temperature (T_core) is placement of a Swan-Ganz catheter in the pulmonary artery, which is a highly invasive procedure. Therefore, T_core is commonly examined in the urine bladder and rectum. However, these procedures are known for their inaccuracy and delayed record of temperatures. Zero-heat-flux (ZHF) thermometry is an alternative, non-invasive method quantifying T_core in human patients by applying a thermosensoric patch to the lateral forehead. Since the porcine cranial anatomy is different to the human’s, the optimal location of the patch remains unclear to date. The aim was to compare three different patch locations of ZHF thermometry in a porcine hypothermia model. Hypothermia (33.0°C T_core) was conducted in 11 anesthetized female pigs (26-30kg). T_core was measured continuously by an invasive Swan-Ganz catheter in the pulmonary artery (T_pulm). A ZHF thermometry device was mounted on three different defined locations. The smallest average difference between T_pulm and T_ZHF during stable temperatures was 0.21 ± 0.16°C at location A, where the patch was placed directly behind the eye. Also during rapidly changing temperatures location A showed the smallest bias with 0.48 ± 0.29°C. Location A provided the most reliable data for T_core. Therefore, the ZHF thermometry patch should be placed directly behind the left temporal corner of the eye to provide a non-invasive method for accurate measurement of T_core in pigs.

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

Context:

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

Evidence Acquisition:

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

Results:

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

Conclusions:

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

Primary outcomes for resuscitation science studies: a consensus statement from the American Heart Association

BACKGROUND AND PURPOSE

The guidelines presented in this consensus statement are intended to serve researchers, clinicians, reviewers, and regulators in the selection of the most appropriate primary outcome for a clinical trial of cardiac arrest therapies. The American Heart Association guidelines for the treatment of cardiac arrest depend on high-quality clinical trials, which depend on the selection of a meaningful primary outcome. Because this selection process has been the subject of much controversy, a consensus conference was convened with national and international experts, the National Institutes of Health, and the US Food and Drug Administration.

METHODS

The Research Working Group of the American Heart Association Emergency Cardiovascular Care Committee nominated subject leaders, conference attendees, and writing group members on the basis of their expertise in clinical trials and a diverse perspective of cardiovascular and neurological outcomes (see the online-only Data Supplement). Approval was obtained from the Emergency Cardiovascular Care Committee and the American Heart Association Manuscript Oversight Committee. Preconference position papers were circulated for review; the conference was held; and postconference consensus documents were circulated for review and comments were invited from experts, conference attendees, and writing group members. Discussions focused on (1) when after cardiac arrest the measurement time point should occur; (2) what cardiovascular, neurological, and other physiology should be assessed; and (3) the costs associated with various end points. The final document underwent extensive revision and peer review by the Emergency Cardiovascular Care Committee, the American Heart Association Science Advisory and Coordinating Committee, and oversight committees.

RESULTS

There was consensus that no single primary outcome is appropriate for all studies of cardiac arrest. The best outcome measure is the pairing of a time point and physiological condition that will best answer the question under study. Conference participants were asked to assign an outcome to each of 4 hypothetical cases; however, there was not complete agreement on an ideal outcome measure even after extensive discussion and debate. There was general consensus that it is appropriate for earlier studies to enroll fewer patients and to use earlier time points such as return of spontaneous circulation, simple "alive versus dead," hospital mortality, or a hemodynamic parameter. For larger studies, a longer time point after arrest should be considered because neurological assessments fluctuate for at least 90 days after arrest. For large trials designed to have a major impact on public health policy, longer-term end points such as 90 days coupled with neurocognitive and quality-of-life assessments should be considered, as should the additional costs of this approach. For studies that will require regulatory oversight, early discussions with regulatory agencies are strongly advised. For neurological assessment of post-cardiac arrest patients, researchers may wish to use the Cerebral Performance Categories or modified Rankin Scale for global outcomes.

CONCLUSIONS

Although there is no single recommended outcome measure for trials of cardiac arrest care, the simple Cerebral Performance Categories or modified Rankin Scale after 90 days provides a reasonable outcome parameter for many trials. The lack of an easy-to-administer neurological functional outcome measure that is well validated in post-cardiac arrest patients is a major limitation to the field and should be a high priority for future development.

MLC901, a traditional Chinese medicine protects the brain against global ischemia

Global ischemia leads to damage in the hippocampal CA1 region and is associated with behavioral deficits. NeuroAid (MLC601 and MLC901), a Traditional Chinese Medicine is used in China for patients after stroke. We have investigated here the effects of MLC901 on brain injury and deficits after global ischemia in the rat. Global ischemia induced by four-vessel occlusion resulted in degeneration of CA1 neurons. MLC901 (0.074 mg/ml) prevented both necrosis and apoptosis of neurons up to 3 h after ischemia. These positive MLC901 effects were associated with a decrease in Bax expression and in levels of the lipid peroxidation product malondialdehyde. Using the PI3-kinase inhibitor LY294002 we also demonstrated the critical role of the Akt pathway in MLC901-mediated neuroprotection. MLC901 enhanced neurogenesis. Furthermore, MLC901 improved functional recovery of rats after global ischemia as assessed by the Morris water maze. In this test MLC901 reduced the increase in escape latency and in swim distance induced by ischemia. MLC901 also improved post-ischemic grip strength. If observations made with rats can be extended to humans, then MLC901 will represent a novel therapeutic strategy after cardiac arrest with a clinically interesting time window of protection.

Temperature monitored on the cuff surface of an endotracheal tube reflects body temperature

OBJECTIVE

When treating patients with cardiac arrest with mild therapeutic hypothermia, a reliable and easy-to-use temperature probe is desirable. This study was conducted to investigate the accuracy and safety of tracheal temperature as a measurement of body temperature.

DESIGN

Observational cohort study.

SETTING

Emergency department of a tertiary care university hospital.

PATIENTS

Patients successfully resuscitated from cardiac arrest intended for mild hypothermia therapy.

INTERVENTIONS

Intubation was performed with a newly developed endotracheal tube that contains a temperature sensor inside the cuff surface. During the cooling, mild hypothermia maintenance, and rewarming phases, the temperature was recorded minute by minute. These data were compared with the temperature assessed by esophageal and blood temperature probes. Thereafter, tracheoscopy was performed to evaluate the condition of the tracheal mucosa.

MEASUREMENTS AND MAIN RESULTS

Approximately 2000 measurements per temperature sensor per patient were recorded in 21 patients. The mean bias between the blood temperature and the tracheal temperature was -0.16 degrees C (limits of agreement: -0.36 degrees C to 0.04 degrees C). The mean bias between the esophageal and tracheal temperatures was -0.22 degrees C (limits of agreement: -0.49 degrees C to 0.07 degrees C). Agreement between temperature probes investigated by the Bland-Altman method showed a mean bias of less than -(1/4) degrees C, and time lags assessed graphically by hysteresis plots were negligible. No clinically relevant injury to the tracheal mucosa was detected.

CONCLUSION

Temperature monitoring at the cuff surface of an endotracheal tube is safe and provides accurate and reliable data in all phases of therapeutically induced mild hypothermia after cardiac arrest.

Non-invasive continuous cerebral temperature monitoring in patients treated with mild therapeutic hypothermia: an observational pilot study

AIM OF THE STUDY

To investigate if body temperature as measured with a prototype of a non-invasive continuous cerebral temperature sensor using the zero-heat-flow method to reflect the oesophageal temperature (core temperature) during mild therapeutic hypothermia after cardiac arrest.

METHODS

In patients over 18 years old with restoration of spontaneous circulation after cardiac arrest, a temperature sensor that uses the zero-heat-flow principle was placed on the forehead during the periods of cooling and re-warming. This temperature was compared to oesophageal temperature as the primary temperature-monitoring site. To assess agreement, we used the Bland-Altman approach and Lin's concordance correlation coefficient.

RESULTS

From September 2008 to April 2009, data from 19 patients were analysed. The median time from restoration of spontaneous circulation until temperature sensor application was 53min (interquartile range, 31; 96). All sensors were removed when a core temperature of 36 degrees C was reached. These measurements were in agreement with oesophageal temperature measurements. No allergic reaction, rash or other irritation occurred on the skin around or under the probes. Bland-Altman results showed a bias of -0.12 degrees C and 95% limits of agreement of -0.59 and +0.36 degrees C. Lin's concordance correlation coefficient was 0.98.

CONCLUSIONS

Body temperature measurements using a non-invasive continuous cerebral temperature sensor prototype that uses the zero-heat-flow method accurately reflected oesophageal temperature measurements during mild therapeutic hypothermia in patients with restoration of spontaneous circulation after cardiac arrest.

Surface cooling for rapid induction of mild hypothermia after cardiac arrest: design determines efficacy

OBJECTIVES

Recently, a novel cooling pad was developed for rapid induction of mild hypothermia after cardiac arrest. The aim of this study was to evaluate the cooling efficacy of three different pad designs for in-hospital cooling.

METHODS

Included in this prospective interventional study were patients with esophageal temperature (Tes) > 34 degrees C on admission. The cooling pad consists of multiple cooling units, filled with a combination of graphite and water, which is precooled to -18 degrees C (design A) or to -9 degrees C (designs B and C) before use. The designs of the cooling pad differed in number, shape, and thickness of the cooling units, with weights of 9.7 kg (design A), 5.3 kg (design B), and 6.2 kg (design C). All three designs were tested in sequential order and were changed according to the results found in the previous trial. Cooling was started after admission until Tes = 34 degrees C, when the cooling pad was removed. The target temperature of Tes = 32-34 degrees C was maintained for 24 hours. Data are presented as medians and interquartile ranges (IQRs = 25%-75%) or proportions.

RESULTS

Cooling rates were 3.4 degrees C/hour (IQR = 2.5-3.7) with design A (n = 12), 2.8 degrees C/hour (IQR = 1.6-3.3) with design B (n = 7), and 2.9 degrees C/hour (IQR = 1.9-3.6) with design C (n = 10; p = 0.5). To reach 34 degrees C, the cooling pad had to be exchanged with a new one due to melting and therefore depleting cooling capacity in three patients with design A, in five patients with design B, and in no patient with design C (p = 0.004).

CONCLUSIONS

With adequate design and storage temperature, the cooling pad proved to be efficient for rapid in-hospital cooling of patients resuscitated from cardiac arrest.

Effects of global cerebral ischemia in the pregnant rat

BACKGROUND AND PURPOSE

Stroke during pregnancy is an emerging concern. Although females undergo many physiological, endocrine, and neurological alterations during pregnancy, the consequences of such changes on outcome after stroke are unclear. It is predicted that increases in steroid hormones observed during pregnancy may confer protective effects against the neurological and pathological sequelae of stroke.

METHODS

We therefore investigated behavioral and histological consequences of a global cerebral ischemia (2-vessel occlusion; 2VO), and how these outcomes correlated with pregnancy-related changes in hormones in Sprague-Dawley rats.

RESULTS

After the 2VO, pregnant rats exhibited poorer memory in a contextual fear conditioning test of learning and memory than sham-treated controls, whereas nonpregnant rats did not. They also showed enhanced CA1 hippocampal neuronal injury. This susceptibility to damage is despite significant pregnancy-associated hypothermia and is probably not associated with alterations in 17beta-estradiol or corticosterone levels.

CONCLUSIONS

These findings are the first to show enhanced neuronal damage in pregnant animals after global cerebral ischemia. They also suggest that the mechanism may be independent of changes in estrogen, corticosterone, and body temperature.

Therapeutic hypothermia after cardiac arrest: implementation and outcome in Finnish intensive care units

BACKGROUND

Therapeutic hypothermia (TH) has been shown to increase survival after out-of-hospital resuscitation. The aim of our study was to find out nationwide implementation and the actual utilization of TH after cardiac arrest in Finnish intensive care units (ICUs). We also determined the outcomes and describe demographic variables of the patients treated with TH.

METHODS

We analyzed a nationwide prospective database and included all adult patients (1,555) treated in ICUs after cardiac arrest during 2004 and 2005.

RESULTS

During 2004 and 2005, 407 patients were treated with TH and TH was used in 19 out of the 20 ICUs. The proportion of cardiac arrest patients treated with TH had increased from 4% in 2002 to 28% in 2005. The incidence of cardiac arrest patients admitted to ICUs was 15/100,000 inhabitants/year. The use of TH varied in different areas of the country from 3.4 to 5.0/100,000 inhabitants/year. In-hospital mortality of TH patients was 32.7% and increased from 13.2% in age group <45 years to 46.0% in age group >75 years (P = 0.0002). Six-month survival was 55.3%. Median (interquartile range) length of stay in the ICU was 3.7 (2.7-5.3) days.

CONCLUSION

In Finland, TH is implemented in almost all ICUs but it is applied only to a selected group of patients. Six months after cardiac arrest, more than half of the patients treated with TH were alive. Among patients treated with TH, younger patients had lower in-hospital mortality.

Feasibility and efficacy of a new non-invasive surface cooling device in post-resuscitation intensive care medicine

AIM OF THE STUDY

There is sufficient evidence that therapeutic hypothermia after non-traumatic cardiac arrest improves neurological outcome and reduces mortality. Many different invasive and non-invasive cooling devices are currently available. Our purpose was to show the efficacy, safety and feasibility using a non-invasive cooling device to control patient temperature within a range of 33-37 degrees C.

MATERIALS AND METHODS

A convenience sample of patients who have been resuscitated successfully from cardiac arrest and were intended for mild hypothermia therapy according to the guidelines and inclusion criteria were studied in a prospective observational case series at an emergency department of a tertiary care university hospital. The Medivance Arctic Sun System provides a new, non-invasive approach to reach a target temperature of 33 degrees C quickly, to maintain the target temperature for 24h, and then to actively re-warm at 0.4 degrees C/h to normothermia. Cooling was applied using the Arctic Sun in 27 patients. Data are presented as median and the interquartile range (25, 75%).

RESULTS

Median age was 58 (49.5, 70) years. Time from cooling start to target temperature was 137 (96, 168)min, cooling rate was 1.2 degrees C/h (0.8, 1.5), stability of target temperature during hypothermia maintenance phase was satisfactory at 33.0 degrees C (32.9, 33.1), and duration of re-warming was 428 (394, 452)min.

CONCLUSION

Using the Arctic Sun System in post-resuscitation care medicine for cooling cardiac arrest survivors is feasible and has proven to be highly effective in lowering patients' temperature rapidly without inducing skin irritations.