Cardiopulmonary Arrest and Cardiopulmonary Resuscitation
When breathing has ceased though the heart continues beating is considered as respiratory arrest. Cardiopulmonary arrest occurs when both effective circulation and ventilation have stopped.
What are the Causes of Cardiopulmonary Arrest?
There are quite a few possible causes:
Hypoxia - Due to windpipe or chest problem (e.g. upper airway obstruction, lung tumours, fluid in the chest cavity, ruptured diaphragm.)
Hypotension - Due to decreased blood volume (e.g. bleeding), sepsis or drug administration.
Hypoglycemia (low blood glucose level) - Especially in young puppies.
Hypothermia - Especially under extreme conditions.
Hyperkalemia (high blood potassium level) - As is seen with Addison's disease or with certain urinary problems.
Increased vagal tone - May occur with vomiting, respiratory or abdominal diseases, and with brachycephalic breeds.
Iatrogenic - Such as giving certain medications too quickly, or via the wrong means of administration.
Anaesthetic related arrest - Such as anaesthetic overdose, or using hypotensive drugs.
When Should Resuscitation be Attempted?
Patients with cardiopulmonary arrest usually fall into two categories: those with potentially reversible causes and those with irreversible causes. Resuscitation should not be attempted when the arrest is due to metastatic tumours, chronic renal failure, end stage heart disease, very end stage systemic inflammatory response syndrome and overwhelming injuries or diseases.
What Basic Procedures are Used During Resuscitation?
Initially basic life support procedures are put into place. They are the 'ABC' of resuscitation.
Airway - Place an endotracheal tube from the mouth to the windpipe, or a tracheostomy tube in the windpipe if it is not feasible.
Breathing - The lungs are then ventilated using 100% oxygen at about 30 to 40 breaths per minute.
Circulation - Circulation is established using either open or closed chest cardiopulmonary resuscitation, with the aim being to maximise blood flow to the heart muscle and brain. Closed chest cardiopulmonary resuscitation involves compression over the side of the chest cavity, whilst open chest cardiopulmonary resuscitation involves direct heart massage. Open cardiac massage is usually reserved for situations when the closed technique cannot establish sufficient increase in intrathoracic pressure to cause adequate venous circulation. This occurs when, for example, the dog is suffering from air or fluid filling the chest cavity (but outside the lungs), or chest wall damage.
In some cases advanced support procedures may also be required. This involves the use of a defibrillator, medications (e.g. adrenaline) and fluids to assist in reversing the arrested heart.
How Successful is Cardiopulmonary Resuscitation?
The success rate is low to moderate in cases that have a full cardiopulmonary arrest. The success rate does improve if cardiopulmonary resuscitation commences very soon after the arrest occurs.
If arrest has lasted for over 5 to 10 minutes, post-resuscitation sequelae may occur. They include cardiopulmonary rearrest (in about 66% of resuscitated patients), permanent brain damage, heart muscle damage, kidney failure, shock gut, coagulation problem due to disseminated intravascular coagulation, hypoventilation and septic infection.