Cardiopulmonary—cerebral resuscitation (Proceedings)
Cardiopulmonary arrest (CPA) is defined as the cessation of functional ventilation and effective circulation. Factors predisposing to CPA may include respiratory or cardiovascular abnormalities (hypoxia, hypercarbia, hypotension, cardiac arrhythmias, or severe anemia); acid-base, electrolyte, or metabolic abnormalities (acidosis, hyperkalemia, hypoglycemia); or hypothermia. Cardiopulmonary-Cerebral Resuscitation (CPCR) is the combination of basic life support and advanced life support techniques, as well as post-resuscitation care.
Reports on the rate of return of spontaneous rhythm vary from 30% to 60%. However, reported rate of survival to discharge is only 2-14% in human patients. A study in veterinary patients showed 1-week survival post CPCR to be only 4%.
The prognosis improves if the patient has a reversible underlying disease process. These conditions can include anesthetic overdose, vagally mediated arrest, upper airway obstruction, hemorrhage, and electrolyte abnormalities. Successful resuscitation from arrests secondary to these reversible conditions may lead to long-term survival, so aggressive resuscitation efforts are warranted.A grave prognosis exists for patients with severe predisposing conditions such as sepsis, SIRS, neoplasia, or severe cardiac, pulmonary or neurologic disease. In these instances, the clinician and owner need to consider carefully whether or not to institute resuscitative efforts.
Regardless of cause, a better prognosis is associated with CPCR instituted immediately after witnessed CPA. The sooner the CPCR is instituted following CPA, the better the prognosis for return to spontaneous rhythm, therefore it is very important to closely monitor patients with predisposing conditions.
Once CPCR is instituted, a grave prognosis exists if there is no return of spontaneous rhythm within 20 minutes. In patients that do respond to CPCR, re-arrest rates are reported to be 68% in dogs and 37.5% in cats following initial resuscitation.
Basic Life Support is the ABC's. A = Airway. Check for and relieve any obstructions to breathing such as pharyngeal or tracheal foreign bodies. Suction any blood or fluid from the airway. The patient should be intubated immediately. If intubation is impossible, an emergency tracheostomy may be necessary. Verify placement of the tracheal tube, inflate the cuff, and tie securely in place.
B = Breathing. Positive pressure ventilation should be instituted with 100% oxygen. The rate should be 10-24 breaths/min, depending on the size of animal. Inspiratory pressure should reach approximately 15 cmH2O in the cat or approximately 20 cmH2O in the dog. Monitor for adequate chest wall movement with each breath. If chest movements are inadequate, search for the cause: tube malposition, occlusion, or pleural space diseases (pneumothorax, pleural effusion, diaphragmatic hernia). Always allow complete exhalation before beginning the next inhalation.
Hyperventilation should be avoided, as this is associated with a poor outcome. This is due to increased intrapleural pressure, which, in turn, decreases coronary perfusion pressures and blood pressure.
C = Circulation. Our most important goal in CPCR is to maximize myocardial and cerebral perfusion. Myocardial perfusion pressure is determined by the difference between aortic diastolic pressure and right atrial pressure. Cerebral perfusion pressure is determined by the difference between mean arterial pressure and intracranial pressure.
External chest compressions should be initiated first. Apply pressure to compress the chest a minimum of 25-30% at a rate of 100-120 compressions per minute. The animal can be in lateral or dorsal recumbency, depending on the body type. Allow the chest to fully recoil between compressions. It is extremely important to limit any interruptions in chest compressions, as continuous, properly performed chest compressions is the one component of CPCR that has been associated with an improved outcome.
Hand position for chest compressions depends on the size of the patient, as there are two different theories behind the use of chest compressions to improve circulation. The heart pump theory is employed in cats, small exotic species, small dogs, and neonates 9<10kg). This theory assumes direct compression of the heart ventricles causes blood to flow out of the ventricle into the aorta. These chest compressions should be performed directly over the heart using one or two hands.
The thoracic pump theory is employed in dogs greater than 10-15kg. In these patients, compressions are performed over the widest part of the chest. These compressions cause a generalized increase in thoracic pressure, causing blood to move out of the heart and aorta. The pressure-induced collapse of the great veins prevents backward flow of blood; so oxygenated blood is pumped out of the heart into the arteries.