Hypovolemic shock develops when there is inadequate circulating blood volume to deliver oxygen effectively to the tissues. Hypovolemic shock results from either blood loss or progressive interstitial dehydration leading to intravascular depletion.
Successful treatment is aimed at restoring deficits and correcting the initial cause of the loss. Hypovolemic shock is considered the most common type of shock detected in animals. Estimates for the volumes of blood loss that may be tolerated vary depending on the patient. Certainly, a young healthy dog will tolerate blood loss significantly better than an older pet. Healthy dogs may tolerate up to a 40% loss of blood volume, or approximately 35–40 ml/kg.
The treatment approach to hypovolemic shock requires several steps:
Hypotensive resuscitation is a specific form of therapy for hypovolemic shock from hemorrhage. The goal of this therapy is to maintain blood pressure in a range that is adequate for perfusion to vital organs but not so high as to ‘blow off’ developing clots. In people, this form of therapy is linked with operative control of hemorrhage, so this may not be directly applicable to dogs and cats. However, it may be prudent to carefully titrate fluid therapy and patient manipulations to avoid disrupting any forming clot. Coagulopathy may develop by dilution of clotting factors with crystalloids and colloids, particularly in the face of ongoing hemorrhage.
Hypovolemic shock is very rewarding to treat. It is essential to continually reassess the patient to ensure adequate volume status. Animals that have significant ongoing losses, such as severe vomiting, diarrhea, PU/PD, or hemorrhage are particularly challenging.
Two specific scenarios may be used to highlight the therapeutic approach in hypovolemia.