Pulmonary Capillary Hemorrhage Induced by Diagnostic Ultrasound in Ventilated Rats

Abstract

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.