Hemodynamics Dalhousie Critical Care Lecture Series

ICU 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

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

ICU Determinants of SV

ICU The Need for Preload

ICU Preload LVEDV LVEDP PAWP PAD RVEDP Estimates with error

ICU Right Atrial Waveform

ICU Looking Carefully at the JVP/CVP

ICU The Role of Afterload

ICU 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

ICU 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 )

ICU What happens when VO 2 > DO 2 ?

ICU

All of Cardiac Physiology in a Nut Shell

ICU 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

ICU 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

ICU post operative CABG patients retrospective analysis to determine the prognostic cutoff number for SVO 2 as it pertains to mortality 2.SVO 2 < 55% at admission was the cutoff for significant mortality difference 3.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

ICU

1.Retrospective cohort study of 111 critically ill patients with septic shock 2.Time spent below SVO 2 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

ICU ConditionHRMAPCO/CICVP/RAPPAP/PAWPNotes Left ventricular failure Cardiogenic pulmonary edemaN/ PAWP > 25mmHg Massive pulmonary embolism PAD>PAWP by >5 mmHg Pulm Vasc Res Acute venticular septal defect giant ‘v’ waves on PAWP trace O 2 step up noted in SvO 2 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 O 2 extraction + SVR Cardiogenic shock O 2 extraction + SVR Septic shock O 2 extraction + SVR Using the Swan-Ganz catheter to diagnose type of shock

ICU 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