Shock Recognition & Treatment — Lesson 5

Overview

Learning Objectives

Define shock and explain the pathophysiology of inadequate tissue perfusion
Classify the major types of shock (hypovolemic, distributive, obstructive, cardiogenic)
Recognize early and late signs of shock in a wilderness casualty
Treat shock using field-appropriate interventions
Determine evacuation urgency for shock patients

Shock is one of the most critical life-threatening emergencies in wilderness medicine. It represents the body's failure to deliver adequate oxygen to vital organs and tissues. Despite being common in trauma, shock is frequently underrecognized, leading to delayed treatment and poor outcomes.

Shock kills quietly, and the early signs are easy to wave off. Learn to spot them before the blood pressure falls — because by then you're behind.

Critical Point: Shock is progressive. Early recognition and treatment are essential. A patient in compensated shock may appear relatively well but can deteriorate rapidly to decompensated shock and death if untreated.

What is Shock?

Definition and Pathophysiology

Shock is a state of inadequate tissue perfusion leading to cellular hypoxia and inability to meet metabolic demands.

At the cellular level, oxygen delivery can be understood through a simple relationship — the oxygen delivery relationship:

Oxygen Delivery (DO₂) = Cardiac Output (CO) × Arterial Oxygen Content (CaO₂)

This equation shows that adequate oxygen delivery requires:

Sufficient cardiac output (heart rate × stroke volume)
Adequate oxygen content in blood (hemoglobin, oxygen saturation)

Why Do Cells Need Oxygen?

Cells use oxygen for aerobic metabolism to produce ATP, the energy currency of life. Without adequate oxygen, cells switch to anaerobic metabolism, which produces lactate and leads to:

Lactic acidosis
Decreased ATP production
Cellular dysfunction and death
Organ system failure

Compensatory Mechanisms

When tissue perfusion first decreases, the body activates compensatory responses:

Increased Heart Rate (Tachycardia): The sympathetic nervous system increases HR to maintain cardiac output despite reduced stroke volume (e.g., from blood loss).

Vasoconstriction: Peripheral vessels constrict to maintain central perfusion pressure and redirect blood to vital organs (brain, heart).

Increased Respiratory Rate (Tachypnea): Breathing increases to maximize oxygen uptake.

Compensated vs. Decompensated Shock

Compensated Shock: The body's compensatory mechanisms are working. Blood pressure remains normal, but the patient shows signs of sympathetic activation (anxiety, tachycardia, tachypnea). If treated in this phase, the patient usually survives.

Decompensated Shock: Compensatory mechanisms have failed. Blood pressure drops, mental status changes, organs begin to fail. This phase is life-threatening and must be managed as an emergency.

Critical Pearl: Hypotension is a LATE sign of shock. A normal blood pressure does NOT rule out shock. Look for tachycardia and other early signs!

Types of Shock

Shock is classified by the underlying cause. Understanding the type helps guide treatment.

Type	Cause	Example Scenario	Key Field Signs	Field Treatment Priority
Hypovolemic	Loss of blood or body fluids	Hemorrhage, severe dehydration, burns	Tachycardia, pale skin, weak pulse, low BP (late)	Stop bleeding, position, keep warm, evacuate
Distributive	Massive vasodilation; loss of vascular tone	Sepsis, anaphylaxis, neurogenic (spinal injury)	Tachycardia, flushed or blotchy skin, wide pulse pressure (early)	Address cause (help patient use their OWN epinephrine auto-injector for anaphylaxis; spinal motion restriction for neurogenic), keep warm, evacuate
Obstructive	Physical blockage to blood flow	Tension pneumothorax, cardiac tamponade, massive PE	Tachycardia, JVD, muffled heart sounds, difficulty breathing	Recognize the pattern, position of comfort, EMERGENT evacuation — definitive treatment is hospital-level
Cardiogenic	Heart failure as a pump	Myocardial infarction, severe arrhythmia	Tachycardia, pulmonary edema, pale, weak pulse	Position upright if conscious, oxygen if available, urgent evacuation

Hypovolemic Shock (Most Common in Wilderness)

Results from loss of circulating blood volume (hemorrhage) or other body fluids (dehydration, severe burns). Treatment focuses on controlling bleeding, giving oral fluids when safe, keeping the patient supine (flat) and warm, and evacuating.

Distributive Shock

Septic Shock: Severe infection causes vasodilation and capillary leak. Usually develops over hours in wilderness (e.g., infected wound).

Anaphylactic Shock: Allergic reaction causes rapid histamine release and profound vasodilation. True emergency requiring immediate epinephrine.

Neurogenic Shock: Spinal cord injury disrupts sympathetic outflow, causing loss of vascular tone and bradycardia (a unique finding — hypotension WITH a slow heart rate). It can persist for days to weeks. Field care: supine (flat), maintain spinal motion restriction, aggressively prevent heat loss, evacuate.

Obstructive Shock

Physical obstruction prevents blood return to or ejection from the heart. Examples: tension pneumothorax (collapsed lung compressing heart), cardiac tamponade (fluid around heart), massive pulmonary embolism. Field care: recognize the pattern, position of comfort, EMERGENT evacuation — definitive treatment is hospital-level.

Cardiogenic Shock

The heart itself fails as a pump (MI, severe arrhythmia). Less common in wilderness but must be recognized. Treatment is supportive positioning and urgent evacuation.

Recognizing Shock

Early (Compensated) Shock Signs

Look for these subtle but critical findings:

Tachycardia: Heart rate >100 bpm at rest (earliest measurable sign)
Tachypnea: Respiratory rate >20 breaths/min
Anxiety and Restlessness: Patient feels ill, fearful
Pale or Cool Skin: From vasoconstriction (check core body areas)
Weak Pulse: Diminished amplitude

Late (Decompensated) Shock Signs

These indicate irreversible shock is developing:

Bradycardia: Heart rate drops as cardiac function fails (bad sign)
Hypotension: Systolic <90 mmHg
Altered Mental Status: Confusion, lethargy, loss of consciousness
Mottled Skin: Blotchy, cyanotic appearance
Cold Extremities: Severe peripheral vasoconstriction
Weak or Absent Pulse: Central pulse barely palpable

Vital Sign Thresholds

Finding	Concerning Value	Interpretation
Systolic BP	<90 mmHg	Decompensated shock (immediate treatment)
Heart Rate	>100 bpm at rest	Early shock compensation
Respiratory Rate	>20 breaths/min	Compensation for metabolic acidosis
Mental Status	Altered, confused	Cerebral hypoperfusion (urgent)

Field Treatment of Shock

Position: Supine (Flat)

Place the patient flat on their back (supine). The shock treatment standard is: supine, prevent heat loss, treat the cause, evacuate. Routine leg elevation is no longer taught — it has been dropped from first-aid guidance because it does not improve outcomes.

Keeps the heart and brain at the same level, supporting cerebral perfusion
Do NOT move patients with suspected spine, pelvis, or leg injuries just to reposition them
Makes monitoring and reassessment easier

Exceptions: A patient with difficulty breathing may need the head and torso elevated slightly; a conscious patient who is vomiting or at risk of vomiting may need the recovery position (on their side). Comfort and airway come first.

Keep Warm

Prevent heat loss by:

Removing wet clothing
Covering with blankets or insulation
Avoiding excessive cooling (hypothermia worsens shock)

Why Keep Warm? Hypothermia causes vasoconstriction and shunts blood away from skin, worsening shock. Additionally, the combination of shock + hypothermia dramatically increases mortality.

Address the Cause

Treat the underlying condition:

Hemorrhage: Control bleeding with direct pressure and tourniquet as needed
Dehydration: Oral rehydration — small frequent sips (if conscious and able to swallow safely)
Anaphylaxis: Help the patient use their OWN epinephrine auto-injector immediately
Spinal Injury: Maintain spinal motion restriction (neurogenic shock)

Oral Fluids (When Appropriate)

A conscious, alert patient with no signs of abdominal injury who can swallow safely may be given oral fluids:

Water or dilute electrolyte solution
Small frequent sips, not boluses
DO NOT give fluids if patient is vomiting, has altered mental status, or suspected abdominal injury (fluid may worsen internal bleeding)

Monitoring

Reassess vital signs and mental status frequently:

Heart rate and rhythm
Blood pressure (if possible)
Skin temperature and color
Level of consciousness
Note trends: improving or worsening?

Evacuation Urgency

ANY patient with signs of shock is an urgent/emergent evacuation.

Decompensated shock (hypotension, altered mental status): EMERGENT — immediate evacuation with ALS (advanced life support) en route
Compensated shock (tachycardia, anxiety, normal BP): URGENT — evacuate immediately but may tolerate slower movement if necessary
Suspected shock from any mechanism: Do not delay evacuation for field interventions

Clinical Scenarios

Scenario 1: Hemorrhagic Shock

A 35-year-old hiker was using an axe to cut firewood when the blade slipped, causing a deep laceration to the medial thigh. You arrive 10 minutes later to find the patient sitting upright, looking anxious. Vital signs: HR 112, RR 22, BP 118/82 (baseline unknown), pale skin, visible bleeding continuing from the wound.

Analysis: This is compensated hypovolemic shock (hemorrhagic shock). Early signs present: tachycardia, tachypnea, anxiety, pale skin. BP is still normal but this patient is decompensating.

Immediate Actions:

Deep thigh wound with ongoing bleeding in a patient showing shock signs = life-threatening hemorrhage: apply a tourniquet above the wound IMMEDIATELY (direct pressure while it is readied)
Position supine (flat) — do not elevate the legs
Keep warm with blankets
Give nothing by mouth
URGENT evacuation — call for helicopter or organize ground evacuation immediately
Reassess vitals q5-10 min; monitor for deterioration to decompensated shock

Expected Outcome: With prompt bleeding control and evacuation, this patient has good survival chance. Delay increases risk of decompensation.

Scenario 2: Anaphylactic Shock

While camping, a 28-year-old woman unknowingly sits on a yellow jacket nest. She is stung multiple times and runs to the tent. Within 5 minutes, she reports difficulty breathing, tongue swelling, and widespread itching. Vital signs: HR 128, RR 28, BP 92/60, skin mottled and flushed, wheezing audible, facial edema present.

Analysis: This is anaphylactic shock (distributive shock), a medical emergency. The patient shows signs of severe allergic reaction with shock (hypotension, tachycardia, altered perfusion).

Immediate Actions:

IMMEDIATELY help her use her OWN epinephrine auto-injector (0.3 mg IM into the outer thigh) — this is life-saving and should NOT be delayed
Repeat the epinephrine in 5-15 minutes if symptoms do not improve or return
Place supine (flat); if breathing is difficult, allow her to sit up slightly — do not elevate the legs
Manage airway — patient has airway compromise (swelling); monitor closely
Administer supplemental oxygen if available
After epinephrine, an oral antihistamine may be given as an adjunct — it is never a substitute for epinephrine
Keep warm
EMERGENT evacuation to hospital (anaphylaxis can recur in biphasic reactions)
Monitor airway patency and vital signs continuously

Key Pearl: Epinephrine is the only definitive field treatment for anaphylaxis. Do not delay it for other medications.

Knowledge Check

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Summary & Key Takeaways

Key Concepts to Remember:

Shock = inadequate tissue perfusion leading to cellular hypoxia
Tachycardia is often the EARLIEST sign; hypotension is a LATE sign
Four types: hypovolemic (most common), distributive, obstructive, cardiogenic
Compensated vs. decompensated: compensated may look well but can deteriorate rapidly
Field treatment: position supine (flat), prevent heat loss, treat the cause, monitor, evacuate urgently
ALL suspected shock = urgent evacuation

Clinical Pearl Summary

In wilderness settings, you will most commonly encounter hypovolemic shock (from trauma) and distributive shock (from anaphylaxis or infection). Remember: a patient can be in significant shock with a normal blood pressure. Look for the complete clinical picture—tachycardia, anxiety, pale skin, weak pulse—not just BP numbers.

Glossary of Terms

Aerobic Metabolism

Energy production in cells using oxygen; produces ATP efficiently and is the normal state. When oxygen supply falls, cells switch to anaerobic metabolism.

Anaerobic Metabolism

Energy production without oxygen; produces lactate and less ATP. Occurs during shock and hypoxia; leads to lactic acidosis.

Cardiogenic Shock

Shock caused by heart pump failure (e.g., MI, severe arrhythmia); less common in wilderness.

Compensated Shock

Early shock where the body's compensatory mechanisms (tachycardia, vasoconstriction) maintain near-normal blood pressure. Patient appears anxious but may not look critically ill.

Decompensated Shock

Late shock where compensatory mechanisms fail; blood pressure drops, mental status changes, organ failure begins. Life-threatening.

Distributive Shock

Shock caused by vasodilation and loss of vascular tone (septic, anaphylactic, neurogenic); characterized by wide pulse pressure.

Hypovolemic Shock

Shock from loss of circulating volume (blood or other fluids); most common type in trauma and wilderness emergencies.

Lactic Acidosis

Accumulation of lactate in blood due to anaerobic metabolism during shock; worsens cellular dysfunction and is a marker of tissue hypoxia.

Mottled Skin

Blotchy, cyanotic appearance of skin in decompensated shock from severe peripheral vasoconstriction and poor perfusion.

Neurogenic Shock

Shock from spinal cord injury causing loss of sympathetic tone and peripheral vasodilation; can persist for days to weeks. Distinguished by hypotension WITH bradycardia.

Obstructive Shock

Shock caused by physical blockage to blood flow (tension pneumothorax, cardiac tamponade, PE); requires EMERGENT evacuation — definitive treatment is hospital-level.

Oxygen Delivery Relationship

Oxygen delivery (DO₂) = cardiac output × arterial oxygen content. Shows that perfusion requires both heart function and oxygen content in the blood.

Perfusion

The flow of blood (and oxygen) to tissues. Inadequate perfusion is the core problem in shock.

Shock

A state of inadequate tissue perfusion and cellular hypoxia; if untreated, leads to organ failure and death.

Tachycardia

Elevated heart rate (>100 bpm at rest); one of the earliest signs of shock as the heart attempts to maintain cardiac output.

Tachypnea

Elevated respiratory rate (>20 breaths/min); occurs in shock due to sympathetic activation and metabolic acidosis.

Vasoconstriction

Narrowing of blood vessels to increase peripheral resistance and redirect blood to vital organs; an important compensatory mechanism in shock.