Cardiopulmonary Resuscitation

Chapter 17 Cardiopulmonary Resuscitation



Steven G. Cole, Kenneth J. Drobatz



INTRODUCTION


Cardiopulmonary resuscitation (CPR) describes a set of techniques to provide circulatory and ventilatory support following cardiopulmonary arrest (CPA). CPR encompasses both basic life support and advanced life support. Basic life support includes the ABCs of resuscitation and involves establishing an airway, providing manual ventilation, and performing external chest compressions or internal cardiac compressions to generate blood flow. Advanced life support includes the Ds and Es of resuscitation, including drug therapy, defibrillation, and electrocardiogram (ECG) analysis during resuscitation. The goal of CPR is to maximize blood flow and oxygen delivery to the heart and brain until return of spontaneous circulation (ROSC) is achieved and the underlying cause of the arrest may be addressed.



• CPA is defined as the cessation of spontaneous circulation and ventilation. Causes of CPA include primary myocardial disease (although this is rare in veterinary patients), hypotension (secondary to hypovolemia, sepsis, or drug administration), hypoxemia (secondary to hypoventilation or lung disease), metabolic derangements (e.g., severe metabolic acidosis) or electrolyte abnormalities (e.g., hyperkalemia). It is important to recognize that these predisposing causes of arrest may be associated with either reversible or irreversible underlying disease processes.

• The prognosis for patients requiring CPR is guarded, and long-term survival is generally less than 10%. The likelihood of a successful outcome is improved when an arrest is rapidly recognized and a reversible cause is identified and addressed.

• CPR is most likely to be successful when the team is prepared, the techniques are practiced, communication is clear, and the resuscitation takes place in a well-equipped area within the hospital.


Key Point


CPR is a potentially lifesaving procedure that requires preparation, coordination, and communication to achieve optimal results.



BASIC LIFE SUPPORT



Airway


• Establishing an airway is the first step in performing basic life support. Orotracheal intubation is generally performed in a routine fashion, and this may be facilitated by the use of a laryngoscope and/or a stylet for the endotracheal tube. It is also helpful to have suction available if secretions or blood obscure visualization of the glottis. In situations where the glottis cannot be visualized, the larynx may be directly palpated and the endotracheal tube may be guided by feel.

• In rare situations, an emergency tracheostomy is required. This technique may be performed in less than 30 seconds after rapidly clipping and prepping the ventral cervical region. A midline incision is performed and sharp dissection is used to expose the trachea. Care is taken during dissection to remain on midline (between the sternohyothyroideus muscles) in order to avoid vascular structures. Once the trachea has been isolated, a transverse incision is made between cervical rings (approximately 50% of the diameter) and a cuffed tracheostomy tube is inserted. A standard endotracheal tube may also be used in this situation.

• Once an airway is in place, it is important to confirm correct tube placement. This may be done by direct visualization, cervical palpation, auscultation of lung sounds, and observing chest wall movement. The use of end-tidal carbon dioxide (CO2) monitoring in this situation is also useful, as tracheal gas is always higher in CO2 than esophageal gas. Once placement is confirmed, it is vital to secure the endotracheal tube, as inadvertent tube dislodgement is very common in an arrest situation.

• Problems during an arrest (i.e., unable to auscult lung sounds, chest wall not moving with ventilation) should prompt rapid reevaluation of endotracheal tube placement. It is also important to ensure that the cuff has been inflated, as this is often the source of problems. If airway problems have been ruled out, difficulty ventilating a patient during an arrest suggests severe pleural space, airway, or parenchymal disease.


Breathing


• Patients should be manually ventilated with 100% oxygen. Methods for providing positive pressure ventilation in an arrest situation include the use of an Ambu-bag or an anesthesia machine.

• Respiratory rate should be between 10 to 24 breaths/minute. It should be noted that excessive ventilation often occurs during CPR. It has been shown in animal models that increasing respiratory rates results in higher mean intrathoracic pressures, decreased myocardial perfusion pressure, and decreased survival.

• Normal chest wall motion should be observed and peak pressure of less than 20 cm H2O should be maintained if possible. Problems with decreased compliance or diminished chest wall motion may include airway obstruction, severe parenchymal disease, or pleural space disease (e.g., pneumothorax, pleural effusion, diaphragmatic hernia, mass lesions).


Circulation


• Artificial circulation during CPR may be provided by performing external chest compressions or internal cardiac massage. The goal of either technique is to maximize blood flow to the coronary and cerebral vasculature.

• Myocardial perfusion pressure is the best predictor of ROSC in human patients and animal models of CPR, and it is represented by the following equation: MPP = aortic diastolic pressure − central venous pressure.

• Cerebral perfusion pressure drives cerebral blood flow and is represented by the following equation: CPP = Mean arterial pressure − Intracranial pressure.

• There are two theories describing the mechanism of blood flow during external chest compressions. The cardiac pump theory describes actual compression of the heart through the chest wall and is likely to occur in small patients (< 15 kg). The thoracic pump theory describes blood flow as a result of phasic increases in intrathoracic pressure and has been documented in larger animals (> 15 kg).

• External chest compressions should be performed with the patient in lateral recumbency. The chest may be compressed circumferentially or directly over the heart in small patients (< 15 kg) and at the widest point of the chest in larger patients (> 15 kg). The rate of chest compressions should be 100 to 120 per minute with a ratio of compression to relaxation of 50:50. While higher compression rates have been shown to generate greater cardiac output, it is difficult to sustain higher rates for extended periods of time during CPR. Compressions should be given with enough force to decrease the diameter of the chest wall by approximately 25% to 33%.

• Interposed abdominal compression (IAC) may be used to improve the efficacy of external chest compressions. With this technique, the abdomen is compressed during “diastole” (relaxation phase of chest compression) in order to increase the pressure gradient favoring blood return to the chest, thereby improving cardiac output, blood pressure, and myocardial and cerebral perfusion pressure.

• Even optimal external chest compression produces approximately 20% of normal cardiac output. Open-chest CPR and internal cardiac compression may produce 100% of normal cardiac output, with dramatic increases in blood flow to the heart and brain. Indications for open-chest CPR include pleural space disease (e.g., pneumothorax, pleural effusions, diaphragmatic hernia), pericardial effusion, penetrating wounds, chest wall trauma, intraoperative arrests, hemoperitoneum, large dogs in which closed-chest compressions are unlikely to generate effective blood flow, or in prolonged resuscitations (> 2 to 5 min without ROSC).

• To perform open-chest CPR, the heart may be accessed via a left lateral thoracotomy (or transdiaphragmatically in patients undergoing abdominal surgery). Following a rapid clip and preparation of the left chest, an emergency thoracotomy may be performed in approximately 30 seconds. A skin incision is made in the fourth or fifth intercostal space and is extended through the chest wall musculature. Ventilation is temporarily suspended and the pleural space is accessed. A rib spreader is used to retract the ribs. Once the heart is exposed, the ventricles may be compressed with one or two hands depending upon the size of the patient. A rate of 100 to 120 compressions per minute is recommended. It is often easier to perform direct cardiac compression once an incision has been made in the pericardium (below the level of the phrenic nerve).

• Open-chest CPR allows for compression or cross-clamping of the descending aorta to direct blood flow to the heart and brain, and to avoid additional volume loss in cases of abdominal hemorrhage. In the absence of an atraumatic vascular clamp, the aorta may be manually compressed, or a Penrose drain or red rubber catheter may be tightened around the aorta. When appropriate, aortic flow may be gradually restored (over 5 to 10 minutes).

• Open-chest CPR requires that appropriate facilities and expertise be available for post-resuscitation care and management of the emergency thoracotomy.


Key Point


Basic life support measures are the basis for all resuscitation efforts. These techniques are easily learned and are effective in maintaining ventilation and artificial circulation in patients suffering CPA.



ADVANCED LIFE SUPPORT



Establishing Access for Drug and Fluid Therapy


• Rapid access to the circulation is vital in CPR. Central venous access (e.g., jugular vein) is ideal, as drug circulation times are significantly decreased when compared to peripheral sites. Because of the low-flow state that occurs during CPR, large flush volumes are necessary, especially when peripheral catheters are employed. Short, large bore catheters are ideal, as these provide the highest flow rates for drug and fluid administration.

• Surgical cutdown should be performed immediately if an initial attempt at percutaneous vascular access is not successful. Surgical cutdown involves making a skin incision adjacent and parallel to the long axis of the vein (usually jugular, cephalic, or saphenous) to be isolated. Blunt dissection with a hemostat is used to expose the vein, and an intravenous catheter is introduced. Cutdown catheters should be secured with suture and bandaged appropriately.

• Intraosseous (IO) access is an alternative to peripheral venous access, especially in small puppies, kittens, and exotic species. The intertrochanteric fossa of the femur, proximal humerus, and proximal tibia are readily accessible sites to obtain intraosseous access.

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Aug 15, 2016 | Posted by in SMALL ANIMAL | Comments Off on Cardiopulmonary Resuscitation

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