Luis H. Tello, MV, MS, DVM
During 2011, we celebrated the 50th anniversary of the first articles published about CPR based on the work of Dr. Guy Knickerbocker, at the J. Hopkins Medical School in Baltimore, Maryland, USA.
Sadly, after more than 50 years, with an impressive advance in technology, basic science and pharmacology, the rates of success have not improved dramatically, and still we do not have a clear understanding about which are the best interventions and what protocols we should adopt.
The published reports of success rates in veterinary medicine after cardiac arrest and CPR are around 13% in dogs and 15.4% in cats, and the rate of hospital discharge following successful CPR is < 16%.
Cardiopulmonary resuscitation is a very complex and challenging situation, and because of that, periodic reexamination of the protocols and recommendations by experts, institutions, and senior leaders in that field occur, leading to changes that sometimes may be perceived as drastic. Even the name has been changed, and different denominations have been proposed. However, by the last consensus, it seems that the term CPR is more simple and easy to understand for everyone, even if it does not describe completely all the interventions and maneuvers that will be attempted.
Every five years the American Heart Association (AHA) releases International Liaison Committee on Resuscitation (ILCOR)-based updates on CPCR - this information is a review of the previous 5 years of research to determine if there is any new evidence that impacts guidelines for CPCR; the AHA guidelines are available free online through the Circulation journal. This information is primarily based on human research, and application in veterinary medicine may be inappropriate or simply wrong. However, the good news is that a group of very well-known and dedicated specialists and professionals put together the Reassessment Campaign on Veterinary Resuscitation (RECOVER) in order to publish the first evidence-based consensus CPR guidelines for veterinary medicine.
RECOVER identified 5 areas to be investigated:
Basic life support (BLS)
Advanced life support (ALS)
Training the team is critical for success and expecting the unexpected is part of the preparation.
Include regular drills in the training refreshers.
Setting up an area and a well-stocked "crash cart" is vital.
Developing a consistent Triage system.
Establish a leadership system for ER/CPR cases.
Practice a protocol for reception, intervention, and monitoring for all the people in the hospital.
Recognition of CPA is critical for the success. If in doubt, start CPR.
If patient is under anesthesia, monitor to prevent cardiopulmonary arrest (CPA), apply aggressive CPR.
Patients under anesthesia have better chance to survive than any other cause of CPA.
Do not waste time looking - checking for pulse, or auscultation or watching respirations.
We Do Not Know
No 100% effective single method exists to determine CPA.
The usage of manikins for training does not necessarily improve efficiency of CPR.
It is not clear how many people should be the minimum size for the CPR team.
Basic Life Support
Because there is no 100% effective way to identify CPA, it is reasonable for rescuers to start CPR on unresponsive, non-breathing patients with no palpable pulses or heartbeat.
Serious adverse effects are very uncommon in human patients that are not in CPA and receive chest compressions, so CPR should be initiated in dogs and cats as soon as possible if CPA cannot be definitively ruled out.
Every effort needs to be done to avoid delay on chest compressions.
The classic ABCs approach may be changed to CABs as a more realistic approach in veterinary patients where respiratory arrest is more common than cardiac arrest.
May be reasonable to use a mouth-to-snout breathing for dogs and cats with respiratory arrest in a 30:2 ratio with chest compressions when endotracheal intubation is not possible.
For a one-rescuer situation, the immediate delivery of chest compressions should be the main priority. If more rescuers are available, then intubation and ventilation should be attempted as soon as possible, while compressions are being performed.
About the controversy of ABC v/s CAB, in dogs and cats with unwitnessed CPA and with only 1 rescuer present, traditional ventilation first (ABC) CPR is recommended, but that should not significantly delay the initiation of chest compressions. In witnessed CPA due to primary cardiac disease, compression first (CAB) CPR is recommended.
During chest compressions, complete chest wall recoil should be allowed during CPR in dogs and cats (so no leaning over the patient!).
Whenever it is possible, interposed abdominal compression (IAC) could be used to increase venous return and CO.
We Do Not Know
The ideal tidal volume for ventilation during CPR is not clear. Based on human and animal experimental studies, a volume of 10 ml/kg may be adequate.
No clear evidence supports a specific ventilation rate. It may be reasonable to recommend a ventilation rate of 10 breaths/min during CPR in dogs and cats, targeting normocapnia and avoiding arterial hypoxemia.
There is no clear evidence about the depth of the compression and the ideal ratio between compressions:ventilations. At this time, the human recommendations of "push hard, push fast and do not stop" are advisable. Also, a ratio of 30:2 for compressions:ventilations may be recommended. 100 compressions per minute are recommended at this point.
No clear recommendations can be made about the position of the hands or the animal during CPR in dogs and cats. Classical lateral recumbency for patients over 10 kg and dorsal recumbency for less than 10 kg.
No specific timing could be recommended for interruptions of the chest compressions to diagnose the rhythm or to stop the CPR to declare the patient deceased.
Following the human protocol of 2 minutes of uninterrupted CPR before checking sounds reasonable. However, rescuer fatigue has been documented after 1 minute of CPR, so replacing him/her is advised.
Advanced Life Support
Administration of the drugs needs to be IV. Intratracheal is accepted (naloxone, atropine, vasopressin, epinephrine and lidocaine: NAVEL) but diluted 1:10 in saline. When IV access is not available, intraosseous catheterization is a good method for administering medication during CPR, especially in the young and small patients.
Atropine is recommended when you suspect that excessive vagal tone could be the cause of the CPA.
Standard dose of epinephrine is recommended (0.01 mg/kg).
Aggressive fluid therapy should only be administered if there is a trigger condition which may result in hypovolemia.
The use of vasopressin (0.8 U/kg IV), with or without epinephrine, is a reasonable intervention during CPR. Vasopressin may also be used for asystole, pulseless electrical activity (PEA), defibrillatory-resistant V-fib, and pulseless ventricular tachycardia.
Severe electrolyte abnormalities should be addressed and corrected during the ALS of the CPR.
The use of prompt electrical defibrillation is recommended over medical treatment for VF and VT. Biphasic is preferable over monophasic defibrillation.
We Do Not Know
The real benefits on specific patients of a high dosage of epinephrine (0.1 mg/kg).
The real benefits of using atropine in dogs and cats under cardiac arrest that have cardiac rhythms such as asystole, PEA, pulseless ventricular tachycardia (VT) or ventricular fibrillation (VF). No study has evaluated the monotherapy with atropine under those rhythms.
In patients under cardiac arrest, there is no strong evidence that supports the use of antiarrhythmic drugs. In pulseless VT and VF, a rapid defibrillation is advised before any drugs are administered. In dogs with shock-resistant pulseless VT or VF, amiodarone may be recommended, but hypotension and anaphylactic reactions have been described in dogs.
At this point it is not clear the role of corticosteroids on CPR and no evidence of improving success, so they could not be recommended at this point.
Specific recommendations about the usage of naloxone or sodium bicarbonate cannot be made at this point. Not enough evidence is available about them.
Monitoring and post-arrest care should be provided based on the individual patient. End-tidal carbon dioxide (EtCO2) monitoring is advised to identify return of spontaneous circulation (ROSC) and as a tool to evaluate CPR's quality.
References are available upon request.