The RECOVER initiative (Reassessment Campaign on Veterinary Resuscitation) began as a review of literature and case studies to identify a set of guidelines for veterinary CPR (Cardiopulmonary Resuscitation). Veterinary CPR has, in the past, been modeled after human CPR and personal experience in the field. The RECOVER initiative has been progressive in forming a protocol for veterinary patients requiring CPR, to maximize patient outcome while decreasing detrimental effects by taking a species specific approach. These guidelines were presented at IVECCS 2011, and were published in JVECC in June, 2012. Guidelines for CPR and how to implement them with a team approach are necessary to increasing the likelihood for ROSC (Return of Spontaneous Circulation). It is important to remember the goal of CPR is to restore blood flow to the tissues. While post resuscitation monitoring is important in patient survival, initial CPR guidelines including BLS (Basic Life Support) and ALS (Advanced Life support) will be discussed further.
When suspicious of CPA (Cardiopulmonary Arrest) in a patient, CPR should be initiated immediately. Taking the time to confirm CPA prior to initiating compressions is time consuming and not recommended, as the time it takes to confirm CPA decreases patient outcome. The damage and risk associated with CPR are low in comparison to the effects of delayed CPR when it is indicated. A step by step process with instructions has been outlined below.
- Initiate CPR immediately upon suspicion of CPA.
- BLS (Basic Life Support)
- Chest Compressions: Should be performed at 100-120 compressions/min allowing full recoil of the chest between compressions. This is necessary for optimizing blood flow and gas exchange. Depth of chest compressions should be 1/3-1/2 the width of the thorax. Chest compressions should be performed in 2 minute cycles without interruption. Rotate out the technician performing chest compressions every 2 minutes to avoid fatigue which increases lean and reduces compression efficacy. Patient positioning and hand placement is discussed below, based on breed and size.
- Large or giant breeds require chest compressions in lateral recumbency, with the positioning of both hands over the widest part of the chest. This incorporates the Thoracic Pump Theory which increases the overall intrathoracic pressure causing blood flow out of the thorax.
- Keel-chested, or narrow/deep chested breeds require chest compressions in lateral recumbency with the hands positioned directly over the heart (4th-6th intercostal space). This incorporates the Cardiac Pump Theory which directly compresses the ventricles between the ribs simulating a normal heart contraction.
- Barrel chested dogs require chest compressions in dorsal recumbency with the hands positioned directly over the heart using sternal chest compressions. This incorporates the Cardiac Pump Theory which compresses the ventricles between the spine and the sternum simulating a normal heart contraction.
- Cats and small dogs with more compliant chest walls require chest compressions in lateral recumbency using a 1 hand technique (Cardiac Pump Mechanism). This technique is performed by wrapping the hand around the sternum of the patient at the level of the heart and compressing both sides of the chest simultaneously.
- Ventilation: Patient ventilation should be addressed after chest compressions have been initiated.
- Manual Ventilation via Intubation: Chest compressions should not cease to facilitate intubation of the patient. Intubation in lateral recumbency is required in patients receiving chest compressions to allow compressions to continue. Once the patient has been intubated, the endotracheal tube cuff should be inflated and the tube should be secured to the muzzle. Manually breathing (“bagging”) for the patient with an ambu bag, or anesthetic machine, using 100% oxygen at 10 breaths/min is recommended. (Ventilating the patient with room air is warranted only if blood gas analysis is available.) Tidal volume of each breath should be 10ml/kg (<20cm/H2O) for 1 second duration. It is important to continue ventilation with chest compression simultaneously.
- Mouth to Snout: The mouth to snout technique should be used when there are no additional technicians readily available to assist in CPR. This technique requires the technician to perform a cycle of 30 chest compressions (rate 100-120/min) to 2 breaths. Each breath requires a full seal of the technicians mouth around the patient' closed mouth and snout.
- Non-invasive Ventilation: This technique should be used when intubation is unable to be facilitated. A tight fitting mask with a secure seal is required. Using an ambu bag, or anesthetic machine, with 100% oxygen affixed to a mask to allow manually “breathing” for the patient may supply adequate ventilation. Though this technique is not ideal, it may be practical in some situations.
- ALS (Advanced Life Support)
- Monitoring: It is important to monitor the patient during CPR, without impeding chest compressions and ventilation. Monitoring equipment recommended is discussed below.
- ECG: Continuous ECG monitoring is crucial in identifying abnormal heart rhythm, and rate. It also allows us to monitor the rate of chest compressions applied. ECG is also important in determining if defibrillation is warranted.
- EtCO2: End Tidal CO2 monitoring of the CPR patient can be done on intubated patients during chest compressions and ventilation. EtCO2 >15mm Hg correlates with ROSC, myocardial perfusion pressure, and pulmonary blood flow.
- Electrolytes: It is important to monitor electrolyte disturbances during CPR due to the likelihood of hyperkalemia and hypocalcemia, especially with prolonged CPR.
- Blood Gas Analysis: It may be beneficial to use blood gas analysis during CPR, however controversial. It is thought that ventilation and perfusion can still be assessed with mixed venous samples. (Arterial blood gas analysis is not recommended.)
- Additional Parameters: Monitoring of SpO2, Doppler blood pressure, palpation of pulses, corneal Doppler, temperature, mucous membrane color, and cranial nerve response will likely be unattainable. However, it is important to document the absence or abnormality of these parameters in the medical record. Periodic monitoring of these vitals will also alert the technician of their return, possibly indicating ROSC.
- Obtaining Vascular Access for Drug Delivery: It is important to obtain vascular access during chest compressions, ventilation, and monitoring.
- Vascular Access: This may be obtained through a peripheral catheter, or intraosseous catheter and may need to be facilitated with a cut down technique. This is the preferred method of delivery for emergency drugs. When vascular access is delayed, it is important to consider alternative methods of drug delivery.
- Intratracheal Administration: When unable to obtain vascular access, administering drugs via the endotracheal tube can be considered. Using a red rubber catheter that is longer than the endotracheal tube, diluted drugs can be administered down the tube via the red rubber catheter. Drugs can be diluted with sterile water or saline, however drug doses may need to be increased up to 10 times the standard dose.
- Administer Drugs, Reversal Agents and Fluids: Correcting acid-base abnormalities, pressure inadequacies, and volume deficits with drug and fluid therapy is an essential part of ALS. Using drugs and fluids appropriately adds to ROSC. Inappropriate drug and fluid administration can cause further damage to the CPA patient.
- Reversal Agents: When recent opioid use or known sedation has been administered, reversal of those drugs should occur during CPR. Naloxone should be used during CPR for potential opioid toxicity (0.04mg/kg IV). Flumazenil can be considered when benzodiazepines have been used (0.01mg/kg IV). Antipamezole is warranted for α2 agonists (100µg/kg IV).
- Emergency Drugs: It is important to know what emergency drugs are warranted during CPR, and appropriate dosing. Below is a list of emergency drugs, doses, and potential complications.
- Epinephrine: It is important to start with a low epinephrine dose, as the adrenergic effects of epinephrine can cause increased myocardial ischemia. Low dose epinephrine (0.01mg/kg IV) every 3-5 minutes in early CPR is recommended. Consider high dose epinephrine (0.10mg/kg IV) only after prolonged CPR.
- Vasopressin: This drug is often used as an alternative to epinephrine during CPR. Though it can be used in combination with epinephrine. The recommended dose is 0.8U/kg IV every 3-5 minutes.
- Atropine: It is recommended to use atropine in animals with asphyxia induced PEA (Pulseless Electrical Activity), asystole, or bradycardia. Standard dosing of 0.04mg/kg IV is recommended.
- Corticosteroids: Though steroids have a place in veterinary medicine, there is no evidence showing beneficial effects of steroid use during CPR. Due to the detrimental side effects associated with steroids, their use is not recommended during BLS or ALS.
- Antiarrhythmics: Amiodarone is an antiarrhythmic used for ventricular fibrillation or pulseless ventricular tachycardia that does not respond to defibrillation. Amiodarone dosing of 5mg/kg IV should be used, though hypotension has been associated with its use. Lidocaine (2mg/kg IV over 2-3 min) can be used in place of Amiodarone.
- Calcium: In patients with moderate to severe hypocalcemia, IV calcium may be considered for administration.
- Potassium: There is no conflicting or supporting evidence regarding the use of potassium in hypokalemic patients during CPR.
- Sodium Bicarbonate: Metabolic dysfunction due to acidosis is expected during CPA. Correcting deficits with bicarbonate therapy (sodium bicarbonate 1mEq/kg IV) should only be attempted after prolonged CPA (>10-15 minutes), due to the potential metabolic complications. It is not recommended to give bicarbonate therapy during early CPR efforts.
- Fluid Therapy: It is imperative to know the volume status of the CPA patient when starting fluid therapy. Fluid therapy is only indicated in hypovolemic patients. It can be detrimental to euvolemic or hypervolemic patients by decreasing myocardial perfusion pressure. In patients with known cardiac disease, conservative fluid therapy may be warranted.
- Defibrillation: It is currently recommended that biphasic defibrillation (2-4J/kg externally/0.2-0.4J/kg internally) be used in patients with ventricular fibrillation or pulseless ventricular tachycardia. The dose may be increased once by 50%. It is important to use adequate gel when using paddles, and be sure to have good contact on either side of the thorax at the costochondral junction, directly over the heart. Be sure to have all staff clear of the animal and table during defibrillation. It is also strongly recommended to avoid using alcohol on any animal potentially needing defibrillation. Early defibrillation is crucial to success in suspected cases of ventricular fibrillation/pulseless ventricular tachycardia. If CPA has been longer than 4 minutes, it is recommended to initiate a cycle of chest compressions and ventilation prior to defibrillation. In the event a defibrillator is not available, a precordial thump can be attempted. Though minimally effective, this can be performed by striking down on the thorax, over the heart, with the heel of the hand.
It is important to note that internal resuscitation or open chest CPR is warranted in patients with compromised chest walls (such as pneumothorax, or rib fractures), pericardial disease, or if CPR attempts have lasted longer than 2-5 minutes with a failure to revive. Interposed abdominal compressions can also be considered when sufficient trained staff is available. This can be achieved by placing the hands half way between the umbilicus and xyphoid process and compressing during the decompressing phase of chest compressions allowing venous return to the heart. ITD (Impedance Threshold Device) should also be considered in larger animals undergoing CPR. The device increases negative intrathoracic pressure, causing increased venous return to the heart thus improving circulation.
To optimize the success of CPR, a team approach is necessary. The veterinary team should designate a leader of the CPR team (DVM or LVT). All others who are a part of the team should also have designated roles. Each technician should decide who will be the; chest compressor, ventilator, monitor, recorder, drug administrator, and diagnostic technician. It is important to practice these roles during down time to prepare for a CPA event. It is strongly recommended to “run through” CPR protocols and a practice CPA event every 6 months. This will ensure everyone knows their role, and executes it seamlessly. In addition to role designation, and CPR practice is hospital preparedness. Having a crash cart that is easily accessible and contains supplies needed for CPR can prevent delays in CPR administration. Crash carts should include the drugs listed above, crystalloids, colloids, endotracheal tubes with laryngoscope, IV catheters, fluid lines, red rubber catheters, ambu bags, oxygen hoses and flow meters, syringes, blood tubes, needles, tape, defibrillator with paddles, and CPR monitoring sheets. It is imperative the crash cart be stocked on each shift to ensure adequate supply and monitor drug expiration dates. A fluid warmer to keep warm crystalloids available is another tool to consider when preparing the hospital. It is helpful to have CPR algorithm charts, CPR dose charts and monitoring equipment easily visible for staff. Monitoring equipment should be kept readily available. It may be beneficial to have a CPR sheet prepared on each patients' cage in the hospital. Computer programs are available to calculate emergency drugs, fluid rates, and defibrillation doses based on the patients' weight. Having calculated doses ready prevents delays in CPR when administering drugs. In addition to supply readiness, it is important for the CPR team to have a debriefing about the previous CPA case. This can help address complications within the team approach, as well as acknowledge the progressive measures that took place.
For more information on the RECOVER initiative, go to acvecc-recover.org, or Journal of Veterinary Emergency and Critical Care volume 22, June 2012. There are also training courses on CPR guidelines at veritasdvm.com.