Focused Cardiac Ultrasound in the Pediatric Perioperative Setting

Karen R. Boretsky, MD; David B. Kantor, MD, PhD; James A. DiNardo, MD; Achikam Oren-Grinberg, MD

Disclosures

Anesth Analg. 2019;129(4):925-932. 

In This Article

Basic Principles of Scanning

Image acquisition can be easier in children compared to adults because the heart is more shallowly located relative to the transducer. This shallower location of the target structure requires smaller sector depth and results in less attenuation of ultrasound signal with better overall image quality. In very young infants, the incomplete ossification of the ribs creates acoustic windows that allow visualization of structures sometimes obscured by rib shadowing in adults and older children. In the operating room, the FoCUS examination is mostly performed in anesthetized children which renders the child immobile but may also limit access. In pediatric patients, hypotension from a primary myocardial etiology is more likely the result of global, rather than regional, myocardial dysfunction. Thus, it is less likely that a pediatric FoCUS examination will require multiple complementary views to clearly delineate regional wall motion.

Challenges with image acquisition in children include smaller size of interrogated cardiac and vascular structures, faster heart rates, probe to patient size mismatch, limited windows in smaller patients under draped surgical fields, and potentially uncooperative awake patients. When imaging is difficult due to limited windows and interfering lung tissue, tilting the operating room bed to the patient's left or placing the patient in the left lateral decubitus position may position the heart closer to the chest wall and improve the image quality. However, removing the surgical drapes and major patient repositioning must be reserved for clinical situations justifying interruption of the surgical procedure.

To optimize image quality in patients ranging in size from newborn to adolescent, frequency, depth, and gain settings should be properly set. In infants and smaller patients (<40 kg), higher frequency should be selected (4.5–5.0 MHz), while in larger patients (>40 kg), lower frequency is used (3.0–4.0 MHz). The image depth setting should be adjusted so that the heart and relevant posterior structures fill the sector. Children and especially infants have faster heart rates, thus requiring higher frame rates for optimal image resolution. Frame rate is automatically increased when sector depth is decreased, so adjusting to the minimum acceptable sector depth improves image quality. For pediatric FoCUS, it may be beneficial to have preexisting settings available for infants (up to 10 kg), toddlers (10–20 kg), children (20–40 kg), and adolescents (>40 kg; Table 1).

Acoustic Windows and Primary Views

The FoCUS examination and standard echocardiographic views in infants and children are similar in many aspects to the adult examinations.[17] The standard acoustic windows and primary views for FoCUS examination in children are shown in Figure 1.

Figure 1.

Windows and views for a basic FoCUS examination. Arrows indicate direction of the index marker. 1 indicates aortic valve; 2, mitral valve; FoCUS, focused cardiac ultrasonography; IVC, inferior vena cava; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

We describe the screen index marker position as per standard adult cardiology and pediatric critical care practice, that is, the marker is placed at the top of the screen on the right side. This orientation should be preselected for phased array transducers.

  1. Subcostal 4-chamber (S4CH) view: The transducer is placed below the xiphoid with the index marker directed to the left axillary line. This view images all 4 cardiac chambers in long axis. If a phased array transducer is not available, a small footprint curved linear array transducer (used in regional anesthesia for deeper nerve blocks) is a good alternative, especially for babies and toddlers <20 kg (Figure 2). This view is useful for assessing systolic function and the presence of pericardial fluid or air emboli.[14] The S4CH is considered to be one of the easier windows to access for beginning echocardiographers due to the reliability of landmarks and the signal ultrasound path through the liver.[2] Infants especially have a relative lack of abdominal musculature, which facilitates imaging. A deep inspiration (if possible) or Valsalva maneuver displaces the heart downward and may improve imaging. In patients with poor acoustic windows due to hyperinflated lungs, distorted rib cages, or overlying bandages and surgical dressings, the S4CH view may allow imaging that is otherwise not possible.

  2. Apical 4-chamber view (A4CH): The transducer is placed over the point of maximal impulse (PMI) of the heart on the left anterior chest with the index marker directed to the left axillary line. All 4 chambers are viewed in long axis. In infants and small children, the PMI is usually the fourth rib interspace medial to the nipple. In older children and adults, the transducer is placed in the fifth rib interspace at or slightly medial to the midclavicular line. The PMI can be laterally displaced in small children if lung compliance is increased. The A4CH view is useful for assessment of ventricular systolic function and relative and absolute chambers' size.[17] The A4CH view is considered more difficult to acquire and optimize.[2]

  3. Subcostal inferior vena cava (SIVC) view: The transducer is placed below the xiphoid with the index marker directed anterior and perpendicular to the skin. The inferior vena cava (IVC) is visible in the long axis as it courses through the liver and empties into the right atrium. The size and dynamic collapsibility of the IVC can be seen in this view. Collapse of the IVC or >50% respiratory variability in maximum diameter may correlate with a fluid responsive state in children.[12] The maximum diameter is assessed during exhalation in spontaneously breathing children and during inspiration in mechanically ventilated children.[12]

  4. Parasternal short-axis (PSAX) view: The transducer is positioned with the index marker directed at the left shoulder and just to the left of the sternum between the third and fourth ribs in infants and children and between the second and fourth ribs in older children and adolescents. This view images the right ventricle (RV) and left ventricle (LV) in short axis. The PSAX at the level of the papillary muscles is ideal for assessing LV size and systolic function, movement of the intraventricular septum, and to evaluate for the presence of a pericardial effusion. This window is generally the most accessible in children who are positioned and draped for surgery. This is also considered an easier view for novices to master.[2]

  5. Parasternal long-axis (PLAX) view: The transducer is positioned in the same parasternal location as the PSAX, but the index marker is now directed toward the patient's right shoulder. This view presents the heart in a long axis and allows visualization of the LV, interventricular septum, and mitral and aortic valves. This view is useful in assessing LV size, systolic function, qualitative assessment of valvular pathology, and to evaluate for the presence of a pericardial effusion.

Figure 2.

Comparison of phased array and curvilinear transducers. S4CH in a 6 kg infant showing images obtained using a linear phased array transducer (A) and curvilinear sequential array transducer (B). The arrow indicates the direction of the index marker. LV indicates left ventricle; RA, right atrium; RV, right ventricle; S4CH, subcostal 4-chamber view.

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