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Basics ⬇

Basics

Definition

  • Cessation of effective perfusion and ventilation because of the loss of coordinated cardiac and respiratory function.
  • Cardiac arrest invariably follows respiratory arrest if not recognized and corrected.

Pathophysiology

  • Generalized or cellular hypoxia may be the cause or effect of sudden death.
  • After 1–4 minutes of airway obstruction, breathing efforts stop while circulation remains intact.
  • If obstruction continues for 6–9 minutes, severe hypotension and bradycardia lead to dilated pupils, absence of heart sounds, and lack of palpable peripheral pulse.
  • After 6–9 minutes, myocardial contractions cease even though the ECG may look normal-pulseless electrical activity (formerly electrical mechanical dissociation).
  • Ventricular fibrillation, ventricular asystole, and pulseless electrical activity are rhythms indicating cessation of myocardial contractility.

Systems Affected

  • All systems are affected, but those requiring the greatest supply of oxygen and nutrients are affected first.
  • Cardiovascular.
  • Renal/Urologic.
  • Neurologic.

Signalment

  • Dog and cat
  • Any age, breed, or sex

Signs

  • Lack of response to stimulation
  • Loss of consciousness
  • Dilated pupils
  • Cyanosis
  • Agonal gasping or absence of ventilation
  • Absence of peripheral pulses
  • Hypothermia
  • Absence of audible heart sounds

Causes

  • Hypoxemia caused by ventilation perfusion mismatch, diffusion barrier impairment, hypoventilation, or shunting.
  • Poor oxygen delivery due to anemia or vasoconstriction.
  • Myocardial disease-infectious, inflammatory, infiltrative, traumatic, neoplastic, or embolic.
  • Acid-base abnormalities.
  • Electrolyte derangements-hyperkalemia, hypocalcemia, and hypomagnesemia.
  • Hypovolemia.
  • Shock.
  • Anesthetic agents.
  • Sepsis/septic shock.
  • CNS trauma.
  • Electrical shock.

Risk Factors

  • Cardiovascular disease
  • Respiratory disease
  • Trauma
  • Anesthesia
  • Septicemia
  • Endotoxemia
  • Ventricular arrhythmias-ventricular tachycardia, R on T phenomenon, multiform ventricular complexes
  • Increased parasympathetic tone-gastrointestinal disease, respiratory disease, manipulation of eyes, larynx, or abdominal viscera
  • Prolonged seizing
  • Invasive cardiovascular manipulation-pericardiocentesis, surgery, angiography

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Severe hypovolemia and absence of palpable pulses.
  • Pericardial effusion with cardiac tamponade, decreased cardiac output, and muffled heart sounds.
  • Pleural effusion with respiratory arrest.
  • Respiratory arrest can be confused with CPA.
  • Upper airway obstruction can rapidly progress to CPA.

CBC/Biochemistry/Urinalysis

May help identify an underlying cause for CPA but should not be part of initial triage.

Other Laboratory Tests

  • Arterial blood gas evaluation may be useful during or after resuscitative procedures, but is not part of initial emergency management.
  • Venous blood gas evaluation may be more useful during resuscitation than arterial blood gas and provides electrolyte and lactate concentrations.

Imaging

  • Thoracic FAST (TFAST) focused assessment with sonography for trauma may be useful in identifying underlying disease.
  • Abdominal FAST (AFAST) focused assessment with sonography for trauma may be useful in identifying underlying disease.
  • Thoracic radiographs may help identify underlying disease processes but only consider after the patient has been stabilized.
  • Echocardiography may confirm pericardial effusion or underlying myocardial disease but should not interfere with resuscitative procedures.
  • Abdominal radiographs or ultrasound may be useful once patient is stabilized to identify underlying disease.

Diagnostic Procedures

Once CPA has developed, continuous ECG monitoring, blood pressure monitoring, pulse oximetry, and capnography may be useful in monitoring effectiveness of resuscitative procedures.

Treatment ⬆ ⬇

Treatment

Basic Life Support

Immediate recognition of CPA

A-Airway

  • Assessment-visualize the airway by extending the patient's head and neck and pulling the tongue forward; clear any debris (e.g., secretions, blood, or vomitus), manually or with suction.
  • Establish an airway by either oral endotracheal intubation or, if complete obstruction exists, emergency tracheostomy.
  • Correct endotracheal placement should be confirmed visually, by auscultation and or capnography.

B-Breathing

  • Assessment-make sure animal is not breathing.
  • Institute artificial ventilation-administer two short breaths of ∼2 seconds in duration each and reassess; if no spontaneous respiration occurs, continue ventilations at a rate of approximately 10 breaths per minute with a tidal volume of 10 mL/kg and an inspiratory time of 1 second. Peak airway pressures should not exceed 20 cm H2O.
  • Techniques for ventilation include mouth to mouth, mouth to nose, or mouth to endotracheal tube; these techniques provide ∼16% oxygen; use of a mechanical resuscitator (Ambu bag) and room air provides 21% oxygen.
  • The preferred technique is endotracheal intubation and ventilation with 100% oxygen using an Ambu bag or an anesthesia machine.
  • The suggested rate of oxygen administration is 150 mL/kg/minute.

C-Circulation

  • Assessment-palpate peripheral pulses and auscultate heart to confirm CPA.
  • External thoracic compression provides at best ∼30% of normal cardiac output; internal cardiac compression is two to three times more effective in improving cerebral and coronary perfusion.
  • Hemodynamic studies in animal models suggest that several different mechanisms exist for generation of blood flow during chest compressions (artificial systole); during external cardiac massage the cardiac pump theory takes advantage of direct compression of the heart in patients weighing <7 kg; in patients >7 kg the thoracic pump theory is used; this technique uses increases in intrathoracic pressures to increase cardiac output via indirect effects on the major

Compression/Ventilation Techniques

  • Perform CPR in continuous, uninterrupted, 2-minute cycles when possible.
  • Perform chest compressions rapidly, at a rate of between 100 and 120 compressions/minute; the chest should be displaced ∼30%.
  • Use the cardiac pump in patients weighing <10 kg body weight; with the patient in right lateral recumbency, perform compressions directly over the heart (intercostal spaces 3–5); this can be performed using one or two hands.
  • Use the thoracic pump for patients weighing >10 kg body; with the patient in right lateral recumbency, apply thoracic compressions at the widest portion of the thorax.
  • Different compression and ventilation regimes have been reported.
  • Providing appropriate compressions (100–120 per minute) and appropriate ventilations (10 per minute) without stopping compressions for ventilations and without trying to synchronize ventilations with compressions is the goal.
  • Try to minimize discontinuing compressions to interpret ECG.
  • Avoid leaning on patient during chest compressions and allow full chest wall recoil.
  • Interposing abdominal compressions between chest compressions enhances cerebral and coronary blood flow by increasing aortic diastolic pressure. This technique has not been shown to improve survival but should be considered if adequate personnel are available.

Open-Chest Cpr

  • Indicated if closed-chest CPR is ineffective or pre-existing conditions such as flail chest, obesity, diaphragmatic hernia, pericardial effusion or other significant intrathoracic disease preclude closed-chest techniques.
  • Perform through a left thoracotomy at the fifth or sixth intercostal space.
  • Perform a pericardectomy.
  • The palmar surface of the fingers and thumb are used to push the ventricular blood toward the great vessel; digital compression of the descending aorta may help improve coronary and cerebral perfusion.

Advanced Life Support

D-Drugs

  • Base drug selection on the arrhythmia present.
  • Atropine and epinephrine are most often correct selections.
  • Atropine-0.04 mg/kg IV (0.54 mg/mL) ∼1 mL/10 kg patient.
  • Epinephrine low dose-0.01 mg/kg IV (1:10,000) 1 mL/10 kg patient.
  • Other agents such as vasopressin (0.8 U/kg IV) may be considered if initial therapy fails.
  • Drugs can be administered every other CPR cycle (approximately every 4 minutes).

E-ECG

  • Accurate ECG interpretation is imperative.
  • Check ECG leads.
  • Minimize discontinuation of chest compressions while reading ECG

F-Fibrillation Control and Fluids

  • Defibrillation is time-dependent; perform immediately.
  • Administer fluids cautiously unless known hypovolemia has led to CPA. Crystalloids, colloids, or blood products may be considered, including Oxyglobin.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

  • Base drug selection on the arrhythmia present.
  • Administer drugs via central vein, intratracheal, intraosseous, or peripheral vein, in descending order of preference. Volumes should be doubled if administering via the intratracheal route and diluted in saline.
  • Use intracardiac drug administration only as a last resort unless open-chest CPR is being performed. Administration of agent into the left ventricle with concurrent digital or mechanical compression of descending aorta is optimal.

Precautions

Only use high rates of fluid administration if there is a known history of hypovolemia; excessive fluid administration may lead to decreased coronary perfusion.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Maintain normal heart rate and blood pressure with fluids and inotropic agents.
  • Arterial blood pressure.
  • Central venous pressure.
  • Blood gas analysis.
  • Support respiration with artificial ventilation and supplemental oxygen.
  • Neurologic status-if signs of increased intracranial pressure develop, consider mannitol, corticosteroids, and furosemide.
  • ECG-continuously.
  • Urine output.
  • Body temperature.
  • Radiograph thorax to assess resuscitative injury.
  • Diagnose and correct factors that led to initial CPA.

Prevention/Avoidance

Careful monitoring of all critically ill patients

Possible Complications

  • Vomiting
  • Aspiration pneumonia
  • Fractured ribs or sternebrae
  • Pulmonary contusions and edema
  • Pneumothorax
  • Acute renal failure
  • Neurologic deficits
  • Cardiac arrhythmias

Expected Course and Prognosis

  • Prognosis depends on underlying disease process.
  • Rapid return to spontaneous cardiac and respiratory function improves the prognosis.
  • Overall prognosis is poor; <10% of patients are discharged.

Miscellaneous ⬆

Miscellaneous

Zoonotic Potential

None

Synonyms For Cpa

  • Cardiac arrest
  • Heart attack

Synonyms For Cpr

CPCR = cardiopulmonary cerebral resuscitation

Abbreviations

  • CNS = central nervous system
  • CPA = cardiopulmonary arrest
  • CPR = cardiopulmonary resuscitation
  • ECG = electrocardiogram
  • FAST = focused assessment with sonography for trauma

Suggested Reading

American Heart Association. Guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2010, 122(18) Supplement.

Fletcher DJ, Boller M, et al. RECOVER evidence and knowledge gap analysis on veterinary CPR. Part 7:Clinical guidelines. J Vet Emerg Crit Care 2012, 22(S1): 102–131.

Hofmeister EH, Brainard BM, et al. Prognostic indicators for dogs and cats with cardiopulmonary arrest treated by cardiopulmonary cerebral resuscitation at a university teaching hospital. J Am Vet Med Assoc 2009, 235:50–57.

McIntyre RL, Hopper K et al. Assessment of cardiopulmonary resuscitation in 121 dogs and 30 cats at a university teaching hospital (2009–2012). J Vet Emerg Crit Care 2014, 24(6):693–704.

Plunkett SJ, McMichael M. Cardiopulmonary resuscitation in small animal medicine: An update. J Vet Intern Med 2008, 22:9–25.

Author Steven L. Marks

Consulting Editors Larry P. Tilley and Francis W.K. Smith, Jr.