Thiopental combination treatments for cerebral resuscitation after prolonged cardiac arrest in dogs. Exploratory outcome study

2024 RECOVER Guidelines: Advanced Life Support. Evidence and knowledge gap analysis with treatment recommendations for small animal CPR

OBJECTIVE

To systematically review the evidence and devise clinical recommendations on advanced life support (ALS) in dogs and cats and to identify critical knowledge gaps.

DESIGN

Standardized, systematic evaluation of literature pertinent to ALS following Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) methodology. Prioritized questions were each reviewed by Evidence Evaluators, and findings were reconciled by ALS Domain Chairs and Reassessment Campaign on Veterinary Resuscitation (RECOVER) Co-Chairs to arrive at treatment recommendations commensurate to quality of evidence, risk:benefit relationship, and clinical feasibility. This process was implemented using an Evidence Profile Worksheet for each question that included an introduction, consensus on science, treatment recommendations, justification for these recommendations, and important knowledge gaps. A draft of these worksheets was distributed to veterinary professionals for comment for 4 weeks prior to finalization.

SETTING

Transdisciplinary, international collaboration in university, specialty, and emergency practice.

RESULTS

Seventeen questions pertaining to vascular access, vasopressors in shockable and nonshockable rhythms, anticholinergics, defibrillation, antiarrhythmics, and adjunct drug therapy as well as open-chest CPR were reviewed. Of the 33 treatment recommendations formulated, 6 recommendations addressed the management of patients with nonshockable arrest rhythms, 10 addressed shockable rhythms, and 6 provided guidance on open-chest CPR. We recommend against high-dose epinephrine even after prolonged CPR and suggest that atropine, when indicated, is used only once. In animals with a shockable rhythm in which initial defibrillation was unsuccessful, we recommend doubling the defibrillator dose once and suggest vasopressin (or epinephrine if vasopressin is not available), esmolol, lidocaine in dogs, and/or amiodarone in cats.

CONCLUSIONS

These updated RECOVER ALS guidelines clarify the approach to refractory shockable rhythms and prolonged CPR. Very low quality of evidence due to absence of clinical data in dogs and cats continues to compromise the certainty with which recommendations can be made.

Irreversibility: cardiac death versus brain death

The acceptance of brain death (BD) as death of the human being has been progressively accepted beginning in the early 1960s. The issue of irreversibility is directly related to the diagnosis of human death, and it is closely associated with the concept of potentiality, i.e., that some patients still have the potentiality of living. In recent years several authors have proposed to use a cardiocirculatory criterion for death determination in transplant donors. This has aroused ethical and medical controversies regarding concerns to accept that a non-heart-beating donor is really dead. We conclude that the cardiocirculatory criterion of death only assures irreversibility when asystole is prolonged enough to assure that ischemia and anoxia have destroyed the brain. On the contrary, BD fulfills both requirements for death determination: cessation of functions and irreversibility

Clinical application of therapeutic hypothermia in stroke

OBJECTIVE

Hypothermia has long been known to be a potent neuroprotectant. In this mini-review, we highlighted clinical experience that hypothermia protects the brain from cerebral injury. We discussed the clinical practice of hypothermia in ischemic stroke.

RESULTS

Multiple factors play a significant role in the mechanisms. Clinical application drew first from two clinical trials with comatose patients after cardiac arrest is attractive. The Australian and European study have led to renewed interest in these patients. More and more evidences bring the insight into its effects on cerebral ischemia. The type of cooling technique to be used, the duration of cooling and speed of rewarming appear to be key factors in determining whether hypothermia is effective in preventing or mitigating neurological injury. Although until now, there are no clear therapeutic standards of the parameters in therapeutic hypothermia, it is well accepted that cooling should be initiated as soon as possible. By combining hypothermia with other neuroprotectants, it may be possible to enhance protective effects, reduce side effects and lengthen the maximum time.

CONCLUSION

In addition to its neuroprotective properties, hypothermia may extend the therapeutic window for other neuroprotective treatment. Thus, combination therapies with neuroprotective, anti-inflammatory and thrombolytic agents are likely to be investigated in the clinical setting in the future.

Post-cardiac arrest syndrome: Epidemiology, pathophysiology, treatment, and prognostication: A scientific statement from the International Liaison Committee on Resuscitation; the American Heart Association Emergency Cardiovascular Care Committee; the Council on Cardiovascular Surgery and Anesthesia; the Council on Cardiopulmonary, Perioperative, and Critical Care; the Council on Clinical Cardiology; the Council on Stroke (Part 1)

AIM OF THE REVIEW

To review the epidemiology, pathophysiology, treatment and prognostication in relation to the post-cardiac arrest syndrome.

METHODS

Relevant articles were identified using PubMed, EMBASE and an American Heart Association EndNote master resuscitation reference library, supplemented by hand searches of key papers. Writing groups comprising international experts were assigned to each section. Drafts of the document were circulated to all authors for comment and amendment.

RESULTS

The 4 key components of post-cardiac arrest syndrome were identified as (1) post-cardiac arrest brain injury, (2) post-cardiac arrest myocardial dysfunction, (3) systemic ischaemia/reperfusion response, and (4) persistent precipitating pathology.

CONCLUSIONS

A growing body of knowledge suggests that the individual components of the postcardiac arrest syndrome are potentially treatable.

Post-cardiac arrest syndrome: epidemiology, pathophysiology, treatment, and prognostication. A Scientific Statement from the International Liaison Committee on Resuscitation; the American Heart Association Emergency Cardiovascular Care Committee; the Council on Cardiovascular Surgery and Anesthesia; the Council on Cardiopulmonary, Perioperative, and Critical Care; the Council on Clinical Cardiology; the Council on Stroke

AIM OF THE REVIEW

To review the epidemiology, pathophysiology, treatment and prognostication in relation to the post-cardiac arrest syndrome.

METHODS

Relevant articles were identified using PubMed, EMBASE and an American Heart Association EndNote master resuscitation reference library, supplemented by hand searches of key papers. Writing groups comprising international experts were assigned to each section. Drafts of the document were circulated to all authors for comment and amendment.

RESULTS

The 4 key components of post-cardiac arrest syndrome were identified as (1) post-cardiac arrest brain injury, (2) post-cardiac arrest myocardial dysfunction, (3) systemic ischaemia/reperfusion response, and (4) persistent precipitating pathology.

CONCLUSIONS

A growing body of knowledge suggests that the individual components of the post-cardiac arrest syndrome are potentially treatable.

Determination of prognosis after cardiac arrest may be more difficult after introduction of therapeutic hypothermia

A 50-year-old patient had status epilepticus and no adequate reactions nine days after prolonged out-of-hospital cardiac arrest. The cause of the arrest was acute myocardial infarction which was treated successfully with percutaneous cardiac intervention (PCI) and a stent placement. He was treated with therapeutic hypothermia (33 degrees C) for 24h and in intensive care with respiratory support for 42 days. One year later he has fully recovered and is back to normal life and academic work. The previously reported 100% prognosis of a poor neurological outcome in the presence of seizures 72 h post arrest may need to be re-examined after introduction of therapeutic hypothermia.

Post resuscitation care: what are the therapeutic alternatives and what do we know?

A large proportion of deaths in the Western World are caused by ischaemic heart disease. Among these patients a majority die outside hospital due to sudden cardiac death. The prognosis among these patients is in general, poor. However, a significant proportion are admitted to a hospital ward alive. The proportion of patients who survive the hospital phase of an out of hospital cardiac arrest varies considerably. Several treatment strategies are applicable during the post resuscitation care phase, but the level of evidence is weak for most of them. Four treatments are recommended for selected patients based on relatively good clinical evidence: therapeutic hypothermia, beta-blockers, coronary artery bypass grafting, and an implantable cardioverter defibrillator. The patient's cerebral function might influence implementation of the latter two alternatives. There is some evidence for revascularisation treatment in patients with suspected myocardial infarction. On pathophysiological grounds, an early coronary angiogram is a reasonable alternative. Further randomised clinical trials of other post resuscitation therapies are essential.

Strain specific differences in a cardio-pulmonary resuscitation rat model

An asphyxial cardiac arrest rat model, originally developed for Sprague-Dawley rats, was transferred to a Wistar rat model. Several strain specific life support adjustments, i.e. ventilator settings, anaesthesia, and drug requirements, were necessary to stabilize the model for Wistar rats. Despite these arrangements numerous resuscitation related variables appeared different. Three groups were evaluated and compared: a temperature monitored Wistar group 1 (n=34), a temperature controlled Wistar group 2 (n=26) and a temperature controlled Sprague-Dawley group 3 (n=7). Overall, Wistar rats seem to have more sensitive cardio-circulatory system evidenced by a more rapid development of cardiac arrest (164 vs. 201 s), requiring higher adrenaline/epinephrine doses (10 vs. 5 microg/kg) and requiring more time for recovery after resuscitation (i.e. for return of blood pressure and blood gases). Without strict temperature control (as in groups 2+3 rats) group 1 rats went into spontaneous mild to moderate hypothermia during the first 24 h after restoration of spontaneous circulation (ROSC). Spontaneous hypothermia delayed the development of overall visible CA1 neuronal damage 24-48 h, but did not prevent it; therefore the model seemed to be suitable for future studies. Neuronal damages in the CA1 region in Wistar rats appeared to be more as shrunken cell bodies and pyknotic nuclei before resorption took place, whereas in Sprague-Dawley rats appeared in the same region.

Fructose-1,6-bisphosphate and MK-801 by aortic arch flush for cerebral preservation during exsanguination cardiac arrest of 20 min in dogs. An exploratory study

In our exsanguination cardiac arrest (CA) outcome model in dogs we are systematically exploring suspended animation (SA), i.e. preservation of brain and heart immediately after the onset of CA to enable transport and resuscitative surgery during CA, followed by delayed resuscitation. We have shown in dogs that inducing moderate cerebral hypothermia with an aortic arch flush of 500 ml normal saline solution at 4 degrees C, at start of CA 20 min no-flow, leads to normal functional outcome. We hypothesized that, using the same model, but with the saline flush at 24 degrees C inducing minimal cerebral hypothermia (which would be more readily available in the field), adding either fructose-1,6-bisphosphate (FBP, a more efficient energy substrate) or MK-801 (an N-methyl-D-aspartate (NMDA) receptor blocker) would also achieve normal functional outcome. Dogs (range 19-30 kg) were exsanguinated over 5 min to CA of 20 min no-flow, and resuscitated by closed-chest cardiopulmonary bypass (CPB). They received assisted circulation to 2 h, mild systemic hypothermia (34 degrees C) post-CA to 12 h, controlled ventilation to 20 h, and intensive care to 72 h. At CA 2 min, the dogs received an aortic arch flush of 500 ml saline at 24 degrees C by a balloon-tipped catheter, inserted through the femoral artery (control group, n=6). In the FBP group (n=5), FBP (total 1440 or 4090 mg/kg) was given by flush and with reperfusion. In the MK-801 group (n=5), MK-801 (2, 4, or 8 mg/kg) was given by flush and with reperfusion. Outcome was assessed in terms of overall performance categories (OPC 1, normal; 2, moderate disability; 3, severe disability; 4, coma; 5, brain death or death), neurologic deficit scores (NDS 0-10%, normal; 100%, brain death), and brain histologic damage scores (HDS, total HDS 0, no damage; >100, extensive damage; 1064, maximal damage). In the control group, one dog achieved OPC 2, one OPC 3, and four OPC 4; in the FBP group, two dogs achieved OPC 3, and three OPC 4; in the MK-801 group, two dogs achieved OPC 3, and three OPC 4 (P=1.0). Median NDS were 62% (range 8-67) in the control group; 55% (range 34-66) in the FBP group; and 50% (range 26-59) in the MK-801 group (P=0.2). Median total HDS were 130 (range 56-140) in the control group; 96 (range 64-104) in the FBP group; and 80 (range 34-122) in the MK-801 group (P=0.2). There was no difference in regional HDS between groups. We conclude that neither FBP nor MK-801 by aortic arch flush at the start of CA, plus an additional i.v. infusion of the same drug during reperfusion, can provide cerebral preservation during CA 20 min no-flow. Other drugs and drug-combinations should be tested with this model in search for a breakthrough effect.

Therapeutic hypothermia after cardiac arrest

This review discusses the mechanisms of neurologic damage during and after global cerebral ischemia caused by cardiac arrest. The different pathways of membrane destruction by radicals, free fatty acids, excitatory amino acids (neurotransmitters), calcium, glucose metabolism, and oxygen availability and demand in relation to metabolic rate are briefly discussed. The main focus of this review paper, however, lies in therapeutic (resuscitative) hypothermia after cardiac arrest. Two pioneering studies of the 1950s and four recent publications (in part preliminary results of ongoing studies) in humans are discussed in detail. The conclusions are as follows: (1) hypothermia holds promise as the only specific brain therapy after cardiac arrest so far; (2) hyperthermia is not tolerable after successful resuscitation; and (3) if the ongoing European multicenter trial of hypothermia after cardiac arrest finds a significant benefit to mild hypothermia, withholding hypothermia may be ethically hard to defend.

Brain energetics of cardiopulmonary cerebral resuscitation

Recovery of normal brain energetic conditions during and after resuscitation from cardiac arrest is critical for survival and good neurologic outcome. This review emphasizes the glucose-driven metabolic processes during and after ischemia and on the post-resuscitation development of secondary energy derangements. It also explores some potential therapeutic interventions designed to attenuate these energy derangements. The article summarizes some bench research and is not intended to provide treatment strategies for clinical application.

Thiopental and phenytoin by aortic arch flush for cerebral preservation during exsanguination cardiac arrest of 20 minutes in dogs. An exploratory study

We are systematically exploring in our exsanguination cardiac arrest (CA) outcome model in dogs suspended animation (SA), i.e. immediate preservation of brain and heart for resuscitative surgery during CA, with delayed resuscitation. We have shown in dogs that inducing moderate cerebral hypothermia with an aortic arch flush of 500 ml normal saline solution of 4 degrees C, at start of CA 20 min no-flow, leads to normal functional outcome. We hypothesized that, using the same model, adding thiopental (or even better thiopental plus phenytoin) to the flush at ambient temperature (24 degrees C), which would be more readily available in the field, will also achieve normal functional outcome. Thirty dogs (20-28 kg) were exsanguinated over 5 min to CA of 20 min no-flow, and resuscitated by closed-chest cardiopulmonary bypass. They received assisted circulation to 2 h, 34 degrees C post-CA to 12 h, controlled ventilation to 20 h, and intensive care to 72 h. At CA 2 min, the dogs received an aortic arch flush of 500 ml saline at 24 degrees C by a balloon-tipped catheter, inserted through the femoral artery (control group 1, n=14). In group 2 (n=9), thiopental (variable total doses of 15-120 mg/kg) was added to the flush and given with reperfusion. In group 3 (n=7), thiopental (15 or 45 mg/kg) plus phenytoin (10, 20, or 30 mg/kg) was given by flush and with reperfusion. Outcome was assessed in terms of overall performance categories (OPC 1, normal; 2, moderate disability; 3, severe disability; 4, coma; 5, brain death), neurologic deficit scores (NDS 0-10%, normal; 100%, brain death), and histologic deficit scores (HDS, total and regional). The flush reduced tympanic temperature to about 36 degrees C in all groups. In control group 1, one dog achieved OPC 1, three OPC 2, six OPC 3, and four OPC 4. In thiopental group 2, two dogs achieved OPC 1, two OPC 3, and five OPC 4. In thiopental/phenytoin group 3, one dog achieved OPC 1, two OPC 3, and four OPC 4 (p=0.5). Median NDS were 36% (IQR 22-62%) in group 1; 51% (IQR 22-56%) in group 2; and 55% (IQR 38-59%) in group 3 (p=0.7). Median total HDS were 67 (IQR 56-127) in group 1; 60 (IQR 52-138) in group 2; and 76 (IQR 48-132) in group 3 (p=1.0). Thiopental and thiopental/phenytoin dogs achieved significantly lower HDS only in the putamen. Thiopental in large doses caused side effects. We conclude that neither thiopental alone nor thiopental plus phenytoin by flush, with or without additional intravenous infusion, can consistently provide 'clinically significant' cerebral preservation for 20 min no-flow. Other drugs and drug-combinations should be tested with this model in search for a breakthrough effect.