A comparison of epinephrine and methoxamine for resuscitation from electromechanical dissociation in human beings

Adrenaline and vasopressin for cardiac arrest

BACKGROUND

Adrenaline and vasopressin are widely used to treat people with cardiac arrest, but there is uncertainty about the safety, effectiveness and the optimal dose.

OBJECTIVES

To determine whether adrenaline or vasopressin, or both, administered during cardiac arrest, afford any survival benefit.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials, MEDLINE, Embase and DARE from their inception to 8 May 2018, and the International Liaison Committee on Resuscitation 2015 Advanced Life Support Consensus on Science and Treatment Recommendations. We also searched four trial registers on 5 September 2018 and checked the reference lists of the included studies and review papers to identify potential papers for review.

SELECTION CRITERIA

Any randomised controlled trial comparing: standard-dose adrenaline versus placebo; standard-dose adrenaline versus high-dose adrenaline; and adrenaline versus vasopressin, in any setting, due to any cause of cardiac arrest, in adults and children. There were no language restrictions.

DATA COLLECTION AND ANALYSIS

Two review authors independently identified trials for review, assessed risks of bias and extracted data, resolving disagreements through re-examination of the trial reports and by discussion. We used risk ratios (RRs) with 95% confidence intervals (CIs) to compare dichotomous outcomes for clinical events. There were no continuous outcomes reported. We examined groups of trials for heterogeneity. We report the quality of evidence for each outcome, using the GRADE approach.

MAIN RESULTS

We included 26 studies (21,704 participants).Moderate-quality evidence found that adrenaline increased survival to hospital discharge compared to placebo (RR 1.44, 95% CI 1.11 to 1.86; 2 studies, 8538 participants; an increase from 23 to 32 per 1000, 95% CI 25 to 42). We are uncertain about survival to hospital discharge for high-dose compared to standard-dose adrenaline (RR 1.10, 95% CI 0.75 to 1.62; participants = 6274; studies = 10); an increase from 33 to 36 per 1000, 95% CI 24 to 53); standard-dose adrenaline versus vasopressin (RR 1.25, 95% CI 0.84 to 1.85; 6 studies; 2511 participants; an increase from 72 to 90 per 1000, 95% CI 60 to 133); and standard-dose adrenaline versus vasopressin plus adrenaline (RR 0.76, 95% CI 0.47 to 1.22; 3 studies; 3242 participants; a possible decrease from 24 to 18 per 1000, 95% CI 11 to 29), due to very low-quality evidence.Moderate-quality evidence found that adrenaline compared with placebo increased survival to hospital admission (RR 2.51, 95% CI 1.67 to 3.76; 2 studies, 8489 participants; an increase from 83 to 209 per 1000, 95% CI 139 to 313). We are uncertain about survival to hospital admission when comparing standard-dose with high-dose adrenaline, due to very low-quality evidence. Vasopressin may improve survival to hospital admission when compared with standard-dose adrenaline (RR 1.27, 95% CI 1.04 to 1.54; 3 studies, 1953 participants; low-quality evidence; an increase from 260 to 330 per 1000, 95% CI 270 to 400), and may make little or no difference when compared to standard-dose adrenaline plus vasopressin (RR 0.95, 95% CI 0.83 to 1.08; 3 studies; 3249 participants; low-quality evidence; a decrease from 218 to 207 per 1000 (95% CI 181 to 236).There was no evidence that adrenaline (any dose) or vasopressin improved neurological outcomes.The rate of return of spontaneous circulation (ROSC) was higher for standard-dose adrenaline versus placebo (RR 2.86, 95% CI 2.21 to 3.71; participants = 8663; studies = 3); moderate-quality evidence; an increase from 115 to 329 per 1000, 95% CI 254 to 427). We are uncertain about the effect on ROSC for the comparison of standard-dose versus high-dose adrenaline and standard-does adrenaline compared to vasopressin, due to very low-quality evidence. Standard-dose adrenaline may make little or no difference to ROSC when compared to standard-dose adrenaline plus vasopressin (RR 0.97, 95% CI 0.87 to 1.08; 3 studies, 3249 participants; low-quality evidence; a possible decrease from 299 to 290 per 1000, 95% CI 260 to 323).The source of funding was not stated in 11 of the 26 studies. The study drugs were provided by the manufacturer in four of the 26 studies, but neither drug represents a profitable commercial option. The other 11 studies were funded by organisations such as research foundations and government funding bodies.

AUTHORS' CONCLUSIONS

This review provides moderate-quality evidence that standard-dose adrenaline compared to placebo improves return of spontaneous circulation, survival to hospital admission and survival to hospital discharge, but low-quality evidence that it did not affect survival with a favourable neurological outcome. Very low -quality evidence found that high-dose adrenaline compared to standard-dose adrenaline improved return of spontaneous circulation and survival to admission. Vasopressin compared to standard dose adrenaline improved survival to admission but not return of spontaneous circulation, whilst the combination of adrenaline and vasopressin compared with adrenaline alone had no effect on these outcomes. Neither standard dose adrenaline, high-dose adrenaline,vasopressin nor a combination of adrenaline and vasopressin improved survival with a favourable neurological outcome. Many of these studies were conducted more than 20 years ago. Treatment has changed in recent years, so the findings from older studies may not reflect current practice.

Vasopressors During Cardiopulmonary Resuscitation. A Network Meta-Analysis of Randomized Trials

OBJECTIVES

Several randomized controlled trials have compared adrenaline (epinephrine) with alternative therapies in patients with cardiac arrest with conflicting results. Recent observational studies suggest that adrenaline might increase return of spontaneous circulation but worsen neurologic outcome. We systematically compared all the vasopressors tested in randomized controlled trials in adult cardiac arrest patients in order to identify the treatment associated with the highest rate of return of spontaneous circulation, survival, and good neurologic outcome.

DESIGN

Network meta-analysis.

PATIENTS

Adult patients undergoing cardiopulmonary resuscitation.

INTERVENTIONS

PubMed, Embase, BioMed Central, and the Cochrane Central register were searched (up to April 1, 2017). We included all the randomized controlled trials comparing a vasopressor with any other therapy. A network meta-analysis with a frequentist approach was performed to identify the treatment associated with the highest likelihood of survival.

MEASUREMENTS AND MAIN RESULTS

Twenty-eight studies randomizing 14,848 patients in 12 treatment groups were included. Only a combined treatment with adrenaline, vasopressin, and methylprednisolone was associated with increased likelihood of return of spontaneous circulation and survival with a good neurologic outcome compared with several other comparators, including adrenaline. Adrenaline alone was not associated with any significant difference in mortality and good neurologic outcome compared with any other comparator.

CONCLUSIONS

In randomized controlled trials assessing vasopressors in adults with cardiac arrest, only a combination of adrenaline, vasopressin, and methylprednisolone was associated with improved survival with a good neurologic outcome compared with any other drug or placebo, particularly in in-hospital cardiac arrest. There was no significant randomized evidence to support neither discourage the use of adrenaline during cardiac arrest.

Towards cardiopulmonary resuscitation without vasoactive drugs

PURPOSE OF REVIEW

Whereas there is clear evidence for improved survival with cardiopulmonary resuscitation (CPR) and defibrillation during cardiac arrest management, there is today lacking evidence that any of the recommended and used drugs lead to any long-term benefit for the patients. In this review, we try to discuss our current view on why advanced life support (ALS) today can be performed without the use of drugs, and instead gain all focus on improving the tasks we know improve survival: CPR and defibrillation.

RECENT FINDINGS

Previous and recent cardiac arrest drug studies have been reviewed. These are mostly consisting of retrospective register data, some experimental data and a few new randomized trials. The alternative drug-free ALS concept is also discussed with relevant studies.

SUMMARY

There is currently no evidence to support any specific drugs during cardiac arrest. Good-quality CPR, early defibrillation and goal-directed postresuscitation care is more important. Healthcare systems should not prioritize implementation of unproven drugs before good quality of care can be documented. More drug studies are indeed required, and future research needs to incorporate better diagnostic tools to test more specific and tailored therapies that account for underlying causes and individual responsiveness.

Use of alpha-agonists for management of anaphylaxis occurring under anaesthesia: case studies and review

Anaphylaxis is an uncommon but serious complication of anaesthesia. Most current guidelines for the management of anaphylaxis list only epinephrine as a vasopressor to use in the event of cardiovascular collapse. We present two cases of anaphylaxis under anaesthesia where return of spontaneous circulation was refractory to epinephrine, but occurred following the administration of the alpha-agonist metaraminol. Potential advantages and disadvantages of using epinephrine in this setting, the role of alpha-agonists and some potential mechanisms accounting for their role in successful management are reviewed.

Vasopressin and epinephrine are equally effective for CPR in a rat asphyxia model

Epinephrine has been administered as a drug essential for cardiopulmonary resuscitation (CPR). Recently, vasopressin has been reported to be more effective than epinephrine for CPR in a ventricular fibrillation (VF) model. As a different myocardial pathology is speculated to exist between the VF model and the asphyxia model, we investigated whether vasopressin is also effective in a rat asphyxia model. Twenty-one Sprague-Dawley male rats were divided into three groups: vasopressin 0.8 U/kg (Vaso-Gr), epinephrine 0.05 mg/kg (Epi-Gr), and saline same volume as the other two drugs (Sal-Gr). Five minutes after suffocation induced by obstruction of the tracheal tube, CPR was performed using each drug. Although only one animal survived (17%) in the Sal-Gr, 6/7 (85%) survived in both Vaso-Gr and Epi-Gr (P<0.01). Vasopressin is as effective as epinephrine for CPR in asphyxia-induced rats.

Use of methoxamine in the resuscitation of epinephrine-resistant electromechanical dissociation

We describe three cases of electromechanical dissociation under anaesthesia that were unresponsive to doses of intravenous epinephrine given according to current Advanced Life Support guidelines, but which responded immediately to the intravenous administration of the pure alpha agonist, methoxamine. We suggest a possible mechanism to explain this finding and review the literature on vasopressor drugs used for cardiopulmonary resuscitation during electromechanical dissociation. An intravenous alpha agonist, such as methoxamine 20 mg, should be considered for any case of cardiac arrest secondary to electromechanical dissociation which is unresponsive to epinephrine given according to current guidelines.

Cardiopulmonary resuscitation: a promise as yet largely unfulfilled

After failure of initial external defibrillation, restoration of spontaneous circulation is largely contingent on rapid and effective reversal of myocardial ischemia by both mechanical and pharmacologic means. Despite the introduction of modern cardiopulmonary resuscitation (CPR) more than 35 years ago, its universal acceptance, and its wide implementation, no improvements in outcome excepting early defibrillation have been documented over these many years. The science of CPR therefore is still in its infancy. It was incorrectly assumed that all that needs to be known is known and that the need for scientific research was therefore not apparent. Accordingly, serious resuscitation research was neither encouraged nor equitably supported. The ABCs of CPR currently provide for the establishment of a patent airway (A) and intermittent positive pressure ventilation, preferably with oxygen-enriched air (B). These are to be immediately followed with precordial compression (C). This ordering of priorities, however, is based on consensus rather than objective outcome measurements. The ABCs recently have been seriously challenged on the basis of results of both experimental and clinical studies. Conventional external precordial compression restores systemic blood flow. It may be used by both professional and nonprofessional CPR providers, especially bystanders, because of its apparent simplicity and noninvasiveness. However, manual or mechanical external precordial compression typically generates cardiac outputs that represent less than 30% of normal values. Coronary blood flow, which is critical for restoration of spontaneous circulation, is correspondingly reduced. Accordingly, several alternatives to conventional precordial compression have been proposed with the intent of increasing cardiac output and both coronary and cerebral blood flows. Among the large number of pharmaceutical agents initially recommended for cardiac resuscitation, only agents that produce peripheral vasoconstriction are of proved benefit. Epinephrine has been the preferred vasopressor agent for the management of cardiac arrest for more than 35 years because of its alpha-adrenergic effects. However, the potentially adverse effects of epinephrine are related to its beta-adrenergic inotropic actions. The beta-adrenergic actions account for disproportionate increases in myocardial oxygen consumption with increased severity of myocardial ischemic injury and provocation of ectopic ventricular tachycardia and ventricular fibrillation. Nevertheless, epinephrine remains the drug of choice, although adrenergic drugs with selective alpha-adrenergic actions or nonadrenergic vasoconstrictor drugs are likely to emerge as useful alternatives. Experimental and clinical observations have led to identification of continuous monitoring of both end-tidal carbon dioxide and ventricular fibrillation waveforms as practical noninvasive guides because they are highly correlated with both cardiac output and coronary blood flow. Both end-tidal carbon dioxide and ventricular fibrillation waveforms now serve as predictors of the likelihood of successful resuscitation. These two measurements may now be used to guide interventions and especially to assure optimal precordial compression. It is well established that sudden death among adults is predominantly due to malignant ventricular arrhythmias and ventricular fibrillation. Early defibrillation serves as an unequivocally effective immediate intervention. Minimally trained first responders and members of the general public are being enfranchised to use automated external defibrillators for very early defibrillation. Use of these devices by bystanders is the most promising new intervention since CPR was first proposed in the early 1960s. Postresuscitation ventricular dysrhythmias and heart failure are now called postresuscitation myocardial dysfunction. This complication has been recognized as a leading cause of the high postresuscitation mor

Recent advances in cardiopulmonary resuscitation

Mechanical and pharmacologic measures intended to increase blood flow to vital organs are the mainstay of therapy for patients in cardiac arrest. Several new cardiopulmonary resuscitation (CPR) techniques as well as novel devices and pharmacologic agents have been developed and tested since the first report of manual closed chested CPR over three decades ago. These recent mechanical and pharmacologic advances in the treatment of cardiac arrest are described. Some of these new techniques, devices, and drug therapies are presently undergoing clinical evaluation in patients in cardiac arrest. While many of these new methods and techniques have shown promise in small clinical trials in humans, none have yet to be found to be conclusively superior to manual closed chested CPR and treatment with standard pharmacologic agents.

Pharmacology of pediatric resuscitation

The resuscitation of children from cardiac arrest and shock remains a challenging goal. The pharmacologic principles underlying current recommendations for intervention in pediatric cardiac arrest have been reviewed. Current research efforts, points of controversy, and accepted practices that may not be most efficacious have been described. Epinephrine remains the most effective resuscitation adjunct. High-dose epinephrine is tolerated better in children than in adults, but its efficacy has not received full analysis. The preponderance of data continues to point toward the ineffectiveness and possible deleterious effects of overzealous sodium bicarbonate use. Calcium chloride is useful in the treatment of ionized hypocalcemia but may harm cells that have experienced asphyxial damage. Atropine is an effective agent for alleviating bradycardia induced by increased vagal tone, but because most bradycardia in children is caused by hypoxia, improved oxygenation is the intervention of choice. Adenosine is an effective and generally well-tolerated agent for the treatment of supraventricular tachycardia. Lidocaine is the drug of choice for ventricular dysrhythmias, and bretylium, still relatively unexplored, is in reserve. Many pediatricians use dopamine for shock in the postresuscitative period, but epinephrine is superior. Most animal research on cardiac arrest is based on models with ventricular fibrillation that probably are not reflective of cardiac arrest situations most often seen in pediatrics.

Future directions for resuscitation research. IV. Innovative advanced life support pharmacology

The topics discussed in this session include a partial review of laboratory and clinical studies examining the effects of adrenergic agonists on restoration of spontaneous circulation after cardiac arrest, the effects of varying doses of epinephrine, and the effects of novel vasopressors, buffer agents (NaHCO3, THAM, 'Carbicarb') and anti-arrhythmics (lidocaine, bretylium, amiodarone) in refractory ventricular fibrillation. Novel therapeutic approaches include titrating electric countershocks against electrocardiographic power spectra and of preceding the first countershocks with single or multiple drug treatments. These approaches need to be investigated further in controlled animal and patient studies. Epidemiologic data from randomized clinical outcome studies can give clues, but cannot document pharmacologic mechanisms in the dynamically changing events during attempts to achieve restoration of spontaneous circulation from prolonged cardiac arrest. Also, rapid drug administration by the intraosseous route was compared with intratracheal and intravenous (i.v.) drug administration. Many studies on the above treatments have yielded conflicting results because of differences between healthy hearts of animals and sick hearts of patients, differences in arrest (no-flow) times and cardiopulmonary resuscitation (CPR) (low-flow) times, different pharmacokinetics, different dose/response requirements, and different timing of drug administration during low-flow CPR versus during spontaneous circulation. The need to stabilize normotension and prevent rearrest by titrated novel drug administration, once spontaneous circulation has been restored, requires research. Most of the above topics require some re-evaluation in clinically realistic animal models and in cardiac arrest patients, especially by titration of old and new drug treatments against variables that can be monitored continuously during resuscitation.

Reporting approval by research ethics committees and subjects' consent in human resuscitation research

OBJECTIVE

To determine how frequently reports of research in human cardiopulmonary resuscitation mention approval by a research ethics committee and address subjects' consent.

METHODS

Retrospective review of published reports of interventional research in human cardiopulmonary resuscitation. Reports were retrieved from the MEDLINE database and selected according to pre-established criteria. Data were abstracted independently by the two authors with differences resolved by mutual agreement. Results were analyzed according to whether the research took place in the prehospital setting, the emergency department, or the hospital; whether it was conducted within or outside the United States; whether it received any funding from the US government; its randomization scheme; the year of publication; and whether the journal's instructions required mention of REC approval or subjects' consent.

RESULTS

Reports of 47 studies met our criteria for inclusion. Of these, 24 (51%) mentioned approval by a research ethics committee and 12 (26%) addressed subjects' consent. Significantly more studies reported ethics committee approval or addressed consent during more recent years. Authors were more likely to report consent, REC approval, or both when journal instructions required that REC approval be mentioned.

CONCLUSION

Reports of resuscitation research have not consistently mentioned approval from a research ethics committee or addressed subjects' consent for interventional studies using human subjects. However, they are doing so more frequently in recent years as journal requirements for reporting change. REC approval is now almost always being reported, but subjects' consent is often not addressed. Journal editors and reviewers should ensure that authors adhere to the journal's instructions about reporting ethical conduct of experiments.

Cardiac arrest

This article reviews the critical resuscitations necessary during prehospital and emergency department treatment of cardiac arrest. Standard therapy for cardiac arrest rhythms is presented. Novel pharmacologic agents, types of cardiopulmonary resuscitation, and circulatory-assist devices are discussed.

Comparison of adrenergic agonists for the treatment of ventricular fibrillation and pulseless electrical activity

The primary role of epinephrine for the treatment of ventricular fibrillation (VF) and pulseless electrical activity (PEA) is to increase blood flow to the myocardium and central nervous system and ultimately improve survival. However, despite the administration of epinephrine, survival following VF or PEA is low. In an attempt to improve outcome from VF and PEA, alternative adrenergic agonists (methoxamine, phenylephrine, norepinephrine) which have different pharmacological properties than epinephrine have been evaluated. In order to determine the role of alternative adrenergic agonists for the treatment of VF and PEA this paper will compare the pharmacological properties and pharmacodynamic effects of these drugs to epinephrine. Specifically, receptor physiology along with the effects of adrenergic agonists on coronary perfusion pressure, survival, myocardial oxygen demand, and cerebral blood flow will be discussed.

Beta-adrenergic blockade reduces myocardial injury during experimental cardiopulmonary resuscitation

OBJECTIVES

We attempted to determine the effects of beta-adrenergic blockade during cardiopulmonary resuscitation (CPR) on defibrillation rates and postresuscitation left ventricular function.

BACKGROUND

The results of previous studies suggest that propranolol administration can both reduce myocardial oxygen requirements and increase coronary perfusion pressure during CPR.

METHODS

Left ventricular pressure and segment length were measured before and after 5 min of CPR in 22 dogs either given epinephrine (0.015 mg/kg body weight at the onset and after 4 min) or pretreated with propranolol (2 mg/kg) and given epinephrine during CPR.

RESULTS

Despite identical epinephrine doses, coronary perfusion pressure during CPR was higher in the epinephrine plus propranolol group (p < 0.05), and defibrillation was successful in 9 of 11 dogs given both epinephrine and propranolol versus 6 of 11 dogs given epinephrine alone (p = NS). Peak and developed left ventricular pressures, left ventricular end-diastolic pressure and the peak rate of left ventricular pressure development (+dP/dt) did not differ between study groups when measured either 5 or 15 min after successful defibrillation. However, when survivors in the epinephrine group were given propranolol after CPR to eliminate compensatory sympathetic stimulation, left ventricular developed pressure and peak +dP/dt were lower (p < 0.05) despite trends toward higher left ventricular end-diastolic pressures and normalized end-diastolic segment lengths compared with dogs given propranolol before CPR.

CONCLUSIONS

These findings suggest that beta-adrenergic blockade reduces myocardial injury during CPR without decreasing the likelihood of successful defibrillation or compromising spontaneous postresuscitation left ventricular function.

Use of adrenergic agonists during CPR in adults

Adrenergic therapy is indicated during CPR to increase the coronary and cerebral perfusion pressure. Epinephrine hydrochloride at a dosage of 1.0 mg has been the most commonly used adrenergic agonist for resuscitation of adults, but there has been considerable controversy over whether higher doses should be given. At the 1992 National Conference on Emergency Cardiac Care and CPR, preliminary data were presented from three large, prospective, blinded, unpublished clinical trials that included a comparison of standard-dose (0.02 mg/kg or approximately 1.0 mg) and high-dose (approximately 0.1-0.2 mg/kg) epinephrine in 2,415 adults. Although the studies differed from each other somewhat in design, the results were remarkably consistent across all three studies: there was no difference in survival between the standard- and high-dose epinephrine regimens. There were no consistent adverse effects associated with the use of higher-than-standard doses of epinephrine. The consensus of the Adrenergic Agonist Panel was that: 1) epinephrine by i.v. bolus should remain the drug of choice for use during resuscitation in adults; 2) data presented from the clinical trials in adults do not support an increase in the recommended dose of epinephrine; 3) because there was no evidence of significant harm from the use of high-dose epinephrine, it was felt that use of such dosages should receive a II-b recommendation pending the results of further ongoing clinical trials; 4) the standard i.v. bolus dosage of epinephrine should be simplified to 1.0 mg every three to five minutes; and 5) the endotracheal dosage of epinephrine should be at least 2 to 2.5 times larger than the peripheral i.v. dosage.

Pediatric resuscitation pharmacology. Members of the Medications in Pediatric Resuscitation Panel

The goal of resuscitation pharmacology is to restart the heart as quickly as possible while preserving vital organ function during chest compression. Unfortunately, the application of advanced life support to pediatric cardiac arrest patients is often unsuccessful. The goal of this paper is to review the scientific rationale and educational considerations used to derive the guidelines for medication use in the pediatric patient during CPR. The first step in drug delivery during CPR is to achieve vascular access. The endotracheal route and intraosseous route may be used, although the former is not reliable. To maximize endotracheal drug effect, a larger dose should be instilled into the airway as deeply as possible. Any vascular access, including intraosseous, is preferable to endotracheal drug administration. Although other alpha-adrenergic agents are theoretically superior, epinephrine remains the drug of choice in pediatric resuscitation. The previously recommended dose, however, may be inadequate; a dose 10 to 20 times larger (100-200 micrograms/kg) should be considered, particularly if the standard dose is ineffective. Lacking convincing data, the indications and dose for calcium are unchanged. Similarly, there are no data advocating a change in the indications or dose for lidocaine, bretylium, or atropine. The treatment of arrest-induced acidosis remains controversial. The mainstay of therapy consists of efforts to maximize oxygenation and tissue perfusion. Bicarbonate is not a first-line drug; its use should be considered when the patient fails to respond to advanced life support efforts, including the administration of high-dose epinephrine. Bicarbonate may be helpful in the postresuscitation setting, but its use should not supplant efforts to maximize tissue perfusion. Adenosine is an effective and generally safe medication for the treatment of supraventricular tachycardia in infants and children. Therefore, its indications, dose, and toxicities should be included in the new guidelines. Finally, a summary of research initiatives are included, including a call for the development of a multi-institutional pediatric clinical resuscitation research group. Large numbers of patients must be enrolled in a standardized manner to better evaluate the benefits and adverse effects of various therapies. This includes the use of high-dose epinephrine, calcium, bicarbonate, and other buffer agents such as Carbicarb and THAM. Animal models simulating the etiology and pathophysiology of pediatric arrest also are needed. In both clinical and animal studies, neurologic outcome and long-term survival should be assessed rather than simply the rate of restoration of spontaneous circulation.

Use of cardiopulmonary bypass, high-dose epinephrine, and standard-dose epinephrine in resuscitation from post-countershock electromechanical dissociation

STUDY OBJECTIVE

To determine the effects of cardiopulmonary bypass with standard-dose epinephrine, high-dose epinephrine, and standard-dose epinephrine on perfusion pressures, myocardial blood flow, and resuscitation from post-countershock electromechanical dissociation.

DESIGN

Prospective, controlled laboratory investigation using a canine cardiac arrest model randomized to receive one of three resuscitation therapies.

INTERVENTIONS

After the production of post-countershock electromechanical dissociation, 25 animals received ten minutes of basic CPR and were randomized to receive cardiopulmonary bypass with standard-dose epinephrine, high-dose epinephrine, or standard-dose epinephrine.

MEASUREMENTS AND MAIN RESULTS

Myocardial blood flow was measured using a colored microsphere technique at baseline, during basic CPR, and after intervention. Immediate and two-hour resuscitation rates were determined for each group. Return of spontaneous circulation was achieved in eight of eight cardiopulmonary bypass with standard-dose epinephrine compared with four of eight high-dose epinephrine and three of eight standard-dose epinephrine animals (P less than .04). One animal was resuscitated with CPR alone and was excluded. Survival to two hours was achieved in five of eight cardiopulmonary bypass with standard-dose epinephrine, four of eight high-dose epinephrine, and three of eight standard-dose epinephrine animals (NS). Coronary perfusion pressure increased significantly in the cardiopulmonary bypass with standard-dose epinephrine group when compared with the other groups (cardiopulmonary bypass with standard-dose epinephrine, 76 +/- 45 mm Hg; high-dose epinephrine, 24 +/- 12 mm Hg; standard-dose epinephrine, 3 +/- 14 mm Hg; P less than .005). Myocardial blood flow was higher in cardiopulmonary bypass with standard-dose epinephrine and high-dose epinephrine animals compared with standard-dose epinephrine animals but did not reach statistical significance. Cardiac output increased during cardiopulmonary bypass with standard-dose epinephrine (P = .001) and standard-dose epinephrine (NS) compared with basic CPR but decreased after epinephrine administration in the high-dose epinephrine group (NS).

CONCLUSION

Resuscitation from electromechanical dissociation was improved with cardiopulmonary bypass and epinephrine compared with high-dose epinephrine or standard-dose epinephrine alone. However, there was no difference in survival between groups. Cardiopulmonary bypass with standard-dose epinephrine resulted in higher cardiac output, coronary perfusion pressure, and a trend toward higher myocardial blood flow. A short period of cardiopulmonary bypass with epinephrine after prolonged post-countershock electromechanical dissociation cardiac arrest can re-establish sufficient circulation to effect successful early resuscitation.

Aortic pressure during human cardiac arrest. Identification of pseudo-electromechanical dissociation

We measured aortic pressure during clinically apparent cardiac electromechanical dissociation (EMD). Patients with pulse pressures were designated as having pseudo-EMD; those without, as having true EMD. Of the 200 patients studied, 54 presented with EMD, and 40 others developed it during resuscitation. Of the 94 with EMD, 39 were found to have pseudo-EMD. We compared the two types of EMD for electrocardiographic duration, return of palpable pulses, and response to standard- and high-dose epinephrine. The mean resting aortic pressure was 18 +/- 11 mm Hg in patients with true EMD and 28 +/- 11 mm Hg in those with pseudo-EMD. The mean pulse pressure in patients with pseudo-EMD was 6.3 +/- 3.5 mm Hg. Patients with pseudo-EMD had a higher proportion of witnessed arrests, higher PaO2, and lower PaCO2 than patients with true EMD. Patients with pseudo-EMD had shorter QR and QRS durations than patients with true EMD. They had a better response to standard- and high-dose epinephrine than patients with true EMD. Many patients diagnosed clinically to be in EMD have mechanical cardiac activity; this should be considered when interpreting the results of cardiac arrest research.

Epinephrine in cardiopulmonary resuscitation

This review assesses the role of epinephrine in cardiopulmonary resuscitation from the perspective of mechanisms of action, cardiac and cerebral effects, and use in human beings. We reviewed the literature from 1966 onward, using a Medline Search of the National Library of Medicine with the key words: "heart arrest," "resuscitation," and "epinephrine." Pertinent articles that represented original research were critically appraised by at least two authors. We concluded that the Advanced Cardiac Life Support recommended dose of epinephrine (1 mg or 0.007 to 0.014 mg/kg) has little scientific basis. Evidence from animal studies demonstrates that doses of 0.1 to 0.2 mg/kg are required to significantly improve myocardial and cerebral blood flow and resuscitation rates. Limited human data confirm the dose-dependent vasopressor response to epinephrine and the potential for improved immediate survival with higher doses. We suggest that randomized controlled human trials are needed to document the usefulness of higher doses of epinephrine in cardiopulmonary resuscitation.

Adrenergic agonists during cardiopulmonary resuscitation

A number of studies have suggested that following a prolonged cardiopulmonary arrest, large doses of alpha-adrenergic agonists that possess post-synaptic alpha-2 agonist properties, i.e. epinephrine and norepinephrine, may be required to enhance myocardial and cerebral hemodynamics. While initial human studies using large doses of epinephrine have shown improved hemodynamics over standard therapy, hospital discharge rates and neurological outcome have been discouraging. This probably reflects the fact that the administration of epinephrine was employed late in the resuscitation effort. Future studies using larger doses of epinephrine as the initial pharmacologic intervention during cardiopulmonary resuscitation (CPR) will help to determine whether there is any therapeutic benefit. In addition, a number of questions still remain unanswered in delineating the specific alpha and beta adrenergic agonist components which will maximally enhance hemodynamics and resuscitation rates during CPR. This will help determine whether norepinephrine or a yet unsynthesized adrenergic agonist may be more beneficial for use during cardiac arrest.