Shock is defined as a condition in which the body’s tissues do not receive enough oxygen and nutrients to allow cells to function.
Ultimately, this leads to cell death, progresses to organ failure, and eventually, if left untreated, death occurs.
Cells need two things to function: oxygen and glucose. These elements allow cells to generate energy and do their specific jobs.
Oxygen in the air enters the body through the lungs. The oxygen molecules cross from the alveoli of the lungs into the smallest blood vessels, the capillaries, and are taken up by the red blood cells and attached to the hemoglobin molecules .
Red blood cells are pushed through the body by the activity of the heart which pumps and delivers oxygen to the cells to all tissues in the body.
Hemoglobin then picks up carbon dioxide, the waste product of metabolism, which is then carried back into the lungs and exhaled into the air. The whole cycle begins again.
Glucose is made in the body from the food we eat. This glucose travels in the bloodstream and uses an insulin molecule to “open the door,” where it then enters the cell to provide energy for cellular metabolism.
If cells are deprived of oxygen, instead of using aerobic (with oxygen) metabolism to function, cells use the anaerobic (without oxygen) pathway to produce the energy the body requires.
Unfortunately, lactic acid is formed as a by-product of anaerobic metabolism. This lactic acid changes the acid-base balance in the blood, making it more acidic and can lead to a situation where cells begin to leak toxic chemicals into the bloodstream, damaging the walls of the blood vessels.
The anaerobic process ultimately leads to cell death. If enough cells die, the organs begin to fail and eventually death occurs.
The oxygen supply system to the body’s cells can fail in several ways:
The amount of oxygen in the air that is inhaled can be decreased
- Examples include breathing at a high altitude or carbon monoxide poisoning.
- The lung may be injured and unable to transfer oxygen into the bloodstream. Examples of this cause include: pneumonia (an infection of the lung), congestive heart failure (the lung fills with fluid or pulmonary edema), trauma with collapse, bruising to the lung, and pulmonary embolism.
The heart cannot adequately pump blood to the tissues of the body.
Examples of these causes include:
- A heart attack in which muscle tissue is lost and the heart cannot beat as hard and pump blood throughout the body.
- A heart rhythm disturbance occurs when the heart cannot beat in a coordinated manner.
- Inflammation of the sac around the heart also called pericarditis .
- Inflammation of the heart muscle due to infections or other causes, in which the effective beating abilities of the heart are lost.
Not enough red blood cells in the blood
If there are not enough red blood cells (anemia), not enough oxygen can be delivered to the tissues with each heartbeat. Examples of causes may include: acute or chronic bleeding, inability of the bone marrow to produce red blood cells.
Increased destruction of red blood cells by the body also causes low levels of red blood cells, an example of this is sickle cell disease.
Not enough fluids in the blood vessels
The bloodstream contains blood cells (red blood cells, white blood cells, and platelets, and plasma, which is more than 90% water, in addition to many important proteins and chemicals.
Loss of body water or dehydration can cause shock.
Thus, metabolic shock may be related to dehydration, internal or external bleeding, loss of gastrointestinal fluid due to diarrhea or vomiting, secondary urinary loss due to diuretics or kidney dysfunction, or loss of intravascular volume to the interstitium as a result of decreased of vascular permeability (in response to sepsis or trauma).
Since one of the steps in the cascade of events that cause shock is damage to blood vessel walls, this loss of integrity can cause blood vessels to leak fluid, leading to dehydration, initiating a cycle vicious worsening of shock.
That blood vessels cannot maintain enough pressure within their walls to allow blood to pump to the rest of the body
Normally, blood vessel walls are stressed to allow blood to pump 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 such as adrenaline (epinephrine) and acetylcholine.
If the adrenaline system fails, the walls of the blood vessels dilate and blood pools in the parts of the body closest to the ground (lower extremities), and it can be difficult to return to the heart to be pumped again throughout the body.
Clinical features include pale, cold, clammy skin (often mottled), tachycardia or, in severe shock, bradycardia, tachypnea, flat, undistended peripheral veins, decreased jugular venous pulse, decreased urine output, and a altered mental state.
Metabolism and shock
Basically cells, they need oxygen to be able to create energy. This is called “aerobic metabolism,” an energy metabolism with the help of oxygen, and this is really why we breathe.
We carry out respiration because we need oxygen to help create energy. However, the cells of the body can also create energy through anaerobic metabolism.
Cells in the body can survive without oxygen for only a short time. However, there is a problem with going from anaerobic metabolism to aerobic metabolism.
With oxygen, much more energy can be created to meet the needs of every cell in the body. However, if the body is forced to undergo anaerobic metabolism, it cannot create enough energy to meet the requirements for maintaining cellular life.
But another problem that occurs with anaerobic metabolism is a by-product that is formed when trying to create this energy. It is a substance called: lactic acid.
Aerobic metabolism is necessary to create the amount of energy we need to maintain cell function to sustain life, the body has to deliver oxygen, and the body cannot do this in shock.
Oxygen is transported in red blood cells in hemoglobin, so this is how oxygen is delivered to tissues, through hemoglobin, that is, through red blood cells.
In shock, the problem is tissue perfusion. Tissues and cells don’t get enough oxygen, they don’t get enough blood they need for oxygenation, and without this oxygen they can’t create the energy needed to sustain life.
In shock, there are two scenarios that we can see:
In the first scenario, there is increased oxygen extraction
This is because there is a greater demand for the cells to have oxygen and there is a greater requirement. These cells have very little oxygen in them.
It’s not really an active process, but because there is very little oxygen here and more oxygen in the blood, oxygen easily diffuses into cells.
These cells are deprived of oxygen and take out more oxygen, therefore that would mean that there is less oxygen return to the heart.
Two types of shock that are an example of this increased extraction: cardiogenic shock and hypovolemic shock.
In hypovolemic and cardiogenic shock, the blood is not pumping fast enough. It is not delivered properly, so the cells are using their oxygen faster than it is being delivered.
There is a lower supply, despite the fact that the required oxygen remains practically the same. Ultimately the cardiovascular system simply cannot deliver that oxygen to these cells.
In the second scenario the cells are still in shock and require more than they can deliver.
If oxygen does not reach the cells, extraction is reduced. This is what happens in the type of shock known as a “distributive shock.”
Oxygen cannot be distributed to cells. For example, in septic shock when there is a lot of inflammation and swelling in the space between the cells, the interstitial space, oxygen has a more difficult time to diffuse through this space, so it is difficult for oxygen to pass through all this fluid thick.
This additional fluid creates a diffusion barrier so that oxygen cannot be distributed. So oxygen demand has increased due to poor oxygen supply.
In anaerobic metabolism when there is little oxygen inside the cells, energy is created through this process, and as a by-product lactic acid is created.
Patients with shock may experience lactic acidosis where they have a greatly increased amount of lactic acid. Initially, this can be overcome and does not cause harm to the body.
However, over time due to this increase in lactic acid, the body will have a general decrease in pH, which means a more acidic composition and the structures that are normally intact in cells begin to degrade and denature, leading to a cascade of events that can eventually spell cell death.
So, although initially this process is reversible, if the shock continues long enough, cells can begin to die, as they are deprived of oxygen and energy.
Changes in metabolism
Hemodynamic alterations in shock create new conditions for cellular respiration and metabolism.
All tissues and systems of the body undergo shock-induced changes in cells of peripheral tissues and vital organs apparently occur primarily in energy pathways.
The normal flow of these pathways is inhibited by the lack of oxygen; and both this anoxia and the consequent energy deficit inhibit the function of the membranes.
As a result, the active transport of gluconeogenic substrates, such as glucose, amino acids, and fatty acid, is blocked. This allows potassium outflow and sodium in.
Gluconeogenesis is inhibited either by a direct effect of endotoxin on gluconeogenic enzymes or by a lack of ATP.
Prolonged anoxia interferes with pyruvate oxidation and increases intracellular and extracellular lactate levels.
Intracellular acidosis or the direct effect of endotoxin on membranes ultimately causes permeability or lysis of cell and lysosomal membranes.
Lysosomal hydrolases have been implicated in the cellular pathology of shock and adverse effects on endothelial cells of the vascular system.
An increased ATP deficiency can disrupt protein biosynthesis, blood flow, and poor oxygen supply.
Diagnosis and treatment
Metabolic shock is a life-threatening condition that requires prompt diagnosis and therapy.
Despite new insights into pathophysiology and new horizons for treatment, the fundamental principles of treatment remain the rapid and complete replacement of circulating blood volume and treatment of the underlying cause.
- Treatment initiation: The earlier treatment begins, the more likely the individual will survive.
- Age – Older people are less likely to tolerate the effects of shock on their body and may not respond as well to treatment as younger individuals.
- The cause of shock: Causes that tend to respond well to early treatment are less likely to be fatal than causes that do not respond well, such as a massive heart attack.
- Underlying medical condition: A person with no prior medical history is more likely to survive than a person with one or more medical conditions, such as heart failure or a bleeding disorder.
- The extent of organ failure: If organs, such as the kidneys, liver, or brain, have started to fail before or during shock treatment, the chances of survival are lower than in a person who is in shock but has organs functional ..