Episode 7 - Shock Talk I: Pathophysiology & Classification

Jun 7

Summary

In this episode, we review the pathophysiology and classification of a common and potentially fatal condition, shock. Starting with the concept of oxygen delivery, we’ll examine the relationship between supply and demand, in an effort to grasp the concept of critical DO2. Further, we’ll review a 4 category classification system for shock which we should all have at the front of our minds as we begin our initial resuscitaton, sift through the data, and examine our patients in an effort to determine the etiology for this common yet elusive condition.

Learning Objectives

1. Understand the common pathophysiologic mechanisms underlying shock (critical DO2)

2. Immediately recall the 4 key categories of shock, and finally

3. Provide a differential diagnosis for the common causes of shock across the 4 key categories

Take Home Points

Shock is dynamic and elusive. Therefore, a HIGH INDEX OF SUSPICION is necessary in order to identify shock in our patients.
Once shock is recognized IMMEDIATE intervention is required. These interventions are designed to INCREASE oxygen delivery and DECREASE oxygen demand.
Patients may be “sick” versus “not sick”. They may also be in compensated versus uncompensated shock. Try to avoid using terms like “stable” versus “unstable”.

Time Stamps

00:12 Introduction
01:40 Objectives
02:01 Shock defined
02:28 DO2 equation revisited
03:27 Oxygen uptake or VO2
04:20 Aerobic glycolysis
05:03 Anaerobic glycolysis
05:36 DO2 : VO2
06:25 Oxygen extraction ratio or VO2 / DO2
08:16 Critical DO2 & dysoxia
09:25 Shock DOES NOT EQUAL blood pressure
10:20 Importance of flow (Q)
11:05 Stages of shock
12:48 Why classify shock?
14:25 Classification of shock
15:10 Hypovolemic shock
16:21 Cardiogenic shock
17:14 Distributive shock
18:42 Obstructive shock
19:50 Traumatic, occult, and undifferentiated shock
22:02 Outro

Core Concepts, Equations, and Other Stuff

DO2 = Q x [(1.34 x Hb x SaO2) + (paO2 x 0.0031)]

Q = HR x SV; determinant of SV are: preload, contractility, and afterload

MAP = Q x SVR

VO2 = CO x (CaO2 - CvO2) x 10 mL / min

Fick equation: CO = VO2 / CaO2 - CvO2

Reverse Fick equation: VO2 = CO x CaO2 - CvO2

*because CaO2 and CvO2 share common term or 1.34 x Hb, can re-write as:

VO2 = CO x 1.34 x Hb x (SaO2 - SvO2) x 10

O2ER = VO2 / DO2

Also, because VO2 and DO2 share common terms (Q x 1.34 x [Hb] x 10) *factor of 10 is used to convert CaO2 from mL/dL to mL/L

O2ER = (SaO2 - SvO2) / (SaO2) or O2ER = 1 - SvO2

VO2 = DO2 x O2ER or VO2 = DO2 - (SaO2 -SvO2)

Critical DO2 or Maximal O2 Extraction in Hemorrhagic Shock

*Crit Care*. 2004 Oct;8(5):373-81. Epub 2004 Apr 2.

Classification of Shock Table

Coming Soon