The use of portable ultrasound to estimate intravascular volume status and extravascular lung water has been validated in the management of acute respiratory failure and heart failure. The literature validates the use of ultrasound for evaluation and management of fluid resuscitation in hypovolemic states. We propose a sample protocol which integrates lung and IVC ultrasound to guide diuresis and renal replacement therapy in volume overload states and specific pulmonary edema.
Use a phased array low frequency probe. Select the appropriate machine setting. The abdominal setting will be used for this exam.
In this setting the screen marker should be operator left. The depth can be adjusted to provide optimal image resolution. For this exam the machine depth is set to eight to 12 centimeters.
Place the patient in a supine or semi recumbent position and expose the anterior chest. The probe should be held with the probe marker facing cephalad. With it's probe marker facing cephalad, the transducer is placed at a 90 degree angle to the patient in the third and fourth intercostal space of the right anterior chest wall at the mid clavicular and anterior axillary lines.
This protocol is to be performed at two locations:the mid-clavicular line at the second to third or third to fourth intercostal space, and the mid-clavicular line at the fourth to fifth or fifth to sixth intercostal space. The same protocol and evaluation is repeated at the left anterior chest for a total of four locations of ultrasound imaging at the chest. An A-line predominant pattern is seen here.
A-lines are horizontal, regularly spaced, hyperechoic lines representing reverberations of the plural surface, and suggest a dry lung without pulmonary edema. This image represents a normal aeration pattern. Up to one B-line is occasionally noted.
A B-line pattern is seen here. B-lines are vertical hyperechoic artifacts that extend from the inferior aspect of the plural line to the lower edge of the screen without fading. They fan out from the plural surface and move synchronously with the lung during respiration.
B-lines arise due to extra vascular lung fluid, and their presence suggests pulmonary edema in the appropriate clinical context. The severity of the B-line pattern predicts the degree of pulmonary edema and will indicate the aggressiveness of diuresis or renal replacement therapy needed to resolve the pulmonary edema. Seen here is an example of a mild B-line pattern.
Two or three B-lines are visible during at least 50%of the video clip. This pattern suggests the presence of mild pulmonary edema. A mild regimen for diuresis or fluid removal is indicated.
Seen here is a moderate B-line pattern. There are four or more B-lines visible for the duration of the clip. Moderate to severe pulmonary edema is suggested.
Aggressive diuresis or renal replacement therapy is indicated. Seen here is an example of a whiteout B-line pattern. No A-lines are present.
The B-line pattern is one of total confluence and a whiteout of the space below the plural surface. This represents very severe pulmonary edema. Very aggressive diuresis or fluid removal by renal replacement therapy is indicated.
Use a phased array low frequency probe. Select the appropriate machine setting. The cardiac setting will be used for this portion of the exam.
In this setting the screen marker should be operator right. Adjust the depth to achieve optimal image resolution. The depth is set to 12 to 21 centimeters for this exam.
Place the patient in a supine or semi recumbent position, exposing the anterior chest. The probe marker will be held cephalad. With it's probe marker facing cephalad, the transducer must be placed at a 90 degree angle to the patient at the subxiphoid region, slightly right lateral and tilted slightly cephalad.
The objective is to visualize the proximal inferior vena cava in it's longitudinal plain, the cavoatrial junction, as well as the diaphragm, the liver, and the hepatic vein. These structures are labeled on the image shown. Select M-mode from the ultrasound machine interface.
Using the touch pad scroll back and forth to select an M-mode beam which passes through the inferior vena cava. The location of the beam should be two to four centimeters distal to the cavoatrial junction in a perpendicular incidence. Select the M-mode button a second time.
Freeze the screen after the M-mode reading is complete through at least one respiratory cycle, as shown in the image. Measurements may be performed on screen using the caliper function on the machine interface as shown. Measurements should be performed from inside edge to inside edge.
Shown here is an example of a large caliber plethoric inferior vena cava with minimum to no variation throughout the respiratory cycle. The minimum diameter is greater than 2.1 centimeters. This finding suggests an intravascular volume replete state, or a hypervolemic state.
There is a high likelihood that the subject will tolerate aggressive diuresis or renal replacement therapy. Shown here is an example of a small incompliant vena cava with excess variation throughout the respiratory cycle. The maximum diameter is less than one centimeter.
This finding suggests intravascular volume depletion, and the likelihood that the subject will not tolerate aggressive diuresis or fluid removal. A summary of chest ultrasound observations and their corresponding results are shown in the table. These conclusions are to be drawn in the correct clinical context.
Inferior vena cava caliber as described in the next section to be used to refine and maintain fluid removal goals. A summary of inferior vena cava ultrasound measurements and their corresponding results are shown in the table. Inferior vena cava caliber as determined by machine caliper measurements can determine the patient's ability to withstand aggressive diuresis.
These values should be used in the assessment of pulmonary edema to help guide fluid removal. Portable ultrasound is a versatile tool that can be used to accurately and reliably assess a patient's volume status. A patient with a clinical presentation suggestive of pulmonary edema may be evaluated for the extend of pulmonary edema by quantitative measurements of B-lines.
This measurement detects the amount of extravascular volume present. Further investigation of intravascular fluid may be done via ultrasound of the IVC. Taken together, these data can guide fluid management in patients with pulmonary edema or patients requiring renal replacement therapy.
