CPR: preparing for the ultimate emergency (Proceedings)
In its earliest forms, cardiopulmonary resuscitation (CPR) is most likely as old as human society itself. Depictions of mouth-to-mouth ventilation appear in ancient Egyptian hieroglyphics, and descriptions appear in the bible. Modern CPR techniques emerged in the late 1950's and early 1960's. Since that time, there has been widespread acceptance of CPR as the cornerstone of basic cardiac life support. Despite more than 30 years of research, the methods used during CPR have changed very little. Survival rates in humans requiring CPR remain low (between 5% and 15% depending upon the study). In veterinary patients, rates for survival to hospital discharge have been reported to be between 5% and 10%. In recent years the term cardiopulmonary cerebral resuscitation (CPCR) has come into vogue. This change in terminology reflects a recognition, on the part of researchers, that maintenance of cerebral blood flow plays a central role in the success of resuscitation attempts.
Recently, the development of automated electrical defibrillators has provided an important step forward in CPR. The success of these devices is due to the fact that ventricular fibrillation and pulseless ventricular tachycardia are the most common arrest rhythms in people. In contrast, only about 20% of dogs had either of these two rhythms as their initial rhythm in one study. This means that a much smaller percentage of dogs and cats are likely to benefit from early defibrillation.
This discussion will assume a basic knowledge of both basic and advanced cardiac life support and will focus upon new advances and theories that may have an impact on the way CPCR is performed in small animals.Importance of early intervention/defibrillation:
Defibrillation is considered the definitive therapy for ventricular fibrillation and pulseless ventricular tachycardia. The sooner defibrillation occurs, the higher the likelihood of successful resuscitation. When it is provided immediately after the onset of ventricular fibrillation the success rate of defibrillation is extremely high. Current recommendations in people are that chest compressions should be delayed in order to provide early defibrillation when indicated and the appropriate equipment is available. Some newer studies in people have questioned this approach. These studies showed that a short period of chest compressions (typically 2-3 minutes) followed by defibrillation may be more successful than immediate defibrillation. The theory behind this approach is that providing the myocardium with a short period of perfusion prior to defibrillation may improve outcome. In our institution, the installation of a continuous telemetry unit that records a history of EKG tracings for the prior 24 hours has shown that a significant number of patients have a period ventricular fibrillation before developing asystole. Intervention during this period of fibrillation would potentially improve patient outcome.
Interposed abdominal compression:
Interposed abdominal compression includes all the steps of ordinary CPR with the addition of external mid-abdominal compressions by a second or third individual, timed between chest compressions. The abdominal compressions are delivered in counterpoint to the rhythm of chest compressions, so that abdominal pressure is maintained whenever the chest is not being compressed. Pulses of central abdominal pressure are applied just cranial to the umbilicus. Hand position, depth, rhythm, and rate of abdominal compression are similar to those for chest compressions. This technique achieved some notoriety in the1990's after Sack et al. published a clinical study, involving several hundred patients, that suggested an approximate doubling or immediate resuscitation success and neurologically intact, long term survival. A recent meta-analysis of human clinical trials was favorable showing significant improvement in short-term survival.
Implementation of interposed abdominal compressions has occurred slowly in both humans and animals. This likely has occurred due to the practical difficulty associated with performing this technique. The way the technique is described, the individual performing chest compressions should say "one-and-two-and-three". The interposed abdominal compressions should be performed and the "and". In smaller patients, one individual may perform both the thoracic compressions and interposed abdominal compressions. Interposed abdominal compressions should not be performed in patients with hemoperitoneum due to the possibility of dislodging an established blood clot and causing further abdominal hemorrhage. We have found it difficult to coordinate the activity between the individual performing the thoracic compressions and the person performing the interposed abdominal compression. Potential improvement in patient outcome warrants strong consideration for the inclusion of interposed abdominal compressions in veterinary patients.