Automated external defibrillators--experiences with their use and options for their further development.

The purpose of this session at the Wolf Creek IV Conference was to explore future improvements in automatic external defibrillators (AEDs). Rather then conduct a general brain-storming session where any and all ideas are encouraged, participant comments were based on either direct personal experience or based on the experience of others. This article captures the comments in the words of the speakers. Generic improvements in AEDs such as making them smaller, lighter, less expensive, more reliable, and easy to use are always desired. The importance of data collection and analysis was stressed. Of particular concern was the importance of time and time interval measurements. System clock and defibrillator clock synchronization is desired. Concern over liability was voiced by many. The role of the American Heart Association was discussed by both panel members and members of the audience.

Hemodynamics in humans during conventional and experimental methods of cardiopulmonary resuscitation.

High-fidelity hemodynamic recordings of aortic and right atrial pressures and the coronary perfusion gradient (the difference between aortic and atrial pressure) were made in nine patients during cardiopulmonary resuscitation (CPR). Findings during conventional manual CPR were compared with those during high-impulse CPR (rate, 120 cycles/min with a shorter compression:relaxation ratio) as well as during pneumatic vest CPR with and without simultaneous ventilation and abdominal binding. Aortic peak pressure during conventional CPR averaged 61 +/- 29 mm Hg but varied widely (range, 39-126 mm Hg) among patients. Although the magnitude of improvement was modest, the high-impulse method was the only technique tested that significantly elevated both aortic peak pressure and the coronary perfusion gradient during cardiac arrest. During conventional CPR, aortic pressure rose from 61 +/- 29 to 80 +/- 39 mm Hg during high-impulse CPR, and the gradient rose from 9 +/- 11 to 14 +/- 15 mm Hg, respectively; p less than 0.01. The pneumatic vest method significantly improved peak aortic pressure but not the coronary perfusion gradient. Simultaneous ventilation and chest compression created high end-expiratory pressure and lowered the coronary perfusion gradient. Abdominal binding had no significant hemodynamic effects. This evaluation of experimental resuscitation methods in humans shows that the high-impulse chest compression method augments aortic pressure over levels achieved during conventional CPR methods; however, the improvement in pressure is modest and may not be clinically important. Simultaneous ventilation as well as abdominal binding during CPR were associated with no benefit; in fact, simultaneous ventilation appears to adversely affect cardiac perfusion and, therefore, should not be used during clinical resuscitation.

Vest inflation without simultaneous ventilation during cardiac arrest in dogs: improved survival from prolonged cardiopulmonary resuscitation.

Myocardial and cerebral blood flow can be generated during cardiac arrest by techniques that manipulate intrathoracic pressure. Augmentation of intrathoracic pressure by high-pressure ventilation simultaneous with compression of the chest in dogs has been shown to produce higher flows to the heart and brain, but has limited usefulness because of the requirement for endotracheal intubation and complex devices. A system was developed that can produce high intrathoracic pressure without simultaneous ventilation by use of a pneumatically cycled vest placed around the thorax (vest cardiopulmonary resuscitation [CPR]). The system was first tested in a short-term study of the maximum achievable flows during arrest. Peak vest pressures up to 380 mm Hg were used on eight 21 to 30 kg dogs after induction of ventricular fibrillation and administration of epinephrine. Microsphere-determined myocardial blood flow was 108 +/- 17 ml/min/100 g (100 +/- 16% of prearrest flow) and cerebral flow was 51 +/- 12 ml/min/100 g (165 +/- 39% of prearrest). Severe lung or liver trauma was noted in three of eight dogs. If peak vest pressure was limited to 280 mm Hg, however, severe trauma was no longer observed. A study of the hemodynamics during and survival from prolonged resuscitation was then performed on three groups of seven dogs. Vest CPR was compared with manual CPR with either conventional (300 newtons) or high (430 newtons) sternal force. After induction of ventricular fibrillation, each technique was performed for 26 min. Defibrillation was then performed.(ABSTRACT TRUNCATED AT 250 WORDS)

Predictive indices of successful cardiac resuscitation after prolonged arrest and experimental cardiopulmonary resuscitation.

To determine if clinically accessible hemodynamic and blood gas measurements are of value in predicting outcome of countershock after prolonged ventricular fibrillation (VF) and artificial cardiopulmonary support, 14 dogs were studied during 30 minutes of VF using two randomly assigned closed-chest techniques. Seven dogs underwent conventional CPR; the other seven were supported with a pneumatic thoracic vest and abdominal binder, which were inflated synchronously with the airway. Ascending aortic (Ao), right atrial (RA), and instantaneous coronary perfusion pressures (Ao - RA) were measured at five-minute intervals. Ao and RA blood samples were analyzed at 10, 20, 25 and 30 minutes for PO2, PCO2, and pH. After 25 minutes, 1 mg epinephrine was given intravenously, and five minutes later defibrillation was attempted. If unsuccessful, repeated countershocks, conventional pharmacologic therapy, and artificial support were continued. If a perfusing spontaneous cardiac rhythm did not result within an additional 30 minutes, the experiment was terminated. Six animals developed a perfusing cardiac rhythm after one or more countershocks (Group 1); eight failed to develop a perfusing rhythm after repeated countershocks and an additional 30 minutes of resuscitative effort (Group 2). Five Group 1 dogs received vest/binder artificial support. When measured values were averaged over the study period, Group 1 was found to have a significantly greater Ao end-diastolic pressure (AoEDP) and peak diastolic coronary perfusion pressure (CPP) when compared to Group 2 (23 +/- 6 vs 14 +/- 8 mm Hg, P less than .05; and 22 +/- 6 vs 5 +/- 10 mm Hg, P less than .01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical "cough" cardiopulmonary resuscitation during cardiac arrest in dogs.

Hemodynamic findings during ventricular fibrillation (VF) and closed-chest cardiopulmonary resuscitation (CPR) are similar to those described during VF and vigorous coughing. Interventions during CPR that mimic the physiologic events of coughing (high intrathoracic pressure and high intraabdominal pressure) improve perfusion during VF and CPR. An external circulatory assist apparatus was devised to emulate cough physiology, i.e., simultaneous pulsatile increases in intrathoracic pressure (pneumatic vest), intraabdominal pressure (abdominal binder) and airway pressure (high-pressure airway inflation). In this study, vest/binder CPR was compared with conventional CPR during 30 minutes of VF and artificial support in 18 randomized dogs. Defibrillation and long-term (more than 24 hours) survival were chosen as end points. During VF and artificial support, aortic and right atrial (RA) pressures, the instantaneous aortic-RA pressure difference (coronary perfusion pressure) and blood gas levels were measured. After 30 minutes of VF and administration of 1 mg of epinephrine, countershock was attempted. Systolic aortic and RA pressures, mean aortic-RA pressure difference and blood gas levels were not significantly different between dogs that were successfully resuscitated and those that were not. However, peak diastolic coronary perfusion pressure (peak diastolic aortic-RA pressure) for survivors averaged 23 +/- 6 mm Hg, but only 6 +/- 10 mm Hg for nonsurvivors (p less than 0.001). A peak diastolic coronary perfusion pressure 16 mm Hg or greater had a positive and negative predictive value for a successful outcome of 1.00. Only 1 of 9 conventional CPR dogs survived 24 hours; 7 of 9 dogs supported with the vest/binder device were alive and neurologically normal at 24 hours (p = 0.007).(ABSTRACT TRUNCATED AT 250 WORDS)

Regional blood flow during cardiopulmonary resuscitation in dogs.

We studied regional blood flow (QR) using radiolabeled microspheres in 12 anesthetized dogs during cardiopulmonary resuscitation (CPR). A circumferential vest and abdominal binder were used with a mechanical ventilator to deliver 30 simultaneous chest compressions and ventilations per minute. When this device was modified to increase aortic pressure (Pao) during compression and the aortic-to-right atrial pressure gradient (Pao-Pra) during relaxation, cerebral and myocardial QR increased significantly. These findings suggest that QR during CPR can be improved by augmenting perfusion-pressure gradients across the cerebral and coronary circulations.

Circulatory support during cardiac arrest using a pneumatic vest and abdominal binder with simultaneous high-pressure airway inflation.

Animal and clinical studies suggest that blood flow during closed-chest cardiopulmonary resuscitation (CPR) results from phasic intrathoracic pressure fluctuations produced by rhythmic sternal depressions rather than from cardiac compression. Using physiologic observations made in animals and human beings during circulatory collapse and vigorous coughing, a pneumatic thoracic vest garment and abdominal binder device has been designed to emulate "cough CPR." Hemodynamic findings and microsphere regional perfusion observed during cardiac arrest and airway/vest/binder inflation are comparable to those observed during simultaneous chest compression and pulmonary ventilation CPR (SCV-CPR). Resuscitation and survival using the device has been compared to survival rates using conventional closed-chest CPR. The vest/binder apparatus significantly improved the coronary perfusion gradient and survival. Further studies are in progress to determine the clinical utility of this promising resuscitation adjunct.

Regional blood flow during cardiopulmonary resuscitation in dogs using simultaneous and nonsimultaneous compression and ventilation.

We studied regional blood flow (QR) using radiolabeled microspheres and measured hemodynamic variables in 20 anesthetized dogs in normal sinus rhythm and during ventricular fibrillation treated with cardiopulmonary resuscitation (CPR). Nonsimultaneous compression and ventilation CPR (NSCV-CPR) was performed in seven dogs with a pneumatic piston that gave 50 chest compressions/min with an open airway with 10 ventilations at an airway pressure of 33 mm Hg interposed between each fifth and sixth compression. Simultaneous compression and ventilation (SCV-CPR) was performed in seven dogs with the piston and in six other dogs with a circumferential pneumatic vest. Both devices gave 30 compressions/min simultaneously with 30 ventilations that elevated airway pressure to 80 mm Hg., The abdomen was bound during SCV-CPR. Regional blood flow (mean +/- SD) to the cerebral hemispheres, cardiac ventricles, and kidneys, expressed as ml/min/100 g tissue, was 3.1 +/- 4.0, 3.4 +/- 3.3 and 1.5 +/- 1.5, respectively, during NSCV-CPR; 11.5 +/- 5.9, 4.9 +/- 4.7 and 2.7 +/- 2.7 during SCV-CPR (vest); and 16.2 +/- 7.2, 11.0 +/- 4.0 and 20.1 +/- 20.2 during SCV-CPR (piston) (all p less than 0.05 compared with NSCV-CPR). These results indicate that QR to all organs studied is reduced below normal sinus rhythm levels during CPR for ventricular fibrillation, QR to the brain is proportionately greater than QR to the heart and kidneys, and QR to the brain is greater with both forms of SCV-CPR than with NSCV-CPR.