HemodynamicsHemodynamicsDalhousie Critical Care Lecture

Series

ICUObjectives

Discuss the basic cardiac physiology that is routinely used in the management of critically ill patients

Determinants of MAP Determinants of CO Determinants of DO2

Be able to describe the various states of shock using the above concepts.

Describe how and why we monitor CVP

ICUEquations to Live By

MAP = CO x SVR CO = SV x HR

Therefore:

MAP = SV x HR x SVR

ICUDeterminants of SV

ICU The Need for Preload

ICU Preload

JVPCVPRAPRVEDPPADPAWPLVEDPLVEDV

Estimates with error

ICURight Atrial Waveform

ICU

Looking Carefully at the JVP/CVP

ICU

The Role of Afterload

ICUAfterload 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

ICU

In the end why do we need CO?

It’s all about oxygen delivery to the tissues

DO2 is delivery VO2 is consumption CaO2 is arterial oxygen content CvO2 is venous arterial content

DO2 = CO x CaO2

VO2 = CO x (CaO2 – CVO2)

ICU

What happens when VO2 > DO2?

ICU

ICU

ICUAll of Cardiac Physiology

in a Nut Shell

ICU

It’s Really All About the SvO2

Generally believed that it’s better to have a normal SVO2 than a lower one.

Early normalization of SVO2 as a goal of therapy is desired

The unknown:1. low SVO2 after the initial resuscitation

2. what number to treat and what to treat to3. conditions other than obvious shock

ICU

What number to treat and what is “The Magic

Number”? The SVcO2 of 70% is

based on normal physiology

“Over treating” may result in increased mortality through a variety of mechanisms

Increased VO2

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

ICU

1. 488 post operative CABG patients retrospective analysis to determine the prognostic cutoff number for SVO2 as it pertains to mortality

2. SVO2 < 55% at admission was the cutoff for significant mortality difference

3. As low SVO2 was aggressively treated the question of whether it was the number or the treatment that caused the increased mortality

The Magic Number

ICU

ICU

1. Retrospective cohort study of 111 critically ill patients with septic shock

2. Time spent below SVO2 of 70% was an independent predictor of mortality along with lactate, MAP and CVP

3. Supporting validation of Rivers septic shock algorithm

The Magic Number

ICU

Using the Swan-Ganz catheter to diagnose type

of shock

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Condition HR MAP CO/CI CVP/RAP

PAP/PAWP Notes

Left ventricular failure

Cardiogenic pulmonary edema

N/ PAWP > 25mmHg

Massive pulmonary embolism

PAD>PAWP by >5 mmHg

Pulm Vasc Res

Acute venticular septal defect

giant ‘v’ waves on PAWP trace

O2 step up noted in SvO2

Acute mitral regurgitation giant ‘v’ waves on PAWP trace

Cardiac tamponade PAD/PAWP equalised

Right ventricular failure V

V PAP /N PAWP RVEDV

Hypovolemic shock O2 extraction + SVR

Cardiogenic shock O2 extraction + SVR

Septic shock O2 extraction + SVR

Using the Swan-Ganz catheter to diagnose type of shock

ICUSummary

We use basic cardiac physiology in the ICU to:

1. Diagnose various states of shock2. Optimize tissue perfusion3. We will next talk about various drugs that

can be used to manipulate the parameters set out in these equations