Lecture 15 - Cardiac Output and Shock

Question 1

Define shock

Answer 1

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

Question 2

Circulatory shock

Answer 2

failure of circulation to deliver sufficient oxygen to meet tissue demand

Question 3

normally does oxygen delivery exceed demand?

Answer 3

yes

Question 4

Describe a delivery independent scenario of oxygen delivery and consumption

Answer 4

normally O2 delivery exceeds demand with 25% of available oxygen removed from arterial blood

Question 5

Describe a delivery dependent scenario of oxygen delivery and consumption

Answer 5

as oxygen delivery decreases, critical oxygen delivery will be reached, at this point consumption becomes dependent on delivery

Question 6

when does tissue hypoxia occur, what happens

Answer 6

beyond the delivery dependent stage, tissue hypoxia occurs –> achieve definition of shock

Question 7

what are the 2 levels that shock can impact

Answer 7

cellular level and systemic level

Question 8

what does the cellular impact of shock represent?

Answer 8

represents the initial impact of shock, before systemic responses occur

Question 9

What happens when the cellular level is impacted by shock

Answer 9

mitochondria begins to fail
- switches from aerobic to anaerobic metabolism
- generation of lactic acid
- lactic acidosis results in cellular failure

Question 10

what does the systemic response attempt to compensate for

Answer 10

systemic response represents attempted compensation for cellular damage from shock

Question 11

What is the systemic response to the cellular impact of shock (what are the phases of shock)

Answer 11

1. compensated shock
2. decompensated shock
3. irreversible phase

Question 12

Describe the hyper-dynamic phase of shock (compensated shock)

Answer 12

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

Question 13

describe decompensated shock

Answer 13

second phase of shock: gradual failure of compensation - hypotension, increased lactate, bradycardia

Question 14

What are some clinical signs of shock

Answer 14

• altered tissue perfusion (cold periphery, pale mucous membrane, slow CRT)
• decreased urine output
• altered mental state (obtunded, disorientated)

Question 15

what is diagnosis of shock based on

Answer 15

based on clinical, hemodynamic (variable depending on phase) and biochemical signs (elevated blood lactate), (and history!)

Question 16

What are the general goals of treatment of shock

Answer 16

restoring relationship between O2 delivery ad consumption by restoring tissue perfusion (volume and or ABP) and oxygen delivery (provide oxygen as required

Question 17

what are the 4 categories of circulatory shock

Answer 17

hypovolemic, obstructive, distributive, cardiogenic

Question 18

most common cause of circulatory shock

Answer 18

distributive shock

Question 19

can more than one type of shock be present in a patient

Answer 19

yes

Question 20

most common circulatory shock in animals

Answer 20

hypovolemic shock

Question 21

What results from distributive shock

Answer 21

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

Question 22

what is distributive shock

Answer 22

critical loss of vascular tone (vasodilation) that results in inappropriate distribution of blood flow (ex. sepsis, anaphylaxis)

Question 23

What is hypovolemic shock

Answer 23

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)

Question 24

What is cardiogenic shock

Answer 24

failure of heart to function as a pump: loss of contractility (ex. cardiomyopathy) or major arrhythmia (ex. ventricular tachycardia, 3rd degree AV block)

Question 25

what is obstructive shock

Answer 25

obstruction of blood flow (ex. pericardial tamponade, pulmonary enabolism)

Question 26

is obstructive shock rare or common

Answer 26

relatively rare

Question 27

3 steps to stabilization

Answer 27

1. improve circulating volume with combination of crystalloid fluids +/- blood
   2 provide analgesia
2. provide oxygen

Question 28

what does no discernible relationship between P waves and QRS complex on an ECG tell you

Answer 28

3rd degree atrioventricular block HR set by ectopic pacemaker (escape rhythm)

Question 29

what is the procedural plan for Chronic bradycardia

Answer 29

1. risk of severe hypotension as a result of severe bradycardia; worsened by analgesia
2. control heart rate ( and ABP) with temporary external pacing
3. placing permanent internal pacemaker