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Physiology of Perfusion

Definition Of Shock

"A rude unhinging of the machinery of life" is a quote from the 1850's by Gross.

A more recent version of the definition would be from Robert M. Hardaway, a professor of surgery at Texas Tech University School of Medicine in El Paso, Texas. He states: "I believe that the best definition of shock is inadequate capillary perfusion. As a corollary of this broad definition, almost anyone who dies, except those who are instantly destroyed, must go through a stage of shock. A momentary pause in the act of death".

Shock is a lack of perfusion caused by several factors. In trauma, the #1 related factor is hypovolemia, or more specifically hemorrhage, the loss of blood either internally or externally, or a combination of the two. And in the medical situation, anaphylaxis, sepsis, and hypovolemia brought about by dehydration, excessive vomiting or diarrhea. As an advanced provider of pre-hospital care a deeper understanding of the physiology of perfusion is needed to accurately assess and treat this condition we call shock.

There are a number of complex physiological abnormalities caused by any number of disease states or injuries that contribute to shock. Simply thinking of shock in terms of blood pressure, pulse rate, or heart function is not enough. Simplifying shock as a condition of hypovolemia or vascular dilation is not enough. Shock can occur at any level within the human body starting at the cellular level and progressing to specific organs and eventually to the patient as a whole affecting several or all body systems. This can occur even with normal hemodynamics. To properly assess the patient and various stages of shock, you need a more thorough understanding of cellular physiology.

Tissue Oxygenation

A basic tenet is that the body's cells require 3 things to function properly:

  • A good pump, a healthy heart.
  • Veins and arteries that function correctly, ones that dilate and constrict as needed by the body under various demands placed on them.
  • The lungs must function properly with adequate ventilations and good oxygen and waste exchange taking place.

Any one of these three things that doesn't function properly can cause a decrease in cellular oxygenation, let's look at each one of these components in greater detail.

The Heart

The heart, of course, is responsible for circulating blood throughout the body. It accomplishes this by producing pressure with the pumping action of each heartbeat. Then it must relax long enough for the heart's top chambers to be refilled with returning blood from the venous system. This cycle is called the "cardiac cycle".

The total amount of blood pumped by your heart each minute is termed "minute volume". This includes the blood pumped to the lungs as well as the systemic circulation and that relatively small amount used to supply the myocardium. This amount is expressed in liters per minute and is termed the "cardiac output".

Cardiac output is an important factor (very important) in organ perfusion and is dependent upon several factors. The heart rate (beats per minute), strength of contractions, and the availability of blood brought back to the heart by the venous system (preload). This brings us to the "Fick Principle".

Adolph Fick developed a method of measuring cardiac output in animals and humans in 1870. Perhaps oversimplifying a bit, he found that organs that received oxygenated blood through the arterial circulation used part of the oxygen and there was still some measurable oxygenation left in the venous blood. So by measuring the amounts of oxygen in the arteries and measuring the oxygen left in the venous blood after the blood passed through the capillaries, you could measure the oxygen consumption of the particular organ. In other words the perfusion of the organ. This principle is founded on three items:

The red blood cells must be adequately oxygenated at the alveolar level of the lungs. Therefore, there must be adequate ventilations to assure this.

The red blood cells must be circulated to the tissues, which requires an adequate pumping action of the heart and unobstructed pathways to the organ involved, in other words, a healthy vascular system.

The red blood cells must be able to take on adequate amounts of oxygen as well as be able to off-load the oxygen at the cells. To do this, red blood cells must have adequate amounts of hemoglobin and adequate circulation to the site of delivery, and proper levels of pH, temperature, and other metabolic conditions.

The Vasculature

The veins and arteries, as well as their smaller counterparts, the venules and arterioles, have muscular linings that respond to counteract the effects of pressure. Remember the system maintains pressure and blood flow by dilating or constricting according to the demands of oxygen needed in the respective area in which they are located.

There is a high pressure side (arteries) and a low pressure side (veins). There are two phases of systemic and pulmonic pressure known as diastolic and systolic pressure. The difference between the systolic pressure and the diastolic pressure is termed the pulse pressure. The pressure is highest nearest the heart on the side of delivery (whether pulmonic or systemic) and the pressure is least at the vena cava.

The resistance against which the blood must be pumped is termed afterload. The resistance is governed primarily by the size of the vessels. When resistance to flow increases, the flow remains constant and there is a resultant rise in blood pressure. The resistance to flow can be caused by blood viscosity (thickness), length of the blood vessel, and the size of the blood vessel. As mentioned earlier the size is the primary factor as the other two factors, length and viscosity remain relatively constant.

The larger vessels do not create much resistance to flow. The smaller venules and arterioles cause much greater resistance and depending upon the amount of constriction can cause up to five times the resistance within the vessel. These smaller vessels have a more profound effect on blood pressure.

The Lungs

The lungs must have adequate input to make possible an adequate exchange of gases at the alveolar level. So there must be an adequate ventilatory rate, volume, and depth as well as a matched gas exchange between the blood and the lungs. The lungs must be in a healthy state for this to occur. Respiratory diseases such as emphysema or bronchitis can decrease the diffusion of oxygen and carbon dioxide across the alveolar membrane ultimately resulting in inadequate perfusion to the tissues.

The Body As A Container

This is a simple concept stating that the body is the container for the fluid needed to maintain adequate perfusion. Even though different individuals contain different amounts of fluid in their systems, (smaller folks have less than larger folks), the volume of the container is directly dependent upon the size of the vessels. If all the blood vessels were to dilate at the same time we would not have enough fluid to allow for proper preload of the heart and our blood pressure would fall. Cardiac output is directly dependent upon preload. Two things can cause this effect on preload:

  • If the patient becomes hypovolemic, the container remains the same size but the patient has become hypotensive because of the decreased cardiac output caused by insufficient preload.
  • The container can become too large due to vasodilation resulting from illness or injury and there is not enough fluid in the system to fill the space. Preload is insufficient which adversely affects cardiac output. There are several outside factors which can have an effect on vessel diameter such as blood pressure medications, allergies, heat- and cold-related emergencies, alcohol and drugs.

Blood And Blood Components

The amount of blood found in the human body is around 5 liters (give or take a little) in the normal, healthy adult. This accounts for about 7% of the total body weight.

The watery, salty portion of the blood is the plasma and accounts for about 92% of the blood volume. The plasma is the solvent of the blood. It also contains minerals, sugars, fats, and proteins.

Three major proteins found in the plasma are:

  • Albumin - The most plentiful protein and it gives blood its texture.
  • Globulins - (Alpha, Beta, and Gamma) Globulins do two things, Alpha and Beta transport other proteins and Gamma Globulins aid the body in fighting off pathogens such as bacteria, viruses, parasites and fungi.
  • Fibrinogen - Helps in clotting of the blood by forming web-like protein fibers to help bind together blood cells.

Proteins also act together to aid in correcting pH imbalances and also meet the temporary nutritional needs if the body runs short of food.

Plasma only carries about 1% of the oxygen found in the blood; the other 99% is carried by the hemoglobin found in the red blood cells, or erythrocytes. Red blood cells make up about 45% of the blood and are the most abundant cells in the body. Oxygen is carried on hemoglobin, which is a protein molecule that contains iron. Hemoglobin is what gives the blood its red coloring. The more oxygen in the blood, the brighter red the blood is.

The hematocrit is the volume percentage of red blood cells in whole blood. The average hematocrit for a man is 45 and for a woman is 42.

There are several different blood types which are determined by heredity. The blood type is determined by the type of antigens on the surface of the red blood cell membranes. An antigen is a substance that causes the formation of antibodies. If a foreign blood type is transfused in the body and antibodies are formed, the blood cells will clump together, or agglutinate. The three main antigens in the blood are A, B, and Rh. Blood types are named according to the type of antigens present.

Someone with type O blood has no antigens on the RBC's, so they are considered the universal donor. A person with type AB blood has both types of antigens on the RBC's, so they are considered the universal recipient. The Rh antigen is either present (positive) or absent (negative).

The following is a summary of the different blood types:








A, O




B, O


A, B


A, B, AB, O



A, B, AB, O


White blood cells, or leukocytes, help fight off various disease organisms such as bacteria, viruses, parasites, and fungi. These cells are produced in the bone marrow and lymph glands and are held in reserve until needed by the body. Very few are found in the bloodstream normally. Red blood cells outnumber white cells at a ratio of about 600:1

Platelets, or thrombocytes, also play a role in the body's defense mechanism. They are formed in the red bone marrow and help initiate clotting by swelling and sticking together to form a plug at the injury site.

Physiology of Perfusion II

Fluids and Electrolytes

Water accounts for about 50% - 60% of the body's total weight in adults. Water is important for two main reasons:

  • It is needed for all metabolic reactions.
  • The regulation of the volume of water as well as the chemical makeup of water is essential in maintaining health.

 There are two fluid compartments found in the body:

  • The extracellular compartment
  • The intracellular compartment

Let's look at each one individually.

Extracellular Compartment

This is the fluid found outside the body's cells, it accounts for about 20% of total body weight and it is contained in two separate areas:

  • Intravascular Fluid - The fluid found inside the blood vessels but not inside the cells. This accounts for about 2/3 of the extracellular fluid.
  • Interstitial Fluid - The fluid found outside the blood vessels but not inside the body cells. The interstitial fluid accounts for about 15 - 16% of the total body weight.

Categorized within the interstitial fluids are fluids such as cerebrospinal fluid and the fluid found within the eyes.

Intracellular Fluid

This is the fluid found within the cells and accounts for 40% of the total body weight.


These are salt substances that when placed in water, separate into negatively and positively charged particles. These substances are known as ions. The negative ion is called an anion and a positively charged ion is called a cation. The most important cations in the body are as follows:

  • Sodium

  • Potassium

  • Calcium

  • Magnesium

  • Iron

  • Hydrogen

The important anions include the following:

  • Chloride

  • Phosphate

  • Bicarbonate

Typically the number of positively charged ions equals the number of negatively charged ions to form an electrically neutral solution.

There are also some non-electrolytes in the body. These are substances which possess no electrical charge and include glucose and urea.

Particles and Solutions

You can think of a solution as any liquid that contains a solute or solutes. So any water solution containing charged particles can be called an electrolyte solution. This electrolyte solution is the solvent of the blood.


Proteins account for about 50% of the organic (carbon containing) material in the body. These play roles in the chemical reactions that occur in the body. Proteins are responsible for coagulation, digestion, immunity to disease, and other functions within the body.


Movement of Body Fluids

The body is in a constant state of fluid shift. The shifting of fluids back and forth between the cells and outside the cells is necessary to maintain a balanced environment within the body called homeostasis. It is necessary to maintain the same volume of fluid found in each body compartment. The body uses methods called osmosis, diffusion, and mediated transport to do this. Let's look at each method individually.


Each cell and fluid compartment has a lining called a semi-permeable membrane which has the ability to allow the passage of certain components and restrict the passage of others. This selective process helps maintain homeostasis. The restrictions in movement or the lack of restriction is based on the following:

  • Size

  • Shape

  • Electrical Charge

  • Chemical Properties

There are passageways within these semi-permeable membranes which may allow unrestricted passage to certain specific solutes while not allowing others to pass based on the above listed criteria.

Osmosis is defined as the flow of fluid (solvent) across a semi-permeable membrane from an area of lower solute (electrolytes, and other particles) concentration to an area of higher solute concentration.

This shift occurs with the intention of flooding the higher concentrated solutes in order to dilute the concentration of solutes and balance out the mix.

The fluid containing the higher solute concentration in comparison to the concentration of solutes in the cell is known as a hypertonic solution.

The fluid is hypertonic for the time being but not for long if all goes well, the body will make both sides equal and that is called isotonic. This refers to the equality of the distribution of the solutes.

This is one method used to try and attain homeostasis. Another method is by diffusion.


Diffusion is a method by which molecules or ions shift from an area of higher solute (electrolytes and other molecules) concentration to an area of lesser solute concentration.

This is done in order to attain the balance on both sides of the membrane but in the opposite direction from that of osmosis. Diffusion takes longer than osmosis. When the balance is achieved, movement stops. Both occur simultaneously to achieve the balance, one just takes a little longer.

If you were to place a living cell in a solution that was hypertonic, the water in the solution would leave the cell in order to help balance the solution and the cell would be dehydrated initially.

If you were to place a living cell in a hypotonic solution, water would enter the cell overhydrating it initially.

If you placed the living cell in an isotonic solution, there would be no fluid shift.


Mediated Transport

Mediated transport is the third method by which the body attempts to correct imbalances in fluid and solute concentrations. There are two types of mediated transport.

1. Active Transport - Active transport is required when trying to move certain proteins against the osmotic gradient. The proteins combine with carrier molecules and are actively pushed against the osmotic gradient into the cell. Glucose is a good example. This must be moved from an area of lower concentration to an area of higher concentration and this process requires energy. It's like riding your bike uphill with the osmotic gradient being the hill.

2. Facilitated Diffusion - This is a carrier method process that moves substances into and out of cells along the osmotic gradient which is downhill. These are moved from an area of higher concentration to an area of lower concentration and require no energy, like coasting on your bike downhill with the hill being the osmotic gradient. This is a faster process than active transport as you can imagine, it's easier and faster to go with the osmotic gradient than to go against it

Body Fluids and Fluid Imbalances

The intake and output of water on a daily basis in the human body must be in equal amounts to maintain health. Dehydration occurs if the input is less than the output. Dehydration may also occur if the input consists of only water, without replacing electrolytes. Overhydration occurs if the input exceeds the output. We gain water by drinking fluids, eating foods that contain moisture, and through certain metabolic processes within the body. We lose fluids as urine, feces, perspiration, tears, exhaled air, and salivation.


Dehydration may be isotonic (losing water and salts at the same levels), hypernatremic (losing water faster than salts) and hyponatremic (losing salts faster than water).


Overhydration is usually a result of overzealous administration of IV fluids, or parenteral fluid, poor cardiac output as a result of congestive heart failure or other causes including renal failure, and endocrine dysfunctions.


Acid-Base Balance

Remember that pH is measured on a numerical scale. The scale indicates that the number 7.0 is considered to be neutral, that is to say that it is neither acid nor alkaline. Any number that is less than 7.0 is considered to be acidic and any number higher than 7.0 is considered to be alkaline. The human body has a pH reading of between 7.35 and 7.45 when everything is in good working order. That puts us in a slightly alkaline state. Whenever the pH of the blood reads below 7.35 we are considered to be acidotic and whenever the pH of the blood is above 7.45 we are considered alkalotic. This doesn't leave much room for error. The body is constantly producing acids and bases (alkalis), and therefore it is constantly trying to maintain a state of balance. The hydrogen ion plays an important role in this balancing act. The higher the concentration of hydrogen ions in a solution, the more acidic the solution becomes. The lower the concentration of hydrogen ions, the more alkalotic (basic) the solution becomes. There are several compensatory mechanisms that the body uses to help keep the body’s pH in constant balance.

Compensatory Mechanisms

The body uses three different mechanisms to try and maintain the pH of extracellular fluid in the range of 7.35 - 7.45. These are:

  • The bicarbonate-carbonic acid buffer system, better known as the buffer system.
  • The respiratory system (the lungs)
  • The renal system (the kidneys)

The Buffer System

When carbon dioxide mixes with water it forms carbonic acid. This is formed in the extracellular fluid of the blood. When cations such as sodium, potassium, magnesium contact the anion bicarbonate, they form a base, or alkali. As long as the ratio of carbonic acid and bicarbonate remains at about 20:1 (20 mEq of base bicarbonate to 1 mEq of carbonic acid) then the pH of the blood remains in a normal range (7.35 - 7.45). Whenever there is excessive carbon dioxide in the blood, then there is an excessive amount of the hydrogen ion produced which will make the blood acidic. The pH will fall below the 7.35 range. The bicarbonate buffer system acts immediately to change the pH back to normal by producing bicarbonate and buffering the acid. This is the fastest compensatory mechanism the body has.

The Respiratory System

The lungs are responsible for the exchange of gases such as oxygen and carbon dioxide. When you breathe in oxygen, it is diffused into the bloodstream and combines with hemoglobin as carbon dioxide diffuses in the opposite direction. Why does this occur? Gases diffuse from the area of higher concentration to an area of lower concentration, as stated before when we explained diffusion. There is more oxygen in the lungs during inspiration than there is in the bloodstream, therefore the oxygen diffuses into the bloodstream. There is less carbon dioxide in the lungs during inspiration than there is in the blood, so carbon dioxide leaves the blood and diffuses into the lungs to try and create a balance. When you exhale, you get rid of the carbon dioxide and the cycle starts all over again. This is why the respiratory system is a big help when it comes to maintaining the pH of the blood. Remember that excessive amounts of carbon dioxide turn into excessive amounts of the hydrogen ion which lowers blood pH making the blood acidic. The body's response to unbalanced pH is what stimulates the respiratory rate in healthy adults. The response to this imbalance happens within minutes. This is the second fastest compensatory mechanism the body has to correct pH imbalances

The Renal System

The kidneys are the slowest of the three compensatory mechanisms used to keep the acid-base balance. The kidneys do their part in maintaining the balance three different ways. First, they reabsorb bicarbonate so you don't lose it through urination. Second, they excrete hydrogen ions into the urine to be flushed out of the body. Third, the kidneys excrete ammonium ions which carry hydrogen ions along with them. This system takes several hours to several days to restore pH to normal levels.

Remember that any time there is an increase in carbonic acid or a decrease in bicarbonate this will cause a shift of the pH towards the acid side. Also, anytime there is a decrease in carbonic acid or an increase in bicarbonate this will cause a shift of pH towards the alkaline side of the scale.

Usually respiratory problems will tend to affect the carbonic acid concentration because of either retaining carbon dioxide due to respiratory depression which makes pH go down, or by increased respirations such as hyperventilations which rids the body of its carbon dioxide raising pH.

Remember carbon dioxide and the hydrogen ions are closely related with each other. Carbon dioxide when placed in a solution forms the hydrogen ion.

Conversely, metabolic problems tend to affect the bicarbonate concentration because the cations must be within normal limits to create enough bicarbonate to buffer the hydrogen ion and maintain the pH balance. It takes about 20 mEq of bicarbonate to buffer 1 mEq of the hydrogen ion.

Respiratory Acidosis

The retention of carbon dioxide due to respiratory depression is the culprit in respiratory acidosis. Respiratory carbon dioxide retention can be caused by trauma to the chest, obstructed airway, COPD, pulmonary edema, respiratory arrest, cardiac arrest, nervous system impairment, medications, and drugs.

The treatment for respiratory acidosis is to increase ventilations. Without adequate respirations the body is left with the renal system to back up the buffer system in keeping pH stability. The renal system is too slow to keep up, and acidosis results. Give supplemental oxygen and increase rate and depth of respirations to correct respiratory acidosis in the field.

Respiratory Alkalosis

Basically, blowing off excessive amounts of carbon dioxide, as in hyperventilation syndrome, is the problem. The treatment would be to look for the underlying causes of the increased respiratory rate. Patients tend to have increased respiratory rates when they become acutely ill. Peritonitis, shock, sepsis, and acute respiratory disorders all cause rapid respirations to develop. Try to bring the rate back to normal by treating the cause.

Metabolic Acidosis

Whenever there is an excessive production of acid or a reduction of bicarbonate the body's pH will go down, become acidic. Usually the respiratory system kicks in to help correct the problem. By removing carbon dioxide, this will aid in reducing the hydrogen ion concentration and help raise pH.

The kidneys start to excrete more hydrogen ions into the urine in an attempt to raise pH levels.

The overproduction of hydrogen ions is most commonly associated with such medical problems as diabetic ketoacidosis, lactic acidosis, renal failure, and ingestion of toxins.

Metabolic Alkalosis

Usually this condition is due to a loss of hydrogen ions through the stomach contents as in excessive vomiting. It may be due to ingesting large amounts of sodium bicarbonate (baking soda) or perhaps from eating too many antacid tablets containing calcium carbonate. It may be due to excessive IV administration of sodium bicarbonate in an attempt to correct acidosis in the field. The use of diuretics such as Furosemide (Lasix) may flush out the hydrogen ion through the urine. This is why you see potassium prescribed along with diuretics to aid in replenishing the bicarbonate to keep the kidneys from reabsorbing sodium in large amounts, which the kidneys tend to do when defending against volume depletion. When sodium is reabsorbed, potassium or hydrogen ions must be excreted to maintain the electrical balance of the body. When there is excess excretion of hydrogen ions, this leads to excess bicarbonate production which may lead to metabolic alkalosis.

The respiratory system will try to compensate for the imbalance by slowing the rate of respirations in order to retain carbon dioxide and acidify the blood. This cannot continue however due to the development of hypoxemia. When hypoxemia develops, the accumulation of carbon dioxide stimulates the respiratory centers of the brain and increases the respiratory rate.

The treatment for metabolic alkalosis is aimed at correcting the underlying cause. Treat volume depletion with isotonic fluids. Treat hypokalemia with potassium replacement.


Mixed Acid-Base Disturbances

Everything is not black and white when it comes to acid-base problems. There may be conditions leading to simultaneous respiratory and metabolic imbalances. When a patient goes into shock, some of the compensatory mechanisms described earlier may not work as expected. You may find:

  • Respiratory-Metabolic Acidosis
  • Metabolic Acidosis-Respiratory Alkalosis
  • Respiratory Acidosis-Metabolic Alkalosis
  • Respiratory-Metabolic Alkalosis

These conditions are impossible to diagnose in the field and care should be aimed at treatment of underlying causes such as shock, respiratory depression, cardiac arrest, etc. Pulse oximetry is useful in determining the need for supplemental oxygen if available.


Blood Gas Analysis

Blood gases are normally obtained from arterial samples because the arterial blood gives a better measure of how the lungs are doing in removing carbon dioxide and delivering oxygen to the bloodstream.

Blood gases are obtained at the hospital to determine oxygen content, levels of carbon dioxide, and pH levels. Normal blood gas values are as follows:

pH........... 7.35 - 7.45

PaO2........80 - 100 mmHg

PaCO2.....35 - 45 mmHg

O2..........95% or greater


Pathophysiology of Shock


Capillary-Cellular Relationship in Shock

As shock progresses, there is a sequence that follows related to changes in capillary perfusion and leading to cell death.


Vasoconstriction (Stage #1)

When perfusion to the capillaries is decreased, as in shock, the blood vessels supplying the capillaries constrict. The amount of oxygen and nutrients reaching the capillaries is reduced, and this reduces the supply of oxygen and nutrients to the cells. Metabolism continues, but without the needed oxygen, so metabolism becomes anaerobic. Anaerobic metabolism produces an increase in the production of the hydrogen ion and lactate. The body's major organs begin to use more of the available blood flow causing less and less blood to be supplied to the capillaries.

The sympathetic nervous system kicks in causing the skin to become pale and diaphoretic and the pulse to become rapid and weak. Epinephrine is released which dilates coronary, cerebral, and skeletal muscle arterioles, and constricts the other arterioles of the body. This causes blood to be shunted to the heart, brain, and skeletal muscle.

Capillary flow to the kidneys and the abdomen decreases. If this early stage of shock is not treated with adequate fluid replacement, the next stage of shock begins.

Capillary and Venule Opening (Stage #2)

Blood begins to pool in the capillary system and fills the capillary beds. Capillaries and venules not ordinarily open to circulating blood flow open their gates and blood is pooled in these areas. Hypotension and arteriole constriction means less blood flow to the arterioles, which adds to the pooling of blood in the capillaries since the flow is reduced and the blood cannot be pushed through to the venules.

The increased production of acid and lack of oxygen leads to the opening of the aforementioned capillaries and venules which expands the vascular space. There may not be enough blood volume available to fill this extra space even if there were no loss of blood due to injury. These additional capillaries and venules using the available blood may create a depletion of available blood supply to the vena cava which results in a loss of blood return to the heart, this decreases preload and in turn reduces cardiac output.

Low blood pressure, restricted arterioles, and the shunting of blood results in further stagnation of capillary blood. The sluggish flow of blood in the capillaries results in the production of lactic acid. The acidic pH prompts the respiratory system to try and compensate by increasing respirations. The red blood cells in response to the low pH begin to cluster together which further reduces blood flow to the capillaries. All this reduces the nutritional flow to the cells and the removal of wastes from the cell. This second stage quickly progresses to the third stage if not recognized and treated with volume replacement quickly.

If the underlying cause of this sequence of events was cardiac disease or severe trauma, there may be no reversal possible.

Intravascular Coagulation (Stage #3)

When stage three begins, shock may still be reversible, however resistant to treatment. The blood begins to coagulate due to the lack of circulation. This further reduces perfusion at the capillary level preventing removal of wastes. This only serves to increase lactic acid production and anaerobic metabolism. Homeostasis cannot be maintained and water as well as sodium leak into the cells and potassium leaks out of the cells causing the cells to swell and die. The viscera develop pockets of infarcted tissue. Pulmonary capillaries start to become inflated with fluid (pulmonary edema) and this inhibits the exchange of oxygen in the lungs as well as the release of carbon dioxide into the lungs. This ultimately leads to respiratory failure and multiple organ failure.

Multiple Organ Failure (Stage #4)

Some organs tolerate cell death better than others. The primary health of the affected organ plays a role in how well it deals with necrosis as well. Generally, the liver goes first, then kidney failure, and finally heart failure.

This is where blood pressure falls rapidly and cell death progresses to the point where metabolism ceases entirely. If the affected organ or organs are subjected to gross cell necrosis, the organ soon dies.

This is apparent when patients are revived in the field, delivered to the hospital breathing and heart beating, only to die several days later. Cell necrosis in the organs has taken its toll.


Classifications of Shock

Generally, shock is classified in relationship to the cause. In other words shock due to cardiac failure is called cardiogenic shock. Shock due to severe infection is known as septic shock. Regardless of the cause, the end result is still inadequate perfusion.

Common Types of Shock






Hypovolemic Shock

The most common cause of hypovolemic shock is hemorrhage due to trauma. The massive loss of blood leads to low volume. Hypovolemia may be caused by the massive loss of plasma as often seen in severe burns. It could be due to the massive loss of body fluids as seen in patients with prolonged diarrhea or vomiting. There may be an internal "third space loss" of fluids as seen in peritonitis.

Cardiogenic Shock

This is caused by the inability of the heart to circulate adequate amounts of blood needed to assure adequate capillary perfusion. There are many reasons for decreased cardiac output. Chest trauma, including the many cardiac injuries such as cardiac tamponade, myocardial contusion, etc. Multiple AMI's or one serious AMI may reduce cardiac output. Serious dysrhythmias can cause decreased output. Diseased heart valves can be the culprit as can an enlarged heart (cardiomyopathy) or a pulmonary embolism.

Neurogenic Shock

This is a result of injury to the spinal cord. The injury causes a loss of muscle tone and paralysis below the level of injury.

The patient's body loses the ability to communicate with the nervous system which is responsible for the control of blood vessel constriction and dilation. The result is a dilation of the blood vessels. The container becomes too large for the available blood to fill even if there is no subsequent blood loss associated with the injury. This is also known as "high space shock". Because of the lack of communication with the nervous system, catecholamines are not released in response to the lowered blood pressure. Signs and symptoms of neurogenic shock will be different from other types of shock in that the patient's heart rate remains in the normal range, rather than increasing, as the blood pressure decreases and their skin will remain warm and dry.

Anaphylactic Shock

This is caused by a severe allergic reaction to a substance encountered by the patient. The reaction can result in a release of histamines which cause arterioles and capillaries to dilate. The other agents released with the histamines can cause the swelling of the upper and lower airways to a point of complete blockage.

Septic Shock

Septic shock usually results from a severe bacterial infection. There are toxins released by the invading pathogen which affect arterioles, capillaries, and veins. It is usually seen in older adults or very young children. Septic shock is most often associated with staphylococcal infections, streptococcal infections, pneumonia, post-operative infections, and urinary catheters. It is most commonly seen in nursing homes, with alcoholics, and with neonates.


Stages of Shock

Shock can be categorized into three stages. Each stage represents the body's response to shock. The three stages are as follows:

  • Compensated Shock
  • Uncompensated Shock
  • Irreversible Shock

Compensated shock

In this early stage of shock, there is some decrease in tissue perfusion. The body senses and responds to the decrease by trying to compensate for it. Compensation begins by an increase in catecholamine release. Catecholamines help the body maintain cardiac output which in turn helps keep the blood pressure up.

As perfusion decreases, there is an excess production of acid. The body responds to this by increasing respiratory rate and depth in an attempt to remove carbon dioxide from the blood stream.

The body's sympathetic nervous system responds by increasing heart rate and contractions, dilates bronchioles, and constricts certain blood vessels which in turn decrease blood flow to the capillaries. This is an attempt to shunt blood away from capillaries so that the vital organs are perfused.

Early signs and symptoms of this first stage include:

  • Delayed capillary refill
  • Cool skin
  • Decreased level of consciousness

If left untreated, the body will soon lose its ability to keep up.


Uncompensated Shock

In this stage the body is losing its ability to maintain blood pressure. The pulse pressure becomes narrow. This is sometimes difficult to detect with a blood pressure cuff and may be mistaken for no diastolic reading at all. The blood flow to the brain has slowed due to low blood pressure. The respiratory system is able to compensate for the acidotic state by blowing off excess carbon dioxide unless there is a head injury or chest injury that results in hypoventilation.

Signs and symptoms of uncompensated shock include:

  • Low blood pressure
  • Rapid pulse
  • Rapid breathing
  • Delayed capillary refill
  • Cyanosis of the extremities
  • Extremities that are cool to the touch

The heart starts to suffer from the effects of low venous return. Due to the release of catecholamines though, it continues to beat harder and faster. The lack of oxygen saturation and the reduction of circulating red blood cells lead to ischemia. The coronary arteries are perfused less and soon the myocardium begins to die. Acidosis becomes more profound leading to possible cardiac dysrhythmias.

All of this as well as the lack of recognition and treatment lead to stage three.


Irreversible Shock

The organs are starting to feel the effects of ischemia and necrosis. Even if the restoration of oxygen and perfusion takes place, the organs are beyond reclamation.

Death can occur suddenly or may take several days or weeks after experiencing this level of shock.

Signs and symptoms include:

  • Bradycardia
  • Cardiac dysrhythmias
  • Severe hypotension
  • Organ failure
  • Pale, cool, clammy, skin

There are several factors that have an effect on how each individual responds to shock. These include:

  • Age
  • Physical condition
  • Health
  • Medications
  • Specific organ involvement


Assessment and Treatment of Shock

Primary Survey

Assessing perfusion of the various body organs is a major part of the evaluation process of the shock patient. The ABCDE's are still the assessment priorities. Airway maintenance includes assuring proper oxygenation is occurring through proper rate and depth of respirations. Restoration of perfusion, however, is the end goal. After initial assessment of the ABCDE's take note of the condition of the skin. Is it moist? Does it have normal color? Is it cool or warm to the touch? Is capillary refill time within two seconds? Note the level of consciousness, this reflects cerebral perfusion. Is the patient restless, agitated or confused?

Use the acronym AVPU to describe the level of consciousness. AVPU stands for:

A = Alert

V = Responds to verbal stimuli

P = Responds to painful stimuli

U = Unresponsive

Use the Glasgow Coma Scale to evaluate the level of consciousness and neurological response. Expose the patient's body to uncover any hidden injuries that may be underneath clothing, especially in trauma victims.

Secondary Survey

We are now looking for conditions that may be potentially life-threatening if left untreated. A closer look at the patient's overall status is the goal here. We should have discovered immediately life-threatening injuries or conditions while performing the primary survey.

Check the patient's vital signs. Look for increased pulse rates, which will occur after about a 10 - 15% fluid reduction. Be aware that some patients will not exhibit tachycardia after this amount of blood loss. Look for causes of bradycardia, if present, such as:

  • Hypoxemia
  • Neurological injury
  • Increased vagal response
  • Pre-existing injuries or illness
  • Prescribed medications
  • Illicit drug use

Check the blood pressure, as the blood vessels constrict in response to shock, the diastolic pressure may rise initially, narrowing the pulse pressure. When the heart can no longer keep up the pace, then the diastolic pressure will drop. Soon after, the systolic pressure begins to fall, usually in response to a loss of fluid volume of around 25%.

Check orthostatic blood pressures if possible. This is checking blood pressure while the patient is lying down or in a sitting position, then have the patient stand and check blood pressure again. A drop of 10 - 15 mm Hg may be indicative of volume depletion.


The goal in resuscitating the patient in shock is restoring tissue oxygenation as soon as possible. This is accomplished through ensuring adequate oxygenation, maintaining fluid volume, and rapid transport to the appropriate medical facility.

Remember the "Fick Principle". It tells us that first a patient must have adequate red blood cell oxygenation. For this to occur, ventilations may need to be assisted and supplemental oxygen may need to be delivered. Positive pressure ventilations may be necessary to achieve adequate depth. If chest trauma is present, treat it promptly to aid in producing adequate ventilations.

The "Fick Principle" also states that there must be enough fluid in the vascular container to carry the needed oxygenated red blood cells to their destination. There are several methods by which we can accomplish this including:

  • Application of PASG
  • Fluid replacement via I.V. therapy
  • Medications to increase vascular resistance and to enhance blood pressure

Current Uses for the PASG or MAST

PASG (pneumatic anti-shock garment) or MAST (military anti-shock trousers) is an inflatable garment that is wrapped around the legs and abdominopelvic area. Typically, the garment consists of three separate compartments and each can be inflated separately or simultaneously. The intent behind the initial use of this garment was to stabilize the patient's falling blood pressure. This is accomplished by compressing the arteries of the legs and abdomen and thereby increasing the peripheral vascular resistance (PVR). When this is done there is typically a subsequent rise in blood pressure. However, when PVR is increased there is often a corresponding decrease in cardiac output. We do not want to decrease cardiac output in a patient already suffering the effects of low blood pressure. This is only one reason for the controversy over the use of PASG. If there is uncontrolled bleeding internally, raising the blood pressure may actually increase bleeding.

The initial use of PASG in the field, was to use the garment on a patient suffering post-traumatic hypotension. There was no real clinical evidence supporting the effectiveness of PASG.

Over the past few years there have been controlled clinical trials to determine if the use of PASG will improve vital signs, survival to the hospital, and survival until discharge from the hospital. The general consensus among informed medical personnel is that the PASG not be used when bleeding cannot be controlled.

Another question is, do indications for the use of PASG exist? The patient suffering from spinal shock has lost the ability to control vascular tone. So, theoretically this patient could benefit from the use of PASG. In a patient suffering from anaphylaxis who has a dilation of blood vessels due to the release of histamines may also benefit. However, there is no real proof that PASG helps in these situations at this time.

Some feel that PASG may be helpful when pelvic fractures or femur fractures are found. It is also possible that PASG may reduce pelvic hemorrhage. Remember that the elevation of systolic blood pressure beyond 90 - 100 mm Hg should be done with caution when the patient may be suffering uncontrolled internal hemorrhage. Consult with local medical direction and allow this to guide your use of PASG.

There are the standard contraindications to the use of PASG, these include:

  • Pulmonary Edema
  • Cardiogenic Shock
  • Thoracic Hemorrhage
  • Impaled Objects
  • Pregnancy
  • Eviscerations

Training specific to the individual PASG garment being used is crucial to its successful operation. There are many designs in use and they come in several different sizes for use with adults and children. Deflation of the garment in the field is generally not recommended without physician supervision. The general rule of inflation is to inflate enough to maintain an adequate blood pressure.

Some potential problems associated with the use of PASG are as follows:

  • As ambient temperatures rise, the pressure inside the garment increases.
  • As ambient temperature falls, the pressure inside the garment also falls.
  • If transporting the patient by air, the decrease in atmospheric pressure results in the decrease of the pressure in the garment.
  • If the garment is being used for long transport, say of 1 - 2 hours, then the loss of perfusion to the lower extremities may result in the loss of the limb.

Of course, the loss of the limb is somewhat minor compared to the alternative which may be the loss of life. The benefits must be weighed carefully against the risks and a decision must be made regarding the use of PASG.


Fluid Resuscitation in Shock

There are few exceptions when it comes to fluid replacement in shock victims. Most need it! Cardiogenic shock is one of those exceptions. The heart cannot stand the extra load that infused fluids would create. The most common types of shock requiring fluid replacement are shock due to hemorrhage and dehydration. The choice of fluid for this replacement will depend upon medical direction and protocol.

Crystalloids, such as lactated Ringer's and normal saline are a common choice. It generally requires a replacement ratio of 3:1 to provide sufficient volume. For every ml of blood lost, give 3 ml of replacement crystalloid solution. This is due to the fact that 2/3 of the crystalloid will be lost due to fluid shift outside the vascular system in an hour or so.

Colloid solutions are fluids that contain large protein molecules that are too large to pass through the capillary membrane. These fluids remain in the vascular compartment for several hours. Some examples of colloid solutions are: whole blood, plasma, plasma substitutes, and packed red blood cells. These are generally reserved for in-hospital use due to their short shelf life and relative expense.


Principles in Shock Management

As in all patients, management priorities of patients in shock starts with establishing and maintaining the airway. Give high flow supplemental oxygen and assist in ventilations if the patient cannot maintain adequate rate and depth of respirations. Controlling any excessive external bleeding after tending to the airway is the next step. Replacement of fluids goes hand in hand with excessive bleeding control but time should not be wasted on scene in order to place an IV. This can be accomplished en route to the hospital in most cases.

The placement of two large bore IV's (a minimum of 16 gauge catheter if possible) is recommended. These two IV's do not have to be located in separate limbs however. The two lines can be placed in the same limb or anywhere access is available. Again, do not waste transport time trying to start IV's. The fluid in a crystalloid solution does not have the ability to carry oxygen as the blood does, it will only aid in restoring cardiac output and blood pressure.

The use of PASG should be considered if they are available and allowed by local protocol.

The patient's body temperature must be maintained as close to normal as possible. The patient suffering from shock will be more likely to become hypothermic than hyperthermic. Be aware of the ambient temperatures and don't overheat the patient.

Monitor the heart rhythm. Frequently assess the vital signs and record them carefully.


Management of Specific Forms of Shock


Hypovolemic Shock

Treating the cause of the fluid deficit and the replacement of the lost fluid is the key to managing hypovolemia. If simple dehydration is the cause, use a crystalloid solution (per protocol) to replace lost fluids. If the cause is hemorrhage, the replacement of volume at a ratio of 3:1 is indicated and delivery to the appropriate medical facility as quickly as possible is vital to the patients survival.

Cardiogenic Shock

The idea here is to try and improve the heart's ability to pump fluid. The paramedic will want to monitor the heart rhythm and treat any irregularities with the proper medications indicated by the individual arrhythmias. Remember to treat the patient, not the heart monitor. If there is an arrhythmia, look at the patient to see if it is causing the patient to be symptomatic of the rhythm. Then treat the causes and symptoms if possible.

Fluid replacement may be useful and an initial bolus of 100 ml - 200 ml should be given to avoid any fluid overload which may place too much stress on the heart, doing more harm than good. After giving the initial bolus reassess the patient, if the patient’s condition improves, continue the fluid therapy until a satisfactory blood pressure and pulse is attained.

Always pay close attention to the lungs, check breath sounds periodically and if congestion develops during fluid administration, then slow the infusion rate to TKO.

Consider drug therapy, consider the causes of the associated symptoms and ask yourself:

  • Will vasopressors help?
  • Will inotropics help?
  • Does the patient need an anti-dysrhythmic medication?

Neurogenic Shock

This type of shock requires treatment similar to hypovolemic shock. The vessels have all dilated causing a relative hypovolemia to occur. Be careful not to overload the patient by constantly monitoring lung sounds and blood pressure. The paramedic may want to consider vasopressors to help constrict blood vessels.

Anaphylactic Shock

For the patient who is suffering from acute anaphylaxis, the administration of subcutaneous epinephrine is indicated. Other treatment therapy will depend on the severity of the allergic reaction. Treatment may include:

  • Administration of antihistamines - Counteracts the release of histamines by the body.
  • Bronchodilators - To treat bronchospasm
  • Steroids - Reduces inflammation
  • Fluid replacement may be useful to compensate for the dilation of blood vessels caused by the release of histamines.

Anticipate the need for aggressive management of possible airway problems which may require intubation.

Septic Shock

The metabolic response to infection may create an acid-base disturbance in the body. Look for signs of acidosis such as increased respiratory rate.

Look for other metabolic signs as discussed in the acid-base portion of this lesson. You may encounter hypovolemia due to prolonged vomiting or diarrhea. The patient may need cardiac medications to improve cardiac output. Get a thorough patient history and be on the lookout for the following:

  • HIV infection - causes the immune system to be depressed leading to infection.
  • Chemotherapy - Suppresses the immune system
  • Indwelling urinary catheters - A possible cause of infection


Techniques of IV Therapy


IV insertion is used to attain access to the body's circulation. In the pre-hospital setting there are three basic indications for its use. These are:

  • Fluid volume replacement
  • Drawing blood samples
  • Administer medications

The preferred site is in a peripheral vein located in one of the upper extremities. Any available vein from the top of the hand to the antecubital fossa, the area opposite the elbow, is acceptable. These are the areas of first choice. There are times when these areas may not be accessible due to massive trauma or other reasons that would exclude access to the arms. The use of the veins of the feet and lower extremities are an acceptable substitute. In some EMS systems the use of the external jugular vein is allowed.

Choice of IV Catheters

There are two main types of IV needles used in the field. These are:

  • Butterfly - A hollow needle with no catheter, the needle remains in the vein.
  • Over-the-needle catheter - There is a catheter covering the needle, the needle is used to insert the catheter into the vein then the needle is removed leaving the straw-like catheter in the vein.

The butterfly type needle is used in pediatric fluid replacement and occasionally to draw blood samples. The use of the butterfly to draw blood samples is not generally a good idea, especially if using vacuum tubes and a Vacutainer setup. The diameter of the butterfly needle is so small in most cases that the rapid flow of the blood cells entering the needle causes the cells to be torn apart (hemolyzed) and rendered useless for lab testing. The use of the larger bore needles such as the over-the-needle angiocath is better suited for blood draws as well as the delivery of IV fluid.

The over-the-needle catheter is the preferred choice in the field. It offers a wide variety of bore diameters and lengths, both of which are important factors in fluid volume delivery. The angiocath is easily placed in the vein and affords more comfort to the patient.


Fluid Flow Characteristics

The laws of fluid flow tell us that fluid flows easier through larger holes. The larger the hole the less friction placed on the fluid. The length of the tube carrying the fluid plays a role too. The longer the fluid has to stay in the tube the more friction is placed on the fluid and this affects fluid volume by slowing the flow. So bigger is better and shorter is better when fluid volume is important. The administration tubing size and length are also factors in fluid volume delivery. Usually the diameter of the tubing is not a choice you have while in the ambulance preparing to start an IV, however the length of the tubing is usually something more under our control. Choose shorter lengths when trying to deliver large amounts of fluid in short amounts of time.

Other factors affecting fluid delivery rates are temperature and viscosity. The viscosity (thickness) of the fluid is affected by temperature. Colder fluids will become thicker and will flow more slowly than warmer fluids.

Using pressure on the IV bag is one method of increasing flow rate. Pressure can be applied by hand or by wrapping a blood pressure cuff around the bag and inflating it to squeeze the fluid out at a higher rate. There are commercially prepared pressure delivery systems available as well.


Choice of IV Fluids

The fluids of choice for patients suffering from shock would be fluids that are isotonic to the blood. These solutions will remain in the vasculature longer and increase the blood pressure and increase cardiac output. Normal Saline, Lactated Ringer's and Plasmalyte are examples of isotonic crystalloid solutions. 5% Dextrose in Water (D5W), D5 1/2 Normal Saline (D5 1/2NS), and D5 1/4 Normal Saline (D5 1/4NS) are examples of hypotonic solutions. 50% Dextrose in Water would be an example of a hypertonic solution.


Gaining Confidence in IV Techniques

The technique of placing an IV catheter in a vein is one which is best learned through practice and experience. Practice comes in two forms: practice on mannequins and practice on real people. Mannequin practice is probably a good place to gain confidence in the handling of the equipment and learning the steps required for maintaining aseptic techniques. The real learning begins with the actual patient contact during hospital clinical rotations. It only gets easier with practice which includes some success and some failures. Gaining confidence is easier when you can practice in the clinical setting such as in the emergency room during clinical rotations. This is a great place to learn the little tricks that aid in successful IV insertion.

The real experience that will help you master the skill comes when you are on duty. Starting an IV in a car that is turned on its side in the pouring down rain with an uncooperative patient screaming at you while the fire fighters are using the Jaws of Life to try and pry the metal away in order to remove the patient, is training you can't get anywhere else. This is something most nurses and doctors can only imagine and is what most EMT's thrive on. So keep at it, take advantage of every situation and opportunity you get to start an IV, as long as the patient gives consent, and you'll master the skill in no time.


Complications of IV Therapy

The complications that can result from performing venous cannulation can be separated into two categories, systemic and local.

The systemic complications are ones such as sepsis and emboli of various types.


Sepsis can be caused by careless handling of the catheter or the associated equipment. Always use an aseptic technique when handling any of the parts of the IV equipment and especially those parts which will be exposed to the patient. These parts include the injection ports, IV tubing on either end, IV catheters, etc. Cleanse the area of insertion with an alcohol prep or iodine to further prevent infection.

The various forms of emboli can be caused by shearing of the catheter during inspection when you slide the catheter up over the end of the needle. This practice should be avoided if possible. Air emboli are caused when too much air is introduced in the vein through the IV tubing or from an empty IV solution bag. It only takes about 10 ml of air to become fatal, especially in a patient who is already suffering from illness or injury. This is a rare occurrence. The risk is increased when cannulation of central sites such as the external jugular vein, subclavian vein, or the femoral vein is attempted.

Signs and symptoms of possible air embolism include hypotension, cyanosis, weak and rapid pulse, decreased levels of consciousness. All of the previous signs and symptoms are going to be difficult at best to recognize when the patient is suffering from stages of shock to begin with. So prevention is the best alternative. Pay close attention to the air in the IV tubing, be careful when changing IV solutions, don't let the IV solution run out completely before changing it. This will reduce the possibility of emboli occurring.

Local Effects

Infiltration of the site may occur when the catheter has punctured both sides of the vein allowing blood and IV fluid to leak out. The catheter may be pulled out of the vein accidentally, or blood, or IV fluid leaks around the catheter that has been properly placed. Some indications that infiltration has occurred are:

  • An obvious hematoma
  • Coolness of the skin surrounding the IV site
  • Swelling of the area surrounding the IV site
  • Pain
  • Slow or absent flow rates

To check for possible infiltration you can lower the fluid bag below the level of the IV site and look for blood return, no blood return is a good indication that infiltration has occurred. If this is the case, an alternative site should be chosen and the previous site dressed to prevent bleeding.


Regulating Flow Rates

IV flow rates are not usually calculated in a routine, everyday type of ambulance run. There are usually two rates that are used in the field: TKO, and wide open depending on the nature of the call encountered. Wide open is used for fluid replacement and the rate is reduced to TKO after a favorable patient response. TKO is used for keeping the vein open in case medications are needed or fluid replacement becomes necessary. This is true of the vast majority of emergency cases and probably encountered more in the transfer operation. The need for calculating flow rates during long transport times may be another time when it is encountered. The very fact that it is not done as a routine everyday duty is all the more reason to keep practicing it.

The paramedic may need it to calculate drip rates when administering cardiac medications to a patient recently converted from a cardiac dysrhythmia. There are several methods of calculating flow rates. They all need some basic information in order to work. Here are three main things you will need to know if you are going to do a simple IV flow rate calculation:

  • How much fluid is to be given
  • Over what time period is the fluid to be given
  • How many drops per ml does your infusion set deliver (gtts/ml)

Some common infusion set sizes are:

  • 10 gtts/ml   (macrodrip)
  • 15 gtts/ml
  • 20 gtts/ml
  • 60 gtts/ml   (minidrip)

Drip Rate Calculations

Here are two methods used to calculate IV drip rates.

The first method is by the use of a mathematical equation which takes the three main factors mentioned above into consideration.

Amt = Amount to be infused (ml)

Drp = Drops per ml (gtts/ml) delivered by the administration set

T = Total time to be infused in minutes

Drops per minute (gtts/min) = (Amt x Drp) / T.

 f you are mathematically inclined, this is a simple formula to use and it needs no further explanation. However, if you are not mathematically inclined, here is a simpler way....

 1. First determine how many cc's are to be delivered per hour. No matter what the time period the orders are for, relate the amount to one hour.

Example (for orders covering more than 1 hour): If the order is to deliver 500 cc's in 5 hours, then divide the cc's by the number of hours.

500 cc's ÷ 5 hours = 100 cc's/hour

 If the orders are for less than 1 hour, take the cc's ordered and multiply by the appropriate number.

 Example: 100 cc's in 20 minutes, there are three 20 minute blocks in 60 minutes (1 hour = 60 minutes). Therefore multiply 100 cc's x 3 = 300 cc's/hour.

2. Find the administration set to be used. Like one of the following: 10 drop set (macrodrip), 15 drop set, 20 drop set, 60 drop set (microdrip). Each administration set will have a factor associated with it that relates to 60. Like this:

10 drop set (10 gtts/ml) - Factor = 6, because it takes six 10's to equal 60

15 drop set (15 gtts/ml) - Factor = 4, because it takes four 15's to equal 60

20 drop set (20 gtts/ml) - Factor = 3, because it takes three 20's to equal 60

60 drop set (60 gtts/ml) - Factor is 1, because it takes one 60 to equal 60

3. Divide the cc's/hr you figured in step one, by the factor that is associated with the administration set to be used;

10 drop set - Factor = 6

15 drop set - Factor = 4

20 drop set - Factor = 3

60 drop set - Factor = 1

Example: if the 15 drop set is to be used, and 100 cc's per hour is to be infused,

100 cc's/hr ÷ 4 (factor) = 25 gtts/min is the answer.

There is nothing to it if you practice it a little.



A liter is the same amount of fluid as 1000 ml's or 1000 cc's. You must convert liters to cc's first, then use the three steps.

The different administration sets get their names (e.g., 10 drop set) because it takes 10 drops to deliver 1 cc. A 20 drop set takes 20 drops to deliver 1 cc, a 15 drop set takes 15 drops to deliver 1 cc, and a 60 drop set takes 60 drops to deliver 1 cc.

Whichever method you learn to use to calculate IV drip rates, stick with the same method and practice it occasionally to remain proficient at it.

Try our Advanced Shock and IV Therapy Quiz on the RAEMS Blog (here)