 Xenon has been used as a general anesthetic . Although it is expensive , anesthesia machines that can deliver xenon are about to appear on the European market , because advances in recovery and recycling of xenon have made it economically viable . 
 Xenon <a href='been_done' title='1'><mark>has</mark></a> been used as a general anesthetic . Although it <a href='drop_aux' title='2'><mark>is</mark></a>expensive , anesthesia machines <a href='null_relcl' title='3'><mark>that</mark></a>can deliver xenon <a href='drop_aux' title='4'><mark>are</mark></a>about to appear on the European market , because advances in recovery and recycling of xenon <a href='been_done' title='5'><mark>have</mark></a> made it economically viable . 
Xenon done been used as a general anesthetic . Although it expensive , anesthesia machines can deliver xenon finna appear on the European market , because advances in recovery and recycling of xenon done made it economically viable .