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 ReturnCurve
Venous Return 0 P ra VR = CO = (P = = COVR Guyton et al. Am J Slope = 1 /RVR =1 Slope ms P - P ms ra Physiol ) /RVR P ra 189:609 = P = ms - 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 dobutamine
30 dobutamine
Rv
Rv
Pao, Pcv and Psf [mmHg] Psf and Pcv Pao,
20
baseline dobutamine Psf dobutamine
10
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
Venous Return Cardiac Output and Venous Return Together Maximize Blood Flow 0 Right Atrial Pressure Dobutamine Rest Cardiac Output 20 VenousReturn 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