FOAM CUFFED TRACHEAL TUBES: CLINICAL AND LABORATORY ASSESSMENT

Transcription

1 British Journal of Anaesthesia 99; 65: FOAM CUFFED TRACHEAL TUBES: CLINICAL AND LABORATORY ASSESSMENT K. J. POWER SUMMARY The efficiency of a foam cuffed tracheal tube has been studied in protecting the pulmonary tree from aspiration of oropharyngeal and gastric contents. Following instillation of methy/ene blue dye above the cuff, subsequent fibreoptic bronchoscopy revealed no instance of dye staining of the trachea/ mucosa. A "bench " study was undertaken subsequently to estimate the likely pressure that the cuff would exert on the trachea/ mucosa as a result of elastic recoil properties of the foam. The results suggested that, under normal clinical conditions, the pressure is not likely to exceed a value at which impairment of the mucosa/ blood supply would occur. KEY WORDS Equipment: cuffs, trachea! tubes. Complications: aspiration. The inflatable cuff of a tracheal tube serves two functions: it should seal the airway to prevent aspiration of pharyngeal contents and permit leakfree positive pressure ventilation. Excessive inflation of cuffs is a well known cause of morbidity because of impairment of the blood supply to the tracheal mucosa []. Despite this, measurement of intracuff pressure is not commonly practised during routine anaesthesia. A postal questionnaire to members of The Intensive Care Society of The United Kingdom [] revealed that cuff pressures were measured in only % of units. Attempts to solve this problem have been directed to the use of low-pressure, high-volume cuffs. However, these large volume cuffs inevitably develop folds when placed in the trachea, and Seegobin and Van-Hasselt have demonstrated % incidence of dye aspiration past the cuffs of three different tubes of this type [3]. Whilst evidence of dye aspiration should not be equated with clinically significant pulmonary aspiration [4], the results indicate that these cuffs are not sealing the trachea. The concept of foam cuffed tracheal tubes is not new [5], but they did not enter widespread clinical use. However, they are now marketed widely as the Bivona "Fome-Cuff" tracheal tube (fig. ). The foam-filled cuff is evacuated for passage into the trachea. When correctly placed, the cuff is connected to the breathing circuit by means of a pilot tube and the foam cuff expands to seal the airway. The danger of excessive pressure damage to the tracheal mucosa should be minimized as the cuff is not inflated by the operator and any increase in intracuff pressure caused by diffusion of nitrous oxide is equilibrated with the airway via the pilot tube. The aim of this study was to evaluate the performance of this tube in protecting against aspiration of pharyngeal contents and to obtain an estimate of the pressure that the cuff might exert on tracheal mucosa. PATIENTS AND METHODS An open study was performed in patients (nine male) undergoing orthopaedic procedures and requiring tracheal intubation. All patients gave informed consent to the study, which had been approved by the local Ethics Committee. Following induction of anaesthesia and muscle relaxation, an evacuated and lubricated foam cuffed tracheal tube was inserted (size 8. mm i.d. for women and size 9. mm i.d. for men). Following insertion, the pilot tube of the cuff was connected to the airway by means of a T-piece attached to the proximal end of the tube (fig. ), to equilibrate K. J. POWER, B.M., M.R.C.P., F.F.A.R.C.S., Royal United Hospital, Combe Park, Bath BA 3NG. Accepted for Publication: March, 99.

2 434 BRITISH JOURNAL OF ANAESTHESIA FIG.. Foam cuffed tracheal tube with cuff expanded and pilot tube attached to T-piece connector. Mercury column FIG.. Apparatus to determine the recoil pressure of the foam cuff at different volumes of air evacuated. intracuff pressure with the airway pressure throughout the ventilatory cycle. After the pilot tube is connected to the airway, the foam cuff expands almost instantaneously. When the patient's lungs had been inflated manually to ensure that there was no apparent leak, methylene blue dye.5 ml was placed above the cuff of the tracheal tube using a plastic quill. The patient underwent either mechanical ventilation (n = 5) by means of a Manley ventilator or was allowed to breathe spontaneously (n = 5). Towards the end of the procedure, whilst the tube was still in situ, the tracheal mucosa was inspected via a flexible fibreoptic bronchoscope for evidence of dye aspiration past the cuff of the tube. Before extubation the air was evacuated from the foam before withdrawing the tube. This

3 FOAM CUFFED TRACHEAL TUBE 435 TABLE I. Bronchoscopy results following instillation of methylene blue Dye seen at bronchoscopy No. Mean age (yr) Duration of intubation (min) Totally clear Minimal on tube Mucosal staining Mechanical ventilation 6M 9F Spontaneous ventilation 3M F TABLE II. Pressure differences across cuff wall (from outside to inside) for a range of volumes of air within the cuff (mean (SD) of tubes of each size) Size 8. mm i.d. (Mean volume of air required to effect seal = 5.5 ml) Size 9. mm i.d. (Mean volume of air required to effect seal = 8. ml) Volume of air (ml) Pressure diff. (mmhg) 35. (.66) 3.9(.).(.84) 4.4(.69).(.4).3(.59) 8.9(.3) 8. (.43) 6.9(.36) 5.6(.) 3.3(.) 8. (.) 3.9 (.59) 3.5 (.6) 8.(.83) 3.8(.4).6 (.93) 8. (.89) 3.9 (.) to produce a table relating the volume of air aspirated from the cuff and the subsequent recoil pressure of the foam. RESULTS Passage of the tube was satisfactory in all subjects and there were no episodes of air leak or cuff rupture during the trial. Fifteen patients underwent bronchoscopy after mechanical ventilation and five after spontaneous ventilation. There was no evidence of dye staining the tracheal mucosa below the tube. In six patients a feint blue discolouration was observed below the level of the cuff on the tube, but it was not possible to differentiate this from light reflected from above. If it did represent leakage, it was insufficient in amount to stain the tracheal mucosa itself. There was no difference in the performance of the 8.-mm and the 9.-mm tubes (table I). Table II shows the results of the experiment with the Poddy mercury manometer. The recoil pressure was maximal when the cuff was deflated fully and was related inversely to the volume of air drawn in to effect a seal. volume of air was noted and a mean value obtained for the volume of air drawn into each size of cuff to effect a seal. The pressure that the cuff exerts on the tracheal mucosa bears a relationship to the elastic recoil of the foam and this is an inverse function of the volume of air drawn into the cuff to effect a seal (see Appendix). Therefore a " bench " experiment was conducted using a Poddy mercury manometer. Air was aspirated from the cuff in increments of ml and the resulting recoil pressure noted (fig. ). From this, it was possible DISCUSSION The results of this study suggest that the use of a foam cuffed tracheal tube may offer protection against aspiration. The technique of placing the dye directly above the cuff is similar to that described by Seegobin and Van-Hasselt [3] and Petting and colleagues [6] and affords a more severe test of the integrity of the seal compared with other studies in which the dye has been placed in the oropharynx [, 8] or on the back of the tongue [9]. There is a considerable literature on the

4 436 BRITISH JOURNAL OF ANAESTHESIA incidence of silent regurgitation and aspiration [3,6,9-]. Red rubber tubes with low volume cuffs inflated to effect a seal appear to offer protection [3,], but at the expense of high intracuff pressures which would result in cuff to tracheal wall pressures (c-t pressures) greatly in excess of the capillary perfusion pressure of the tracheal mucosa (-3 mm Hg [,, 3]). The usual response to this problem is to use tubes with low-pressure, high-volume cuffs in circumstances where prolonged intubation is required. However, a recent study [3] demonstrated a % incidence of dye positive aspiration using three different tubes of this type. It is not established to what extent minor degrees of aspiration contribute to the morbidity of postoperative and intensive care patients. Dye aspiration does not signify evidence of clinically significant aspiration [4], but it has been suggested that up to % of postoperative pulmonary complications may be caused by silent aspiration [4]. It has also been suggested that tracheal colonization is the result of aspiration in 3 % of patients in the ITU [5]. Long term ventilation with overinflated airfilled cuffs may cause occlusion of the blood supply to the tracheal mucosa which may subsequently result in tracheal stenosis. For highvolume, low-pressure cuffs, it has been shown that the pressure exerted by the cuff on the tracheal wall approximates to the intracuff pressure [6]. However, even these cuffs may be overinflated and are still subject to pressure increases caused by diffusion of nitrous oxide through the cuff wall []. The pilot tube principle of the foam cuff tube permits the intracuff pressure to be equilibrated with the airway pressure throughout the ventilatory cycle whilst maintaining an adequate seal [8]. Use of this tube should obviate the need for measurement of cuff pressures or the use of pressure regulating devices such as the Cardiff Cuff Controller [9]. When a foam cuff is used, the average c-t pressure is a function of the elastic recoil of the foam [] and of mean airway pressure. As an example in this study, consider the 8.-mm cuff with a maximum capacity of 5 ml. To evacuate 4 ml of air such that ml remains within the cuff requires a negative pressure of.3 mm Hg; thus if a fully evacuated cuff is allowed to expand with ml of air to effect a seal, there is a positive recoil pressure of.3 mm Hg which is exerted as a mean pressure on the tracheal mucosa. This does not imply, of course, that the pressure over the entire tracheal mucosa in contact with the cuff at all points is always.3 mm Hg. The less compliant anterior trachea is subject to greater pressure than the more compliant posterior wall and pressures may increase during coughing. Furthermore, folds and wrinkles in the cuff material may result in areas of localized high pressure, but this should occur only if too large a tube is used, thereby permitting only minimal expansion of the foam. However, as shown previously [3], it is the folds in the cuff material which permit dye positive aspiration in lowpressure, high-volume cuffs. As there were no episodes of aspiration in this study, it is reasonable to assume that localized pressure problems caused by folds in the cuff material should be minimized. A reduced incidence of tracheal dilatation has been reported in dogs subjected to ventilation for prolonged periods via a foam cuffed tube []. This has been explained on the basis of the increase in calibre of the trachea with positive pressure ventilation leading to expansion of the foam cuff, but a reduction in mean recoil pressure exerted. Several studies [5, 3, ] have attempted to measure c-t pressures exerted by foam cuffed tubes, but all have failed to state the degree of expansion of the foam when the measurements were taken. Furthermore, the measurements are dependent on the model and method used; none is entirely satisfactory []. However, as observed in this and another study [], considerable pressure may be required to evacuate the foam fully and it is important to select a tube of appropriate size, to ensure a reasonable degree of foam expansion. The advantage of the foam cuff is that it may permit measurement of the volume of air expanding the foam and relate this (from table II) to a recoil pressure which reflects the mean c-t pressure. In summary, it would appear that the foam cuffed tracheal tube may offer protection against aspiration, whilst exerting a pressure on the tracheal mucosa that is acceptable and predictable. The chief indication for a tube of this type would be for patients who require or are likely to require long term tracheal intubation and ventilation.

5 FOAM CUFFED TRACHEAL TUBE A P B \ Pa FIG. 3. Pressures inside and outside the foam cuff, A: In the laboratory experiment, B: In use. APPENDIX The volume of gas in the cuff is a function of the pressure difference across the cuff wall (table II). In the bench experiments, the pressure outside the cuff (P,) was atmospheric; the pressure inside (P,) was negative (fig. 3A). In clinical use, the pressure inside (at end-expiration and in the absence of PEEP) is approximately atmospheric. At the ends of the cuff, a small area is exposed to a pressure, P v which is also approximately atmospheric. Therefore, any longitudinal recoil pressure from the foam is taken up by distension of the ends of the cuff. However, most of the wall of the cuff is in contact with the tracheal mucosa. Therefore, assuming negligible distension of that part of the wall, the pressure applied to most of the outside of the cuff is that exerted by the tracheal wall on the cuff (and hence by the recoil pressure of the foam on the tracheal wall) (P,) (fig. 3 B). Therefore, for any given cuff volume, the pressure difference (P t P t ) during use (fig. 3B) is similar to that during the bench experiment, and the pressure on the tracheal mucosa approximates to the sum of that pressure difference and the airway pressure subject to the caveats in the main text about the effects of the trachea not being a uniform cylindrical tube. REFERENCES W. W. Mapleson. Seegobin RD, Van-Hasselt GL. Endotracheal cuff pressure and tracheal mucosal blood flow: endoscopic study of effects of four large volume cuffs. British Medical Journal 984; 88: Pippin LK, Short DH, Bowes JB. Long term tracheal intubation practice in the United Kingdom. Anaesthesia 983; 38: Seegobin RD, Van-Hasselt GL. Aspiration beyond endotracheal cuffs. Canadian Anaesthetists Society Journal 986; 33: Stoetling RK. Year Book of Anaesthesia 98. London: Year Book Medical Publishers Incorporated, 98;. 5. Kamen JM, Wilkinson CJ. A new low pressure cuff for endotracheal tubes. Anesthesiology 9; 34: Petring OU, Adelhoj B, Jensen BN, Pedersen NO, Lomholt N. Prevention of silent aspiration due to leaks around cuffs of endotracheal tubes. Anesthesia and Analgesia 986; 65: -8.. Bernhard WN, Cotrrell JE, Sirakumaran C, Patel K, Yost L, Turndorf H. Adjustment of intracuff pressure to prevent aspiration. Anesthesiology 99; SO: Spray SB, Zuidema GD, Cameron JL. Aspiration pneumonia. Incidence of aspiration with endotracheal tubes. American Journal of Surgery 96; 3: Browning DA, Graves SA. Incidence of aspiration with endotracheal tubes in children. Journal of Pediatrics 983; : Turndorf H, Rodis ID, Clark TS. "Silent" regurgitation during general anesthesia. Anesthesia and Analgesia 94; 53: -3.. Blitt CD, Gutman HL, Cohen DD, Weisman H, Dillon JB. "Silent" regurgitation and aspiration during general anesthesia. Anesthesia and Analgesia 9; 49: -3.. Ching NP, Ayres SM, Spina RC, Nealon TF. Endotracheal damage during continuous ventilatory support. Annals of Surgery 94; 9: Leigh JM, Maynard JP. Pressure on the tracheal mucosa from cuffed tubes. British Medical Journal 99; : Garibaldi RA, Britt MR, Coleman ML, Reading JC, Pace NL. Risk factors for postoperative pneumonia. American Journal of Medicine 98; : Atherton ST, White DJ. Stomach as source of bacteria colonizing respiratory tract during artificial ventilation. Lancet 98; : Cross DE. Recent developments in tracheal cuffs. Resuscitation 93;: -8.. Revenas B, Lindholm CE. Pressure and volume changes in tracheal tube cuffs during general anaesthesia. Acta Anaesthesiologica Scandinavica 96; : Greene SJ, Cane RD, Shapiro BA. A foam cuff endotracheal tube 'T' piece system for use with nitrous oxide anesthesia. Anesthesia and Analgesia 986; 65: Willis BA, Larto IP, Dyson A. Tracheal rube cuff pressure. Clinical use of The Cardiff Cuff Controller. Anaesthesia 988; 43: King K, Mandava B, Kamen JM. Tracheal tube cuffs and tracheal dilatation. Chest 95; 6: Wu W, Lim I, Simpson FA, Turndorf H. Pressure dynamics of endotracheal and tracheostomy cuffs.. Use of a tracheal model to evaluate performance. Critical Care Medicine 93; : 9-.. Latto IP, Rosen M, eds. Difficulties in Tracheal Intubation. Eastbourne: Balliere TindaU, 985; 5.