Chris Kouwenhoven

Circulatory shock in animals

Today I'd like to discuss a rather general topic that has been the subject of concern for a number of readers. When an animal is injured, especially if the injury is fairly severe, it may go into what is known as shock. Those of you who watch any of the many medical shows on television are likely familiar with this topic and realize how serious and even life-threatening shock can be. In humans, shock can also result following a major emotional event, such as the serious injury or death of a loved one. This type of shock causation is not known in animals, so we will not discuss it further here.

Animals depend upon the circulatory system to provide oxygen and nutrients to the tissues of the entire body and to remove waste products from those same tissues. When there is a lack of either sufficient amounts of either oxygen or nutrients at the cellular level, tissues begin to die. The same is true when toxic levels of waste products begin to build up in tissues because the circulation is unable to move them to those organs of the body, such as the lungs and kidneys, that act to remove them from the body. Obviously, when the efficiency of the circulation decreases significantly, the animal is in serious trouble.

Circulatory shock is an event that dramatically impairs the efficiency of the circulation. There are three major types of circulatory shock.

Hypovolemic shock (hypo = below or less than normal) occurs following a significant loss of circulating blood volume. Hemorrhage due to injury often causes this reduction in circulatory volume. There must be at least 15-25% loss to result in purely hypovolemic shock and in serious trauma, this loss in volume may be seen. Treatment here is centered on increasing the volume in the circulation, generally using intravenous fluids and/or blood transfusions. Fluids other than blood are commonly used because there is no time lost in cross-matching blood types. These other fluids do not carry oxygen, but the bone marrow will quickly replace the missing blood cells.

Cardiogenic shock occurs with the failure of the heart to act as a efficient pump. This failure may result from a clot from the lungs blocking a value or vessel, a rupture of a heart valve, blunt trauma to the heart itself, or even the presence of abnormal amounts of fluids in the pericardial sac which covers the heart. This type of shock is extremely difficult to treat.

Distributive shock results when the normal distribution of blood is directed away from the central circulation. This occurs when those vessels suppling the less oxygen sensitive tissues, such as the skin and limbs, dilate and allow pooling of blood in them. There is no hemorrhage of the blood outside the vessels, but the effect is the same on those critical tissues such as the heart and brain.

Of the three types of shock, hypovolemic shock is by far the most common. This is fortunate for us, since it is the easiest to treat. Because of the serious, even fatal, outcome of shock, time is critical in treating it. If your pet is involved in an accident it is important to have your family veterinarian examine it as quickly as possible, even in those cases in which bleeding is not obvious. The reason for this is that internal hemorrhage into the chest or abdominal cavities may be occurring without obvious outward signs until it becomes life-threatening.