Lecture 15 - Cardiac Output and Shock Flashcards
Define shock
A state of cellular and tissue hypoxia due to either reduced oxygen delivery, increased oxygen consumption, inadequate oxygen utilization or a combination of all of these
Circulatory shock
failure of circulation to deliver sufficient oxygen to meet tissue demand
normally does oxygen delivery exceed demand?
yes
Describe a delivery independent scenario of oxygen delivery and consumption
normally O2 delivery exceeds demand with 25% of available oxygen removed from arterial blood
Describe a delivery dependent scenario of oxygen delivery and consumption
as oxygen delivery decreases, critical oxygen delivery will be reached, at this point consumption becomes dependent on delivery
when does tissue hypoxia occur, what happens
beyond the delivery dependent stage, tissue hypoxia occurs –> achieve definition of shock
what are the 2 levels that shock can impact
cellular level and systemic level
what does the cellular impact of shock represent?
represents the initial impact of shock, before systemic responses occur
What happens when the cellular level is impacted by shock
mitochondria begins to fail
- switches from aerobic to anaerobic metabolism
- generation of lactic acid
- lactic acidosis results in cellular failure
what does the systemic response attempt to compensate for
systemic response represents attempted compensation for cellular damage from shock
What is the systemic response to the cellular impact of shock (what are the phases of shock)
- compensated shock
- decompensated shock
- irreversible phase
Describe the hyper-dynamic phase of shock (compensated shock)
systemic response to perfuse tissues with oxygenated blood - sympathetic activation (positive chronotropy, dromotropy, inotropy, vasoconstriction), “thready pulses (narrow pulse press), leading to increased CO + ABP. Renin-angiotensin system activation –> reduced urine output
describe decompensated shock
second phase of shock: gradual failure of compensation - hypotension, increased lactate, bradycardia
What are some clinical signs of shock
- altered tissue perfusion (cold periphery, pale mucous membrane, slow CRT)
- decreased urine output
- altered mental state (obtunded, disorientated)
what is diagnosis of shock based on
based on clinical, hemodynamic (variable depending on phase) and biochemical signs (elevated blood lactate), (and history!)
What are the general goals of treatment of shock
restoring relationship between O2 delivery ad consumption by restoring tissue perfusion (volume and or ABP) and oxygen delivery (provide oxygen as required
what are the 4 categories of circulatory shock
hypovolemic, obstructive, distributive, cardiogenic
most common cause of circulatory shock
distributive shock
can more than one type of shock be present in a patient
yes
most common circulatory shock in animals
hypovolemic shock
What results from distributive shock
critical loss of vascular tone (vasodilation) –> inappropriate distribution of blood flow –> depressed cardiac function, abnormal oxygen extraction, fluid loss from vasculature, mucous membranes red and warm during compensation phase
what is distributive shock
critical loss of vascular tone (vasodilation) that results in inappropriate distribution of blood flow (ex. sepsis, anaphylaxis)
What is hypovolemic shock
loss of circulating volume from intravascular space leading to a critical loss in venous return. Loss of circulating volume can be internal or external (ex. hemorrhage)
What is cardiogenic shock
failure of heart to function as a pump: loss of contractility (ex. cardiomyopathy) or major arrhythmia (ex. ventricular tachycardia, 3rd degree AV block)
