Pulmonary transit of sonicated albumin microbubbles during controlled mechanical ventilation: A transthoracic echocardiographic study

Air-filled human serum albumin microspheres are ultrasonic contrast tracers that pass through the right ventricle, traverse the lungs, and effectively opacify the left heart chambers in spontaneously breathing patients. In th is clinical study, we assessed whether they also do so in anesthetized pati ents during and after mechanical ventilation. In 20 anesthetized patients u ndergoing intermittent positive pressure ventilation (IPPV) for elective pe ripheral neurosurgical procedures, a sonicated ultrasound contrast drug (0. 06 mL/kg) was injected TV before inducing anesthesia in spontaneously breat hing patients (baseline), during IPPV, and 5 and 30 min after tracheal extu bation. Transthoracic echocardiograms were obtained in the four-chamber api cal view and were recorded for off-line analysis. Time to contrast appearan ce in the right ventricle and pulmonary transit time were measured in cardi ac cycles. The peak intensity of right and left ventricular chamber opacifi cation were scored on a scale ranging from 1 (no contrast or traces only) t o 5 (attenuation). After each injection, the time for contrast appearance i n the right ventricle was similar in all patients. Pulmonary transit time i ncreased significantly during IPPV and was normal 5 min and 30 min after ex tubation. Right ventricular chamber opacification achieved high-grade inten sity and remained constant before, during, and after IPPV. Conversely, alth ough the baseline contrast injection resulted in high-grade left ventricula r chamber opacification, the intensity decreased significantly during IPPV, remained low 5 min after extubation, and was normalized 30 min after extub ation. Implications: During intermittent positive pressure ventilation, TV sonicated albumin microbubbles pass through the lungs poorly and inefficien tly opacify the left ventricle compared with the effects observed during sp ontaneous ventilation.