Does diffusion hypoxia occur following the withdrawal of 1:1 nitrous oxide-oxygen anesthesia? / 中华麻醉学杂志

ABSTRACT

This study was performed for the output of nitrous oxide (N_2O) after N_2O cessation. The breathing bag with the volume of 3000 ml served as the simulator lung,and 5 patients, ASA grade Ⅰ,aged 18-48 years scheduled for elective surgery,acted as the clinical subiects. After the equilibration of end-expiratory N_2O concentration of 50% was developed,the N_2O administration was cut off,then was expelled with oxygen flow rate at 3L/min or 6L/min. The inspiration-expiration N_2O concentration difference of simulator or patient lung (SC_(I-E) N_2O or PC_(I-E) N_2O)was recorded with an infra-red gas analyser. The N_2O dilution induced by the anesthesia circuit volume and the functional residual capacity, was similar to that by simulator lung,so the clinical output of N_2O in one minute was calculated as followed N_2O output=(PC_(I-E) N_2O-SC_(I-E) N_2O)?minute volume of ventilation. The results showed that in the first minute after N_2O termination,there was no N_2O output,but from the second to the tenth minute the N_2O output increased gradually and was kept at the high level,additionally,the levels of N_2O output at the oxygen flow rate of 6L/min were higher than those at 3L/min in the corresponding times, respectively. It is suggested that following the withdrawal of 11 N_2O-O_2 anesthesia ,the N_2O output is related to the oxygen flow rate,and there is not the occurance of diffusion hypoxia.