role of neonatal cardiac ultrasound in guiding...

Department of Newborn Care

Role of Neonatal Cardiac

Ultrasound in Guiding

Cardiovascular Support.

Nick Evans

Neonatal Medicine

Royal Prince Alfred Hospital

Sydney


Lack of Evidence

• Almost no outcome based evidence to

guide circulatory support.

• Blood pressure has been the input and

the outcome in most trials.

• Role for cardiac ultrasound

– Pathophysiology based treatment.

• Define the haemodynamic.

• Apply logical treatment to correct that

haemodynamic.


Blood Pressure and the Circulation

Pressure = Flow x Resistance

Circulatory

determinant of

tissue oxygen

delivery.

Volume

or Filling

Myocardial or

Pump function


Low Systemic Blood Pressure

Pressure = Flow x Resistance

Can only resolve with a measure of pressure and flow


When to use cardiac ultrasound to

guide support.

• Reactively:

– Any clinical evidence of circulatory compromise

including hypotension.

• Prospectively in high risk situations mostly

within first 12 postnatal hours

– Very preterm (<28 weeks or 28/29 weeks if sick)

– Term with hypoxic respiratory failure/PPHN

– Asphyxia

– Sepsis (anytime)


What information do we need?

• An impression of cardiac filling

• Subjective ventricular filling

• A measure of cardiac function

–Subjective and/or fractional shortening

• A measure of systemic blood flow

–MPA Velocity, RV Output, SVC flow

• Blood pressure


Scenario:

• 25 weeker, 10 hours old, MBP 35mmHg

RV Output = 100 mls/kg/min

NR 150-300


Scenario:

• 27 weeker, 7 days old, MBP 18mmHg on

maxiumum inotropes.

RV Output = 600 mls/kg/min

NR 150-400


WHAT’S THE CARDIAC FILLING?

Hypovolaemia

After 20mls/kg volume


Myocardial or Pump Function?


Poor Apparent Myocardial

Function

• Can result from:

–Low Pre-load.

–Sick or immature myocardium.

–High afterload or obstruction.


Immature Fetal Myocardium

25 weeks Term

If myocardial function looks good….

It probably is good.

If myocardial function looks bad

It probably is bad.


LV Ejection Fraction and Fractional

Shortening.

• Essentially calculated from the difference

between the end-diastolic (LVED) and

end systolic (LVES) dimension.


Shortening.

RV

LV

LA

RV

LV


Shortening.

LV End-Diastolic Diameter

LV End-Systolic Diameter

FS = (LVED – LVES)/LVED

EF = (LVED3 – LVES3)/LVED3

LV

RV

External Impacts on Pump

Function: Tamponade

External Impacts on Pump

Function: Obstruction


SYSTEMIC BLOOD FLOW

MEASURES

The purpose of myocardial function is

to generate flow.


Physics of fluid flow volumes

Flow = Velocity of fluid

x

Cross-sectional area of flow

•Can be measured

with Doppler.

•Needs flow direction

close to 0o or 180o.

•Can be derived from

diameter measurement

using r2.

•Needs to view vessel at

right angles. (90o)


RA LA

RV LV

DUCT

Lungs

RV

Output

LV

Output

Body

Why do shunts

confound

ventricular

outputs as

estimates of

systemic flow?

Ventricular output is often not

systemic blood flow!

Right Ventricular OutputDiameter measurement-2D view.

Mean 5.0 mm (SD 0.5 mm)(range 0.35 - 0.68)

Babies < 30weeks.

Right Ventricular OutputVelocity Time Integral (VTI) measurement.


Measure cardiac input rather than

output?

SVC Flow

• Not bad angle for insonation.

• OK window for diameter (early on).

• Not corrupted by intra-cardiac shunts.

Measure Cardiac Input: Superior vena cava flow; good window for

velocity.

SVC diameter

Max

MinSVC

RA

SVC


Calculations.

• Stroke volume = VTI x ( x Diam2/4)

• Cardiac output (mls/min) = Stroke volume x Ht Rate

• Cardiac index (mls/kg/min) = Cardiac output / BW (kg)


What’s normal?

RV Output

mls/kg/min

SVC Flow

mls/kg/min

Normal 150 - 300 50 - 100

Low <150 <50

Very Low <100 <40


Screening for Low Systemic Blood

Flow: MPA Velocity

Vmax


When do you see low flow?

• Preterm babies:

– Within first 12 hours of life, improves after that

time.(Arch Dis Child 2000)

– Strong association with IVH when flow improves.(Arch

Dis Child 2000, Pediatrics 2004)

• Term babies:

– Post Asphyxia

– With severe respiratory problems again within the first

24 hours. (Arch Dis Child 1996)

• In all babies:

– Low flow is poorly predicted by blood pressure. (J Pediatr

1996 and Arch Dis Child 2000)


When do you see high flow?

• With shunts:

• Inter-atrial and VSDs increase RV Output.

• PDA increases LV Output.

• With vasodilation.

• Septic shock

• Late/resistant shock in premature babies

• With A-V malformations


Possible Haemodynamics

Filling Pump

Function

Systemic

Blood Flow

Blood

Pressure

Hypovolaemia Low Normal or

Low

Low Low

Pump failure Normal

or dilated

Low Low Low

Vasoconstrictive Normal Normal or

low

Low Normal or

high

Vasodilatory Normal Normal or

High

Normal or

high

Low


Other considerations

• Interaction between pulmonary and systemic

circulations.

– Pulmonary BF will be low if Systemic BF is low but

– Low PBF with primary PPHN can restrict SBF,

particularly if ductus is closed.

• Ductal and atrial shunts

– Right to left shunt will support systemic BF

– Left to right shunt may drain systemic BF


Conclusions

• Cardiac Doppler ultrasound allows

estimated of global haemodynamic

status through:

– Estimation of volume status

– Exclusion of structural problems

– Estimation of pump function

– Estimation of systemic and pulmonary

blood flow.

– Estimation of resistance using blood

pressure and blood flow.

role of neonatal cardiac ultrasound in guiding...

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