Using Point of Care Ultrasound to Augment Acquisition of Physical Exam Skills: Organs

Point of care ultrasound, or POCUS, is a portable and less comprehensive technique than conventional ultrasound. It is typically performed at the bedside to supplement regular physical exams, usually with a focus on a specific clinical question. For example, POCUS can be used for diagnostic purposes, such as to confirm the presence of gallstones. Alternatively, it can be used for guidance during clinical procedures such as vascular access, thoracentesis, arthrocentesis, and local anesthesia.

POCUS involves the use of a small handheld device called a transducer. The transducer releases ultrasound waves into the body. Some of these waves are reflected from the body tissues back to the transducer, and these are used to construct the image.  The amplification of the reflected waves or brightness can be regulated using the gain function. An increase in the gain causes the amplification of the reflected waves or signals, resulting in a proportionate increase in the brightness of the image.   

There are mainly three types of signals received from the body. Hyperechoic signals appear bright and are produced when structures like bones and hard tissues reflect all the emitted waves back to the transducer. Hypoechoic signals produce varying shades of grey and are generated when structures like soft tissues reflect only some of the waves.  Anechoic signals result in black areas and are observed when body fluids such as blood, urine, and amniotic fluid do not reflect any waves.

Different transducers are used depending on the organ type and penetration depth required. The frequency of the waves determines the penetration depth. A linear array transducer with 10 to 15 megahertz high-frequency waves has a lower depth but gives a higher resolution. In contrast, a curvilinear and phased array transducer with 2 to 5 megahertz low-frequency waves allows deeper penetration but gives a low resolution. Therefore, a linear array transducer would be used to examine skin lesions, whereas a curvilinear transducer is preferred to examine an organ such as the liver. The phased array transducer has a small footprint, and therefore, it is commonly used for echocardiography.

In teaching, ultrasound can facilitate the learning of difficult skills, such as the examination of the cardiovascular system, lungs, abdomen, and thyroid. Ultrasound provides visual clues to auscultation and allows real-time visualization of the closing of heart valves and the timing of systole and diastole.

Also, palpation of certain body parts such as the abdominal aorta, the thyroid, and the liver edge, is often met with uncertainty. Ultrasound increases the accuracy of the palpation as it allows confirmation of hand placement and verification of the findings. In percussion, measurements of diaphragmatic excursion and liver span can be further compared and confirmed with ultrasound measurements, helping learners to hone the percussion technique.

In part one of this video series, we will demonstrate how to use POCUS to facilitate learning the examination of the thyroid, lung, heart, liver, and spleen in a healthy subject.

To begin, first, choose the appropriate probe based on the body organ you plan to examine. For superficial structures, such as the thyroid, choose the linear probe, and for deeper structures, such as the gallbladder, choose the curvilinear probe. In the case of cardiac imaging, the phased array probe should be used.

Next, select the suitable exam preset according to the body area to be examined. For example, select the cardiac preset for the examination of the heart. Apply the gel to the probe to allow transmission of the ultrasound beam from the probe to the body. After that, place the probe above the organ of interest.

To avoid sliding, firmly hold the probe with a thumb on one side and index and middle fingers on the opposite side, allowing the little finger and lower palm to rest on the body surface for stability.

For cardiac examination, the indicator is typically on the right side of the screen, though some point of care ultrasound practitioners will have it on the left side. For all other applications, the indicator is on the left side of the screen. The indicator on the probe is generally directed to the patient's right side or head, except during cardiac ultrasound.

Now, the image should be optimized on the screen using the depth and gain options. To do this, first, adjust the depth so that the structure of interest is in the middle of the screen. After that, adjust the gain until the target structure is bright enough to see clearly without washing out the anechoic structures.

The palpation of the thyroid has been discussed in the previous JoVE video "Thyroid Exam".

Learners usually do not feel confident while palpating the thyroid because of its subtle nature. Ultrasound allows the live visualization of the thyroid location, which helps to increase the confidence of the learners and hone their palpation skills.

As the thyroid is a superficial structure, use the linear probe for its examination. Then, select the superficial preset option present on the ultrasound screen. With the patient in a seated position, gently tilt their head in a slightly upward direction to provide better access to the neck area. With the gel-lubricated probe in a transverse position, gently slide it onto the patient's neck. As the image appears on the screen, optimize the view using the depth, gain, and other options.

The isthmus of the thyroid should appear on the screen. Now, gently move the probe to the right and left of the patient's neck and identify the right and left lobes of the thyroid, carotid artery, and sternocleidomastoid muscle. Mark the level of the isthmus on the patient's neck using a skin marking pen.

Now, turn the probe 90 degrees such that the indicator is oriented towards the patient's head. This orientation of the probe gives the sagittal view of the isthmus of the thyroid. With the probe placed on the neck, ask the patient to swallow and observe the upward movement of the isthmus. Remove the ultrasound probe and clean the patient's neck.

Finally, palpate the thyroid guided by the skin marking and knowledge obtained through visualization of the surrounding structures.

The percussion of the lung has been previously demonstrated in the JoVE video "Respiratory Exam II: Percussion and Auscultation".

Most of the time, learners do not feel confident enough while percussing the diaphragms. Ultrasound allows the real-time visualization of the movements of the diaphragm, which helps to increase the learners' confidence and improve their percussion skills.

To begin the ultrasound exam, first, select the curvilinear probe and apply gel to it. Then, click on the abdominal preset present on the screen. Now, place the patient in a sitting position with their arms crossed, and palms reaching to the shoulder. Orient the probe with the indicator directed towards the patient's head and slide it onto the posterior thorax. When the image of the lungs and other abdominal organs appears on the screen, optimize the view with the help of the depth and gain functions and then identify the diaphragm.

Now, ask the patient to inhale and hold their breath. Next, identify the diaphragm and mark its level on the patient's body. After that, ask the patient to exhale and hold their breath, note the movement of the diaphragm, and mark its level. Finally, use percussion to identify the excursion of the diaphragm with inhalation and exhalation.

The auscultation of the heart has been discussed in the previous JoVE videos "Cardiac Exam II: Auscultation" and "Cardiac Exam III: Abnormal Heart Sounds".

Early learners of the heart exam often have difficulty correlating heart sounds to the cardiac anatomy, which can affect their understanding of the origins of heart sounds and the diagnosis of heart diseases in patients. POCUS allows a direct correlation between heart-valve movements and related sounds and therefore helps in the accurate examination of the heart.

To begin, take the phased array probe and apply lubricant gel to it. Next, select the cardiac preset available in the preset selection tab. For the purposes of learning the physical exam, have the ultrasound screen indicator on the right side of the screen. With the probe indicator directed towards the patient's right shoulder, place the probe at the left upper sternal border and slide inferiorly until the parasternal long axis view is seen. Optimize the obtained ultrasound image using the applicable dials. After that, record a short video clip of the ultrasound image.

In the ultrasound image, note the movement of the mitral valve and correlate it to the first heart sound, S1, caused by the closure of the mitral and tricuspid valves. Next, note the movement of the aortic valve and correlate this to the second heart sound, S2, produced due to the closure of the aortic and pulmonic valves. While observing the movement of the valves, also review the timing of the murmurs of aortic regurgitation and mitral regurgitation. Now return to the parasternal long-axis view of the heart and auscultate the heart while observing the movement of the valves.

Next, palpate the point of maximal impulse and place the probe at this spot with the indicator directed to the left side of the patient. Such orientation of the probe provides the apical 4 chamber view of the heart. Optimize the obtained ultrasound image and then capture a short video clip of the apical 4 chamber view. On the video clip, observe the opening and closing of the mitral and tricuspid valves and correlate it with the first heart sound, S1. Observe the ventricles during the diastolic and systolic phases of each cardiac cycle and time it with the opening and closing of the mitral valve. Also, correlate the third, S3, and fourth, S4, heart sounds with early and late diastole.  

The percussion and palpation of the liver have been discussed in the previous JoVE videos "Abdominal Exam II: Percussion" and "Abdominal Exam III: Palpation".

The beginners often struggle to confidently find the liver edge with palpation and approximate the liver size using the percussion method. POCUS provides a non-invasive way to visualize the liver and, therefore, can assist learners in the proper examination of the liver.

For the liver examination, use the curvilinear probe and apply the gel to it. Next, select the abdominal preset available on the ultrasound screen. Now place the patient in the supine position. With the probe indicator directed towards the patient's head, position the probe at the midclavicular line in a sagittal plane. An image of the liver should appear on the screen. Optimize the obtained image using the depth and gain functions.

Now, ask the patient to inhale and exhale and observe the liver movement with respirations. Next, freeze and acquire the image and use it to measure the vertical span of the liver. Now, slide the probe in the mid-clavicular line first cranially and then caudally to identify and mark the upper and lower edges of the liver on the patient's skin.

Finally, percuss the liver span in the midclavicular line and compare the measurements obtained by percussion and ultrasound scanning. Use the reference mark of the lower edge of the liver identified during the ultrasound to guide palpation of the liver edge.

The percussion and palpation of the spleen have been discussed in the previous JoVE videos "Abdominal Exam II: Percussion" and "Abdominal Exam III: Palpation".

Usually, it is not possible to palpate a normal-sized spleen. However, during the examination, POCUS allows the learners to understand the normal location of the spleen and observe the spleen movement towards the hand with inspiration.

For examination of the spleen, select the curvilinear probe and apply the gel to it. Next, choose the abdominal preset present on the ultrasound screen. With the probe indicator directed towards the patient's head, place the probe in a coronal plane at the left mid-axillary line. Optimize the obtained image using the depth and gain functions, until the ultrasound image of the spleen appears clearly on the screen.

Next, ask the patient to inhale and exhale, and note the movement of the spleen with respirations. Now, use palpation to identify the lowest intercostal space in the anterior axillary line, also known as Castell's point. Mark Castell's point on the skin. As the patient inhales and holds, slide the ultrasound probe caudally to find the lowest intercostal space where the spleen can still be seen on inspiration. Mark this point on the skin. The comparison between these two marked lines can be helpful in understanding how percussion at Castell's point can identify splenomegaly.