Shock

When things go wrong

If cells are deprived of oxygen, instead of using aerobic (with oxygen) metabolism to function, the cells use the anaerobic (without oxygen) pathway to produce energy. Unfortunately, lactic acid is formed as a by-product of anaerobic metabolism.

This acid changes the acid-base balance in the blood, making it more acidic, and can lead to a situation in which cells begin to leak toxic chemicals into the bloodstream, causing blood vessel walls to become damaged. The anaerobic process ultimately leads to the death of the cell. If enough cells die, organs start to fail, and the body starts to fail and, eventually, death occurs.

Think of the cardiovascular system of the body as similar to the oil pump in your car. For efficient functioning, the electrical pump needs to work to pump the oil, there needs to be enough oil, and the oil lines need to be intact. If any of these components fail, oil pressure falls and the engine may be damaged. In the body, if the heart, blood vessels, or bloodstream (circulation) fail, then eventually, death occurs.

Where things go wrong

The oxygen delivery system to the body's cells can fail in a variety of ways.

• The amount of oxygen in the air that is inhaled can be decreased.
• Examples include breathing at high altitude or carbon monoxide poisoning.

The lung may be injured and not be able to transfer oxygen to the blood stream. Examples of causes include:

• pneumonia (an infection of the lung),
• congestive heart failure (the lung fills with fluid or pulmonary edema), or
• trauma with collapse or bruising of the lung, or
• pulmonary embolism.

The heart may not be able to adequately pump the blood to the tissues of the body. Examples of these causes examples include:

• Heart attack in which  muscle tissue is lost and the heart cannot beat as strong and pump blood throughout the body.
• A rhythm disturbance of the heart occurs when the heart can't beat in a coordinated way.
• Inflammation of the sac around the heart (pericarditis) or inflammation of the heart muscle due to infections or other causes, in which the effective beating capabilities of the heart are lost.

There may not be enough red blood cells in the blood. If there aren't enough red blood cells (anemia), then not enough oxygen can be delivered to the tissues with each heart beat. Examples of causes may include:

• acute or chronic bleeding,
• inability of the bone marrow to make red blood cells, or
• the increased destruction of red blood cells by the body (an example, sickle cell disease).

There may not be enough other fluids in the blood vessels. The blood stream contains the blood cells (red, white, and platelets), plasma (which is more than 90% water), and many important proteins and chemicals. Loss of body water or dehydration can cause shock.

The blood vessels may not be able to maintain enough pressure within their walls to allow blood to be pumped to the rest of the body. Normally, blood vessel walls have tension on them to allow blood to be pumped against gravity to areas above the level of the heart.

This tension is under the control of the unconscious central nervous system, balanced between the action of two chemicals, adrenaline (epinephrine) and acetylcholine. If the adrenaline system fails, then the blood vessel walls dilate and blood pools in the parts of the body closest to the ground (lower extremities), and may have a difficult time returning to heart to be pumped around the body.

Since one of the steps in the cascade of events causing shock is damage to blood vessel walls, this loss of integrity can cause blood vessels to leak fluid, leading to dehydration which initiates a vicious circle of worsening shock.

Septic shock results from bacteria multiplying in the blood and releasing toxins. Common causes of this are pneumonia, urinary tract infections, skin infections (cellulitis), intra-abdominal infections (such as a ruptured appendix), and meningitis.

Anaphylactic shock is a type of severe hypersensitivity or allergic reaction. Causes include allergy to insect stings, medicines, or foods (nuts, berries, seafood), etc.

Cardiogenic shock happens when the heart is damaged and unable to supply sufficient blood to the body. This can be the end result of a heart attack or congestive heart failure.

Hypovolemic shock is caused by severe blood and fluid loss, such as from traumatic bodily injury, which makes the heart unable to pump enough blood to the body, or severe anemia where there is not enough blood to carry oxygen through the body.

Neurogenic shock is caused by spinal cord injury, usually as a result of a traumatic accident or injury.

Hypovolemic Shock

• There needs to be enough red blood cells and water in the blood for the heart to push the fluids around within the blood vessels. When the body becomes dehydrated, there may be enough red blood cells, but the total volume of fluid is decreased, and pressure within the system decreases.
• Cardiac output is the amount of blood that the heart can pump out in one minute. It is calculated as the stroke volume (how much blood each heart beat can push out) multiplied by the heart rate (how fast the heart beats each minute). If there is less blood in the system to be pumped, the heart speeds up to try to keep its output steady.
• Water makes up 90% of blood. If the body becomes dehydrated because water is lost or fluid intake is inadequate, the body tries to maintain cardiac output by making the heart beat faster. But as the fluid losses mount, the body's compensation mechanisms fail, and shock may ensue.
• Hypovolemic (hypo=low + volemic=volume) shock due to water loss can be the endpoint of many illnesses, but the common element is the lack of fluid within the body.
• Gastroenteritis can cause significant water loss from vomiting and diarrhea, and is a common cause of death in third world countries. Heat exhaustion and heat stroke is caused by excessive water loss through sweating as the body tries to cool itself.
• Patients with infections can lose significant amounts of water from sweating. People with diabetes who have diabetic ketoacidosis lose significant water because of because of elevated blood sugar that cause excess water to be excreted in the urine.
• Ultimately in hypovolemic shock, the patient cannot replace the amount of fluid that was lost by drinking enough water, and the body is unable to maintain blood pressure and cardiac output. In all shock states, when cells start to malfunction waste products build up, a downward spiral of cell death begins, increased acidosis occurs, and a worsening body environment leads to further cell death - and ultimately organ failure.

Hemorrhagic Shock

A subset of hypovolemic shock occurs when there is significant bleeding that occurs relatively quickly. Trauma is the most common example of bleeding or hemorrhage, but bleeding can occur from medical conditions such as:

• Bleeding from the gastrointestinal tract is common; examples include stomach or duodenal ulcers, colon cancers or diverticulitis.
• In women, excessive bleeding can occur from the uterus.
• People with cancers or leukemia have the potential to bleed spontaneously from a variety of sources if their liver does not make enough clotting factors.
• Patients who are taking blood thinners (anticoagulant medications) can bleed excessively as well.
• Blood loss has two effects on the body. First, there is a loss of volume within blood vessels to be pumped (see hypovolemic shock) and second, a reduced oxygen carrying capacity occurs because of the loss of red blood cells. Otherwise healthy people can lose up to 20% of their blood volume (about twice the amount that a person donates at a blood drive) without becoming symptomatic with weakness, lightheadedness, low blood pressure or shortness of breath.
• The treatment of hemorrhagic shock depends on the cause. Finding and controlling the source of bleeding is of paramount importance. Intravenous fluids are used to help with resuscitation to increase the fluid volume within the blood vessel space, but blood transfusion is not always mandatory. If the bleeding is controlled and the patient becomes more stable, the bone marrow may be able to replenish the red blood cells that were lost.
• If the red blood cell count in the blood decreases gradually over time, either because of bleeding or the inability of the body to make enough new red cells, the body can adjust to the lower levels to maintain adequate cell perfusion, but the individual's exercise tolerance may decrease. This means that they may do well in normal daily activities but find that routine exercise or household activities bring on weakness or shortness of breath. The treatment depends on the underlying diagnosis, since it isn't a total fluid problem as in hypovolemic shock.

Cardiogenic Shock

• When the heart loses its ability to pump blood to the rest of the body, blood pressure decreases. Although there may be enough red blood cells and oxygen, they can't get to the cells that need them.
• The heart is a muscle itself and needs blood supply to work. When a heart attack occurs, the blood supply to part of the heart is lost, and that can stun and irritate the heart muscle so that it isn't able to beat with an appropriate squeeze to push blood out to the rest of the body. This decreases stroke volume, and cardiac output falls.
  • Treatment includes trying to restore blood supply and the use of medications to support blood pressure. In more dire circumstances, machines can be used to assist the heart to support blood pressure.

Neurogenic Shock

• There are involuntary muscles within blood vessel walls that maintain the squeeze so that the volume within the vessel walls constant even if the body changes position against gravity.
  • An example is when you get up out of bed in the morning. If your blood vessels didn't squeeze a little tighter, gravity would make the blood flow to your feet, the lowest part of your body, away from your brain, and you might pass out. The squeeze is maintained by signals from nerves in the sympathetic trunk, a long bundle of fibers running from the skull to the tailbone alongside the vertebral column.
• In brain or spinal injury, the sympathetic trunk stops working and blood vessels dilate and result in blood pooling away from the heart. Since there isn't enough blood returning to the heart, the heart has a hard time pumping blood through the body.
• Treatment includes fluids and medications to increase the tone in the blood vessel walls.

Hypoglycemic Shock and Hyperglycemia

• High or low blood sugars are almost always associated with diabetes. In people with diabetes, the body does not make enough insulin to permit glucose to enter the cells for aerobic metabolism, or the cells are resistant to the effects of insulin. As treatment, insulin needs to be injected, or medication needs to be taken to boost the body's lower insulin sensitivity. There must be a balance between how much medication is taken and how much food is eaten.
• If not enough food is ingested, then the blood sugar drops (hypoglycemia) and no glucose is available to enter the cells, even if there is enough insulin to permit glucose to enter the cells. The brain is very susceptible to low blood sugars, and coma has a very quick onset.
  • Treatment is providing sugar. If the person is awake enough to swallow, a sugar solution by mouth is used, otherwise, intravenous fluids containing glucose are provided. If the lack of sugar was of short duration, the person will awaken almost immediately after treatment. If blood sugars remain low for prolonged periods of time, the brain's ability to recover is potentially lost.
• When blood sugar levels spiral high out of control, there is risk of significant dehydration and shock. If there is not enough insulin in the blood stream, cells cannot use the glucose that is present, and instead turn to an alternative anaerobic metabolism to generate energy. Since glucose can't enter cells to be used, hyperglycemia (hyper= high + gly=sugar = emia) occurs as the glucose level builds up in the blood stream.
• The kidneys try to excrete excess sugar, but because of chemical concentration gradients between blood and urine, significant amounts of water also are lost. The body quickly becomes dehydrated and blood pressure drops, decreasing blood flow to cells. Cells which are now lacking glucose inside them are now starved of oxygen and turn to anaerobic metabolism, causing acid waste product build up.
• Excess acid in the body changes the metabolism for all organs, making it more difficult for oxygen to be used. Conditions will continue worsen until insulin and significant fluids are given to the patient.

When the body develops an allergic reaction to some outside chemical or substance, it can activate its immune system to combat that substance. On occasion, there can be an excess response and multiple organ systems in the body can be affected and fail. This is known as anaphylaxis. Mast cells and basophils (a type of white blood cell) that contain histamine become unstable and leak their contents to affect the muscles of the lung, heart and blood vessels. These are smooth muscles that are part of the regulatory system of the body and are not under conscious control.

• The muscles that surround bronchial tubes go into spasm and cause wheezing and shortness of breath.
• The muscles that surround blood vessels dilate, causing blood pressure to drop.
• The histamine also causes flushing of the skin, urticaria (hives), vomiting and diarrhea.
• A variety of mechanisms cause the heart muscle to pump weakly and blood vessels to leak fluid.
• The combination of these effects decrease blood flow and oxygen supply to cells in the body and can result in shock.
• The most common causes of anaphylactic shock include allergic reactions to foods (especially peanuts), antibiotics, and bee and wasp stings. Children are often allergic to eggs, soy, and milk.
• These allergens can cause the immune system to turn on the potential cascade to shock. Many patients have allergic reactions that are less severe and can just involve hives, but others can develop shortness of breath, wheezing, swelling of the tongue and mouth, and difficulty swallowing.
• Initial treatment for major allergic reactions include calling 911 and activating the emergency response system. Medical interventions include injections of antihistamine like diphenhydramine (Benadryl), corticosteroids and adrenaline (epinephrine).
• Patients with major allergic reactions must try to avoid the chemical trigger. They also often carry an Epipen (epinephrine injection kit) to inject themselves with epinephrine should an allergic reaction occur.

Shock is defined as abnormal metabolism at the cellular level. Since it is not easy to directly measure cellular problems, the symptoms of shock are indirect measurements of cellular function. Shock is the end stage of all diseases, and symptoms will often be dependent on the underlying cause.

Vital signs

• As the patient goes through the various stages of shock, vital signs change. In the early stages, the body tries to compensate by moving fluids around from within cells to the blood stream with an attempt to maintain blood pressure in a normal range. However, there may be a slight rise in the heart rate (tachycardia = tachy or fast + cardia or heart).
• For example, donating blood. A unit of blood (or about 10% of the blood volume) is removed, yet the body compensates well, except for a little lightheadedness, which is often resolved by drinking fluids. Another example is exercising and forgetting to drink enough fluids and feeling a little tired at the end of the day.
• As the body loses the ability to compensate, the breathing rate gets faster and the tachycardia increases as the body tries to pack as much oxygen onto the remaining red blood cells as possible and deliver them to the cells. Unfortunately, blood pressure starts to drop (hypotension=hypo or low + tension= pressure) as compensation mechanisms fail.

Body function

Cells don't receive enough oxygen and the organs that they comprise begin to fail. All organs may be affected.

• As the brain is affected, the patient may become confused or lose consciousness (coma).
• There may be chest pain as the heart itself doesn't get an adequate oxygen supply.
• Diarrhea may occur as the large intestine becomes irritated due to hypotension.
• Kidneys may fail and the body may stop producing urine.
• The skin becomes clammy and pale.

The approach to the patient in shock requires that treatment occur at the same time as the diagnosis occurs. The source of the underlying disease needs to be found. Sometimes it is obvious, for example, a trauma victim bleeding from a wound. Other times, the diagnosis is elusive. The type of tests will depend upon the underlying condition.

The diagnosis is most often found through the medical history. A thorough physical examination will be undertaken and the patients vital signs monitored.

• Patient vital signs monitored might include continual blood pressure and heart rate monitoring, and oxygen measurement. Special catheters may be inserted into the large veins in the neck, chest, arm, or groin and threaded near the heart or into the pulmonary artery, to measure pressures close to the heart, which may be a better indicator of the body's fluid status. Other catheters may be inserted into arteries (arterial lines) to measure blood pressures more directly. Tubes may be placed in the bladder (Foley catheter) to measure urine output.
• Blood laboratory tests will be performed (the type dependent on the underlying disease or condition).
• Radiologic tests may be performed dependent on the underlying illness.

If you come upon a person in shock, the initial response should be to call 911 and activate the emergency response system. Self-care at home is not appropriate.

Lay the person down in a safe place and try to keep them warm and comfortable.

If the patient is not awake, is not breathing, and has no heartbeat, it is appropriate to start chest compressions following the American Heart Association guidelines. It is important to send someone to get an AED if one is available.

• EMS personnel are well trained in the initial assessment of the patient in shock. The first course of action is to make certain that the ABCs have been assessed. The so-called ABCs are:

• Airway: assessment of whether the patient is awake enough to try to take their own breaths and/or if there is there anything blocking the mouth or nose.
• Breathing: assessment of the adequacy of breathing and whether it may need to be assisted with mouth-to-mouth resuscitation or more aggressive interventions like a bag and mask or intubation with an endotracheal tube and a ventilator.
• Circulation: assessment of the adequacy of the blood pressure and determination of whether intravenous lines are needed for delivery of fluid or medications to support the blood pressure.

• If there is bleeding that is obvious, attempts to control it with direct pressure will be attempted.
• A fingerstick blood sugar will be checked to make certain that hypoglycemia (low blood sugar) does not exist.
• In the emergency department, diagnosis and treatment will occur at the same time.
• Patients will be treated with oxygen supplementation through nasal cannula, a face mask, or endotracheal intubation. The method and amount of oxygen will be titrated to make certain enough oxygen is available for the body to use. Again, the goal will be to pack each hemoglobin molecule with oxygen.
• Blood may be transfused if bleeding (hemorrhage) is the cause of the shock state. If bleeding is not the case, intravenous fluids will be given to bolster the volume of fluids within the blood vessels.
• Intravenous drugs can be used to try to maintain blood pressure (vasopressors). They work by stimulating the heart to beat stronger and by squeezing blood vessels to increase the flow within them.

• Patients in shock are critically ill and will be admitted to an intensive care unit. Depending on the underlying condition, a variety of specialists will be involved with their care. Nurses with advanced training, respiratory therapists, and pharmacists will be added to the team of doctors assigned to one patient.
• When the body is in a stressed state, it becomes more susceptible to infection. When a patient has tubes in in the body for prolonged periods, they are at risk to higher infection. While in the hospital, the staff will be vigilant in trying to prevent nosocomial (hospital-borne) infections.
• Extended nursing care is often needed if one survives shock. Rehabilitation may take a prolonged period of time as different organs recover their function. The amount of time the body was in a shock state often determines the extent of organ damage, and full recovery may never be complete. Brain injury can lead to stroke and thought impairment. Heart and lung damage can lead to significant disabilities that may include reduced exercise tolerance. Kidney damage can lead to the need for dialysis.

Shock is a culmination of multiple organ systems in the body that have failed or are in the process of failing. Even with the best of care, there is a significant risk of death. The mortality rate for shock depends upon the type and reason for the shock, and the age and underling health condition of the patient.