Anesth Analg 2002;95:238-242
© 2002 International Anesthesia Research Society
GENERAL ARTICLES
Rapid Deflation of the Bronchial Cuff of the Double-Lumen Tube After Decreasing the Concentration of Inspired Nitrous Oxide
Fujio Karasawa, MD,
Akira Takita, MD,
Isao Takamatsu, MD,
Tomohisa Mori, MD,
Takashi Oshima, MD, and
Yasushi Kawatani, MD
Department of Anesthesiology, National Defense Medical College, Saitama, Japan
Address correspondence and reprints requests to Fujio Karasawa, MD, Department of Anesthesiology, National Defense Medical College, Tokorozawa, Saitama 359-8513, Japan. Address e-mail to karasawa{at}me.ndmc.ac.jp
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Abstract
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Deflationary phenomena of the endotracheal tube cuff may occur after inspired nitrous oxide (N2O) concentrations are reduced, but deflationary phenomena of the double-lumen tube (DLT) cuff have not been investigated. In this study, tracheal and bronchial cuffs of left-sided Mallinckrodt (Athlone, Ireland) DLTs were inflated with air, 40% N2O, or 67% N2O (Air, N40, or N67 groups, respectively) in 24 patients undergoing thoracic surgery; 40 min later, O2 was substituted for N2O in some of the patients in the N40 group (N40-c group). Intracuff gas volumes, N2O concentrations, and cuff compliance were also measured. Both tracheal and bronchial cuff pressures significantly increased in the Air group but decreased in the N67 group. Neither pressure significantly changed in the N40 group, but both decreased in the N40-c group after terminating N2O anesthesia; the time required for bronchial cuff pressures to decrease by half (12.0 ± 5.5 min) was less than that for tracheal cuff pressures (31.2 ± 11.0 min, P < 0.01). The volume change in the N40-c group was not significantly different between the tracheal and bronchial cuffs, but tracheal cuff compliance was significantly higher than bronchial compliance. Therefore, filling DLT cuffs with 40% N2O stabilizes cuff pressure during anesthesia with 67% N2O, but bronchial cuffs deflate more quickly than tracheal cuffs after cessation of N2O administration through smaller compliance.
IMPLICATIONS: We demonstrated that after cessation of nitrous oxide (N2O) administration, bronchial N2O-filled cuffs of the double-lumen tube deflate more rapidly than tracheal cuffs. To avoid insufficient separation of the lungs by the bronchial cuff, a frequent check of the cuff pressure is recommended after the inspired N2O concentration is decreased.
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Introduction
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The maintenance of a stable cuff pressure is important in any breathing tube because excessive cuff pressure can damage the mucosa of the tracheobronchial tree and underinflation can cause air leaks. Cuff pressure increases during anesthesia with nitrous oxide (N2O) because of N2O diffusion despite the correct initial inflation of the cuff (1); therefore, filling cuffs with N2O can effectively preserve a stable cuff pressure during anesthesia (2,3). There is, however, another problem: deflationary phenomena of the cuff might occur after inspired N2O concentrations are reduced, leading to the risk of air leaks and/or aspiration of gastric contents (4).
These are also risk factors when using endobronchial cuffs of double-lumen endobronchial tubes (DLTs), which are introduced to achieve isolation of the lungs during thoracic surgery (5–7). There have been few reports, however, of changes in the bronchial cuff pressure/volume through N2O diffusion and/or rediffusion. Furthermore, compared with the tracheal cuff of DLTs or standard endotracheal tube cuffs, the bronchial cuff has a different volume, shape, resting pressure, and location in the lung (8–10). Thus, bronchial cuff pressures might change differently during anesthesia. We measured intracuff pressure to determine whether filling the cuff with N2O was effective for maintaining pressure in both tracheal and bronchial cuffs, and whether the tracheal and bronchial DLT cuff pressures differed during and after N2O anesthesia.
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Methods
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Patients enrolled in this study (n = 24, aged 18–77 yr, ASA physical status class I or II) were undergoing elective thoracic surgery requiring lung isolation using a left DLT (Mallinckrodt, Athlone, Ireland). The investigation was approved by the Ethics Committee of the National Defense Medical College. Informed consent was obtained from the patients. Patients were allocated to 4 groups with a random shuffle (n = 6 in each). The cuff was then inflated with air, 40% N2O, or 67% N2O (Air, N40, or N67 groups), and inspired 33% O2 and 67% N2O; the cuff was inflated with 40% N2O, and 40 min later O2 was substituted for the inspired 67% N2O (N40-c group). The study was completed before one-lung ventilation. The N2O gas mixture used to inflate the cuffs was aspirated from the common gas outlet of the anesthesia machines. The N2O concentration of the gas mixture for inflating cuffs was measured by using a multigas monitor (Capnomac Ultima; Datex, Helsinki, Finland) that was calibrated with standard gases.
Hydroxyzine and atropine sulfate were administered IM 1 h preoperatively. After inserting a thoracic epidural catheter, anesthesia was induced with fentanyl and propofol. Vecuronium (0.1 mg/kg) was administered to relax the muscles and the left bronchus was then intubated with a disposable polyvinyl chloride DLT (Mallinckrodt) by skilled anesthesiologists. The pilot balloons of the tracheal and bronchial cuffs were connected to a pressure transducer through a three-way stopcock to measure the mean intracuff pressure using a monitor (AS3; Datex). The size of the left-sided DLT for each patient was chosen based on the measurement of the left bronchial diameter on chest radiograph or computed tomographic scan, as described by Hannallah et al. (11,12). After auscultation of both sides of the chest, proper placement of the DLT was confirmed by using fiberoptic bronchoscopy in every patient. The tracheal and bronchial cuffs were aspirated as much as possible and then the tracheal cuff was inflated with the lowest volume of gases mentioned above that would not leak when the intra-airway pressure was 18 cm H2O. The bronchial cuff was then inflated as described above. The assessment of air leaks by auscultation or through detection of gas flow was performed while the right lumen of the DLT was open to the atmosphere (13). When no leak was detected despite lower intracuff pressure (<12 mm Hg), the bronchial cuff was inflated with the volume of gases that would induce an intracuff pressure of 12 mm Hg. The initial volume used to fill the cuff was recorded. A circle absorber breathing system (an Omeda Excell 210SE, Madison, WI, or a Narcomed 2B, Dräger Medical, Telford, PA) was used. Anesthesia was maintained with N2O and O2, which were supplemented with sevoflurane or fentanyl. The concentration of the inspired gas mixture was monitored by using a multigas monitor. The lungs were ventilated mechanically, and the end-tidal CO2 was maintained between 35 and 40 mm Hg by adjusting the tidal volume (8–10 mL/kg) and respiratory frequency (8–12/min). A humidifier (Thermovent 600, Portex, UK) was used.
The mean intracuff pressure was measured every 10 min during anesthesia. At the end of the study, air leaks were assessed in all groups. Gases were aspirated from the cuff at the end of the study to measure the volume and N2O concentration. 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 decompressed, and the mean value was used to avoid a possible error caused by friction between the barrel and piston of the syringe. The N2O concentration was measured by using a multigas monitor (Type 1302; Brüel & Kjær, Nærum, Denmark). The cuff volume and pressure at the beginning and at the end of study were plotted, and regression lines for cuff volume and pressure were derived by using the least-squares method. The compliance of the tracheal and bronchial cuffs was calculated as the reciprocal of the gradient (i.e., elastance) of each intracuff’s volume and pressure.
Data were presented as the number of patients or mean ± SD, as indicated. 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 the raw data among groups. A post hoc analysis to allow for multiple comparisons was performed by using a Bonferroni/Dunn correction. The Student’s t-test was used to make single comparisons of cuff pressure, volume, and concentration of N2O. Proportional data were evaluated by using the 
2 test. A P value < 0.05 was considered statistically significant.
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Results
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The four groups of patients were comparable in sex, age, height, and weight (Table 1). The initial volume to inflate the tracheal or bronchial cuff and the initial cuff pressure were not significantly different among the groups (Table 2). The initial bronchial cuff pressure, however, was significantly higher than the tracheal cuff pressure in all groups (P < 0.05 for each).
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Table 2. Changes in Volume, Pressure, Compliance, and N2O Concentrations of Tracheal and Bronchial Cuffs of the Double-Lumen Endotracheal Tube in the Air, N40, N67, and N40-c Groups
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In the Air group, both tracheal and bronchial cuff pressures increased significantly during N2O anesthesia (Fig. 1). The volume of gases aspirated from tracheal or bronchial cuffs was larger than the initial volume used to inflate them (P < 0.05, Table 2). In the N40 group, tracheal and bronchial cuff pressures did not change significantly during anesthesia with N2O, and the volume aspirated from the tracheal or bronchial cuffs did not change significantly during anesthesia (Table 2). The N2O concentration in the tracheal cuff was higher than that in the bronchial cuff in the N40 group (P < 0.05). In the N67 group, tracheal and bronchial cuff pressures decreased significantly during anesthesia. There was no significant difference between tracheal and bronchial cuff pressures in the Air, N40, or N67 groups (P = 0.216, 0.187, and 0.666, respectively). There was a case in the N67 group in which a tracheal cuff leak was detected at the end of the study.
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Figure 1. Changes in tracheal and bronchial cuff pressures (open and closed symbols, respectively) during anesthesia with 67% N2O. Both cuffs were filled with air (circle = air) or N2O (diamond = 40% N40, triangle 67% N67). Data are expressed as mean ± SD (n = 6). *P < 0.05 versus initial pressure.
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Although the initial pressure in the N40-c group was significantly different between the tracheal and bronchial cuffs (P < 0.01), the cuff pressure measured at 40 min was not (P = 0.67). After pure O2 was substituted for the inspired 67% N2O, both tracheal and bronchial cuff pressures decreased significantly (Fig. 2); bronchial cuff pressure was significantly lower than tracheal cuff pressure in the N40-c group (P = 0.003). N2O concentration in the tracheal cuff was higher than that in the bronchial cuff in the N40-c group (P < 0.05, Table 2), but there was no significant difference in volume change between the tracheal and bronchial cuffs. Deflationary half-time of the bronchial cuff pressure (12.0 ± 5.5 min) was significantly less than that of the tracheal cuff pressure (31.2 ± 11.0 min, P = 0.003). In three cases, a bronchial cuff leak was detected at the end of the study.
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Figure 2. Changes in tracheal and bronchial cuff pressures (open and closed diamonds, respectively) during and after anesthesia with 67% N2O. Both cuffs were filled with 40% N2O (N40-c group). O2 was substituted for inspired 67% N2O at 40 min. Data are expressed as mean ± SD (n = 6). *P < 0.05 versus pressure at 40 min;  P < 0.05 between groups.
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The compliance of the tracheal cuff was significantly higher than that of the bronchial cuff (0.46 ± 0.43 versus 0.13 ± 0.22 mL/mm Hg, P < 0.0001) (Fig. 3).
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Figure 3. Relationship between tracheal cuff volume and pressure (open circles); bronchial cuff volume and pressure (closed circles). Cuff volume and pressure were measured at the beginning and at the end of study in the Air, N40, N67, and N40-c groups (n = 6 for each). Regression lines are indicated by solid lines for the tracheal (y = 2.93x, r = 0.41) and bronchial cuffs (y = 11.67x, r = 0.32), which were derived by using the least-squares method.
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Discussion
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Our data demonstrate that inflating cuffs with 40% N2O is effective for maintaining stable pressure of both tracheal and bronchial cuffs. We recently demonstrated that 40% N2O is optimal for inflating cuffs of standard endotracheal tubes to avoid excessive cuff pressure and air leaks during anesthesia with 67% N2O (2,3). Differences in N2O concentrations between cuffs and the gas mixture with which patients are ventilated are caused by N2O rediffusion into the pharyngeal cavity and air (2). It is rational that diffusion and rediffusion of N2O through the cuff wall may be affected by volume, shape, or location in the lung of the cuff as well as the pilot balloon. In the present study, however, the technique of inflating cuffs with 40% N2O was validated in the DLT cuffs regardless of their differences in volume, shape, or location in the lung.
Although there were no differences between tracheal and bronchial cuff pressures in the Air, N40, and N67 groups, the N2O concentration of the bronchial cuffs was higher than that of the tracheal cuffs in the Air and N40 groups. The size of the pilot balloon is relatively larger in the bronchial cuff-pilot balloon system than in the tracheal cuff-pilot balloon system because both pilot balloons are the same shape and volume irrespective of different inflating volumes. Therefore, we speculate that higher rediffusion into the relatively higher volume of the bronchial pilot balloon might cause the difference in N2O concentrations between the tracheal and bronchial cuffs. Although the precise mechanism of this difference in N2O concentrations is not clear, the relatively higher diffusion into the bronchial cuff might be another possible mechanism, because the surface area-to-volume ratio in the bronchial cuff is larger by 17% compared with that in the tracheal cuff (data not shown).
After O2 was substituted for 67% N2O, the deflationary phenomena of the tracheal and bronchial cuffs were observed, as it was in the standard endotracheal tubes (4). The bronchial cuff pressure decreased more quickly than the tracheal cuff pressure: the deflationary half-time of the tracheal cuff (31.2 ± 11.0 minutes) was similar to that of the standard endotracheal tubes in our previous report (4), whereas that of the bronchial cuff (12.0 ± 5.5 minutes) was comparatively much less. Quick deflation of the bronchial cuffs might cause a possible risk of insufficient separation of the lungs, but we did not demonstrate a significantly frequent incidence of air leaks in the present study; air leaks were detected in only a few patients. Despite the careful choice of tube size, an airtight seal can be achieved in some patients without inflating the bronchial cuffs (13). This might partly explain why leaks were detected in a few patients in the present study. Although we did not assess the fluid-tight seal, this might have more significance in clinical practice because folding and tunneling of large-volume cuffs could permit liquids to migrate below the cuffs in the absence of an air leak (14,15). Further study in a larger number of patients is needed to assess the clinical outcome of the rapid deflation of bronchial cuffs.
Cuff pressure is dependent on volume and compliance. The present study demonstrated that this discrepancy is caused by a difference in compliance between the tracheal and bronchial cuffs. Furthermore, the low compliance of the bronchial cuff is, at least in part, the underlying mechanism of the rapid deflation of the bronchial cuff. Although the resting volume (10) is also an important factor during in vitro inflation, similar factors relating to tracheobronchial tree diameters and volumes in DLT cuffs might induce in vivo differences in the volume-pressure relationships. This might be why there was a poor correlation between the volume and pressure in the bronchial cuff (Fig. 3).
In clinical practice, the O2 concentration must be increased by substituting O2 for N2O during anesthesia for thoracic surgery because one-lung ventilation using DLT often decreases oxygenation (16–18). Our results demonstrate that reducing the N2O concentration might induce deflation of the DLT cuff when stable pressure has been preserved with an N2O-filled cuff. It should also be stressed that deflation of the bronchial tube cuff occurs very quickly. However, based on our recent findings in endotracheal tube cuffs (19), it is speculated that intracuff N2O concentrations might increase and approach the equilibrating concentration when air-filled DLT cuffs are repeatedly deflated to avoid excessive pressure; deflation might occur because circumstances are very similar to those in the N2O-filled cuffs. Therefore, frequent monitoring of the cuff pressure and for air leaks is recommended after the inspired N2O concentration is decreased; furthermore, the monitoring should be carefully performed because it is difficult to detect insufficient separation of the lungs by the bronchial cuff during anesthesia.
In conclusion, filling the cuffs of the DLT with 40% N2O is effective for maintaining stable pressure of tracheal and bronchial cuffs during anesthesia with 67% N2O. Bronchial cuff pressure decreases rapidly after the cessation of N2O administration, however, because of its lower compliance compared with the tracheal cuff. Based on these results, we recommend that, after reducing the inspired N2O concentration, the cuff pressure be monitored frequently to avoid insufficient separation of the lungs and/or possible risk of channeling of fluid, if present in the lungs, during anesthesia.
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Footnotes
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IT’s present address is Department of Anesthesia, National Central Hospital in West Saitama, Wakasa 1671-1, Saitama 359-1151, Japan.
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References
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Accepted for publication February 5, 2002.
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Abstract
Introduction
