Potential Mucosal Injury Related to Continuous Aspiration of Subglottic Secretion Device

ASPIRATION of oropharyngeal secretions that pool above the cuff of the endotracheal tube has been one of many factors implicated in the pathogenesis of ventilator-associated pneumonia.1–3The advent of continuous aspiration of subglottic secretion (CASS) devices has generated interest in their potential to minimize ventilator-associated pneumonia risk, especially when prolonged tracheal intubation is anticipated.4–6However, despite their potential benefits, there may be adverse consequences of device use that may only be recognized as use increases. We report two cases of tracheal injury that may be attributable to the use of a CASS device.A previously healthy 36-yr-old man was admitted to the trauma service with multiple orthopedic injuries, splenic laceration, shock, and hypothermia sustained in a roll-over motor vehicle accident. Tracheal intubation was completed with a Mallinckrodt Hi-Lo Evac® (Mallinckrodt, Inc., St. Louis, MO) CASS endotracheal tube (ETT) in the emergency department. The CASS feature was used according to the manufacturer's published guidelines and maintained with regulated low-wall suction (−20 cm H2O, or less) within the intensive care unit. During a tracheostomy performed on hospital day 35, the surgeons noted “maceration” of the tracheal mucosa in a linear distribution adjacent to the tracheostomy site. Subsequent fiberoptic evaluation demonstrated a tracheoesophageal fistula, which was confirmed with a barium swallow esophagram. Endoscopy demonstrated that the fistula and tracheal injury extended slightly above where the previous endotracheal tube cuff was in contact with the mucosa along the posterior aspect of the trachea to the level of the cricoid cartilage. During surgical correction, the tracheal origin of the tracheoesophageal fistula was identified at the likely position of the CASS ETT suction port orifice. The patient was subsequently weaned from ventilatory support and was discharged to a rehabilitation facility after a total of 5 months.A previously healthy 48-yr-old woman was admitted to the trauma service with inhalational injury and orthopedic injuries sustained from a second story fall while fleeing a house fire. The patient's trachea was intubated with a Mallinckrodt Hi-Lo Evac® ETT secondary to reports of inhalation thermal injuries. The CASS device was maintained with regulated low-wall suction (−20 cm H2O, or less) according to manufacturer's guidelines. After multiple failed attempts at weaning mechanical ventilatory support, the patient underwent a tracheostomy on hospital day 22. Extensive tracheal mucosal injury with a fistulous tract in the posterior wall of the trachea was noted 1.5 cm above the tracheostomy site extending cephalad an additional 2–3 cm. The surgeon felt that the tracheal component of the fistula was above where the cuff of the endotracheal tube was in contact with the trachea, a location not generally seen with tracheoesophageal fistula attributed to endotracheal cuff mucosal injury. Upon further discussion with the surgeon, the injury was localized to the area underlying the suction port of the CASS ETT. Definitive repair of the tracheoesophageal fistula was completed on hospital day 30, and the patient was discharged to a rehabilitation facility on hospital day 44.Oropharyngeal, laryngeal, and tracheal structures in contact with an artificial airway are at increased risk for injury.7–15It is well established that risk factors for airway injury include cuff pressures, ETT diameter, duration of intubation, and patient movement. Donnelly et al. 12described tracheal injury in many cases within an hour of ETT placement, and longer intubations resulted in broader and deeper ulceration. It is reasonable to associate tracheal injury and subsequent ulceration observed with artificial airways with increased risk for development of a fistula connecting the trachea and the esophagus.The suction port of the current CASS endotracheal tube (fig. 1) may add another potential etiology for tracheal injury. An incidental notation of tracheal mucosal injury in sheep at the level of the CASS suction port was reported by Berra et al. 6during their investigation of CASS efficacy. Our two cases of tracheoesophageal fistula along with this report prompted us to investigate the anatomical relation of the suction port in human patients. Retrospective review of the available computed tomography (CT) images from our two patients with tracheoesophageal fistula revealed suction port and mucosal relations that may have been conducive to mucosal injury with tracheal mucosa incorporated into the suction port. To better assess this anatomical relation of the suction port and laryngeal mucosa, a high-resolution CT scan of the neck was obtained in a separate patient who was undergoing pulmonary CT angiography for a suspected pulmonary embolism and who was intubated with an Evac® ETT (fig. 2). This high-resolution CT scan demonstrated invagination of the posterior tracheal mucosa into the suction port orifice of the ETT, and asymmetric inflation of the cuff (figs. 2A and B). Of note in this patient who did not develop clinically apparent tracheal injury is the proximity of the invagination of mucosa into the suction port and the orogastric tube in the esophagus. This tube–mucosa relation is further illustrated in reconstructed CT images (fig. 3). Similar invaginations of tracheal mucosa into the suction port of the ETT were observed in scans from other patients who had the Evac® ETT (not shown).In an evaluation of 41 autopsy specimens from patients with an antemortem artificial airway, Stauffer et al. 14reported mucosal ulceration at the epiglottis in 12%, at the posterior glottic rim in 51%, and at the level of the tracheal cuff in 15%. In both of our cases, the site of mucosal injury was posterior and immediately proximal to the ETT cuff, extending cephalad up to the cricoid cartilage. This distribution of mucosal injury, which is not a commonly reported location for airway injury, corresponds to the position where the suction port would have been located. The linear distribution of the lesions may be attributed to cephalad–caudad displacement of the suction orifice due to endotracheal tube movement commonly seen with patient positioning and/or ETT adjustments.There are a few unique features of the CASS ETT that distinguish it from other ETT designs. Most importantly, there is a suction port located in the posterior (dorsal) aspect of the tube at the proximal attachment of the cuff membrane (fig. 1). As recommended by the manufacturer, this port is connected to a regulated suction device not to exceed −20 mmHg to keep the area above the cuff free from pooled secretions that migrate down from the oropharynx. The additional structural elements of the CASS ETT design may further contribute to mucosal injury. To accommodate the suction conduit lumen, the diameter of the ETT has been increased slightly, a factor that has been documented to increase the risk for airway injury.13In a case report by Siobal et al. ,15the rigidity of the Hi-Lo Evac® ETT was suspected to have contributed to mucosal injury and subsequent development of a tracheoinnominate artery fistula during the prolonged intubation of a patient with extensive burn injuries. In their evaluation of the CASS ETT, they reported significantly greater tube rigidity compared with other ETTs tested. It is conceivable that decreased flexibility of an ETT could result in increased pressure at points of contact between the tube and the airway, and potentially increase the risk of injury to the airway.The cuff associated with the Hi-Lo Evac® ETT is of the high-volume, low-pressure type, which seems to be designed to suspend the tracheal mucosa away from the suction port when the cuff is inflated. What we observed, however, was that the ETT cuff assumed an asymmetrical shape because of nonuniform volume distribution (figs. 2C and D). Failure of port orifice suspension would subject the adjacent mucosa to the applied suction force. It is likely that the increased rigidity of the CASS tube places disproportionate pressure along the dorsal aspect of the tube, contributing to the observed cuff asymmetry.The images we present demonstrate mucosal invagination into the CASS ETT suction port orifice and reveal a potential design flaw. It is possible that mucosal injury is sustained by exposure to prolonged suction and/or a “cheese grater” shearing effect of the suction port orifice against the mucosa with endotracheal tube movement in situ . Although the mucosal entrapment within the CASS suction port visualized on CT imaging does not define causality of tracheoesophageal fistula, it is reasonable to identify it as a potential source of mucosal injury. Of certainty is that the etiology of tracheoesophageal fistula is multifactorial. We recognize that the risks of tracheoesophageal fistula must be weighed against the risks of ventilator-associated pneumonia and acknowledge that the Evac® ETT may also be mucosal protective against chemical injury from laryngopharyngeal reflux pooling and bacterial colonization of injured mucosa. It is also possible that design modifications and/or intermittent suction protocols16may lessen the risk for mucosal injury while maintaining ventilator-associated pneumonia prophylaxis.