Stenosis at Cuff Level

Evidence pointing to pressure necrosis as the most important etiologic agent has been presented. Adriani and Phillips noted that variables such as cuff site, materials, and tracheal shape affected intracuff pressure.22 They found that intracuff pressure was not a direct index of pressure exerted on the tracheal wall. Knowlson and Bassett found that small increments over the minimal occlusive volume required to effect a seal in patients with a conventional endotracheal cuff, with 20 cm of water inspiratory pressure, caused a rapid rise in the pressure exerted on the tracheal mucosa.23 This exceeded arterial capillary pressure, especially against the anterior tracheal wall. Carroll and colleagues correlated intracuff pressures with pressures exerted on the tracheal wall by a variety of cuffs and found the relationship to be generally proportional.24 They set forth as criteria for ideal cuffs that these should have "large sealing areas, inflate evenly, and center the tube within the tracheal lumen;____have large residual volumes requiring small additional volumes for 'seal,' low tracheal wall sealing pressure with overinflation." Lomholt described a large-volume Teflon cuff with an attached trap, intended to maintain a constant cuff inflation pressure.25

Cooper and Grillo proposed the use of a large-volume, low-pressure cuff which would conform to the irregular shape of the trachea when inflated, rather than establish a seal by expanding circumferential-ly and deforming an elliptical trachea to the shape of the cuff (Figure 11-16).15 The prototype of such a cuff was tested in experimental canine preparations. Conventional cuffs produced erosive and stenotic lesions (see Figure 11-13), whereas in equivalent time periods, the prototype large-volume, low-pressure cuffs resulted in no injuries other than slight submucosal inflammation (Figure 11-17). A latex cuff suitable for clinical use was designed, and when tested in humans for its sealing characteristics, it was found to require a tenth of the pressure required by a conventional high-pressure Rusch cuff.14 The cuff, roughly cylindrical in shape, measured approximately 2.4 cm in length and 3.0 cm in diameter when inflated to a pressure of 1 cm of water. At this point, the latex wall was unstretched, and the total volume of air that the cuff accepted prior to stretching was 12 cc (Figures 11-18A,B). The cross-sectional area of the filled but undistended cuff was greater than that of most adult tracheas, and could therefore fill out the configuration of the normal ovoid tracheal shape without applying stretch to the wall of the cuff itself. Initially, these cuffs were placed on conventional metal Jackson tracheostomy tubes, with care taken to prevent slippage.

Randomized clinical trials following tests for safety compared the cuff's performance in 25 patients, with 20 having standard cuffs.14 "Blind" endoscopic evaluation of damage to the tracheal wall on a scale of 0

Bronchoscopy Form

figure 11-16 Diagram of a tracheal seal, attained by a high-pressure cuff versus a large-volume, low-pressure cuff. A, Cross section of the trachea and esophagus. B, The low-volume cuff is necessarily inflated to a high pressure to occlude the irregularly shaped tracheal lumen. C, The large-volume cuff expands to occlude the lumen, conforming to the shape of the lumen at low inflation pressure.

figure 11-16 Diagram of a tracheal seal, attained by a high-pressure cuff versus a large-volume, low-pressure cuff. A, Cross section of the trachea and esophagus. B, The low-volume cuff is necessarily inflated to a high pressure to occlude the irregularly shaped tracheal lumen. C, The large-volume cuff expands to occlude the lumen, conforming to the shape of the lumen at low inflation pressure.

figure 11-17 Experimental use of large-volume, low-pressure cuff in dogs. A, After 2 weeks of seal at the same ventilatory pressure used with high-pressure cuffs, only minimal mucosal inflammation results. Compare with Figures 11-13B,C. B, Experimental cuff, deflated.

figure 11-18 A, Rusch standard cuff (1971) at the left and experimental latex cuff on the right, mounted on Jackson metal tracheostomy tubes, both in a "resting" state at resting volume. The experimental cuff is deflated for insertion. B, Standard cuff (left) is inflated with 8 cc of air and has high intracuff pressure, and is asymmetric and quite rigid. The large-volume, low-pressure cuff is undistended with a similar volume of air, has no intracuff pressure, and is soft and symmetrical.

to 4 was made immediately after deflation of the cuff as weaning began. Patients with the new cuffs had an average rating of 1.3 (median 1.0) in comparison with an average rating of 2.6 (median 2.5) for those with the standard cuffs. All patients in the minimum injury group had the new cuff in place. Few with the new cuff were in a category showing more serious damage. In contrast, the bulk of patients with the standard cuff fell into groups with progressively more severe damage, many lying in the ranges which were predictably likely to go on to clinical stenosis (Figure 11-19). The average intracuff pressure developed in the experimental cuff was 33 mm Hg compared to an average intracuff pressure of 270 mm Hg in the standard cuff. During the period of development of the cuff, following initial indicative experiments, Geffin and Pontoppidan proposed the interim use of prestretched Portex cuffs to approximate these conditions.26 Despite the limitations of this method, the incidence of cuff strictures in our respiratory care unit dropped noticeably with the prestretched cuffs, and totally disappeared following routine use of large-volume latex cuffs.

Despite this clear enunciation of desirable standards for sealing cuffs for ventilation, followed by years of favorable experience, clinically available equipment still varies in characteristics. Latex is almost indefinitely extensible so that damaging pressures are not developed. However, the short shelf life of latex and the cost of attaching it to plastic tubes led to its abandonment. Large-volume cuffs are now generally available, but are made of relatively inextensible plastic materials. When the resting volume of the fully inflated, but unstretched, cuff is exceeded by only a few cc of overinflation, the lack of extensibility of the material leads to a rapid climb in intracuff pressure. The margin of safety is thus reduced with the relatively nonextensible material now used to fabricate cuffs. Ching and Nealon, and Ching and colleagues analyzed comparative characteristics of cuffs in several studies, confirming these findings (Figure 11-20).27,28 More extensible plastic would further improve safety. Large-volume cuffs should not be inflated beyond the minimum pressure that is adequate to provide ventilation without leakage. Personnel must also understand that cuffs have to be reinflated with care after routine deflation. Otherwise, the inflation volume, and consequently the pressure, creeps upward. It is principally the failure of proper management of cuff volume that continues to produce cuff stenoses today.

Skoliose Diagramm

figure 11-19 Damage to trachea from standard low-volume, high-pressure cuffs versus large-volume, low-pressure tracheostomy tube cuffs. Sixty-eight percent of patients with the experimental cuff showed no exposed cartilage (rating less than 2.0). No patient with standard cuff was in this category. Reproduced with permission from Grillo HC et al.14

figure 11-19 Damage to trachea from standard low-volume, high-pressure cuffs versus large-volume, low-pressure tracheostomy tube cuffs. Sixty-eight percent of patients with the experimental cuff showed no exposed cartilage (rating less than 2.0). No patient with standard cuff was in this category. Reproduced with permission from Grillo HC et al.14

Grillo Trachea

figure 11-20 Comparison of intracuff and lateral tracheal wall pressures engendered by a then-standard Portex plastic cuff on the left and the newly developed latex large-volume cuff on the right. The occlusion volume for the trachea is indicated by an arrow in each case. If volume is exceeded, high intracuff and lateral tracheal wall pressures do not result in the large-volume cuff. (Illustration courtesy of Dr. NPH Ching and Dr. TF Nealon Jr.)

figure 11-20 Comparison of intracuff and lateral tracheal wall pressures engendered by a then-standard Portex plastic cuff on the left and the newly developed latex large-volume cuff on the right. The occlusion volume for the trachea is indicated by an arrow in each case. If volume is exceeded, high intracuff and lateral tracheal wall pressures do not result in the large-volume cuff. (Illustration courtesy of Dr. NPH Ching and Dr. TF Nealon Jr.)

Seals other than air-filled balloons have been proposed, including flexible discs and a compressible synthetic sponge in an outer bag, which fills by expansion of the sponge matrix.29 A low-pressure pilot balloon was designed to relieve pressure in excess of a sealing level of 25 cm of water.30 It was also proposed to reduce the time of exposure of an area of trachea to pressure, by alternate inflation of double cuffs in series. This proved to be unsatisfactory and, if anything, produced longer stenoses. Intermittent cuff inflation cycled to inspiration was also tried, with no instances of damage seen.31 None of these methods gained currency perhaps because of their relative complexity. Furthermore, they provide less protection against aspiration than sealing cuffs. Substitution of high-volume flow respirators has been suggested. Although it is possible to maintain children without sealing cuffs, adults with poor compliance and severe degrees of respiratory failure cannot currently be managed without a tracheal seal.

Thus, we see that stomal strictures may be reduced to a minimum and perhaps eliminated. Information is available to eliminate cuff strictures. No cuff strictures have been produced at MGH since the initial introduction of a large-volume cuff. The problems that remain are the dissemination of information on management, coordination of manufactured equipment, and evolution of better materials. Prop-

er use of large-volume, low-pressure cuffs and cessation of prolonged use of stiff nasogastric tubes should prevent tracheoesophageal fistulae (see Chapter 12, "Acquired Tracheoesophageal and Bronchoesophageal Fistula). Tracheo-innominate artery fistulae from cuff injury would also disappear. Those at the stomal level can be avoided by choosing the proper level for tracheostomy (see Chapter 13, "Tracheal Fistula to Brachiocephalic Artery").

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