What is shock and how does it affect critical veterinary patients?
Circulatory shock occurs when oxygen delivery to the tissues is compromised, and the circulatory system fails to deliver enough blood to the tissues to meet tissue oxygen demand.
Shock plays a key role in fatal critical illnesses because circulatory failure is part of the final common pathway of cardiopulmonary arrest. By recognising shock early and initiating appropriate treatment, veterinarians have the chance to improve outcomes for their critically ill patients. If they fail to recognise shock and treat it effectively, the consequences can be dire.
There are four categories of circulatory shock – hypovolemic shock, distributive shock, cardiogenic shock and obstructive shock. Hypovolemic shock is the most common in emergency veterinary patients. It often occurs secondary to hemorrhage, with fluid loss from the intravascular space. Even small losses of intravascular volume may result in hypovolemic shock.
“Almost every veterinary patient who dies of acute illness dies of, or with, shock.”Dr Claire Sharp BSc, BVMS, MS, DACVECC
What needs to be considered before a shock fluid therapy plan can be established?
As hypovolemic shock is caused by the loss of intravascular fluid, the goal of intravenous fluid therapy in dogs and cats is to increase the fluid volume in the intravascular space. Fluid replacement then increases preload, thereby increasing stroke volume and cardiac output.
When treating hypovolemic shock, the correct shock fluid administration rate for dogs and cats depends on the clinical signs of the patient. Typically, dogs and cats with moderate to severe shock will receive fluid boluses over 10–20 minutes, while perfusion parameters are monitored. The first line fluid choice is often a buffered isotonic crystalloid (lactated ringers’ solution or Hartmann’s). Repeat boluses and other therapies may be necessary if there is no response or other complicating factors.
In developing a complete fluid plan it is important to consider the patient’s existing fluid deficits (both intravascular and interstitial) as well as ongoing fluid losses that may be experienced. This includes normal fluid losses in urine and insensible losses through the respiratory tract (maintenance losses) plus abnormal losses, through the GI tract, or urinary tract. While the treatment of hypovolemic shock is a priority, the overall replacement of these fluid deficits is part of the planning.
Dr Claire Sharp
Why would you use fluids other than lactated Ringer’s solution (LRS) to treat shock?
Respected veterinary critical care specialist, Dr Claire Sharp recently shared her insights Veterinary critical care specialist, Dr Claire Sharp recently shared her insights on intravenous fluid therapy in dogs and cats in a recent Accelerated Emergency Program Webinar session. She noted that an isotonic buffered crystalloid solution, such as lactated Ringers, is the common default treatment fluid for hypovolemic shock and raised the question, when might a fluid other than lactated Ringer’s solution be a consideration?
Hypertonic saline is a good choice for the treatment of hypovolemic shock in traumatic brain injury since it will aid in expanding the intravascular volume while protecting the brain against cerebral oedema. The use of hypertonic saline, in combination with isotonic crystalloids, as an alternative to other products, such as artificial colloids and blood product, can also be an appropriate option in some cases. Nonetheless, patients with significant blood loss will benefit from blood product transfusion as part of their resuscitation.
Regardless of the choice of fluid for hypovolemic shock, there is an opportunity for life-saving intervention when shock is recognised early, and treated appropriately.
If you would like more insights from veterinary emergency professionals like Dr Sharp and want to broaden your critical care knowledge, contact us about the Accelerated Emergency Program today.