Bretylium in hypothermia-induced ventricular fibrillation in dogs

Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update

To provide guidance to clinicians, the Wilderness Medical Society convened an expert panel to develop evidence-based guidelines for the out-of-hospital evaluation and treatment of victims of accidental hypothermia. The guidelines present the main diagnostic and therapeutic modalities and provide recommendations for the management of hypothermic patients. The panel graded the recommendations based on the quality of supporting evidence and a balance between benefits and risks/burdens according to the criteria published by the American College of Chest Physicians. The guidelines also provide suggested general approaches to the evaluation and treatment of accidental hypothermia that incorporate specific recommendations. This is the 2019 update of the Wilderness Medical Society Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2014 Update.

Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia

Accidental hypothermia is an unintentional drop in core temperature to 35°C or below. Core temperature is best measured by esophageal probe. If core temperature cannot be measured, the degree should be estimated using clinical signs. Treatment is to protect from further heat loss, minimize afterdrop, and prevent cardiovascular collapse during rescue and resuscitation. The patient should be handled gently, kept horizontal, insulated, and actively rewarmed. Active rewarming is also beneficial in mild hypothermia but passive rewarming usually suffices. Cardiopulmonary resuscitation should be performed if there are no contraindications to resuscitation. CPR may be delayed or intermittent.

Wilderness Medical Society practice guidelines for the out-of-hospital evaluation and treatment of accidental hypothermia: 2014 update

To provide guidance to clinicians, the Wilderness Medical Society (WMS) convened an expert panel to develop evidence-based guidelines for the out-of-hospital evaluation and treatment of victims of accidental hypothermia. The guidelines present the main diagnostic and therapeutic modalities and provide recommendations for the management of hypothermic patients. The panel graded the recommendations based on the quality of supporting evidence and the balance between benefits and risks/burdens according the criteria published by the American College of Chest Physicians. The guidelines also provide suggested general approaches to the evaluation and treatment of accidental hypothermia that incorporate specific recommendations. This is an updated version of the original Wilderness Medical Society Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia published in Wilderness & Environmental Medicine 2014;25(4):425-445.

Wilderness Medical Society practice guidelines for the out-of-hospital evaluation and treatment of accidental hypothermia

To provide guidance to clinicians, the Wilderness Medical Society (WMS) convened an expert panel to develop evidence-based guidelines for the out-of-hospital evaluation and treatment of victims of accidental hypothermia. The guidelines present the main diagnostic and therapeutic modalities and provide recommendations for the management of hypothermic patients. The panel graded the recommendations based on the quality of supporting evidence and the balance between benefits and risks/burdens according the criteria published by the American College of Chest Physicians. The guidelines also provide suggested general approaches to the evaluation and treatment of accidental hypothermia that incorporate specific recommendations.

Severe bradycardia with a prominent J wave refractory to atropine: was it a cause or a result of a fall? A case report and a brief review on the treatment of hypothermia

We report on an eighty five year old male who had presented with bradycardia and a prominent J wave on EKG. Initial attemps to treat bradycardia with atropine were unsuccessful and on further evaluation the patient was found to have hypothermia.

Practical pharmacologic aspects of therapeutic hypothermia after cardiac arrest

Abstract Therapeutic hypothermia has emerged as an effective means of improving neurologic outcomes among cardiac arrest survivors. To achieve optimal results, clinicians must understand and anticipate potential adverse effects of cooling and provide rigorous monitoring and/or pharmacologic interventions as appropriate. Using pharmacotherapy to counter adverse effects of cooling or to treat an intrinsic process under hypothermic conditions requires understanding how hypothermia will influence the clinical effects of the drug, including the drug's pharmacokinetics and pharmacodynamics. The pharmacologic aspects of therapeutic hypothermia in relation to physiology and adverse effects are reviewed.

Application of normothermic cardiac arrest algorithms to hypothermic cardiac arrest in a canine model

BACKGROUND

International guidelines (2000) do not recommend vasopressor and antiarrhythmic medications during ventricular fibrillation (VF) with a core temperature below 30 degrees C. The efficacy of normothermic AHA algorithms using standard doses of epinephrine (EPI) (adrenaline) followed by amiodarone (AMIO) in hypothermic VF is uncertain.

OBJECTIVES

To determine the effects of EPI followed by the combination of EPI/AMIO in the treatment of VF in a canine model of severe hypothermia.

METHODS

An un-blinded, placebo controlled experiment using 21 mechanically ventilated dogs. Coronary perfusion pressure (CPP), temperature, and electrocardiogram (ECG) were monitored. Animals were cooled to 22 degrees C or the onset of spontaneous VF. VF was induced if necessary. Animals in the treatment group received EPI (0.01 mg/kg IV) and defibrillation. This was followed by EPI (0.01 mg/kg IV), AMIO (10 mg/kg IV) and defibrillation if there was no sustained return of spontaneous circulation (ROSC) for 15 min.

RESULTS

Mean CPP in the treatment group increased after the administration of EPI/AMIO (24.7+/-13.3 mmHg to 46.6+/-7.7 mmHg, p<0.004). Cumulatively, the administration of EPI followed by EPI/AMIO achieved ROSC after defibrillation in 10 of 11 animals compared to 3 of 10 in the control group (91% versus 30%, n=21, p=0.0075).

CONCLUSIONS

In this model of severe hypothermia, the use of standard 2000 protocols for VF resulted in a significant increase of CPP, and, a higher ROSC rate compared to placebo controls. This study suggests that AHA normothermic algorithms may be beneficial in severe hypothermia.

Hypothermia and localized cold injuries

Hypothermia and localized cold injuries are largely preventable with proper preparation for activities in cold environments. Proficient field management is crucial to the final outcome in terms of function and viability because proper care is vital to preventing exacerbation of the initial exposure and injury. Rapid rewarming is optimal when further cold exposure can be avoided reliably. Repetitive freeze-thaw cycles are associated with increased morbidity and tissue loss caused by progressive microvascular injury and thrombosis. The subsequent care is largely supportive and consists of wound care and physical and hydrotherapy to promote optimal functional recovery.

Neither vasopressin nor amiodarone improve CPR outcome in an animal model of hypothermic cardiac arrest

BACKGROUND

Aim of this experimental animal study was to investigate the influence of vasopressin and amiodarone on cardiopulmonary resuscitation (CPR) outcome in a pig model of hypothermic cardiac arrest.

METHODS

After surface cooling to a core temperature of 26 degrees C, ventricular fibrillation was induced in 14 12-16-week-old domestic pigs. After 15 min of untreated cardiac arrest, a manual closed chest CPR was started and pigs were randomly assigned to two treatment groups: Group 1 pigs (n = 7) received vasopressin 0.4 U kg-1 as initial drug therapy, followed by a combination vasopressin (0.4 U kg-1) and amiodarone (4 mg kg-1) as subsequent drug therapy. Subsequent drug therapy was administered in animals without permanent restoration of spontaneous circulation after a first series of electrical countershocks 10 min after drug administration. Group 2 pigs (n = 7) received saline placebo as initial drug therapy and saline placebo and amiodarone (4 mg kg-1) as subsequent drug therapy.

RESULTS

Vasopressin significantly increased coronary perfusion pressure and defibrillation success (successful defibrillation in five of seven Group 1 vs. none of seven Group 2 pigs, P = 0.02). Due to refibrillation within 30-150 s, the 60-min survival rate was not improved by vasopressin. Subsequent drug therapy with amiodarone had no further effect on defibrillation success or the refibrillation rate.

CONCLUSIONS

Data from this experimental animal model suggest that vasopressin and amiodarone may not be beneficial for treatment of ventricular fibrillation associated with severe hypothermia when concomitant measures at core rewarming are not applied.

Management of the Organ Donor

Advances in immunosuppressive therapy have led to increased use of organ transplantation to treat end- organ failure. This has led to a consistent shortage of transplantable organs, with many patients dying while awaiting heart, liver, or lung transplantation. Traditional donor criteria are expanding and increase the pool of available donor organs. The organ procurement process often begins with the diagnosis of brain death, which must be made by clinical criteria and is usually con firmed by clinical testing. Because brain-dead patients suffer a variety of hemodynamic, cardiac, endocrine, respiratory, and hematologic abnormalities, manage ment in the intensive care unit demands meticulous attention and expertise. Living and, occasionally, non- heart-beating donors are also a source of donor organs. Management of the various types of donors in the operating room requires specific skills and knowledge. The persistent need for donor organs requires that poten tial organ donors be recognized and appropriately man aged to maximize the pool of available organs for the ever- increasing number of potential organ recipients.

The cardiac transplant donor: identification, assessment, and management

In the previous 2 decades, there have been many advances in the treatment of coronary and valvular heart disease. However, these treatments remain imperfect, and more patients are surviving only to have congestive heart failure develop later in life. During the same 2 decades, advances in surgical techniques and immunosuppression made cardiac transplantation the treatment of choice for severe, end-stage heart failure. Despite concomitant legislation designed to promote organ donation, there remains a severe shortfall in the number of organ donors compared with the number of potential recipients. This article discusses identification of the potential organ donor, assessment of the heart for donation, medical management of the brain-dead organ donor from pronouncement to procurement, and finally, some of the ethical issues raised in the wake of further efforts to increase the potential donor pool.

Effect of bretylium tosylate on ventricular fibrillation threshold during hypothermia in dogs

How bretylium tosylate affected the ventricular fibrillation threshold, electrophysiological parameters, and plasma catecholamine levels during hypothermia in dogs was studied. Threshold for ventricular fibrillation was determined by programmed electrical stimulation using a stimulation protocol that involved applying a maximum of five extrastimuli at body temperatures 37, 34, 31, 28, and 25 degrees C, and at the same temperatures during rewarming. Electrocardiogram, epicardial monophasic action potentials (MAP), and electrograms were recorded, and ventricular effective refractory period (VERP) was determined at each of the above temperatures. In one group (n = 7), a bolus dosage of bretylium tosylate (BT), 6 mg/kg body wt, was administered at 25 degrees C before rewarming. Another group (n = 4) was exposed to cooling and rewarming without addition of BT. Cooling to 25 degrees C reduced ventricular fibrillation threshold linearly, reduced heart rate, increased VERP and MAP, and slowed myocardial conduction velocity in both groups. There was no overall increase in plasma catecholamine levels during cooling. Addition of BT at 25 degrees C increased ventricular fibrillation threshold during rewarming compared with cooling. Addition of BT at 25 degrees C increased VERP by +/- 32 milliseconds and the corrected JT time by 0.06 +/- 0.02 seconds. VERP and JTc increased during rewarming with BT compared with cooling with no drug. BT had no effect on conduction velocity, and plasma catecholamine levels were not reduced. The antiarrhythmic effect of BT during hypothermia was attributed to an increased wavelength of refractoriness by its increase in the refractory period. This increased wavelength of refractoriness may prevent excitable gaps or increase circuit pathway in the setting of reentry arrhythmias.

Hypothermia

Significant hypothermia is an increasing clinical problem that requires a rapid response with properly trained personnel and techniques. Although the clinical presentation may be such that the victim appears dead, aggressive management may allow successful resuscitation in many instances. Initial management should include CPR if the victim is not breathing or is pulseless. Further core heat loss should be prevented by removing wet garments, insulating the victim, and ventilating with warm humidified air/oxygen to help stabilize core temperature. Core temperature and cardiac rhythm should be monitored in the prehospital setting, if possible, and CPR should be continued during transport. In-hospital management should consist of rapid core rewarming in the severely hypothermic victim with heated humidified oxygen, centrally administered warm IV fluids (43 C), and peritoneal dialysis until extracorporeal rewarming can be accomplished. Postresuscitation complications should be monitored; they include pneumonia, pulmonary edema, cardiac arrhythmias, myoglobinuria, disseminated intravascular thrombosis, and seizures. The decision to terminate resuscitative efforts must be individualized by the physician in charge.

Bretylium tosylate and electrically induced cardiac arrhythmias during hypothermia in dogs

The effect of bretylium tosylate on plasma catecholamines and on electrically induced arrhythmias was evaluated in anesthetized hypothermic dogs. Bretylium at a dose of 7.5 mg/kg was administered prior to cooling from 37 degrees C to 27 degrees C. During cooling, the ventricular arrhythmia threshold (VAT) in control animals decreased from 10.1 +/- 1.9 to 4.4 +/- 1.3 impulses, while the VAT in bretylium-treated animals increased from 9.8 +/- 2.9 to 23.2 +/- 2.7 impulses. Catecholamine levels increased during cooling in all animals. In control animals, the epinephrine/norepinephrine ratio was unchanged, but in animals treated with bretylium tosylate, the ratio increased more than 10-fold (from 0.48 +/- 0.1 to 5.49 +/- 0.32 at 29.9 degrees C). The demonstrated increase in catecholamine levels during hypothermia suggests that the protection offered by bretylium tosylate against cardiac arrhythmias is not explained by modification of catecholamine levels, and is more likely due to an alteration of the electrophysiologic properties of cardiac tissues.

Comparison of bretylium and lidocaine in the prevention of ventricular fibrillation after aortic cross-clamp release in coronary artery bypass surgery

The authors compared bretylium and lidocaine for reducing the incidence and persistence of ventricular fibrillation following aortic cross-clamp release performed during coronary artery bypass surgery. Thirty-three adult patients scheduled for elective bypass surgery were randomly assigned in a double-blind fashion to receive a bolus of bretylium, 10 mg/kg, lidocaine, 2 mg/kg, or saline, in equal volumes prior to the release of the aortic cross-clamp. Coronary artery bypass surgery was conducted using standard cardiopulmonary bypass (CPB) procedures with systemic cooling to 24 degrees to 28 degrees C. Temperature, arterial blood gases, and electrolytes were recorded. After clamp release, the first electrical rhythm was noted. Abnormal rhythms (ventricular fibrillation) were allowed to persist for 1 to 2 minutes, and if spontaneous conversion to a supraventricular rhythm did not occur, defibrillation with internal DC countershocks was applied. Patients were compared with respect to occurrence of ventricular fibrillation, need for DC countershocks, antiarrhythmic drugs, and inotropic support. There was no significant difference among the groups with respect to age, sex, preoperative medications, past medical histories, ejection fractions, average number of bypasses, cross-clamp times, or temperatures during bypass. The incidence of ventricular fibrillation after aortic cross-clamp removal was: saline 91%, lidocaine 64% (P less than 0.01), and bretylium 36% (P less than 0.01). The number of countershocks required to defibrillate, while lower in the bretylium group, did not reach statistical significance. After cardiopulmonary bypass, cardiac output and systemic vascular resistance were comparable. Bretylium warrants further study in this setting.

Use of bretylium tosylate as prophylaxis and treatment in hypothermic ventricular fibrillation in the canine model

We conducted a study to determine if bretylium tosylate (BT) is effective in the prophylaxis and treatment of hypothermic ventricular fibrillation (VF) in the setting of various maneuvers thought to induce this lethal arrhythmia. Twenty-two mongrel dogs were cooled to 24 C after being placed in a cold room. At 24 C, a double-blinded placebo or BT solution was infused. The dogs then were removed from the cold. They underwent the following sequential maneuvers: oral endotracheal extubation and intubation, central line and nasogastric tube placement, vigorous movement, and Swan-Ganz catheter insertion. If VF ensued, arterial blood gases were drawn, and BT was given only if refractory to countershock and epinephrine. Of the dogs that were given placebo, six of 11 (55%) fibrillated with manipulation, as compared with one of 11 (9%) dogs pretreated with BT (P = .067). Three of the 11 dogs that received BT fibrillated within minutes of its infusion. In the placebo dogs that fibrillated, four required BT and two defibrillated with countershock alone or with epinephrine prior to achieving stable rhythms.

Ventricular fibrillation during orotracheal intubation of hypothermic dogs

Physical manipulation of the hypothermic patient is well known to cause ventricular fibrillation. Careful review of the literature fails to demonstrate a true temporal relationship between orotracheal intubation and ventricular fibrillation (VF) when acceptable temperature-corrected arterial blood gases have been obtained. Eleven mongrel dogs were anesthetized and cooled, with orotracheal intubation and extubation performed every two degrees centrigrade, starting at 27 C. Ventilator setting were adjusted to maintain normal pH according to arterial blood gases drawn every two degrees and corrected for temperature. There was only one episode of VF during 42 intubations performed at temperatures less than 28 C (2.38%). There were eight separate episodes of spontaneous VF unrelated to intubation in five dogs. Four of these five with spontaneous VF were resuscitated with countershock only, further cooled, and reintubated an additional 11 times without a single episode of VF during intubation. Our data suggest that the incidence of VF during intubation in the hypothermic patient is much less than previously described, provided that normal pH is maintained and hypoxemia is corrected.