Comparison of adrenaline and phenylephrine in out-of-hospital cardiopulmonary resuscitation. A double-blind study

The cerebral and cardiac effects of Norepinephrine in an experimental cardiac arrest model

Introduction

Epinephrine has been the main drug recommended for decades during cardiopulmonary resuscitation (CPR). But epinephrine's ß-adrenergic effects might increase myocardial oxygen consumption and may cause arrythmias after ROSC. Norepinephrine has a weaker ß-adrenergic effect and could be useful during CPR. Studies on norepinephrine's effect on hemodynamic parameters and cerebral perfusion are scarce. This study aimed to assess norepinephrine's hemodynamic impact in an experimental model of cardiac arrest.

Methods

After an initial dose study to determine the optimal dose, we conducted a prospective randomized study with 19 pigs. After 3 minutes of untreated ventricular fibrillation, animals received boluses of 0.5 mg Epinephrine (EPI) or 1 mg Norepinephrine (NE) every 5 minutes during CPR. Coronary perfusion pressure (CPP), carotid blood flow (CBF) and cerebral perfusion pressure (CePP) were evaluated.

Results

At baseline, hemodynamic parameters did not differ between the two groups. During CPR, CPP and CBF were similar: 17.3 (12.8; 31.8) in the EPI group vs 16.0 (11.1; 37.7) in the NE group, p = 0.9 and 28.4 (22.0; 54.8) vs 30.8 (12.2; 56.3) respectively, p = 0.9. CePP was not significantly lower during resuscitation in the NE group compared to the EPI group: 12.2 (-8.2; 42.2) vs 7.8 (-2.0; 32.0) p = 0.4. Survival rate was low with only one animal in the EPI group and 2 in the NE group.

Conclusion

Cerebral perfusion pressure, coronary perfusion pressure and carotid blood flow during CPR did not significantly differ between the norepinephrine group and the epinephrine group. Further investigations should evaluate different options such as a continuous NE infusion.

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.

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.

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.

Current pharmacological advances in the treatment of cardiac arrest

Cardiac arrest is defined as the sudden cessation of spontaneous ventilation and circulation. Within 15 seconds of cardiac arrest, the patient loses consciousness, electroencephalogram becomes flat after 30 seconds, pupils dilate fully after 60 seconds, and cerebral damage takes place within 90–300 seconds. It is essential to act immediately as irreversible damage can occur in a short time. Cardiopulmonary resuscitation (CPR) is an attempt to restore spontaneous circulation through a broad range of interventions which are early defibrillation, high-quality and uninterrupted chest compressions, advanced airway interventions, and pharmacological interventions. Drugs should be considered only after initial shocks have been delivered (when indicated) and chest compressions and ventilation have been started. During cardiopulmonary resuscitation, no specific drug therapy has been shown to improve survival to hospital discharge after cardiac arrest, and only few drugs have a proven benefit for short-term survival. This paper reviews current pharmacological treatment of cardiac arrest. There are three groups of drugs relevant to the management of cardiac arrest: vasopressors, antiarrhythmics, and other drugs such as sodium bicarbonate, calcium, magnesium, atropine, fibrinolytic drugs, and corticosteroids.

Part 8: adult advanced cardiovascular life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care

The goal of therapy for bradycardia or tachycardia is to rapidly identify and treat patients who are hemodynamically unstable or symptomatic due to the arrhythmia. Drugs or, when appropriate, pacing may be used to control unstable or symptomatic bradycardia. Cardioversion or drugs or both may be used to control unstable or symptomatic tachycardia. ACLS providers should closely monitor stable patients pending expert consultation and should be prepared to aggressively treat those with evidence of decompensation.

Drug treatment and thrombolytics during cardiopulmonary resuscitation

PURPOSE OF REVIEW

During cardiopulmonary resuscitation, no specific drug therapy has been shown to improve survival to hospital discharge after cardiac arrest, and only few drugs have a proven benefit for short-term survival. This article reviews recent experimental and clinical data about vasopressor, antiarrhythmic and thrombolytic agents.

RECENT FINDINGS

General use of high-dose epinephrine (>1 mg) can not be recommended, whereas it should be considered during prolonged cardiopulmonary resuscitation. No catecholamine superior to epinephrine has been identified. Arginine vasopressin has been shown to be as effective as epinephrine in patients with ventricular fibrillation and pulseless electrical activity, and may be more effective in patients presenting with asystole or as the second vasopressor (after epinephrine) in refractory cardiac arrest. Sodium bicarbonate should not be 'blindly' administered during cardiopulmonary resuscitation unless an arterial blood gas analysis can be obtained, or after prolonged unsuccessful cardiopulmonary resuscitation. Amiodarone should be preferred over lidocaine, since it may improve short-term survival. Thrombolytic therapy during cardiopulmonary resuscitation may be beneficial if a pulmonary embolism or acute myocardial infarction is suggested to be the cause of the cardiac arrest.

SUMMARY

Epinephrine still represents the first-line vasopressor during cardiopulmonary resuscitation. Arginine vasopressin may be considered in patients presenting with asystole or who are unresponsive to initial treatment with epinephrine. Amiodarone should be preferred to other antiarrythmic agents in patients with cardiac arrest. Thrombolytic therapy during cardiopulmonary resuscitation is a promising new therapeutic option, but its general use in cardiac arrest cannot be recommended until the results of a large multicentre trial become available.

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.

Pressor drugs in the treatment of cardiac arrest

The importance of vital organ perfusion in patients suffering cardiac arrest makes arterial vasomotor tone, and the resultant perfusion pressure, critical in resuscitation from sudden death. Although there are multiple mechanisms that may affect arterial vascular tone, historically, the therapy most commonly used has been catecholamine-induced adrenergic receptor stimulation, with catecholamine epinephrine being the commonest drug used. Over the last decade, however, it has become widely known that the utility of epinephrine during cardiopulmonary resuscitation is undefined. This has led to research into alternative agents, in particular nonadrenergic vasoactive peptides. Other agents appear promising. This article addresses pressor drugs and adrenergic agonists, including a review of their history, basic science, mechanism of action, and efficacy. Epinephrine is reviewed.

Differences in the pharmacodynamics of epinephrine and vasopressin during and after experimental cardiopulmonary resuscitation

Vasopressin has been investigated as a possible alternative to epinephrine during cardiopulmonary resuscitation (CPR). We tested the hypothesis that vasopressin, in comparison with epinephrine, would improve cerebral blood flow and metabolism during CPR as well as after restoration of spontaneous circulation (ROSC). A total of 22 anaesthetised piglets were subjected to 5 min of ventricular fibrillation followed by 8 min of closed-chest CPR. The piglets were randomly allocated to receive repeated boluses of either 45 microg/kg epinephrine or 0.4 U/kg vasopressin IV. Haemodynamic parameters, cerebral cortical blood flow and cerebral tissue pH and PCO(2) were continuously monitored during CPR and up to 4 h after ROSC. Cerebral oxygen extraction ratio was calculated. Cerebral cortical blood flow increased transiently after each bolus of epinephrine, while only the first bolus of vasopressin resulted in a sustained increase. The peak in cerebral cortical blood flow was reached approximately 30 s later with vasopressin. During the initial 5 min following ROSC, cerebral cortical blood flow was greater in the vasopressin group. In conclusion, there is a difference between epinephrine and vasopressin in the time from injection to maximal clinical response and the duration of their effect, but their overall effects on blood pressures and cerebral perfusion do not differ significantly during CPR. In contrast, vasopressin results in a greater cerebral cortical blood flow during a transient period after ROSC.

Management of cardiopulmonary resuscitation

Since cardiopulmonary resuscitation was first described in 1960, it has become a standardized medical intervention. Separate guidelines have been developed for the neonatal and pediatric population, but none exist for the elderly population. This review will discuss recent available outcome data on resuscitation of the elderly and the known physiologic changes with aging that may affect decisions made during resuscitation.

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.

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.

Proarrhythmic effects of intravenous vasopressors

OBJECTIVE

To review the electrophysiologic properties and the in vitro, ex vivo, animal, and human data regarding proarrhythmic effects of intravenous vasopressors.

DATA SOURCES

A comprehensive (MEDLINE) search (1960-1994) was conducted for dopamine, epinephrine, norepinephrine, phenylephrine, and methoxamine.

STUDY SELECTION

In vitro and ex vivo studies and investigations performed in animals or humans reporting electrophysiologic and/or proarrhythmic effects of the above intravenous vasopressors were selected. A comprehensive search of all human studies involving these agents was conducted to reveal any proarrhythmic effects that may have been reported. In addition, case reports of proarrhythmic effects associated with these agents were reviewed.

DATA EXTRACTION

Data regarding electrophysiologic and proarrhythmic effects of these agents were extracted from in vitro, ex vivo, animal, and human studies. Because few studies with the specific purpose of investigating proarrhythmic effects of vasopressors have been performed in humans, all studies involving these drugs for evaluation of hemodynamic effects, clinical efficacy, or other endpoints in humans were reviewed. In addition, data were extracted from case reports of proarrhythmic effects associated with these agents.

DATA SYNTHESIS

Dopamine increases automaticity in Purkinje fibers and has a biphasic effect on action-potential duration. Dopamine has caused both atrial and ventricular tachyarrhythmias in animals. Human data have revealed dose-related sinus tachycardia, with few reports of clinically significant ventricular arrhythmias. Epinephrine shortens sinus cycle length, increases atrial and ventricular automaticity, promotes atrioventricular nodal conduction, and decreases ventricular effective refractory period (ERP). It is well known to induce ventricular fibrillation and decrease the ventricular fibrillation threshold (VFT) in ex vivo models as well as intact animals. In humans, epinephrine may cause dose-related sinus tachycardia, supraventricular arrhythmias, or, more commonly, ventricular arrhythmias. Norepinephrine increases automaticity of the sinoatrial node, atria, and ventricles; promotes atrioventricular nodal conduction; and decreases ventricular ERP. In vitro/ex vivo and animal data have shown that norepinephrine significantly decreases VFT. Although electrophysiologic studies suggest that norepinephrine may be proarrhythmic, few supporting data exist in humans. Phenylephrine demonstrates differential electrophysiologic effects in atrial and ventricular tissue. Most data suggest that phenylephrine causes prolongation of the ventricular ERP. Rather than being proarrhythmic, phenylephrine may be protective against arrhythmias. The drug elevates VFT in dogs. In humans, phenylephrine effectively terminates supraventricular tachycardias and may be protective against ventricular arrhythmias. Like phenylephrine, methoxamine elevates the repetitive extrasystolic, atrial, and ventricular fibrillatory thresholds. Methoxamine also may have antiarrhythmic effects because of alpha-receptor stimulation and reflex vagal activity. Despite the relatively low risk of arrhythmogenicity associated with intravenous vasopressors, patients should be monitored for potential proarrhythmic effects and appropriate action taken as necessary. Critically ill patients often have concurrent conditions, electrolyte disturbances, and underlying arrhythmias that predispose them to a higher risk of vasopressor proarrhythmic effects.

CONCLUSIONS

Controlled data supporting the proarrhythmic potential of intravenous vasopressors in humans are lacking. Sinus tachycardia, asymptomatic ventricular ectopic activity, and other ventricular or supraventricular arrhythmias have been reported in association with dopamine and epinephrine. Phenylephrine and methoxamine have been associated with sinus bradycardia, but otherwise may be antiarrhythmic. Intravenous vasopressors appear relatively safe w

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.

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.

Pharmacologic intervention in prehospital care: a critical appraisal

In more than 15 years of paramedic operation, fewer than 15 prehospital studies have been undertaken on the pharmacologic intervention by paramedics. Many of these studies suffer from inadequate sample size or deficient study design. There is no evidence that any medication given by the prehospital care provider is beneficial or cannot safely be delayed until arrival at hospital. Multicenter trials must be designed and implemented if we are to provide the evidence necessary to evaluate our current practice.

Adverse effect of early high-dose adrenaline on outcome of ventricular fibrillation

Resuscitation for cardiac arrest was monitored over 4 years to examine the effect on survival of a change in the ventricular fibrillation (VF) protocol to include the routine early use of "high-dose" intravenous or transbronchial adrenaline. A significant reduction in the immediate survival of patients with VF was seen when the protocol was changed (22% after the change, 43% before). Prior predictors of poor response were similar in each group, except for the number of witnessed arrests, delay until cardiopulmonary resuscitation, and occurrence of endotracheal intubation, but multiple logistic regression showed the use of adrenaline to be an independent predictor of outcome. Early high-dose adrenaline was associated with a reduction in immediate survival in patients with persistent VF.