Effects of manual high-impulse CPR on myocardial perfusion during cardiac arrest in pigs

Metrics of impulsiveness of manual chest compressions for out-of-hospital cardiopulmonary resuscitation

Aim

Propose new metrics of impulsiveness of manual chest compressions (CCs) that account for shape and duration, separate the characteristics of the compressive part of the CC cycle from those of the recoil part, and are uncorrelated to CC depth and rate.

Methods

We conducted a retrospective analysis of adult out-of-hospital cardiac arrest monitor-defibrillator recordings having CPR data. Specifically, episodes of adult patients with ≥ 1000 compressions free of leaning were examined. CCs were obtained from the depth signal of the valid episodes, and we calculated the novel metrics: compression area index (CAI), recoil area index (RAI), compression impulsiveness index (CII) and recoil impulsiveness index (RII). Generalized linear mixed-effects models and Jonckheere-Terpstra trend analyses were employed to measure differences between populations and trends, and the absolute value of Pearson's correlation coefficient | r | was used to report dependence between variables. Statistics are reported as median and interquartile range.

Results

We analyzed 982,340 CCs corresponding to 453 episodes, for which we calculated their CAI, RAI and duty cycle (DC). We analyzed the metrics for various populations: age, sex, any ROSC achieved and disposition, and found that CAI was significantly different according to patient disposition and RAI relative to age and sex (p < 0.05 ). None of the metrics was correlated strongly to depth or rate (| r | values of 0.22 or smaller), and all of them varied for CC series corresponding to the same rescuer over the course of resuscitation (p trend < 0.05 ). However, we observed that the metrics are not balanced, in that for any value of DC, CAI and RAI span almost their entire ranges.

Conclusion

The proposed metrics correctly and completely describe manual CC waveforms, improve upon the DC, since they depend on the signal waveform, and provide additional information to current indicators of quality CPR, depth and rate. Furthermore, they allow to differentiate the compressive and recoil parts of the CC cycle, reflecting influence of the rescuer (via CAI or CII) and of the biomechanics of the patient's chest (via RAI or RII). Thus, they have the potential to contribute to better understanding CPR dynamics and, eventually, to enhanced quality of CPR practice as additional indicators of proper manual CC technique.

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.

The Donders Model of the Circulation in Normo- and Pathophysiology

The solution of some recent as well as of long standing problems, unanswerable due to experimental inaccessibility or moral objections are addressed. In this report, a model of the closed human cardiovascular loop is developed. This model, using one set of 88 equations, allows variations from normal resting conditions to exercise, as well as to the ultimate condition of a circulation following cardiac arrest. The principal purpose of the model is to evaluate the continuum of physiological conditions to cardiopulmonary resuscitation (CPR) effects within the circulation.Within the model, Harvey's view of the circulation has been broadened to include impedance-defined flow as a unifying concept, and as a mechanism in CPR. The model shows that depth of respiration, sympathetic stimulation of cardiac contractile properties and baroreceptor activity can exert powerful influences on the increase in cardiac output, while heart and respiratory rate increases tend to exert an inhibiting influence, with the pressure and flow curves compatible with accepted references. Impedance-defined flow encompasses both positive and negative effects.The model also demonstrates the limitations to cardiopulmonary resuscitation caused by external force applied to intrathoracic structures, with effective cardiac output being limited by collapse and sloshing. Stroke volumes from 6 to 51 ml are demonstrated. It shows that the clinical inclination to apply high pressures to intrathoracic structures may not be rewarded with improved net flow.

Endothelin-1 elevates regional cerebral perfusion during prolonged ventricular fibrillation cardiac arrest in pigs

Since adrenaline (epinephrine) also has negative effects during and after cardiopulmonary resuscitation (CPR) a non-adrenergic vasoconstrictor like endothelin might be an alternative to increase vital organ blood flow. We studied the effect of different doses of endothelin-1 compared with adrenaline on the ability to resuscitate, cerebral and myocardial blood flow (MBF) in a closed chest cardiac arrest pig model. After 5 min of ventricular fibrillation, CPR with a ventilator and a mechanical compression device was started. At 10 min, 31 pigs were randomized to receive a single dose of endothelin-1 50, 100 or 200 microg or repeated doses of adrenaline 0.04 mg kg(-1) or saline every 3 min. After 25 min, the pigs were defibrillated to achieve restoration of spontaneous circulation. Blood flow was measured with the fluorescent microsphere method. In animals receiving endothelin-1 50, 100 and 200 microg the cerebral blood flow (CBF) increased from median 28 (25th; 75th quartile: 16; 40), 32 (15; 48) and 17 (4; 65) to 36 (31; 54), 47 (39; 57) and 63 (35; 83) ml min(-1) per 100 g, respectively, 6 min after drug administration (P<0.05 endothelin-1 50 microg vs. Control, P<0.01 endothelin-1 100 and 200 microg vs. Control). At the same time CBF decreased in the control and adrenaline group from 36 (21; 41) and 39 (15; 50) to 12 (2; 25) and 24 (15; 26) ml min(-1) per 100 g, respectively, (P<0.05 adrenaline vs. endothelin-1 200 microg). There was no difference in MBF between the treatment groups despite a higher coronary perfusion pressure (CoPP) in the endothelin-1 groups. Restoration of spontaneous circulation could be only achieved in the endothelin-1 50 microg (3 of 7; 43%) and 100 microg (5 of 7; 71%) group. This study suggests that endothelin-1 enhances CBF during CPR better than adrenaline and increases resuscitation success.

A novel wavelet transform based analysis reveals hidden structure in ventricular fibrillation

We report a new method of interrogating the surface ECG signal using techniques developed in the field of wavelet transform analysis. Previously unreported structure within the ECG during ventricular fibrillation (VF) is found using a high-resolution decomposition of the signal employing the continuous wavelet transform. We believe that wavelet transform methods could lead to the development of powerful tools for use in the resuscitation of patients with cardiac arrest.