Effect of standard doses of epinephrine on myocardial oxygen delivery and utilization during cardiopulmonary resuscitation

Establishing a multicenter, preclinical consortium in resuscitation: A pilot experimental trial evaluating epinephrine in cardiac arrest

BACKGROUND

Large animal studies are an important step in the translation pathway, but single laboratory experiments do not replicate the variability in patient populations. Our objective was to demonstrate the feasibility of performing a multicenter, preclinical, randomized, double-blinded, placebo-controlled cardiac arrest trial. We evaluated the effect of epinephrine on coronary perfusion pressure (CPP) as previous single laboratory studies have reported mixed results.

METHODS

Forty-five swine from 5 different laboratories (Ann Arbor, MI; Baltimore, MD; Los Angeles, CA; Pittsburgh, PA; Toronto, ON) using a standard treatment protocol. Ventricular fibrillation was induced and left untreated for 6 min before starting continuous cardiopulmonary resuscitation (CPR). After 2 min of CPR, 9 animals from each lab were randomized to 1 of 3 interventions given over 12 minutes: (1) Continuous IV epinephrine infusion (0.00375 mg/kg/min) with placebo IV normal saline (NS) boluses every 4 min, (2) Continuous placebo IV NS infusion with IV epinephrine boluses (0.015 mg/kg) every 4 min or (3) Placebo IV NS for both infusion and boluses. The primary outcome was mean CPP during the 12 mins of drug therapy.

RESULTS

There were no significant differences in mean CPP between the three groups: 14.4 ± 6.8 mmHg (epinephrine Infusion), 16.9 ± 5.9 mmHg (epinephrine bolus), and 14.4 ± 5.5 mmHg (placebo) (p = NS). Sensitivity analysis demonstrated inter-laboratory variability in the magnitude of the treatment effect (p = 0.004).

CONCLUSION

This study demonstrated the feasibility of performing a multicenter, preclinical, randomized, double-blinded cardiac arrest trials. Standard dose epinephrine by bolus or continuous infusion did not increase coronary perfusion pressure during CPR when compared to placebo.

Effect of Epinephrine Administered during Cardiopulmonary Resuscitation on Cerebral Oxygenation after Restoration of Spontaneous Circulation in a Swine Model with a Clinically Relevant Duration of Untreated Cardiac Arrest

Severe neurological impairment was more prevalent in cardiac arrest survivors who were administered epinephrine than in those administered placebo in a randomized clinical trial; short-term reduction of brain tissue O2 tension (PbtO2) after epinephrine administration in swine following a short duration of untreated cardiac arrest has also been reported. We investigated the effects of epinephrine administered during cardiopulmonary resuscitation (CPR) on cerebral oxygenation after restoration of spontaneous circulation (ROSC) in a swine model with a clinically relevant duration of untreated cardiac arrest. After 7 min of ventricular fibrillation, 24 pigs randomly received either epinephrine or saline placebo during CPR. Parietal cortex measurements during 60-min post-resuscitation period showed that the area under the curve (AUC) for PbtO2 was smaller in the epinephrine group than in the placebo group during the initial 10-min period and subsequent 50-min period (both p < 0.05). The AUC for number of perfused cerebral capillaries was smaller in the epinephrine group during the initial 10-min period (p = 0.005), but not during the subsequent 50-min period. In conclusion, epinephrine administered during CPR reduced PbtO2 for longer than 10 min following ROSC in a swine model with a clinically relevant duration of untreated cardiac arrest.

Epinephrine's effects on cerebrovascular and systemic hemodynamics during cardiopulmonary resuscitation

BACKGROUND

Despite controversies, epinephrine remains a mainstay of cardiopulmonary resuscitation (CPR). Recent animal studies have suggested that epinephrine may decrease cerebral blood flow (CBF) and cerebral oxygenation, possibly potentiating neurological injury during CPR. We investigated the cerebrovascular effects of intravenous epinephrine in a swine model of pediatric in-hospital cardiac arrest. The primary objectives of this study were to determine if (1) epinephrine doses have a significant acute effect on CBF and cerebral tissue oxygenation during CPR and (2) if the effect of each subsequent dose of epinephrine differs significantly from that of the first.

METHODS

One-month-old piglets (n = 20) underwent asphyxia for 7 min, ventricular fibrillation, and CPR for 10-20 min. Epinephrine (20 mcg/kg) was administered at 2, 6, 10, 14, and 18 min of CPR. Invasive (laser Doppler, brain tissue oxygen tension [PbtO₂]) and noninvasive (diffuse correlation spectroscopy and diffuse optical spectroscopy) measurements of CBF and cerebral tissue oxygenation were simultaneously recorded. Effects of subsequent epinephrine doses were compared to the first.

RESULTS

With the first epinephrine dose during CPR, CBF and cerebral tissue oxygenation increased by > 10%, as measured by each of the invasive and noninvasive measures (p < 0.001). The effects of epinephrine on CBF and cerebral tissue oxygenation decreased with subsequent doses. By the fifth dose of epinephrine, there were no demonstrable increases in CBF of cerebral tissue oxygenation. Invasive and noninvasive CBF measurements were highly correlated during asphyxia (slope effect 1.3, p < 0.001) and CPR (slope effect 0.20, p < 0.001).

CONCLUSIONS

This model suggests that epinephrine increases CBF and cerebral tissue oxygenation, but that effects wane following the third dose. Noninvasive measurements of neurological health parameters hold promise for developing and directing resuscitation strategies.

WITHDRAWN: Adrenaline - Proven benefit in cardiac arrest at last?

The Publisher regrets that this article is an accidental duplication of an article that has already been published, doi:10.1016/j.resuscitation.2011.07.001. The duplicate article has therefore been withdrawn.

Vasopressors for cardiopulmonary resuscitation. Does pharmacological evidence support clinical practice?

Adrenaline (epinephrine) has been used for cardiopulmonary resuscitation (CPR) since 1896. The rationale behind its use is thought to be its alpha-adrenoceptor-mediated peripheral vasoconstriction, causing residual blood flow to be diverted to coronary and cerebral circulations. This protects these tissues from ischaemic damage and increases the likelihood of restoration of spontaneous circulation. Clinical trials have not demonstrated any benefit of adrenaline over placebo as an agent for resuscitation. Adrenaline has deleterious effects in the setting of resuscitation, predictable from its promiscuous pharmacological profile. This article discusses the relevant pharmacology of adrenaline in the context of CPR. Experimental and clinical evidences for the use of adrenaline and alternative vasopressor agents in resuscitation are given, and the properties of an ideal vasopressor are discussed.

ACLS Guidelines 2000: Focus on What’s “New” in the Pulseless Ventricular Tachycardia/Ventricular Fibrillation Algorithm

Despite the use of conventional treatment modalities, the probability of survival for patients experiencing cardiac arrest due to ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT) remains quite poor. Therefore, the management of cardiac arrest remains a challenge. The most recent Advanced Cardiovascular Life Support (ACLS) guidelines have adopted an evidence-based approach toward the treatment of pulseless VT/VF. A number of evidence-based changes have been made in the treatment algorithms for these life-threatening arrhythmias, including the new recommendations for using vasopressin and intravenous amiodarone. This article will provide an overview of the evidence-based approach that was used in the development of the 2000 ACLS guidelines and will summarize the key trials that were used to support the inclusion of vasopressin and intravenous amiodarone in the pulseless VT/VF treatment algorithm. Additionally, dosing and administration issues for these agents will be discussed.

Cardiopulmonary resuscitation: a review for clinicians

Attempts at cardiopulmonary resuscitation (CPR) date from antiquity, but it is only in the last 50 years that a scientifically-based methodology has been developed. External chest compressions is the standard method for managing circulatory arrest, however, numerous alterations of this technique have been proposed in attempts to improve outcome from CPR. Defibrillation is the single most important therapy for the management of ventricular fibrillation or pulseless ventricular tachycardia. Adrenergic agents used to improve myocardial and cerebral perfusion are also the subject of considerable investigation with new agents entering clinical study. This paper reviews the history, current techniques and pharmacotherapy as well as controversial issues in the management of patients with cardiac arrest.

Comparison of high-dose epinephrine versus standard-dose epinephrine in adult cardiac arrest in the prehospital setting

OBJECTIVE

To compare the efficacy of high-dose epinephrine (HDE) with standard-dose epinephrine (SDE) in the management of cardiac arrest in adults in the prehospital setting.

HYPOTHESIS

The use of HDE will improve the outcome of adult patients in cardiac arrest.

METHODS

In a general population of 700,000 persons, in a mixed geographical area of 2,200 square miles, a 12-month retrospective study of SDE and a 12-month prospective trial of HDE were conducted involving adult patients in cardiac arrest in the prehospital setting. Treatment was provided by paramedic-level clinicians. In the control group, patients were treated according to existing American Heart Association cardiac resuscitation guidelines using SDE (defined as 1.0 mg boluses to a maximum dose of 4 mg). In the test group, the same guidelines were revised to use HDE (defined as a rapid sequence of 5, 10, and 15 mg boluses to a total dose of 30 mg).

RESULTS

The control group included 594 patients; the test group consisted of 580 patients. The overall survival rate to hospital admission in the control group was 14.5% (84 patients) and in the test group 15.3% (89 patients). The survival rate to hospital discharge in the control group was 4.9% (29 patients) versus 4.8% (28 patients) in the test group. For patients whose initial rhythms were ventricular fibrillation, survival to admission in the control group was 20.4% (39 patients) versus 24.4% (43 patients) in the test group. Survival to discharge for patients with ventricular fibrillation in the control group was 8.9% (17 patients) versus 10.8% (19 patients) in the test group.

CONCLUSION

There was no statistically significant difference in overall rate of survival to hospital admission or discharge between patients treated with SDE and those treated with HDE, regardless of the initial rhythm.

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.

Outcome of insulin-treated diabetics receiving epinephrine during cardiac arrest

The purpose of this study was to determine the effects of epinephrine in insulin-treated diabetics (DM) compared with nondiabetic (ND) controls during cardiopulmonary resuscitation (CPR). A retrospective analysis from a multicenter study of out-of-hospital cardiac arrest included 62 DM and 1,151 ND. Outcome parameters included return of spontaneous circulation (ROSC), blood pressure (BP), emergency department admissions (EDA), hospital admissions (HA), and hospital discharge (DC). In DM treated with standard-dose epinephrine (SDE), there were trends toward improved ROSC, BP, EDA, and HA compared with ND. DC was not different. With high-dose epinephrine (HDE) these outcomes were not different. Comparison of the outcomes of DM given SDE versus those given HDE were not different. However, none of the DM given HDE (n = 24) were discharged from the hospital. These results suggest that DM may have improved resuscitation rates with SDE and may be adversely affected with HDE. Larger prospective studies are needed to confirm these findings.

Augmented efficacy of external CPR by intermittent occlusion of the ascending aorta

BACKGROUND

After prolonged cardiac arrest, conventional methods of closed-chest cardiac compression are ineffective. This is primarily because of failure to generate minimal threshold levels of coronary perfusion pressure for cardiac resuscitation. This report introduces a new option for cardiac resuscitation by use of a combination of intermittent ascending aortic balloon occlusion, aortic infusion, and precordial compression to increase the pressure gradient for coronary perfusion.

METHODS AND RESULTS

Twenty anesthetized, mechanically ventilated, normovolemic domestic pigs were investigated. A 10F balloon catheter was advanced from the left femoral artery into the ascending aorta. Ventricular fibrillation was induced with an AC current delivered through an electrode catheter advanced into the right ventricle. Precordial compression was initiated after 7 minutes of untreated ventricular fibrillation. The animals were randomized to one of four groups: (1) balloon occlusion with proximal infusion of oxygenated saline, (2) balloon occlusion alone, (3) proximal aortic infusion together with epinephrine without balloon occlusion, and (4) injection of epinephrine without balloon occlusion or proximal infusion. For balloon occlusion, the balloon was inflated for 30 seconds during each minute of cardiopulmonary resuscitation. In the subsets of animals that received infusions, oxygenated saline (30 mL) was injected into the proximal aorta immediately after balloon occlusion. Epinephrine was used in two subsets: It was injected as a bolus in amounts of 30 micrograms/kg into the right atrium at 30 seconds after start of precordial compression and repeated as required to maintain coronary perfusion pressure within the range of 25 to 30 mm Hg. Defibrillation was attempted at 1 minute after start of precordial compression and at 1-minute intervals thereafter. Resuscitation attempts were continued until there was return of spontaneous circulation or for a total of 30 minutes after start of precordial compression. Coronary perfusion pressure generated by precordial compression was significantly increased after balloon occlusion. Each of 10 animals was successfully resuscitated and survived for 48 hours after balloon occlusion whether or not it was combined with infusion. Three of five animals were resuscitated by a combination of infusion and epinephrine in the absence of aortic occlusion, but none survived for 48 hours (P = .02). Only one epinephrine-treated animal was successfully resuscitated and survived for 48 hours in the absence of balloon occlusion or infusion (P < .05).

CONCLUSIONS

Ascending aortic balloon occlusion with or without proximal aortic infusion strikingly increased resuscitability and 48-hour survival after cardiac arrest under conditions when conventional methods failed.

Pulmonary ventilation/perfusion defects induced by epinephrine during cardiopulmonary resuscitation

BACKGROUND

Epinephrine has been shown to impair pulmonary excretion of CO2 during resuscitation. This phenomenon was investigated in a rodent model of cardiac arrest and conventional resuscitation.

METHODS AND RESULTS

The effects of racemic epinephrine were compared with the selective alpha 1-agonist methoxamine and with saline placebo during cardiac resuscitation in 15 Sprague-Dawley rats mechanically ventilated with gas containing 70% oxygen. Epinephrine and methoxamine but not saline placebo significantly increased coronary perfusion pressure from approximately 32 to 55 mm Hg. Following epinephrine, end-tidal PCO2 decreased from approximately 10 to 5 mm Hg. This was associated with a time-coincident decrease in PaO2 from approximately 130 to 74 mm Hg and an increase in PaCO2 from approximately 26 to 40 mm Hg. These changes indicated increases in alveolar dead space ventilation concomitant with increases in pulmonary arteriovenous admixture. No such effects were observed after administration of either methoxamine or saline placebo. Each of the 15 rats was successfully resuscitated. However, a significantly larger number of transthoracic countershocks were required after epinephrine compared with methoxamine or placebo before return of spontaneous circulation.

CONCLUSIONS

Epinephrine induced ventilation/perfusion during cardiopulmonary resuscitation as a result of redistribution of pulmonary blood flow.

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.

Controversies in cardiopulmonary resuscitation: pediatric considerations

This article addresses some therapeutic controversies concerning medications that may be needed during advanced pediatric life support (APLS) and the routes of administration that may be selected. The controversies that are discussed include the appropriateness and selection of various routes for drug administration during APLS; the determination of whether epinephrine hydrochloride is the adrenergic agent of choice for APLS and its appropriate dose; treatment of acidosis associated with a cardiopulmonary arrest; recommendations for atropine sulfate doses; and the role, if any, of calcium in APLS. Background information differentiating pediatric from adult cardiopulmonary arrest is presented to enable the reader to have a better understanding of the specific needs of children during this life-threatening emergency. The article also presents an overview of various drugs used for APLS and a table of their typically recommended doses and routes of administration.

Comparison of two doses of endotracheal epinephrine in a cardiac arrest model

STUDY OBJECTIVE

The objective of this study was to measure plasma catecholamine levels and the cardiovascular response before and after endotracheal administration of epinephrine in a swine cardiac arrest model.

DESIGN

Prospective, controlled laboratory investigation.

TYPE OF PARTICIPANTS

Twenty-one swine weighing 10 to 12 kg, anesthetized with ketamine and alpha-chloralose and ventilated with room air.

INTERVENTIONS

Ventricular fibrillation was induced with 90 V of 60 Hz current delivered to the right ventricle by transvenous pacemaker. Blood samples for epinephrine were drawn before arrest and every two minutes thereafter. At five minutes, external mechanical cardiac compressions were initiated. Nine animals received no further therapy and served as controls. Two groups of six animals received either 0.01 mg/kg or 0.1 mg/kg of epinephrine through the endotracheal tube at ten and 20 minutes. Blood samples were assayed for epinephrine.

MEASUREMENTS

Arterial blood pressure, lead II ECG, and plasma epinephrine.

MAIN RESULTS

Swine receiving epinephrine 0.01 mg/kg had an increase in epinephrine levels after drug administration, but these were not significantly different from control levels. The 0.1-mg/kg dose group had a significant increase in plasma epinephrine levels compared with controls and the 0.01-mg/kg dose group after receiving epinephrine at ten and 20 minutes. These increases were from 14 +/- 3 to 215 +/- 40 ng/mL (+/- SEM) at 12 minutes after arrest and from 151 +/- 56 to 402 +/- 80 ng/mL at 22 minutes after arrest.

CONCLUSION

These data suggest that standard dosing of epinephrine through the endotracheal tube during arrest does not produce significant increases in plasma catecholamines or blood pressure. Epinephrine 0.1 mg/kg produces a significant increase in plasma epinephrine levels, but it is not sufficient to produce a significant change in blood pressure.

The clinical rationale of cardiac resuscitation

After failure of external defibrillation, return of cardiac activity with spontaneous circulation is contingent on rapid and effective reversal of myocardial ischemia. Closed-chest cardiopulmonary resuscitation (CPR) evolved about 30 years ago and was almost universally implemented by both professional providers and lay bystanders because of its technical simplicity and noninvasiveness. However, there is growing concern since the limited hemodynamic efficacy of precordial compression accounts for a disappointingly low success rate; especially so if there is a delay of more than 3 minutes before resuscitation is started. There is also increasing concern with the lack of objective hemodynamic measurements currently available for the assessment and quantitation of the effectiveness of resuscitation efforts. Accordingly, the resuscitation procedure proceeds without confirmation that it increases systemic and myocardial blood flows to levels that would be likely to restore spontaneous circulation. Continuous monitoring of end-tidal carbon dioxide (PETCO2) now appears to be a practical measurement which provides a noninvasive quantitative indication of both systemic blood flow and coronary perfusion pressure. Consequently, PETCO2 predicts the likelihood of successful resuscitation and guides the operator who may modify the technique of precordial compression to improve systemic and myocardial perfusion. Among the large polypharmacy for cardiac resuscitation, only alpha-adrenergic agents (which increase coronary perfusion pressure) and especially epinephrine are of proven benefit. Neither buffer agents nor calcium salts appear to improve outcome except under unique conditions. To the contrary, there is increasing awareness of adverse effects of pharmacologic interventions such that they may hinder the return of viable myocardial and cerebral function. This has constrained the routine use of all drugs except for the use of alpha-adrenergic agonists. More invasive interventions by which blood flow is restored such as open-chest cardiac massage or extra-corporeal pump oxygenation (ECPO) are consistently more effective than conventional CPR. Experimentally, both methods promptly restore systemic and myocardial perfusion to viable levels and thereby increase the likelihood that spontaneous circulation is restored even after prolonged cardiac arrest or failure of conventional CPR.

Epinephrine and norepinephrine in cardiopulmonary resuscitation. Effects on myocardial oxygen delivery and consumption

Norepinephrine, an alpha 1,2-beta 1,2-adrenergic agonist, seems to be an alternative to epinephrine, an alpha 1,2-beta 1,2-agonist, for restoration of spontaneous circulation in VF. We therefore studied the effect of epinephrine and norepinephrine on MDO2 and MVO2 using OCCM after five minutes of cardiopulmonary arrest in 21 pigs. After OCCM of three minutes, seven animals each received placebo (controls) or epinephrine (45 micrograms/kg) or norepinephrine (45 micrograms/kg). All drugs were given blindly. At 90 seconds after epinephrine or norepinephrine, mean arterial blood pressure was significantly higher than in the control group. Prior to cardiac arrest, MBF, measured with radioactive microspheres, was 193 +/- 30 ml/min/100 g. During CPR but before drug administration, MBF was 51 +/- 23 in the control group, 71 +/- 10 in the group with epinephrine, and 74 +/- 11 ml/min/100 g in the group with norepinephrine. At 90 seconds after epinephrine, MBF increased to 126 +/- 18 and after norepinephrine to 107 +/- 30 ml/min/100 g (p less than 0.05). Compared to OCCM alone, MDO2 increased from 9.6 +/- 1.7 to 17.1 +/- 3.2 ml/min/100 g after epinephrine and from 9.4 +/- 1.8 to 13.6 +/- 4.2 ml/min/100 g after norepinephrine (p less than 0.05). There was an increase in MVO2 from 4.0 +/- 1.5 to 9.4 +/- 3.0 ml/min/100 g after epinephrine (p less than 0.05), whereas MVO2 increased only from 4.2 +/- 0.8 to 5.1 +/- 2.0 ml/min/100 g after norepinephrine. Because epinephrine led to a greater increase in MVO2 than norepinephrine, the myocardial oxygen ER remained unchanged. The oxygen requirements of the fibrillating heart seemed to be increased via beta 2-adrenergic stimulation. In both the control and epinephrine-treated groups, only three of the seven animals could be successfully resuscitated, whereas all of the animals in the group with norepinephrine survived the 15-minute period of observation. In this model, norepinephrine, in contrast to epinephrine, improves the balance between MDO2 and MVO2 and eases restoration of spontaneous circulation.

Effect of high dose norepinephrine versus epinephrine on cerebral and myocardial blood flow during CPR

Several animal studies have demonstrated an improvement in cerebral blood flow (CBF) and myocardial blood flow (MBF) after the administration of epinephrine (E) 0.20 mg/kg during closed chest CPR. The administration of norepinephrine (NE) in doses of 0.12 and 0.16 mg/kg demonstrated a trend toward improved CBF and MBF during CPR over that seen with E 0.20 mg/kg in the same animal model. The purpose of this study was to compare the effects of a higher dose of NE 0.20 mg/kg to E 0.20 mg/kg to determine if increasing doses of NE would demonstrate further improvement in CBF and MBF during CPR. Fourteen immature swine were anesthetized and instrumented for regional blood flow and hemodynamic measurements. After 10 min of ventricular fibrillation (VF), CPR was begun using a mechanical thumper. After 3 min of CPR, the animals received either E 0.20 mg/kg (n = 7) or NE 0.20 mg/kg (n = 7) through a right atrial catheter. CPR was continued for an additional 3.5 min and defibrillation was then attempted. CBF (ml/min/100 g), MBF (ml/min/100 g), myocardial oxygen delivery (MDo2; ml O2/min/100 g), myocardial oxygen consumption (MVo2; ml O2/min/100 g), and myocardial oxygen extraction ratios (ER, MVo2/MDo2) were measured during normal sinus rhythm (NSR), during CPR, and during CPR following drug administration. Following drug administration, CBF, MBF, MDo2 and MVo2 rose while ER fell in both E and NE groups. There were no significant differences between groups in CBF, ER, or intravascular pressures following drug administration (P greater than or equal to 0.07). The NE group demonstrated significantly higher MBF (118.9 +/- 73.1 vs. 62.2 +/- 45.3, P = 0.04), MVo2 (14.2 +/- 7.7 vs. 7.0 +/- 3.8, P = 0.05), and MDo2 (19.9 +/- 13.4 versus 9.4 +/- 6.3, P = 0.05) compared to the E group following drug administration While NE improved MBF and MDo2 over E during CPR, there was a trend toward lower resuscitation rates with NE (57.1% vs. 85.7% P = 0.56). Any benefit of higher MBF and MDo2 with NE 0.20 mg/kg appears to be offset by proportionately high MVo2 and a trend toward lower resuscitation rates in the NE 0.20 mg/kg animals.

The median frequency of the ECG during ventricular fibrillation: its use in an algorithm for estimating the duration of cardiac arrest

Recent studies have suggested that the initial therapeutic intervention for ventricular fibrillation (VF) may depend on downtime (DT), i.e., the time duration of VF. We characterized the dynamics of the frequency distribution in the power spectrum of the ECG recorded from eleven swine during VF to determine if enough information existed in this domain to estimate DT. We used the median frequency (FM) of the power spectrum to track the frequency distribution. The FM followed a dynamic repeatable course during the first 10 min of VF. Intersubject variability was small. We modeled the FM data of the eleven subjects with a set of first-order polynomial equations and tested the algorithm with data from an additional ten subjects. The algorithm predicted VF duration with an average error of -0.86 min; 71.5% of the predictions fell within the 95% confidence limits of the model. This paper has identified a signal processing tool which may be useful in the prehospital treatment of VF.

Four case studies: high-dose epinephrine in cardiac arrest

Animal and human studies have suggested that higher doses of epinephrine than currently recommended may improve resuscitation rates after prolonged cardiac arrest. Because of our failure to resuscitate four patients with the standard American Heart Association protocol for cardiac arrest, we used a larger dose of epinephrine in an attempt to enhance resuscitative efforts. All patients required CPR and had nonperfusing rhythms for at least 20 minutes. The four patients received from 0.12 to 0.22 mg/kg epinephrine. Within five minutes of high-dose epinephrine, all four patients developed perfusing rhythms with maximum systolic blood pressures ranging from 134 to 220 mm Hg. Cardiac dysrhythmias did not occur after these doses of epinephrine. Only one of four patients had ECG evidence of an acute myocardial infarction. In this patient, the history suggested that the myocardial infarction was a primary event, not the consequence of epinephrine. All four patients sustained severe brain injury leading to their demise. This injury was probably due to prolonged cardiopulmonary arrest and global brain ischemia. Pharmacologic and potential pathophysiologic mechanisms of high-dose epinephrine are reviewed.

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.

Comparison of standard versus high-dose epinephrine in the resuscitation of cardiac arrest in dogs

A prospective, randomized, blinded study was conducted to evaluate the efficacy of standard compared with high-dose epinephrine in cardiac arrest in dogs. Twenty-five mongrel dogs were anesthetized and monitored by central venous catheter, intra-arterial catheter, and ECG. A left lateral thoracotomy was performed, and the proximal left anterior descending artery was ligated. After ten minutes of myocardial ischemia, ventricular fibrillation was obtained by application of 6-V AC. Mechanical ventilation was stopped. Total arrest time was ten minutes. All animals were randomized into one of five resuscitation protocols; each protocol was identical except for the dose and route of epinephrine administration. Group 1 animals comprised the control group and received normal saline. Group 2 and 3 animals received epinephrine in doses of 0.014 mg/kg by central venous and intracardiac injection, respectively. Group 4 and 5 animals received epinephrine in doses of 0.071 mg/kg by central venous and intracardiac injection, respectively. None of the dogs receiving normal saline had a return of spontaneous circulation, defined as a spontaneous systolic blood pressure of more than 50 mm Hg. Nine of the ten animals from groups 2 and 3 and all of the ten animals from groups 4 and 5 had a return of spontaneous circulation. However, animals receiving the standard dose of epinephrine had a significantly longer resuscitation time compared with the high-dose group (P = .05) and required more doses of epinephrine for successful resuscitation than did animals receiving high doses (P less than .02).(ABSTRACT TRUNCATED AT 250 WORDS)

Estimating the duration of ventricular fibrillation

As the duration of time between the onset of ventricular fibrillation and the application of defibrillation (downtime) increases, the rate of successful resuscitation decreases. Results of recent animal studies suggest that the rate of successful resuscitation may be increased after a prolonged cardiorespiratory arrest when pharmacologic therapy is instituted before defibrillation. An accurate estimation of downtime could be critical in selecting the most appropriate therapeutic intervention. The purpose of our study was to determine whether changes in the frequency or amplitude of the ventricular fibrillation ECG signal during cardiac arrest could be used to estimate downtime. We characterized the dynamics of both total power and frequency distribution of the power in the ECG during ventricular fibrillation in 11 swine to determine whether enough information existed in either parameter to estimate downtime. The median frequency of the power spectrum was used to track power distribution. Both parameters followed a dynamic, repeatable pattern. However, median frequency showed less intersubject variability than did total power. A mathematical model of median frequency was developed and used with data obtained from ten additional swine to estimate downtime. The model estimated downtime to within 1.3 minutes of actual downtime between one and ten minutes of ventricular fibrillation. Our study has identified a new, potentially useful parameter for studying various management strategies in ventricular fibrillation as a function of downtime.

The effect of norepinephrine versus epinephrine on myocardial hemodynamics during CPR

Alpha-adrenergic agonists improve myocardial blood flow during CPR by increasing aortic diastolic pressure. Adrenergic agonists with beta-2 properties may enhance peripheral vasodilation and may prove less beneficial during CPR. The purpose of this study was to compare epinephrine (E), an alpha-1,2; beta-1,2 agonist, versus norepinephrine, an alpha-1,2; beta-1 agonist, on myocardial hemodynamics during CPR. Twenty swine were instrumented for pressure, arterial and coronary sinus oxygen content (CAO2 and CCSO2, respectively), and myocardial blood flow measurements using tracer microspheres. CAO2, CCSO2, myocardial blood flow, myocardial oxygen delivery (MDO2) and myocardial oxygen consumption (MVO2), extraction ratio, and aortic diastolic pressure were determined during normal sinus rhythm and during CPR following a ten-minute arrest. After three minutes of CPR, the animals were allocated to receive either norepinephrine 0.08 mg/kg (n = 5), norepinephrine 0.12 mg/kg (n = 5), norepinephrine 0.16 mg/kg (n = 5), or epinephrine 0.20 mg/kg (n = 5). One minute after drug administration, all hemodynamic parameters were again determined. Three and one half minutes after drug administration defibrillation was attempted. A Newman-Keuls multiple comparison procedure was used to compare differences following drug administration. During CPR, aortic diastolic pressure averaged less than 13 mm Hg, and myocardial blood flow averaged less than 6 mL/min/100 g. All doses of norepinephrine and epinephrine improved all hemodynamic parameters over those seen during CPR. The two highest doses of norepinephrine significantly improved extraction ratio compared with norepinephrine 0.08 mg/kg (P = .04).(ABSTRACT TRUNCATED AT 250 WORDS)