Bedside Ultrasound for Guiding Fluid Removal in Patients with Pulmonary Edema: The Reverse-FALLS Protocol

Summary

We describe an imaging protocol that enables the clinician to visualize, in real-time, the patient's intravascular and extravascular space volumes and set diuresis and fluid removal parameters accordingly for the safe and efficient treatment of pulmonary edema.

Abstract

Fluid retention is the most common risk factor for mortality and cardiovascular complications in patients with volume-overloaded disease states. The extent of diuresis or fluid removal is frequently determined by physical examination which is subject to inaccuracies.

Bedside ultrasound (US) is a portable tool that brings real-time diagnostic imaging to the patient's bedside. This versatile modality makes it possible for the clinician to investigate patients' extravascular and intravascular volume states. The extravascular volume, particularly in the case of pulmonary edema, can be quantitatively assessed by US of the anterior chest. Intravascular volume is estimated by visualizing the inferior vena cava (IVC) caliber. Taken together, the degree of extravascular lung water and the IVC caliber provide objective data that can guide the clinician to determine the level of diuresis needed to effectively yet safely treat pulmonary edema.

The objective of this article is threefold: 1) to summarize the findings of previous studies on the efficacy of portable US to guide fluid management, 2) to describe a proposed ultrasound protocol to help guide fluid management, and 3) to elucidate techniques that address the measurement of intravascular and extravascular volumes using portable US.

Introduction

Fluid retention is the most common modifiable risk factor for mortality and cardiovascular events in volume overloaded patients¹. Fluid retention leads to poorly controlled hypertension, cardiac dysfunction and pulmonary edema, and has been associated with excess mortality in this population. The clinical estimation of a patient's volume status by combining the patient's symptoms, blood pressure, and weight changes represent a clinical assessment that is prone to imprecision². This article proposes a protocol that utilizes bedside ultrasound (US) techniques to guide the effective management of pulmonary edema. Chest and inferior vena cava (IVC) US form the cornerstone of this proposed clinical protocol for fluid removal. Both Chest and IVC US have a long track record in the literature for a spectrum of applications including the management of acute respiratory failure, end-stage renal disease (ESRD), and circulatory shock.

Chest US has been shown to provide objective data for the assessment of pulmonary edema in ESRD patients, and accurately reflects the decreasing severity of pulmonary edema as dialysis goes on³. Similarly, US of the inferior vena cava (IVC) has long been utilized for various clinical applications. IVC US is recommend as a routine component of transthoracic echocardiographic examination and serves several purposes, including for the estimation of right atrial pressure (RAP) that is a mark of volume status and pre- load to the heart⁴. Several studies have elucidated a correlation between IVC caliber and fluid responsivity in shock states^5,6. Also notable in the management of shock states, chest ultrasound has been used to detect the onset of new pulmonary edema during fluid resuscitation in circulatory shock, commonly by way of a bedside US application referred to as the Fluid Administration Limited by Lung Sonography (FALLS) protocol^7,8. The protocol proposed here, named the Reverse-FALLS protocol, combines well-documented features of chest and IVC ultrasound for the safe and effective management of pulmonary edema.

Portable, or bedside, US is an imaging modality that offers immediate and reliable data that reduces exposure to radiation, eliminates the need for patient transport, and reduces resource utilization. Due to its availability and the essential absence of associated adverse effects, bedside US can be repeated to monitor and tailor diuretic therapy. Finally, bedside US is easy for clinicians to perform and interpret in real-time⁹.

Chest US is a widely-accepted technique that detects specific artifact patterns that represent various pleural and parenchymal pathologies. For instance, "A-lines" are horizontal hyperechoic (bright) reverberation artifacts of the pleural surface and they indicate normal parenchyma that is free of fluid. Alternatively, "B-lines" are hyperechoic vertical artifacts that begin at the inferior aspect of the pleural line and extend to the end of the screen, moving synchronously with respiration. The presence of B-lines in the setting of suspected volume overload indicates extravascular lung water. These B-lines characteristically dissipate during diuresis in a manner that corresponds to volume removal leading to the re-emergence of the dry A-line artifact pattern³. Studies indicate that these US findings are closely associated with elevated pulmonary filling pressures, as assessed by invasive methods¹⁰.

US may also be used to measure the IVC vessel diameter and collapsibility index, which is the percentage of diameter reduction during spontaneous breathing. Several studies have shown a correlation between IVC measurements and volume changes during diuresis, demonstrating the feasibility and applicability of this tool for patients with pulmonary edema¹¹.

Here, we propose a sample US protocol, the Reverse-FALLS protocol, which integrates both lung and IVC US to guide fluid removal therapy in patients with pulmonary edema.

Protocol

1. Assess Extravascular Compartment Before Diuresis: Chest Ultrasound

1. Use a low-frequency, phased array probe.
2. Select the appropriate machine setting (abdomen or lung) with the screen marker operator-left.
3. Adjust the depth to 8-12 cm.
4. Place the patient in supine or semi-recumbent position and expose the anterior chest. Place the transducer at a 90° angle to the patient's anterior chest with the probe marker facing cephalad.
   1. Perform this protocol at the midclavicular line in two locations on each side of the chest for a total of four locations: in the 2^nd-3^rd or the 3^rd-4^th intercostal space, and in the 4^th-5^th or 5^th-6^th intercostal space.
   2. Visualize B-lines, if present.
      NOTE: B lines are echogenic artifacts with a narrow origin on the pleural line, and they move synchronously with respiratory movements (Figure 1).
5. Count the number of B-lines in each scan plane to quantify the extent of pulmonary edema.
   NOTE: Up to one B-line is normal; two to three B-lines represent mild pulmonary edema, whereas 4 or more B-lines represent moderate to severe edema; a whiteout pattern with no A-lines represents very severe pulmonary edema (Figure 2).

2. Assess Intravascular Compartment Before Diuresis: IVC Ultrasound

1. Use a low frequency, phased array probe.
2. Select the cardiac machine setting with the screen marker operator-right and adjust the depth to 12-21 cm for optimal image resolution.
3. Place the patient in a supine position and expose the anterior chest. Place the transducer at a 90° angle to the patient's sub-xiphoid region with the probe marker facing cephalad.
   1. Perform this protocol with the transducer located just right of the midline, tilted slightly right-lateral and cephalad.
   2. By scanning right-to-left, visualize both the IVC and the aorta.
   3. Note that the objective is to visualize the cavo-atrial junction, diaphragm, liver, hepatic vein, and IVC in its longitudinal plane. The aorta is visualized by angulating the scan plane medially (Figure 3).
4. Once the IVC and the cavo-atrial junction have been identified, set the ultrasound to M-Mode to measure the anterior-posterior diameter of the IVC.
   1. Using the touch pad, select the M-mode beam that corresponds to a near-orthogonal section, 2-4 cm distal to the cavo-atrial junction just beyond the visible hepatic vein.
   2. Select the M-mode button a second time, and freeze the screen after the M-mode reading is complete through at least 1 respiratory cycle.
   3. Use machine calipers for all measurements, measuring the vessel from internal edge to internal edge.
5. Measure D-max and D-min during a normal respiratory cycle.

3. Set Fluid Management Goals Based on Gradation of Pulmonary Edema and Diameter of IVC

1. Assess the lung ultrasound to determine the need for diuresis (Figure 2).
2. Assess the IVC ultrasound to determine the patient's ability to withstand diuresis (Figure 3).

4. Reassess Extravascular and Intravascular Compartments Throughout Diuretic Therapy.

1. Repeat the protocol as outlined above every 6 hours to evaluate the progress of diuretic therapy and to guide fluid management goals.

Results

Lung ultrasound estimates the amount of fluid in the extravascular compartment by visualizing A-line or B-line artifacts, as illustrated in Figure 1. The quantity of B-lines on lung ultrasound helps determine the amount of fluid removal required as illustrated in Figure 2. A mixed A-line and B-line pattern, or an A-line predominant pattern suggests lung parenchyma that is relatively free from extra fluid. Mild diuresis may be nec...

Discussion

Many studies have demonstrated that bedside US is a reliable diagnostic tool that can be used to guide the management of various disease states such as shock and dyspnea⁵. The correlation of B-lines with extravascular lung water has good sensitivity and specificity in evaluating for pulmonary edema, and studies have shown that lung US can reliably detect even modest variations in extravascular lung water^2,10. Similarly, studies have shown ...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Portable Ultrasound machine	Shown in video: FUGIFILM/Sonosite	Shown in video:  M- Turbo	Any portable ultrasound machine with the following capabilities •  B- Mode •  M- Mode •  Caliper measurement tool
Transducer	Shown in video: FUGIFILM/Sonosite	Shown in video:  P21	Any ultrasound transducer probe with the following capabilities: •  Phased Array •  Low frequency (1-5MHz)