Cardiopulmonary cerebral resuscitation for techs
DENVER, CO − Cardiopulmonary resuscitation (CPR) or cardiopulmonary cerebral resuscitation (CPCR) is still one of the most important interventions performed in human or veterinary medicine. Although it is not performed frequently, when needed it must be used appropriately and using the most effective techniques in order to maximize the possibility of success, explained Steven L. Marks, BVSc, MS, MRCVS, DACVIM, speaking at the American College of Veterinary Internal Medicine (ACVIM) Forum.
Comparative CPR
The American Heart Association 2000 guidelines for cardiopulmonary resuscitation and emergency cardiovascular care represent significant changes in protocols; the most significant changes included the incorporation of immediate electrical defibrillation into Basic Life Support (BLS). The successful impact of rapid electrical defibrillation on survival in patients with cardiopulmonary arrest led to this change in recommendations. Although ventricular fibrillation does occur in dogs and rarely in cats, it is not necessarily the most common rhythm disturbance recognized and is not recognized in the majority of veterinary patients who experience cardiopulmonary arrest.
Dr. Marks said that while the use of epinephrine and atropine has not significantly improved survival in people, these drugs would still be considered the cornerstone of therapy for veterinary CPCR.
Techniques
Basic life support
In veterinary medicine basic life support (BLS) or basic CPR is still denoted by A, B, C (Airway, Breathing, and Circulation). The common dysrhythmias associated with cardiopulmonary arrest in dogs and cats include ventricular asystole, pulseless electrical activity (PEA), and ventricular fibrillation. Current recommendations for veterinary BLS include, if required, assessing and providing an airway, breathing, and circulation if required.
Airway: Establishing an airway is usually accomplished with oral endotracheal intubation. Confirmation of correct tube placement is recommended by visual assessment, digital palpation, and/or by ETCO2 monitoring. It has been suggested that airway be prioritized below circulation and breathing, therefore the priority would be C, A, B. Following this protocol, external thoracic compressions should be started immediately and prior to providing an airway. It has been shown in pigs that animals can be resuscitated from ventricular fibrillation only by performing chest compressions. It has been hypothesized that when performing external chest compressions, enough passive ventilation occurs for the patient to survive. Another important factor is that during ventricular fibrillation, oxygen delivery is dependent on blood flow, not ventilation.
Breathing: The only innovations with breathing have been the use of simultaneous compression ventilation protocols. It has been demonstrated that cardiac output can be improved by increasing intrathoracic pressure. The cardiac pump involves direct compression of the myocardium to promote cardiac output. The thoracic pump utilizes compression of the thoracic cavity to indirectly improve cardiac output by effecting blood flow through the giant vessels. The incorporation of simultaneous ventilations dramatically increases intrathoracic pressure. Dr. Marks noted however that potential complications associated with this technique include barotrauma and pulmonary contusions.
Circulation: The cardiac pump theory suggests that direct compression of the myocardium accounts for the majority of cardiac output. In veterinary medicine this would apply to patients with body weights of < 15 kg. In patients with body weights of > 15 kg, the thoracic pump would better explain cardiac output. The latter suggests that compressions of the widest portion of the thorax increase intrathoracic pressures, which indirectly lead to increased cardiac output. This may be combined with simultaneous ventilation, which should further increase intrathoracic pressures. The use of interposed abdominal compressions during CPR has become more common and has been shown to increase venous return by up to 25%.
Advanced cardiac life support
Drugs: The most commonly reported dysrhythmias identified during cardiopulmonary arrest in the dogs and cats are bradyarrhythmias, asystole, and pulseless electrical activity (PEA) formerly known as electrical mechanical dissociation. Atropine and epinephrine may be useful for management of these dysrhythmias. The current recommendation for the use of epinephrine is using the low dose protocol (.01-.02 mg/kg). There is some renewed interest in the use of vasopressin at a dosage of .8 U/kg and recent publications have shown some increase in survival in people who have failed conventional medical therapy. The advantage of vasopressin may be its performance in the face of hypoxia and acidemia. In addition its mechanism of action is via direct stimulation of receptors in vascular smooth muscle and it does not appear to increase myocardial oxygen consumption. Atropine is still administered at .04 mg/kg or approximately 1 ml/10 kg body weight.
Recommended routes of administration include intravenous through a central line, intravenous via a peripheral line with bolus to follow, intraosseous administration, and intratracheal administration. The drugs that can be safely administered via the intratracheal route can be remembered by the pneumonic NAVLE and include Naloxone, Atropine, Vasopressin, Lidocaine and Epinephrine. The doses should be twice the intravenous dose and should be diluted in sterile water.
ECG: Intervention and outcome will be dependent on this diagnosis because it is difficult to predict which rhythm is present.
Fibrillation control: Defibrillation is a lower priority mainly because patients must be in ventricular fibrillation for this intervention to be used. Secondly, it still appears that many veterinary hospitals do not have access to this equipment. The advances in the area of defibrillation are the use of biphasic defibrillators, which may be more effective than the monophasic defibrillators.
Fluid resuscitation: Fluid resuscitation should be a component of CPR, however aggressive volume expansion should only be utilized if it is suspected that volume depletion has contributed to the cardiopulmonary arrest. Volume overload can have detrimental effects on these patients. An increase in central venous pressure and right-sided pressures may lead to reduced coronary perfusion pressures.
Monitoring
Physical examination along with palpation of peripheral pulses, venous blood gas analysis, and end tidal capnography are the most reliable tools. Other suggested techniques include the use of a Doppler blood pressure probe on the cornea to evaluate cerebral artery perfusion but Dr. Marks said he has found this method unreliable. Return of spontaneous ventilation is often a limiting step, as it appears that return to spontaneous circulation occurs more commonly. The frequent cessation of external thoracic compressions in order to examine the ECG or auscultate the thorax may lead to decreased success.
Post-resuscitative care
Post-resuscitative care is primarily symptomatic and is dependent on close monitoring and excellent nursing care. Oxygen supplementation should be considered in all of these patients and ventilatory support may also be required. Fluid therapy should be continued as required and inotropic and pressor therapy may be indicated to maintain mean arterial pressures. Neurologic dysfunction may be common following resuscitation and infusion of mannitol at .5-1 g/kg over 30 minutes may help treat cerebral edema and has free radical scavenging properties. It has also been demonstrated that hyperglycemia may have a negative impact on outcome and therefore should be monitored. Due to the lack of evidence for their use, corticosteroids should be avoided. If possible, prognosis should not be based on neurologic signs within the first 24-48 hrs due to the possibility of significant change. Finally, nutritional support via feeding tubes or total parenteral nutrition should be provided if patients have not returned to reasonable function within 48-72 hrs.CVT
