Anesth Analg 2007;104:655-658
© 2007 International Anesthesia Research Society
doi: 10.1213/01.ane.0000255171.94527.c7
CRITICAL CARE AND TRAUMA
Pressures Exerted by Endobronchial Devices
Andrew Roscoe, FRCA,
George W. Kanellakos, FRCPC,
Karen McRae, FRCPC, and
Peter Slinger, FRCPC
From the Department of Anesthesia and Pain Management, Toronto General Hospital, Toronto, Ontario.
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Abstract
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BACKGROUND: High endotracheal cuff pressures have been shown to cause high mucosal pressures and a reduction in mucosal blood flow, with the risk of mucosal ischemia. We aimed to directly measure the pressure exerted by the bronchial cuffs of double-lumen tubes (DLT) and by the cuffs of three new designs of endobronchial blocker (EBB).
METHODS: Using a validated in vitro model and a previously described technique, we measured the static pressures exerted by the cuff of DLTs and EBBs with 1 mL increments in cuff volume until maximum inflation was achieved. The study was repeated under dynamic conditions of simulated positive pressure ventilation.
RESULTS: The pressures exerted by the cuffs of DLTs ranged from 16–155 mm Hg. Pressures exerted by the EBB cuffs ranged from 39–194 mm Hg. At intra-cuff volumes required to create a seal to 25 cm H2O positive pressure, the pressures exerted by the cuffs of all the devices were <30 mm Hg.
CONCLUSIONS: A transmitted pressure <30 mm Hg has been recommended to avoid mucosal injury. Our study shows that at clinically relevant cuff volumes, the pressures exerted by the cuffs do not exceed the recommended safe limit.
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Introduction
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Double-lumen endobronchial tubes (DLT) and endobronchial blockers (EBB) may be used to achieve one-lung ventilation. Previous studies have measured the tracheal mucosal pressure exerted by the cuff of endotracheal tubes (1,2). High cuff pressures have been shown to cause high mucosal pressures and a reduction in mucosal blood flow in both animal and human studies, with the increased risk of mucosal ischemia (3,4). We hypothesized that, because the intracuff pressures of EBB balloons are higher than those of DLT cuffs, the transmitted pressures to the wall of a bronchial model would be higher. We aimed to directly measure the pressure exerted by the bronchial cuff of a DLT and by the cuff of three new designs of EBB, using a validated in vitro model.
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METHODS
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We studied left-sided DLT (Bronchopart® Rüsch, France) sizes 35, 37, 39 and 41, and three types of EBB, the Arndt, the Cohen (both Cook® Critical Care) and the Fuji (Fuji Systems Corporation, Japan) (Fig. 1). Silicon tubing (Cole-Parmer) with a 12.8-mm internal diameter (model EW-06411-55) was used as a model of an adult mainstem bronchus, as previously described (5). We measured the pressures exerted by the cuff using four strain-gauge microchip sensors (Codman® MicroSensor, Johnson & Johnson Medical, UK), positioned on the anterior, posterior, and lateral surfaces of the cuff (Fig. 2), as previously described and validated (1,6). The experiment was performed on three of each device to minimize the chance of defective equipment affecting the results. The pressures exerted were recorded with 1 mL increments in cuff volume. Of the four transducers, the highest pressure displayed was recorded. The mean pressure of all four transducers from all three of each device was also noted. Maximum cuff volume was 6 mL in the DLTs and 10 mL in the EBBs. Simultaneously, we measured the intracuff pressure using a simple air-filled pressure gauge system. The experiment was repeated under dynamic conditions with a cyclical pressure of 25 cm H2O within the silicon tubing to simulate the effects of positive pressure ventilation. This was achieved by inserting a size 6.5-mm internal diameter cuffed endotracheal tube (Intermediate Hi-Lo®, Mallinckrodt Inc) into the silicon tubing. A positive pressure of 25 cm H2O was applied using a standard anesthetic breathing circuit and anesthetic machine (Datex·Ohmeda). For the EBBs, the distal end of the silicon tubing was positioned underwater. The EBB cuff was inflated until a seal was achieved, as indicated by a lack of air bubbling under the water, and the pressures were recorded. For the DLTs, the bronchial cuff of the DLT was positioned in the proximal end of the silicon tubing and positioned underwater. The endotracheal tube was placed in the distal end of the silicon model. The bronchial lumen of the DLT was clamped and a pressure of 25 cm H2O was applied retrograde to the bronchial cuff. The cuff of the DLT was inflated until a seal was achieved, as indicated by a lack of air bubbling under the water. The pressures were then recorded.
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Figure 1. Three designs of EBB. (A) The Arndt wire-guided EBB. (B) The Cohen torque-controlled EBB. (C) The Fuji uniblocker EBB. EBB = Endobronchial blocker.
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Figure 2. (A) The Cohen EBB with four strain-gauge microchip sensors attached. (B) The Cohen EBB positioned in the silicon model bronchus. EBB = Endobronchial blocker.
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RESULTS
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Increases in the intracuff volume produced linear increases in the intracuff pressure to a maximum of 126 mm Hg for the DLTs and 160 mm Hg for the EBBs (Fig. 3). The variability in pressure recordings among the three of each individual device was <2 mm Hg. The mean pressures exerted by the cuffs varied between 12 and 133 mm Hg (Fig. 4). The highest pressures exerted on the silicon model under static conditions by the DLT cuffs at maximum inflation ranged from 16 to 155 mm Hg and by the EBB cuffs from 39 to 194 mm Hg (Fig. 5).
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Figure 3. Intracuff pressures of endobronchial devices. DLT = Double-lumen tube, EBB = endobronchial blocker.
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Figure 4. The mean pressures exerted by endobronchial devices on the model bronchus, under static conditions. DLT = Double-lumen tube, EBB = endobronchial blocker.
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Figure 5. The highest pressures exerted by endobronchial devices on the model bronchus, under static conditions. DLT = Double-lumen tube, EBB = endobronchial blocker.
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Under the effects of simulated positive pressure ventilation, the intracuff volume required to create a seal to a positive pressure of 25 cm H2O was 6 mL for the Arndt EBB, 5 mL for the Cohen EBB, 4 mL for the Fuji EBB, 6 mL for the size 35 DLT, 4 mL for the size 37 DLT, 3 mL for the size 39 DLT, and 2 mL for the size 41 DLT (Fig. 6). The highest pressures exerted by the cuffs under the dynamic conditions of simulated positive pressure ventilation, up to an intracuff volume required to create a seal, ranged from 12 to 24 mm Hg (Fig. 6).
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Figure 6. The highest pressures exerted by endobronchial devices on the model bronchus with 25 cm H2O positive pressure applied, up to a cuff volume required to create a seal. DLT = Double-lumen tube, EBB = endobronchial blocker.
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DISCUSSION
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Previous work has suggested that the pressure transmitted by an EBB cuff to the bronchial mucosal wall is 40–60 mm Hg (5). This value was calculated as a percentage of the intracuff pressure and not directly measured. It exceeds the recommended pressure of 30 mm Hg to avoid mucosal injury (7). We noted that the intracuff pressures of the new EBBs during routine clinical use were high (80–100 mm Hg), which raised a concern that the EBBs may cause mucosal ischemia. However, by direct measurement, we have shown that at intracuff volumes needed to create a seal to a positive pressure of 25 cm H2O (2–6 mL for a DLT and 4–6 mL for an EBB), the transmitted pressures are <30 mm Hg. This suggests that the high intracuff EBB pressures are balanced by the internal elastic recoil of the cuffs. At the inflation volumes commonly used during lung isolation only a small fraction of the intracuff pressure (10%–20%) is transmitted to the bronchial wall. Our results may differ from the previous work (5) because of the types of EBB studied. The previous work was performed using the Univent® tube (Fuji Systems Corporation, Japan). The size and shape of the EBB cuffs vary among different manufacturers. All three EBB cuffs in this study were made of a silicon rubber polymer. However, the Arndt EBB cuff is elliptical, unlike the spherical shape of the other two EBB cuffs, and is approximately 2 mL larger in size than the other two EBB cuffs.
A 12.8-mm internal diameter silicon model was selected because this approximates the diameter and stiffness of the adult left main bronchus (8). This is not ideal, because the silicon model is slightly more distensible than an adult human mainstem bronchus (9). It is possible that the transmitted pressures may be expected to be higher in a human bronchus. Validation of these data on a human bronchus is required. The investigator recording the data was not blinded to the device being tested, but as the study involved the recording of objective numerical data, we felt that this did not bias the results.
In summary, this in vitro model demonstrates that the pressures transmitted to the bronchial mucosa during clinical lung isolation by these three new designs of EBB are similar to the pressures exerted by the cuffs of DLTs. These pressures do not exceed the threshold pressures associated with mucosal ischemia.
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ACKNOWLEDGEMENTS
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Equipment for the study was funded by Cook® Critical Care, USA.
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Footnotes
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Accepted for publication November 22, 2006.
Address correspondence and request reprints to Peter Slinger, FRPC, Department of Anesthesia and Pain Management, Toronto General Hospital, Toronto, OT M5G 2C4. Address e-mail to Peter.Slinger{at}uhn.on.ca.
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REFERENCES
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- Dobrin P, Canfield T. Cuffed endotracheal tubes: mucosal pressures and tracheal wall blood flow. Am J Surg 1977;133:562–8.[Web of Science][Medline]
- 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 (Clin Res Ed) 1984;288:965–8.[Medline]
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- Hampton T, Armstrong S, Russell WJ. Estimating the diameter of the left main bronchus. Anaesth Intensive Care 2000;28:540–2.[Web of Science][Medline]
- Benumof JL. Anesthesia for thoracic surgery. 1st ed. Philadelphia: WB Saunders, 1987:251.
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Abstract
Introduction
