Introduction

CPCR represents a series of assessments and interventions designed to restore spontaneous circulation in a patient with cardiopulmonary arrest. The principal steps of CPR include the establishment of an airway, provision of intermittent positive pressure ventilation, and circulatory support both by mechanical and pharmacological means with the goals of establishing return of spontaneous circulation (ROSC) and spontaneous respiration, and minimizing the likelihood of CNS dysfunction. Guidelines for CPCR in people are published in Circulation every 5 years or so. Due to the lack of prospective studies in animals, veterinarians must extrapolate information from the AHA guidelines recognizing that there exist notable differences between cardiopulmonary arrest in people and in animals. For example, the predominance of ventricular fibrillation at the time of collapse in people (40%) may not carry the same importance in animals. Special attention must be given to the recommendations for CPCR in children and adults experiencing sudden cardiac arrest due to asphyxiation, as these recommendations may be more applicable to our patient population.

2005 AHA Guidelines for CPCR--Ventilation

The purpose of ventilation during CPR is to maintain adequate oxygenation, but the optimal tidal volume, respiratory rate, and inspired oxygen concentration to achieve this is not known. To keep the guidelines as simple as possible, general recommendations have been made:

1.  Two rescue breaths should be given over 1 second each, with enough volume to produce visible chest rise.

2.  Avoid rapid or forceful breaths. In people, ventilation is often provided without intubation, and forceful breaths can lead to gastric inflation and regurgitation.

3.  Ventilate at a rate of 8-10 breaths per minute without attempting to synchronize breaths between compressions. In normal adults, this rate can maintain adequate oxygenation and ventilation. The harmful effects of hyperventilation include increased intrathoracic pressure, decreased venous return, and reduced cardiac output. Greater than 12 breaths/min during CPR has been shown to lead to reduced cardiac output, and reduced coronary and cerebral perfusion.

Note: Effective chest compressions are likely more important than rescue breaths in the first few minutes of CPR, as myocardial and cerebral oxygen delivery is initially limited more by poor cardiac output than reduced oxygenation of blood. However, ventilation and compressions are important in prolonged cardiac arrest and in cases of arrest due to asphyxiation or drowning where hypoxemia likely predominate at the time of arrest.

Veterinary Recommendations

2 breaths 1-2 seconds in duration with positive pressure ventilation using 100% inspired oxygen, followed by evaluation for spontaneous ventilation. Reversal agents for medications that may cause apnea should be administered. In the absence of spontaneous ventilation, ventilations should be given at 10-12 breaths/min at airway pressures <20cm H₂0. Give breaths over 1 second with sufficient volume to cause a visual rise in the chest wall, then allow normal relaxation of the chest wall.

2005 AHA Guidelines for CPCR--Chest Compressions

The goal is to pump blood to vital organs during chest compression, and to enhance venous return to the chest during relaxation of the chest wall. Maintenance of cerebral blood flow and function depends on adequate cerebral perfusion pressure (Cerebral perfusion pressure = MAP-ICP). Recognition of the absence of a pulse was removed from the CPR guidelines due to the delay in the delivery of CPR. Current recommendations are to initiate CPR in any patient that is unresponsive and not breathing:

1.  To give effective chest compressions, 'push hard and push fast'. Compress the chest at a rate of 100/min with a depth of 1½ to 2 inches and without pauses for ventilation. Chest compressions create blood flow by increasing intrathoracic pressure (the thoracic pump) and by direct compression of the heart (cardiac pump). Blood flow generated by chest compressions delivers a small but important amount of oxygen to the brain and myocardium. External chest compressions generate systolic arterial pressure peaks of 60-80 mmHg and a cardiac output 25-40% of pre-arrest values.

2.  Allow the chest to recoil completely after each compression, and allow approximately equal compression and relaxation times. Complete chest recoil allows venous return to the heart and is necessary for effective CPR. Studies in people have identified ineffective chest compressions in up to 40% of chest compressions.

3.  Minimize interruptions in chest compressions and do not pause for ventilation. In some human studies, chest compressions were not provided for 24-49% of arrest time. Interruptions in chest compressions is associated with reduced coronary artery perfusion pressure, reduced return of spontaneous circulation, reduced survival, and reduced post resuscitation myocardial function.

4.  Reassess the pulse every 2 minutes but do not spend more than 10 seconds doing so.

5.  Rotate position every 2 minutes to prevent 'compressor fatigue' and deterioration in the quality of compressions.

6.  For single rescuer CPR, a compression ventilation ratio of 30:2 is recommended.

Veterinary Recommendation

Minimize interruptions to <10 Seconds. Patient should be placed in right lateral recumbency. Compressions should be provided at 80-100 compressions per minute with 1:1 compression to relaxation ratio. Compress 30% of the chest diameter, allow the chest wall to recoil completely. There is no real evidence for or against the use of interposed abdominal compression. Indications for internal cardiac massage include penetrating chest wounds, thoracic trauma with rib fractures, pleural space disease, diaphragmatic hernia, pericardial effusion, intra operative arrest and failure to achieve adequate circulation within 2-5 minutes of external chest compressions.

2005 AHA Guidelines for CPCR--Defibrillation

Defibrillation refers to the delivery of the lowest effective current through the chest and to the heart to depolarize myocardial cells, with the goal of eliminating ventricular fibrillation. A successful defibrillation is defined as termination of ventricular fibrillation for at least 5 seconds following shock. Defibrillation 'stuns' the heart, briefly stopping all electrical activity. Normal pacemakers then resume firing and produce a perfusing rhythm. Since it may take > 60 seconds following shock delivery for a perfusing rhythm to be established, CPR is needed for several minutes following defibrillation until adequate perfusion is present. Basic CPR alone is unlikely to eliminate ventricular fibrillation and restore a perfusing rhythm. Since ventricular fibrillation causes myocardial oxygen depletion, a brief period of CPR prior to defibrillation may increase delivery of oxygen, increasing the likelihood that defibrillation will work. For witnessed cardiac arrest with ventricular fibrillation as the predominant rhythm, the current recommendation is for initiation of CPCR until defibrillation can be performed. In non-witnessed cardiac arrest, 5 cycles of CPR should be administered before checking the ECG rhythm and attempting defibrillation. One cycle of CPR consists of 30 chest compressions and 2 breaths, and 5 such cycles should take roughly 2 minutes.

Most studies have shown that frequent or long interruptions in chest compressions for rhythm analysis or breathing were associated with reduced probability of conversion of ventricular fibrillation to another rhythm, and reduced survival. Because of the negative effect of any delay, the recommendation is to deliver one shock and then resume CPR beginning with chest compressions. After 5 cycles, the rhythm can be analyzed and another shock can be delivered if indicated.

Veterinary Recommendations

The initial energy for external defibrillation is 2-5 J/kg. For internal defibrillation, saline soaked sponges should be placed between the paddles and the heart. The energy for internal defibrillation should be 0.2-0.5 J/kg. One shock should be administered and CPR should be resumed for 2 minutes before re-assessing the ECG rhythm.

2005 AHA Guidelines for CPCR--Drugs

Epinephrine (0.01-0.1mg/kg) can be given every 3-5 minutes for asystole, and after 1-2 shocks with CPR if ventricular fibrillation is present. Vasopressin (0.2-0.8 U/kg) may be more effective with asystole (no evidence yet in animals). Antiarrhythmics have not been shown to increase survival during CPR, though amiodarone may increase short term survival. A central line is preferred, followed by intraosseous route then intratracheal route.

References

1.  Hofmeister, et al. J Am Vet Med Assoc 2009; 235(1):50-57.

2.  Plunkett, et al. J Vet Intern Med;

3.  Gueugniaud, et al. New Engl J Med 2008;359:21-30.

4.  Olasveengen, et al. J Am Med Assoc 2009; 302(20):222-222.