Shock
A life-threatening condition in which the body's tissues do not receive enough oxygenated blood to function, most commonly caused in trauma by severe blood loss.
In the Field
Shock is the engine that drives most preventable trauma deaths. The textbooks teach you to assess shock by checking blood pressure, looking at skin color, watching for diaphoresis, monitoring an EKG. None of that works in a tactical environment. You are in low light, behind cover, with gloves on, and the patient is wearing a uniform you cannot easily expose. The single most reliable shock indicator you have under those conditions is the radial pulse: whether you can feel it, how fast it is, and whether it is strong or weak. Everything else comes later, when the environment allows it.
Common Mistake
Trying to apply hospital-style shock assessment in a tactical setting where most traditional indicators are not observable, instead of using the radial pulse as the primary field indicator.
Technical Detail
Shock is a state of inadequate tissue perfusion, in which oxygen delivery to cells throughout the body falls short of what they need to maintain normal function. Untreated, shock progresses to organ dysfunction and death.
Categories of shock. Several distinct mechanisms can produce shock, each requiring different treatment:
Hypovolemic shock. Caused by loss of circulating blood volume. In trauma, this is almost always hemorrhagic shock from external or internal bleeding. The dominant form of shock in tactical medical contexts.
Distributive shock. Caused by abnormal dilation of blood vessels and redistribution of blood flow. Includes septic shock (infection), anaphylactic shock (allergic reaction), and neurogenic shock (spinal cord injury). Neurogenic shock typically presents with a slow heart rate and warm, dry skin, the opposite of the pattern seen in hemorrhage.
Cardiogenic shock. Caused by failure of the heart as a pump. More common in medical settings such as heart attack, though blunt cardiac injury can produce it in trauma.
Obstructive shock. Caused by physical obstruction of blood flow into or out of the heart. In trauma, the two most relevant causes are tension pneumothorax, where rising pressure in the chest impairs the return of blood to the heart, and cardiac tamponade, where blood collecting around the heart prevents it from filling.
Classes of hemorrhagic shock. The American College of Surgeons categorizes hemorrhagic shock into four classes based on the percentage of blood lost and the physiologic response:
Class I (up to 15 percent blood loss). Minimal physiologic compensation. Mild anxiety. Normal vital signs.
Class II (15 to 30 percent blood loss). Increased heart rate, mild anxiety, narrowed pulse pressure. Blood pressure typically remains normal due to compensation.
Class III (30 to 40 percent blood loss). Significant tachycardia, normal to decreased blood pressure, confusion, decreased urine output. Compensation is failing.
Class IV (over 40 percent blood loss). Severe tachycardia, marked hypotension, lethargy or unconsciousness. Death is imminent without intervention.
These classes are useful as a teaching framework, but real patients rarely follow them precisely and blood loss percentage cannot be measured in the field. Field assessment relies on observable surrogate signs.
Field assessment in the tactical environment. Many of the shock assessment methods that hospital and routine EMS practitioners rely on are not feasible in a tactical setting:
Blood pressure measurement. A blood pressure cuff requires time, a stable patient, an uninjured arm, and an environment quiet enough to hear or read the result. None of these are reliably available under threat conditions or during a mass casualty incident.
Skin color and capillary refill. Low light, vehicle interiors, night operations, dust and contamination, dark or camouflaged uniforms, and the patient's own skin tone all interfere with visual assessment of color and refill.
Diaphoresis (sweating). Difficult to assess on a patient who is already wet from exertion, environmental conditions, blood, or contamination, and it cannot be reliably distinguished from sweating unrelated to shock.
ECG monitoring. Requires patient exposure, electrode placement on bare skin, a stable cable run, and a working monitor. Generally available only during evacuation or at a Casualty Collection Point, and rarely at the point of injury.
Mental status. Altered mental status in the absence of head injury is one of the two primary shock indicators in TCCC guidance. It requires interpretation, because a patient who is anxious from the threat itself or quiet from training may not show obvious changes, and head trauma, intoxication, or medications can produce changes unrelated to blood loss. Confusion and lethargy are reliable findings but indicate the patient is already decompensating.
The radial pulse. The radial pulse is the other primary shock indicator and the most feasible one to assess in the tactical environment. It can be checked without removing equipment, in low light, from behind cover, and through tactical gloves with practice. Four findings carry significant weight:
Absent radial pulse. An absent radial pulse has traditionally been associated with a systolic blood pressure below roughly 80 mmHg. Research has shown this correlation to be imprecise, but an absent radial pulse in a bleeding casualty indicates significant shock requiring immediate intervention regardless of the exact pressure.
Present radial pulse. A palpable radial pulse confirms that the heart is still generating enough pressure to reach the extremities, regardless of the exact systolic value. This makes it a useful baseline for trending and one of the endpoints TCCC uses to guide resuscitation. A present pulse does not rule out shock, since compensatory mechanisms maintain peripheral pulses through early and moderate blood loss. Its quality, its rate, and any change over time carry more meaning than its presence alone.
Weak or thready radial pulse. A pulse that is present but difficult to feel reflects reduced stroke volume and constriction of peripheral vessels. It can accompany both compensated and decompensated shock and warrants close reassessment.
Rapid pulse rate. A radial pulse rate above roughly 100 beats per minute in an adult, particularly with weak quality, suggests compensatory tachycardia from blood loss. Heart rate alone is a limited indicator in this setting, because adrenaline from the threat, physical exertion, and fear raise the heart rate in uninjured operators. Beta blockers can blunt the response, and some patients with significant hemorrhage present with a relatively slow heart rate.
Combined with mental status, the mechanism of injury, and any visible bleeding, the radial pulse provides actionable shock assessment in the time and conditions available at the point of injury.
Other findings available in the field. When operational conditions permit, providers can also use patient reports of anxiety, restlessness, or a sense of impending doom; a visual estimate of blood loss when the wound is accessible; mental status compared to the patient's known baseline; and respiratory rate when the patient is exposed for chest seal application or other interventions.
When formal vital signs become possible. Once the patient reaches Tactical Field Care or an evacuation platform, more comprehensive assessment becomes feasible. Blood pressure measurement, pulse oximetry, ECG monitoring, and a more thorough physical exam are appropriate at that point. Providers use the assessment tools the environment allows and begin treatment based on the findings available, without delaying for equipment that is not yet accessible.
Treatment priority. In hemorrhagic shock, effective treatment depends on stopping the bleeding and replacing lost blood. Tourniquets, wound packing with hemostatic agents, and pressure dressings control compressible hemorrhage at the point of injury. Bleeding inside the chest, abdomen, or pelvis cannot be controlled in the field and requires rapid evacuation to surgical care. Tranexamic acid (TXA) should be given as early as possible, and within three hours of injury, to casualties at risk of significant hemorrhage. Whole blood is the preferred resuscitation fluid, followed by blood component therapy, with crystalloid reserved for situations where no blood products are available. Resuscitation follows the principle of permissive hypotension, restoring enough perfusion to sustain vital organs without raising pressure high enough to disrupt early clot formation. Casualties with suspected traumatic brain injury are the exception, because low blood pressure worsens brain injury outcomes and higher pressure targets apply. Preventing hypothermia is part of shock treatment, since a cold patient loses the ability to form clots effectively.
Decreased blood pressure, when it can be measured, is a late sign of hemorrhagic shock and indicates the patient has already exhausted compensatory mechanisms. Treatment begins well before measurable hypotension develops and is guided by mechanism of injury, visible bleeding, mental status, and the radial pulse.
Categories of shock. Several distinct mechanisms can produce shock, each requiring different treatment:
Hypovolemic shock. Caused by loss of circulating blood volume. In trauma, this is almost always hemorrhagic shock from external or internal bleeding. The dominant form of shock in tactical medical contexts.
Distributive shock. Caused by abnormal dilation of blood vessels and redistribution of blood flow. Includes septic shock (infection), anaphylactic shock (allergic reaction), and neurogenic shock (spinal cord injury). Neurogenic shock typically presents with a slow heart rate and warm, dry skin, the opposite of the pattern seen in hemorrhage.
Cardiogenic shock. Caused by failure of the heart as a pump. More common in medical settings such as heart attack, though blunt cardiac injury can produce it in trauma.
Obstructive shock. Caused by physical obstruction of blood flow into or out of the heart. In trauma, the two most relevant causes are tension pneumothorax, where rising pressure in the chest impairs the return of blood to the heart, and cardiac tamponade, where blood collecting around the heart prevents it from filling.
Classes of hemorrhagic shock. The American College of Surgeons categorizes hemorrhagic shock into four classes based on the percentage of blood lost and the physiologic response:
Class I (up to 15 percent blood loss). Minimal physiologic compensation. Mild anxiety. Normal vital signs.
Class II (15 to 30 percent blood loss). Increased heart rate, mild anxiety, narrowed pulse pressure. Blood pressure typically remains normal due to compensation.
Class III (30 to 40 percent blood loss). Significant tachycardia, normal to decreased blood pressure, confusion, decreased urine output. Compensation is failing.
Class IV (over 40 percent blood loss). Severe tachycardia, marked hypotension, lethargy or unconsciousness. Death is imminent without intervention.
These classes are useful as a teaching framework, but real patients rarely follow them precisely and blood loss percentage cannot be measured in the field. Field assessment relies on observable surrogate signs.
Field assessment in the tactical environment. Many of the shock assessment methods that hospital and routine EMS practitioners rely on are not feasible in a tactical setting:
Blood pressure measurement. A blood pressure cuff requires time, a stable patient, an uninjured arm, and an environment quiet enough to hear or read the result. None of these are reliably available under threat conditions or during a mass casualty incident.
Skin color and capillary refill. Low light, vehicle interiors, night operations, dust and contamination, dark or camouflaged uniforms, and the patient's own skin tone all interfere with visual assessment of color and refill.
Diaphoresis (sweating). Difficult to assess on a patient who is already wet from exertion, environmental conditions, blood, or contamination, and it cannot be reliably distinguished from sweating unrelated to shock.
ECG monitoring. Requires patient exposure, electrode placement on bare skin, a stable cable run, and a working monitor. Generally available only during evacuation or at a Casualty Collection Point, and rarely at the point of injury.
Mental status. Altered mental status in the absence of head injury is one of the two primary shock indicators in TCCC guidance. It requires interpretation, because a patient who is anxious from the threat itself or quiet from training may not show obvious changes, and head trauma, intoxication, or medications can produce changes unrelated to blood loss. Confusion and lethargy are reliable findings but indicate the patient is already decompensating.
The radial pulse. The radial pulse is the other primary shock indicator and the most feasible one to assess in the tactical environment. It can be checked without removing equipment, in low light, from behind cover, and through tactical gloves with practice. Four findings carry significant weight:
Absent radial pulse. An absent radial pulse has traditionally been associated with a systolic blood pressure below roughly 80 mmHg. Research has shown this correlation to be imprecise, but an absent radial pulse in a bleeding casualty indicates significant shock requiring immediate intervention regardless of the exact pressure.
Present radial pulse. A palpable radial pulse confirms that the heart is still generating enough pressure to reach the extremities, regardless of the exact systolic value. This makes it a useful baseline for trending and one of the endpoints TCCC uses to guide resuscitation. A present pulse does not rule out shock, since compensatory mechanisms maintain peripheral pulses through early and moderate blood loss. Its quality, its rate, and any change over time carry more meaning than its presence alone.
Weak or thready radial pulse. A pulse that is present but difficult to feel reflects reduced stroke volume and constriction of peripheral vessels. It can accompany both compensated and decompensated shock and warrants close reassessment.
Rapid pulse rate. A radial pulse rate above roughly 100 beats per minute in an adult, particularly with weak quality, suggests compensatory tachycardia from blood loss. Heart rate alone is a limited indicator in this setting, because adrenaline from the threat, physical exertion, and fear raise the heart rate in uninjured operators. Beta blockers can blunt the response, and some patients with significant hemorrhage present with a relatively slow heart rate.
Combined with mental status, the mechanism of injury, and any visible bleeding, the radial pulse provides actionable shock assessment in the time and conditions available at the point of injury.
Other findings available in the field. When operational conditions permit, providers can also use patient reports of anxiety, restlessness, or a sense of impending doom; a visual estimate of blood loss when the wound is accessible; mental status compared to the patient's known baseline; and respiratory rate when the patient is exposed for chest seal application or other interventions.
When formal vital signs become possible. Once the patient reaches Tactical Field Care or an evacuation platform, more comprehensive assessment becomes feasible. Blood pressure measurement, pulse oximetry, ECG monitoring, and a more thorough physical exam are appropriate at that point. Providers use the assessment tools the environment allows and begin treatment based on the findings available, without delaying for equipment that is not yet accessible.
Treatment priority. In hemorrhagic shock, effective treatment depends on stopping the bleeding and replacing lost blood. Tourniquets, wound packing with hemostatic agents, and pressure dressings control compressible hemorrhage at the point of injury. Bleeding inside the chest, abdomen, or pelvis cannot be controlled in the field and requires rapid evacuation to surgical care. Tranexamic acid (TXA) should be given as early as possible, and within three hours of injury, to casualties at risk of significant hemorrhage. Whole blood is the preferred resuscitation fluid, followed by blood component therapy, with crystalloid reserved for situations where no blood products are available. Resuscitation follows the principle of permissive hypotension, restoring enough perfusion to sustain vital organs without raising pressure high enough to disrupt early clot formation. Casualties with suspected traumatic brain injury are the exception, because low blood pressure worsens brain injury outcomes and higher pressure targets apply. Preventing hypothermia is part of shock treatment, since a cold patient loses the ability to form clots effectively.
Decreased blood pressure, when it can be measured, is a late sign of hemorrhagic shock and indicates the patient has already exhausted compensatory mechanisms. Treatment begins well before measurable hypotension develops and is guided by mechanism of injury, visible bleeding, mental status, and the radial pulse.