Assessment of volume status

Echocardiography

B. Assessment of volume status

Preload responsiveness & volume status assessment in ICU

Def-

Preload can be defined as the initial stretching of the cardiac myocytes prior to contraction.

Hence, Preload is

Related to muscle sarcomere length

Cannot be measured directly

Surrogate measures-

Ventricular end-diastolic volume

Ventricular end-diastolic pressure

Preload responsiveness/Fluid responsiveness-

An increase of stroke volume by 10-15% after a fluid challenge (500 ml of crystalloid over 10-15 minutes) (as defined by Paul Marik)

Measures of Preload responsiveness-

1. Static parameter

A) Clinical

heart rate
blood pressure
collapsed veins
capillary refill time
previous urine output)

B) Objective

CVP/PCWP (also delta CVP post fluid challenge)
CXR
PiCCO
Echo- EDV
EVLW and ITBV
Trend in lactate or SvO2

2. Dynamic parameter

Pulse pressure variation (PPV) with - PLR, End-exp occlusion test, & Mechanical ventilation
Strove volume variation (SVV) with- PLR, Mechanical ventilation
Subaortic velocity time index (VTI) allows measurement of stroke volume

Echo for assessment of volume status & fluid responsiveness

A) IVC-

IVC diameter
IVC collapsibility index
IVC distensibilty index
Delta IVC

B) Volume-

LV end diastolic volume (LVEDV)

C) Stroke volume-

LVOT VTI variation with respiration
LVOT VTI variation with passive leg raise

A) IVC evaluation-

View- Subcostal view with marker pointing cephloid

Obtain the image

If Spontaneously breathing- Ask to do quick sniff (Rapid inspiratory effort)
If Mechanically ventilated- Obtain image for 4 respiratory cycles.

Measure- IVC diameter

Interpretation-

Index for spontaneously breathing subjects

Collapsibility index (CI) = (Maximum Diameter - Minimum Diameter)/ Maximum Diameter

CI > 50 % in spontaneously breathing subjects implies hypovolumia

(Note it’s not same as volume responsiveness)

Indices for mechanically ventilated subjects

Distensibility index (DI) & Delta IVC

Distensibility index (DI)= (Maximum Diameter - Minimum Diameter)/ Minimum Diameter
Delta IVC = (Maximum Diameter - Minimum Diameter)/ Mean Diameter

DI > 18% and Delta IVC > 12% implies hypovolumia.

B) Volume [LV end diastolic Area (LVEDA) & LV end diastolic volume (LVEDV)]

LV end diastolic Area (LVEDA)

View- Parasternal short axis- endiastolic- peak of QRS- papillary muscle view

Measure- Endiastolic area

Interpretation-

<10 cm2 - hypovolumia
>20 cm2 - hypervoulmia

LV end diastolic Volume (LVEDV)

View- Apical 4 chamber

Measure- LV volume

Interpretation-

Normal male :- 67-155 ml
Normal Female:- 56-104 ml

Note-

Visual impression-

In shortaxis view if the papillary muscles are kissing each other- Hypovolumia

C1) Stroke volume (Left ventricular outflow tract velocity time integral (LVOT - VTI) variation with respiration-

View- Apical 5 chamber

Measure- Pulse wave Doppler across LVOT. (See LVOT in video)

Trace the wave form going into the software under Aortic valve

Decrease the horizontal sweep to capture few LVOT traces (at least 2-3 respiratory cycles)

Measure the tallest LVOT VTI (happens at end inspiration in mechanically ventilated patient) and the shortest LVOT VTI

Interpretation-

Any variation in LVOT VTI >12% predicts fluid responsiveness.

LVOT VTI variation with respiration = Maximum LVOT VTI - Minimum LVOT VTI /Mean of the two values in numerator

C2) Left ventricular outflow tract velocity time integral (LVOT - VTI) variation with passive leg raising-

Views- First- Apical 5 chamber, Patient in semi-recumbent (45 degrees)

Second- Apical 5 chamber, head end made supine and both legs lifted by 45 Dgrees.

Measure- Pulse wave Doppler across LVOT. (See LVOT in video)

Measure the LVOT VTI in both these conditions.

Interpretation-

Any variation in LVOT VTI >12.5% (Increase in stroke volume by 15%) predicts fluid responsiveness.

Echocardiography

B. Assessment of volume status

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