1. UC Irvine Medicine Residency Mini Lecture Series Updated May 2018
Shock
UC Irvine Medicine Residency
Mini Lecture Series
Updated May 2018

2. Objectives Know the definition of shock
Understand the pathophysiology of shock
Identify different types of shock

3. Shock: Definition Tissue hypoperfusion
Oxygen consumption > delivery
Cell death > End-organ damage > Multi-system organ failure > Death
Shock occurs when there is decreased tissue perfusion. When oxygen consumption exceeds its delivery, cell death occurs and if prolonged, leads to organ failure and death. Shock is associated with high mortality, and reversing it in a timely fashion is crucial!

4. Signs/Symptoms Evidence of end organ dysfunction:
Evidence of hypo-perfusion:
SBP <90, or decreased SBP by 40 mmHg
MAP <65
Elevated lactic acid
lack of BP response to fluid bolus
prolong capillary refill time
Evidence of end organ dysfunction:
Lightheadedness
AMS
Decreased urine output
Increase serum Cr
Chest pain, changes in EKG, elevated troponin
Signs to suggest shock include the above. Evidence of hypoperfusion results in end organ damage

5. Key Elements of Blood Pressure
Fluid
Pump
Pipes
The cardiovascular system can be simplified into 3 key elements: a fluid (blood), a pump (the heart) that collects and moves the fluid forward, and the pipes (vessels) that distributes it. Hypotension results when one of these parts fails AND the other two are unable to compensate for its loss.
(Figure. Prevent-stroke-and-heart-attack.com)

6. What constitutes blood pressure?
Cardiac output (pump)
Heart rate
Stroke volume
Preload (fluid)
Contractility
Afterload
Systemic vascular resistance (pipe)
(MAP- CVP) = Cardiac Output (CO) x Systemic vascular resistance (SVR)
CO = Heart rate (HR) x Stroke Volume (SV)
Credit -> MKSAP 17
*MAP- mean arterial pressure. *CVP- central venous pressure (which is normally close to 0)
mean arterial blood pressure is determined by the cardiac output (the pump) and systemic vascular resistance (pipes). Cardiac output, in turn, is a function of heart rate and stroke volume.
The heart rate, stroke volume, and peripheral resistance work in equilibrium to maintain circulation.

7. Types of Shock Cardiogenic Hypovolemic Distributive
Three types of shock: cardiogenic, hypovolemic and distributive shock
Distributive

8. Cardiogenic Shock MAP- CVP = (HR x SV) x SVR
1. Abnormal heart rate:
- Tachycardia
- Bradycardia
- Other causes: CHF, MI, valvular abnormalities
“Obstructive Shock”
venous return & outflow
obstruction
- Pulmonary embolism
- Tamponade
- Tension pneumothorax
Heart Rate
Cardiogenic shock results from changes in heart rate.
- Tachycardia decreases short filling time, bradycardia results not enough forward flow. Both can result in inadequate perfusion. Other examples include heart failure (reduced EF, myocardial infarction, valvular dysfunction (AS, MS, mitral regurgitation)
Obstructive shock is a subset of cardiogenic shock, it’s caused by decreased venous return and outflow obstruction.
Causes can be from PE, tamponade, and tension pneumothorax
Note: Can ask audience for examples of each category first.

9. Distributive Shock MAP- CVP = (HR x SV) x SVR
2. Low vascular resistance:
Sepsis
Anaphylaxis
Other Causes: adrenal insufficiency, myxedema coma, drug reaction, toxic shock syndrome
“Neurogenic Shock”
Distribute shock is caused by decrease in systemic vascular resistance
Examples include sepsis, which decreases SVR, anaphylaxis
Other example include adrenal insufficiency, myxedema coma, drug reaction like toxic shock syndrome and neurogenic (vaso vagal)
Systemic vascular resistance

10. Hypovolemic Shock MAP- CVP = (HR x SV) x SVR
3. Low Stroke Volume:
Intravascular volume:
- Dehydration
- Hemorrhage
- 3rd space
A third type of shock is hypovolemic shock, which is caused by low stroke volume.
- Examples of low stroke volume include dehydration, hemorrhage, and third spacing like pancreatitis

11. Three types of shock Wedge Pressure (Preload) Cardiac Output (SV x HR)
Systemic Valve Resistance (afterload)
Hypovolemic shock
Cardiogenic shock
Distributive shock
Another way to look at shock, ask the student to explain why

12. MAP - CVP = (HR x SV) x SVR cardiogenic Hypovolemic distributive
MAP (mean arterial pressure), CVP (central venous pressure), SVR (systemic vascular resistance), CO (cardiac output), HR (heart rate), SV (stroke volume), B1 (beta 1 receptors)
In response to the amount of fluid within the pipes:
The pump can adjust by slowing or speeding up the HR, and changing its contractility.
The pipes/peripheral vessels can vasoconstrict into lead pipes or vasodilate into a compliant plastic bag that collects fluid without any resistance.
distributive

13. Case 1
54 year old female with lupus on chronic steroids presents with fatigue, decreased appetite, and worsening cough with thick yellow sputum x 2 days. This morning she became diaphoretic and began experiencing new shortness of breath.
In the ED, T 101.3F, HR 107, BP 96/56, RR 20, SpO2 94% RA with increasing lethargy
Is she in shock?
If so, what kind of shock and what’s the most likely cause?
Note: can refer to slide 10 for pictorial representation as needed while working through cases.
Immunocompromised female on chronic steroids, presenting with worsening productive cough concerning for infection.
Is she in shock? Hypotension with evidence of CNS dysfunction reflective of hypoperfusion = shock
If so, what is the most likely cause? Meeting ¾ SIRS criteria (fever, tachycardia, tachypnea) in sepsis (likely pneumonia) -> septic shock (distributive)

14. Case 2
27 year old male with chronic alcohol abuse presents with lightheadedness, nausea, and sharp epigastric abdominal pain radiating to back. He reports alcohol binge over past 3 nights, followed by intractable vomiting.
In the ED, T 98.7, HR 112, BP 96/56, RR 12, SpO2 99% RA, 10/10 pain. Repeat BP after 5L normal saline bolus, 88/43. Urine output 15cc/h
Is he in shock?
If so, what kind of shock and what’s the most likely cause?
Alcoholic with epigastric pain and GI losses, presenting with tachycardia and hypotension.
Is he in shock? Tachycardia and hypotension not responding to fluid resuscitation. Oliguria indicative of hypoperfusion -> shock.
If so, what is the most likely cause? Consider GI losses, hematemesis (variceal bleeding, Mallory-Weiss tear, peptic ulcer disease), pancreatitis -> all point to hypovolemic shock.

15. Case 3
62 year old female hospitalized for right hip fracture s/p ORIF on POD#2, develops acute onset shortness of breath and substernal chest pain with respirations.
In the ED, T 98.5F, HR 109, BP 87/56, RR 22, SpO2 86%. JVP 13 cm H2O. Lactate 5.1
Is he in shock?
If so, what kind of shock and what’s the most likely cause?
Elderly female with hip fracture and decreased ambulation, presenting with respiratory distress.
Is she in shock? Elevated lactate indicates tissue hypoperfusion -> shock
If so, what is the most likely cause? History concerning for DVT and possible pulmonary embolism. Cannot exclude myocardial infarction given concurrent chest pain, although likely pleuritic. -> obstructive or cardiogenic shock. How would you differentiate between LV systolic dysfunction and pulmonary embolism? (no rales in PE).

16. Take Home Points Shock = tissue hypoperfusion
Remember the 3 elements of circulation to identify the type of shock
Restore perfusion as quickly as possible
Think fluid, pump, pipes. Hypovolemic, cardiogenic, distributive shock.
Related mini-lectures available on website: Vasopressors & Inotropes, ACS, Pulmonary embolism, Sepsis, Adrenal insufficiency

17. References
Gaieski, David. Shock in adults: Types, presentation, and diagnostic approach. Uptodate.com
Maier RV. Chapter 270. Approach to the Patient with Shock. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, eds. Harrison's Principles of Internal Medicine. 18th ed. New York: McGraw-Hill; 2012.
Neligan, Patrick. Critical Care Medicine Tutorials, UPenn
Young WF. Chapter 11. Shock. In: Humphries RL, Stone C, eds. CURRENT Diagnosis & Treatment Emergency Medicine. 7th ed. New York: McGraw-Hill; 2011.
MKSAP 17