Hemodynamics In The Icu

Hemodynamics Dalhousie Critical Care Lecture Series

Objectives
Discuss the basic cardiac physiology that is routinely used in the management of critically ill patients
Determinants of MAP
Determinants of CO
Determinants of DO 2
Be able to describe the various states of shock using the above concepts.
Describe how and why we monitor CVP

Equations to Live By
MAP = CO x SVR
CO = SV x HR
Therefore:
MAP = SV x HR x SVR

Determinants of SV

The Need for Preload

Preload Estimates with error JVP CVP RAP RVEDP PAD PAWP LVEDP LVEDV

Right Atrial Waveform

Looking Carefully at the JVP/CVP

The Role of Afterload

Afterload paradigm
If CO increases with decreased afterload then wouldn’t the body work better with a very low afterload?
What pathologic condition is this called?
Video

In the end why do we need CO?
It’s all about oxygen delivery to the tissues
DO 2 is delivery
VO 2 is consumption
CaO 2 is arterial oxygen content
CvO 2 is venous arterial content
DO 2 = CO x CaO 2
VO 2 = CO x (CaO 2 – CVO 2 )

What happens when VO 2 > DO 2 ?

All of Cardiac Physiology in a Nut Shell

It’s Really All About the SvO 2
Generally believed that it’s better to have a normal SVO 2 than a lower one.
Early normalization of SVO 2 as a goal of therapy is desired
The unknown:
low SVO 2 after the initial resuscitation
what number to treat and what to treat to
conditions other than obvious shock

What number to treat and what is “The Magic Number”?
The SVcO 2 of 70% is based on normal physiology
“ Over treating” may result in increased mortality through a variety of mechanisms
Increased VO 2
Oxidative injury
It is suggested that the ideal number is patient dependent and that we should be titrating to the inflection point on the curve rather than an absolute number

The Magic Number
488 post operative CABG patients retrospective analysis to determine the prognostic cutoff number for SVO 2 as it pertains to mortality
SVO 2 < 55% at admission was the cutoff for significant mortality difference
As low SVO 2 was aggressively treated the question of whether it was the number or the treatment that caused the increased mortality

The Magic Number
Retrospective cohort study of 111 critically ill patients with septic shock
Time spent below SVO 2 of 70% was an independent predictor of mortality along with lactate, MAP and CVP
Supporting validation of Rivers septic shock algorithm

Using the Swan-Ganz catheter to diagnose type of shock

Using the Swan-Ganz catheter to diagnose type of shock O 2 extraction + SVR Septic shock O 2 extraction + SVR Cardiogenic shock O 2 extraction + SVR Hypovolemic shock RVEDV PAP /N PAWP V V Right ventricular failure PAD/PAWP equalised Cardiac tamponade giant ‘v’ waves on PAWP trace Acute mitral regurgitation O 2 step up noted in SvO 2 giant ‘v’ waves on PAWP trace Acute venticular septal defect Pulm Vasc Res PAD>PAWP by >5 mmHg Massive pulmonary embolism PAWP > 25mmHg N/ Cardiogenic pulmonary edema Left ventricular failure Notes PAP/PAWP CVP/RAP CO/CI MAP HR Condition

Summary
We use basic cardiac physiology in the ICU to:
Diagnose various states of shock
Optimize tissue perfusion
We will next talk about various drugs that can be used to manipulate the parameters set out in these equations

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Hemodynamics In The Icu

by Andrew Ferguson on Mar 04, 2008

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Hemodynamics In The Icu — Presentation Transcript