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Venous Return and Effective Circulatory Blood Volume Michael R Venous Return and Effective Circulatory Blood Volume Michael R. Pinsky, MD, Dr hc Department of Critical Care Medicine University of Pittsburgh Bedside Cardiovascular Physiology • Exploring the Determinants of Cardiac Output – Mean systemic pressure – Cardiac performance – Blood flow distribution • Deconstructing Systemic Vascular Resistance – Arterial critical closing pressure – Arterial and venous resistance The Cardiac Function Curve Cardiac Output Q (l/min) 0 10 Pra (mm Hg) Defining the Determinants of Venous Return Using a Right Heart Bypass Preparation Guyton et al. Am J Physiol 189:609-15, 1957 The Venous Return Curve VR = CO = (Pms-Pra) / RVR Slope = 1 / RVR Pra = Pms Venous Return Venous Pra Pms 0 Guyton et al. Am J Physiol 189:609-15, 1957 Matching of the Venous Return Curve with the Cardiac Function Curve Cardiac Output Equilibrium Point Q (l/min) Venous Return 0 Pra (mm Hg) 10 Guyton et al. Am J Physiol 189:609-15, 1957 Venous Return and LV Output DPVR= Pms - Pra CO Eh = [Pms-Pra]/Pms RVR = [Pms - Pra]/CO Pms 0 0 Pra Matching of the Venous Return Curve with the Cardiac Function Curve A. Normal A B. Reduced Cardiac Q C Performance B (l/min) C. Volume Infusion 0 10 Pra (mm Hg) Mean Systemic Pressure • Static determinants: – Blood volume – Vasomotor tone • Dynamic determinants: –Blood flow distribution –Venous conductance (1/resistance) The Venous Return Curve Static Determinants Hypervolemia Normal Blood Volume Q (l/min) Hypovolemia 0 10 Pra (mm Hg) The Venous Return Curve Static Determinants Increased Vasomotor Tone Normal Vasomotor Tone Q (l/min) Decreased Vasomotor Tone 0 10 Pra (mm Hg) How to Measure Pms • Total circulatory arrest equilibrium pressure – Guyton et al. Am J Physiol 189:609-15, 1957 • Dynamic swings in the SVrv/Pra relation – Pinsky. J Appl Physiol 56:1237-45, 1984 • End-inspiratory hold (CPAP) – Versprille & Jansen. Pfliigers Arch 405:226-33, 1985 – Maas et al. Crit Care Med 37: 912-8, 2009 • Modeling flow capacitance and resistance – Parkin. Crit Care Resusc 1: 311-21, 1999 • Peripheral vascular stop flow equilibrium – Maas et al. Crit Care 12: S37, 2008 Spontaneous Ventilation Positive-Pressure Ventilation SVrv (ml/kg) Time (sec) Pratm (mm Hg) Ppl (mm Hg) CVP (mm Hg) Pinsky. J Appl Physiol 56:1237-45, 1984 Instantaneous Venous Return Curve SVRV (ml) 0 10 Pra (mm Hg) Pinsky. J Appl Physiol 56:1237-45, 1984 Instantaneous Venous Return Curve n=26 r = 0.9014 p < 0.001 Pinsky. J Appl Physiol 56:1237-45, 1984 Inspiratory Pause Method of Calculating Pmcf Vesprille & Jansen. Pfliigers Arch 405:226-33, 1985 Measuring Mean Systemic Filling Pressure at the Bedside Using Inspiratory Holds Maas et al. Crit Care Med 37: 912-8, 2009 Measuring Pms at the Bedside using Inspiratory Holds CPAP 5, 7.5, 10 and 12.5 6 Supine Head up position Supine + volume 4 Volume loading Post-op (L/min) (L/min) Cardiac Surgery Patient 2 COmf COmf a b c Head-up tilt b a c 0 0 5 10 15 20 25 30 35 Pcv (mmHg) Maas et al. Crit Care Med 37:912-8, 2009 Measuring Pms at the Bedside Calculating Vascular Compliance 35 30 25 20 15 Pmsf (mmHg) 10 5 b a c 0 -300 -200 -100 0 100 200 300 400 500 600 change in blood volume (mL) Maas et al. Crit Care Med 37:912-8, 2009 Measuring Pms at the Bedside using peripheral pressure stop-flow technique Radial arterial pressure Vascular Occlusion Stop-flow Equilibrium pressure Venous pressure Maas et al. Intensive Care Med 38:1452-60, 2012 Measuring Pms at the Bedside using Peripheral Arterial Pressure Stop- Flow Technique Maas et al. Intensive Care Med 38:1452-60, 2012 Measuring Pms at the Bedside using peripheral pressure stop-flow technique 20 15 10 5 0 -5 change Parm [mmHg] Parm change -10 -15 -20 -20 -10 0 10 20 change Pmsf [mmHg] Maas et al. Intensive Care Med 38:1452-60, 2012 Alternative to Measuring Pms Navigator Applied Physiology Pms = (Vs + Vus)/(Cvs + Cas) Vs = (Rvs x CO + Pra) Cv assuming Cas/Cvs = 1/24 and Ras/Rvs = 25/1 Pms = 0.96Pra + 0.04Pa + 0.96 x c x CO Where c = 0.96 x 1/26 x resting SVR (mm Hg/L/min) SVR dependent on anthropomorphic data Parkin. Crit Care Resusc 1: 311-21, 1999 (age, weight, length). Calculated Pms (Pmsa) tracks measured Pmsf with definable bias Mass et al. Intensive Crit Care 38:1452-60, 2012 Changes is calculated Pms tract measured Pmcf in humans 20 y = 0,5262x R2 = 0,7606 15 10 5 dPmsa (mmHg) dPmsa 0 -10 -5 0 5 10 15 20 -5 -10 dPmsf (mmHg) Mass et al. Intensive Crit Care 38:1452-60, 2012 If you know Pms you know the Effective Circulating Blood Volume • Pms is a function of stressed and unstressed volume • Changes in Pms are a function of changes in blood flow distribution and vascular compliance • DPms/Dvolume = Functional Compliance Changes in Pmsa during Fluid challenge in Post-surgical ICU patients dVR = Pmsa - Pra Pmsa increased with infusion dVR increased in responders Cecconi et al. Intensive Care Med 39:1299-1305, 2013 Relation Between Blood Volume Vessel and Mean Systemic Pressure cross-sectional area Volume Stressed Compliance = DV/DP Blood Volume Capacitance = Total Volume Vascular Pressure Unstressed Volume Unstressed Mean Systemic Pressure Effect of Changes in Total Blood Volume and Unstressed Volume on Mean Systemic Pressure Volume Expansion Vasoconstriction Volume Stressed Blood Volume Dilation Volume Constriction Unstressed Volume Unstressed Mean Systemic Pressure Primary Mechanism for Increasing Venous Return Decrease Unstressed Volume 1500 simultaneous measurements of Blood Volume and CVP in a heterogeneous cohort of 188 ICU patients CVP r=0.27 (mmHg) Deficit or Excess Blood Volume (ml/M2) Shippy et al. Crit Care Med 12:107-12, 1984 Instantaneous Venous Return and Endotoxic Shock +400 +300 +200 +100 Baseline Endotoxemia +400 +300 +200 +100 Endotoxemia increases Rrv and Unstressed Volume Pinsky & Matuschak J Crit Care 1:16-36, 1986 Pmsa accurately follows Pmsi in dogs during normal and endotoxic volume changing conditions 30,00 20,00 Pms (mmHg) 10,00 Endotoxin-Pmsi Endotosin-Pmsa Control-Pmsi Control-Pmsa Pooled standard error 0,00 0 +100 +200 +300 +400 -300 -200 -100 0 Volume Challenge (mL) Lee et al. J Crit Care 28:880, 2013 Measuring Stressed Volume (Vs) in a Humans Using the Stop-Flow Parm Technique Systemic VascularSystemic Compliance Vascular Compliance Curves curve of for Responders volume responders 500 400 Stressed300 volume was estimated to be ~20 ml/kg 200 100 0 0 5 10 15 Systemic Vascular ComplianceCompliance curve nonresponders Curves of Non-Responders 500 400 300 Stressed200 volume was estimated to be ~30 ml/kg Volume change (mL) 100 0 0 5 10 15 20 25 30 35 40 45 50 Pmsf (mmHg) Geerts et al. J Clin Monit Comp 24:377-84, 2010 The Venous Return Curve Dynamic Determinants: Changes in Resistance to Venous Return Increased Vasomotor Tone Q (l/min) Decreased Vasomotor Tone 0 10 Pra (mm Hg) Decreasing Norepinephrine Decreases Cardiac Output in Septic Patients Stable on norepinephrine Following a decrease in norepinephrine Persichini et al. Crit Care Med 40:3146-53, 2012 Effect of Dobutamine on Mean Systemic Pressure 100 Right atrium Aorta 90 Pao dobutamine Pao baseline Pao 80 70 60 50 40 baseline baseline dobutamine 30 dobutamine Rv Rv Rv Rv Pao, Pcv and Psf [mmHg] [mmHg] Psf Psf and and Pcv Pcv Pao, Pao, 20 baseline baseline dobutamine Psf dobutamine 10 Rsys Rsys Rsys Pcv Rsys 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Rv and Rsys [mmHg.s.ml-1) Geerts et al. J Clin Monit Comp 24:377-84, 2010 Effect of Dobutamine on Mean Systemic Pressure Geerts et al. J Clin Monit Comp 24:377-84, 2010 Cardiac Output and Venous Return Together Maximize Blood Flow Dobutamine Cardiac Output Venous Return Venous Rest CardiacOutput Venous Return 0 Right Atrial Pressure 20 Hemodynamic Effect of Propofol de Wit et al. BJA 116:784-9, 2016 Hemodynamic Effect of Propofol de Wit et al. BJA 116:784-9, 2016 Hemodynamic Effect of Propofol de Wit et al. BJA 116:784-9, 2016 Systemic Venous Return Conclusions Venous return is the primary determinant of cardiac output Cardiac output can only increase if DVR increases, RVR decreases or both But DVR and RVR are defined by arterial blood flow distribution to the tissues Which itself is defined by tissue oxygen demands Ventricular pump function defines the mean circulating blood volume necessary to maintain this steady state by setting right atrial pressure Thank You.
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