Peritoneal cooling for mild cerebral hypothermia after cardiac arrest in dogs

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.

Therapeutic hypothermia after cardiopulmonary resuscitation

Full cerebral recovery after cardiopulmonary resuscitation is still a rare event. Unfortunately, up to now, no specific and outcome-improving therapy was available after such events. From several cases it is known that low body and brain temperature during a cardiocirculatory arrest improves the neurological outcome following these events. As it is not possible in acute events to induce hypothermia beforehand, whether cooling after the insult could also be protective was evaluated. After animal studies in the 1990s and first clinical pilot trials of mild therapeutic and induced hypothermia, two randomized trials of hypothermic therapy after successful resuscitation after cardiac arrest were conducted. These studies demonstrated that hypothermia after cardiac arrest could improve neurological outcome as well as overall mortality.

Induced hypothermia for trauma: current research and practice

Induction of hypothermia with the goal of providing therapeutic benefit has been accepted for use in the clinical setting of adult cardiac arrest and neonatal hypoxic-ischemic encephalopathy (HIE). However, its potential as a treatment in trauma is not as well defined. This review discusses potential benefits and complications of induced hypothermia (IH) with emphasis on the current state of knowledge and practice in various types of trauma. There is excellent preclinical research showing that in cases of penetrating trauma with cardiac arrest, inducing hypothermia to 10 degrees C using cardiopulmonary bypass (CPB) could possibly save those otherwise likely to die without causing neurologic sequelae. A human trial of this intervention is about to get underway. Preclinical studies suggest that inducing hypothermia may be useful to delay cardiac arrest in penetrating trauma victims who are hypotensive. There is potential for IH to be used in cases of blunt trauma, but it has not been well studied. In the case of traumatic brain injury (TBI), clinical trials have shown conflicting results, despite almost uniform efficacy seen in preclinical experiments. Major studies are analyzed and ways to standardize its use and optimize future clinical trials are discussed. More preclinical and clinical research is needed to better define whether there could be a role for IH in the case of spinal cord injuries.

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.

Peritoneal cooling may provide improved protection for uncontrolled donors after cardiac death: an exploratory porcine study

Uncontrolled donation after cardiac death (DCD) renal transplantation relies on rapid establishment of organ preservation interventions. We have developed a model of the uncontrolled DCD, comparing current in situ perfusion (ISP) techniques with additional peritoneal cooling (PC). Ten pigs were killed and subjected to a 2 h ischemia period. The ISP group modeled current DCD protocols. The PC group (PC) modeled current protocols plus PC. Two animals were used as controls and subjected to 2 h of warm ischemia. Core renal temperature and microdialysis markers of ischemia were measured. Preservation interventions began at 30 min, with rapid laparotomy and kidney recovery performed at 2 h, prior to machine perfusion viability testing. The final mean renal temperature achieved in the ISP group was 26.3 degrees C versus 16.9 degrees C in the PC group (p = 0.0001). A significant cryopreservation benefit was suggested by lower peak microdialysate lactate and glycerol levels (ISP vs. PC, p = 0.0003 and 0.0008), and the superiority of the PC group viability criteria (p = 0.0147). This pilot study has demonstrated significant temperature, ischemia protection and viability assessment benefits with the use of supplementary PC. The data suggests a need for further research to determine the potential for reductions in the rates of ischemia-related clinical phenomena for uncontrolled DCDs.

Therapeutic hypothermia for neuroprotection

This review briefly discusses induced therapeutic hypothermia (TH), which represents the intentional induction of a lowered core body temperature of 35 degrees C or less. The focus is on resuscitative or postarrest hypothermia, the data that support it, and the practical issues pertaining to TH implementation.

Devices for rapid induction of hypothermia

In industrial countries it is estimated that the incidence of out-of-hospital sudden cardiac arrest lies between 36 and 128 per 100,000 inhabitants per year. Almost 80% of patients who initially survive a cardiac arrest present with coma lasting more than 1 h. Current therapy during cardiac arrest concentrates on the external support of circulation and respiration with additional drug and electrical therapy. Therapeutic hypothermia provides a new and very effective therapy for neuroprotection in patients after cardiac arrest. It is critical that mild hypothermia has to be applied very early after the ischaemic insult to be effective, otherwise the beneficial effects would be diminished or even abrogated. There are numerous methods available for cooling patients after ischaemic states. Surface cooling devices are non-invasive and range from simple ice packs to sophisticated machines with automatic feedback control. Other non-invasive methods include drugs and cold liquid ventilation. The newer devices have cooling rates comparable to invasive catheter techniques. Invasive cooling methods include the administration of ice-cold fluids intravenously, the use of intravascular cooling catheters, body cavity lavage, extra-corporeal circuits and selective brain cooling. Most of these methods are quite invasive and are still in an experimental stage. The optimal timing and technique for the induction of hypothermia after cardiac arrest have not yet been defined, and it is currently a major topic of ongoing research. The induction of hypothermia after cardiac arrest needs to be an integral component of the initial evaluation and stabilization of the patient.

Use of induced hypothermia for neuroprotection: indications and application

Therapeutic temperature regulation has become an exciting field of interest. Mild-to-moderate hypothermia is a safe and feasible management strategy for neuroprotection and control of intracranial pressure in neurological catastrophies such as traumatic brain injury, subarachnoid and intracerebral hemorrhage, and large hemispheric stroke. Fever is associated with worse neurological outcome in patients with brain injury, normothermia may be of benefit in this patient population. The efficacy of mild-to-moderate hypothermia has been proven for neuroprotection after cardiac arrest with ventricular fibrillation as initial rhythm, and after neonatal asphyxia. Application of hypothermia and fever control in neurocritical care, available cooling technologies and systemic effects and complications of hypothermia will be discussed.

Therapeutic Hypothermia after Cardiac Arrest: Performance Characteristics and Safety of Surface Cooling with or without Endovascular Cooling

INTRODUCTION

Various methods are available to induce and maintain therapeutic hypothermia after cardiac arrest, but little data is available comparing device-mediated cooling to simple surface methods in this setting.

METHODS

To assess the performance characteristics of simple surface cooling with or without an endovascular cooling catheter system, we retrospectively reviewed all cases of hypothermia for comatose survivors of cardiac arrest treated at a single academically affiliated urban hospital. Forty two comatose survivors of cardiac arrest were treated over a 3.5-year period. Hypothermia was induced and maintained by simple surface methods (ice packs, cooling blankets) with or without placement of an endovascular cooling catheter system with automated temperature feedback regulation.

RESULTS

Overall, the rate of active cooling was not different between patients treated with endovascular catheter-assisted hypothermia and patients treated with surface cooling alone. However, use of a larger (14 F) catheter was associated with faster cooling rates. Maintenance of goal temperature (33 degrees C) was far better controlled with the use of a cooling catheter. Use of surface cooling alone was associated with significant temperature overshoot. Patients treated with surface cooling alone spent more time bradycardic.

CONCLUSION

Use of an endovascular cooling catheter as part of a treatment protocol for hypothermia after cardiac arrest provides better control during maintenance of hypothermia, preventing temperature overshoot. Active cooling rates may be enhanced by the use of a larger cooling catheter.

Systematic review of randomized controlled trials of therapeutic hypothermia as a neuroprotectant in post cardiac arrest patients

OBJECTIVE

Several randomized controlled trials have suggested that mild induced hypothermia may improve neurologic outcome in comatose cardiac arrest survivors. This systematic review of randomized controlled trials was designed to determine if mild induced hypothermia improves neurologic outcome, decreases mortality, or is associated with an increased incidence of adverse events.

DATA SOURCES

The following databases were reviewed: Cochrane Controlled Trials Register (Issue 4, 2005), MEDLINE (January 1966 to November 2005), EMBASE (1980 to November 2005), CINAHL (1982 to November 2005) and Web of Science (1989 to November 2005). For each included study, references were reviewed and the primary author contacted to identify any additional studies.

STUDY SELECTION

Studies that met inclusion criteria were randomized controlled trials of adult patients (>18 years of age) with primary cardiac arrest who remained comatose after return of spontaneous circulation. Patients had to be randomized to mild induced hypothermia (32 degrees C-34 degrees C) or normothermia within 24 hours of presentation. Only studies reporting pre-determined outcomes including discharge neurologic outcome, mortality or significant treatment-related adverse events were included. There were no language or publication restrictions.

DATA SYNTHESIS

Four studies involving 436 patients, with 232 cooled to a core temperature of 32 degrees C-34 degrees C met inclusion criteria. Pooled data demonstrated that mild hypothermia decreased in-hospital mortality (relative ratio [RR] 0.75; 95% confidence interval [CI], 0.62-0.92) and reduced the incidence of poor neurologic outcome (RR 0.74; 95% CI, 0.62-0.84). Numbers needed to treat were 7 patients to save 1 life, and 5 patients to improve neurologic outcome. There was no evidence of treatment-limiting side effects.

CONCLUSIONS

Therapeutically induced mild hypothermia decreases in-hospital mortality and improves neurologic outcome in comatose cardiac arrest survivors. The possibility of treatment-limiting side effects cannot be excluded.

Successful resuscitation from cardiac arrest associated with extradural lidocaine in a dog

BACKGROUND

Extradural lidocaine exerts several adverse effects which are seldom fatal. While cardiac arrest following extradural lidocaine injection has been reported in human beings, it has not hitherto been reported in dogs.

OBSERVATIONS

The emergency management of a dog with complete urethral obstruction is described. We intended to perform vaginoscopy and cystostomy under extradural lidocaine anaesthesia, but cardiac asystole occurred a few minutes after injection. Resuscitation was successful. About 20 minutes later cardiac arrest recurred, and was treated successfully. The dog remained hypothermic for approximately 7 hours. Complete recovery without neurological deficit occurred the next day and the dog remained normal for at least 3 months. The probable cause of the problem was cranial lidocaine dispersion causing a drop in cardiac preload and cardiac arrest. The successful neurological outcome was attributed to early diagnosis and effective treatment. Hypothermia may have conferred cerebral protection during ischemia.

CONCLUSIONS

Extradural local anaesthetic administration is not without risk and the technique should be tailored to individual animals. Constant monitoring is required to detect potentially fatal complications and increase the likelihood of successful outcome.

Cold simple intravenous infusions preceding special endovascular cooling for faster induction of mild hypothermia after cardiac arrest--a feasibility study

OBJECTIVE

Mild therapeutic hypothermia has shown to improve neurological outcome after cardiac arrest. Our study investigated the efficacy and safety of cold simple intravenous infusions for induction of hypothermia after cardiac arrest preceding further cooling and maintenance of hypothermia by specialised endovascular cooling.

METHODS

All patients admitted after cardiac arrest of presumed cardiac aetiology were screened. Patients enrolled received 2000 ml of ice-cold (4 degrees C) fluids via peripheral venous catheters. As soon as possible endovascular cooling was applied even if the cold infusions were not completed. The target temperature was defined as 33 +/- 1 degrees C. All temperatures recorded were measured via bladder-temperature probes. The primary endpoint was the time from return of spontaneous circulation to reaching the target temperature. Secondary endpoints were changes in haemodynamic variables, oxygenation, haemoglobin, clotting variables and neurological outcome.

RESULTS

Out of 167 screened patients 26 (15%) were included. With a total amount of 24 +/- 7 ml/kg cold fluid at 4 degrees C the temperature could be lowered from 35.6 +/- 1.3 degrees C on admission to 33.8 +/- 1.1 degrees C. The target temperature was reached 185 +/- 119 min after return of spontaneous circulation, 135 +/- 112 min after start of infusion, and 83 +/- 85 min after start of endovascular cooling. Except for two patients showing radiographic signs of mild pulmonary edema no complications attributable to the infusions could be observed. Thirteen patients (50%) survived with favourable neurological outcome.

CONCLUSION

Our results indicate that induction of mild hypothermia with infusion of cold fluids preceding endovascular cooling is safe and effective.

Rapid induction of cerebral hypothermia is enhanced with active compression-decompression plus inspiratory impedance threshold device cardiopulmonary resusitation in a porcine model of cardiac arrest

OBJECTIVES

A rapid, ice-cold saline flush combined with active compression-decompression (ACD) plus an inspiratory impedance threshold device (ITD) cardiopulmonary resusitation (CPR) will cool brain tissue more effectively than with standard CPR (S-CPR) during cardiac arrest (CA).

BACKGROUND

Early institution of hypothermia after CPR and return of spontaneous circulation improves survival and outcomes after CA in humans.

METHODS

Ventricular fibrillation (VF) was induced for 8 min in anesthetized and tracheally intubated pigs. Pigs were randomized to receive either ACD + ITD CPR (n = 8) or S-CPR (n = 8). After 2 min of CPR, 30 ml/kg ice-cold saline (3 degrees C) was infused over the next 3 min of CPR via femoral vein followed by up to three defibrillation attempts (150 J, biphasic). If VF persisted, epinephrine (40 microg/kg) and vasopressin (0.3 U/kg) were administered followed by three additional defibrillation attempts. Hemodynamic variables and temperatures were continuously recorded.

RESULTS

All ACD + ITD CPR pigs (8 of 8) survived (defined as 15 min of return of spontaneous circulation [ROSC]) versus 3 of 8 pigs with S-CPR (p < 0.05). In survivors, brain temperature (degrees C) measured at 2-cm depth in brain cortex 1 min after ROSC decreased from 37.6 +/- 0.2 to 35.8 +/- 0.3 in ACD + ITD CPR versus 37.8 +/- 0.2 to 37.3 +/- 0.3 in S-CPR (p < 0.005). Immediately before defibrillation: 1) right atrial systolic/diastolic pressures (mm Hg) were lower (85 +/- 19, 4 +/- 1) in ACD + ITD CPR than S-CPR pigs (141 +/- 12, 8 +/- 3, p < 0.01); and 2) coronary perfusion pressures (mm Hg) were higher in ACD + ITD CPR (28.3 +/- 2) than S-CPR pigs (17.4 +/- 3, p < 0.01).

CONCLUSIONS

A rapid ice-cold saline infusion combined with ACD + ITD CPR during cardiac arrest induces cerebral hypothermia more rapidly immediately after ROSC than with S-CPR.

Induction of mild hypothermia with infusion of cold (4°C) fluid during ongoing experimental CPR

INTRODUCTION

Therapeutic hypothermia after resuscitation has been shown to improve the outcome regarding neurological state and to reduce mortality. The earlier hypothermia therapy is induced probably the better. We studied the induction of hypothermia with a large volume of intravenous ice-cold fluid after cardiac arrest during ongoing cardiopulmonary resuscitation (CPR).

METHODS

Twenty anaesthetised piglets were subjected to 8 min of ventricular fibrillation, followed by CPR. They were randomized into two groups. The hypothermic group was given an infusion of 4 degrees C acetated Ringer's solution 30 ml/kg at an infusion rate of 1.33 ml/kg/min, starting after 1 min of CPR. The control group received the same infusion at room temperature. All pigs received a bolus dose of vasopressin after 3 min of CPR. After 9 min, defibrillatory shocks were applied to achieve restoration of spontaneous circulation (ROSC). Core temperature and haemodynamic variables were measured at baseline and repeatedly until 180 min after ROSC. Cortical cerebral blood flow was measured, using Laser-Doppler flowmetry.

RESULTS

All pigs had ROSC, except one animal in the hypothermic group. Only one animal in the hypothermic group died during the observation period. The calculated mean temperature reduction was 1.6+/-0.35 degrees C (S.D.) in the hypothermic group and 1.1+/-0.37 degrees C in the control group (p=0.009). There was no difference in cortical cerebral blood flow and haemodynamic variables.

CONCLUSION

Inducing hypothermia with a cold infusion seems to be an effective method that can be started even during ongoing CPR. This method might warrant consideration for induction of early therapeutic hypothermia in cardiac arrest victims.

Effect of ifenprodil, a polyamine site NMDA receptor antagonist, on brain edema formation following asphyxial cardiac arrest in rats

OBJECTIVE

Brain edema occurs in experimental and clinical cardiac arrest (CA) and is predictive of a poor neurological outcome. N-Methyl--aspartate (NMDA) receptors contribute to brain edema elicited by focal cerebral ischemia/reperfusion (I/R). Ifenprodil, a NMDA receptor antagonist, attenuates brain edema and injury size in rats after focal cerebral I/R. We assessed the hypothesis that ifenprodil reduces CA-elicited brain edema.

METHODS

Eighteen male Sprague-Dawley rats were assigned to group 1 (normal control, n=6), group 2 (placebo-treated CA, n=6), or group 3 (ifenprodil-treated CA, n=6). CA was induced by 8 min of asphyxiation and the animals were resuscitated with cardiopulmonary resuscitation (CPR), ventilation, epinephrine (adrenaline), and sodium bicarbonate (NaHCO3). Ifenprodil of 10 mg/kg or a placebo vehicle was given intraperitoneally 5 min before CA. Brain edema was determined by brain wet-to-dry weight ratio at 1 h after resuscitation.

RESULTS

There were no differences between groups 2 and 3 in all physiological variables at baseline. Time from asphyxiation to CA was 201.5 +/- 7.5 s in group 2 and 160.7 +/- 10.4 s in group 3 (P<0.001). Resuscitation time was 68.2 +/- 13.3 s in group 2 and 92.8 +/- 18.2 s in group 3 (P<0.05). Ifenprodil decreased mean arterial pressure (MAP) before asphyxiation, from 128 +/- 7 in group 2 to 82 +/- 15 mmHg in group 3 (P<0.001), and negated immediate post-resuscitation hypertension. Brain wet-to-dry weight ratio was 5.64 +/- 0.44 in group 1, 7.34 +/- 0.95 in group 2 (P<0.01 versus group 1), and 5.93 +/- 0.40 in group 3 (P<0.05 versus group 2).

CONCLUSIONS

Ifenprodil reduces CA-elicited brain edema. In addition, we observed significant hemodynamic changes caused by ifenprodil.

Application of therapeutic hypothermia in the intensive care unit. Opportunities and pitfalls of a promising treatment modality--Part 2: Practical aspects and side effects

Induced hypothermia can be used to protect the brain from post-ischemic and traumatic neurological injury. Potential clinical applications and the available evidence are discussed in a separate paper. This review focuses on the practical aspects of cooling and physiological changes induced by hypothermia, as well as the potential side effects that may develop. These side effects can be serious and, if not properly dealt with, may negate some or all of hypothermia's potential benefits. However, many of these side effects can be prevented or modified by high-quality intensive care treatment, which should include careful monitoring of fluid balance, tight control of metabolic aspects such as glucose and electrolyte levels, prevention of infectious complications and various other interventions. The speed and duration of cooling and rate of re-warming are key factors in determining whether hypothermia will be effective; however, the risk of side effects also increases with longer duration. Realizing hypothermia's full therapeutic potential will therefore require meticulous attention to the prevention and/or early treatment of side effects, as well as a basic knowledge and understanding of the underlying physiological and pathophysiological mechanisms. These and other, related issues are dealt with in this review.

Systemic hypothermia, but not regional gut hypothermia, improves survival from prolonged hemorrhagic shock in rats

BACKGROUND

Extracorporeal blood perfusion of the gut or enterectomy can improve survival during hemorrhagic shock (HS), suggesting that the gut may be of primary importance in resuscitation. We hypothesized that cooling the gut alone could improve survival in a rat HS model and avoid potential deleterious effects of systemic hypothermia.

METHODS

Thirty-two Sprague-Dawley rats were anesthetized with halothane. The gut (small intestine, cecum, and colon) was exteriorized. The right atrial (T ), rectal, and gut (T ) intraluminal temperatures were monitored. HS was induced by withdrawal of 2 mL of blood per 100 g body weight over 10 minutes. Mean arterial pressure was then maintained at 35 to 40 mm Hg to HS 90 min. From HS 20 min to resuscitation time 1 h, rats were randomized into four groups (n = 8 each): normothermia (T and T approximately 38.0 degrees C), gut-25 degrees C (T approximately 38 degrees C, T approximately 25 degrees C, induced by rinsing the gut with cooled saline), gut-33 degrees C (T approximately 38 degrees C, T approximately 33 degrees C), and systemic hypothermia (T approximately 33 degrees C, T approximately 25 degrees C). At HS 90 min, shed blood and Ringer's solution were infused to restore normotension. Survival, metabolism, and tissue damage were observed to 72 hours.

RESULTS

Blood pressure was not different between groups. Compared with the normothermia group, the systemic hypothermia group had lower base deficit and lactate, and needed less fluid during resuscitation for normotension (p < 0.05), but these values were not different in the gut hypothermia groups. In addition, there were no significant improvements in tissue protection induced by regional gut hypothermia, whereas the systemic hypothermia group had lower plasma potassium, lower ornithine carbamoyltransferase (marker of liver injury), and higher glucose levels after HS (all p < 0.05). All rats in the systemic hypothermia group survived to 72 hours, whereas there was only one survivor in the normothermia group, two in the gut-33 degrees C group, and none in the gut-25 degrees C group (all p < 0.05 vs. systemic hypothermia).

CONCLUSION

Cooling the gut alone does not improve acute survival from HS, suggesting that early deaths are not secondary to gut ischemia. Mild systemic hypothermia allowed 100% survival from prolonged HS.

Extending the golden hour of hemorrhagic shock tolerance with oxygen plus hypothermia in awake rats. An exploratory study

In a previous study of volume-controlled hemorrhagic shock (HS) in awake rats, without fluid resuscitation, either breathing of 100% oxygen or moderate hypothermia while breathing air, increased survival time. We hypothesized that combining oxygen and hypothermia can maximally extend the "golden hour" of HS from which resuscitation can be successful in terms of survival rate. Rats were prepared under light general anesthesia, breathing spontaneously via face mask, and then awakened for 2 h. Then, 3.25 ml arterial blood/100 g were withdrawn over 20 min. At the end of HS of 30, 60, 90 or 180 min duration, the shed blood was reinfused. Breathing was spontaneous. Survival endpoint was 24 h or earlier death. HS of 30 or 60 min was used for preliminary experiments; HS of 90 or 180 min for 35 definitive experiments. Control groups A-1 and B-1 had normothermia (rectal temperature 37.5 degrees C) and were breathing air. Treatment groups A-2 and B-2 had total body surface cooling during HS to rectal temperature 32 degrees C and were breathing 100% O(2). Arterial pressure during HS was higher in the hypothermia-O(2) groups. With HS of 90 min, in the normothermia-air group A-1 (n=10), none of the 10 rats survived to 3 h; while in the hypothermia-O(2) group A-2 (n=5), all rats survived to 24 h (P<0.001). With HS of 180 min, in the normothermia-air group B-1 (n=10), three of 10 rats survived to 3 h and 24 h (hypotension during HS in these three survivors was less severe than in the non-survivors); and in the hypothermia-O(2) group B-2 (n=10) all 10 rats survived to 24 h (P<0.003). We conclude that moderate hypothermia (32 degrees C) plus 100% oxygen inhalation during volume-controlled HS in awake rats mitigates hypotension and increases the chance of survival. It enables survival even after 3 h of moderate HS.

Feasibility of external cranial cooling during out-of-hospital cardiac arrest

Hypothermia during brain ischemia can improve neurological outcome. This study tested whether local cranial cooling during the low-flow state of cardiopulmonary resuscitation (CPR) could produce clinically significant cerebral cooling. Ice was applied to the heads and necks of subjects (hypothermia group) with out-of-hospital cardiac arrest (OOHCA) during CPR. Nasopharyngeal and tympanic temperatures were measured as surrogates for cerebral temperature. The rate of cranial cooling in the hypothermia group (-0.06 +/- 0.06 degrees C/min) was not significantly increased compared with a control group without ice (-0.04 +/- 0.07 degrees C/min), although older age was associated with more rapid cranial cooling. Of note, many subjects with OOHCA are already mildly hypothermic (mean cranial temperature= 35.0 +/- 1.2 degrees C) when they are first encountered in the field. This study suggests that brief cranial cooling is ineffective for rapidly lowering brain temperature. However, most cardiac arrest victims are spontaneously mildly hypothermic and preventing rewarming may provide some of the desired benefits of cerebral hypothermia.

Mild hypothermia induced by a helmet device: a clinical feasibility study

STUDY OBJECTIVE

To test the feasibility and the speed of a helmet device to achieve the target temperature of 34 degrees C in unconscious after out of hospital cardiac arrest (CA).

METHODS

Patients with cardiac arrest due to asystole or pulseless electrical activity (PEA) who remained unconscious after restoration of spontaneous circulation (ROSC) were enrolled in the study and randomised into two groups: a normothermic group (NG) and a hypothermic group (HG). Bladder and tympanic temperature were monitored every 15 min. A helmet device was used to induce mild hypothermia in the HG. Later on, the effect of mild hypothermia on the haemodynamics, electrolytes, lactate, arterial pH, CaO2, CvO2 and O2 extraction ratio were analysed and compared to the values obtained from the NG.

RESULTS

Thirty patients were eligible for the study, 16 were randomised into the HG and 14 were randomised into the NG. The median tympanic temperature at admission in both groups was 35.5 degrees C (range: 33.3-38.5 degrees C) and the median tympanic temperature after haemodynamic stabilisation was 35.7 degrees C (range: 33.6-38.2 degrees C). In the HG, the core and the central target temperature of 34 degrees C were achieved after a median time of 180 and 60 min, respectively after ROSC. At the start of the study, no significant differences between the NG and HG were seen. At the end of the study, lactate concentration and O2 extraction ratio were significantly lower in the HG; however the CvO2 was significantly lower in the NG.

CONCLUSIONS

Mild hypothermia induced by a helmet device was feasible, easy to perform, inexpensive and effective, with no increase in complications.

Peritoneal ventilation with oxygen improves outcome after hemorrhagic shock in rats

OBJECTIVE

In experimental pulmonary consolidation with hypoxemia in rabbits, peritoneal ventilation (PV) with 100% oxygen (PV-O2) improved PaO2. We hypothesized that PV-O2 could improve outcome after hemorrhagic shock (HS) with normal lungs, by mitigating dysoxia of the abdominal viscera.

DESIGN

Randomized, controlled, laboratory animal study.

SETTING

University animal research facility.

SUBJECTIVE

Male Sprague-Dawley rats.

INTERVENTIONS

Thirty rats under light anesthesia (N2O/oxygen plus halothane) and spontaneous breathing underwent blood withdrawal of 3 mL/100 g over 15 mins. After volume-controlled HS phase 1 of 60 mins, resuscitation phase 2 of 60 mins included infusion of shed blood and, if necessary, additional lactated Ringer's solution intravenously to control normotension from 60 to 120 mins. This was followed by observation phase 3 for 7 days. We randomized three groups of ten rats each: group I received PV-O2, starting at 15 mins of HS at a rate of 40 inflations/min, and a peritoneal "tidal volume" of 6 mL, until the end of phase 2. Group II received the same PV with room air (PV-Air). Control group III was treated without PV.

MEASUREMENTS AND MAIN RESULTS

During the second half of HS phase 1, mean arterial pressures were higher in the PV-O2 group I compared with the PV-Air group II and control group III (p < .05). All 30 rats survived the 120 mins of phases 1 and 2. Survival to 7 days was achieved by ten of ten rats in PV-O2 group I; by nine of ten in PV-Air group II; and by five of ten in control group III (p < .05 vs. group I; NS vs. group II). Survival times of <7 days were 5 days in the one death of group II and ranged between 6 hrs and 4 days in the five deaths of group III. In 7-day survivors, neurologic deficit scores (0% to 10% = normal, 100% = death) were normal, ranging between zero and 8%. Necropsies of rats that died during phase 3 showed multiple areas of necrosis of the gut, some with perforations. Necropsies in the five survivors to 7 days of group III showed marked macroscopic and microscopic changes (scattered areas of necrosis of stomach and intestine, adhesions, and pale areas in the liver). These changes were absent or less severe in the nine survivors of group II. Viscera appeared normal in all ten rats of PV-O2 group I.

CONCLUSIONS

Peritoneal ventilation with oxygen during and after severe hemorrhagic shock in rats seems to decrease morbidity and mortality by helping preserve viability of abdominal viscera.

Rapid induction of mild cerebral hypothermia by cold aortic flush achieves normal recovery in a dog outcome model with 20-minute exsanguination cardiac arrest

OBJECTIVES

Resuscitation attempts in trauma victims who suffer cardiac arrest (CA) from exsanguination almost always fail. The authors hypothesized that an aortic arch flush with cold normal saline solution (NSS) at the start of exsanguination CA can preserve cerebral viability during 20-minute no-flow.

METHODS

Twelve dogs were exsanguinated over 5 minutes to CA of 20-minute no-flow, resuscitated by cardiopulmonary bypass, followed by post-CA mild hypothermia (34 degrees C) continued to 12 hours, controlled ventilation to 20 hours, and intensive care to 72 hours. At CA 2 minutes, the dogs received a 500-mL flush of NSS at either 24 degrees C (group 1, n = 6) or 4 degrees C (group 2, n = 6), using a balloon-tipped catheter inserted via the femoral artery into the descending thoracic aorta.

RESULTS

The flush at 24 degrees C (group 1) decreased tympanic membrane temperature [mean (+/-SD)] from 37.5 degrees C (+/-0.1) to 35.7 degrees C (+/-0.2); the flush at 4 degrees C (group 2) to 34.0 degrees C (+/-1.1) (p = 0.005). In group 1, one dog achieved overall performance category (OPC) 2 (moderate disability), one OPC 3 (severe disability), and four OPC 4 (coma). In group 2, four dogs achieved OPC 1 (normal), one OPC 2, and one OPC 3 (p = 0.008). Neurologic deficit scores (0-10% normal, 100% brain death) [median (25th-75th percentile)] were 62% (40-66) in group 1 and 5% (0-19) in group 2 (p = 0.01). Total brain histologic damage scores were 130 (62-137) in group 1 and 24 (10-55) in group 2 (p = 0.008).

CONCLUSIONS

Aortic arch flush of 4 degrees C at the start of CA of 20 minutes rapidly induces mild cerebral hypothermia and can lead to normal functional recovery with minimal histologic brain damage. The same model with aortic arch flush of 24 degrees C results in survival with brain damage in all dogs, which makes it suitable for testing other (e.g., pharmacologic) preservation potentials.

Mild resuscitative hypothermia to improve neurological outcome after cardiac arrest. A clinical feasibility trial. Hypothermia After Cardiac Arrest (HACA) Study Group

BACKGROUND AND PURPOSE

Recent animal studies showed that mild resuscitative hypothermia improves neurological outcome when applied after cardiac arrest. In a 3-year randomized, prospective, multicenter clinical trial, we hypothesized that mild resuscitative cerebral hypothermia (32 degrees C to 34 degrees C core temperature) would improve neurological outcome after cardiac arrest.

METHODS

We lowered patients' temperature after admission to the emergency department and continued cooling for at least 24 hours after arrest in conjunction with advanced cardiac life support. The cooling technique chosen was external head and total body cooling with a cooling device in conjunction with a blanket and a mattress. Infrared tympanic thermometry was monitored before a central pulmonary artery thermistor probe was inserted.

RESULTS

In 27 patients (age 58 [interquartile range [IQR] 52 to 64] years; 7 women; estimated "no-flow" duration 6 [IQR 1 to 11] minutes and "low-flow" duration 15 [IQR 9 to 23] minutes; admitted to the emergency department 36 [IQR 24 to 43] minutes after return of spontaneous circulation), we could initiate cooling within 62 (IQR 41 to 75) minutes and achieve a pulmonary artery temperature of 33+/-1 degrees C 287 (IQR 42 to 401) minutes after cardiac arrest. During 24 hours of mild resuscitative hypothermia, no major complications occurred. Passive rewarming >35 degrees C was accomplished within 7 hours.

CONCLUSIONS

Mild resuscitative hypothermia in patients is feasible and safe. A clinical multicenter trial might prove that mild hypothermia is a useful method of cerebral resuscitation after global ischemic states.

On the future of reanimatology

This article is adapted from a presentation given at the 1999 SAEM annual meeting by Dr. Peter Safar. Dr. Safar has been involved in resuscitation research for 44 years, and is a distinguished professor and past initiating chairman of the Department of Anesthesiology and Critical Care Medicine at the University of Pittsburgh. He is the founder and director of the Safar Center for Resuscitation Research at the University of Pittsburgh, and has been the research mentor of many critical care and emergency medicine research fellows. Here he presents a brief history of past accomplishments, recent findings, and future potentials for resuscitation research. Additional advances in resuscitation, from acute terminal states and clinical death, will build upon the lessons learned from the history of reanimatology, including optimal delivery by emergency medical services of already documented cardiopulmonary cerebral resuscitation, basic-advanced-prolonged life support, and future scientific breakthroughs. Current controversies, such as how to best educate the public in life-supporting first aid, how to restore normotensive spontaneous circulation after cardiac arrest, how to rapidly induce mild hypothermia for cerebral protection, and how to minimize secondary insult after cerebral ischemia, are discussed, and must be resolved if advances are to be made. Dr. Safar also summarizes future technologies already under preliminary investigation, such as ultra-advanced life support for reversing prolonged cardiac arrest, extending the "golden hour" of shock tolerance, and suspended animation for delayed resuscitation.

Therapeutic hypothermia in traumatology

Despite its proven clinical application for protection-preservation of the brain and heart during cardiac surgery, hypothermia research has fallen in and out of favor many times since its inception. Since the 1980s, there has been renewed research and clinical interest in therapeutic hypothermia for resuscitation of the brain after cardiac arrest or TBI and for preservation-resuscitation of extracerebral organs, particularly the abdominal viscera in low-flow states such as HS. Although some of the fears regarding the side effects of hypothermia are warranted, others are not. Without further laboratory and clinical studies, the significance of these effects cannot be determined and ways to overcome these problems cannot be developed. Currently, at the turn of the century, there are significant data demonstrating the benefit of mild-to-moderate hypothermia in animals and humans after cardiac arrest or TBI and in animals during and after HS. The clinical implications of uncontrolled versus controlled hypothermia in trauma patients and the best way to assure poikilothermia for cooling without shivering are still unclear. It is time to consider a prospective trial of therapeutic, controlled hypothermia for patients during traumatic HS and resuscitation. The authors believe that the new millennium will witness remarkable advantages of the use of controlled hypothermia in trauma. Starting in the prehospital phase, mild hypothermia will be induced in hypovolemic patients, which will not only decrease the immediate mortality rate but perhaps also will protect cells and reduce the likelihood of secondary inflammatory response syndrome, multiple organ failure, and late deaths. The most futuristic applications will be hypothermic strategies to achieve prolonged suspended animation for delayed resuscitation in traumatic exsanguination cardiac arrest.

Moderate hypothermia for 48 hours after temporary epidural brain compression injury in a canine outcome model

In a previous study with this dog model, post-insult hypothermia of 31 degrees C for 5 h prevented secondary intraventricular pressure (IVP) rise, but during 35 degrees C or 38 degrees C, one-half of the dogs developed delayed IVP rise to brain death. We hypothesized that 31 degrees C extended to 48 h would prevent brain herniation. Using epidural balloon inflation, we increased contralateral IVP to 62 mm Hg for 90 min. Controlled ventilation was to 72 h and intensive care to 96 h. Group 1 dogs (n = 10) were normothermic controls (37.5 degrees C). Group 2 dogs (n = 10) were surface-cooled from 15 to 45 min of balloon inflation and maintained at moderate hypothermia (31 degrees C) to 48 h. Rewarming was from 48 to 72 h. Four additional dogs of hypothermia Group 2 had to be excluded from analysis for pneumonia and/or bleeding diathesis. After balloon deflation, IVP increased to 20 mm Hg or greater at 154 +/- 215 (range 15-720) min following the insult in Group 1 and at 1394 +/- 1191 (range 210-3420) min in Group 2 (p = 0.004), still during 31 degrees C but without further increase during hypothermia. Further IVP rise led to brain death in Group 1 in 6 of 10 dogs at 44 +/- 18 (range 21-72) h (all during controlled ventilation); and in Group 2, in 6 of 10 dogs at 87 +/- 11 (range 72-96) h (p = 0.001), all after rewarming, during spontaneous breathing. Survival to 96 h was achieved by 4 of 10 dogs in Group 1, and by 7 of 10 dogs in Group 2 (NS). Three of the six brain deaths in Group 2 occurred at 96 h. The macroscopically damaged brain volume was only numerically smaller in Group 2. The vermis downward shift was 6.8 +/- 3.5 mm in Group 1, versus 4.7 +/- 2.2 mm in Group 2 (p = 0.05). In an adjunctive study, in 4 additional normothermic dogs, hemispheric cerebral blood flow showed post-insult hypoperfusion bilaterally but no evidence of hyperemia preceding IVP rise to brain death. In conclusion, in this model, moderate hypothermia during and for 48 h after temporary epidural brain compression can maintain a low IVP during hypothermia but cannot prevent lethal brain swelling after rewarming and may cause coagulopathy and pulmonary complications.

Mild protective and resuscitative hypothermia for asphyxial cardiac arrest in rats

It has been shown in dogs that mild hypothermia (34 degrees C) during or immediately after ventricular fibrillation cardiac arrest can improve cerebral outcome. The effect of mild hypothermia on outcome after 8 minutes of asphyxiation (5 minutes' cardiac arrest) was studied for the first time in rats. Restoration of spontaneous circulation was with external cardiopulmonary resuscitation and observation to 72 hours. Three groups of 10 rats each were studied. At 72 hours postarrest, compared with the normothermic control group 1, final overall performance categories (OPC) and neurological deficit scores (NDS) were numerically better in the resuscitative (post-arrest) hypothermia group 2 and significantly better in the protective (pre-intra-arrest) hypothermia group 3 (P < .05). Total brain histopathological damage scores (HDS) were 17 +/- 5 in group 1, 14 +/- 6 in group 2 (NS), and 6 +/- 2 in group 3 (P < .001 versus group 1). HDS correlated with OPC (r = .6, P < .05) and NDS (r = .7, P < .05). Mild hypothermia improved cerebral outcome after asphyxial cardiac arrest in rats, more when induced before than after arrest. The model's insult is within the therapeutic window, which makes it also suitable for screening other cerebral resuscitation potentials.