When a patient falls into cardiopulmonary arrest in your hospital and the team responds to perform cardiopulmonary resuscitation (CPR), what does that look like? Is it organized or chaotic? Is it based on a protocol or left up to individual judgment? Is it…evidence-based? Since the Reassessment Campaign on Veterinary Resuscitation (RECOVER) guidelines were published in 2012, the veterinary field now has evidence-based recommendations made through a collaboration of over 100 emergency and critical care experts to base their practice in veterinary CPR. The RECOVER guidelines divide CPR into basic life support (BLS) involving compressions and ventilation, and advanced life support (ALS) which include monitoring, vascular access, drug administration, and defibrillation. The knowledge gained in veterinary CPR can be summarized in the algorithm provided by the RECOVER Initiative. The RECOVER Initiative is a collaborative effort between the American College of Veterinary Emergency and Critical Care and the Veterinary Emergency and Critical Care Society. How have these guidelines changed the way we perform CPR?
The AB“C” Assessment
Every CPR situation starts with the discovery of a patient that is unresponsive. Assessment of whether an unresponsive patient is in cardiopulmonary arrest (CPA) starts with the ABC assessment; airway, breathing, and circulation. First, confirm the patient does not have an occluded airway by opening the mouth and visualizing the throat by pulling on the tongue. Care should be taken to not be bitten by the patient. The presence of spontaneous breathing should also be checked by visualizing chest excursions or lightly placing one’s hand on the chest to sense movement. If the patient is not breathing, the next step would be to confirm whether the patient’s heart is spontaneously beating. However, there is evidence that suggests the presence of pulses and auscultation of heartbeats can be easily mistaken and is thought to be unreliable. Because of this, any assessment of circulation in an unresponsive patient must be brief, if at all, and the entire assessment process should be done in less than 10–15 seconds.
Immediately Start Effective Compressions
Immediately starting compressions effective in creating blood flow is the most important part of CPR. The longer it takes to create blood flow for the patient, the lower the chance of survival becomes. The goals of chest compression are to create blood flow to the brain, heart, and lungs. The sooner we create blood flow we can deliver oxygen to these organs. Chest compressions are performed at 100 to 120 compressions per minute, forceful enough to depress the chest by 1/3 to 1/2 the normal width and allowing for the chest to fully recoil in between compressions. This can be best accomplished with the palms superimposed over each other, fingers interlocked, and placed on a compression point appropriate for their chest conformation. Round-chested animals with their chest width close to as they are deep should have compressions focused on the widest portion of their chest in lateral recumbency. Narrow-chested animals that are much deeper than they are wide (such as greyhounds and collies) should have compressions focused directly over the heart in lateral recumbency. Less commonly, a patient may be wider than they are deep (having a flat-chested conformation) and would benefit from compressions being focused over the sternum in dorsal recumbency. In these larger animals, compressions are performed with the elbows locked, and shoulders positioned straight above the patient to create a perpendicular angle with your arm and the patient and pressing down with upper body weight and core muscles of the waist. Cats and small dogs may be able to have compression performed over the heart with a one-handed technique.
Don’t Interrupt Those Compressions
Compressions are performed consistently for 2 minutes long at a time without interruption. Achieving maximal blood flow that can be created with compressions, which is only up to about 30% of spontaneous circulation created by a beating heart, takes up to 60 seconds of consistent compression to achieve. Any interruption of compression will significantly reduce the blood flow created, leading to submaximal perfusion of vital organs during CPR. Even tasks that compressions have typically been Interrupted for such as auscultation of the heart, endotracheal intubation, assessment of the ECG, and responsiveness of the patient should not be performed in the 2-minute “compression cycle.”
This shift in protocol has changed the phrase “ABCs of CPR” implying an airway being established (A for airway) and ventilation started (B for breathing) being a priority over compressions (C for circulation) to CAB; compressions are prioritized over establishing an airway and providing ventilation. Circulation is more valuable to the patients because without circulation, the oxygen provided to the blood in the pulmonary vasculature will not be delivered to the organs that require it. Even without manual ventilation, compression-induced ventilation (air movement in and out of the lungs due to changes in intrathoracic pressure created by chest compressions) provides a small amount of ventilation while endotracheal intubation is performed. This necessitates endotracheal intubation to be performed while the patient is in lateral, and less commonly in dorsal recumbency, and becoming familiar with intubation in lateral and dorsal recumbency utilizing opportunities during routine anesthetic procedures is recommended.
Ventilation Is Kept at 10 Breaths Per Minute
Once endotracheal intubation is completed, ventilation can be delivered with a manual resuscitation bag or the reservoir bag on an anesthetic machine (ensuring there is no anesthetic gas being used). Ventilation is performed at 10 breaths per minute, accomplished by providing a breath with 1 second inspiratory time once every 5 seconds for a total of 6 seconds per breath cycle.
A normal tidal volume is estimated to be 10–15 mL/kg though accurate delivery of volumes while chest compressions are being delivered can be difficult. The use of a manometer to keep the pressure between 20–40 cm H2O would keep any damage to lung tissue minimal. Manual resuscitation bags typically come equipped with a pressure safety valve rated at 40 cm H2O.
End-Tidal Carbon Dioxide and ECG Are the Only Useful Monitors
Once compressions and ventilations have been started, the next priority is to establish monitoring. The two useful modes of monitoring during CPR are end-tidal CO2 (ETCO2) and electrocardiogram (ECG).
Capnometry is useful in three different ways. First, it can be useful in assessing the effectiveness of the compressions being employed. The amount of CO2 expired is directly related to the amount of perfusion that exists in the pulmonary vasculature and passing by the blood-gas barrier. Evidence points to ETCO2 values of 15 mm Hg or higher being associated with a higher chance of achieving return of spontaneous circulation (ROSC) when compared to compressions that achieve ETCO2 values less than 15 mm Hg. If ETCO2 values of at least 15 mm Hg cannot be achieved, the manner in which compressions are being performed in posture, technique, and consistency as well as verification of proper endotracheal intubation must be pursued.
Capnometry is also useful in verifying appropriate endotracheal intubation. When the esophagus is intubated, there is no ETCO2 reading expected as the gastrointestinal tract does not produce a significant amount of CO2. However, having no ETCO2 reading does not necessarily mean the esophagus is intubated as it could also mean there is no perfusion to the lungs. The presence of ETCO2 will indicate that endotracheal intubation was successful.
A sudden rise in ETCO2 value will be seen when the patient achieves ROSC as a significantly higher amount of perfusion will exist in the pulmonary vasculature leading to values of 45 mm Hg and often much higher, which will be a stark contrast from when compressions are being performed. When a large increase in ETCO2 is observed, attempts to palpate pulses and confirm presence of a spontaneous rhythm should be attempted prior to stopping compressions to ensure continuation of blood flow.
The ECG rhythm is evaluated at the end of each 2-minute compression cycle since ECG evaluation is unreliable while compressions are performed since the compression creates mechanical ECG artifacts. The four rhythms seen during CPR include asystole, pulseless electrical activity (PEA), pulseless ventricular tachycardia (PVT), and ventricular fibrillation (VF). Asystole and PEA are considered non-shockable rhythms and require continued compressions. PVT and VF are considered shockable rhythms which also require continued compressions, though electrical defibrillation is performed as soon as possible as the appropriate ALS intervention.
Intraosseous Access Is Second Choice
Establishment of vascular access is necessary to deliver fluids and drugs and should be accomplished within the first minutes of CPR. While intravenous catheters are often able to be placed, especially in larger patients, it may be difficult in smaller patients. Venous cutdown procedures are one option to achieve venous access during CPR. The second option to swiftly obtain venous access is by placement of an intraosseous (IO) catheter.
Intraosseous catheters can be placed in the femur, tibia, or humerus with a hypodermic needle, spinal needle, biopsy needle, or an IO needle driver. The IO space has the advantage of maintaining its structure to serve as a space to cannulate even when vasoconstriction or collapse of the vasculature is present. Fluid administration and drug administration through IO catheters are just as effective as when given IV.
In the very rare occasion that neither IV nor IO access can be established, intratracheal (IT) administration of drugs can be attempted. When employed, the dosage of the drugs is increased by 2–10 times and chased with a small amount of saline to push into the airway, all without interrupting compressions. How well drugs delivered IT is absorbed is uncertain and could theoretically lead to significant increase in absorption when ROSC is achieved, making it a less desirable route than IV or IO.
Intracardiac route of administration is not recommended as it is a relatively difficult task to perform without interruption or delay in resumption of compressions and it can potentially lacerate the coronary vessels which serve as the source of perfusion to the myocardium.
Reversible Drugs Are Reversed
Many patients that fall into CPA are under the effects of analgesic or anesthetic agents which can alter the cardiovascular and respiratory status. It is reasonable to reverse the effects of these agents when possible to alleviate the effects. Common reversible agents include opioids that are reversed by naloxone, benzodiazepines reversed by flumazenil, and alpha-2 agonists reversed by atipamezole. Dosages of reversals and other drugs can be found in a CPR drug chart within the RECOVER guideline.
Don’t Give Fluids Every Time
Intravenous fluid administration, while often performed during CPR, is not always beneficial. Whether the patient can benefit from fluid administration depends on their fluid balance and intravascular volume status. Hypovolemic patients would benefit from fluid administration to increase the circulating blood volume and facilitate better perfusion. In a euvolemic or hypervolemic patient, fluid administration can lead to coronary perfusion pressure being reduced because of an increase in right atrial and central venous pressure reducing the delivery of oxygen to the brain and the heart, leading to a poorer chance of ROSC. The patient’s condition and history should be carefully considered to determine whether administration of fluids is warranted.
Epinephrine Is Not Always Used
Epinephrine administration is used in CPR for its alpha- and beta-adrenergic effects promoting vasoconstriction leading to improved perfusion pressure and shifting of blood volume to the core of the body. Epinephrine is administered as an ALS intervention recommended when non-shockable ECG rhythms (asystole and PEA) are observed. Because an ECG rhythm diagnosis cannot be made without the ECG leads attached, whether epinephrine should be administered cannot be determined until the end of the first compression cycle for patients that have monitoring initiative when compressions are being performed. In patients that arrest with ECG monitoring already established, the arrest rhythm can be identified just prior to compressions being started, allowing the CPR team to determine the appropriate ALS intervention and necessity of epinephrine.
When epinephrine is determined to be appropriate, it can be given at a low dose (0.01 mg/kg) or high dose (0.1 mg/kg). Because high dose epinephrine has been associated with lower survival despite higher chances of ROSC, the guidelines reserve its use for prolonged CPR and recommend the use of low-dose epinephrine. Epinephrine is given first upon diagnosis of asystole or PEA, and once every other compression cycle (every 3–5 minutes).
Because epinephrine provides beta-1 adrenergic stimulation, it can induce inotropic and chronotropic effects that can increase myocardial oxygen demands and exacerbate myocardial ischemia. The inotropic and chronotropic effect is thought to be harmful when patients are experiencing shockable rhythms (PVT and VF) which emphasizes the importance of a rhythm diagnosis prior to the decision of epinephrine administration being made.
Atropine is a drug commonly given during CPR; however, it does not have any evidence pointing towards benefit or harm during CPR. It is thought that the use of atropine as a sympatholytic agent is reasonable when the patient arrest may be associated with high vagal tone such as in the case of an anesthetic arrest during ophthalmic surgery or in brachycephalic patients.
Defibrillation Is Needed to Treat Some Rhythms
Instead of epinephrine, patients experiencing shockable rhythms require prompt defibrillation to treat. Both VF and PVT occur because of abnormal firing of myocardial cells out of synchronization with the pacemaker. Defibrillation, provided with a jolt of electricity to depolarize the myocardial cells and place them in a refractory period, may allow the pacemaker to regain control of the myocardial depolarization in unison. Many veterinary practices do not own electrical defibrillators and may need to rely on mechanical defibrillation by performing precordial thumps. However, its efficacy is uncertain and likely poor, thus encouraging veterinary practices that perform CPR on any frequent basis to invest in an electrical defibrillator and conduct training to use safely use the equipment.
The Cycle Is Continued Until ROSC
The first cycle begins once the unresponsive patient is determined to have fallen into CPA after the AB“C” assessment. While the first 2 minutes of compressions are performed, endotracheal intubation and commencement of ventilation, attachment of ETCO2 and ECG monitors, optimizing of compressions through evaluation of ETCO2, obtaining vascular access, administration of reversal agents, and coordination of the CPR team through a team leader should ideally be completed.
The patient is assessed after each 2-minute compression cycle within a 10-second period to determine if the patient has achieved ROSC. If the patient has achieved ROSC, then the veterinary team will employ the post-cardiac arrest care algorithm to support the cardiovascular, respiratory, and neurologic systems to direct the patient towards survival to discharge. In most situations, the patient will not have achieved ROSC and will require the repeating of this cycle until ROSC is achieved or the patient is pronounced dead.
Subsequent cycles consist of the repetition of 2-minute compressions and optimizing of compression by evaluation of ETCO2 while consistent ventilation is provided. Patient and ECG evaluation is performed after each 2-minute cycle, leading to the appropriate ALS intervention of epinephrine (every other cycle) for non-shockable rhythms and defibrillation (every cycle) for shockable rhythms.
Don’t Yell Out Orders to the General Area
Having a systematic algorithm and protocol is only one part of the solution in bringing order to the chaos that accompanies treatment of CPA. Clear and direct communication from the leader and throughout the entire team is critical not only to organize the CPR but also to prevent mistakes. Assignment of the roles of CPR leader, compressor, ventilator, drug administration, record keeping, and timer to the available team members will prevent confusion on tasks being completed.
Closed-loop communication, a communication technique with the sender of the message clearly indicating the person it is being sent to, the recipient acknowledging the message, and the sender responding to the acknowledgement is useful to be employed in CPR. Mistakes such as mishearing drug names and doses can be caught through overt verbal communication can be caught through this technique all the while notifying the entire team of the current progression of CPR. By every member of the team being situationally aware of every move the team makes, mistakes can be corrected and gaps in employment of the algorithm filled through teamwork.
Certification as an International Standard
Since the publishing of the RECOVER guidelines, the evidence-based guidelines and practice in CPR have been embraced by the veterinary emergency and critical care community, leading to further steps in creating an international standard. The RECOVER Initiative is organized into three branches that pursue goals promoting better veterinary resuscitation science; guidelines, education, and research. The Guidelines branch will continue to develop and update evidence-based veterinary CPR guidelines through an exhaustive review of primary CPR literature and is planning a guideline revision to be published in 2020. The Research branch is currently working on establishing a global veterinary CPR registry to gather CPR data that can then be used to fill some of the knowledge gaps that have been identified through the evidence review process. Research grants directed at studies related to veterinary CPR are also being established.
The Education branch is responsible for establishing standardized certification processes related to veterinary CPR. Veterinary professionals currently can obtain RECOVER CPR certification through the RECOVER website (recoverinitiative.org). The first step involves obtaining knowledge of the concepts in RECOVER BLS and ALS through an online course. The second step is to attend an in-person certification session to become a RECOVER Certified Rescuer. As a further step, rescuers have the option of becoming a RECOVER Certified Instructor with additional training, being able to teach others in performing veterinary CPR according to the RECOVER CPR standards. Every veterinary professional is encouraged to become certified, so we can provide our patients with the best chances for survival.
Prevent CPA and Choose the Right Patients
One thing that is unchanged before and after the publishing of the RECOVER guidelines is that prevention of CPA remains the best way to lead a patient to survive. When admitting a patient into the hospital whether it is for routine procedures or hospitalization, discussion with the owners on the resuscitation order or “code status” of the patient is important so that the veterinary team is in alignment with the beliefs of the owner regarding performing CPR on their pets.
Recommendations from the veterinary team should be based on the realistic assessment of chances of a meaningful recovery from CPA, which depends on the overall health and severity of conditions the patient is experiencing prior to admission. A geriatric patient with multiple chronic systemic diseases presenting to emergency with an acute episode could be interpreted as a patient that will have a minimal chance of meaningful recovery, while a young, healthy patient being hospitalized for the day for a routine anesthetic procedure would have a significantly higher likelihood of survival.
The value of proficiency and training in CPR is sometimes argued from a statistics point of view that currently, veterinary CPR has a 2–7% survival to discharge rate and is a poor investment in training resources. Instead, it should be argued that veterinary professionals have the responsibility to know exactly how to perform CPR in the most effective manner to maximize the survival chance, especially in those that fall into the latter group described above. Saving one patient does make a difference, and we should know the best practices of today.