Traditionally, the lungs were considered inappropriate for ultrasound examination because of the bony cage and the presence of air within the lungs. However, in the late 1900s, Lichtenstein et al. [1-4] initiated a new era of lung ultrasound, and reported that artifacts and signs produced by ultrasound beams that penetrate the lungs may have some clinical significance. Since Copetti et al. [5] first using lung ultrasound to diagnose transient tachypnea of newborns in 2007, several reports highlighting the application of lung ultrasound for diagnosing pulmonary diseases such as respiratory distress syndrome, meconium aspiration syndrome, pneumonia, bronchiolitis, and atelectasis in pediatric patients have been published [6-12]. Point-of-care ultrasound is rapidly evolving and becoming the standard of care in numerous clinical situations, such as vascular access in the operating room [13]. The 2012 international evidence-based recommendations for point-of-care lung ultrasound introduced its role in the pediatric population [14]. This review presents current knowledge regarding lung ultrasound in the pediatric population focusing on the perioperative period.

Before performing lung ultrasound, it is important to note that the position of the patient could affect the findings, as air increases and liquid sinks under the influence of gravity. During the perioperative period, lung ultrasound is usually performed with the patient in the supine position. While lung consolidation or pleural effusion is predominantly found in dependent and dorsal lung regions, pneumothorax is primarily found in the anterior chest. However, there is variability in the scanning technique, and as yet there is no standardized protocol for the pediatric population. In children, each hemithorax can be divided into several regions, and different scanning schemes have been suggested [15,16]. A recent editorial recommended that at least six quadrants of each hemithorax should be scanned for a complete lung ultrasound examination [17]. Fig. 1 shows an example of lung ultrasound scanning technique in a pediatric patient. In a given region of interest, the lung surface of all of the adjacent intercostal spaces must be thoroughly explored by moving the probe transversally [18]. Although most transducers can be used for lung ultrasound, the most suitable probe depends on the size of the patient and the suspected pathology. In the pediatric population, a high-frequency (5-15 MHz) linear probe or microconvex probe is suitable for evaluating both superficial and deep pathologies. Although most scanning is performed in two-dimensional mode, motion mode (M-mode) and color Doppler can also be used depending on the suspected pathology [19].

Lung ultrasound begins by understanding artifacts and signs that arise from the pleura. Several studies have previously illustrated normal lung ultrasound findings in the pediatric population [15,20]. Notably, ultrasound beams are not transmitted via a normally aerated lung. Only the pleura, which appears as a hyperechoic and sliding line moving forward and backward with ventilation, can be observed. Beyond this pleural line, motionless and regularly spaced horizontal lines to the pleura, known as A-lines, are visualized, corresponding to standard reverberation artifacts of the pleural line. Both lung sliding and A-lines define normal aeration [18]. By contrast, vertically oriented artifacts, called B-lines, indicate an abnormality in the interstitial or alveolar compartment and are correlated with the lung interstitial fluid content. Moreover, B-lines project from the pleural line to the edge of the screen, erase A-lines, and move with respiration (Fig. 2) [15].

Lung ultrasound has shown good performance in diagnosing lung consolidation, pleural effusion, pneumothorax, and alveolar interstitial syndrome [20,21], which are common during the perioperative period as underlying conditions or complications. Therefore, anesthesiologists should be familiar with lung ultrasound findings of these pathologies.

Despite the proven diagnostic power of lung ultrasound and its impact on decision-making and therapeutic management, there are still significant barriers to the widespread adoption of this tool [17]. Primary challenges in implementing lung ultrasound in daily anesthetic practice are its operator dependency and variable expertise in skill among anesthesiologists. Although lung ultrasound has great promise with the establishment of correct training and accreditation processes, it remains in its infancy, particularly in the pediatric population [21]. The development of a validated lung ultrasound program is mandatory and requires a combination of dedicated personnel, adequate instrumentation, and training protocols [17].

Lung ultrasound is gaining acceptance among anesthesia providers because its application has improved the diagnostic accuracy of potentially life-threatening conditions during the perioperative period. The noninvasive nature of this technique, lack of radiation exposure, and easy access make it a feasible imaging modality for perioperative care [25]. Due to the sensitivity of pediatric patients to radiation hazards and patient transfer, lung ultrasound could be a favorable option or use in the pediatric population. Overall, lung ultrasound is a contemporary skill that anesthesiologists should strongly consider incorporating into their clinical practice.