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Anesth Analg 2002;95:243-248 © 2002 International Anesthesia Research Society
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Abstract |
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Although a nitrous oxide (N2O) gas-barrier cuff effectively limits the increase of cuff pressure during N2O anesthesia, there are few data assessing whether an N2O gas-barrier cuff is more beneficial for stabilizing intracuff pressure than standard endotracheal tubes when cuffs are repeatedly deflated to stabilize pressure during N2O anesthesia. In the present study, the pressure of air-filled standard-type cuffs (Trachelon; Terumo, Tokyo, Japan) and N2O gas-barrier type endotracheal tube cuffs (Profile Soft-Seal Cuff [PSSC]; Sims Portex, Kent, UK) was measured during 67% N2O anesthesia (n = 8 in each), during which the cuffs were repeatedly deflated every 30 min (Trachelon) or 60 min (PSSC) for the first 3 or 4 h. After aspirating the cuffs for 3 h, the cuff pressure exceeded 22 mm Hg in more than half of the patients in both groups. However, aspiration of the cuffs for 4 h decreased the maximal cuff pressure between deflation intervals in both groups (P < 0.01 for each), and increased the intracuff N2O concentration (P < 0.0001 for each). After deflating the cuffs over 4 h, the cuff pressure in both groups never exceeded 22 mm Hg during the subsequent 3 h, and intracuff N2O concentrations did not significantly change. Therefore, deflation of cuffs for 4 h during N2O anesthesia sufficiently stabilized cuff pressure and equilibrated the intracuff N2O concentrations in both groups. The use of the PSSC endotracheal tube might be more practical because of the smaller number of cuff deflations required, but the PSSC does not reduce the duration of cuff deflations to stabilize the pressure.
IMPLICATIONS: We demonstrated that the N2O concentration and pressure in the N2O-barrier Profile Soft-Seal Cuff stabilized when the cuff was aspirated once an hour for 4 h during N2O anesthesia. The Profile Soft-Seal Cuff might be easier to use in clinical practice than standard endotracheal tubes because of the smaller number of cuff deflations required.
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Because the endotracheal tube cuff volume increases through nitrous oxide (N2O) diffusion into the cuff (1,2), cuff pressure increases quickly during N2O anesthesia. Consequently, a sore throat can occur in surgical patients after anesthesia with endotracheal intubation (2–6) unless the cuff pressure is maintained less than the mean mucosal membrane capillary perfusion pressure (7). In clinical practice, some anesthesiologists perform a simple method of repeated cuff deflations to inhibit excessive pressure, and eventually the cuff pressure stabilizes. The basis of this method is that an equilibrating concentration of N2O might be achieved via N2O rediffusion from the cuff of standard endotracheal tubes into the oropharyngeal cavity and from the pilot balloon and tubing into the air. In fact, N2O-filled cuffs can maintain stable cuff pressure during N2O anesthesia (2,8).
To control intracuff pressure during N2O anesthesia, numerous devices, including N2O gas-barrier cuffs (9–14), have been developed and their efficacy has been reported. Because cuffs with an N2O gas-barrier property effectively attenuate increased cuff pressure, these cuffs might contribute to the stabilization of cuff pressure by repeated cuff deflations; however, the influence of the N2O gas barrier on cuff pressure after repeated deflations of the cuff is not known. The purpose of this randomized study was to test the hypothesis that an N2O gas-barrier cuff is more beneficial for stabilizing pressure and equilibrating the N2O concentration in cuffs than standard endotracheal tubes when cuffs are repeatedly aspirated during N2O anesthesia.
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Methods |
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The study included 80 patients (ASA physical status I or II) undergoing elective surgery. The investigation was approved by the Ethics Committee of the National Defense Medical College and informed consent was obtained from the patients. Hydroxyzine and atropine sulfate were administered IM l h preoperatively. Anesthesia was induced with fentanyl (0.1 mg) and propofol (2–2.5 mg/kg) after the patients breathed 100% oxygen. Vecuronium (0.1 mg/kg) was administered to relax the muscles, and the trachea was intubated with either the Trachelon (Terumo, Tokyo, Japan) or the Profile Soft-Seal Cuff (PSSC) endotracheal tube (Sims Portex, Kent, UK) (7.5-mm inside diameter for women and 8.0-mm inside diameter for men). Lubricant was not used. The pilot balloon of the endotracheal tube was connected to a pressure transducer through a three-way stopcock to measure cuff pressure. Immediately after intubation, the cuff was aspirated as much as possible and then inflated with the smallest volume of air that would produce 12 to 14 mm Hg of cuff pressure and seal the airway when the intra-airway plateau pressure was 18 cm H2O. The initial volume used to fill the cuff was recorded. The mean intracuff pressure was measured every 10 min. A circle absorber breathing system was used, and anesthesia was maintained with 67% N2O and 33% oxygen supplemented with isoflurane or sevoflurane. The lungs were ventilated mechanically. The extent of paralysis was constant throughout the study. All patients were supine during the operative procedure. Airway and oropharyngeal suctioning was performed once before extubation using a flexible suction catheter to remove any secretions.
During 67% N2O anesthesia, gases in the cuff were aspirated every 30 min (Trachelon) or 60 min (PSSC) for 3 or 4 h to decrease the cuff pressure to the initial pressure (n = 8 for each); the cuff pressure was monitored for an additional 3 h (Subgroup 3 + 3H or 4 + 3H, respectively). The time of cuff aspiration was based on data from a comparison of the Trachelon and PSSC endotracheal tubes in our previous report (14): in short, the mean cuff pressure of the Trachelon endotracheal tube increased to approximately 22 mm Hg during the first 30 min of anesthesia, whereas that of the PSSC endotracheal tube increased to 22 mm Hg in more than 60 min. At the end of each study, the gases in the pilot balloons and the cuffs were aspirated as completely as possible. Approximately 15 min later, the volume of aspirated gases was measured at room temperature with a calibrated syringe both after the gases were compressed and after they were decompressed, and the mean value was taken to avoid a possible error caused by friction between the barrel and the piston of the syringe. N2O, N2, O2, and CO2 concentrations were measured by using quadrapole mass spectrometry (AMIS 2000; INNVISION A/S, Odense, Denmark), which was calibrated with standard gases. In some other patients, gases in the cuff were aspirated at 1, 2, 3, and 4 h from the start of anesthesia (Subgroup 1H, 2H, 3H, and 4H, respectively; n = 6 for each), and the volume and gas composition were measured.
Data were presented as the number of patients or mean ± SD. Two-way analysis of variance for repeated measurements was used to assess changes over time, within as well as between groups, and one-way analysis of variance was performed to compare raw data between groups. Post hoc analysis to allow multiple comparisons was performed using a Bonferroni/Dunn correction. The Student’s t-test was used to make single comparisons of cuff pressure, volume, and N2O concentration. Proportional data were evaluated by using the 
2 test. A P value < 0.05 was considered to be statistically significant.
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Results |
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All groups of patients were comparable between groups and within subgroups of elapsed time (Table 1). Initial cuff pressures in the Trachelon and PSSC groups did not differ significantly among the elapsed-time subgroups in the Trachelon and PSSC groups (P = 0.799 or 0.202, respectively; data not shown).
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Figure 1 shows changes in cuff pressure of the Trachelon group during and after repeated deflation for 3 or 4 h (Subgroup 3 + 3H [upper panel] and Subgroup 4 + 3H [lower panel], respectively); Figure 2 shows those of the PSSC group. The peak cuff pressure between deflation intervals decreased when the cuffs were repeatedly aspirated for 3 or 4 h (P = 0.0004 or P < 0.0001, respectively, for the Trachelon group; P = 0.201 or P = 0.001, respectively, for the PSSC group). During repeated deflation of the cuff, N2O and CO2 concentrations in the cuff increased significantly (Table 2), whereas N2 and O2 concentrations in the cuff decreased significantly. N2O concentrations in the PSSC group were significantly larger than those in the Trachelon group (P < 0.006); N2 and O2 concentrations were significantly higher in the PSSC group than those in the Trachelon group (P = 0.02 and 0.002, respectively).
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After aspiration was stopped at 3 h, the cuff pressure increased in the Trachelon and PSSC groups (P < 0.0001 for each; Figs. 1 and 2, upper panels); there was no significant difference between groups (P = 0.824). The cuff pressure increased in the Trachelon and PSSC groups after aspiration was stopped at 4 h (P < 0.0001 for each, Figs. 1 and 2, lower panels); there was no significant difference between groups (P = 0.153). When the duration of cuff aspiration was increased from 3 to 4 h, the number of patients whose cuff pressure exceeded 22 mm Hg decreased (6 to 0 in the Trachelon group, P = 0.007; 5 to 0 in the PSSC group, P = 0.026).
Compared with the N2O concentrations in the cuff at 3 h, those in the Trachelon group increased significantly for an additional 3 h (P = 0.001, Table 3); those in the PSSC group tended to increase (P = 0.08). When the duration of cuff aspiration was increased from 3 to 4 h, the N2O concentration did not change significantly in the Trachelon and PSSC groups during the additional 3 h (P = 0.411 and 0.163, respectively).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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In this study, cuff deflation for three hours reduced peak cuff pressure at each deflation interval (Figs. 1 and 2), but the cuff pressure exceeded 22 mm Hg in both groups when the cuffs were not deflated. When the duration of repeated cuff aspiration was increased from 3 to 4 hours, there were no patients whose cuff pressure exceeded 22 mm Hg. We adopted 22 mm Hg as a limit of tracheal mucosal damage because this pressure is the mean capillary perfusion pressure of the tracheal mucosa (7). Our data, therefore, demonstrated that in either the Trachelon or PSSC endotracheal tube, four hours was needed to stabilize cuff pressure using the repeated cuff aspiration technique, and three hours was not sufficient.
During the first three or four hours of repeated cuff deflation, the N2O concentration in the cuff increased and approached a plateau (Table 2). When the cuffs were aspirated for four hours, the N2O concentration in the cuff did not significantly change in either group during the subsequent three hours. Cuff pressure should stabilize when the N2O concentration is equivalent on both sides of the cuff wall (1,2,8,10). Therefore, equilibration of the N2O concentration after repeated deflation for four hours might be the underlying mechanism of this simple technique. However, CO2 in the cuff increased during anesthesia, but this had little effect on the cuff pressure because the changes were very small compared with those in N2O. Furthermore, a large change in N2O might decrease concentrations of other gases in the cuff, which could explain, in part, the decrease in N2 and O2 in this study.
In the present study, the equilibrating concentration of N2O was 30% to 40% in the Trachelon endotracheal tube and approximately 30% in the PSSC endotracheal tube. We previously reported that an equilibrating concentration of N2O was approximately 40% to 50% in standard endotracheal tubes during anesthesia with 67% N2O (2,8). The equilibrating N2O concentration in the Trachelon and PSSC groups was slightly smaller than that in the standard tubes used in previous reports (2,8). Although the precise mechanisms are unclear in the present study, higher N2O rediffusion into the air might reduce the equilibrating concentration of N2O because pilot balloons of Trachelon and PSSC endotracheal tubes are larger than those of the standard endotracheal tubes used in our previous studies (2,8).
The PSSC is made of N2O gas-barrier material and attenuates an increase in cuff pressure during N2O anesthesia (14–16). Therefore, the N2O might have diffused more slowly into the cuff as well as out of the cuff in the PSSC group than in the Trachelon group. This might be, in part, the reason why the N2O in the cuff was more concentrated in the Trachelon group than in the PSSC group (Tables 2 and 3). However, the time required to stabilize cuff pressure was four hours in the PSSC group, which was not different from that in the Trachelon group (a standard endotracheal tube cuff). We previously demonstrated that, although the material of the PSSC cuff has an N2O gas-barrier property, the decrease in N2O diffusion is limited in the PSSC cuff, because the cuff is made thinner to increase the compliance (14). The increased compliance of the cuff, rather than the N2O gas barrier, contributes to the requirement for longer intervals between cuff aspirations to avoid excessive pressure compared with what is needed for standard endotracheal tubes, and this might be why the time required to stabilize the cuff pressure in the PSSC group was not different from that in the Trachelon group.
We did not assess the incidence of tracheal complications caused by intubation; however, controlling the cuff pressure reduces the incidence of sore throat by half (2,3,6). Therefore, the method of repeated cuff aspiration is expected to reduce the incidence of sore throat, although efficacy might be decreased because repeated deflation for four hours is necessary to stabilize cuff pressure. Compared with standard endotracheal tubes, the PSSC attenuates an increase in cuff pressure (14–16), and consequently reduces the number of cuff aspirations needed. Therefore, the PSSC is recommended for clinical practice.
In conclusion, repeated deflation of cuffs every thirty minutes in the Trachelon endotracheal tube or every sixty minutes in the PSSC endotracheal tube for four hours is validated as a simple method to stabilize cuff pressure during N2O anesthesia. Three hours of repeated deflation, however, is insufficient to avoid excessive cuff pressure thereafter. Furthermore, the PSSC with the N2O gas-barrier property reduces the number of necessary cuff deflations, but does not change the time required to equilibrate the N2O concentration in the cuff. Therefore, the use of the PSSC endotracheal tube might be more practical.
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References |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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- Stanley TH, Kawamura R, Graves C. Effects of nitrous oxide on volume and pressure of endotracheal tube cuffs. Anesthesiology 1974; 4l: 256–62.
- Karasawa F, Ohshima T, Takamatsu I, et al. The effect on intracuff pressure of various nitrous oxide concentrations used for inflating an endotracheal tube cuff. Anesth Analg 2000; 9l: 708–l3.
- Loeser EA, Kaminsky A, Diaz A, et al. The influence of endotracheal tube cuff design and cuff lubrication on postoperative sore throat. Anesthesiology 1983; 58: 376–9.[Medline]
- Stout DM, Bishop MJ, Dwersteg JF, Cullen BF. Correlation of endotracheal tube size with sore throat and hoarseness following general anesthesia. Anesthesiology 1987; 67: 419–21.[Web of Science][Medline]
- Monroe M, Gravenstein N, Saga-Rumley S. Postoperative sore throat: effect of oropharyngeal airway in orotracheally intubated patients. Anesth Analg 1990; 70: 512–6.
[Abstract/Free Full Text] - Mandøe H, Nikolajsen L, Lintrup U, et al. Sore throat after endotracheal intubation. Anesth Analg 1992; 74: 897–900.
[Abstract/Free Full Text] - Seegobin RD, van Hasselt GL. Endotracheal cuff pressure and tracheal mucosal blood flow: endoscopic study of effects of four large volume cuffs. Br Med J 1984; 288: 965–8.
- Karasawa F, Tokunaga M, Aramaki Y, et al. An assessment of a method of inflating cuffs with a nitrous oxide gas mixture to prevent an increase in intracuff pressure in five different endotracheal tube designs. Anaesthesia 2001; 56: l55–9.
- Kim JM. The tracheal tube cuff pressure stabilizer and its clinical evaluation. Anesth Analg 1980; 59: 291–6.
[Free Full Text] - Brandt L, Pokar H. The rediffusion system: limitation of nitrous oxide-induced increase of the pressure of endotracheal tube cuffs. Anaesthesist 1983; 32: 459–64.[Medline]
- Resnikoff E, Katz JA. A modified epidural syringe as an endotracheal tube cuff pressure-controlling device. Anesth Analg 1990; 70: 208–11.
[Free Full Text] - Payne KA, Miller DM. The Miller tracheal cuff pressure control valve. Anaesthesia 1993; 48: 324–7.[Medline]
- Fujiwara M, Mizoguchi H, Kawamura J, et al. A new endotracheal tube with a cuff impervious to nitrous oxide: constancy of cuff pressure and volume. Anesth Analg 1995; 81: 1084–6.[Medline]
- Karasawa F, Mori T, Okuda T, Satoh T. Profile soft-seal cuff, a new endotracheal tube, effectively inhibits an increase in the cuff pressure through high compliance rather than low diffusion of nitrous oxide. Anesth Analg 2001; 92: 140–4.
[Abstract/Free Full Text] - Umezono Y, Fujita A, Toi T, Sakio H. Usefulness of tracheal tubes with N2O gas-barrier cuff. Masui 1999; 48: 1250–2.[Medline]
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[Abstract/Free Full Text]
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