In animals, shock is a physiological phenomenon unlike in humans where it can either be physiologic or psychologic. Shock is defined as the reduction of oxygen supply to the body tissues causing the cells to be unable to produce sufficient energy to function. Oxygen is usually carried from the lungs to the tissues by the red blood cells within the circulatory system. Abnormalities in cardiac function, intravascular volume, and vascular tone, integrity, and patency are critical in mainatining a normal blood circulation. Any abnormality in one or more of these components of circulation leads to stimulation of the sympathetic nervous system, which causes compensatory changes to take place to maintain perfusion.
Conditions that affect either the red blood cells, the blood circulation or the amount of oxygen available within the blood stream result in the development of shock, where there is no enough blood circulating through the body system to keep organs and tissues functioning properly. The term ‘Shock’, therefore, refers to a wide range of conditions that result in a failure of the body to continue its essential functions. It can be caused by any injury or condition that affects the flow of blood through the body. Shock can lead to multiple organ failure as well as life-threatening complications. This is a real emergency and early recognition and rapid treatment improves the survival rate.
What are the causes of shock?
Anything that affects the flow of blood through the body can cause shock. The causes of shock may include:
Significant blood loss
Blood infections (Sepsis/Septicaemia)
Dehydration
Burns
How does shock develop?
Hypoxia, low levels of oxygen in body tissues at the cellular level, causes a series of physiologic and biochemical changes, resulting in acidosis and a decrease in regional blood flow, which further worsens the tissue hypoxia.
Acidosis is a condition in which there is too much acid in the body fluids, i.e., airways, blood, or other body fluids.
Where there is a decrease in cardiac output and decreased oxygen transport, hypovolemic, obstructive, or cardiogenic shock develop, whereas where there is decreased peripheral vascular resistance and abnormal oxygen extraction, distributive shock develops. In the early stages of shock, physiologic changes happen that are reversible but if not successful leads to the final stages of shock, which are irreversible with multiorgan failure and death.
Generally, shock has the following three stages:
1. Pre-shock or compensated shock
This stage is characterized by compensatory mechanisms to counter the decrease in tissue perfusion, including increased heart rate, peripheral vasoconstriction, and changes in systemic blood pressure
2. Shock
During this stage, early organ dysfunction happens with most of the classic signs and symptoms of shock appearing, as a result of the progression of the pre-shock stage as the compensatory mechanisms become insufficient.
3. End-organ dysfunction
This is the final stage, where there is multiorgan failure due to irreversible organ dysfunction leading to death
How is shock classified?
There are many types of shock. However, they fall under four main categories, based on what has affected the flow ofblood. The five major types are:
All forms of shock are life-threatening.
Hypovolaemic shock
Low blood volume is the exact definition of hypovolemia. There is a loss of blood circulating in the body with this type of shock. Animals that are bleeding, either internally or externally, commonly experience this kind of shock. The most frequent causes include traumatic incidents including car accidents, gunshot wounds, falls from heights, or issues with the blood clotting system. Animals that have lost significant volumes of bodily fluids rather than blood might also exhibit this kind of shock, i.e., animals with profuse vomiting and diarrhea or extensive burn injuries). Severe dehydration can also cause this type of shock.
Cardiogenic shock
There is usually an underlying heart function issue with cardiogenic shock. Because the heart is not adequately pumping blood throughout the body, circulation is poor. Animals with serious cardiac illness or heart rhythm irregularities are commonly suffer this kind of shock.
Common causes of cardiogenic shock include:
Damage to your heart muscle
Irregular heart rhythm
Very slow heart rhythm
Distributive shock
Distributive shock occurs when the body has the right amount of blood, but it is not distributed evenly. It typically happens as a result of abnormal blood vessel expansion. Conditions that cause blood vessels to lose their tone can cause distributive shock, e.g., conditions that cause blood vessels lose their tone then they become so open and floppy that not enough blood pressure supplies the organs. The blood then tends to "pool" in the blood vessels rather than circulating normally through the body and back to the heart and lungs where it can get oxygenated again. The most common causes of this form of shock are: -
1. Anaphylactic shock.
Anaphylaxis, severe allergic reactions, is a complication of an allergic reaction. Allergic reactions occur when the body mistakenly treats a harmless substance as harmful. This triggers a dangerous immune response. Anaphylaxis is usually caused by allergic reactions to food, insect venom, medications, or latex.
2. Heat exhaustion
Heat stroke is sometimes referred to as "heat stroke",
3. Septic shock.
Sepsis, also known as blood poisoning, is a condition caused by infections that lead to bacteria entering the bloodstream. Septic shock occurs when bacteria and their toxins cause serious damage to tissues or organs in the body. Severe infections that culminate in sepsis and septic shock include pyometra or womb infection in bitches or an abscess which may be deep inside the body.
Neurogenic shock is caused by damage to the central nervous system, usually a spinal cord injury. This causes blood vessels to dilate, and the skin feels warm and flushed. The heart rate slows, and blood pressure drops very low.
5. Drug toxicities and brain injuries
Drug toxicities and brain injuries can also lead to distributive shock.
Distributive shock can result in symptoms that include:
Flushing
Low blood pressure
Loss of consciousness
Obstructive shock
As the name suggests, the obstruction that restricts the normal blood flow to or from the heart causes this sort of shock to happen. The conditions that can cause obstructive include: -
1. A blood clot inside a vessel e.g., pulmonary embolism
2. External vascular compression, such as a severely inflated stomach pressing on large abdominal veins,
3. Fluid buildup in the chest squeezing the heart or blood vessels in the lungs,
4. Accumulate of air or fluid in the chest cavity (pneumothorax - collapsed lung)
5. Hemothorax (blood collects in the space between the chest wall and lung)
6. Heart tamponade (blood or fluids fill the space between the sac that surrounds the heart and the heart muscle)
Hypoxemic shock
Hypoxia is a condition in which the bloodstream does not carry enough oxygen to the tissues. Either oxygen cannot be bound to the red blood cells, which is typically brought on by carbon monoxide poisoning, or because of severe lung disease, such as pneumonia, oxygen cannot be delivered into the blood through red blood cells in adequate amounts, or there are not enough red blood cells to carry all the oxygen required, which is caused by severe anemia.
What are the clinical signs of shock?
Regardless of the underlying cause, animals with shock typically present with the following common signs:
Weakness/collapse
Rapid, shallow breathing (tachypnea)
Poor quality of peripheral pulses (rapid, weak, or absent pulse) and hypotension. Pulses can be “bounding” or hyperdynamic in compensatory shock stages.
On auscultation, crackled, muffled lung or heart sounds, heart murmur, etc can be detected depending on the underlying disease and type of shock.
Dilated pupils
Dry mouth
Low blood sugar
Loss of consciousness
Altered mentation/reduced mental status (usually dull and poorly responsive)
Pale/blue mucous membranes or very red gums except usually in sepsis or other distributive shock.
Very fast or very slow heart rate (irregular heartbeat)
Cold extremities and hypothermia
In septic shock a fever may initially be present but body temperature may be low once shock develops
If any of these changes are noticed in a pet, urgent veterinary care should be sorted. Animals in shock deteriorate very rapidly and any delay in treatment significantly impairs the chances of a successful recovery.
How does one get a pet in shock to the clinic?
If a pet is suspected to be in shock, it's crucial to get him or her to a vet clinic as soon as possible rather than calling a veterinarian out because at the clinic all the equipment needed will be there to treat the pet. It is also always better to call beforehand to confirm that someone will be present to meet you when you arrive at the clinic. Use a clean material to apply pressure to the wound if there is a visible source of bleeding. Wrapping any open wound on a pet with a fresh towel also helps prevent contamination, reduce heat loss, and chilling.
Unpredictable actions are prevalent in animals in shock, particularly following trauma, where they may be in pain or have altered mental states. Even though pets are often quite trustworthy, you should always handle them with utmost caution. If a muzzle won't restrict your pet's breathing, you might need to put one on before any contact to protect yourself from harm.
How is shock diagnosed?
Shock is often recognized by first responders and doctors by its presenting symptoms. Besides, the following may also be checked: -
low blood pressure
weak pulse
rapid heartbeat
Client history
Client or pet owner's is important as it explains what happened before the pet got into state of shock. The history would include: -
History of trauma that can explain external or internal hemorrhage.
History of severe fluid losses (diarrhea, vomiting, polyuria).
Extensive burns.
Clinical signs of pyometra or dystocia in female entire patients.
Ingestion of toxins, foreign body, drug overdose that could cause perforating gastrointestinal tract ulcers.
Previous history of vomiting, dyspnea etc that could explain onset of bronchopneumonia.
Signalment (large breed dogs for GDV Stomach: gastric dilatation/volvulus (GDV) syndrome, etc.)
Once the patient is stable, the cause of shock needs to be diagnosed by performing or ordering one or more tests, such as imaging or blood tests.
Imaging tests
Imaging tests are requested to check for injuries or damage to internal tissues and organs, such as bone fractures, organ ruptures, muscle or tendon tears or abnormal growths. The tests may include:
ultrasound
X-ray
CT scan
MRI scan
Chest x-rays, in hypovolemic shock, the heart may appear small (microcardia) and the caudal vena cava may appear small with marked variation in diameter (through the breathing cycle) on ultrasound.
Imaging tests can aid identification of causes of shock within the thoracic cavity (pneumothorax, bronchopneumonia: bacterial pneumonia, pericardial effusion, pleural space disease, esophageal foreign bodies, mediastinal disease, etc). A point of care ultrasound can rule out almost all of these with less risk to the patient.
Blood tests
Blood tests are used to look for signs of significant blood loss, infection in the blood or poisoning.
How is shock treated?
When the pet arrives at the veterinary practice the veterinarian examines the pet and quickly assesses to see whether the pet is in a stable condition. If the pet’s health is not stable, the pet may be admitted immediately and some emergency treatment started (such as giving intravenous fluids) before a full history from the owner is obtained. The blood tests and the imaging tests are to establish what the underlying problem is and how severely the pet is affected.
Once shock is diagnosed, the first priority is to provide lifesaving treatment to get blood circulating through the body as quickly as possible. The initial shock treatment is emergency life-saving therapy aiming at restoring adequate oxygen delivery to the tissues. The emergency treatment may include drugs that include antibiotics, pain killers and other drugs to improve heart function. Intravenous fluids are given, plus a supplemental oxygen supply and sometimes blood transfusion.
Once the pet’s condition has stabilized a series of tests to identify and treat the underlying cause and to deal with any adverse effects of the damaged caused by the shock itself is carried out. More tests will be needed to monitor response to treatment and to investigate potential causes of the shock. Medical treatment is likely, but many pets that have suffered trauma or have a source of infection inside their body may need surgery.
If treatment is successful and stabilises the pet, there may be a prolonged hospitalization period before the pet returns home for full recovery to be achieved. Since shock is a truly life-threatening emergency, veterinary advice should be sort immediately as the earlier treatment is started the better the chances are of the pet to recover.
Is there full recovery from shock?
It’s possible for a pet in shock to fully recover but if it isn’t treated quickly enough, shock can lead to permanent organ damage, disability, and even death. The chances of recovery and long-term outlook depends on many factors that include:
the cause of shock
the length of time the pet was in shock
the area and extent of organ damage that the pet sustained
the treatment and care that the pet received
pet's age and medical history
Can shock be prevented?
Some forms and cases of shock are preventable if steps are taken to have the pet lead a safe and healthy lifestyle. For example:
If a pet is diagnosed with severe allergies, the triggers should be avoided.
To lower a pet's chances of heart damage, the pet should be on a well-balanced diet and exercised regularly.
The pet should be hydrated by providing plenty of fluids especially when the weather is hot.
References
Girard C & Higgins R (1999) Staphylococcus intermedius cellulitis and toxic shock in a dog. Can Vet J 40 (7), 501-502
De Laforcade A and Silverstein D (2015) Shock. In: Small Animal Critical Care Medicine. 2nd Ed. Philadelphia, pp 26-29.
Macintire D K (2000) Hypotension. In:Textbook of Veterinary Internal Medicine. 5th edn. Eds S J Ettinger & E C Feldman. Philadelphia: W B Saunders Co. pp 183-186.
Haseer Koya H, Paul M. Shock. [Updated 2022 Jul 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK531492/#