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The Associations Between Lung Ultrasonography Scores in the First Day of Life and Clinical Outcomes: Authors' Reply

To the Editor: We would like to thank the authors for their voluminous contributions to the literature in general and our article in particular, and would like to offer some clarifications regarding the points they have raised in the letter. Your letter allowed us to discuss the adverse bio-effects of ultrasound imaging. The debate on the biosafety of ultrasound is still ongoing. The main mechanisms included thermal and mechanical effects. In routine clinical practice, the risk of adverse bio-effects is low for neonates, but there are some animal reports on this topic. These studies reported petechial hemorrhages in the lungs and intestines due to the gas-body effect of ultrasound waves. The exact mechanism is unclear. Inertial cavitation and acoustic-mechanical effects have been discussed as possible damage mechanisms. The conditions under which bubbles may develop are not well known. There is conflicting evidence regarding the effect of the pulse repetition frequency and total exposure duration on the damage thresholds of the lungs. However, animal studies reported adverse bio-effects have not been documented in humans. Current data show that ultrasound imaging seems to be safer in humans. The possible undesired effects (mechanical and thermal tissue damage) of the ultrasound on the neonatal lung were discussed in all ethical aspects during the planning process of our study. The “As low as reasonably practicable” (ALARP) principle along with acoustic safety guidelines was implemented to minimize risk. Repeated chest X-rays expose high ionizing radiation (IR) to infants with long hospitalization periods. In clinical practice, ultrasonography devices are available in most NICUs, and trained neonatologists perform point-of-care ultrasound in real time, simply to perform bedside diagnostic technique for different neonatal issues, and decrease the exposure of IR to neonates and healthcare workers. Exposure to IR due to radiologic examinations is associated with the risk of malignancies. Tissues of neonates are very fragile and have a long life expectancy. However, the lifetime risk associated with IR exposure in neonates is still unknown. Ultrasound uses high-frequency sound waves to view the inside of the body. Unlike X-ray imaging, there is no IR exposure associated with ultrasound imaging. Radiation pressure is also considered a hazard category of ultrasound. Nonionizing radiation does not penetrate deep into the tissues. Depending on the energy and exposure time, nonionizing radiation can cause localized heating or photochemical reactions. Conversely, IR may result in significant damage to deoxyribonucleic acid (DNA) and denaturation of proteins in humans. This is not to say that nonionizing radiation cannot cause injury to humans but the injury is generally limited. Efforts should be taken to reduce the number of radiographs in the NICUs to protect against longterm harmful effects of IR. Consequently, we will give clinicians the message that ultrasound might not be a completely innocent diagnostic technique for neonates, notedly on air-filled organ systems like lungs and bowels. It is still necessary to be aware of thermal, mechanical, and acoustic bio-effects of ultrasound on neonates, without discouraging neonatologists who have a great interest in this field.