Patient and Ultrasound Machine Positioning, Probe Selection and Orientation, Proper Ultrasound Care
Aarti Sarwal
1. A 45-year-old man is undergoing fluid resuscitation and vasopressor administration for suspected septic shock. He is intubated and placed on mechanical ventilation. To mitigate the risk of pulmonary edema, you decide to assess for volume responsiveness with a passive leg raise (PLR) before giving more fluids. Which of the following describes this maneuver most accurately?
A. Move the patient from a supine position to a supine position with the legs raised at 30° to 45°, avoiding femoral vein compression
B. Move the patient from a reverse Trendelenburg position to Trendelenburg position
C. Move the patient from a semi-recumbent (semi-Fowler’s) position to a supine position with the legs raised at 30° to 45°, avoiding femoral vein compression
D. Move the patient from a semi-recumbent (semi-Fowler’s) position to a Trendelenburg position
View Answer
1. Correct Answer: C. Move the patient from a semi-recumbent (semi-Fowler’s) position to a supine position with the legs raised at 30° to 45°, avoiding femoral vein compression
Rationale: The PLR test is a test for volume responsiveness where the reservoir of venous blood is returned into the central circulation quickly and a hemodynamic response is measured. An increase in cardiac output (CO) or stroke volume (SV) or decrease in inferior vena cava variation denotes volume responsiveness. The PLR is best performed by mobilizing the patient from a semi-recumbent position to a supine position (patient’s torso horizontal) with their legs elevated 30° to 45°, and not by manually raising the legs. This avoids compression of the femoral vein, which may reduce the venous return to the heart. Approximately 300 mL of intravascular volume is shifted during a PLR when performed properly. The CO or SV should be assessed 1 minute after the PLR, because at this time the effect seems the highest.
Selected Reference
1. Orde S, Slama M, Hilton A, Yastrebov K, McLean A. Pearls and pitfalls in comprehensive critical care echocardiography. Crit Care. 2017;21:279. doi:10.1186/s13054-017-1866-z.
2. A 75-year-old man with elevated body mass index (BMI) is being admitted to the intensive care unit (ICU) for undifferentiated shock. In order to assess for the etiology, a point-of-care echocardiogram is performed, but with suboptimal images obtained due to his body habitus. Which of the following maneuvers may help improve visualization of the heart from a parasternal or apical window?
A. Place the patient in a left lateral decubitus position
B. Place the patient in a right lateral decubitus position
C. Place the patient in a reverse Trendelenburg position
D. Place the patient in a Trendelenburg position
View Answer
2. Correct Answer A. Place the patient in a left lateral decubitus position
Rationale: The parasternal window is located on the left side of the sternum. The apical window is located below the left nipple, where one can feel the apical impulse. Either of the views can be facilitated by turning the patient to their left side, which repositions the content of mediastinum toward the left and anterior, displacing the lung tissue, and facilitating insonation. In addition, raising the patient’s left arm above their head (if possible) can widen the rib spaces, further improving visualization. A sustained breath-hold may help lower the diaphragm, improving subcostal visualization (although this usually creates more lung interference and impairs imaging in the parasternal and apical windows).
Selected Reference
1. Mitchell C, Rahko PS, Blauwet LA, et al. Guidelines for performing a comprehensive transthoracic echocardiographic examination in adults: recommendations from the American Society of Echocardiography. J Am Soc Echocardiogr. 2019;32(1):1-64. doi:10.1016/j.echo.2018.06.004.
3. You are called to evaluate a patient with acute hypoxemia. You elicit a history of recent rib fractures and perform a point-of-care ultrasound examination to evaluate for pneumothorax. Which of the following statements is most correct regarding proper probe selection for this examination?
A. A high-frequency linear array transducer is optimal for the appreciation of the pleural line for diagnosing pneumothorax.
B. A low-frequency phased array transducer (cardiac probe) is optimal, as its flat and smaller footprint is better suited for imaging in between the ribs and provides better penetration.
C. Either linear array or phased array transducers can be used to assess for pneumothorax with reliable accuracy.
D. Ultrasound is not a suitable modality for accurately ruling out pneumothorax.
View Answer
3. Correct Answer: C. Either linear array or phased array transducers can be used to assess for pneumothorax with reliable accuracy.
Rationale: Linear or phased array probes can be used to assess for pneumothorax. Comparative performance of the three most common probe types (linear, phased array, and curvilinear) has been tested and showed no difference in the diagnostic performance of the three transducers. Experienced observers perceived the best image quality and needed the least amount of time when they judged the linear array transducer clips (Figure 9.1).
 Figure 9.1 A. Linear array probe used at 3.8 cm depth to visualize the lung between the two ribs. B. Insonation of the lung and ribs but utilizing the low-frequency or phased array probe at 13 cm depth. |
Selected References
1. Ketelaars R, Gülpinar E, Roes T, Kuut M, van Geffen GJ. Which ultrasound transducer type is best for diagnosing pneumothorax?. Crit Ultrasound J. 2018;10(1):27. Published 2018 Oct 22. doi:10.1186/s13089-018-0109-0.
2. Husain LF, Hagopian L, Wayman D, Baker WE, Carmody KA. Sonographic diagnosis of pneumothorax. J Emerg Trauma Shock. 2012;5(1):76-81. doi:10.4103/0974-2700.93116.
4. Which of the following statements is most accurate with regard to the routine cleaning of the ultrasound machine after use in clinical care?
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