Mechanisms for Induction of Pulmonary Capillary Hemorrhage by Diagnostic Ultrasound: Review and Consideration of Acoustical Radiation Surface Pressure

Point-of-Care-Ultrasound in Pediatrics: A Review and Update

Point-of-Care-Ultrasound (POCUS) has encountered a tremendous expansion in patient care. POCUS has taken a central role during invasive procedures. POCUS has expanded to most subspecialties from adult to pediatric and neonatal health care. POCUS in pediatrics has also become part of specific critical situations such as myocardial function assessment during cardiac arrest, extracorporeal membrane oxygenation deployment and neurological evaluation. In this review we will go over the most important historical aspects of POCUS. We will also review important aspects of POCUS in the intensive care unit, cardiologist evaluation and in the emergency department among others.

Best Practice Recommendations for the Safe use of Lung Ultrasound

The safety of ultrasound is of particular importance when examining the lungs, due to specific bioeffects occurring at the alveolar air-tissue interface. Lung is significantly more sensitive than solid tissue to mechanical stress. The causal biological effects due to the total reflection of sound waves have also not been investigated comprehensively.On the other hand, the clinical benefit of lung ultrasound is outstanding. It has gained considerable importance during the pandemic, showing comparable diagnostic value with other radiological imaging modalities.Therefore, based on currently available literature, this work aims to determine possible effects caused by ultrasound on the lung parenchyma and evaluate existing recommendations for acoustic output power limits when performing lung sonography.This work recommends a stepwise approach to obtain clinically relevant images while ensuring lung ultrasound safety. A special focus was set on the safety of new ultrasound modalities, which had not yet been introduced at the time of previous recommendations.Finally, necessary research and training steps are recommended in order to close knowledge gaps in the field of lung ultrasound safety in the future.These recommendations for practice were prepared by ECMUS, the safety committee of the EFSUMB, with participation of international experts in the field of lung sonography and ultrasound bioeffects.

Frame Rate Exposimetry for Pulmonary Capillary Hemorrhage During Lung Ultrasound

OBJECTIVES

Lung ultrasound (LUS) is a powerful and accessible clinical tool for pulmonary diagnosis, but risk of pulmonary capillary hemorrhage (PCH) presents a safety issue. The dependence of PCH in a rat model of LUS was evaluated for image frames-per-second (fps) and associated on-screen Mechanical Index (MIOS ) and Thermal Index (TI).

METHODS

A Philips iE33 machine with L15-7io probe was used to scan anesthetized rats in a warmed water bath. B mode was applied at 9 MHz with settings of 34, 61 and 118 fps. After 2 minutes of exposure at an MIOS setting, samples were obtained for assessment of PCH areas on the lung surface. Ultrasound parameters were measured to determine the in situ MIIS at the lung surface.

RESULTS

The PCH trend counter-intuitively decreased with increasing fps, with areas of 19.5 mm2 for 34 fps (MIOS  = 1.0, TI = 0.8, 4080 images), 9.6 mm2 at 61 fps (MIOS  = 1.0, TI = 0.5, 7320 images) and 7.5 mm2 at 118 fps (MIOS  = 1.1, TI = 0.4, 14,160 images). The PCH was not significantly different for 34 fps (TI = 0.5, MIOS  = 0.8) (10.7 mm2 ), compared to 61 and 118 fps, above, indicating some value for the TI as a predictive indicator of PCH. MIIS thresholds were 0.42, 0.46, and 0.49 for 34, 61 and 118 fps, respectively.

CONCLUSIONS

The increase in PCH at low fps was associated with delivering more relatively high amplitude grazing pulse exposures during slower image scans. No significant PCH was found for the MIOS setting of 0.5, corresponding to in MIIS values of 0.35-0.39.

Lung Ultrasound Induction of Pulmonary Capillary Hemorrhage in Rats With Consideration of Exposimetric Relationships to Previous Similar Observations in Neonatal Swine

OBJECTIVE

Lung ultrasound (LUS) has become an essential clinical tool for pulmonary evaluation. LUS has been found to induce pulmonary capillary hemorrhage (PCH) in animal models, posing a safety issue. The induction of PCH was investigated in rats, and exposimetry parameters were compared with those of a previous neonatal swine study.

METHODS

Female rats were anesthetized and scanned in a warmed water bath with the 3Sc, C1-5 and L4-12t probes from a GE Venue R1 point-of-care ultrasound machine. Acoustic outputs (AOs) of sham, 10%, 25%, 50% or 100% were applied for 5-min exposures with the scan plane aligned with an intercostal space. Hydrophone measurements were used to estimate the in situ mechanical index (MIIS) at the lung surface. Lung samples were scored for PCH area, and PCH volumes were estimated.

RESULTS

At 100% AO, the PCH areas were 73 ± 19 mm2 for the 3.3 MHz 3Sc probe (4 cm lung depth), 49 ± 20 mm2 (3.5 cm lung depth) or 96 ± 14 mm2 (2 cm lung depth) for the 3.0 MHz C1-5 probe and 7.8 ± 2.9 mm2 for the 7 MHz L4-12t (1.2 cm lung depth). Estimated volumes ranged from 378 ± 97 mm3 for the C1-5 at 2 cm to 1.3 ± 1.5 mm3 for the L4-12t. MIIS thresholds for PCH were 0.62, 0.56 and 0.48 for the 3Sc, C1-5 and L4-12t, respectively.

CONCLUSION

Comparison between this study and previous similar research in neonatal swine revealed the importance of chest wall attenuation. Neonatal patients may be most susceptible to LUS PCH because of thin chest walls.

New International Guidelines and Consensus on the Use of Lung Ultrasound

Following the innovations and new discoveries of the last 10 years in the field of lung ultrasound (LUS), a multidisciplinary panel of international LUS experts from six countries and from different fields (clinical and technical) reviewed and updated the original international consensus for point-of-care LUS, dated 2012. As a result, a total of 20 statements have been produced. Each statement is complemented by guidelines and future developments proposals. The statements are furthermore classified based on their nature as technical (5), clinical (11), educational (3), and safety (1) statements.

Lung Ultrasound Induction of Pulmonary Capillary Hemorrhage in Neonatal Swine

This study investigated induction of pulmonary capillary hemorrhage (PCH) in neonatal pigs (piglets) using three different machines: a GE Venue R1 point-of-care system with C1-5 and L4-12t probes, a GE Vivid 7 Dimension with a 7L probe and a SuperSonic Imagine machine with an SL15-4 probe and shear wave elastography (SWE). Female piglets were anesthetized, and each was mounted vertically in a warm bath for scanning at two or three intercostal spaces. After aiming at an innocuous output, the power was raised for a test exposure. Hydrophone measurements were used to calculate in situ values of mechanical index (MIIS). Inflated lungs were removed and scored for PCH area. For the C1-5 probe at 50% and 100% acoustical output (AO), a PCH threshold of 0.53 MIIS was obtained by linear regression (r2 = 0.42). The L4-12t probe did not induce PCH, but the 7L probe induced zones of PCH in the scan planes. The Venue R1 automated B-line tool applied with the C1-5 probe did not detect PCH induced by the C1-5 probe as B-line counts. However, when PCH induced by C1-5 and 7L exposures were subsequently scanned with the L4-12t probe using the automated tool, B-lines were counted in association with the PCH. The SWE induced PCH at push-pulse positions for 3, 30 and 300 s of SWE with PCH accumulating at 0.33 mm2/s and an exponential rise to a maximum of 18.4 mm2 (r2 = 0.61). This study demonstrated the induction of PCH by LUS of piglets, and supports the safety recommendation for use of MIs <0.4 in neonatal LUS.

Lung ultrasound to quantitatively evaluate extravascular lung water content and its clinical significance

BACKGROUND

As we all know, pulmonary edema can be diagnosed by lung ultrasound (LUS), but how to accurately and quantitatively evaluate lung water content by ultrasound is a difficult problem that needs to be solved urgently. B-line assessment with LUS has recently been proposed as a reliable, noninvasive semiquantitative tool for evaluating extravascular lung water (EVLW). To date, however, there has been no easy quantitative method to evaluate EVLW by LUS.

OBJECTIVE

(1) To explore the feasibility of establishing a rabbit model with increased EVLW by injecting warm normal saline (NS) into the lungs via the endotracheal tube. (2) To establish a simple, accurate and clinically operable method for quantitative assessment of EVLW using LUS. (3) To develop LUS into a resource for guiding the clinical treatment of patients with increased EVLW.

METHODS

Forty-five New Zealand rabbits were randomized into nine groups (n = 5). After anesthesia, each group of rabbits was injected with different amounts of warm sterile NS (0 ml/kg, 2 ml/kg, 4 ml/kg, 6 ml/kg, 8 ml/kg, 10 ml/kg, 15 ml/kg, 20 ml/kg, 30 ml/kg) via the endotracheal tube. Each rabbit was examined by LUS before and after NS injection. At the same time, the spontaneous respiratory rate (RR, breaths per minute), heart rate (HR, bpm) and arterial blood gas (ABG) of the rabbits were recorded. Then, both lungs were dissected to obtain the wet and dry weight and conduct a complete histological examination.

RESULTS

Injecting NS into the lungs through a tracheal tube can successfully establish a rabbit model with increased EVLW. The extent of EVLW increase is related to the volume of NS injected into the lungs. As the EVLW increases, three different types of B-lines can be seen in the LUS. When the NS injection volume is 2-6 ml/kg, comet-tail artifacts and B-lines are the main patterns found on LUS; as additional NS is injected into the lungs, the rabbits' RR gradually increases, while their HR gradually decreases, ABG remains normal or shows mild metabolic acidosis (MA). Confluent B-lines grow gradually but significantly, reaching a dominant position when the NS injection volume reaches 6-8 ml/kg and predominating almost entirely when the NS injection volume is 8-15 ml/kg; at that time, rabbits' RRs and HRs decrease sharply, and the ABG indicated type I respiratory failure (RF).Compact B-lines occur and predominate almost entirely when the NS injection volume reaches 10 ml/kg and 15-20 ml/kg, respectively. At that time, rabbits begin to enter cardiac and respiratory arrest, and ABG shows type II RF and MA.

CONCLUSION

In this study, the establishment of an animal model with increased EVLW confirmed that different lung water content had corresponding manifestations in ultrasound and was associated with different degrees of clinical symptoms, and the study results can be used to guide clinical practice.

Safe and Effective Treatment of Compromised Clavicle Fracture of the Medial and Lateral Third Using Focused Shockwaves

A delay or failure to heal is the most common possible complication in clavicle fractures, especially in cases primarily treated conservatively. As the current standard therapy, surgical revision achieves good healing results, but is associated with potential surgery-related complications. Shockwave therapy as a non-invasive therapy shows similar reasonable consolidation rates in the non-union of different localizations, but avoids complications. Compromised clavicle fractures in the middle and lateral third treated with focused high-energy shockwave therapy were compared with those treated with surgical revision (ORIF). In addition, a three-dimensional computer simulation for evaluating the pressure distribution during shockwave application accompanied the clinical study. A comparable healing rate in bony consolidation was achieved in both groups. Significantly fewer complications, however, occurred in the shockwave group. The simulations showed safe application in this instance, particularly in avoiding lung tissue affection. When applied correctly, shockwaves represent a safe and promising therapy option for compromised clavicle fractures in the middle and lateral third.

The Influence of Xylazine and Clonidine on Lung Ultrasound-Induced Pulmonary Capillary Hemorrhage in Spontaneously Hypertensive Rats

Induction of pulmonary capillary hemorrhage (PCH) by lung ultrasound (LUS) depends not only on physical exposure parameters but also on physiologic conditions and drug treatment. We studied the influence of xylazine and clonidine on LUS-induced PCH in spontaneously hypertensive and normotensive rats using diagnostic B-mode ultrasound at 7.3 MHz. Using ketamine anesthesia, rats receiving saline, xylazine, or clonidine treatment were tested with different pulse peak rarefactional pressure amplitudes in 5 min exposures. Results with xylazine or clonidine in spontaneously hypertensive rats were not significantly different at the three exposure pulse peak rarefactional pressure amplitudes, and thresholds were lower (2.2 MPa) than with saline (2.6 MPa). Variations in LUS PCH were not correlated with mean systemic blood pressure. Similar to previous findings for dexmedetomidine, the clinical drug clonidine tended to increase susceptibility to LUS PCH.

Hydrophone Spatial Averaging Correction for Acoustic Exposure Measurements From Arrays-Part I: Theory and Impact on Diagnostic Safety Indexes

This article reports underestimation of mechanical index (MI) and nonscanned thermal index for bone near focus (TIB) due to hydrophone spatial averaging effects that occur during acoustic output measurements for clinical linear and phased arrays. TIB is the appropriate version of thermal index (TI) for fetal imaging after ten weeks from the last menstrual period according to the American Institute of Ultrasound in Medicine (AIUM). Spatial averaging is particularly troublesome for highly focused beams and nonlinear, nonscanned modes such as acoustic radiation force impulse (ARFI) and pulsed Doppler. MI and variants of TI (e.g., TIB), which are displayed in real-time during imaging, are often not corrected for hydrophone spatial averaging because a standardized method for doing so does not exist for linear and phased arrays. A novel analytic inverse-filter method to correct for spatial averaging for pressure waves from linear and phased arrays is derived in this article (Part I) and experimentally validated in a companion article (Part II). A simulation was developed to estimate potential spatial-averaging errors for typical clinical ultrasound imaging systems based on the theoretical inverse filter and specifications for 124 scanner/transducer combinations from the U.S. Food and Drug Administration (FDA) 510(k) database from 2015 to 2019. Specifications included center frequency, aperture size, acoustic output parameters, hydrophone geometrical sensitive element diameter, etc. Correction for hydrophone spatial averaging using the inverse filter suggests that maximally achievable values for MI, TIB, thermal dose ( t ₄₃ ), and spatial-peak-temporal-average intensity ( [Formula: see text]) for typical clinical systems are potentially higher than uncorrected values by (means ± standard deviations) 9% ± 4% (ARFI MI), 19% ± 15% (ARFI TIB), 50% ± 41% (ARFI t ₄₃ ), 43% ± 39% (ARFI [Formula: see text]), 7% ± 5% (pulsed Doppler MI), 15% ± 11% (pulsed Doppler TIB), 42% ± 31% (pulsed Doppler t ₄₃ ), and 33% ± 27% (pulsed Doppler [Formula: see text]). These values correspond to frequencies of 3.2 ± 1.3 (ARFI) and 4.1 ± 1.4 MHz (pulsed Doppler), and the model predicts that they would increase with frequency. Inverse filtering for hydrophone spatial averaging significantly improves the accuracy of estimates of MI, TIB, t ₄₃ , and [Formula: see text] for ARFI and pulsed Doppler signals.

How Safe Is the Use of Ultrasound in Prenatal Medicine? Facts and Contradictions. Part 1 - Ultrasound-Induced Bioeffects

The "Ordinance on Protection Against the Harmful Effects of Non-Ionizing Radiation in Human Applications" will go into effect at the beginning of 2021 1. § 10 of this ordinance prohibits non-medical fetal ultrasound exposure thereby resulting in uncertainty, particularly among affected patients, with respect to the generally accepted theory regarding the lack of ultrasound side effects. Although not a single study has shown a detrimental effect on fetal or child development following exposure to ultrasound, the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety has justified the ban with the purely hypothetical possibility of an unidentified side effect. The first part of the following study shows which ultrasound-induced biophysical effects are known and which dose-dependent threshold values must be taken into consideration. In particular, the study focuses on the well-researched heat effect with some in vivo measurements in humans showing that the actual temperature increase is less than the theoretically calculated values. The planned second part of this study will discuss the non-thermal effects and present the most important epidemiological studies.

Experimental Measurements of Ultrasound Attenuation in Human Chest Wall and Assessment of the Mechanical Index for Lung Ultrasound

Knowledge of the acoustic attenuation characteristics of the chest wall is necessary to estimate the acoustic exposure at the pleural surface during lung ultrasound and is useful in the prediction of bio-effects (e.g., pulmonary capillary hemorrhage) and the development of safe, effective lung imaging. Currently, this property is not well characterized in humans. The aim of this work was to characterize ultrasonic attenuation in human chest wall such that the ultrasound exposures of the lung can be estimated for clinically relevant conditions. In this study, we experimentally measured ultrasound transmitted through the intercostal tissue of 15 human cadaver chest wall samples relative to ultrasound transmitted through saline to determine attenuation coefficients for each sample. A GE Vivid 7 diagnostic ultrasound machine (GE Vingmed, Horten, Norway) and 3 S and 5 S phased array probes were used at center frequencies from 1.6 to 5 MHz. The chest wall samples varied in thickness from 2.3-5.5 cm with a median thickness of 3.8 cm. The frequency-normalized attenuation coefficient was approximately 1.44 dB/cm/MHz based on a linear best fit through all attenuation measurements. Attenuation characteristics varied appreciably between samples, and the sample-averaged linear attenuation coefficient was 1.43 ± 0.32 (mean ± standard deviation) dB/cm/MHz. This attenuation is higher than that previously measured in mammalian chest wall samples (1.1-1.3 dB/cm/MHz for mice and rats) and is much greater than that used by the mechanical index (0.3 dB/cm/MHz). Mechanical index values calculated using saline values de-rated by 0.3 dB/cm/MHz were up to 1.2 MPa/MHz^1/2 greater than those calculated using the measured through-tissue ultrasound waves. We conclude that the mechanical index overestimates exposures for lung ultrasound and thus may not be an appropriate dosimetry metric for pulmonary ultrasound.

Diagnostic Ultrasound Safety Review for Point-of-Care Ultrasound Practitioners

Potential ultrasound exposure safety issues are reviewed, with guidance for prudent use of point-of-care ultrasound (POCUS). Safety assurance begins with the training of POCUS practitioners in the generation and interpretation of diagnostically valid and clinically relevant images. Sonographers themselves should minimize patient exposure in accordance with the as-low-as-reasonably-achievable principle, particularly for the safety of the eye, lung, and fetus. This practice entails the reduction of output indices or the exposure duration, consistent with the acquisition of diagnostically definitive images. Informed adoption of POCUS worldwide promises a reduction of ionizing radiation risks, enhanced cost-effectiveness, and prompt diagnoses for optimal patient care.

Pulmonary Capillary Hemorrhage Induced by Acoustic Radiation Force Impulse Shear Wave Elastography in Ventilated Rats

OBJECTIVES

Diagnostic ultrasound (DUS) imaging can induce pulmonary capillary hemorrhage (PCH), possibly related to the ultrasonic radiation surface pressure arising from reflection at the lung blood-air interfaces. Acoustic radiation force impulse (ARFI) elastography is a relatively new DUS mode with high-energy "push pulses" used to move tissue and generate shear waves. The objective of this study was to characterize PCH induced by the ARFI elastographic mode for comparison with other previously tested DUS modes.

METHODS

Pulmonary capillary hemorrhage induction was examined for ARFI elastographic frames with 5.7-MHz push pulses (Acuson S3000; Siemens Medical Solutions, Mountain View, CA), which had a derated PRPA of 2.6 MPa. Groups of rats with tracheal tube placement had no ventilation (spontaneous breathing), intermittent positive pressure ventilation (IPPV), or IPPV plus 8 cm H₂ O of positive end-expiratory pressure (PEEP). Exposure was to 1 or 20 manually triggered image frame acquisitions. The PCH area was measured on the lung surface.

RESULTS

All 20-frame exposure groups, and even the single-frame group, had significant PCH relative to shams. Single-frame exposures produced significantly less PCH (P = .002) than 20-frame exposures in rats with a tracheal tube only (spontaneous breathing). The PEEP inhibited the PCH and produced about half of the PCH area induced for IPPV without PEEP (P = .014).

CONCLUSIONS

The PCH results were comparable with those from a previous study using B-mode or color Doppler exposure for 5 minutes; however, these modes delivered many more pulses for continuous imaging frames, suggesting that the ARFI elastographic frames were individually much more effective.

Acoustic Fountains and Atomization at Liquid Surfaces Excited by Diagnostic Ultrasound

Pulmonary capillary hemorrhage (PCH) has been found in mammalian lungs exposed to diagnostic ultrasound (DUS), although the mechanism is poorly understood. This work investigates acoustic atomization and fountains at liquid-air interfaces subjected to DUS, which has been suggested as a possible PCH damage mechanism. Primarily using a SuperSonic Imagine Aixplorer DUS machine (SuperSonic Imagine, Aix-en-Provence, France), blood and water surfaces were excited in vitro by DUS and recorded with a high-speed camera. The surface was driven by B-mode, color Doppler, pulsed Doppler, and shear wave elastography imaging modes with center frequencies from 5.0-7.2 MHz and mechanical indexes (MI) up to 1.7. Fountains and atomization were only observed for SWE, for MI as low as 1.0. A comparison of the SWE waveforms with the surface dynamics suggests that fountains and atomization were driven by push-pulses and depended on pulse duration and intensity. However, we conclude that atomization and fountaining are unlikely primary mechanisms behind all DUS-induced PCH because neither phenomenon occurred for traditional diagnostic imaging modes.

GalT-KO pig lungs are highly susceptible to acute vascular rejection in baboons, which may be mitigated by transgenic expression of hCD47 on porcine blood vessels

BACKGROUND

Despite recent progress in survival times of xenografts in non-human primates, there are no reports of survival beyond 5 days of histologically well-aerated porcine lung grafts in baboons. Here, we report our initial results of pig-to-baboon xeno-lung transplantation (XLTx).

METHODS

Eleven baboons received genetically modified porcine left lungs from either GalT-KO alone (n = 3), GalT-KO/humanCD47(hCD47)/hCD55 (n = 3), GalT-KO/hD47/hCD46 (n = 4), or GalT-KO/hCD39/hCD46/hCD55/TBM/EPCR (n = 1) swine. The first 2 XLTx procedures were performed under a non-survival protocol that allowed a 72-hour follow-up of the recipients with general anesthesia, while the remaining 9 underwent a survival protocol with the intention of weaning from ventilation.

RESULTS

Lung graft survivals in the 2 non-survival animals were 48 and >72 hours, while survivals in the other 9 were 25 and 28 hours, at 5, 5, 6, 7, >7, 9, and 10 days. One baboon with graft survival >7 days, whose entire lung graft remained well aerated, was euthanized on POD 7 due to malfunction of femoral catheters. hCD47 expression of donor lungs was detected in both alveoli and vessels only in the 3 grafts surviving >7, 9, and 10 days. All other grafts lacked hCD47 expression in endothelial cells and were completely rejected with diffuse hemorrhagic changes and antibody/complement deposition detected in association with early graft loss.

CONCLUSIONS

To our knowledge, this is the first evidence of histologically viable porcine lung grafts beyond 7 days in baboons. Our results indicate that GalT-KO pig lungs are highly susceptible to acute humoral rejection and that this may be mitigated by transgenic expression of hCD47.

Pulmonary Capillary Hemorrhage Induced by Diagnostic Ultrasound in Ventilated Rats

Pulmonary capillary hemorrhage (PCH) can be induced by diagnostic ultrasound-a potential safety issue. Anesthetized rats were intubated for intermittent positive-pressure ventilation (IPPV) with 0 end-expiratory pressure, +4 cm H₂O end-expiratory pressure (PEEP) and -4 cm H₂O end-expiratory pressure (NEEP). Rats were imaged at 7.6 MHz with a Philips HDI 5000 ultrasound machine. The output was low (mechanical index [MI] = 0.22) for aiming and then was raised for 5 min in 20 different exposure groups with n = 8. Peak rarefactional pressure amplitudes were measured in water and de-rated for chest attenuation. The PCH areas were measured on the lung surface. At 2.2 MPa, PCH was 9.3 ± 6.6 mm² for IPPV, 1.6 ± 3.2 mm² for PEEP (p <0.001) and 26.8 ± 6.4 mm² for NEEP (p <0.001). Thresholds were 1.3 MPa for IPPV, 2.1 MPa for PEEP and 1.0 MPa for NEEP. The small ventilator pressures subtracted or added to trans-capillary stress generated by diagnostic ultrasound pulses, virtually eliminating PCH for PEEP but enhancing PCH for NEEP.

Does Intravenous Infusion Influence Diagnostic Ultrasound-Induced Pulmonary Capillary Hemorrhage?

OBJECTIVES

Pulmonary diagnostic ultrasound (US) can induce pulmonary capillary hemorrhage (PCH) in mammals. This singular biological effect of diagnostic US imaging was discovered more than 25 years ago but remains poorly understood. Our objective here was to investigate rapid infusion of intravenous fluids as a possible stressor for capillaries, which might enhance pulmonary diagnostic US-induced PCH.

METHODS

Rats were anesthetized with Telazol (Zoetis, Inc, Kalamazoo, MI), which yielded relatively low pulmonary diagnostic US-induced PCH, or Telazol and xylazine, which yielded relatively high pulmonary diagnostic US-induced PCH. Groups of rats were not infused or infused either with normal saline, 10% mannitol, or 5% albumin. Rats were scanned in a warmed water bath with B-mode US for 5 minutes with a 7.6-MHz linear array set to different mechanical index values to obtain exposure response information. Pulmonary capillary hemorrhage was observed as comet tail artifacts in the image and measured on the lung surface.

RESULTS

For Telazol anesthesia, all of the PCH results were very low, with no significant differences at the maximum output with an in situ peak rarefactional pressure amplitude of 2.1 MPa (on-screen mechanical index, 0.9). The addition of xylazine to the Telazol anesthetic significantly enhanced the PCH (P < .001) without infusion and likewise for the mannitol and albumin infusion. Saline infusion eliminated this enhancement, with significantly reduced PCH for Telazol-plus-xylazine anesthesia (P < .001); however, both mannitol and albumin infusion resulted in significantly more PCH than saline infusion (P < .01).

CONCLUSIONS

These results show PCH dependence on the specific intravenous infusion fluid and illustrate the complex importance of physiologic parameters for US-induced PCH.

Pulmonary Capillary Hemorrhage Induced by Different Imaging Modes of Diagnostic Ultrasound

The induction of pulmonary capillary hemorrhage (PCH) is a well-established non-thermal biological effect of pulsed ultrasound in animal models. Typically, research has been done using laboratory pulsed ultrasound systems with a fixed beam and, recently, by B-mode diagnostic ultrasound. In this study, a GE Vivid 7 Dimension ultrasound machine with 10 L linear array probe was used at 6.6 MHz to explore the relative PCH efficacy of B-mode imaging, M-mode (fixed beam), color angio mode Doppler imaging and pulsed Doppler mode (fixed beam). Anesthetized rats were scanned in a warmed water bath, and thresholds were determined by scanning at different power steps, 2 dB apart, in different groups of six rats. Exposures were performed for 5 min, except for a 15-s M-mode group. Peak rarefactional pressure amplitude thresholds were 1.5 MPa for B-mode and 1.1 MPa for angio Doppler mode. For the non-scanned modes, thresholds were 1.1 MPa for M-mode and 0.6 MPa for pulsed Doppler mode with its relatively high duty cycle (7.7 × 10^-3 vs. 0.27 × 10^-3 for M-mode). Reducing the duration of M-mode to 15 s (from 300 s) did not significantly reduce PCH (area, volume or depth) for some power settings, but the threshold was increased to 1.4 MPa. Pulmonary sonographers should be aware of this unique adverse bio-effect of diagnostic ultrasound and should consider reduced on-screen mechanical index settings for potentially vulnerable patients.

The safety of pulmonary ultrasonography in the neonatal intensive care unit

OBJECTIVE

Introduction: Due to specific anatomy of children are more vulnerable to the carcinogenic effects of ionizing radiation from chest X-rays. Lung ultrasound (LUS) is a validated procedure which can easily be used in diagnosing pathologies of the neonatal lung. However, experimental studies have shown that low frequency ultrasound may induce pulmonary capillary hemorrhage (PCH). Aim of the study: To evaluate the potential relationship between lung ultrasound and pulmonary hemorrhage in very low birth weight infants.

PATIENTS AND METHODS

Patients and methods: We analysed the medical records of very low birth weight infants admitted to our neonatal tertiary centre between 2008 and 2011 (group 1), when CXR was the main procedure used to evaluate the respiratory system, and between 2013 and 2016 (group 2), when LUS became a routine procedure, replacing the chest X-ray.

RESULTS

Results: 297 infants were enrolled in the first group and 286 in the second group, respectively. There was no difference in the frequency of pulmonary hemorrhages between the two groups (p=1). In the first group there was only one episode of PCH and in the second group no PCH was seen. Statistically significant differences were seen in a number of patients with pulmonary hemorrhage risk factors: surfactant administration (p<0.001), mechanical ventilation (p=0.0003), and hemodynamically significant patent ductus arteriosus (p=0.025).

CONCLUSION

Conclusions: Routine lung ultrasound appears to be safe in very low birth weight infants; there were no episodes of pulmonary hemorrhage.