Understanding Bleeding

It’s just plumbing.

Understanding Bleeding
By: Andrew Dennis

Understanding bleeding is one of the most challenging things to teach. There is so much instinctive emotion associated with bleeding that separating the objective nature of the injury from the emotional reaction is difficult to do.

As much as medicine has advanced over the centuries, one of the most elusive solutions continues to be bleeding control in both the field and in the hospital. Advances have been slow in coming and limited at best. In the end, the principles of bleeding are similar and related to the laws of physics and cannot be changed. We must work with them in order to come up with solutions.

Bleeding is all about 1) plumbing and the principles of fluids and flow; and 2) the physiology of blood and clotting. 

Think Pipes and Plumbing

Blood in the human body is moved around by a series of pipes. There are feeds (inflow) and returns (outflow). Inflow is maintained by arteries and outflow is achieved by veins.  The ultimate reason this complex series of pipes exists is to provide blood, rich in oxygen, via the inflow, to the cells in your body that need it. Second, the outflow exists in order to remove the oxygen depleted and carbon dioxide-rich blood from those same areas. It is that simple. 

In the pipe system, there are large main pipes, such as the aorta for inflow and the vena cava for outflow. Both connect directly to the heart, which is the circulating pump. The aorta and vena cava break off into moderate size vessels and eventually small ones similar to a tree’s branches. The main arteries and veins frequently run together but when they branch into smaller networks, they take separate paths, again, mimicking a tree with small terminal branches and leaves. 

In the end, it is a loop. Blood arrives via the arteries and leaves via the veins. Typically, if the pipe or vessel has a name, it is significant in both importance and in size. 

Pipes Are Protected

The human body was designed with a remarkable resilience and with some amazing protective mechanisms. It is no accident of nature that all your important pipes of any significant size run deep in the core, along the bony skeleton and are thus protected. The bigger the pipe, the deeper and more protected it is. 

Take, for example, your aorta and vena cava. These are the largest blood vessels in the body. They run together in the deepest most protected part of your core. They run along the front of your spine so they are protected from the back by the bones of your spine. In the front, they are exposed but still reside deep in the torso with layers of fat, muscle, intestine, bone and lung providing shielding. In the end, it is very difficult to get to any of those pipes.

When it comes to the extremities such as your arms and legs, again, these pipes are protected by fat and muscle on the exposed sides and by the bones on the backsides.  There is one significant piping exception. In the upper arms and thighs, we have only one moderately large pipe from the torso to the elbow and knee. In the arm, this is the brachial artery, and in the leg this is the superficial femoral artery. 

Although there are some early branches that feed the upper arms and legs, for the most part, this exposed segment of the piping highway is devoid of branches and is the only road in for the lower arm and leg. 

Once we get to the elbow and knee, these moderately large pipes divide into three separate tubes, so if one is taken out, the others will compensate and the limb will not be lost. It is only in the thigh and upper arm that one single pipe exists and hence this is the vulnerable area as it relates to limb survival, should it be injured. Even the head has four pipes in and four pipes out, so if one set is injured, the others will be able to compensate. 

High and Low Pressure

The other important blood flow concept is that blood pressure varies by blood vessel. Arteries are high pressure pipes. They are designed with a thick wall to contain the pressure of the blood flowing through them. Your body uses the muscles within the walls of the arteries to contract and expand in order to adjust pressure throughout the system as necessary. The veins, on the other hand, are a very low-pressure system since they are only transporting the returning blood which is now far down system and far away from the pump (the heart). 

The inflow is a high-pressure system and the outflow is a low-pressure system. That translates to the fact that pressure to shut down any given pipe depends on what type of pipe it is. If you are trying to shut down or even decrease flow to an inflow pipe such as an artery, you need to apply significantly more external pressure than if you were trying to shut down or slow flow to an outflow pipe such as a vein. 

For example, if you lacerated a superficial vein on the top of your hand, it may appear to bleed significantly, especially if it is a big vein; however, a small amount of pressure over the vein will stop blood flow completely. 

Broken Pipes

Aside from the principles of blood and clotting, there are other simultaneous safety mechanisms that come into play. One such example is spasm of the vessels. When a pipe is injured, specifically an inflow pipe such as an artery, the muscle fibers within the wall of the pipe contract and shrink the tube’s diameter significantly. This dramatically slows the flow of the blood moving through it, allowing the protective mechanisms of the blood itself to work, i.e., the blood clots. 

Certain triggers cause blood to clot. In this case, a decrease in the speed of movement, i.e., a decrease in flow and also a disruption in the evenness of flow. When the inner layers of the blood vessels are injured, they release chemicals that direct blood to clot.  So, when an injury to a pipe exists, your body shrinks the pipe to slow the flow and the vessel releases chemical triggers that initiate a clot to form.

When clot forms, bleeding stops and the life is potentially saved. This too is where pressure comes in. Keeping the principles of blood clotting in mind, when external pressure is applied on a bleeding injury, the pipe is being collapsed, thus slowing the flow and allowing for a clot to form so bleeding will stop. Again, we are simply working with the body’s protective mechanisms.

How Much Blood Loss?

Your body has about 5 liters of blood. Of those 5 liters, how much can you lose and still survive? The answer is not exact, especially since estimating the amount of loss is very difficult.

To put blood loss in perspective, when you donate blood you typically give up about a half a liter of blood. For some, this is significant and can make them dizzy, while for most others this will be unnoticeable. In the end, any blood loss is not a good thing, but certainly there are tolerable limits. 

The American College of Surgeons offers guidance on this by breaking blood loss into four categories. Class 1 is a loss of less than 15 percent of the blood volume. Typically few people feel the effects and this would be similar to donating blood. 

Class 2 is a loss of 15-30 percent of blood. Here most people will show some of the protective mechanisms kicking in. We typically see an elevation in heart rate, maybe some loss of skin color, as they may look a little pale. Some may demonstrate dizziness, especially if they are standing up where the heart must work harder to overcome gravity to pump blood to the brain. Typically, however, in class 2 blood loss, the blood pressure is maintained. 

When we reach Class 3 hemorrhage, we have lost greater than 30 percent of our blood volume, and our protective mechanisms of compensation such as heart rate and lying down, are barely able to keep up. We begin to see drops in blood pressure. This frequently results in some deprivation of oxygen to the brain and thus some confusion may occur. 

Again, here we see the body attempt to protect itself. As the blood pressure falls, the flow through the bleeding vessel is hopefully decreased, thus enhancing the chance for a blood clot to take form. The temporary treatment for this is to have the individual lie down, keep him/her as warm as possible, raise the feet, and begin replacement of the blood loss with fluid and human blood products as soon as possible. 

With Class 4 hemorrhage, we have lost greater than 40 percent of our blood volume and we have exceeded our body’s ability to compensate. Emergent aggressive intervention with blood, fluids and surgery are typically required.

Survival on the Street

With these percentages in mind and how they relate to survival, how do we translate this to actual practice for the officer on the street? Here is where the disconnect occurs. How can you estimate a 15 percent blood loss from a 30 percent blood loss? In times of stress, don’t attempt to evaluate the victim’s heart rate. This will ultimately have little value, especially without a baseline reference point.

The answer is two-fold. First, the goal is not to allow such blood loss in the first place.  So prevention and early intervention is key. Second, if we arrive late and blood loss has already occurred, this is where simple treatment methods become universal. The universal answer is to apply a countermeasure to stop bleeding and to divert as much blood from other parts of the body to the heart and brain. 

Of equal importance is the need to preserve body warmth. A loss in temperature prevents blood from clotting, thus causing one to bleed faster and more extensively. All of this can be accomplished by lying the individual down, calming him/her, raising the legs, and covering him/her with a blanket or coat. 

Blood Loss Intervention

Recognizing ongoing blood loss and choosing the correct intervention is difficult to teach for two reasons. First, the sheer emotion to all involved with bleeding. Second, the lack of reference as to what is severe bleeding and what is not. 

Certainly, we must teach to the most universal solution as everyone’s points of reference and levels of experience differ. However, I am a big proponent of teaching, not so much the details in the technique, but in teaching to the final intended result. It is not always the “means” to the end that matters so much, as it is the “end” result itself. 

In the case of bleeding, I would rather everyone be able to achieve complete cessation of bleeding and not worry so much as to how you got there. So, in an effort to do just that, it is important to understand just a little anatomy and the associated principles of bleeding so that one’s decisions can be best maximized. 

Ask yourself this question when looking at a bleeding wound. Is it compressible, that is, will local direct pressure work? This is certainly the case with extremity injuries, injuries to the head and scalp, and some neck injuries. All soft tissue injuries, even in the torso should be amendable to external pressure.

It is injuries to the trunk and core that we must recognize our limitations. Because these large pipes run deep in the core, essentially within cavities that can accommodate large amounts of blood without showing signs to the exterior, we must have respect and be able to recognize them. 

There is little we can do in the field for such injuries other than simple countermeasures for shock, i.e., raising the legs, lying down, and keeping warm. The next most important thing that one can do is to get the person to definitive care as quickly as possible. 

Two Pressure Levels

Unlike deep penetrating and blunt torso injuries, extremity injuries and soft-tissue injuries should be able to be managed in the field to a definitive end—the cessation of active bleeding. All such injuries will subscribe to the concepts of pressure, recognizing that there are extremes of pressure. Keeping in mind what you are trying to achieve, it is critical to choose the method that suits the moment and the injury. 

A dynamic tactical moment where fighting is still occurring or the area of operation is hostile may dictate different countermeasures than a safe covered area. Tactics should come first as good tactics are the best medicine. 

Remember the two different levels of pressure. Depending on the injury, the type of pressure is the next step in solving the bleeding problem. If we base our response on what is most common, then we should recognize direct injury to a large artery is possible, but due to its protected positioning, it is infrequent. 

More common is the injury of smaller arteries and veins within muscles and soft tissues. These can appear to be significant, and certainly can be, but because they are more often than not, very amendable to compression, the use of some form of moderate pressure will often suffice. 

In most cases, this pressure can be accomplished by a wide circumferential pressure dressing or by simple firm, direct pressure. If there is significant tissue loss and a large cavity, then filling the space with gauze or some other material will allow the superficial pressure from the wound surface to be directed downward into the depths of the wound, thus achieving the necessary result. This is known as wound packing.   

Tourniquet Use

There will be occasion where moderate pressure either circumferential or direct is not enough to stop bleeding. This should signal a deeper, more significant injury to a larger pipe. Although not very common, these injuries do exist and we should all be prepared to address them. This is where a circumferential pressure dressing with a pressure bar can be of great assistance. This allows one to convert moderate pressure to greater extremes partially or totally shutting off inflow from the deep pipe/artery and thus allowing a clot to set up. 

If, however, this is still insufficient, then the next step would be a tourniquet. The definition of tourniquet is a device intended to “stop” blood flow both in and out.  Recognize even moderate pressure will stop outflow but preserve inflow. A tourniquet is essentially a shut-off valve placed above the point of injury, but close to it. It will completely shut down flow to the limb from the point it is placed. 

This extreme measure is very useful where limb loss has already occurred and there exists an open-ended vessel or where there is clear bright red, fountain-like high-pressure bleeding occurring in large volumes, such as one could anticipate liters of blood loss in a short period of time.

Keep in mind, the placement of a tourniquet is extremely painful. It hurts terribly at the place it is applied simply by compressing the skin and tissues beneath it. It also causes extreme pain downstream from where it has shut off the blood flow as tissues deprived of oxygen are very painful. 

Typically, application of a tourniquet frequently demands medication to modify the significant associated pain. If it does not hurt to an extreme, then it is likely not applied tight enough. If that is the case and bleeding has been stopped, one should consider re-evaluating the actual need for a tourniquet.

It is important to understand that tourniquets have saved thousands of lives in the military. However, the injury patterns associated with such saves are frequently limb loss or limb destruction in the field and the extreme has been reached. Also, even the applications in the military are frequently applied too loose or the device was not needed. 

So my advice to all who carry tourniquets, and I think we should all have them, is to be able to articulate in clear and certain terms the reasons behind its uses should you ever choose to apply it in the street. 

Hemostatic Agents

What about hemostatic agents? This is a commonly asked question and in my mind, the answer is relatively straightforward and simple. In the end, if a hemostatic agent is applied and it required nothing else, then the bleeding was quite insignificant and probably did not warrant even the application of the product. 

However, when it comes to these products, they must be thought of as adjuncts to the means to the end. No hemostatic agent alone can stop significant bleeding. All must be coupled with pressure and the principles of flow and blood clotting. When applied in conjunction to pressure, then the product can certainly accelerate clotting and thus slow and stop bleeding. Such agents work great as the material used to pack deep wounds and when combined with surface pressure, the results are commonly favorable.

In the end, bleeding is just plumbing. It subscribes to the same rules of physics as any fluid flowing through pipes with the added benefit of blood’s ability to clot. If one understands the associated principles and that all the techniques from pressure to tourniquets are simply variations of pressure intended to achieve the same end, then one’s decisions can be best fortified so as to achieve the desired outcome.

Dr. Andrew Dennis is a trauma & burn surgeon at the Cook County Trauma & Burn Unit in Chicago. He is a police officer and Director of Medical Operations for the Cook County Sheriff’s Office and the Northern Illinois Police Alarm System. Dr. Dennis is the CEO of Leomedicus and the developer of the Medical Tactics for Law Enforcement program. He is the author of the recently published and acclaimed book Officer Down, a Practical Tactical Guide to Surviving Injury in the Street. He can be reached at adennis@medicaltactics.com or www.medicaltactics.com.

Published in Tactical Response, Jul/Aug 2013

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