INTRODUCTION

Proficiency in cardiopulmonary resuscitation (CPR) is essential for every veterinarian practicing in an emergency or critical care setting. Given the nature of the patient population in these environments, cardiopulmonary arrest is not uncommon. In many cases, this represents a situation in which intervention can be lifesaving. Proper technique and timing may result in the return of spontaneous circulation and can make the difference between life and death. Guidelines for CPR in humans exist, with recommendations determined from an evidence-based review of clinical and experimental studies by an international consensus committee.¹ Unfortunately, no large-scale clinical studies of CPR have been done in veterinary patients, and recommendations for performing CPR in animals have been extrapolated from human guidelines, as well as experimental studies with animal models.^2-4 In general, the prognosis for dogs and cats suffering cardiopulmonary arrest is poor, with less than 10% of patients surviving to hospital discharge; however, the possibility for a successful outcome does exist.^5,6 Despite prevailing conventional wisdom, a retrospective study indicates that most of the animals that do survive are neurologically intact at the time of hospital discharge.⁷

The likelihood of a successful outcome is increased when the resuscitation team is well prepared. Preparation begins with a well-defined and well-equipped resuscitation area. Ideally, this area should include a “crash cart” with supplies for venous access, airway management, and drug therapy, as well as monitoring equipment and a defibrillator (see Appendix 1). Oxygen should also be available, along with supplies necessary to perform manual ventilation, such as an Ambu bag, Bain circuit, or anesthesia machine. Essential to this preparation is the training of staff and their practice of specific roles and techniques in controlled situations. Each resuscitation team should have a defined leader to allow rapid decision making and clear communication during the resuscitation. Knowing the wishes of the owner before CPR is performed facilitates this process. This may be accomplished by establishing a resuscitation code at the time of hospital admission. In the author’s hospital, a green code means all appropriate measures (including open-chest CPR) will be performed, a yellow code limits the team to closed-chest CPR only, and a red code means do not resuscitate. Finally, it is very useful to have a debriefing session following CPR to enhance the effectiveness of the team in future resuscitations.

CAUSES OF CARDIOPULMONARY ARREST

Cardiopulmonary arrest is defined as the complete cessation of effective circulation and ventilation. Common causes of cardiac arrest in veterinary patients include hypotension (secondary to hypovolemia, sepsis, or drug administration), hypoxemia (secondary to hypoventilation or lung disease), metabolic derangements (e.g., severe metabolic acidosis) and/or electrolyte abnormalities (e.g., hyperkalemia). Primary myocardial disease, which is a common cause of cardiac arrest in humans, is uncommon in veterinary patients. In some patients, full cardiopulmonary arrest is preceded by respiratory arrest, and chances for survival are markedly better if intervention is performed at this stage.⁶ It is important to recognize that there are two subsets of patients that suffer cardiopulmonary arrest, those with reversible causes of arrest and those with disease processes that cannot be reversed. In the latter case, when the patient suffers cardiopulmonary arrest secondary to an end-stage disease, CPR offers little chance of a successful long-term outcome. In these cases, it is often appropriate to discuss the various resuscitation orders and the prognosis for recovery with the owner while obtaining a resuscitation code at the time of hospital admission.

BASIC LIFE SUPPORT

Basic life support encompasses the ABCs (airway, breathing, circulation) of CPR and is the foundation for all resuscitation efforts. Although many clinicians focus on drug therapy and defibrillation during resuscitation, establishing an airway, ensuring adequate ventilation, and generating blood flow via external chest compression or internal cardiac compression must be performed quickly and properly to maximize the chance for recovery. Traditionally, the ABC mnemonic has been followed for determining the order of intervention in basic life support. This often results in a delay in the initiation of chest compressions until the patient is intubated. Recent guidelines stress the importance of early initiation of chest compressions with minimal interruptions.¹ This concept may be extended to veterinary CPR, and although an airway should be established as soon as possible, chest compressions should not be delayed until after the patient is intubated.

Airway

An airway may be established rapidly by routine orotracheal intubation in most patients suffering respiratory or cardiopulmonary arrest (see Chapter 17, Endotracheal Intubation). This may be facilitated by the use of a laryngoscope and, if necessary, a stylet to stiffen the endotracheal tube. In some patients, the airway is obscured by saliva, gastric contents, blood, or edema fluid, and in these situations it is useful to have suction available to help clear the pharynx and aid in the visualization of the glottis. In other cases, the airway is obscured by pharyngeal swelling or a mass effect, and in many cases the patient may be intubated by directly palpating the larynx and then manually directing the tube into the glottis.

After the patient is intubated, the cuff should be inflated and the tube secured. Given the stress of an arrest situation, as well as the manipulation of the patient that occurs during CPR, it is not uncommon for the tube to be misplaced or to become displaced into the esophagus. Because of this, it is important to verify placement. This may be accomplished by direct visualization of the tube entering the larynx, palpation of the neck to ensure that the tube is not felt within the esophagus, auscultation of breath sounds, and proper chest wall movement during ventilation. End-tidal carbon dioxide (ETCO₂) monitoring is also useful to verify tube placement because tracheal gas should contain carbon dioxide (as long as blood flow to the lungs is present), but esophageal gas does not. If problems are encountered, the airway should be reevaluated and the patient should be reintubated if necessary. It is also important to verify that the cuff is inflated, because this is often a source of problems.

In rare instances, the patient cannot be intubated orotracheally. These situations include airway obstruction by foreign bodies that cannot be retrieved easily, massive pharyngeal swelling or mass effects, trauma with laryngeal or proximal tracheal disruption, and trismus or dental fixation devices that prevent normal jaw motion. When orotracheal intubation is not possible, an emergency tracheostomy is indicated (see Chapter 18, Tracheostomy). Should a tracheostomy tube not be available, a standard endotracheal tube may be used, with care taken not to place the tube distal to the carina, resulting in bronchial intubation. If necessary, the tube may be cut to a more appropriate length, with care taken not to cut the cuff balloon tubing.