Dermatology    

    & Allergy

Recognition and Management of Shock

Melissa Garcia-Lacaze, DVM, DACVECC

There are several stages of shock seen classically in the dog; compensatory, early de-compensatory and late de-compensatory. Unfortunately in cats, we often do not see the compensatory stage, with many presenting in the de-compensatory stages. Cats have a different set of rules in regards to shock that we will address a bit later. Studies have shown that the treatment of shock relies heavily on fluid therapy and steroids have not shown to be of benefit in the treatment of shock and may in fact do more harm in the compromised patient.

Compensatory shock can be difficult to recognize, unless we are looking for it. When there is acute blood or fluid loss, the body tries its best to compensate and hide the outward appearance of illness. The fluid deficit is sensed by the aortic baroreceptors that respond to stretch. When they are not as stretched, because of decreased circulating volume, the body responds by increasing the circulating levels of catecholamines. Typically these animals are hyper-dynamic-with an increased heart rate, normal/increased blood pressure, snappy or bounding pulses and brick red mucous membranes. A lot of times, these patients are mis-labeled as stable because they "look" so good. However, these patients require immediate treatment. The body's compensatory responses take a lot of energy and they will not be able to maintain this hyper-dynamic state for long. Treatment should be aimed at replacing the volume of fluid that has been lost in order to decrease the body's stimulation for the compensatory response.

If shock is not identified in the compensatory phase, it progresses to the de-compensatory stages. As shock ensues, the body runs out of energy. The body is no longer able to maintain such a high heart rate and as a result, an adequate blood pressure can no longer be maintained. These patients are often pale, mentally dull and have poor pulses. At this stage, aggressive fluid therapy is still indicated in addition to oxygen and temperature support until these patients are more stable. Fluid resuscitation should happen immediately and quickly with a veterinarian standing by to re-assess response to fluids and therapy.

Despite our best effort, some patients will continue to progress into late de-compensatory shock. In many instances, patients are not presented to us until they are in late de-compensatory shock. Once this occurs, there is cell death and despite our efforts to improve blood flow and oxygen delivery, there may be too much damage at the cellular level. Aggressive therapy should still be instituted, but the prognosis is very guarded and recovery may be complicated. If an organ has been compromised enough due to poor blood flow and poor oxygen delivery, we may have to deal with the consequences of systemic inflammation or multiple organ dysfunction syndrome (MODS) in the days to come once the pet is stabilized.

The cat responds to shock much differently than the dog. They do not typically have a compensatory phase and often present with a triad of symptoms in regards to shock. Cats are often hypothermic, bradycardic and hypotensive. Conservative or small volume resuscitation is needed in these pets at the same time as aggressive re-warming. Hypothermic cats (less than 98 degrees C) do not have the ability to vasoconstrict and so it is important to correct hypothermia as quickly as possible to prevent fluid overload from aggressive fluid therapy. Blood pressure and heart rate should be reassessed frequently to monitor response to fluid therapy.

There are many fluids available to help replace fluid deficits in our veterinary patients. Most commonly, crystalloids are used as the first line treatment in shock. These fluids contain sodium primarily and in many instances a buffer. Although these fluids are good choices in shock, their effect is not long lived and 2/3 of the fluid administered will be out of the blood vessel within the first hour, redistributing primarily to the interstitial or SQ space. When prolonged intravenous volume support is needed, colloids should be considered. Hetastarch is the most commonly used synthetic colloid and requires 1/3 the volume to reach the same endpoint compared to crystalloid use alone. Colloids should be considered as a first line therapy in shock for small dogs or cats, when giving a large amount of fluid is not possible. If the patient is losing blood, then whole blood should be considered early on in the treatment of shock. Although a type and crossmatch is ideal, in an emergent situation, A-negative blood can be used and even bloused to help restore the circulating volume.

Although the most common type of shock is hypovolemic shock, it is not the only type. Maldistributive shock is often seen in patients with systemic inflammatory response (SIRS) or sepsis. In these scenarios, there is poor vascular tone and blood is often sequestered in the capillary beds, which in effect decreases the effective circulating volume. Thrombosis in the microvasculature also makes adequate blood flow difficult in these patients. In addition to fluid therapy, many of these patients often need vasopressor support.

Restrictive shock is a type of shock seen in patients with pneumothorax or severe pericardial effusion. In these situations, there is a lot of pressure surrounding the heart and the great vessels. As a result, there is poor cardiac filling and as a result, poor cardiac outflow. Treatment of restrictive shock involves fluids, but also relies upon relieving the source of pressure through a thoracocentesis or pericardial centesis.

Finally, cardiogenic shock is a serious form of shock affecting many patients with heart disease. In this instance, fluid therapy may cause more harm than good and treatment should be aimed at improving cardiac function with afterload reducers or pimobendan and oxygen until heart function improves.

When patients present in shock, it can certainly be overwhelming. Often with a good history and physical examination, the cause of shock can be identified and treated appropriately. Time is of the essence and so the sooner the patient can be stabilized, the more likely we are to see decreased organ damage and improved survival.

Jake is an AMAZING 16yo Beagle. He was initially seen at Gulf Coast in November 2010 for vomiting. At that time, bloodwork showed elevated liver values. An ultrasound was done to evaluate further and at that time, he was diagnosed with a liver tumor. This tumor was in a bad place, very close to a large blood vessel near the heart, and so surgery was not recommended. We decided that the best course of action would be to monitor the liver mass serially with ultrasound.

We did not see Jake back until January of 2011 at which time he had recently been diagnosed with atypical Cushing's disease. This is an endocrine condition where the adrenal glands make too much steroid. He was being treated with medications and had been responding well. This recheck ultrasound showed that there was no change in the liver mass and so we were all thankful to see him doing so well.

In May 2011, Jake presented for another recheck ultrasound. His liver mass had become a little bit larger, but nothing that indicated a change in our current treatment plan. However, Mom noted that he was coughing more. Chest x-rays showed some inflammation around the airways and an ultrasound of Jake's heart showed increased pressures in the lungs called pulmonary hypertension. Pulmonary hypertension can be very serious and cause pets to have decreased activity levels in addition to coughing or being exercise intolerant. He was started on Viagra to treat the pulmonary hypertension and seemed to be on the fast track to feeling better.

In July 2011 we saw Jake for a serious and life threatening emergency. He was admitted to the emergency clinic for acting lethargic. They were able to diagnose a significant anemia (low red blood cell count) in addition to fluid in the abdomen. Unfortunately, further evaluation revealed that the fluid in his abdomen was blood. The tumor that had been slowly growing in the liver had ruptured a blood vessel and was now bleeding. After he was stabilized, he was taken immediately to surgery. The liver mass was wrapped around the caudal vena cava (the vessel that brings blood to the heart), but with gentle dissection, the surgeons were able to remove the majority of the mass and stop the bleeding. He also had the urinary bladder masses removed. Jake did remarkably well post operatively and was sent home shortly after his surgery. The liver mass returned as hepatocellular carcinoma, which is a slow growing tumor of the liver. However the urinary bladder mass was more concerning. It returned as a transitional cell carcinoma which is typically an aggressive tumor of the urinary system. In most patients with this tumor, the median survival time is about 6 months once diagnosed. However, in Jake's case, we were hoping for a better survival time because of the location of the tumor and the fact that it was caught and removed early, before it could affect the other structures of the urinary system.

Jake continued to do well and was enjoying life until recently when we saw him on emergency for vomiting, diarrhea and acting uncoordinated. He was seen by the Urgent Care service and we were concerned about a neurological condition affecting his balance. This type of condition, vestibular disease, can be caused by a peripheral middle ear infection or a primary brain mass. Unfortunately, Jake's ears looked good and so because of that, in addition to the type of neurological signs we were seeing, we strongly suspected a right brain stem lesion. We opted to treat him symptomatically for his condition and focus on giving him a great quality of life for as long as possible. True to Jake's previous stays, he rallied and recovered much sooner than any of us anticipated.   We even celebrated his 16th birthday in ICU-complete with cupcakes and candles and even a memorable rendition of "Happy Birthday" from the ICU nurses and doctors who have come to know and love Jake so much.

Jake still visits us from time to time as he does have some hiccups in his health ranging from not eating well to diarrhea and ongoing tremors. However, overall, he is thrilled with life and thrilled to be hanging out with his Mom and Dad who do an AMAZING job taking care of Jake! We love Jake so much here at Gulf Coast and are excited to have him be our patient of the month for the New Year!

1111 W. Loop South, Suite 140  Houston, TX 77027

713-693-1144   fax- 713-693-1145

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