Minimally invasive Doppler-based measurement of blood velocity in superior vena cava - a new tool for detection of

early hypovolemia and fluid responsiveness and cardiac output trending assessment

Tomas Kovarnik, MD, PhD.Charles University Hospital, Prague, Czech Republic

Conflict of interest

• I, Tomas Kovarnik, have no conflict of interest

Challenges of volume therapy in critically ill patients

• Hypovolemia is not rare in ICU and frequently is not properly recognized

• Hypovolemia is treated by either vasopressors ( which increases afterload) or volume

• Volume overload in ICU worsens patients prognosis and prolong time spent in ICU

• Accurate assessment of volume status is an essential part of a treatment (not only) in ICU

Challenges of hemodynamic monitoring in critically ill patients

• Classical Swan-Ganz catheter– Invasive, increase risk for infection, high variability of CO in critically ill

patients– Stable parameters (CVP, PAP, PCw pressures do not correlate well with

hemodynamic status a do not predict reaction to volume therapy)

• Pulse pressure variation– Limited marker for right side hemodynamics

• Ultrasonographic measurement of flow in superior / inferior vena cava– Need experienced echocardiographers– Cannot be continuous– BUT: well related to right side hemodynamic, able to predict response

to volume therapy

Pulse Doppler of the SVC flow velocity was measured by Combowire (Volcano comp.) and displayed on the console, which automatically detected and plotted the envelope of the SVC flow velocity pattern. SVC flow measurement was respiratory and ECG gated. In 20 sec long intervals we have analyzed flow variations during each individual respiratory cycle. Minimal flow occurred during inspiration, maximal flow was recorded in expiration. Doppler envelope data were continuously recorded with a custom PC-based application specifically designed for the purposes of this trial.

Animal study protocol (10 pigs)bleeding & volume substitution & volume overload

- Bleeding through was 6 F sheath introduced to the femoral artery- Bleeding period was 10% of estimated blood volume (EBV), calculated

as 65 ml/kg and five times 5% of EBV during10 minutes each- Two steps of 500 ml blood return (each during 30 minutes) separated by

10 minutes steady states. - Saline 1 000 ml/30min two times was given separated by 10 minutes of

steady state after reinfusion of blood.

Venous Return Variation index (VRVi)

• New index of fluid responsiveness

• calculated as: VRV= (VTImax- VTImin) / (VTImax+VTImin)/2

• 43 individual measurement of VRV in confirmed volemia status events

SVC flow monitoring with ComboMap

First version of interphase and analyzer

Correlation of VTImin with static markers of hypovolemia.

Values are normalized to 100 points at the baseline

Comparison of cardiac output measurementDoppler based vs. continuous pulmonary artery thermodilution

r = 0.95

Doppler-based indices vs. standard measurements

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1 2 3 4 5 6 7 8 9 10 11 12 13

EDP

PCWP

CVP

VTImin

VRV

PCWP 0.98EDP 0.89CVP 0.97

VRV index

Normal SVC flow pattern

Limitation of PPV during noradrenalin infusion

Case description: young patient with cerebral oedema with therapeutic hypovolemia and noradrenalin infusion for keeping systemic blood pressure. Notice low PPV and extreme elevation of VRV index. Significant low volume status would not be recognized just based on PPV tracing.

Normal RV function and non-elevated RA pressureS/D 1-2sensitivity 86%, specificity 78%

Reduction of RV function with normal RA pressureS/D > 2Sensitivity 69%, specificity 81%

Reduction of RV function with elevated RA pressureS/D < 1Sensitivity 52%, specificity 95%

The spectra of SVC in the respiratory cycle in patients with right heart failure

The spectra of SVC of healthy subjects in the respiratory cycle

Right heart failure with tricuspid regurgitation

Dominant diastolic flow

Significant retrograde systolic flow

Description of first cases from clinical practice

AbbreviationsRHD: right heart disease, TR: tricuspid regurgitation, PAH: pulmonary artery hypertension, AoCo: aorto-coronary bypass

Summary

• Continuous measuring of SVC flow is safe, feasible and user-friendly• Parameters of SVC flow closely correlate with traditional

hemodynamic parameters • VRV has the steepest slope of increase and decrease and highest

change from basal level compared to traditional markers of volemiaand can predict reaction to volume challenge

• VRV better correlated with changes of volume status than PPV• SVC Doppler flow closely followed changes of cardiac output

measured by thermodilution• Parameters of SVC flow are suitable for continuous monitoring of

volume status during bleeding and volume supplementation • S/D ratio from SVC is a sensitive marker for right heart dysfunction

and elevation of right atrium pressure• Future directions: prediction of fluid responsiveness during

spontaneous breathing and cardiac arrhythmias

contact: tomas.kovarnik@vfn.cz