Resuscitative hypothermia after cardiac arrest in adults:

An experimental study and finite element modeling of head and neck cooling for brain hypothermia

Reducing brain temperature by head and neck cooling is likely to be the protective treatment for humans when subjects to sudden cardiac arrest. This study develops the experimental validation model and finite element modeling (FEM) to study the head and neck cooling separately, which can induce therapeutic hypothermia focused on the brain. Anatomically accurate geometries based on CT images of the skull and carotid artery are utilized to find the 3D geometry for FEM to analyze the temperature distributions and 3D-printing to build the physical model for experiment. The results show that FEM predicted and experimentally measured temperatures have good agreement, which can be used to predict the temporal and spatial temperature distributions of the tissue and blood during the head and neck cooling process. Effects of boundary condition, perfusion, blood flow rate, and size of cooling area are studied. For head cooling, the cooling penetration depth is greatly depending on the blood perfusion in the brain. In the normal blood flow condition, the neck internal carotid artery temperature is decreased only by about 0.13°C after 60min of hypothermia. In an ischemic (low blood flow rate) condition, such temperature can be decreased by about 1.0°C. In conclusion, decreasing the blood perfusion and metabolic reduction factor could be more beneficial to cool the core zone. The results also suggest that more SBC researches should be explored, such as the optimization of simulation and experimental models, and to perform the experiment on human subjects.

Hypothermia for neuroprotection in adults after cardiopulmonary resuscitation

BACKGROUND

Good neurologic outcome after cardiac arrest is hard to achieve. Interventions during the resuscitation phase and treatment within the first hours after the event are critical. Experimental evidence suggests that therapeutic hypothermia is beneficial, and a number of clinical studies on this subject have been published. This review was originally published in 2009.

OBJECTIVES

We performed a systematic review and meta-analysis to assess the effectiveness of therapeutic hypothermia in patients after cardiac arrest. Neurologic outcome, survival and adverse events were our main outcomes. We aimed to perform individual patient data analysis, if data were available, and to form subgroups according to the cardiac arrest situation.

SEARCH METHODS

We searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2001, Issue 7); MEDLINE (1971 to July 2011); EMBASE (1987 to July 2011); CINAHL (1988 to July 2011); PASCAL (2000 to July 2011); and BIOSIS (1989 to July 2011). The original search was performed in January 2007.

SELECTION CRITERIA

We included all randomized controlled trials assessing the effectiveness of therapeutic hypothermia in patients after cardiac arrest, without language restrictions. Studies were restricted to adult populations cooled with any cooling method, applied within six hours of cardiac arrest.

DATA COLLECTION AND ANALYSIS

Validity measures, the intervention, outcomes and additional baseline variables were entered into a database. Meta-analysis was only done for a subset of comparable studies with negligible heterogeneity. For these studies, individual patient data were available.

MAIN RESULTS

We included four trials and one abstract reporting on 481 patients in the systematic review. The updated search resulted in no new studies to include. Quality of the included studies was good in three out of five studies. For the three comparable studies on conventional cooling methods all authors provided individual patient data. With conventional cooling methods, patients in the hypothermia group were more likely to reach a best cerebral performance categories (CPC) score of one or two (five point scale: 1 = good cerebral performance, to 5 = brain death) during the hospital stay (individual patient data; RR 1.55; 95% CI 1.22 to 1.96) and were more likely to survive to hospital discharge (individual patient data; RR 1.35; 95% CI 1.10 to 1.65) compared to standard post-resuscitation care. Across all studies, there was no significant difference in reported adverse events between hypothermia and control.

AUTHORS' CONCLUSIONS

Conventional cooling methods to induce mild therapeutic hypothermia seem to improve survival and neurologic outcome after cardiac arrest. Our review supports the current best medical practice as recommended by the International Resuscitation Guidelines.

Hypothermia for neuroprotection in adults after cardiopulmonary resuscitation

BACKGROUND

Good neurologic outcome after cardiac arrest is hard to achieve. Interventions during the resuscitation phase and treatment within the first hours after the event are critical. Experimental evidence suggests that therapeutic hypothermia is beneficial, and a number of clinical studies on this subject have been published.

OBJECTIVES

We performed a systematic review and meta-analysis to assess the effectiveness of therapeutic hypothermia in patients after cardiac arrest. Neurologic outcome, survival and adverse events were our main outcome parameters. We aimed to perform individual patient data analysis if data were available, and to from subgroups according to the cardiac arrest situation.

SEARCH STRATEGY

We searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, 2007 Issue 1); MEDLINE (1971 to January 2007); EMBASE (1987 to January 2007); CINAHL (1988 to January 2007); PASCAL (2000 to January 2007); and BIOSIS (1989 to January 2007).

SELECTION CRITERIA

We included all randomized controlled trials assessing the effectiveness of the therapeutic hypothermia in patients after cardiac arrest without language restrictions. Studies were restricted to adult populations cooled with any cooling method applied within six hours of cardiac arrest.

DATA COLLECTION AND ANALYSIS

Validity measures, the intervention, outcome parameters and additional baseline variables were entered into the database. Meta-analysis was only done for a subset of comparable studies with negligible heterogeneity. For these studies individual patient data were available.

MAIN RESULTS

Four trials and one abstract reporting on 481 patients were included in the systematic review. Quality of the included studies was good in three out of five included studies. For the three comparable studies on conventional cooling methods all authors provided individual patient data. With conventional cooling methods patients in the hypothermia group were more likely to reach a best cerebral performance categories score of one or two (CPC, five point scale; 1= good cerebral performance, to 5 = brain death) during hospital stay (individual patient data; RR, 1.55; 95% CI 1.22 to 1.96) and were more likely to survive to hospital discharge (individual patient data; RR, 1.35; 95% CI 1.10 to 1.65) compared to standard post-resuscitation care. Across all studies there was no significant difference in reported adverse events between hypothermia and control.

AUTHORS' CONCLUSIONS

Conventional cooling methods to induce mild therapeutic hypothermia seem to improve survival and neurologic outcome after cardiac arrest. Our review supports the current best medical practice as recommended by the International Resuscitation Guidelines.

Prehospital resuscitated cardiac arrest patients: role for induced hypothermia

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

A new method for inducing hypothermia during cardiac arrest

OBJECTIVE

It has been shown that hypothermia induced after successful resuscitation of comatose survivors of ventricular fibrillation cardiac arrest improves survival and neurologic function. Recent studies also suggest that earlier induction of hypothermia may yield even more improvement. We sought to determine if a new pump system, in addition to vigorous external chest compression, could rapidly induce hypothermia during cardiopulmonary resuscitation in a porcine model of cardiac arrest.

METHODS

Nine pigs (25-37 kg) were instrumented with micromanometers and thermocouple probes. Two 8-Fr catheters were placed into the femoral veins. Cardiac arrest was induced with 60-Hz current. After 5 mins of no support, chest compression was performed by a circumferential pneumatic bladder (vest-cardiopulmonary resuscitation). Blood was withdrawn from one catheter by a pump system that maximized flow by servo-control of inlet pressure, was cooled, and was returned through the other catheter. Four dogs were instrumented similarly, and cooling was performed during normal circulation.

RESULTS

In the pigs, baseline temperatures were (mean +/- SEM) 37 +/- 1 degree C. With blood cooling in the external chiller to 10 degrees C, cerebral and right atrial temperatures were reduced by 0.49 +/- 0.09 and 0.67 +/- 0.21 degrees C/min, respectively, for 10 mins. With blood cooling in the external chiller to 4 degrees C, cerebral and right atrial temperatures were reduced by 0.61 +/- 0.18 and 1.56 +/- 0.33 degrees C/min, respectively. Cerebral cooling lagged behind right atrial cooling. There was a strong correlation between coronary perfusion pressure (aortic to right atrial mean decompression-phase pressure) and cerebral cooling rate (r = .79; p < .022). Rates of cooling during normal circulation in dogs were similar.

CONCLUSIONS

Rapid induction of mild hypothermia is feasible with a system that uses venous access, standard access techniques, and external chest compression. Induction of mild hypothermia during cardiac arrest in the field appears feasible and may allow the benefit of very early induction of hypothermia to be determined in patients.