UC Irvine Medicine Residency Mini Lecture Series Shock UC Irvine Medicine Residency Mini Lecture Series

Case Vignette 54 year old female with lupus on chronic steroids and methotrexate presents with fatigue, decreased appetite, and worsening cough with thick yellow sputum x 2 days. This morning she became diaphoretic and began experiencing shortness of breath. In the ED, T 101.3F, HR 107, BP 96/56, RR 20, SpO2 94% RA, with increasing lethargy Note: Read case and following questions for audience to keep in mind throughout lecture: Is she in shock? If so, what is the most likely cause?

Objectives Learn the definition of shock Understand its pathophysiology Identify different types of shock

Key Elements of Blood Pressure Fluid Pump Pipes The cardiovascular system can be simplified into 3 key elements: a fluid, a pump that collects and moves the fluid forward, and the plumbing 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)

Shock: Definition Impaired tissue perfusion Oxygen consumption > delivery Cell death > End-organ damage > Multi-system organ failure > Death Signs: tachycardia, tachypnea, acidosis, oliguria, confusion 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! Signs to suggest progressive shock include tachycardia, tachypnea, metabolic acidosis, oligoanuria, and lethargy.

Mean Arterial Pressure (MAP) MAP - CVP = Cardiac Output x SVR Cardiac Output (CO)= HR x Stroke Volume MAP (mean arterial pressure), CVP (central venous pressure), SVR (systemic vascular resistance), CO (cardiac output), HR (heart rate), SV (stroke volume) To understand decreased tissue perfusion and shock, recall that mean arterial blood pressure is determined by the cardiac output through resistant arterioles. Cardiac output, in turn, is a function of heart rate and stroke volume. The noncompliant pipes (systemic vascular resistance) maintains the pressure gradient (BP) generated by the pump (heart). The heart rate, stroke volume, and peripheral resistance work in equilibrium to maintain circulation.

MAP - CVP = (HR x SV) x SVR Heart Rate, Contractility (ß1) Resistance 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. Resistance

Etiologies of Shock MAP – CVP = (SV x HR) x SVR Sepsis, anaphylaxis Abnormal heart rate: “Cardiogenic” Tachycardia (short filling time) Bradycardia Low vascular resistance: “Distributive” Sepsis, anaphylaxis Other: adrenal insufficiency, myxedema coma, drug reaction, toxic shock syndrome, neurogenic Heart Rate, Shock occurs when the stroke volume, HR, or peripheral resistance are abnormal, and the compensation is inadequate for perfusion. Note: Can ask audience for examples of each category first. Resistance

Etiologies of Shock (2) Low Stroke Volume: MAP – CVP = (SV x HR) x SVR Low Stroke Volume: Intravascular volume: “Hypovolemic” Dehydration, hemorrhage, 3rd space Venous return & Outflow obstruction “Obstructive” Tamponade, tension pneumothorax, PEEP, Pulmonary embolism Ejection: “Cardiogenic Myocardial infarct, valvular defect

Types of Shock Cardiogenic (Obstructive) Hypovolemic Distributive (Obstructive shock can be thought of as an extracardiac source of cardiogenic shock.) Hypovolemic Distributive

Case 1, Re-visited 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 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)

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 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.

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. Vitals: T 98.5F, HR 109, BP 87/56, RR 22, SpO2 86%. JVP 13 cm H2O. Lactate 5.1 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).

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

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.