Module 3 · Page 1
MODULE 3: Circulation, Blood Pressure & Shock MEMORIZE → UNDERSTAND → CONNECT → APPLY Goal: Understand WHY heart rate, blood pressure, breathing, skin, and mental status change together. Use the explanation to reason through new EMT patient scenarios. Source note: Original supplemental study material based on the supplied Emergency Care, 14th edition review topics, not a reproduction of its unseen chapters. Check procedures and exact treatment algorithms against Army course instructions and current local EMS protocols. 1 | Memorize the basic terms Heart rate (HR): Beats per minute; typical resting adult range 60–100. Stroke volume (SV): Blood pumped by the heart with each beat. Cardiac output (CO): Total blood pumped each minute: CO = HR × SV. Systolic BP: Top number, pressure during heart contraction. Diastolic BP: Bottom number, pressure during relaxation.
Module 3 · Page 2
Preload: Blood returning to and filling the heart before contraction. Vasoconstriction: Blood vessels narrow, increasing resistance. Perfusion: Blood actually reaching tissues to supply oxygen and nutrients. Shock: Inadequate tissue perfusion/oxygen delivery relative to need; it does not require low BP. Memory aid: HR = how often the pump beats. SV = blood per beat. CO = blood per minute. BP = pressure in the pipes. Perfusion = whether organs get the flow they need. 2 | Understand WHY HR rises when blood is lost Blood loss → less blood returns to heart → lower filling (preload) → lower stroke volume → threatened cardiac output.
Module 3 · Page 3
The body senses a threat to circulation. The sympathetic nervous system makes the heart beat faster and many vessels constrict. This can preserve blood pressure temporarily, even as blood volume falls. Compensation blood loss less blood pumped per beat HR rises; vessels constrict BP may stay normal early Key distinction: A normal blood pressure is not proof of adequate perfusion. Low BP may appear only after the body can no longer compensate. Look at the entire patient. 3 | Connect each sign to its cause Fast HR: The body tries to preserve CO when SV falls. Pain and fear can also raise HR. Pale, cool skin: Vasoconstriction reduces blood flow to skin to prioritize vital organs. Clammy skin: Sympathetic activation can stimulate sweating.
Module 3 · Page 4
Rapid RR: Pain and stress increase breathing; poor perfusion can cause metabolic acidosis that stimulates faster ventilation. Restlessness/confusion: Pain, fear, and insufficient cerebral oxygen delivery can affect mental status; worsening confusion is dangerous. Weak pulse: A lower SV may produce a weaker peripheral pulse despite fast HR. Falling BP: Volume, pumping ability, or vascular resistance can no longer maintain pressure. 4 | Compensated versus decompensated shock Compensated example: After a fall: HR 126, BP 118/76, RR 27, cool clammy skin. WHY? HR and vessel constriction may still maintain BP despite threatened tissue perfusion. Decompensated example: After a fall: HR 140, BP 82/48, RR 32, confusion. WHY? Compensatory mechanisms are no longer maintaining adequate pressure and flow. These are patterns, not absolute rules. Age, medications (such as beta blockers), and the shock mechanism can change the expected vital signs.
Module 3 · Page 5
5 | Four reasons shock can happen Hypovolemic: Too little circulating volume → less preload/SV. Examples: bleeding, severe fluid loss. Cardiogenic: Pump fails → insufficient forward flow despite available blood. Example: major heart injury. Distributive: Abnormal vessel dilation/distribution → inadequate effective circulation. Examples: sepsis, anaphylaxis; neurogenic shock may cause bradycardia. Obstructive: Mechanical obstruction prevents normal filling or forward flow. Examples: tension pneumothorax, cardiac tamponade. Ask yourself: Is the problem the volume, the pump, the vessels, or an obstruction? Hypovolemic volume Cardiogenic pump Distributive vessels Obstructive obstruction 6 | Connect the lungs and circulation
Module 3 · Page 6
Oxygen-delivery chain: Open airway → adequate ventilation → oxygen enters blood → heart pumps blood → blood reaches tissues. Oxygen delivery open airway adequate ventilation oxygen enters blood heart pumps blood blood reaches tissues If ventilation fails, oxygenation and CO2 removal can fail, and the heart may speed up in response to stress. If circulation fails, even oxygen-rich blood may not reach tissues. Why SpO2 can be normal in shock: It estimates the percentage of hemoglobin carrying oxygen, not blood volume, cardiac output, or tissue perfusion. A 99% reading does not rule out hemorrhage.
Module 3 · Page 7
7 | How to think through “What do you do FIRST?” 1. Look for immediate life threats. 2. Control catastrophic external bleeding when present. 3. Assess airway and breathing adequacy; support ventilation if inadequate. 4. Assess circulation and perfusion, control other bleeding, prevent heat loss, and arrange prompt transport for suspected shock according to protocol. The priority changes with the scenario. Massive external bleeding and inadequate ventilation both demand immediate intervention; read which threat is actually present. 8 | Fully guided patient scenario Scene: A 21-year-old male fell from a roof. HR 126, BP 120/78, RR 28, pale cool skin, alert but restless. No obvious external bleeding. What is abnormal? High HR, high RR, cool skin, and restlessness; BP is not hypotensive. What could cause this? Internal bleeding is concerning after major trauma; pain and anxiety are also possible. WHY does it fit? Blood loss may lower SV. Sympathetic activity raises HR and constricts skin
Module 3 · Page 8
vessels to preserve BP. Stress or impaired perfusion may increase RR. What else should you assess? Mechanism, mental-status trend, pulse quality, repeat vital signs, signs of bleeding, and airway/breathing. What is the priority? Manage immediate threats, evaluate for bleeding and shock, prevent heat loss, and prioritize transport per protocol. Do not dismiss shock because BP is 120/78. 9 | Memory retrieval (answer before revealing)
What is cardiac output?Think through your answer, then select to reveal
HR × SV.
Why does HR rise in hemorrhage?Think through your answer, then select to reveal
It may compensate for falling stroke volume.
Module 3 · Page 9
Why can BP stay normal early?Think through your answer, then select to reveal
Tachycardia and vasoconstriction help maintain pressure.
Why is skin cool and pale?Think through your answer, then select to reveal
Peripheral vasoconstriction decreases skin blood flow.
Why can RR increase in shock?Think through your answer, then select to reveal
Stress and sometimes metabolic acidosis.
Does SpO2 measure perfusion?Think through your answer, then select to reveal
No. It estimates oxygen saturation.
Name four shock mechanisms.Think through your answer, then select to reveal
Hypovolemic, cardiogenic, distributive, obstructive.
Practice — Question 1
Practice — Question 2
Practice — Question 3
Practice — Question 4
Practice — Question 5
Practice — Question 6
Practice — Question 7
Practice — Question 8
Practice — Question 9
Practice — Question 10
Practice — Question 11
Practice — Question 12
Module 3 · Page 22
12 | Study check Score: ____ / 12. Aim for 10/12 on fresh questions as a study target, not as a stated NREMT passing score. A correct guess is not mastery: explain WHY aloud before checking. Missed questions 1–3 or 9? Revisit sections 2–4. Missed 4 or 6? Revisit section 6. Missed 5 or 11? Revisit section 5. Missed 10? Revisit section 7. One-minute recap: CO = HR × SV. Blood loss can lower SV. HR and vasoconstriction may preserve BP early. Skin and mental status reveal perfusion clues. Normal BP or SpO2 does not rule out shock. Always identify the immediate life threat.