Cessation of effective circulating blood flow and ventilation constitutes cardiopulmonary arrest (CPA) that leads to inadequate oxygen delivery to tissue, shock, and death. Cardiopulmonary arrest is typically associated with loss of consciousness, collapse, lack of a palpable pulse, pale or cyanotic mucous membranes, lack of effective respirations, and lack of measurable blood pressure.

Cardiopulmonary resuscitation refers to re-establishing blood flow to the cerebral and coronary systems in the event of CPA by performing manual cardiac and thoracic compressions and manual ventilation until spontaneous circulation and ventilation occurs.

In human medicine, the International Liaison Committee on Resuscitation (ILCOR) allowed the development of specific, evidence-based clinical guidelines for human cardiopulmonary resuscitation (CPR), based upon extensive surveys of the literature leading directly to improved outcomes; these guidelines are reviewed and published every 5 years. In veterinary medicine, we lacked specific guidelines focused on our target species until in 2012, the Reassessment Campaign on Veterinary Resuscitation (RECOVER) developed a set of clinical consensus guidelines for the practice of CPR in dogs and cats.

These guidelines cover a wide variety of CPR-related topics in 5 domains: Preparedness and prevention, basic life support (BLS), advanced life support (ALS), monitoring, and post-cardiac arrest care.

In this presentation we will review the new guidelines and how they apply to each single domain:

1.  Preparedness and prevention

2.  Basic life support (BLS)

3.  Advanced life support (ALS)

4.  Monitoring

5.  Post-resuscitation care

Preparedness and Prevention

There are many predisposing causes for CPA, including sepsis, cardiac failure, pulmonary disease, neoplasia, coagulopathies, anesthesia, toxicities, multisystem trauma, traumatic brain injury, and systemic inflammatory response syndrome. Additionally, abnormally high vagal tone such as may accompany severe vomiting, tenesmus, or upper-respiratory tract obstruction might initiate some CPA events.

Closed and careful monitoring for deterioration in critical patients is essential as the most successful CPCR is the one that is avoided. Before a possible episode of CPA the patient may become obtunded, hypothermic, bradycardic, or hypotensive, develop dilated, unresponsive pupils, and change his respiratory pattern progressing to gasping and agonal breaths at the time of CPA.

Cardiopulmonary arrest is recognised by rapid (less than 10 sec) ABC of the patient:

a.  Evaluation of mental state (unresponsiveness)

b.  Evaluation of breathing (gasping or no breathing)

c.  (Evaluation of peripheral pulse)

Basic Life Support

Basic life support involves starting manual cardiac and thoracic compression to re-establish circulation (C) establishing and maintaining an airway (A), with supplemental oxygen initiating and initiating artificial ventilation (B).

Circulation

External chest compressions are intended to move blood from the chest to the vital organs and enhance venous return. External chest compressions should be performed at a rate of 100–120 compressions/minute with the patient on a firm surface in lateral recumbency. Compressions should be performed with a 1:1 ratio of compression to relaxation and the chest wall should be allowed to expand fully between compressions. External chest compressions employ either the thoracic pump (the compressor's hand should be placed over the widest part of the chest wall) for animal heavier than 15 kg, or the cardiac pump (the compressor's hand placed directly over the apex of the heart [4th–6th intercostal spaces]) for smaller animals.

Airway

An airway should be rapidly established by placing a well-fitting, cuffed endotracheal tube. When orotracheal intubation cannot be performed, an emergency tracheostomy or mouth-to-nose respiration should be considered.

Breathing

Manual ventilation should be instituted with 100% oxygen at a rate of 10–12 breaths per minute. All breaths should be given over 1 second followed by a pause to allow normal relaxation of the chest. High volumes and high pressures (> 20 mm Hg) must be avoided to prevent iatrogenic barotrauma. An Ambu® bag or an anaesthetic breathing system delivering 100% oxygen should be used.

In patients with conditions like pneumothorax, hemothorax, flail chest or rib fractures, diaphragmatic hernia, pericardial effusion or unsuccessful closed-chest CPCR (> 5 min), open-chest CPCR (direct cardiac massage through a lateral thoracotomy) should be considered.

Advanced Life Support (ALS)

Following BLS (if possible simultaneously), a venous access should be gained often through cut-down procedure or the placement of an intraosseous catheter should be considered. Alternatively, the endotracheal route offers a simple and rapid approach to drug administration during CPR. Epinephrine, atropine, vasopressin, and most drugs can be administered (not sodium bicarbonate), but with at least 2 to 3 times the intravenous dose, diluted in an appropriate volume (e.g., 5 mL/20 kg) of normal saline and injected via a catheter through the ET tube.

Fluid therapy is necessary only if the patient was hypovolaemic before the CPA. If a patient was on any medication that is a potential cardiac or respiratory depressant, that drug must be immediately reversed.

An electrocardiogram should be performed to determine the cardiac rhythm. Drugs should be administered based on a particular cardiac rhythm and timing during CPR. The anticholinergic compound atropine (0.02–0.04 mg/kg) might be considered at initiation of CPR in cases in which the arrest rhythm is severe bradycardia, pulseless electrical activity or asystole (the majority of feline and canine CPA patients). Epinephrine (0.01 mg/kg) repeated every 3–5 min should be used also in case of asystole. Transthoracic defibrillation should be attempted if ventricular fibrillation/tachycardia is the primary arrest rhythm.

Monitoring

If the chest compressions are successful we should be able to detect the presence of a peripheral femoral pulse and the patient should have an end tidal CO₂ > 10 mm Hg on a capnograph.

The last phase of CPCR consists of post-resuscitation care: protection of the heart and brain from the adverse effects of CPA, providing perfusion to vital organ systems, and addressing any underlying condition that caused CPA in the first place.

Respiratory function should be supported with supplemental oxygen and many patients will need ventilatory support. Crystalloid or colloid IV fluid therapy should be administered cautiously to restore and then to maintain euvolaemia. It the animal remains hypotensive despite adequate intravascular volume, then vasopressors may be required. Patients with post-resuscitation myocardial dysfunction may require a positive inotrope such as dobutamine. Arrhythmias should be treated if they are compromising the patient's haemodynamic status.

Neurologic dysfunction is common after CPR because of cerebral edema secondary to decreased cerebral perfusion and cerebral hypoxia. Many of these abnormalities might resolve with 1–2 days of return to spontaneous circulation (ROSC). Patients should be allowed a minimum of 48 hours before any judgement on their neurological status is made. Antiepileptic treatment should be administered to any post-CPA patient with seizures and interventions that may decrease intracranial hypertension secondary to brain oedema such as mannitol (0.5–2 g/kg in 30–45 min) should be considered.

Cardiovascular, respiratory parameters and body temperature should be regularly evaluated. Urine output, electrolytes, blood glucose concentration, central venous pressure, electrocardiogram, blood pressure, neurologic function, and patient comfort should be monitored.

Criteria for Terminating Resuscitation

Various objective criteria can be used to decide the appropriate time to discontinue resuscitative efforts. Typically, the duration of resuscitative efforts is most commonly used and a figure of < 20 minutes is suggested.

References

1.  Fletcher D, et al. RECOVER evidence and knowledge gap analysis on veterinary CPR. Part 7: Clinical guidelines. J Vet Emerg Crit Care. 2012;22(S1):S102–S131.

2.  Cole SG. Cardiopulmonary resuscitation. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. 1st ed. St Louis, MO: Saunders, Elsevier; 2009: 14–21.

3.  Plunkett SJ, McMichael M. Cardiopulmonary resuscitation in small animal medicine: an update. J Vet Intern Med. 2008;22(1):9–25.