A review of pulmonary injury by diagnostic ultrasound

Abstract

Diagnostic ultrasound (DUS) induction of pulmonary capillary hemorrhage (PCH) presents a unique clinical safety issue. Pulmonary DUS has become routine in clinical and point-of-care settings worldwide for diagnosis of edema, effusion, pneumonia, etc. Our experiments in rats have shown that DUS-induced PCH increased rapidly above exposure thresholds, which depended on specific conditions. Using a linear array at 6.6 MHz, peak rarefactional pressure amplitude thresholds were 1.5 MPa for B mode, 1.1 MPa for Angio Doppler, 1.1 MPa for M mode, and 0.6 MPa for pulsed Doppler. Thresholds were nearly constant from 1.5 MHz to 12 MHz, suggesting involvement of a frequency-independent mechanism, such as radiation pressure. Physiological conditions were found to be as important as physical exposure parameters. Infusion of saline reduced the effect. Xylazine in the normal ketamine/xylazine anesthesia enhanced PCH relative to ketamine only, and the clinical sedative dexmedetomidine also lowered thresholds. Rats with positive-pressure ventilation had DUS-induced PCH inhibited by only + 4 cm H2O, or enhanced by only -4 cm H2O end expiratory pressure acting on the blood-air barrier. With subsequent studies and better understanding of this phenomenon, DUS-induced PCH will be avoidable by use of sub-threshold output by sonographers using DUS machines with output control. Diagnostic ultrasound (DUS) induction of pulmonary capillary hemorrhage (PCH) presents a unique clinical safety issue. Pulmonary DUS has become routine in clinical and point-of-care settings worldwide for diagnosis of edema, effusion, pneumonia, etc. Our experiments in rats have shown that DUS-induced PCH increased rapidly above exposure thresholds, which depended on specific conditions. Using a linear array at 6.6 MHz, peak rarefactional pressure amplitude thresholds were 1.5 MPa for B mode, 1.1 MPa for Angio Doppler, 1.1 MPa for M mode, and 0.6 MPa for pulsed Doppler. Thresholds were nearly constant from 1.5 MHz to 12 MHz, suggesting involvement of a frequency-independent mechanism, such as radiation pressure. Physiological conditions were found to be as important as physical exposure parameters. Infusion of saline reduced the effect. Xylazine in the normal ketamine/xylazine anesthesia enhanced PCH relative to ketamine only, and the clinical sedative dexmedetomidine also lowered thresholds. Rats with po...