Point-of-Care Ultrasound Closer look at the Inferior Vena Cavae & Brief Introduction to Gross Systolic Function Omar S. Darwish, MS, DO Certified in Point-of-Care Ultrasound Hospitalist University of California, Irvine
Objectives Know the Terminology and Basic Concepts of Bedside Ultrasound Learn how to acquire the IVC image Learn how to interpret the diameter and collapsibility of the IVC Know which view is best to assess systolic function Know how to objectively determine the degree of systolic function
Literature Indications for IVC Ultrasound Literature says: Estimation of intravascular status; i.e. any patient undergoing fluid resuscitation in order to monitor for response Differentiate causes of shock Shock States Cardiac Tamponade Acute Pulmonary Embolism Acute Congestive Heart Failure Pneumothorax Sepsis IVC DIAMETER Dilated, low collapsibility index Dilated, low collapsibility index Dilated, low collapsibility index Dilated, low collapsibility index Small, high collapsibility index
My Indications for IVC Ultrasound Unknown history of CHF, but with risk factors requiring high IV fluid rates Known history of CHF who require high IV fluid rates CHF exacerbation à assess response to diuretics Some Examples of patients who require IV fluid rates Rhabdomyolysis (particularly CPK > 5000) Hypercalcemia Acute Pancreatitis Severe Sepsis Diabetic Ketoacidosis
Terminology. Imaging Plans Transverse or Axial Longitudinal or Sagittal
Concept 1. Probes with Different Frequencies Many different types of probes that vary in frequency and foot print size For us you need to know only 3 (The letter represents the type of probe and the number represents the length in millimeters) P21 (phase array, 21 mm) à 1-5 MHz L38 (linear probe, 38 mm) à 5-10 MHz C60 (curvalinear probe, 60 mm) à 3.5-5 MHz Increasing the frequency, improves the resolution At higher frequencies it becomes more difficult to see deeper structures On the machine you can adjust the frequency of a probe. For SonoSite, words are used to describe the different frequencies: RES, GEN, PEN E.g. For a P21 RES: 5 MHz, 3 GEN, 1 PEN C60 P21
Concept 2. Physiology for Spontaneous Breathing Inspiration Expiration Pleural Pressure Pleural Pressure Increase Venous Return IVC collapses Decrease Venous Return IVC expands
Mechanically Ventilated Patients Inspiratory Phase Expiratory Phase Pleural Pressure Pleural Pressure Decrease Venous Return IVC expands Increase Venous Return IVC collapses
Concept 3. Temporal Resolution Effects of Temporal Resolution: the number of frames/second (i.e. cardiac setting has a high temporal resolution) Software setting (cardiac, abdominal) à use the right setting i.e. make sure you are on the cardiac setting when performing a cardiac ultrasound Depth of the image à worsens resolution Using Color flow doppler à worsens resolution
Acquiring the IMAGE
Step 1. Find the Xiphoid Process. Xiphoid Process Acoustic Shadowing Place Probe in the Transverse Position Below Xiphoid Process
Step 2. Rotate Probe 90 degrees clockwise
You can skip the first step and place the probe longitudinally first but make sure you are looking at the IVC and not the aorta
IVC Diameter (cm) Collapsibility (%) Estimated CVP (mm Hg) < 1.5 100 0-5 1.5-2.5 >50 6-10 1.5-2.5 <50 11-15 >2.5 <50 16-20 >2.5 0 >20 Measure IVC 2 cm inferior to hepatic vein Otto CM. Echocardiographic evaluation of left and right ventricular systolic function. Textbook of clinical echocardiography. 2 nd ed. Philadelphia: WB Saunders; 2000.
Measuring IVC in Supine vs Left-Lateral Decubitis Position IVC diameter is larger in the supine position than in the left lateral
European Association of Echocardiography, 2005 Description Small IVC (cm < 1.2 cm Normal Dilated Markedly Dilated 1.2-1.7 cm 1.7-2.5 cm >2.6 cm IVC athletes: 2.31 + 0.46 cm vs controls 1.14 + 0.13 cm Swimmers: 2.66 vs 2.17 cm in other athletes Collapsibility index 58% in athletes compared to 70% in controls
IVC Diameter (cm) Collapsibility Index with Sniff Estimated Right Atrial Pressure (mm Hg) < 2.1 >50% 3 mm Hg (0-5) >2.1 <50% 15 mm Hg (10-20) If it does not fit both criteria, then an intermediate estimated right atrial pressure of 8 mm Hg (5-10) is given
Interpretation of the IVC Diameter Size Only Average People Fluid Overload, Normal Variant in Athletes IVC Diameter Small Dilated 1.0 cm 2.0 cm 2.7 cm Normal Range Dilated My Interpretation
Elevated Right Atrial Pressure Normal Right Atrial Pressure IVC Collapsibility Index 0% 20%** 50% 80% 100% Highly Likely Fluid Tolerant Highly Likely Fluid Intolerant
Bottom Line. The IVC is overall considered dilated > 2.5-2.7 cm, however, this by itself does not mean that with 100% specificity that the patient is fluid overloaded. The IVC collapsibility index has a better predictability value than the diameter of the IVC regarding a patient s fluid status. As to the degree of collapsibility the reference point of 50% has been reported many times to be the best cut off in regards to providing the best combined sensitivity and specificity.
2.37-2.25/2.37 x 100%= 5% During inspiration, IVC measured at 2.25 cm
How to interpret collapsibility of the IVC? Fluid responsiveness vs Fluid tolerance Fluid unresponsiveness vs Fluid intolerance
Fluid Tolerance IVC Diameter (cm) Collapsibility (%) Estimated CVP (mm Hg) < 1.5 100 0-5 1.5-2.5 >50 6-10 1.5-2.5 <50 11-15 >2.5 <50 16-20 >2.5 0 >20 Fluid Intolerance
How to Assess Systolic Function
Parasternal Long Axis View Place P21 probe on the left side of the sternum around the 3-4 intercostal space Make sure you stay close to the sternum Indicator should be pointing to the Left Elbow with the indicator on the screen to be on the left
Parasternal Long Axis View
What is the systolic Function?
Conclusion IVC ultrasound is common data point that can help you in determining fluid status in a patient. Diameter and collapsibility information should then be applied to the clinical context of the patient. The Parasternal long axis view is the best view to determine gross systolic function when using bedside cardiac ultrasound.
Ventilated Patient 1) Sinus rhythm 2) PEEP > 4 mm Hg 3) Tv 8 ml/kg We recommend critical care practitioners consider measuring IVC collapsibility in patients on positive pressure ventilation by bedside cardiac ultrasound to assess fluid responsiveness prior to undergoing large volume fluid resuscitation. Any patient who has more than 15% change in vena caval diameter should be considered preload responsive. Patients with a smaller change in IVC diameter may not respond favorably to fluid resuscitation. Grade 1B, 2016
Measuring IVC in Ventilated Patient Meausuring the difference between the max and min diameters/mean of the two values = Respiration Variation > 12% Meausuring the difference between the max and min diameters/minumum diameter = Distensibility Index > 18% Not perfect, but absence of respiratory variation in a shock patient suggest that volume expansion will be ineffective 90% of cases.
Guidelines Supported goes back to 2008 2008 ACEP Policy Statement on Emergency Ultrasounds includes evaluation of intravascular volume status and estimation of CVP based on imaging of the IVC.
85 year-old woman admitted 4 days ago before I started service on Monday for Severe Sepsis due to Strep Pneumonia with positive blood cultures improving overall, but requiring oxygen 2 liters of oxygen, desaturates to high 80s on room air. Hospitalist Options 1) d/c on home oxygen 2) See if there is alternative explanation of her hypoxia
Pulmonary Pressures are effected by the Intravascular fluid volumes of a patient P = 4v 2 = RVSP - RA --> 4(3.02) 2 = 36.48 36.48 + RAP (est 15 mm Hg) = RVSP =51.5 mm Hg
After removal of nearly 6 liters of fluid At Discharge: O2 saturation 95% on RA