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

  1. heart rate

  2. blood pressure

  3. collapsed veins

  4. capillary refill time

  5. previous urine output)

 

B) Objective

  1. CVP/PCWP (also delta CVP post fluid challenge)

  2. CXR

  3. PiCCO

  4. Echo- EDV

  5. EVLW and ITBV

  6. Trend in lactate or SvO2

 

2. Dynamic parameter

 

  1. Pulse pressure variation (PPV) with - PLR, End-exp occlusion test, & Mechanical ventilation

  2. Strove volume variation (SVV) with- PLR, Mechanical ventilation

  3. Subaortic velocity time index (VTI) allows measurement of stroke volume

Echo for assessment of volume status & fluid responsiveness

A) IVC-

  1. IVC diameter

  2. IVC collapsibility index

  3. IVC distensibilty index

  4. Delta IVC

B) Volume-

  1. LV end diastolic volume (LVEDV)

C) Stroke volume-

  1. LVOT VTI variation with respiration

  2. 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.

  

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