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Published: 19.05.2023

Module 10: Shock Recognition and Management

The Circulation portion of Tactical Field Care consists of determining if a patient is in shock, and if they need intravenous (IV) access. Not all casualties need IVs. The intravenous and intraosseous routes and suggested indications and techniques are discussed. The proper use and administration of tranexamic acid (TXA) is also discussed as an adjunct to help reduce blood loss from internal hemorrhage.

This module will focus on the management of shock and support of circulation.

Shock Recognition and Management


During this second module addressing circulation assessment and management in the Tactical Field Care (TFC) setting, we will focus on shock, access for fluid resuscitation, and administration of tranexamic acid.

Some shock assessment and recognition principles are taught in All-Service Member or Combat Lifesaver training, but the rest of this module’s information begins at the level of the Combat Medic.


There are three terminal learning objectives in this module, resulting in 7 cognitive and 3 performance enabling learning objectives.

In describing shock assessment in TFC, the signs and symptoms of shock, the use of peripheral pulses and level of consciousness in the determination of shock, the lethal triad of shock, and refractory shock will be reviewed.

The section on intravenous (IV) and intraosseous (IO) access involves identifying the indications for and methods of establishing both IV and IO access, as well as performing IV and IO access.

And the section on tranexamic acid (TXA) involves identifying the indications and methods of administering TXA and demonstrating its administration.


Circulation assessment and management is the “C” in the MARCH PAWS sequence.


Shock occurs when the oxygen demands of cells aren’t met, leading to cellular and tissue hypoxia, and it is a life-threatening condition, most commonly manifested as hypotension. Potential etiologies include distributive shock, when there is peripheral vasodilation like you see in sepsis or anaphylaxis; cardiogenic shock like you see in a myocardial infarction or heart failure; obstructive shock, like you see in a massive pulmonary embolism; and hypovolemic shock, like you see in massive bleeding or burns.

Although shock from sepsis can occur in prolonged field care settings, almost all shock in the Tactical Field Care setting is hypovolemic. The most common cause is massive bleeding, but fluid loss from severe burns, usually covering 30% or more of the body surface area, is also an important consideration.

Untreated, the natural progression of shock leads to permanent end-organ damage and death from cellular hypoxia. However, hypoxic injuries are reversible if caught early enough, and organs do recover if adequate oxygenation can be restored.


A high index of suspicion for developing shock should be maintained in the presence of any significant hemorrhage, both external and internal.

The natural response to decreased oxygen delivery is to try to increase the amount of oxygenated blood to the tissues, so early signs of shock will include tachycardia and tachypnea.

If those measures aren’t able to restore adequate oxygenation, signs and symptoms of hypoperfusion will develop. These can include:

  • Mental confusion or altered mental status in the absence of a head injury
  • Weak or absent radial pulses
  • Tachycardia
  • Tachypnea
  • Excessive thirst
  • Cyanosis with pale, grey, or blotchy blue skin
  • Nausea and/or vomiting
  • Diaphoresis with sweaty, cool, clammy skin

Those last two signs warrant additional discussion, as several of the other signs can also occur in non-shock situations on the battlefield. For example, the sweaty, cool skin may be a manifestation of physical exertion (sweat) that has just cooled, or the nausea and vomiting could be from the stress of an injury.


One of the key signs for shock is Altered Mental Status in the absence of head injury. Check casualty every 15 minutes for AVPU.

  • Alertness: Knows who, where they are.
  • Verbal: Orally responds to verbal commands.
  • Pain: Level of pain felt when the sternum is briskly rubbed with the knuckle (if needed)
  • Unconscious: Unresponsive
  • Decreasing: AVPU could indicate condition worsening

Assess for weak or absent radial pulses and confirm all bleeding control measures are still effective. It is better to prevent shock with hemorrhage control than to treat it.

DO NOT WAIT for signs and symptoms of shock to occur.


Tachycardia is typically the first abnormal vital sign of hemorrhagic shock. As the body attempts to preserve oxygen delivery to the brain and heart, blood is shunted away from extremities and nonvital organs.

When cardiovascular changes occur, it could then cause tachypnea. Metabolic acidosis occurs when the acid level is too high in the blood, breathing rate increases to blow off carbon dioxide.

Rapid and substantial loss of blood or decreases in intravascular volume can cause dehydration. Transfusion should occur as soon as possible after life-threatening hemorrhage in order to keep the patient alive.

The body’s response to blood loss is compensatory in nature, resulting in progressive vasoconstriction of cutaneous, muscle, and visceral circulation, which preserves blood flow to the heart and brain.

High levels of epinephrine and other related hormones release to counteract the shock. Stimulation of the sympathetic nervous system will activate the sweat receptors in the skin, causing excessive sweating.

When the body begins to overcompensate, it will release non-vital fluids and chemicals stimulating the sympathetic nervous system causing nausea and/or vomiting.


It is a good idea to let those casualties who are not in shock and who can swallow drink water or other fluids. Dehydration is common on the battlefield and is not good for casualties. Any casualty not in shock but who has lost some blood will benefit from oral rehydration.


The two most reliable indicators of shock in a TFC setting are an altered mental status in the absence of head injury and an absent or weak radial pulse.

In an effort to conserve oxygen for vital functions and organs, the body will begin to shunt blood from the periphery to its core (heart, lungs, kidneys, etc.). The result is that peripheral pulses will diminish and disappear prior to central pulses, like the carotid or femoral pulses. Additionally, the physical distance from the heart to those pulse assessment sites is greater, and with borderline blood pressures, the flow of blood at that level may not be detectable by checking for a pulse.

Likewise, although the core functions of the brainstem may be maintained, the flow to the cortex of the brain that controls fine motor function and determines the level of responsiveness may be compromised. The result of this is a decreased ability to respond properly to commands and, ultimately, an altered level of consciousness.

In the field setting, these are the two most reliable indicators of shock, especially when used over time to monitor for potential progression (either deterioration or improvement).


To help illustrate the importance of following signs and symptoms over time, it might be helpful to review the progression of symptoms you might encounter if someone were to experience ongoing blood losses without appropriate interventions to stop losses or replace them.

  • Usually, up to 500 ml of blood loss is well-tolerated, often with no effects except perhaps a slight tachycardia.
  • 1,000 ml of blood loss will usually produce tachycardia greater than 100, but otherwise, the casualty may appear normal.
  • 1,500 ml of blood loss may be associated with changes in mental status, a weak radial pulse, persistent tachycardia, and tachypnea.
  • 2,000 ml of blood loss is accompanied by confusion and lethargy, a weak radial pulse often greater than 120, and tachypnea greater than 35. This amount of blood loss is possibly fatal if not managed quickly.
  • And 2,500 ml of blood loss will usually present with the casualty unconscious, no radial pulse, a carotid pulse greater than 140, and tachypnea greater than 35. This amount of blood loss will be fatal without immediate and rapid intervention.

So, you can see that by following the patient’s clinical status you may be able to detect persistent blood losses, even if there isn’t an obvious external loss.


Acidosis, coagulopathy, and hypothermia occurring together in a trauma casualty is referred to as the lethal triad.

Acidosis is most commonly the result of lactic acid buildup as cells revert to anaerobic processes in the absence of adequate cellular oxygenation (or shock). Sometimes there is a respiratory contribution if the respiratory drive is blunted and there is a buildup of carbon dioxide, but the metabolic acidosis from lactic acid buildup in trauma tends to be the predominant issue.

Coagulopathy can result from direct losses of clotting factors and platelets due to massive hemorrhage but can be accentuated by hemodilution if fluids are replaced by crystalloid or colloid fluids that do not replace clotting factors and platelets like you would get from using whole blood transfusions as fluid replacement therapy. Additionally, the function of clotting factors is temperature-dependent and hypothermia leads to clotting factor dysfunction, even if there is an adequate quantity.

Hypothermia results from a combination of environmental factors (exposure, even in warmer climates) and physiologic responses to blood loss. As mentioned previously, the functions of the clotting cascade are impaired in hypothermia, and further blood loss from coagulopathy leads to increasing hypothermia. This vicious cycle of acidosis, hypothermia, and coagulation (or the lethal triad) requires prevention management strategies at each level.

In other words, prevent and/or treat hypothermia, as we’ll discuss in module 12, prevent acidosis by correcting hypovolemia with fluids that support increased oxygenation (in particular, blood products), and prevent coagulopathy by decreasing direct losses from hemorrhage and clotting factor dysfunction by treating hypothermia.


Preventative Measures

  • Control Hemorrhage
  • Prevent and treat shock
  • Fluid resuscitation
  • Hypothermia (active/passive)
  • Reassess frequently for recurrence

Indications for Establishing IV Access

  • Shock
  • Significant risk of developing shock
  • Needs medications, cannot take orally
  • 18-gauge IVs are adequate, even for rapid blood transfusions
  • Flush saline locks after insertion and every 2 hours
  • When administering fluids, secure the IV lines to avoid dislodging the catheter

Field-Ruggedized Saline Lock Advantages

  • Easier to move a casualty without an IV line and bag
  • Less likely to dislodge during movement
  • Conservation of limited IV fluids
  • Rapid IV access is still available
  • Reduced equipment loads for the Combat Medic


Occasionally, casualties will not respond to fluid resuscitation, even when blood products are used, and shock will either persist or worsen. If this occurs, a thorough reassessment of the casualty must be performed to ensure that all sources of bleeding have been addressed. This includes reassessing all external hemorrhage control measures (tourniquets, wound packing, etc.), applying or repositioning a pelvic compression device, administering TXA if it has not already been done, and continuing with fluid resuscitation with blood products, if possible.

If these measures do not lead to improvement in the casualty status, consideration of an unrecognized tension pneumothorax should be suspected. Certainly, this would be supported by a decreased oxygen saturation (<90%) and absent breath sounds on one side or in a casualty who previously was treated successfully for a tension pneumothorax; but even without all of those symptoms, treatment with a needle decompression of the chest (NDC) should be considered. If not already done, treat indications with repeated Needle Decompression of the Chest (NDC), up to 2 times.

Also, depending on the mechanism of injury, signs, and if shock persists, consider decompressing the opposite side of the chest if indicated.


Intravenous (IV) access is indicated if the casualty is in hemorrhagic shock or at significant risk of shock or if the casualty needs medications but cannot take them by mouth. So not every casualty needs an IV, and some of them will be able to tolerate oral fluid replacement therapy, saving limited IV fluids and blood products for others.

A saline lock is preferred compared to a Direct Line, for several reasons:

  • It is easier to move a casualty without an IV line and bag.
  • The chance of having the catheter dislodged is less than with an attached IV line.
  • IV fluids are conserved for those who really need them instead of being used to keep a line patent.
  • Rapid IV access is still available, as needed.
  • The amount of equipment the Combat Medic needs to carry and maintain is reduced.


This video will go over the proper techniques for inserting a field-ruggedized IV saline lock.


IO access is preferred when vascular access is needed but two IV attempts have failed and/or access is not quickly obtainable via the IV route. Starting an IV on someone in shock, with diminished perfusion of the extremities, may be very challenging, and IO techniques do not rely on expanded veins for successful placement. Intraosseous access has a higher success rate when compared to IV access in limited visibility environments.

As with IV access, not all IO access requires that fluids be continuously administered.

Currently, there isn’t a list of IO devices that are specifically recommended by the Committee on Tactical Combat Casualty Care (CoTCCC). However, there are a few that seem to be more commonly used in TCCC settings, to include the FAST1® Intraosseous Infusion System and the EZ-IO® system. The FAST1 is used at a sternal insertion site, while the EZ-IO can be used at a sternal, a humeral, or a tibial insertion site. Each system has its own guidance on insertion methods and procedures; it is imperative that you spend time training on the device (or devices) that you are likely to deploy with.

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The FAST1 system should be avoided in casualties of small stature (less than 50 kg) who have had significant chest trauma (in particular a flail chest) or if there is a scar indicating a prior sternotomy.


Of note, studies have been done looking at the flow rates of the devices in cadavers, and over 5 minutes under the same pressure-infusion parameters, the FAST1 infused 469 ml, the EZ-IO at a humeral site infused 286 ml, and the EZ-IO at a tibial site infused 154 ml. Given time, any of them will allow for fluid resuscitation, but in a situation where time is of the essence, consideration of the faster infusion times may be warranted.

Avoid FAST1 devices in casualties with significant chest injuries or who are small in stature.

EZ-IO kits can come with multiple needle sizes based on both the age and size of the casualty and the intended insertion site. And the needles can be inserted using a drill or they can be inserted manually using a twisting motion. The subsequent videos will explain some of these considerations in more detail.


This video will go over the proper techniques for inserting a FAST1 intraosseous device.


This video will go over the proper techniques for inserting an EZ-IO intraosseous device in the humerus.


This video will go over the proper techniques for inserting an EZ-IO intraosseous device in the tibia.


Isolated extremity hemorrhage control has significantly improved with the routine use of tourniquets, and junctional hemorrhage is more effectively addressed with CoTCCC-recommended hemostatic dressings or junctional tourniquets. As a result, noncompressible hemorrhage is now the cause of up to 67% of hemorrhagic deaths on the battlefield.

Tranexamic acid (TXA) has been widely used for decades to prevent blood loss in surgical settings by inhibiting the breakdown in clots that naturally occur in the fibrinolytic process. And since its inclusion in the TCCC guidelines in 2011, additional studies in both military and civilian prehospital care settings have confirmed that it is beneficial in trauma casualties, as well.

Its mechanism of action allows for maintenance of clots that have been formed in areas where external controls measures (tourniquets, hemostatic dressings, etc.) are ineffective, though it is also indicated in severe bleeding from injuries that are likely to be managed with massive hemorrhage control measures you have already learned. In addition to its beneficial effects in cases of severe bleeding, other studies have demonstrated improvement in both mortality and morbidity from head trauma and traumatic brain injury (TBI), and that has recently been added to the list of indications for TXA administration.

The dosage, route(s), and indications for administering TXA include:


2 gm slow IV or IO push, as soon as possible (NOT later than 3 hours after injury)


Tranexamic Acid is available IV or IO form

INDICATIONS for Administering TXA

  • Hemorrhagic shock
  • Elevated lactate
  • One or more major amputations
  • Penetrating torso trauma
  • Evidence of severe bleeding


  • A casualty with signs or symptoms of significant TBI
  • Altered mental status associated with blast injury or blunt trauma.


Although TXA is very stable throughout a range of temperatures for several days (preferably, 59°-86° F), there are no studies to support storage outside of the original packaging (for example, in a pre-drawn syringe). Avoid exposure to extreme environments during missions and store in a more controlled environment between missions.

Remember, administer 2 grams of TXA using a slow IV or IO push as soon as possible, if it is indicated.


Hypersensitivity to TXA, subarachnoid hemorrhage, active intravascular clotting, considered relatively safe in pregnancy, if clinically indicated


Blurred vision or impaired color vision, nausea, vomiting, diarrhea (temporary)


Factor IX complex concentrates or anti-inhibitor coagulant concentrates (risk of thrombosis may be increased)


30 sec - 5 min / 30 min - 2 hr / 24 hr


Administer as soon as possible but not later than 3 hours after injury.

Studies have confirmed that TXA can be safely administered in the same IV line as blood, crystalloid fluids, and Hextend®.



PDF 1 FAST1 Intraosseous Access Skills Card

FAST1 Intraosseous Access

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PDF 2 EZ-IO Humerus Intraosseous Access Skills Card

EZ-IO Humerus Intraosseous Access

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PDF 3 EZ-IO Tibial Intraosseous Access Skills Card

EZ-IO Tibial Intraosseous Access

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This video will recap some of the important concepts of shock recognition and management.


The second part of circulation management in TFC focuses on shock recognition and management, intravenous or intraosseous access, and TXA administration.

The signs and symptoms of shock, the use of peripheral pulses and level of consciousness in the determination of shock, the lethal triad of shock, and refractory shock were discussed.

Additionally, the indications for and methods of establishing both IV and IO access were identified, as well as the indications and methods of administering TXA.

The skills that were taught and practiced included placing a field-ruggedized saline lock and establishing IO access using both the FAST and EZ-IO intraosseous systems, as well as demonstrating the administration of TXA.

The next module will focus on another aspect of the circulation phase of the MARCH-PAWS sequence in the Tactical Field Care environment: hemorrhagic shock fluid resuscitation.


To close out this module, check your learning with the questions below (answers under the image).


Check on learning


What are the most reliable indicators of shock in a TFC setting?

The two most reliable indicators of shock in a TFC setting are an altered mental status in the absence of head injury and an absent or weak radial pulse.

What is the definition of shock?

Progressive cellular and tissue hypoxia leading to organ damage and, if not treated, death.

If all hemorrhage control measures have been applied and fluid resuscitation does not improve shock (refractory shock), what potentially unrecognized injury should be considered, and how would you treat it?

If these measures do not lead to improvement in the casualty status, consideration of an unrecognized tension pneumothorax should be suspected. Treatment with a needle decompression of the chest (NDC) should be considered. And, if two NDCs have failed to provide improvement, it may be necessary to perform a finger thoracostomy or insert a chest tube.

Should you establish IV access on all casualties in case they deteriorate?

Not every casualty needs an IV, and some of them will be able to tolerate oral fluid replacement therapy, saving limited IV fluids and blood products for others.

What is the proper protocol for administering tranexamic acid?

2 grams of tranexamic acid should be administered via slow IV or IO push as soon as possible but NOT later than 3 hours after injury.



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