Vasopressin versus continuous adrenaline during experimental cardiopulmonary resuscitation

Extracellular Glutamate Concentration Increases Linearly in Proportion to Decreases in Residual Cerebral Blood Flow After the Loss of Membrane Potential in a Rat Model of Ischemia

BACKGROUND

Brain ischemia due to disruption of cerebral blood flow (CBF) results in increases in extracellular glutamate concentration and neuronal cell damage. However, the impact of CBF on glutamate dynamics after the loss of the membrane potential remains unknown.

MATERIALS AND METHODS

To determine this impact, we measured extracellular potential, CBF, and extracellular glutamate concentration in the parietal cortex in male Sprague-Dawley rats (n=21). CBF was reduced by bilateral occlusion of the common carotid arteries and exsanguination until loss of extracellular membrane potential was observed (low-flow group), or until CBF was further reduced by 5% to 10% of preischemia levels (severe-low-flow group). CBF was promptly restored 10 minutes after the loss of membrane potential. Histologic outcomes were evaluated 5 days later.

RESULTS

Extracellular glutamate concentration in the low-flow group was significantly lower than that in the severe-low-flow group. Moreover, increases in extracellular glutamate concentration exhibited a linear relationship with decreases in CBF after the loss of membrane potential in the severe-low-flow group, and the percentage of damaged neurons exhibited a dose-response relationship with the extracellular glutamate concentration. The extracellular glutamate concentration required to cause 50% neuronal damage was estimated to be 387 μmol/L, at 8.7% of preischemia CBF. Regression analyses revealed that extracellular glutamate concentration increased by 21 μmol/L with each 1% decrease in residual CBF and that the percentage of damaged neurons increased by 2.6%.

CONCLUSION

Our results indicate that residual CBF is an important factor that determines the extracellular glutamate concentration after the loss of membrane potential, and residual CBF would be one of the important determinants of neuronal cell prognosis.

Effects of different adrenaline doses on cerebral oxygenation and cerebral metabolism during cardiopulmonary resuscitation in pigs

BACKGROUND

The influence of adrenaline during cardiopulmonary resuscitation (CPR) on the neurological outcome of cardiac arrest survivors is unclear. As little is known about the pathophysiological effects of adrenaline on cerebral oxygen delivery and cerebral metabolism we investigated its effects on parameters of cerebral oxygenation and cerebral metabolism in a pig model of CPR.

METHODS

Fourteen pigs were anesthetized, intubated and instrumented. After 5 min of cardiac arrest CPR was started and continued for 15 min. Animals were randomized to receive bolus injections of either 15 or 30 μg/kg adrenaline every 5 min after commencement of CPR.

RESULTS

Measurements included mean arterial pressure (MAP), intracranial pressure (ICP), cerebral perfusion pressure (CPP), cerebral regional oxygen saturation (rSO₂), brain tissue oxygen tension (P_btO₂), arterial and cerebral venous blood gases and cerebral microdialysis parameters, e.g. lactate/pyruvate ratio. Adrenaline induced a significant increase in MAP and CPP in all pigs. However, increases in MAP and CPP were short-lasting and tended to decrease with repetitive bolus administration. There was no statistical difference in any parameter of cerebral oxygenation or metabolism between study groups.

CONCLUSIONS

Both adrenaline doses resulted in short-lasting CPP peaks which did not translate into improved cerebral tissue oxygen tension and metabolism. Further studies are needed to determine whether other dosing regimens targeting a sustained increase in CPP, may lead to improved brain oxygenation and metabolism, thereby improving neurological outcome of cardiac arrest patients.

Study of the Effects of Epinephrine on Cerebral Oxygenation and Metabolism During Cardiac Arrest and Resuscitation by Hyperspectral Near-Infrared Spectroscopy

OBJECTIVES

Epinephrine is routinely administered to sudden cardiac arrest patients during resuscitation, but the neurologic effects on patients treated with epinephrine are not well understood. This study aims to assess the cerebral oxygenation and metabolism during ventricular fibrillation cardiac arrest, cardiopulmonary resuscitation, and epinephrine administration.

DESIGN

To investigate the effects of equal dosages of IV epinephrine administrated following sudden cardiac arrest as a continuous infusion or successive boluses during cardiopulmonary resuscitation, we monitored cerebral oxygenation and metabolism using hyperspectral near-infrared spectroscopy.

SETTINGS

A randomized laboratory animal study.

SUBJECTS

Nine healthy pigs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Our study showed that although continuous epinephrine administration had no significant impact on overall cerebral hemodynamics, epinephrine boluses transiently improved cerebral oxygenation (oxygenated hemoglobin) and metabolism (cytochrome c oxidase) by 15% ± 6.7% and 49% ± 18%, respectively (p < 0.05) compared with the baseline (untreated) ventricular fibrillation. Our results suggest that the effects of epinephrine diminish with successive boluses as the impact of the third bolus on brain oxygen metabolism was 24.6% ± 3.8% less than that of the first two boluses.

CONCLUSIONS

Epinephrine administration by bolus resulted in transient improvements in cerebral oxygenation and metabolism, whereas continuous epinephrine infusion did not, compared with placebo. Future studies are needed to evaluate and optimize the use of epinephrine in cardiac arrest resuscitation, particularly the dose, timing, and mode of administration.

Neural injury after use of vasopressin and adrenaline during porcine cardiopulmonary resuscitation

BACKGROUND

Our aim was to investigate cerebral and cardiac tissue injury subsequent to use of vasopressin and adrenaline in combination compared with vasopressin alone during cardiopulmonary resuscitation (CPR).

METHODS

In a randomized, prospective, laboratory animal study 28 anesthetized piglets were subject to a 12-min untreated cardiac arrest and subsequent CPR. After 1 min of CPR, 10 of the piglets received 0.4 U/kg of arg(8)-vasopressin (V group), and 10 piglets received 0.4 U/kg of arg(8)-vasopressin, 1 min later followed by 20 µg/kg body weight of adrenaline, and another 1 min later continuous administration (10 µg/kg/min) of adrenaline (VA group). After 8 min of CPR, the piglets were defibrillated and monitored for another 3 h. Then they were killed and the brain immediately removed pending histological analysis.

RESULTS

During CPR, the VA group had higher mean blood pressure and cerebral cortical blood flow (CCBF) but similar coronary perfusion pressure. After restoration of spontaneous circulation there was no difference in the pressure variables, but CCBF tended to be (36% ± 16%) higher in the V group. Neuronal injury and signs of a disrupted blood-brain barrier (BBB) were greater, 20% ± 4% and 21% ± 4%, respectively, in the VA group. In a background study of repeated single doses of adrenaline every third minute after 5 min arrest but otherwise the same protocol, histological measurements showed even worse neural injury and disruption of the BBB.

CONCLUSION

Combined use of vasopressin and adrenaline caused greater signs of cerebral and cardiac injury than use of vasopressin alone during experimental cardiopulmonary resuscitation.

Towards cardiopulmonary resuscitation without vasoactive drugs

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Dose-response of vasopressin in a rat model of asphyxial cardiac arrest

The advantage of vasopressin over epinephrine in the treatment of cardiac arrest (CA) is still being debated, and it is not clear whether a high dose of vasopressin is beneficial or detrimental during or after cardiopulmonary resuscitation (CPR) in a rat model of CA. In this study, asphyxial CA was induced in 40 male Sprague-Dawley rats. After 10 minutes of asphyxia, CPR was initiated; and the effects of different doses of vasopressin (low dose, 0.4 U/kg; medium dose, 0.8 U/kg; and high dose, 2.4 U/kg; intravenous; n = 10 in each group) and a saline control (isotonic sodium chloride solution, 1 mL, intravenous) were compared. Outcome measures included the rate of restoration of spontaneous circulation (ROSC) and changes of hemodynamic and respiratory variables after ROSC. The rates of ROSC were 1 of 10 in the saline group and 8 of 10 in each of the 3 vasopressin groups. There were no differences in mean aortic pressure or changes of respiratory function after CPR among the vasopressin groups. However, the heart rate was lower in the high-dose vasopressin group than in the low- and medium-dose groups. These findings indicate that different doses of vasopressin result in a similar outcome of CPR, with no additional benefits afforded by a high dose of vasopressin during or after CPR, in a rat model of asphyxial CA. The mechanism and physiologic significance of the relative bradycardia that occurred in the high-dose vasopressin group are currently unknown and require further investigation.

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.

Drug administration in animal studies of cardiac arrest does not reflect human clinical experience

INTRODUCTION

To date, there is no evidence showing a benefit from any advanced cardiac life support (ACLS) medication in out-of-hospital cardiac arrest (OOHCA), despite animal data to the contrary. One explanation may be a difference in the time to first drug administration. Our previous work has shown the mean time to first drug administration in clinical trials is 19.4min. We hypothesized that the average time to drug administration in large animal experiments occurs earlier than in OOHCA clinical trials.

METHODS

We conducted a literature review between 1990 and 2006 in MEDLINE using the following MeSH headings: swine, dogs, resuscitation, heart arrest, EMS, EMT, ambulance, ventricular fibrillation, drug therapy, epinephrine, vasopressin, amiodarone, lidocaine, magnesium, and sodium bicarbonate. We reviewed the abstracts of 331 studies and 197 full manuscripts. Exclusion criteria included: non-peer reviewed, all without primary animal data, and traumatic models. From these, we identified 119 papers that contained unique information on time to medication administration. The data are reported as mean, ranges, and 95% confidence intervals. Mean time to first drug administration in animal laboratory studies and clinical trials was compared with a t-test. Regression analysis was performed to determine if time to drug predicted ROSC.

RESULTS

Mean time to first drug administration in 2378 animals was 9.5min (range 3.0-28.0; 95% CI around mean 2.78, 16.22). This is less than the time reported in clinical trials (19.4min, p<0.001). Time to drug predicted ROSC (odds ratio 0.844; 95% CI 0.738, 0.966).

CONCLUSION

Shorter drug delivery time in animal models of cardiac arrest may be one reason for the failure of animal studies to translate successfully into the clinical arena.

Evolving role of vasopressin in the treatment of cardiac arrest

Sudden cardiac arrest is a major public heath problem, affecting more than 450,000 individuals annually. Response time and the initiation of cardiopulmonary resuscitation (CPR) remain the most important factors determining successful revival. During resuscitation, sympathomimetics are given to enhance cerebral and coronary perfusion pressures in an attempt to achieve restoration of spontaneous circulation. Epinephrine has been the preferred vasopressor since the inception of advanced cardiac life support, although the lack of definitive evidence regarding its effectiveness has created much controversy surrounding its use, including the optimum dosage. Vasopressin is an alternative vasopressor that, when given at high doses, causes vasoconstriction by directly stimulating smooth muscle V1 receptors. The 2000 American Heart Association (AHA) guidelines commented that vasopressin is a reasonable first-line vasopressor in patients with ventricular fibrillation or pulseless ventricular tachycardia. Since release of those guidelines, additional human studies support an expanded role for vasopressin, whereas other studies cast doubt regarding its efficacy compared with epinephrine. The AHA recently released revised guidelines for CPR and emergency cardiovascular care. The consensus was that vasopressors should remain a part of pulseless sudden cardiac arrest management, with epinephrine 1 mg every 3-5 minutes being the recommended adrenergic of choice. In these revised guidelines, the role of vasopressin expanded beyond previous recommendations, despite the recommendation being downgraded to class indeterminate. The guidelines comment that one dose of vasopressin 40 U may replace the first or second dose of epinephrine in all pulseless sudden cardiac arrest scenarios, including asystole and pulseless electrical activity. A consistent theme with all vasopressors in sudden cardiac arrest is that additional studies are necessary to clearly document greater efficacy compared with no treatment. Further evaluation is warranted to better assess the role of vasopressin in asystolic sudden cardiac arrest, as well as its use with epinephrine, and to determine its optimal timing of administration and potential synergistic effects.

Naloxone and epinephrine are equally effective for cardiopulmonary resuscitation in a rat asphyxia model

BACKGROUND

It is not known whether naloxone is as efficacious as epinephrine during cardiopulmonary resuscitation (CPR). The aim of the study was to compare the effects of naloxone and epinephrine on the outcomes of CPR following asphyxial cardiac arrest in rats.

METHODS

Cardiac arrest was induced with asphyxia by clamping the tracheal tubes. Twenty-four Sprague-Dawley rats were randomized prospectively into a saline group (treated with normal saline, 1 ml intravenously, n = 8), an epinephrine group (treated with epinephrine, 0.04 mg/kg intravenously, n = 8) or a naloxone group (treated with naloxone, 1 mg/kg intravenously, n = 8) in a blind fashion during resuscitation after asphyxial cardiac arrest. After 5 min of untreated cardiac arrest, conventional manual CPR was started and each drug was administered at the same time.

RESULTS

The rates of restoration of spontaneous circulation (ROSC) were one of eight (12.5%), seven of eight (87.5%) and seven of eight (87.5%) in the saline, epinephrine and naloxone groups, respectively. The rates of ROSC in the epinephrine and naloxone groups were equal and significantly greater than that in the saline group (P = 0.01 and P = 0.01, respectively).

CONCLUSION

The administration of naloxone or epinephrine alone may increase the resuscitation rate, and both drugs are equally effective for CPR in a rat asphyxia model. However, the mechanism by which naloxone produces its efficacy during CPR remains unclear and further experimentation will be necessary.

Increased cortical cerebral blood flow with LUCAS; a new device for mechanical chest compressions compared to standard external compressions during experimental cardiopulmonary resuscitation

OBJECTIVE

LUCAS is a new device for mechanical compression and decompression of the chest during cardiopulmonary resuscitation (CPR). The aim of this study was to compare the efficacy of this new device with standard manual external chest compressions using cerebral cortical blood flow, cerebral oxygen extraction, and end-tidal CO2 for indirect measurement of cardiac output. Drug therapy, with adrenaline (epinephrine) was eliminated in order to evaluate the effects of chest compressions alone.

METHODS

Ventricular fibrillation (VF) was induced in 14 anaesthetized pigs. After 8 min non-intervention interval, the animals were randomized into two groups. One group received external chest compressions using a new mechanical device, LUCAS. The other group received standard manual external chest compressions. The compression rate was 100 min(-1) and mechanical ventilation was resumed with 100% oxygen during CPR in both groups. No adrenaline was given. After 15 min of CPR, external defibrillatory shocks were applied to achieve restoration of spontaneous circulation (ROSC). Cortical cerebral blood flow was measured continuously using Laser-Doppler flowmetry. End-tidal CO2 was measured using mainstream capnography.

RESULTS

During CPR, the cortical cerebral blood flow was significantly higher in the group treated with LUCAS (p = 0.041). There was no difference in oxygen extraction between the groups. End-tidal CO2, an indirect measurement of the achieved cardiac output during CPR, was significantly higher in the group treated with the LUCAS device (p = 0.009). Restoration of spontaneous circulation was achieved in two animals, one from each group.

CONCLUSIONS

Chest compressions with the LUCAS device during experimental cardiopulmonary resuscitation resulted in higher cerebral blood flow and cardiac output than standard manual external chest compressions. These results strongly support prospective randomised studies in patients to evaluate this new device.