Shock in dogs – recognising a life-threatening emergency

Overview

A circulatory disturbance affecting the whole body

Normal circulation requires a functioning heart, sufficient circulating blood volume, and open blood vessels that constrict appropriately. An adequate haemoglobin concentration also helps maintain oxygen delivery to tissues. When these are disrupted, the body initially tries to maintain tissue blood flow through compensatory mechanisms. Shock can worsen when these mechanisms no longer meet the cells' needs. Organ failure and death may follow.

Shock is usually classified into 4 main types according to the cause of the circulatory disturbance. Several mechanisms can occur together in the same dog. Recognising shock and identifying its underlying cause are therefore both part of emergency care.

Causes

Too little circulating blood volume

In hypovolaemic shock, too little fluid circulates within the blood vessels. External or internal bleeding may be responsible. Severe vomiting and diarrhoea can also reduce circulating fluid volume. Bleeding may result from an injury, a ruptured tumour or a clotting disorder, for example.

Failure of the heart's pumping action

In cardiogenic shock, the heart's ability to pump blood is impaired. Underlying causes include heart muscle disease, valve disease and a severe arrhythmia. Treatment in this situation focuses on supporting heart function.

Uneven distribution of blood flow

In distributive shock, blood vessel dilation distributes blood flow inappropriately. This can occur in anaphylaxis, a rapidly developing severe hypersensitivity reaction. In dogs, anaphylaxis particularly affects the gastrointestinal tract and liver. An individual dog may not show every possible sign of an allergic reaction. A deficiency of adrenal cortex hormones and severe systemic inflammation can also disrupt blood vessel regulation. In sepsis, a dysregulated response to infection causes organ dysfunction. Sepsis can progress to septic shock.

A mechanical obstruction to circulation

In obstructive shock, a mechanical obstruction prevents blood flow. This can arise with fluid accumulation around the heart or a twisted stomach, for example. An enlarged stomach can compress major abdominal blood vessels and reduce blood returning to the heart.

Risk factors

The risk of shock is primarily linked to the disease or injury causing it. A dog with profuse vomiting or diarrhoea may lose fluid essential for circulation. A clotting disorder may prevent bleeding from stopping until the disorder is treated.

Large, deep-chested dogs are particularly predisposed to gastric dilatation-volvulus, or a twisted stomach. Older age and a close relative with previous gastric dilatation-volvulus are also associated with its risk. These are risk factors for that particular underlying disease, rather than breed or age limits shared by every form of shock. Severe heat-related illness can also lead to shock.

Typical symptoms

The outward signs of shock change as the condition progresses. You may notice:

• Unusual weakness, lack of strength or collapse.
• Faster breathing than usual.
• Pale or white gums and other mucous membranes.
• Cool ears or paws.
• Trembling or vomiting.
• Lethargy and decreasing responses to voice or touch.

In the early stages of shock associated with blood loss, a dog may still be alert and respond normally. The gums may be pink or red, and the pulse may feel strong. An increased heart rate may be the earliest or only detectable circulatory abnormality. As shock progresses, the pulse weakens and the dog becomes less responsive. In the most severe final stage, the heart rate may eventually slow.

Complications and consequences

Oxygen deprivation damages organs

Prolonged shock can cause irreversible cell damage. Blood flow to the kidneys and gastrointestinal tract may fall considerably. In the final stage, urine production may decrease severely. Shock can end in respiratory and circulatory arrest.

Recurrence of anaphylaxis

After anaphylaxis, a severe reaction can recur 24–48 hours after the first episode. A dog may therefore need hospital monitoring for a few days.

Blood loss and outlook

Blood loss of less than 15% may initially cause only mild signs, such as an increased heart rate. A reduction of around 15% in circulating blood volume can already be associated with hypovolaemic shock. In haemorrhage classification, a loss of 15–30% usually causes circulatory changes requiring treatment. A loss of 30–40% often requires blood products. Blood loss of at least 40% is immediately life-threatening. These proportions cannot be assessed reliably at home from the size of a visible pool of blood.

Early recognition and treatment appropriate to the cause reduce the risk of organ damage and death. More than 80% of dogs with gastric dilatation-volvulus survive with medical and surgical treatment. This figure concerns gastric dilatation-volvulus and does not describe the outlook for all dogs in shock.

Diagnosis at the vet

Initial assessment starts with vital functions

The emergency assessment covers breathing, circulation, level of consciousness, temperature and pain. Listening to the heart checks for a murmur, arrhythmia or muffled heart sounds. Listening to the lungs helps identify fluid and possible heart failure. Pulse quality, gum colour and the dog's responsiveness are assessed together.

Capillary refill time describes how quickly a mucous membrane regains its colour after pressure is released. The usual refill time is about 1–2 seconds. A delay of more than 2 seconds may indicate poor peripheral circulation. Refill in less than 1 second may occur with a hyperdynamic circulation, for example in distributive or early hypovolaemic shock. Checking mucous membranes must not delay transport if your dog has already collapsed.

Severe pain or fear can resemble the circulatory changes of early shock.

Blood tests, blood pressure and imaging

Blood pressure measurement and an electrocardiogram, or ECG, help assess circulatory stability and heart rhythm. Rapid blood tests may check glucose, lactate, packed cell volume and total protein. Clotting tests may include prothrombin time and activated partial thromboplastin time. Blood electrolytes, or salts, and kidney and other organ function are also investigated. Repeated lactate measurements can track changes to assess the response to treatment. In sepsis, lactate or low blood pressure alone cannot establish infection-related organ dysfunction.

A rapid ultrasound examination can reveal fluid in the abdomen, chest or sac around the heart. If fluid surrounds the heart, your vet also assesses whether the pressure prevents the heart from filling. Abdominal X-rays can investigate suspected gastric dilatation-volvulus.

Treatment

Supporting oxygen delivery and circulation

Treatment aims to restore tissue blood flow and oxygen delivery. An unstable patient receives supplemental oxygen where needed. Oxygen can be delivered through a mask, oxygen chamber or nasal catheter, for example. Severe respiratory failure may require mechanical ventilation. Pain is treated with medication selected by your vet.

Vascular access allows fluids and blood products to be given directly into the circulation. If intravenous access cannot be obtained, access into the bone marrow may be an alternative. Fluid treatment is tailored to the cause of shock and repeated assessments of circulation. Heart rate, pulse, mucous membranes and blood pressure are among the measures used to assess the response to fluids.

Excess fluid accumulation is avoided particularly carefully in dogs with heart disease. A patient with sepsis can also develop fluid overload and may not benefit from continually increasing fluids. If adequate correction of the fluid deficit does not restore blood pressure, a medicine that constricts blood vessels may be needed. Poor heart contraction may require medication supporting its pumping strength.

Treating the cause of shock at the same time

Stopping bleeding is central to treatment of haemorrhagic shock. Severe bleeding may require red blood cells or other blood products. Internal bleeding may require surgery, for example to remove a ruptured tumour. In cardiac tamponade, fluid is removed from around the heart so that it can fill. Gastric dilatation-volvulus requires stomach decompression and surgery.

Sepsis treatment requires early antimicrobial treatment and control of the infection source alongside circulatory support. In anaphylactic shock, your vet gives adrenaline. Corticosteroids are not a general first aid medicine for every form of shock. They may be used for a confirmed or suspected adrenal hormone deficiency, for example.

Continuous monitoring

Intensive care includes monitoring urine production, heart rhythm and blood pressure. Fluid balance, blood clotting and organ function are also assessed repeatedly. Weight gain, faster breathing and swollen limbs can indicate fluid overload in a patient with sepsis. Medication and fluid treatment are adjusted according to the dog's condition and measurements.

Prevention

Preventing shock focuses on the dangerous situations and diseases that cause it. Vomiting or diarrhoea causing severe dehydration must not be left unmonitored. Parvovirus vaccination prevents a disease that can cause profuse bloody diarrhoea and dehydration. Weaned puppies without vaccine protection are protected from infection.

Do not leave a dog in a car in warm weather, because the temperature inside can quickly become dangerous. In hot weather, provide fresh water and reduce exertion. In a dog predisposed to gastric dilatation-volvulus, preventive gastropexy, which fixes the stomach in place, can reduce the risk of twisting. Fixation does not, however, prevent the stomach from dilating with gas.

Important for dog owners

Call the emergency practice and set off without delay. Describe your dog's level of consciousness, breathing, any injury or bleeding, and any suspected poisoning. Mention current medicines and previous heart or clotting diseases. Ask another person to help with transport if necessary.

Keep an injured dog's movement to a minimum. Cover a dog becoming cold with a blanket, but do not warm a dog with suspected heatstroke. Support a large injured dog on a flat surface during transport. Avoid unnecessary movement of the head, neck and back if injury to these areas is suspected.

Press a clean cloth or dressing against a bleeding wound. If blood soaks through, add more material on top. Do not remove an object embedded in the body during transport. Do not muzzle a dog with breathing difficulties. Do not give an NSAID to a dog in shock on your own initiative.

Frequently asked questions

Can a dog in shock have red gums?

Yes. In the early stages of shock associated with blood loss, the gums may be pink or red and the dog may still appear alert. Later, mucous membranes may become pale and the pulse may weaken. Assessment of a serious injury or collapse therefore does not rely on gum colour alone.

Can you treat circulatory shock by giving a dog water?

Suspected shock requires immediate veterinary treatment because tissue oxygen delivery is at risk. Treatment may require intravenous fluids, supplemental oxygen and, where needed, blood products. A bleeding vessel or a condition obstructing circulation, for example, must also be treated.

Why are dogs in shock not all given the same amount of fluid?

Shock may result from blood loss, failure of the heart's pumping action, blood vessel dilation or an obstruction to circulation. Fluid treatment is tailored to this mechanism and the dog's response. Excessive fluid loading is avoided particularly carefully in a dog with heart disease. A patient with sepsis can also accumulate too much fluid during treatment.

Should you cover a dog that feels cold?

A blanket can help conserve the warmth of an injured dog becoming cold while they are transported for treatment. Heatstroke is an exception: the dog must not be warmed. Keep the dog as calm as possible and avoid unnecessary movement, particularly if an injury is suspected.

Is shock the same as sepsis?

Shock is a severe circulatory disturbance with several possible causes. In sepsis, the body's dysregulated response to infection leads to organ dysfunction. Sepsis can cause septic shock, but shock caused by blood loss or failure of the heart's pumping action, for example, does not require infection.