Dr. Rawan Alrashed (@rawalrashed)

PEM Physician

PoCUS Fellow

Reviewed and edited by: Dr. David Lewis

Case

A 55 year old man known to have hypertension, diabetes, atrial fibrillation, chronic kidney disease presenting with 1 week H/O fever, SOB, chest pain, cough, fatigability, looking distressed on exam with HR 110, SpO2 of 86% on RA and BP of 87/45. No audible crackles or gallop rhythm, bilateral pitting edema noticed.

So, you are asking yourself should your next step be Fluids or Diuresis ??

Background

Patient presenting to the emergency department as critically ill with shock status presents a challenge in the initial hour to balance their fluid requirements with their volume status to reach an improvement in hemodynamics without causing harm.

Volume status assessment and fluid responsiveness have been investigated using multiple measures ranging from physical examination to laboratory work up to invasive measures. Despite all that, no single or multiple factor have been sensitive or specific enough to guide further fluid management. Currently, PoCUS is progressing widely in aiding the emergency physician to take a decision in assessing patient’s  fluid vs vasopressor vs diuretic needs and guide further resuscitation. PoCUS is noninvasive, readily available, reproducible test that can be augmented with other measures to guide fluid management (1).

 

Pathophysiology

To simplify fluid responsiveness, patients are assessed on accordance of the Frank-Starling curve. Patients will respond to fluid administration if they are on the ascending portion of the Starling curve and no benefit will be added if they are at a plateau where more harm can occur which is difficult to be predict form physical examination solely (2).

 

 

Fluid Challenge

Traditionally volume responsiveness has been assessed by small fluid bolus challenge. A safer alternative to this is passive leg raise (PLR) which is an autotransfusion where you mobilize about 300-500 ml of intravascular volume from the lower limb to the heart by raising the patient legs from 0^o to 45^o. A Pre-Post assessment of stroke volume within 30-90 sec from PLR can be done to measure the difference where change of 10% consider to be responsive.

This have been shown to have a sensitivity of 77% to 100%, and a specificity of 88% and 99% (1).

 

 

Volume Status Assessment

PoCUS have been used in volume status assessment and fluid responsiveness using multiple surrogates which can be classified as follows for simplification:

1. Cardiac PoCUS: core and advanced.
2. Stroke volume Assessment: VTI of LVOT/Carotid artery.
3. Vascular Assessment: IVC, IJV.
4. Venous Congestion: Hepatic, portal, & intra-renal doppler.
5. Lung PoCUS.

 

1) Cardiac PoCUS

The target of Cardiac PoCUS is to assess for possible causes of hypotension and shock status using the RUSH or SHoC protocol (3).

 

 

2) Cardiac Output Assessment

Two measures can be used to assess fluid responsiveness: the left ventricular outlet tract (LVOT) and the carotid artery where you assess the velocity time integral (VTI) representing the column of blood passing through the vessel through time. This can be used as surrogate of fluid responsiveness before and after the PLR where a change of 10-15% consider as fluid responsive (4).

 

a. LVOT measurements

Cardiac output variation of greater than 14% has a high positive predictive value for the patient being fluid responsive while values less than 10% are associated with a high negative predictive value (1)

Cardiac output (mL/min) = Stroke Volume (mL/cycle) x Heart Rate (bpm)

Stroke Volume= LVOT area    x    LVOT VTI

 

PoCUS Technique (4)

• Using the cardiac phased array probe to get apical 5 chamber view and parasternal long axis view.
• Apical five chamber view, with visualization of the LVOT (A).
• Pulsed wave Doppler interrogation of the LVOT. The interrogation window is placed just above the aortic valve, and the line of interrogation is positioned parallel to the long-axis of the LVOT itself (B).
• Measuring the area under the curve of the LVOT Doppler waveform to derive the velocity time integral (C) .
• Diameter of the LVOT, measured from a parasternal long-axis view (D)

 

 

b. Common Carotid Artery

Two measurement are applied to the carotid artery: the carotid blood flow and the corrected carotid flow time index. These measure are recently established in the field of cardiac output assessment and accuracy is still under debate with further studies needed.

 

• The carotid blood flow is the integral of blood volume that is ejected through the carotid artery with each cardiac cycle. An increase of carotid blood flow by 20% after PLR is indicative of fluid responsiveness with a sensitivity of 94% and specificity of 86% (6).

 

• The corrected carotid flow time index  (CFTI) representing the flow time between the onset of systole and the closure of the aortic valve as the duration of the full cardiac cycle. A change in the CFTI of 25% following PLR was found to have high specificity but a low sensitivity accordingly a cutoff values of 10% to 15% are more typical, still further studies are needed to specify the accurate cut off value (4).

 

PoCUS Technique (4,5)

a. The linear transducer is placed at approximately at the level of the thyroid cartilage, with the orientation marker pointed toward the patient’s head (A).

b. The Carotid artery identified in long-axis and the bulb before the bifurcation visualized and the doppler is applied within 2–3 cm proximal to the carotid bulb, interrogation line (green) has also been angled to make it more parallel to the long-axis of the artery.

c. The Doppler angle correction cursor is placed parallel to the direction of blood flow with insonation angles <60° .

d. Carotid artery Doppler waveform with measurement of the systolic flow time (SFT) and total cycle time (CCT).

e. Calculate the corrected flow time index using the following formula (Figure-5):

                                           CFTI=SFT/√CCT

f. Calculate the carotid blood flow using velocity time integral tracing and carotid diameter (Intima to intima)  then apply it in this formula (Figure-6):

                                     blood flow=π×(carotid diameter)2/4×VTI×heart rate

 

 

 

 

 

3) Vascular Assessment

a. Inferior vena cava (IVC)

Measurements of IVC diameter and respiratory variation with the collapsibility index as a predictor of fluid responsiveness was found to be having pooled sensitivity and specificity of 63% and 73% respectively (7).  

PoCUS Technique (8)

• Use the curvilinear or phased array probe.
• placed in the sub-xiphoid space with the transducer flat against the abdomen identifying RA and gradually fanning the probe until the intrahepatic IVC can be identified.
• The probe is then rotated 90 degrees with the marker toward patient head to obtain the IVC in long axis view.
• IVC diameter is measured 2 cm inferior to the cavo-atrial junction or about 1 cm inferior to the branching of the hepatic veins (Figure 7).
• M-mode can be used to track IVC collapse during inspiration in spontaneously breathing patients.

 

Measurements:

Collapsibility Index (Caval Index)

The collapsibility index=(maximal vessel diameter – minimal vessel diameter)÷maximal vessel diameter

It has been demonstrated that venous collapsibility may be inversely proportional to CVP: a 1 mmHg change in central venous pressure correlates to about 3.3% change in IVC collapsibility (9).

 

IVC diameter (cm)	CI (%)	CVP (mmHg)
<1.5	100%	<0-5	Volume depleted
1.5-2.5	>50%	<10	Less predictive of responsiveness
1.5-2.5	<50	>10
>2.5	0%	>20	Volume overload

 

Important to note that sole interpretation of the IVC for volume assessment was found to be poorly correlating and thus should be used in conjunction with  other measures and integrated on patient presentation (9).

 

b. Internal Jugular Vein (IJV)

Internal jugular vein is used for the assessment of the central venous pressure in comparable way to IVC. A small study of non-ventilated patients who were simultaneously undergoing CVP monitoring, a mean IJV diameter of 7 mm correlated with a CVP of 10 mmHg (8). 

Collapsibility index of the IJV with change of 39% consider the patient as volume depleted but this carries a limitation of the intrabdominal/ intrathoracic pressure effects (4).

PoCUS Technique

• Use the linear Probe
• Identify the IJV in transverse plane then rotate the probe 90^o toward the patient head.
• Image of IJV is obtained where it narrows into a paintbrush appearance (Figure 8).
• The height where the IJV tapers correlates with jugular venous distension.
• The IJV diameter is measured using M-mode through several respiratory cycles, and the end expiratory diameter is used as the final measurement.

 

4)Venous Congestion (VEXUS):

This includes assessment of the Hepatic/Portal/Intrarenal veins wave forms which has been correlated to the level of venous congestion thus estimating the end organ volume effects.

Hepatic Vein Doppler mainly reflects the right atrium filling pattern, portal and intrarenal venous Doppler provide additional information about right atrial filling pressure and its correlation with congestive organ injury (10).

 

PoCUS Technique (9)

Hepatic Vein Doppler

• The probe is placed over the liver in the subcostal position to visualize the middle hepatic vein. Pulsed-wave Doppler is used 2-4 cm from where the hepatic vein drains into the IVC.

Findings: The waveform of the hepatic vein is reversed with higher velocities seen in diastole in states of volume overload. In severe volume overload, retrograde flow is seen in systole (Figure 9)

 

 

Portal Vein Doppler

• Moving towards the portal vein, the transducer is placed in the right mid-axillary line

Findings: Flow through the portal vein is normally monophasic, but in the presence of hypervolemia, pulsatility will be present. This can be quantified using the pulsatility index where a pulsatility index greater than 50% indicates severe volume overload.

 

 

Intra-renal Doppler

• The curvilinear transducer is placed on the posterior axillary line

Findings: A normal Doppler waveform is continuous. With increasing venous congestion, there is a decrease in the systolic component of the wave with progression to biphasic (systolic/diastolic phases), and with severe renal congestion, there is complete absence of systolic flow showing only diastolic phase.

 

 

 

 

5)Lung Ultrasound 

A meta-analysis showed that LUS is 88% sensitive and 90% specific for acutely decompensated heart failure and was more sensitive at detecting pulmonary edema than CXR (8).

Another meta-analysis determined the sensitivity and specificity of ultrasound for detection of pleural effusions as 93% and 96% respectively. The sensitivity approaches 100% with pleural effusions >100 mL in volume (8).

PoCUS Technique

• Use the linear or curvilinear probe.
• In longitudinal plane, along the midclavicular, midaxillary line then the posterior-lateral point.

Findings:

• B-lines are hyperechoic vertical lines extending from the pleura down to the bottom of the US image (Figure 14). Two or fewer B-lines in each section is considered normal
• Pleural effusion can be identified with presence of V-sign (extension of vertebral line proximal to the diaphragm (Figure-15) .  

 

 

 

 

 

 

 

 

 

 

 

Case Conclusion

Patient was found to have reduced LV function with Dilated IVC and CI of 15%, VExUS grade 2. Assessment of COP after PLR didn’t show a proper change thus patient was started on diuretic and respiratory support with consideration of inotropic support. 

Conclusion

The table below (8) shows a summary of the evidence related to the different used marker for volume assessment from physical exam to the use of PoCUS. Thus, it is imperative that we do not rely on one single tool, but rather integrate both pertinent physical examination and POCUS findings for better probability of coming to the right decision.

 

 

References

1. Pourmand A, Pyle M, Yamane D, Sumon K, Frasure SE. The utility of point-of-care ultrasound in the assessment of volume status in acute and critically ill patients. World J Emerg Med. 2019;10(4):232-238. doi:10.5847/wjem.j.1920-8642.2019.04.007.
2. Praveen P., Shanmugam L., Prasath, P. A review of role of lung ultrasound and clinical congestion score in acute left ventricular failure. International Journal of Advances in Medicine. 2020;7. 720. 10.18203/2349-3933.ijam20201130.
3. Atkinson P, Bowra J, Milne J, et al. International Federation for Emergency Medicine Consensus Statement: Sonography in hypotension and cardiac arrest (SHoC): An international consensus on the use of point of care ultrasound for undifferentiated hypotension and during cardiac arrest – CORRIGENDUM. CJEM. 2017;19(4):327. doi:10.1017/cem.2017.31.
4. Millington SJ, Wiskar K, Hobbs H, Koenig S. Risks and Benefits of Fluid Administration as Assessed by Ultrasound. Chest. 2021;160(6):2196-2208. doi:10.1016/j.chest.2021.06.041.
5. Ma IWY, Caplin JD, Azad A, et al. Correlation of carotid blood flow and corrected carotid flow time with invasive cardiac output measurements. Crit Ultrasound J. 2017;9(1):10. doi:10.1186/s13089-017-0065-0.
6. Marik PE LA, Young A, Andrews L. The use of bioreactance and carotid Doppler to determine volume responsiveness and blood flow redistribution following passive leg raising in hemodynamically unstable patients. Chest. 2013;143(2):364-370. doi:10.1378/chest.12-1274.
7. Long E, Oakley E, Duke T, Babl FE. Does Respiratory Variation in Inferior Vena Cava Diameter Predict Fluid Responsiveness: A Systematic Review and Meta-Analysis. Shock (Augusta, Ga). 2017;47(5):550-559.
8. Kearney, D., Reisinger, N., & Lohani, S. (2022). Integrative Volume Status Assessment. POCUS Journal, 7(Kidney), 65–77.
9. Argaiz Eduardo R, Koratal A., Reisinger N. Comprehensive Assessment of Fluid Status by Point-of-Care Ultrasonography. Kidney360 Aug 2021, 2 (8) 1326-1338; DOI: 10.34067/KID.0006482020. 
10. Galindo P, Gasca C, Argaiz ER, Koratala A. Point of care venous Doppler ultrasound: Exploring the missing piece of bedside hemodynamic assessment. World J Crit Care Med. 2021;10(6):310-322. Published 2021 Nov 9. doi:10.5492/wjccm.v10.i6.310.
11. Dinh, V. (n.d.). Vexus ultrasound score – fluid overload and venous congestion assessment. POCUS 101. Retrieved March 29, 2022, from https://www.pocus101.com/vexus-ultrasound-score-fluid-overload-and-venous-congestion-assessment/.