Optimizing myocardial supply/demand balance with α-adrenergic drugs during cardiopulmonary resuscitation

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.

Effect of adrenaline dose on neurological outcome in out-of-hospital cardiac arrest: a nationwide propensity score analysis

BACKGROUND

Adrenaline is recommended during cardio-pulmonary resuscitation. The optimal dose remains debated, and the effect of lower than recommended dose is unknown.

OBJECTIVE

To compare the outcome of patients treated with the recommended, lower or higher cumulative doses of adrenaline.

DESIGN, SETTINGS, PARTICIPANTS

Patients were included from the French National Cardiac Arrest Registry and were grouped based on the received dose of adrenaline: recommended, higher and lower dose.

OUTCOME MEASURES AND ANALYSIS

The primary endpoint was good neurologic outcome at 30 days post-OHCA, defined by a cerebral performance category (CPC) of less than 3. Secondary endpoints included return of spontaneous circulation and survival to hospital discharge. A multiple propensity score adjustment approach was performed.

MAIN RESULTS

27 309 patients included from July 1st 2011 to January 1st 2019 were analysed, mean age was 68 (57-78) years and 11.2% had ventricular fibrillation. 588 (2.2%) patients survived with a good CPC score. After adjustment, patients in the high dose group had a significant lower rate of good neurologic outcome (OR, 0.6; 95% CI, 0.5-0.7). There was no significant difference for the primary endpoint in the lower dose group (OR, 0.8; 95% CI, 0.7-1.1). There was a lower rate of survival to hospital discharge in the high-dose group vs. standard group (OR, 0.5; 95% CI, 0.5-0.6).

CONCLUSION

The use of lower doses of adrenaline was not associated with a significant difference on survival good neurologic outcomes at D30. But a higher dose of adrenaline was associated with a lower rate of survival with good neurological outcomes and poorer survival at D30.

Mildly Reduced Doses of Adrenaline Do Not Affect Key Hemodynamic Parameters during Cardio-Pulmonary Resuscitation in a Pig Model of Cardiac Arrest

Adrenaline is recommended for cardiac arrest resuscitation, but its effectiveness has been questioned recently. Achieving return of spontaneous circulation (ROSC) is essential and is obtained by increasing coronary perfusion pressure (CPP) after adrenaline injection. A threshold as high as 35 mmHg of CPP may be necessary to obtain ROSC, but increasing doses of adrenaline might be harmful to the brain. Our study aimed to compare the increase in CPP with reduced doses of adrenaline to the recommended 1 mg dose in a pig model of cardiac arrest. Fifteen domestic pigs were randomized into three groups according to the adrenaline doses: 1 mg, 0.5 mg, or 0.25 mg administered every 5 min. Cardiac arrest was induced by ventricular fibrillation; after 5 min of no-flow, mechanical chest compression was resumed. The Wilcoxon test and Kruskal-Wallis exact test were used for the comparison of groups. Fisher's exact test was used to compare categorical variables. CPP, EtCO2 level, cerebral, and tissue near-infrared spectroscopy (NIRS) were measured. CPP was significantly lower in the 0.25 mg group 90 s after the first adrenaline injection: 28.9 (21.2; 35.4) vs. 53.8 (37.8; 58.2) in the 1 mg group (p = 0.008), while there was no significant difference with 0.5 mg 39.6 (32.7; 52.5) (p = 0.056). Overall, 0.25 mg did not achieve the threshold of 35 mmHg. EtCO2 levels were higher at T12 and T14 in the 0.5 mg than in the standard group: 32 (23; 35) vs. 19 (16; 26) and 26 (20; 34) vs. 19 (12; 22) (p < 0.05). Cerebral and tissue NIRS did not show a significant difference between the three groups. CPP after 0.5 mg boluses of adrenaline was not significantly different from the recommended 1 mg in our model of cardiac arrest.

Esmolol during cardiopulmonary resuscitation reduces neurological injury in a porcine model of cardiac arrest

Primary vasopressor efficacy of epinephrine during cardiopulmonary resuscitation (CPR) is due to its α-adrenergic effects. However, epinephrine plays β1-adrenergic actions, which increasing myocardial oxygen consumption may lead to refractory ventricular fibrillation (VF) and poor outcome. Effects of a single dose of esmolol in addition to epinephrine during CPR were investigated in a porcine model of VF with an underlying acute myocardial infarction. VF was ischemically induced in 16 pigs and left untreated for 12 min. During CPR, animals were randomized to receive epinephrine (30 µg/kg) with either esmolol (0.5 mg/kg) or saline (control). Pigs were then observed up to 96 h. Coronary perfusion pressure increased during CPR in the esmolol group compared to control (47 ± 21 vs. 24 ± 10 mmHg at min 5, p < 0.05). In both groups, 7 animals were successfully resuscitated and 4 survived up to 96 h. No significant differences were observed between groups in the total number of defibrillations delivered prior to final resuscitation. Brain histology demonstrated reductions in cortical neuronal degeneration/necrosis (score 0.3 ± 0.5 vs. 1.3 ± 0.5, p < 0.05) and hippocampal microglial activation (6 ± 3 vs. 22 ± 4%, p < 0.01) in the esmolol group compared to control. Lower circulating levels of neuron specific enolase were measured in esmolol animals compared to controls (2[1-3] vs. 21[16-52] ng/mL, p < 0.01). In this preclinical model, β1-blockade during CPR did not facilitate VF termination but provided neuroprotection.

Esmolol in the management of pre-hospital refractory ventricular fibrillation: A systematic review and meta-analysis

BACKGROUND

Esmolol has been proposed as a viable adjunctive therapy for pre-hospital refractory ventricular fibrillation/pulseless ventricular tachycardia (VF/pVT).

OBJECTIVES

We performed a systematic review and meta-analysis to assess the effectiveness of esmolol on pre-hospital refractory VF/pVT, compared with standard of care.

METHODS

MEDLINE, Embase, Scopus, and the Cochrane Central Register of Controlled Trials (CENTRAL) were searched for eligible studies. Two investigators independently extracted relevant data and assessed the methodological quality of each included study using the ROBINS-I tool. The quality of evidence for summary estimates was assessed according to GRADE guidelines. Pooled risk ratios (RRs) with 95% confidence intervals (CIs) for each outcome of interest were calculated.

RESULTS

The search yielded 3253 unique records, of which two studies were found to be in accordance with the research purpose, totaling 66 patients, of whom 33.3% (n = 22) received esmolol. Additional evidence was provided in the paper but was not relevant to the analysis and was therefore not included. Esmolol was likely associated with an increased rate of survival to discharge (RR 2.82, 95% CI 1.01-7.93, p = 0.05) (GRADE: Very low) and survival with favorable neurological outcome (RR 3.44, 95% CI 1.11-10.67, p = 0.03) (GRADE: Very low). Similar results were found for return of spontaneous circulation (ROSC) (RR 2.63, 95% CI 1.37-5.07, p = 0.004) (GRADE: Very low) and survival to intensive care unit (ICU)/hospital admission (RR 2.63, 95% CI 1.37-5.07, p = 0.004) (GRADE: Very low).

CONCLUSION

The effectiveness of esmolol for refractory VF/pVT remains unclear. Trial sequential analysis (TSA) indicates that the evidence is inconclusive and that further trials are required in order to reach a conclusion. Therefore, it is imperative to continue to accumulate evidence in order to obtain a higher level of scientific evidence.

The use of mice and rats as animal models for cardiopulmonary resuscitation research

Cardiopulmonary resuscitation (CPR) after the induction of cardiac arrest (CA) has been studied in mice and rats. The anatomical and physiological parameters of the cardiopulmonary system of these two species have been defined during experimental studies and are comparable with those of humans. Moreover, these animal models are more ethical to establish and are easier to manipulate, when compared with larger experimental animals. Accordingly, the effects of successful CPR on the function of vital organs, such as the brain, have been investigated because damage to these vital organs is of concern in CA survivors. Furthermore, the efficacy of several drugs, such as adrenaline (epinephrine), vasopressin and nitroglycerin, has been evaluated for use in CA in these small animal models. The purpose of these studies is not only to increase the rate of survival of CA victims, but also to improve their quality of life by reducing damage to their vital organs after CA and during CPR.

β-Blockers for the treatment of cardiac arrest from ventricular fibrillation?

More than 160,000 people suffer sudden cardiac death each year in the US. It is estimated that ventricular fibrillation (VF) is the initial rhythm in approximately 30% of these cases. Ventricular fibrillation that does not respond to the first few defibrillation attempts is associated with mortality rates of up to 97%. Currently, no pharmacological intervention has been shown to increase long-term survival in patients with shock-refractory VF. The purpose of this review article is to evaluate whether beta-blocker administration during the resuscitation of cardiac arrest from VF or pulseless ventricular tachycardia (VT) improves outcome. We searched the MEDLINE and EMBASE databases for human clinical trials, animal experimental trials, review articles, case reports and abstracts published between 1966 and September 2006. No human prospective randomized controlled trial has studied the effects of beta-blocker administration during VF directly. Prospective trials of anti-arrhythmics with beta-blocking properties have been published, as well as several case reports/case series and experimental animal studies. The evidence thus far suggests that beta-blockade during resuscitation from VF may be associated with increasing rates of resuscitation, greater post-resuscitation survival, and improved post-resuscitation myocardial function. These positive effects on outcome may be mediated by a decrease in the oxygen requirements of the fibrillating heart, thus improving the overall balance between myocardial oxygen supply and demand during resuscitation. While no significant detrimental effects directly related to low dose beta-blockade during VF have been reported in the studies reviewed, concerns relating to possible loss of myocardial contractility and hypotension remain. To this day, high quality human trials are lacking. Preliminary human studies are needed to assess the effects of beta-blockers in the treatment of cardiac arrest from ventricular fibrillation or pulseless VT further.

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.

Sudden cardiac death: Directing the scope of resuscitation towards the heart and brain

BACKGROUND

The fundamental goal of cardiopulmonary resuscitation (CPR) is recovery of the heart and the brain. This is best achieved by (1) immediate CPR for coronary and cerebral perfusion, (2) correction of the cause of cardiac arrest, and (3) controlled cardioplegic cardiac reperfusion. Failure of such an integrated therapy may cause permanent brain damage despite cardiac resuscitation.

METHODS

This strategy was applied at four centers to 34 sudden cardiac death patients (a) after acute myocardial infarction (n = 20), (b) "intraoperatively" following successful discontinuation of cardiopulmonary bypass (n = 4), and (c) "postoperatively" in the surgical ICU (n = 10). In each witnessed arrest the patient failed to respond to conventional CPR with ACLS interventions, including defibrillation. The cardiac arrest interval was 72 +/- 43 min (20-150 min). Compression and drugs maintained a BP > 60 mmHg to avoid cerebral hypoperfusion. Operating room (OR) transfer was delayed until the blood pressure was monitored. In four patients femoral bypass maintained perfusion while an angiographic diagnosis was made.

RESULTS

Management principles included no repeat defibrillation attempts after 10 min of unsuccessful CPR, catheter-monitored peak BP > 60 mmHg during diagnosis and transit to the operating room, left ventricular venting during cardiopulmonary bypass and 20 min global and graft substrate enriched blood cardioplegic reperfusion. Survival was 79.4% with two neurological complications (5.8%).

CONCLUSIONS

Recovery without adverse neurological outcomes is possible in a large number of cardiac arrest victims following prolonged manual CPR. Therapy is directed toward maintaining a monitored peak BP above 60 mmHg, determining the nature of the cardiac cause, and correcting it with controlled reperfusion to preserve function.

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.

Nonselective β-blocking agent improves the outcome of cardiopulmonary resuscitation in a rat model

OBJECTIVE

Postresuscitation myocardial dysfunction has been recognized as a leading cause of early death after initial successful resuscitation. Recent experimental and clinical studies have indicated that the beta-adrenergic effect of epinephrine significantly increases the severity of postresuscitation myocardial dysfunction. The fact that beta-adrenergic stimulation increases myocardial oxygen consumption during ventricular fibrillation is an important implication with respect to both the exogenous in terms of pharmacologic interventions during cardiopulmonary resuscitation and the endogenous as the result of intense sympathetic activation of cardiovascular collapse. Earlier experimental evidence has indicated that oxygenation improved by beta-blockade and beta1-blocking agent did offset the adverse effect of epinephrine. This prompted us to investigate the effect of beta-blockade on both exogenous and endogenous beta stimulation in an established rat model.

DESIGN

Prospective, randomized, controlled study.

SETTING

Animal research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

In this series of studies, propranolol was administrated before ventricular fibrillation as a pretreatment combined with epinephrine treatment during precordial compression and then alone in a prolonged cardiac arrest setting.

MEASUREMENTS AND MAIN RESULTS

Improved postresuscitation myocardial dysfunction (cardiac index, dP/dt40, -dP/dt) was observed with propranolol, a nonselective beta-adrenergic blocker, in pretreated animals such that the beneficial effects were associated with better postresuscitation survival.

CONCLUSION

Nonselective beta-blockade improved the outcome of cardiopulmonary resuscitation in a rat model and deserves further evaluation in settings of cardiopulmonary resuscitation.

Adrenaline administration during cardiopulmonary resuscitation: poor adherence to clinical guidelines

BACKGROUND

Adrenaline does not appear to improve the outcome after cardiac arrest in clinical trials in spite of beneficial effects in experimental studies. The objective of this study was to determine whether adrenaline was administered in accordance with advanced cardiac life support (ACLS) guidelines during adult cardiopulmonary resuscitation (CPR).

METHODS

From 15 January to 31 December 2000, all patients at Uppsala University Hospital in whom CPR was attempted were registered prospectively. The duration of CPR was documented in the register and the total dose of adrenaline was retrieved retrospectively from patient records. From these data the average interval between adrenaline doses was calculated.

RESULTS

Data for evaluation of the between-dose interval of adrenaline was available in 53 of 107 registered cardiac arrests. In 68% (36/53) the average between-dose interval was longer than the 3-5 min recommended in the guidelines, and 8% (4/53) received no adrenaline. The median interval between adrenaline doses during CPR was 6.5 min (25th-75th percentile: 5.1-10.4). Adherence to guidelines was lower in out-of-hospital cardiac arrest than in in-hospital cardiac arrest (P = 0.01).

CONCLUSIONS

In the majority of cases adrenaline did not appear to be administered according to current ACLS guidelines.

Vasopressin versus continuous adrenaline during experimental cardiopulmonary resuscitation

OBJECTIVE

To evaluate the effects of a bolus dose of vasopressin compared to continuous adrenaline (epinephrine) infusion on vital organ blood flow during cardiopulmonary resuscitation (CPR).

METHODS

Ventricular fibrillation was induced in 24 anaesthetised pigs. After a 5-min non-intervention interval, CPR was started. After 2 min of CPR the animals were randomly assigned to receive either vasopressin (0.4 U/kg) or adrenaline (bolus of 20 microg/kg followed by continuous infusion of 10 microg/(kg min)). Defibrillation was attempted after 9 min of CPR.

RESULTS

Vasopressin generated higher cortical cerebral blood flow (P < 0.001) and lower cerebral oxygen extraction (P < 0.001) during CPR compared to continuous adrenaline. Coronary perfusion pressure during CPR was higher in vasopressin-treated pigs (P < 0.001) and successful resuscitation was achieved in 12/12 in the vasopressin group versus 5/12 in the adrenaline group (P = 0.005).

CONCLUSIONS

In this experimental model, vasopressin caused a greater increase in cortical cerebral blood flow and lower cerebral oxygen extraction during CPR compared to continuous adrenaline. Furthermore, vasopressin generated higher coronary perfusion pressure and increased the likelihood of restoring spontaneous circulation.

Hypertonic-hyperoncotic solutions reduce the release of cardiac troponin I and s-100 after successful cardiopulmonary resuscitation in pigs

In some patients, cardiopulmonary resuscitation (CPR) can revive spontaneous circulation (ROSC). However, neurological outcome often remains poor. Hypertonic-hyperoncotic solutions (HHS) have been shown to improve microvascular conductivity after regional and global ischemia. We investigated the effect of infusion of HHS in a porcine CPR model. Cardiac arrest was induced by ventricular fibrillation. Advanced cardiac life support was begun after 4 min of nonintervention and 1 min of basic life support. Upon ROSC, the animals randomly received 125 mL of either normal saline (placebo, n = 8) or 7.2% NaCl and 10% hydroxyethyl starch 200,000/0.5 (HHS, n = 7). Myocardial and cerebral damage were assessed by serum concentrations of cardiac troponin I and astroglial protein S-100, respectively, up to 240 min after ROSC. In all animals, the levels of cardiac troponin I and S-100 increased after ROSC (P < 0.01). This increase was significantly blunted in animals that received HHS instead of placebo. The use of HHS in the setting of CPR may provide a new option in reducing cell damage in postischemic myocardial and cerebral tissues.

IMPLICATIONS

Infusion of hypertonic-hyperoncotic solutions (HHS) after successful cardiopulmonary resuscitation in pigs significantly reduced the release of cardiac troponin I and cerebral protein S-100, which are sensitive and specific markers of cell damage. Treatment with HHS may provide a new option to improve the outcome of cardiopulmonary resuscitation.

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.

Postischemic inotropic support of the dysfunctional heart

OBJECTIVE

To determine relative adenine nucleotide regeneration and improvement in left ventricular (LV) function using three commonly used adrenergic agents--epinephrine, dobutamine, and phenylephrine---during reperfusion after a period of global ischemia. After initial resuscitation from cardiac arrest, adrenergic agents are frequently required to support postischemic LV dysfunction. However, the relative effectiveness and associated bioenergetic changes associated with these agents in the postischemic heart are unclear.

DESIGN

Prospective, controlled laboratory study.

SETTING

University research laboratory.

SUBJECTS

Isolated, perfused Sprague-Dawley rat hearts.

INTERVENTIONS

After 20 mins of global ischemia, isolated rat hearts were reperfused for 30 mins with Krebs-Henseleit solution alone (control, n = 8), or with the addition of equipotent doses of epinephrine 1 microM (n = 8), dobutamine 0.3 microM (n = 8), or phenylephrine 50 microM (n = 8). In a second experiment, an alpha-1 antagonist, prazosin was given with phenylephrine to block the presumed alpha-1 agonist effect of phenylephrine.

MEASUREMENTS AND MAIN RESULTS

A constant volume balloon was placed in the left ventricle to measure LV pressure and derived parameters of LV function. Adenine nucleotide concentrations were derived at various time points using high-performance liquid chromatography. During reperfusion, the phenylephrine group had significant improvement in LV function and cardiac efficiency in contrast to epinephrine and dobutamine. Total adenine nucleotides tended to be highest in the phenylephrine group with significant increases in adenosine diphosphate and adenosine monophosphate and no significant loss of adenosine triphosphate. The phenylephrine-induced increase in heart rate and developed pressure could be blocked with an alpha-1 antagonist, prazosin.

CONCLUSIONS

In the isolated reperfused heart, phenylephrine, mediated by alpha-1 agonism, significantly improves postischemic LV dysfunction without worsening the overall myocardial metabolic state.

Hemodynamic effects of tracheal administration of vasopressin in dogs

BACKGROUND

Intravenous administration of vasopressin during cardiopulmonary resuscitation (CPR) has been shown to be more effective than optimal doses of epinephrine. Earlier studies had been performed on a porcine model, but pigs produce lysine vasopressin hormone, while humans and dogs do not. This study was designed to compare the effects of tracheal vasopressin with those of NaCl 0.9% (placebo) on haemodynamic variables in a dog model.

METHODS

Five dogs were allocated to receive either vasopressin 1.2 U/kg or placebo (10 ml of NaCl 0.9%) via the tracheal route after being anesthetized and ventilated. Haemodynamic variables were determined and arterial blood gases were measured.

RESULTS

All animals of the vasopressin group demonstrated a significant increase of the systolic (from 135+/-7 to 165+/-6 mmHg, P<0.05), diastolic (from 85+/-10 to 110+/-10 mmHg, P<0.05) and mean blood pressure (from 98.5+/-3 to 142.2+/-5, P<0.05). Blood pressure rose rapidly and lasted for more than an hour (plateau effect). Heart rate decreased significantly following vasopressin (from 54+/-9 to 40+/-5 beats per min, P<0.05) but not in the placebo group. These changes were not demonstrated with placebo injection.

CONCLUSION

Tracheal administration of vasopressin was followed by significantly higher diastolic, systolic and mean blood pressures in the vasopressin group compared with the placebo group. Blood gases remained unchanged in both groups. Vasopressin administered via the trachea may be an acceptable alternative for vasopressor administration during CPR, when intravenous access is delayed or not available, however, further investigation is necessary.

The effects of positive end-expiratory pressure during active compression decompression cardiopulmonary resuscitation with the inspiratory threshold valve

The use of an inspiratory impedance threshold valve (ITV) during active compression-decompression (ACD) cardiopulmonary resuscitation (CPR) improves perfusion pressures, and vital organ blood flow. We evaluated the effects of positive end-expiratory pressure (PEEP) on gas exchange, and coronary perfusion pressure gradients during ACD + ITV CPR in a porcine cardiac arrest model. All animals received pure oxygen intermittent positive pressure ventilation (IPPV) at a 5:1 compression-ventilation ratio during ACD + ITV CPR. After 8 min, pigs were randomized to further IPPV alone (n = 8), or IPPV with increasing levels of PEEP (n = 8) of 2.5, 5.0, 7.5, and 10 cm H(2)O for 4 consecutive min each, respectively. Mean +/- SEM arterial oxygen partial pressure decreased in the IPPV group from 150 +/- 30 at baseline after 8 min of CPR to 110 +/- 25 torr at 24 min, but increased in the PEEP group from 115 +/- 15 to 170 +/- 25 torr with increasing levels of PEEP (P <0.02 for comparisons within groups). Mean +/- SEM diastolic aortic minus diastolic left ventricular pressure gradient was significantly (P < 0.001) higher after the administration of PEEP (24 +/- 0 vs 17 +/- 1 mm Hg with 5 cm H(2)O of PEEP, and 26 +/- 0 vs 17 +/- 1 mm Hg with 10 cm H(2)O of PEEP), whereas the diastolic aortic minus right atrial pressure gradient (coronary perfusion pressure) was comparable between groups. Furthermore, systolic aortic pressures were significantly (P < 0.05) higher with 10 cm H(2)O of PEEP when compared with IPPV alone (68 +/- 0 vs 59 +/- 2 mm Hg). In conclusion, when CPR was performed with devices designed to improve venous return to the chest, increasing PEEP levels improved oxygenation. Moreover, PEEP significantly increased the diastolic aortic minus left ventricular gradient and did not affect the decompression phase aortic minus right atrial pressure gradient. These data suggest that PEEP reduces alveolar collapse during ACD + ITV CPR, thus leading to an increase in indirect myocardial compression.

IMPLICATIONS

Inspiratory impedance during active compression-decompression cardiopulmonary resuscitation improves perfusion pressures, and vital organ blood flow during cardiac arrest. Increasing levels of positive end-expiratory pressure during performance of active compression-decompression cardiopulmonary resuscitation with an inspiratory impedance valve improves oxygenation, and increases the diastolic aortic-left ventricular pressure gradient and systolic arterial blood pressure.

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.

Cardiopulmonary and cerebral resuscitation

The future of cardiopulmonary resuscitation lies in new technologies for monitoring and generating vital organ perfusion during cardiac arrest and the post-resuscitation phase and in pharmacologic agents that will enhance ROSC and reverse ischemia-reperfusion injury. ROSC is the first step toward survival, so interventions that improve ROSC deserve further investigation. Long-term survival with good neurologic recovery is the critical endpoint. Interventions recommended for clinical practice must therefore demonstrate improved long-term survival. The resources required to provide many of the interventions discussed in this article, principally invasive perfusion technologies, cannot be justified unless there is clear benefit. The allocation of such resources to provide intensive resuscitation and post-resuscitation support will need to be addressed from medical and societal viewpoints.

In-vivo myocardial substrate alteration during perfused ventricular fibrillation

OBJECTIVES

Earlier work suggests the in-vivo heart alters its substrate utilization as a function of cardiac work. Previous work has also demonstrated the high oxygen requirements of the heart during ventricular fibrillation (VF). The authors hypothesized that myocardial substrate utilization during VF with perfusion is similar to the normal beating heart under conditions of increased workload.

METHODS

Myocardial substrate selection was studied in the in-vivo porcine myocardium using 13carbon nuclear magnetic resonance (13C NMR) under conditions of increased cardiac work (dobutamine group) and VF with extracorporeal perfusion (VF group). Once the animal preparation was completed, metabolic steady state was achieved with the infusion of unlabeled acetate into the left anterior descending (LAD) coronary artery. The infused substrate was then changed to [2-13C] acetate and glutamate pool labeling was monitored by 13C NMR. The glutamate C4 resonance areas at baseline and after intervention of either increased workload (dobutamine group) or perfused VF (VF group) were compared within groups using paired t-tests.

RESULTS

Baseline aortic and great cardiac vein lactates, glucose levels, blood gases, hemoglobin levels, and temperatures were similar between groups. In both groups, there was a significant decrease from baseline in the labeling of C4 glutamate peaks (dobutamine group: 20.2+/-14.9 vs 84.7+/-32.7, p = 0.002; and VF group: 49.8+/-24.4 vs 83.9+/-24.4, p = 0.02), indicating selection against acetate oxidation in favor of other endogenous substrates.

CONCLUSIONS

In the in-vivo heart, despite the absence of functional contractions, changes in substrate utilization during perfused VF are similar to changes that occur with increased workload in the normal beating heart.

Tribonat--a comprehensive summary of its properties

OBJECTIVE

To review available investigations describing the properties of the buffer mixture Tribonat.

DATA SOURCES

Original reports published in peer-reviewed medical journals.

STUDY SELECTION

Review of 76 citations, including four original studies on the effect of Tribonat performed by or supervised by the author, and six original studies concerning Tribonat originating from the institution to which the author is affiliated.

DATA EXTRACTION

Computer search of the literature regarding treatment with alkaline buffers during cardiopulmonary resuscitation.

DATA SYNTHESIS

Routine buffering of acidosis has been questioned, but clinical situations still exist where such treatment is regarded as indicated. In such cases, a buffer with advantageous qualities and few side-effects is desirable. The hitherto commonly used buffers do not always fulfill these requirements, and a more profound knowledge of the alternative Tribonat may therefore be warranted.

CONCLUSIONS

The reviewed articles support the assumption that Tribonat may offer important advantages over previously used buffers in situations where administration of an alkalinizing agent is indicated.

Vasopressin can increase coronary perfusion pressure during human cardiopulmonary resuscitation

OBJECTIVES

To determine the hemodynamic effect of vasopressin on coronary perfusion pressure (CPP) in prolonged human cardiac arrest.

METHODS

A prospective, open-label clinical trial of vasopressin during cardiac resuscitation was performed. Ten patients presenting in cardiac arrest initially received resuscitative measures by emergency physicians according to Advanced Cardiac Life Support (ACLS) guidelines. A central venous catheter for fluid and drug administration and a femoral artery catheter for measurement of CPP (aortic minus right atrial relaxation phase pressures) were placed. When each patient was deemed nonsalvageable, 1.0 mg epinephrine was given and CPP was measured for 5 minutes, followed by a dose of vasopressin (1.0 U/kg). CPP measurements were continued for another 5 minutes.

RESULTS

The mean duration of cardiac arrest (out-of-hospital interval plus duration of ED ACLS) was 39.6 +/- 16.5 min. There was no improvement in CPP after 1.0 mg of epinephrine. Vasopressin administration resulted in a significant increase of CPP in 4 of the 10 patients. Patients responding to vasopressin had a mean increase in CPP of 28.2 +/- 16.4 mm Hg (range: 10-51.5), with these peak increases occurring at 15 seconds to 4 minutes after administration. The increases in the vasopressin levels after administration did not differ between the responders and nonresponders.

CONCLUSIONS

In this human model of prolonged cardiac arrest, 40% of the patients receiving vasopressin had a significant increase in CPP. This pilot study suggests that investigation of earlier use of vasopressin as a therapeutic alternative in the treatment of cardiac arrest is warranted.

High dose naloxone does not improve cerebral or myocardial blood flow during cardiopulmonary resuscitation in pigs

In a prospective, randomized, placebo-controlled, double-blind trial we tested the hypothesis that naloxone given during cardiopulmonary resuscitation (CPR) enhances cerebral and myocardial blood flow. Twenty-one anesthetized, normoventilated pigs were instrumented for measurements of right atrial and aortic pressures, and regional organ blood flow (radiolabeled microspheres). After 5 min of untreated fibrillatory arrest, CPR was commenced using a pneumatic chest compressor/ventilator. With onset of CPR, an i.v. bolus of 40 micrograms/kg b.w. of epinephrine was given, followed by an infusion of 0.4 micrograms/kg per min. After 5 min of CPR, either naloxone, 10 mg/kg b.w. (group N, n = 11) or normal saline (group S, n = 10) was given i.v. Prior to, and after 1, 15, and 30 min of CPR, hemodynamic and blood flow measurements were obtained. After 30 min of CPR, mean arterial pressure was significantly higher in group N (26 +/- 5 vs. 13 +/- 3 mmHg, P < 0.05). Groups did not differ with respect to myocardial perfusion pressure or arterial blood gases at any time during the observation period. Regional brain and heart blood flows were not different between N and S at any point of measurement. We conclude that high-dose naloxone does not augment cerebral or myocardial blood flow during prolonged closed-chest CPR.

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.

An experimental comparative study on the characteristics of ventricular fibrillation during cardiac arrest and methoxamine administration

The effect of a pure alpha-adrenergic agent, methoxamine on ventricular fibrillation (VF) amplitude and the relation between hemodynamic parameters and survival in a rodent cardiopulmonary resuscitation (CPR) model were studied. Our results suggested that: 1) VF amplitude decreased during untreated VF, but it increased during pericardial chest compression: 2) methoxamine significantly increased the mean aortic pressure (MAP) and coronary perfusion pressure (CPP) but not VF amplitude, and the survival also increased due to elevation of CPP; and 3) all surviving animals with successful defibrillation had a higher VF amplitude.

Adrenaline, cardiac arrest, and evidence based medicine

In this article we review the evidence supporting the clinical application of adrenaline in cardiopulmonary arrest, and summarize the receptor effects of catecholamines and the basic principles producing perfusion during CPR. Animal and human studies show that in cardiac arrest, adrenaline has positive haemodynamic effects, increasing systemic pressures, myocardial perfusion, and cerebrally directed flow. The problems extrapolating from animal to human data are highlighted. Studies showing improvements in short term survival outcomes with high dose regimens have not been confirmed by other large prospective randomised trials. There is no evidence that high doses of adrenaline improve survival to hospital discharge. Most studies comparing adrenaline with placebo have been non-randomised and uncontrolled, with major methodological problems. Conclusions are difficult, but if anything adrenaline is associated with poorer outcomes.

Epinephrine increases the severity of postresuscitation myocardial dysfunction

BACKGROUND

Epinephrine has been the mainstay for cardiac resuscitation for more than 30 years. Its vasopressor effect by which it increases coronary perfusion pressure is likely to favor initial resuscitation. Its beta-adrenergic action, however, may have detrimental effects on postresuscitation myocardial function when administered before resuscitation because it increases myocardial oxygen consumption. In the present study, our focus was on postresuscitation effects of epinephrine when this adrenergic agent was administered during cardiopulmonary resuscitation. Postresuscitation myocardial functions were compared with those of a selective alpha-adrenergic agent, phenylephrine, when epinephrine was combined with a beta 1-adrenergic blocking agent, esmolol, and saline placebo.

METHODS AND RESULTS

Ventricular fibrillation was induced in 40 Sprague-Dawley rats. Mechanical ventilation and precordial compression was initiated either 4 or 8 minutes after the start of ventricular fibrillation. The adrenergic drug or saline placebo was administered as a bolus after 4 minutes of precordial compression. Defibrillation was attempted 4 minutes later. Left ventricular pressure, dP/dt40, and negative dP/dt were continuously measured for an interval of 240 minutes after successful cardiac resuscitation. Except for saline placebo, comparable increases in coronary perfusion pressure were observed after each drug intervention. The number of countershocks required for restoration of spontaneous circulation was significantly greater for epinephrine-treated animals (10 +/- 8) when compared with phenylephrine-treated animals (1.8 +/- 0.4, P < .01) and with animals treated with epinephrine combined with esmolol (1.6 +/- 0.9, P < .01). After resuscitation, dP/dt40 and negative dP/dt were significantly decreased and left ventricular end-diastolic pressure was significantly increased in each animal when compared with prearrest levels. However, the greatest impairment followed epinephrine, and this was associated with significantly greater heart rate and the shortest interval of postresuscitation survival of 8 +/- 4 hours, whereas placebo controls survived for 12 +/- 11 hours. Phenylephrine-treated animals survived for 41 +/- 10 hours (P < .01 versus epinephrine), and animals that received a combination of epinephrine and esmolol survived for 35 +/- 11 hours (P < .01 versus epinephrine). When the duration of untreated cardiac arrest was increased from 4 to 8 minutes, the severity of postresuscitation left ventricular dysfunction was magnified, but disproportionate decreases in postresuscitation survival were again observed with placebo and epinephrine when compared with alpha-adrenergic agonists.

CONCLUSIONS

In an established rodent model after resuscitation following cardiac arrest, epinephrine significantly increased the severity of postresuscitation myocardial dysfunction and decreased duration of survival. More selective alpha-adrenergic agonist or blockade of beta 1-adrenergic actions of epinephrine reduced postresuscitation myocardial impairment and prolonged survival.

Adrenaline in out-of-hospital ventricular fibrillation. Does it make any difference?

BACKGROUND

A large proportion of cardiac arrests outside hospital are caused by ventricular fibrillation. Although it is frequently used, the exact role of treatment with adrenaline in these patients remains to be determined.

AIM

To describe the proportion of patients with witnessed out-of-hospital cardiac arrest found in ventricular fibrillation who survived and were discharged from hospital in relation to whether they were treated with adrenaline prior to hospital admission.

PATIENTS AND TREATMENT

All the patients with out-of-hospital cardiac arrest found in ventricular fibrillation in Göteborg between 1981 and 1992 in whom cardiopulmonary resuscitation (CPR) was initiated by our emergency medical service (EMS). During the observation period, some of the EMS staff were authorized to give medication and some were not.

RESULTS

In all, 1360 patients were found in ventricular fibrillation and detailed information was available in 1203 cases (88%). Adrenaline was given in 417 cases (35%). Among patients with sustained ventricular fibrillation, those who received adrenaline experienced the return of spontaneous circulation more frequently (P < 0.001) and were hospitalized alive more frequently (P < 0.01). However, the rate of discharge from hospital did not differ significantly between the 2 groups. Among patients who converted to asystole or electromechanical dissociation, those who received adrenaline experienced the return of spontaneous circulation more frequently (P < 0.001) and were hospitalised alive more frequently (P < 0.001). However, the rate of discharge from hospital did not differ significantly between the 2 groups.

CONCLUSIONS

On the basis of 2 treatment regimens during a 12-year survey, we explored the usefulness of adrenaline in out-of-hospital ventricular fibrillation. Both patients with sustained ventricular fibrillation and those who converted to asystole or electromechanical dissociation had an initially more favourable outcome if treated with adrenaline. However, the final outcome was not significantly affected. This study does not confirm the hypothesis that adrenaline increases survival among patients with out-of-hospital cardiac arrest who are found in ventricular fibrillation.

Epinephrine and sodium bicarbonate during CPR following asphyxial cardiac arrest in rats

Although high-dose epinephrine during CPR improves coronary perfusion pressure (CoPP) and rate of return of spontaneous circulation (ROSC) in some models, its impact on long term outcome (> or = 72 h) has not been evaluated. Previous studies of sodium bicarbonate (NaHCO3) therapy during CPR indicate that beneficial effects may be dependent on epinephrine (EPI) dose. We hypothesized that EPI and NaHCO3 given during CPR have a significant impact on long term outcome. One hundred male Sprague-Dawley rats were prospectively studied in a block randomized placebo controlled trial. Rats were anesthetized, paralyzed, mechanically ventilated, instrumented, and each underwent 10 min of asphyxia, resulting in 6.8 +/- 0.4 min of circulatory arrest. Resuscitation was performed by mechanical ventilation and manual external chest compressions. EPI 0.0 (placebo), 0.01, 0.1, or 1.0 mg/kg IV was given at the onset of CPR, followed by NaHCO3 0.0 (placebo) or 1.0 mEq/kg IV. Successfully resuscitated rats were monitored and ventilated for 1 h without hemodynamic support. Neurologic deficit scores (NDS), cerebral histopathologic damage scores (CHDS) and myocardial histopathologic damage scores (MHDS) were determined in rats that survived 72 h. EPI improved CoPP and ROSC in a dose-dependent manner up to 0.1 mg/kg. Rats receiving EPI 0.1 and 1.0 mg/kg during CPR exhibited prolonged post-ROSC hypertension and metabolic acidemia, increased A-a O2 gradient, and an increased incidence of post-ROSC ventricular tachycardia or fibrillation. Overall survival was lower with EPI 0.1 and 1.0 mg/kg compared to 0.01 mg/kg. Although NDS was significantly less with EPI 0.1 mg/kg compared to placebo, there was no difference in CHDS between groups. In contrast, MDS was significantly higher with EPI 0.1 mg/kg compared to placebo or EPI 0.01 mg/kg. There was an overall trend toward improved survival at 72 h in rats that received NaHCO3 which was most evident in the EPI 0.1 mg/kg group. We conclude that (1) EPI during CPR has a biphasic dose/response curve in terms of survival, when post-resuscitation effects are left untreated and (2) NaHCO3 doses greater than 1.0 mEq/kg may be necessary to treat the side-effects of high-dose EPI. Further work is needed to determine if treating the immediate post-resuscitation effects of high-dose EPI can prevent detrimental effects on long-term outcome.

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.

Interposed abdominal compression as an adjunct to cardiopulmonary resuscitation

The addition of IAC to otherwise standard CPR provides for the application of external pressure over the abdomen in counterpoint to the rhythm of chest compression. Interposed abdominal compression is a simple manual technique that can supplement the use of adrenergic drugs to increase both coronary perfusion pressure and total blood flow during CPR. Mechanistically, manual abdominal compressions induce both central aortic and central venous pressure pulses. However, owing to differences in venous versus arterial capacitance, the former are usually greater than the latter, so that systemic perfusion pressure is enhanced. Moreover, practical experience and theoretical analysis have suggested subtle refinements in the hand position and technique for abdominal compression that may further improve the ratio of arterial to venous pressure augmentation. Clinical studies confirm that IAC-CPR can improve perfusion pressures and carbon dioxide excretion during CPR in humans. The incidence of abdominal trauma, regurgitation, or other complications is not increased by IAC. Recently, randomized trials have shown that short-term and long-term survival of patients resuscitated in the hospital by IAC-CPR are about twice that of control patients resuscitated by standard CPR. The technique of IAC has thus evolved to become a highly promising adjunct to normal CPR, which is likely to be implemented in an increasing number of clinical protocols in the 1990s.

Phenylephrine plus propranolol improves the balance between myocardial oxygen supply and demand during experimental cardiopulmonary resuscitation

Epinephrine increases coronary blood flow but may not improve the balance between myocardial oxygen supply and demand during cardiopulmonary resuscitation (CPR). The objective of this study was to determine whether this balance can be improved by administering a relatively pure alpha-adrenergic vasoconstrictor, alone or in combination with a beta-adrenergic blocker. We measured coronary perfusion pressures during CPR and myocardial adenosine 5'-triphosphate (ATP) and lactate concentrations in biopsies obtained immediately after 10 minutes of CPR in six control dogs and in three groups of six dogs each given large doses of epinephrine, phenylephrine, or phenylephrine plus propranolol during CPR. Coronary perfusion pressure during CPR was higher in the three treated groups than in the control group, although differences were limited to the early portion of CPR in dogs given epinephrine or phenylephrine alone. Postresuscitation myocardial ATP concentration was significantly higher (29.5 +/- 3.0 vs 22.6 +/- 1.8 nmol/mg of protein, p < 0.05) and myocardial lactate concentration tended to be lower (52.8 +/- 13.6 vs 78.5 +/- 15.2 nmol/mg of protein) than in the control group in dogs given both phenylephrine and propranolol. In contrast, myocardial ATP concentration tended to be lower than in the control group in epinephrine-treated dogs, and myocardial lactate concentrations were higher than in the control group in dogs treated with either epinephrine (p < 0.05) or phenylephrine alone (p = 0.052). We conclude that the balance between myocardial oxygen supply and demand during CPR can be improved by administering a combination of phenylephrine and propranolol, but not by administering large doses of epinephrine or phenylephrine alone.

Angiotensin II improves myocardial blood flow in cardiac arrest

Epinephrine is used to increase coronary perfusion pressure and improve myocardial blood flow during cardiac arrest. Alternative vasopressors may have hemodynamic advantages over epinephrine. The purpose of this investigation was to test the effect of the vasopressor angiotensin II on myocardial blood flow in a swine model of cardiac arrest. Eleven swine were anesthetized and instrumented for regional blood flows by radiolabeled microsphere technique. A baseline blood flow measurement (BFM), coronary sinus and aortic blood gases were obtained in normal sinus rhythm (NSR). Ventricular fibrillation (VF) was induced and mechanical CPR begun after 10 min of VF. A BFM and blood gases were obtained during CPR. Angiotensin II, 50 micrograms/kg, was administered at 13 min of VF. A repeat BFM and blood gases were obtained following angiotensin II. Defibrillation was attempted at 16.5 min of VF. If return of spontaneous circulation (ROSC) occurred a fourth BFM and blood gases were obtained. Myocardial blood flow was 134.2 +/- 40.1 ml/100 g per min during NSR. This fell to 15.1 +/- 19.9 with CPR alone, and rose to 66.9 +/- 69.8 following angiotensin II administration (P = 0.04; by two tailed T-test). Myocardial blood flow following ROSC further increased to 212.6 +/- 58.0. Angiotensin II in a dose of 50 micrograms/kg significantly increases myocardial blood flow in this model of cardiac arrest.

A preliminary study of cardiopulmonary resuscitation by circumferential compression of the chest with use of a pneumatic vest

BACKGROUND

More than 300,000 people die each year of cardiac arrest. Studies have shown that raising vascular pressures during cardiopulmonary resuscitation (CPR) can improve survival and that vascular pressures can be raised by increasing intrathoracic pressure.

METHODS

To produce periodic increases in intrathoracic pressure, we developed a pneumatically cycled circumferential thoracic vest system and compared the results of the use of this system in CPR (vest CPR) with those of manual CPR. In phase 1 of the study, aortic and right-atrial pressures were measured during both vest CPR (60 inflations per minute) and manual CPR in 15 patients in whom a mean (+/- SD) of 42 +/- 16 minutes of initial manual CPR had been unsuccessful. Vest CPR was also carried out on 14 other patients in whom pressure measurements were not made. In phase 2 of the study, short-term survival was assessed in 34 additional patients randomly assigned to undergo vest CPR (17 patients) or continued manual CPR (17 patients) after initial manual CPR (duration, 11 +/- 4 minutes) had been unsuccessful.

RESULTS

In phase 1 of the study, vest CPR increased the peak aortic pressure from 78 +/- 26 mm Hg to 138 +/- 28 mm Hg (P < 0.001) and the coronary perfusion pressure from 15 +/- 8 mm Hg to 23 +/- 11 mm Hg (P < 0.003). Despite prolonged unsuccessful manual CPR, spontaneous circulation returned with vest CPR in 4 of the 29 patients. In phase 2 of the study, spontaneous circulation returned in 8 of the 17 patients who underwent vest CPR as compared with only 3 of the 17 patients who received continued manual CPR (P = 0.14). More patients in the vest-CPR group than in the manual-CPR group were alive 6 hours after attempted resuscitation (6 of 17 vs. 1 of 17) and 24 hours after attempted resuscitation (3 of 17 vs. 1 of 17), but none survived to leave the hospital.

CONCLUSIONS

In this preliminary study, vest CPR, despite its late application, successfully increased aortic pressure and coronary perfusion pressure, and there was an insignificant trend toward a greater likelihood of the return of spontaneous circulation with vest CPR than with continued manual CPR. The effect of vest CPR on survival, however, is currently unknown and will require further study.

Corticosteroid supplementation during cardiac arrest in rats

HYPOTHESIS

Corticosteroids will improve the rate of resuscitation from cardiac arrest.

DESIGN

Prospective blinded randomized placebo-controlled trial.

INTERVENTION

An 8-min cardiac arrest was induced by KCl infusion and chest restriction in 36 male Sprague-Dawley rats with continuous EKG and arterial blood pressure monitoring. At the start of CPR the rats received one of three study drugs: normal saline (placebo); 0.05 mg hydrocortisone (Group A) and 0.25 mg hydrocortisone (Group B). Mechanical ventilation, chest compressions and ACLS drug administration were provided following a standardized algorithm.

RESULTS

The resuscitation rate was significantly higher (P < 0.05) in Group B (92%) compared to Group A (50%) and placebo (50%). For the rats resuscitated, the duration of CPR (placebo = 163 s, Group A = 126 s, Group B = 120 s) and the amount of epinephrine used (placebo = 0.007 mg, Group A = 0.005 mg, Group B = 0.005 mg) did not reach statistical significance (P = 0.15 and P = 0.21).

CONCLUSION

Hydrocortisone significantly increased the rate of ROSC from cardiac arrest. There also appears to be a trend of decreasing duration of CPR and epinephrine requirements with hydrocortisone. Further studies evaluating the mechanism of action and long term effects of hydrocortisone in cardiac arrest need to be conducted.

Potential risks of high-dose epinephrine for resuscitation from ventricular fibrillation in a porcine model

The arterial plasma concentrations and hemodynamic effects of epinephrine, 10 micrograms/kg, IV (group A, N = 8) and 50 micrograms/kg, IV (group B, N = 8) were compared in a porcine resuscitation model after 3 minutes of circulatory arrest induced by ventricular fibrillation. All animals in group A were successfully resuscitated after 4.9 +/- 2.8 minutes and 2.8 +/- 1.6 defibrillations. In group B, only 6 of 8 animals were successfully resuscitated after 6.3 +/- 1.1 minutes and 4.0 +/- 2.7 defibrillations (mean +/- SD). During CPR, cardiac output (CO), left ventricular systolic pressure (LVSP), and mean arterial pressure (MAP) were nearly identical in the groups. The hemodynamic situation during the first hour after restitution of spontaneous circulation in group B was characterized by a significantly higher heart rate, combined with significantly lower values for cardiac inotropy, CO, LVSP, and MAP compared to group A. Mean arterial peak epinephrine concentrations (group A 197 +/- 133 ng/mL, group B 1173 +/- 298 ng/mL) were approximately fivefold higher in group B. After resuscitation, plasma concentrations returned to baseline levels within 7 minutes in group A and 15 minutes in group B. Later hemodynamic differences between the groups are thereby attributed to a detrimental impact of high-dose epinephrine on the heart during resuscitation.

Determinants of survival after rodent cardiac arrest: implications for therapy with adrenergic agents

Coronary perfusion pressure and its relation with the expired carbon dioxide concentration (end-tidal CO2) was examined in a rodent model of sustained ventricular fibrillation and subsequent cardiopulmonary resuscitation. Equipressor dosages of the pure alpha 1-agonist methoxamine, the mixed alpha/beta-agonists epinephrine and norepinephrine were randomly compared with 0.9% NaCl. Thirty two Sprague-Dawley rats were anesthetized and catheters were advanced into the aorta, right ventricle, right atrium and inferior vena cava. After 4 min of untreated ventricular fibrillation external chest compression was initiated and defibrillation was attempted after 8 min. Drugs were infused for 3 min during cardiopulmonary resuscitation into the inferior vena cava. A 60-min survival period followed methoxamine administration in 7 of 8 (P < 0.019 vs. NaCl), after epinephrine in 4 of 8, after norepinephrine in 5 of 8, and after NaCl in only 2 of 8 animals. Resuscitation success was determined by coronary perfusion and mean aortic pressures generated during cardiopulmonary resuscitation but not by arterial or venous blood gases. Adrenergic agents increased coronary perfusion and mean aortic pressures but decreased end-tidal CO2 which failed to correlate with these pressures. Accordingly, alpha-adrenergic agents mitigated the accuracy of end-tidal CO2 as a non-invasive hemodynamic monitor and predictor of survival after rodent cardiopulmonary resuscitation.

Cardiovascular function and neurologic outcome after cardiac arrest in dogs. The cardiovascular post-resuscitation syndrome

We studied cardiovascular changes and neurologic outcome at 72 h in 42 healthy dogs after normothermic ventricular fibrillation cardiac arrest (no blood flow) of 7.5, 10, or 12.5 min duration, reversed by standard external cardiopulmonary resuscitation (CPR) (< or = 10 min) and followed by controlled ventilation to 20 h and intensive care to 72 h. We found no difference in resuscitability, mortality, neurologic deficit scores, or overall performance categories between the three insult groups. There was no major pulmonary dysfunction. During controlled normotension post-CPR, all dogs presented a transient reduction in cardiac output. In the 12.5-min cardiac arrest group the decrease in cardiac output persisted beyond 12 h post-CPR (P < 0.01) and was associated with more severe arrhythmias (P < 0.05) and worse morphologic myocardial damage (P < 0.01). Both cardiac and neurologic malfunction at 72 h correlated with arrest time. Only cardiac malfunction correlated with CPR time. Neurologic recovery correlated with mild (inadvertent) pre-arrest hypothermia, diastolic arterial pressure during CPR and absence of cardiovascular impairment at 12 h post-CPR. We conclude that prolonged cardiac arrest in previously healthy dogs is followed by persistent cardiovascular derangements that correlate with impaired neurologic recovery.

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.

Vasopressor therapy in cardiac resuscitation

The standard 0.5 to 1.0 mg dose of adrenaline used in cardiac resuscitation may be inadequate on the basis of theoretical and experimental evidence. Well designed clinical trials are indicated to test the hypothesis that higher doses of adrenaline could be more effective in specific subgroups of people experiencing cardiac arrest. The success in resuscitation is related to the aortic diastolic pressure and the effectiveness of adrenaline relates to its peripheral vasopressor effect. Other catecholamines such as noradrenaline may be more efficacious, as could be non-adrenergic vasopressors. Clinical studies are required, however, to evaluate these potential alternatives.