RESUMO
Although cuffed tracheal tubes are available in various sizes(ranging from 5 to 11 mm I.D.), many anesthesiologists are apt to use a limited range of sizes in adult patients. In making a selection, we prefer the ease of insertion of a smaller tube and the better gas flow characteristics of a larger tube. However, when the tube in small perimeter of cuff or over-large cuffed tube is selected to seal the trachea, intracuff pressure exceeds tracheal capillary perfusion pressure and results in tracheal complication during prolonged general anesthesia with N2O-O2 mixture. This study was performed to determine the appropriate size of tubes for men(Group A, n=30) and women(Group B, n=30), using the large-volume, low-pressure cuffed tubes(Portex-Blue Line Tubes, U.K.) during prolonged general anesthesia with N2O-O2 mixture. They were subdivided into A-l(7.5 mm I.D.), A-2(8.0 mm I.D.), A-3(8.5 mm I.D.) in men and B-l(6.5 mm I.D.), B-2(7.0 mm I.D.), B-3(7.5 mm I.D.) in women. Each subgmup included 10 patients in number. They were compared in several factors; residual volume of each tube, sealing volume, sealing pressure and the intracuff pressure changes with time. The results were as follows 1) There were no significant differences in age, height, and weight among the subgroups in men and women respectively. 2) There were significant changes of intracuff pressure every 20 minutes in both groups and the changes of slope of pressure were significantly steep in 7.5 mm I.D. in men and 6.5 mm I.D. in women. 3) Although the values of sealing pressure of all groups were less than 22 mmHg, the intracuff pressure were increased and maintained over 22 mmHg after 100 minutes in 7.5 mm I.D. in men and 20 minutes in 6.5 mm I.D. in women. 4) The changes in volumes(delta V) after 2 hours among 6 subgroups were not statistically significant, but the changes in pressures(delta P) were higher in 7.5 mm I.D.in men and 6.5 mm I.D. in women. 5) According to Spearman's Correlation Coeffients, the smaller the residual volume of tube, the higher the sealing pressure to seal the trachea and the larger the pressure changes to volume changes. In conclusion, intracuff pressure of 7.5 mm I.D. in men and that of 6.5 mm 1.D. in women can easily exceed the tracheal capillary perfusion pressure during prolonged general anesthesia with N2O-O2 mixture and when considering the changes of intracuff pressure alone, it seems that 8.0, 8.5 mm I.D. in men and 7.0, 7.5 mm I.D. in women are preferable to seal the trachea.