CPCR 2008: Techniques and updates (Proceedings)

Introduction

CPCR is the restoration of spontaneous circulation AND the preservation of neurologic function.1 CPCR should be instituted in any dog or cat that lacks a patent airway, spontaneous respiration, or spontaneous circulation. The decision to initiate CPCR ultimately lies with the appropriately informed owner of the pet. A "code" status is an important piece of information to require from owners whether the problem that their pet is presenting with is likely to result in a situation requiring CPCR or not. A procedure as routine and straightforward as an ovariohysterectomy or castration could turn into a cardiac arrest. The author recommends a RED / YELLOW / GREEN system in which Red code indicates a DNR (Do Not Resuscitate) status, a Yellow code directs the team to institute all necessary measures short of open chest CPCR, while a Green code authorizes the team to use whatever means necessary to attempt to resuscitate the pet.

Facility Preparedness

A fully stocked "crash cart" is not likely to be practical for the small private practice; however, a large tackle box that is ONLY used for emergencies is an appropriate substitute. The crash box should be restocked after every usage and a seal placed over the latch to document this. The crash box should be opened weekly to check drug expiration dates and to ensure adequate stock of required supplies. These tasks can easily be delegated to a technician or veterinary assistant. A crash box should contain the equipment listed in Table 1. The equipment included therein will allow the practitioner to maintain an open airway, institute rescue breathing, and carry out all aspects of CPCR. In addition, the necessary supplies for venous or intraosseous access, the reversal of sedatives and anesthetics, management of pleural space diseases, emergency tracheostomy, control of arterial or severe venous hemorrhage etc. are included.

CPCR: The Players

One of the keys to a successful "code" is for the team leader to rapidly and effectively assess the patient and delegate tasks to various members of the team. As the leader, the author prefers to endotracheally intubate the patient, as this step is THE MOST COMMON source of error in an arrest situation. Other individuals should be assigned the following tasks when the team is large enough:

One individual should be assigned to administering 10-15 breaths per minute (100% oxygen) and maintaining endotracheal intubation by securing the endotracheal tube. This same individual should serve as a record keeper / timekeeper. Time goes by very rapidly during CPCR and knowing information such as the time elapsed since the previous dose of epinephrine can be helpful.

One individual should institute chest compressions at 100-120/minute. Chest compressions are most easily performed with the patient in right lateral recumbency with the hands placed atop one another over the base of the heart. The heart can be grasped and compressed between the hands in very small dogs and cats. At this point in the "code", the team leader should assess whether compressions are generating a palpable pulse or improvement in mucous membrane color. If the compressions are not generating adequate pulses, the position of the hands should be altered slightly or other technical alterations made, and compressions resumed.

One individual should immediately place ECG leads (previous training should allow this task to be performed rapidly) such that the electrical activity of the heart can be assessed. This same individual should begin to draw up appropriate doses of epinephrine and atropine along with a large volume of flush solution such that they are ready for use should they be necessary. This individual may also start fluid therapy if indicated. Current fluid therapy recommendations in CPCR depend on the cause of the arrest. If significant hypovolemia caused the cardiac arrest (example: exsanguinating abdominal injury after being hit by car), aggressive volume expansion is indicated. Otherwise, fluid therapy is probably not necessary.

In the setting of limited personnel, two individuals can carry out CPCR. The leader may intubate and perform compressions while the second team member can perform all necessary tasks.

Vascular Access and CPCR

Vascular access has many purposes in the CPCR setting. Vascular access will be necessary for the administration of IV fluids in the situation in which the arrest occurred as a result of hypovolemia as may be the case after trauma and universally, vascular access will be necessary for the optimal delivery of drug therapy during CPCR. Key to successful CPCR is speed. The route of vascular access that can be acquired most rapidly is the best one for the situation. Peripheral vasculature, the jugular vein, and the intraosseous route should all be considered. In a neonate, the intraosseous route is probably the most practical. In the event that vascular access cannot be rapidly established, drug therapy (epinephrine and atropine) can be administered at double the recommended dose down the endotracheal tube.

Drug therapy and Defibrillation in CPCR

Electrocardiographic rhythm will dictate the necessity for drug therapy or defibrillation. Ventricular fibrillation necessitates immediate defibrillation. If a defibrillator is unavailable, a firm precordial "thump" may restore a spontaneous rhythm. The success of this technique in the clinical situation has not been assessed in cats and dogs, but is unlikely to be highly efficacious. Energy required for defibrillation should be kept to a minimum if possible and should be based on body weight. Defibrillators can be acquired from human hospitals and can be purchased new for a reasonable price.

Many arrest situations encountered in veterinary medicine are actually severe bradyarrhythmias (aka "vagal" arrests). It is the author's opinion that many of these bradyarrhythmias are associated with vomiting. Consequently, vomiting must be preemptively controlled in the critically ill patient if possible. Bradyarrhythmias encountered in a CPCR setting should be treated with atropine. Atropine should be administered in any unwitnessed arrest and especially in those that may have had a vagal origin.

It is a common misconception that epinephrine "jump starts the heart". Epinephrine is used in the CPCR situation to improve blood pressure, increase blood flow to vital organs, and improve venous return to the heart through peripheral vasoconstriction ((-adrenergic effect). Other pressor agents such as vasopressin have been investigated in the dog for CPCR and show equal although not necessarily improved effectiveness. In the face of asystole or pulseless electrical activity (formerly termed electromechanical dissociation), epinephrine should be administered every 5 minutes.

Should I crack the chest?

There are a number of absolute indications for open chest CPCR. These include cardiac arrest caused by or associated with pleural space disease (pneumothorax, pleural effusion, diaphragmatic hernia), pericardial effusion, or penetrating injury resulted in cardiac arrest. However, debate exists in veterinary medicine as to other indications for performing open chest CPCR. Some advocate open chest CPCR immediately in large breed dogs because of the limited success of restoring adequate circulation with external compressions while others prefer to perform external CPCR for 5 minutes and then open the chest if there is little or no evidence of effective circulation. Open chest CPCR has the advantage of allowing the clinician to directly compress the heart and improve stroke volume. In addition, opening the chest makes assessment of ventricular filling feasible aiding in the decision of volume delivery.

When opening the chest, it is critical to auscult the chest just prior to the incision to rule out ECG dysfunction as the cause of asystole! The left chest should crudely clipped of hair at the left 5th -6th intercostals space and a chlorhexidine based antiseptic solution should be briskly applied. An incision should be made through the skin and subcutaneous tissues from just below the spinal musculature to the level of the costochondral junction. Between positive pressure breaths, mayo scissors should be used to poke through the intercostal musculature and the pleura and the chest is opened by sliding the mayo scissors dorsally and ventrally along the cranial border of the rib (to avoid the neurovascular bundle). The pericardium is opened at the pericardio-diaphragmatic ligament and the heart is compressed from the apex to the base. In large dogs, the heart can be compressed against the opposite chest wall.

In the event of return of spontaneous circulation, antibiotics should be instituted immediately, the chest should be lavaged with copious amounts of warm saline, and should be closed using sterile technique over a chest tube.

Post-Resuscitation Care

In the event that CPCR results in a return of spontaneous circulation, it is important that cardiac rhythm, oxygen saturation, blood pressure, central venous pressure, blood glucose, electrolyte status and urine output be monitored very closely and optimized. However, of even greater importance is that the cause of the arrest be identified and successfully treated. Optimizing neurologic outcome in patients that have undergone successful CPCR is an area about which we know very little in clinical veterinary medicine and consequently, few recommendations can be made for specific treatments. A dose of intravenous mannitol (0.5-1g/Kg) may be indicated if evidence of increased intracranial pressure is present. Mild hypothermia (5-8(F below normal) may have a protective effect on brain function in the post-arrest patient.

Serial physical and neurological exams should be performed in the post-arrest patient, however, a rapid return of all cranial nerve signs (although ideal) should not be expected and the patient should not be immediately euthanized based on their absence. Recovery will take days to weeks. Blindness should be expected on a short-term basis in many post-arrest patients. This frequently resolves in those that survive.

Prognosis

Despite often-heroic efforts, prognosis for dogs and cats that undergo cardiac arrest is extremely poor. A 1992 study from the University of California at Davis identified 198 dogs and cats that underwent cardiac arrest and CPCR. 56 dogs and cats (28.3%) had return of spontaneous circulation, and 6 (3%) lived more than one week following CPCR. Four of these 6 patients had cardiac arrest while undergoing anesthesia. Five (2.5%) were discharged from the hospital alive. Only 3 (1.5%) were still alive one month later.2 In a more recent case series of dogs and cats that survived cardiopulmonary arrest (and left the hospital), good functional outcomes were achieved.7 The general poor prognosis in patients that undergo cardiac arrest should not preclude ongoing attempts to better the performance of our team in CPCR situations nor the advancement of research designed to improve patient survival.

Table 1.

Footnotes:

Ultrasonic Doppler flow detector. Parks Medical, Aloha, OR.

References:

Otto CM. Cardiopulmonary cerebral resuscitation and ACLS guidelines. Proceedings of the 8th International Veterinary Emergency and Critical Care Symposium. San Antonio, TX. September 2002.478-481.

Kass PH, Haskins SC. Survival following cardiopulmonary resuscitation in dogs and cats. Vet Emerg Crit Care 1992; 2: 57-65.

Evans AT. New thoughts on cardiopulmonary resuscitation. Vet Clin N Amer Sm Anim Pract 1999;29: 819-829.

American Heart Association 2005 Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2005.112.

Cole SG, Otto CM, Hughes D. Cardiopulmonary cerebral resusucitation in small animals-a clinical practice review Part I. J Vet Emerg Crit Care 2002;12: 261-267.

Cole SG, Otto CM, Hughes D. Cardiopulmonary cerebral resusucitation in small animals-a clinical practice review Part II. J Vet Emerg Crit Care 2002;13: 13-23.

Waldrop JE, Rozanski EA, Swanke ED et al. Causes of cardiopulmonary arrest, resusucitation management, and functional outcome in dogs and cats surviving cardiopulmonary arrest. J Vet Emerg Crit Care 2004;14:22-29.