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From the Department of Anesthesia, University Children’s Hospital, Zurich, Switzerland.
Address correspondence to: Dr. Alexander Dullenkopf, Department of Anesthesia, University Children’s Hospital, Steinwiesstrasse 75, CH-8032 Zurich, Switzerland. Phone: +41 1 266 77 29; Fax: +41 1 266 79 94; E-mail: alex.dullenkopf{at}kispi.unizh.ch
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Abstract |
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Methods: With approval of the local Ethics Committee, 30 pediatric patients requiring tracheal intubation [tube size internal diameter (ID) 4.0 mm, or ID 7.0 mm) were included. Patients were randomly divided in three groups: A) MPT, baseline cuff pressure 20 cm H2O; B) PVC, baseline cuff pressure 20 cm H2O; and C) MPT, baseline cuff pressure set to sealing pressure. Anesthesia technique and ventilator settings were standardized. The time required for cuff pressure to increase to 25 cm H2O was recorded and pressure reduced to baseline. The number of gas removals required during the first hour was noted. Data are median (range). Groups were compared by the Kruskal-Wallis test (P < 0.05).
Results: There were no differences between groups in patient characteristics. PVC and MPT cuffs inflated to a baseline pressure of 20 cm H2O were similar regarding the time to first removal of gas [A: nine minutes (4–24), B: eight minutes (4–46)], and number of removals required [A: four (2–6), B: three (1–5)]. In MPT with baseline pressure set to sealing pressure [10 cm H2O (8–14)] time to first gas removal and number of removals were significantly less (P < 0.05).
Conclusion: When baseline inflation pressure was set at 20 cm H2O, cuff pressure increased similarly in MPT and PVC tubes. When inflated just to sealing pressure, the MPT allowed a longer time interval until the upper limit of 25 cm H2O was reached.
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Introduction |
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Recently, a new pediatric tracheal tube was introduced into practice. It has a high volume - low pressure cuff made from ultrathin polyurethane [Microcuff pediatric tube (MPT), MicrocuffTM GmbH, Weinheim, Germany]. This new cuff has been reported to allow tracheal sealing at lower cuff pressures than conventional polyvinyl chloride (PVC) cuffs.6–8 For pediatric tubes with a PVC cuff, repeated removal of gas during the first hour of N2O exposure has been reported necessary to avoid hyperinflation of the cuff.9 However, in fact, no data are available with regard to polyurethane cuff pressure behaviour when exposed to N2O.
The aim of the present study was to evaluate cuff pressure changes during N2O exposure in the new MPT cuff, and to compare these to a conventional PVC cuff.
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Methods |
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The cuff pilot balloon was connected to a pressure transducer (Pressure Monitoring Kit, Baxter BV, Ad Uden, Netherlands) with an interposed three-way stopcock and the cuff pressure was monitored by an anesthesia monitoring system (A/S 5, Datex Ohmeda, Helsinki, Finland). The cuffs were carefully emptied and refilled with air ten times using a syringe via the stopcock to remove any N2O from the cuff, and then filled with air. Afterwards the cuff pressure was set to baseline.
Patients were divided into three groups by a computer generated randomization list: A) patients receiving tracheal intubation with a MPT with baseline cuff pressure set at 20 cm H2O; B) patients receiving tracheal intubation with a PVC tracheal tube with baseline pressure set at 20 cm H2O; and C) patients receiving tracheal intubation with a MPT with baseline cuff pressure set at sealing pressure. These groups were further divided into subgroups of five patients receiving tubes with ID 4.0 mm and ID 7.0 mm.
The time was recorded until the cuff pressure increased to 25 cm H2O. At this point the cuff pressure was carefully reduced to baseline again. This procedure was repeated whenever the cuff pressure reached 25 cm H2O. The time and number of times gas removal was required during the first hour of anesthesia was recorded.
Data presentation and statistical analysis
Data are presented as median (range). Patient characteristics were compared using the Kruskal-Wallis test. The time to the first gas removal and number of gas removals were compared using the Kruskal-Wallis test. ID 4.0 and 7.0 mm tubes and measurements starting from the same baseline were compared using the Mann-Whitney test. When no gas removal was necessary during the study period, the period to first gas removal was defined as 61 min for statistical comparison (worst case scenario). P < 0.05 was set as the level of statistical significance for all tests.
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Results |
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PVC and MPT with baseline cuff pressure set at 20 cm H2O behaved similarly regarding the time to first gas removal (A: nine minutes (4–24), B: eight minutes (4–46); P = 0.91) and number of removals (A: four (2–6), B: three (1–5); P = 0.45; Table II). In MPT with a baseline sealing cuff pressure of 10 cm H2O (8–14), time to first gas removal and number of removals were significantly less for all tubes (P < 0.05), and for ID 4.0 and 7.0 mm subgroups (Table II). No differences in time to first gas removal and number of removals were found between 4.0 and 7.0 mm ID tube cuffs (P = 0.72, and P = 0.44, respectively).
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Discussion |
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The use of cuffed tracheal tubes in children remains a controversial topic in pediatric anesthesia.10–15 The main reason for this is the fear of laryngeal and tracheal morbidity associated with the use of cuffed tracheal tubes in children younger than eight years.5 Besides inappropriately designed pediatric tracheal tubes with incorrect placement of cuff and depth markings,16–18 accidental high cuff pressures constitute the main factor for airway damage in children and adults, even if absolutely safe limits still remain to be defined, especially in children.5,19 In this regard, N2O diffusion into the cuff is an important reason for cuff hyperinflation.1–5
Our data demonstrate that, during general anesthesia with N2O, upper limits for cuff pressure were reached rapidly and the need for gas removal occurred within minutes after baseline cuff inflation to 20 cm H2O. Despite different cuff material and thickness of the membrane, N2O diffusion into the cuffs was remarkably similar. The PVC cuff inflated to 20 cm H2O did not effectively seal the trachea in all patients studied.7,8 In contrast, the MPT with an ultrathin cuff membrane provided effective tracheal gas sealing at 20 cm H2O in all patients and, in group C, much lower cuff pressures were required [10 cm H2O (8–14)]. This is because the 10 µ thin polyurethane membrane does not form folds during inflation of the cuff, in contrast to the 50 µ thick PCV cuff membrane.6 The lower sealing pressure required with the MPT significantly prolonged the time required to reach upper cuff pressure limits during N2O exposure.
We reduced high cuff pressures by carefully releasing gas until the baseline pressure was reached again. By doing this, the gas mixture in the cuff is eventually enriched with N2O.20 The result is that the rate of diffusion into the cuff decreases with time, as is indicated by increasing intervals to the next gas removal (Figure
).
Our findings are in agreement with a recently published article from Felten et al. who investigated cuff pressure increases due to N2O in another conventional pediatric cuffed tracheal tube in a very similar setup. They found a median time of 12 min (10–15 min) from the initial adjustment of cuff pressure to first gas removal. Numerous gas deflations were necessary to keep the cuff pressure within the desired range. They concluded that the number of deflations decreased with the duration of mechanical ventilation and was small after 105 min.9 Another study performed by Karasawa et al. in adult patients revealed even longer periods of increasing cuff pressure because of N2O diffusion reaching equilibrium after approximately six hours.20 There are no studies with a similar design in adult patients, but the results from our study and from that of Felten et al.9 show that there is no relationship between the increase in cuff pressure because of N2O and tube size. We studied ID 4.0 mm and ID 7.0 mm cuffed tubes to cover tube sizes from the lower (although not lowest) to the upper end of what is conventionally used in pediatric anesthesia.
Our data have the following clinical implications. Continuous cuff pressure monitoring should be initiated as soon as possible after tracheal intubation. Further, it is not sufficient to control cuff pressure only once after inflating the cuff. Repeated pressure release maneuvers are required for regulating cuff pressure during the first hour of anesthesia with N2O. Even the MPT with its improved sealing properties does not obviate cuff pressure monitoring, albeit pressure release is needed less frequently. Pressure relief valves or continuous cuff pressure controllers may be useful to achieve this goal.13,21–24
In conclusion, N2O exposure increases cuff pressure in the MPT with an ultrathin polyurethane cuff in a fashion similar to conventional PVC cuffs. The improved sealing characteristics of the MPT allows tracheal sealing at lower cuff pressure and will increase the time until pressure adjustments are required. We believe continuous cuff pressure monitoring and repeated adjustments are mandatory when using N2O and cuffed endotracheal tubes in children.
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Footnotes |
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Accepted for publication March 30, 2004. Revision accepted August 2, 2004.
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References |
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2 Chandler M. Pressure changes in tracheal tube cuffs. Anaesthesia 1986; 41: 287–93.[Medline]
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5 Latto P. The cuff. In: Vaughan R (Ed.). Difficulties in Tracheal Intubation. London: WB Saunders Co.; 1997: 51–78.
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24 Willis BA, Latto IP, Dyson A. Tracheal tube cuff pressure. Clinical use of the Cardiff Cuff Controller. Anaesthesia 1988; 43: 312–4.[Medline]
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