Evaluation of a new design of tracheal tube cuff to prevent leakage of fluid to the lungs

Comparison of polyurethane tracheal tube cuffs and conventional polyvinyl chloride tube cuff for prevention of ventilator-associated pneumonia: A systematic review with meta-analysis

BACKGROUND

The aim of this meta-analysis with trial sequential analysis (TSA) was to evaluate the effect of a polyurethane (PU) tracheal tube cuff on the prevention of ventilator-associated pneumonia (VAP).

METHODS

We performed a systematic search using the MEDLINE database through PubMed, Cochrane Central Register of Controlled Trial, SCOPUS, and Web of Science.Randomized controlled trials comparing the incidence of VAP and clinically relevant outcomes between PU cuff tubes and polyvinyl chloride (PVC) cuff tubes in adult patients. Two authors independently extracted study details, patient characteristics, and clinical outcomes such as incidence of VAP, bacterial colonization of tracheal aspirate, duration of mechanical ventilation, ICU stay, and ICU mortality.

RESULTS

From 309 studies identified as potentially eligible, six studies with 1226 patients were included in this meta-analysis. All studies compared the incidence of VAP between PU cuffs and PVC cuffs. Use of a PU cuff was not associated with a reduction in VAP incidence (RR = 0.68; 95% CI, 0.45-1.03) with significant statistical heterogeneity (I2 = 65%). The quality of evidence was "very low." According to the TSA, the actual sample size was only 15.8% of the target sample size, and the cumulative Z score did not cross the trial sequential monitoring boundary for benefit. No positive impact was reported for the other relevant outcomes for PU cuffs.

CONCLUSIONS

The use of a PU cuff for mechanical ventilation did not prevent VAP. Further trials with a low risk of bias need to be performed.

In-vitro analysis of a novel 'add-on' silicone cuff to improve sealing properties of tracheal tubes

Leakage of colonised oropharyngeal secretions across the tracheal tube cuff may cause iatrogenic pulmonary infection. We studied a novel 'add-on' cuff, which can be inserted over an existing tracheal tube and advanced into the subglottic region. The physical properties of the novel silicone cuff (BronchoGuard, Ciel Medical, USA) were evaluated in comparison with the Hi-Lo^® tracheal tube. In a bench study, we identified saline inflation volumes required to transmit pressures between 15 and 30 cmH₂ O against artificial tracheas of 18, 20 and 22 mm internal diameter. We computed cuff compliance, and minimal inflation volume to achieve air sealing during mechanical ventilation. Finally, we compared the leakage flow rate of artificial saliva across the novel cuff. On average, the mean (SD) inflation volumes necessary to transmit tracheal pressures of 15, 20, 25 and 30 cmH₂ O were 4.1 (2.2), 4.4 (2.3), 4.6 (2.4) and 4.8 (2.4) ml for the novel cuff and 7.7 (2.5), 8.0 (2.6), 8.4 (2.6) and 8.7 (2.7) ml for the Hi-Lo tube, respectively (p < 0.001). The minimal inflation volumes to achieve air sealing were 3.8 (0.9) and 10.5 (2.1) ml (p < 0.001), which resulted in transmitted tracheal pressures of 8.3 (9.8) and 27.6 (34.8) cmH₂ O (p < 0.001). Compliance was 0.026 (0.004) and 0.616 (0.324) ml.cmH₂ 0^-1 , respectively (p < 0.001). Although massive leak was found when the novel cuff transmitted pressures ≤ 20 cmH₂ O against the trachea, leakage was avoided with pressures ≥ 25 cmH₂ O, owing to optimal contact between the cuff and the tracheal wall. In contrast, the standard cuff consistently leaked irrespective of the pressure. We conclude that the novel cuff has advantageous properties that warrant clinical corroboration.

Endotracheal tubes and fluid aspiration: an in vitro evaluation of new cuff technologies

BACKGROUND

Aspiration of subglottic secretions past the endotracheal tube (ETT) cuff is a prerequisite for developing ventilator-associated pneumonia (VAP). Subglottic secretion drainage (SSD) ETTs reduce aspiration of subglottic secretions and have demonstrated lower VAP rates. We compared the performance of seven SSD ETTs against a non-SSD ETT in preventing aspiration below inflated cuffs.

METHODS

ETTs were positioned vertically in 2 cm diameter cylinders. Four ml of a standard microbial suspension was added above inflated cuffs. After 1 h, aspiration was measured and ETTs demonstrating no leakage were subjected to rotational movement and evaluation over 24 h. Collected aspirated fluid was used to inoculate agar media and incubated aerobically at 37 °C for 24 h. The aspiration rate, volume and number of microorganisms that leaked past the cuff was measured. Experiments were repeated (×10) for each type of ETT, with new ETTs used for each repeat. Best performing ETTs were then tested in five different cylinder diameters (1.6, 1.8, 2.0, 2.2 and 2.4 cm). Experiments were repeated as above using sterile water. Volume and time taken for aspiration past the cuff was measured. Experiments were repeated (×10) for each type of ETT. Results were analysed using non-parametric tests for repeated measures.

RESULTS

The PneuX ETT prevented aspiration past the cuff in all experiments. All other ETTs allowed aspiration, with considerable variability in performance. The PneuX ETT was statistically superior in reducing aspiration compared to the SealGuard (p < 0.009), KimVent (p < 0.002), TaperGuard (p < 0.004), Lanz (p < 0.001), ISIS (p < 0.001), SACETT (p < 0.001) and Soft Seal (p < 0.001) ETTs. Of the 4 ETTs tested in differing cylinder sizes, the PneuX significantly reduced aspiration across the range of diameters compared to the SealGuard (p < 0.0001), TaperGuard (p < 0.0001) and KimVent (p < 0.0001) ETTs.

CONCLUSIONS

ETTs showed substantial variation in fluid aspiration, relating to cuff material and design. Variability in performance was likely due to the random manner in which involutional folds form in the inflated ETT cuff. The PneuX ETT was the only ETT able to consistently prevent aspiration past the cuff in all experiments.

Aspiration and the Risk of Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is a major concern in the intensive care unit. It is estimated that the risk of developing VAP may be as high as 1% per ventilated day, and the attributable mortality approaches 50% in some series. A growing body of evidence implicates the role of microaspiration of contaminated oropharyngeal and perhaps gastroesophageal secretions into the airways as an integral step in the pathogenesis of VAP. In patients who have been intubated and mechanically ventilated for >72 hours, the majority of VAP is caused by enteric gram-negative organisms, presumably of gastrointestinal origin. As a result, strategies designed to minimize the risk of these contaminated secretions into the normally sterile airways are of paramount importance in terms of VAP prevention. This review highlights the important etiological role of the gut in the development of VAP and also discusses the evidence behind interventions that may modulate the risk of both aspiration and subsequent VAP.

Endotracheal tubes for critically ill patients: an in vivo analysis of associated tracheal injury, mucociliary clearance, and sealing efficacy

BACKGROUND

Improvements in the design of the endotracheal tube (ETT) have been achieved in recent years. We evaluated tracheal injury associated with ETTs with novel high-volume low-pressure (HVLP) cuffs and subglottic secretions aspiration (SSA) and the effects on mucociliary clearance (MCC).

METHODS

Twenty-nine pigs were intubated with ETTs comprising cylindrical or tapered cuffs and made of polyvinylchloride (PVC) or polyurethane. In specific ETTs, SSA was performed every 2 h. Following 76 h of mechanical ventilation, pigs were weaned and extubated. Images of the tracheal wall were recorded before intubation, at extubation, and 24 and 96 h thereafter through a fluorescence bronchoscope. We calculated the red-to-green intensity ratio (R/G), an index of tracheal injury, and the green-plus-blue (G+B) intensity, an index of normalcy, of the most injured tracheal regions. MCC was assessed through fluoroscopic tracking of radiopaque markers. After 96 h from extubation, pigs were killed, and a pathologist scored injury.

RESULTS

Cylindrical cuffs presented a smaller increase in R/G vs tapered cuffs (P = .011). Additionally, cuffs made of polyurethane produced a minor increase in R/G (P = .012) and less G+B intensity decline (P = .022) vs PVC cuffs. Particularly, a cuff made of polyurethane and with a smaller outer diameter outperformed all cuffs. SSA-related histologic injury ranged from cilia loss to subepithelial inflammation. MCC was 0.9 ± 1.8 and 0.4 ± 0.9 mm/min for polyurethane and PVC cuffs, respectively (P < .001).

CONCLUSIONS

HVLP cuffs and SSA produce tracheal injury, and the recovery is incomplete up to 96 h following extubation. Small, cylindrical-shaped cuffs made of polyurethane cause less injury. MCC decline is reduced with polyurethane cuffs.

A Retrospective Review of Patients Managed with the Pneux PY™ VAP Prevention System

Ventilator-associated pneumonia (VAP) is commonplace in intensive care and has implications for patients' morbidity and mortality in hospital. A range of interventions exists to prevent the development of VAP. We reviewed the impact of the PneuX PY™ VAP prevention system on the incidence of VAP and its effects on local practice. In total, 48 patients in a mixed medical and surgical intensive care unit received the PneuX PY VAP prevention system and its associated care package in 2010. The VAP rate for this cohort of patients was found to be 6.25% (n=3) in the local context of historical VAP rates above 26%. Notably, 17% of extubations were unplanned, of which almost two-thirds were self-extubations. The PneuX PY VAP prevention system facilitated lower VAP rates than those documented elsewhere and highlighted the incidence of unplanned extubations in local practice. Further evaluation of the implementation of the PneuX PY VAP prevention system in intensive care areas, in tandem with large-scale evaluation of its effectiveness, are still required.

An in vitro study to assess determinant features associated with fluid sealing in the design of endotracheal tube cuffs and exerted tracheal pressures

OBJECTIVE

To assess the structural characteristics involved in the design of high-volume low-pressure endotracheal tube cuffs that are associated with fluid sealing effectiveness and to determine the extent of transmitted tracheal pressures upon cuff inflation.

DESIGN

In vitro study.

SETTINGS

Pneumology laboratories.

INTERVENTIONS

Eight high-volume low-pressure cuffs of cylindrical or tapered shape, made of polyvinylchloride or polyurethane, were studied. Cuffs were tested within a tracheal model, oriented 30° above horizontal to assess 1 hr leakage of oropharyngeal secretions simulant at cuff internal pressures of 15-30 cm H2O. The four best performing cuffs were evaluated for 24 hrs using an internal pressure of 30 cm H2O. The extent of transmitted tracheal wall pressure throughout the cuff-trachea contact area was determined using an internal pressure sensor within a tracheal model upon cuff inflation up to 30 cm H2O.

MEASUREMENTS AND MAIN RESULTS

Outer diameter, length, and compliance of each cuff were assessed. Multivariate regression analysis was performed to identify the main determinants of simulant leakage rate. The cuff-trachea contact area and the percentage of tracheal wall pressure measurements greater than 50 cm H2O were computed. Cuff design characteristics significantly differ among tubes. The cuffs made of polyurethane showed the best short- and long-term sealing efficacy. Nevertheless, in the multivariate analysis, the cuff outer diameter (n: 288, p = 0.003) and length (n: 288, p < 0.001), along with the internal pressure (n: 288, p < 0.001), were the only predictors of simulant leakage rate. The tapered cuffs showed the lowest tracheal wall contact area (n: 96, p < 0.001). The tracheal wall pressure distribution pattern was heterogeneous, and the percentage of high tracheal wall pressure significantly differs among the cuffs (n: 96, p < 0.001).

CONCLUSIONS

The high-volume low-pressure cuffs' outer diameter, length, material, and internal pressure are the main determinants of sealing efficacy. Despite internal pressure within the safe range, transmitted tracheal pressure is extremely heterogeneous and differs among cuffs, occasionally reaching localized, very high, unsafe levels.

Comparison of air-sealing characteristics of tapered- vs. cylindrical-shaped high-volume, low-pressure tube cuffs

BACKGROUND

This study aimed at comparing air-sealing characteristics of the new tapered-shaped tracheal tube cuffs with cylindrical tube cuffs.

METHODS

Tracheal tubes with tapered-shaped polyurethane (PU) and polyvinyl chloride (PVC) cuffs as well as standard cylindrical-shaped cuffs made of PU and PVC (Covidien, Athlone, Ireland) were investigated. A tracheal model attached to a test lung was intubated, and cuffs were inflated to 10, 15, 20, 25 and 30 cm H(2)O. The test lung was ventilated with intermittent positive pressure ventilation at peak inspiratory pressures (PIPs) of 20 and 25 cm H(2)O. Air leakage was assessed by spirometry and measurement of sevoflurane concentration passing the cuff at the upper cuff border using an anaesthetic gas analyser. Experiments were repeated four times with new tracheal tubes for each run. Statistical comparisons were done using Mann-Whitney U-test with level of significance at P < 0.05.

RESULTS

The tapered-shaped PVC tube cuff demonstrated a significantly lower air leakage determined by spirometry than the cylindrical-shaped cuff at both PIPs (20 and 25 cm H(2)O). Similarly, sevoflurane leakage was less with the tapered PVC cuff particularly at higher cuff pressures. With the PU cuff, reduction in air leakage by a tapered-shaped compared with a cylindrical-shaped tube cuff was not significant.

CONCLUSIONS

A tapered-shaped tube cuff considerably improves air-sealing characteristics of PVC tube cuffs and allows thereby reducing cuff pressure required for sufficient ventilation. In tube cuffs made of PU that exhibits superior sealing characteristics compared with PVC, a tapered shape failed to result in a further reduction of air leakage.

A polyurethane cuffed endotracheal tube is associated with decreased rates of ventilator-associated pneumonia

PURPOSE

The aim of this study was to determine whether the use of a polyurethane-cuffed endotracheal tube would result in a decrease in ventilator-associated pneumonia rate.

MATERIALS AND METHODS

We replaced conventional endotracheal tube with a polyurethane-cuff endotracheal tube (Microcuff, Kimberly-Clark Corporation, Rosewell, Ga) in all adult mechanically ventilated patients throughout our large academic hospital from July 2007 to June 2008. We retrospectively compared the rates of ventilator-associated pneumonia before, during, and after the intervention year by interrupted time-series analysis.

RESULTS

Ventilator-associated pneumonia rates decreased from 5.3 per 1000 ventilator days before the use of the polyurethane-cuffed endotracheal tube to 2.8 per 1000 ventilator days during the intervention year (P = .0138). During the first 3 months after return to conventional tubes, the rate of ventilator-associated pneumonia was 3.5/1000 ventilator days. Use of the polyurethane-cuffed endotracheal tube was associated with an incidence risk ratio of ventilator-associated pneumonia of 0.572 (95% confidence interval, 0.340-0.963). In statistical regression analysis controlling for other possible alterations in the hospital environment, as measured by rate of tracheostomy-ventilator-associated pneumonia, the incidence risk ratio of ventilator-associated pneumonia in patients intubated with polyurethane-cuffed endotracheal tube was 0.565 (P = .032; 95% confidence interval, 0.335-0.953).

CONCLUSIONS

Use of a polyurethane-cuffed endotracheal tube was associated with a significant decrease in the rate of ventilator-associated pneumonia in our study.

The LoTrach system: its role in the prevention of ventilator-associated pneumonia

OBJECTIVES

To discuss the development of the LoTrach system in light of current evidence around the prevention of ventilator-associated pneumonia (VAP) and its practical application in the intensive care setting.

BACKGROUND

VAP causes substantial morbidity and mortality in ventilated patients in the Intensive Care Unit (ICU), increases length of stay in ICU and is extremely costly. Strategies are needed to reduce the risk of VAP.

METHOD

We examine the need for an endotracheal tube (ETT) specifically designed for the critically-ill patient, the development of the LoTrach system from conception to production, and the role of the various components of the system in preventing VAP. Early issues in implementing this revolutionary equipment into ICU are explored and three case studies highlight advantages of this system.

CONCLUSION

The LoTrach system has been designed to facilitate the provision of a number of evidence-based interventions that have been shown to reduce VAP. Pulmonary aspiration is ubiquitous with conventional cuffs but prevented by the cuff of the LoTrach system when held at a constant and safe pressure against the tracheal wall with a cuff pressure controller. Other aspects incorporated in the ETT are aimed at clearing the secretions from the subglottic space, preventing tube occlusion and accidental extubation, and avoiding damage to the airway. In this way the LoTrach system employs a multifactorial approach to the prevention of VAP and the cost savings from LoTrach rather than a standard ETT will be considerable because of an average 3 day reduction in ICU length of stay related to this. It thus has the potential to be a very useful tool in the ICU setting in the prevention of VAP.

Subglottic secretion viscosity and evacuation efficiency

Ventilator-associated pneumonia (VAP) is a common nosocomial pneumonia that occurs in critically ill patients and results in mortality rates as high as 71%. Subglottic secretions (SSs) are a known risk factor. Several clinical trials have shown that continuous aspiration of subglottic secretions (CASS) reduces the risk of VAP by nearly half. Optimal suction pressure levels needed to efficiently evacuate viscous SSs are unknown. The purpose of this study was to describe SSs and the effective suction pressure (20 mmHg, 30 mmHg, 40 mmHg, and 50 mmHg) needed to maximize evacuation efficiency based on SS volume (2 ml, 4 ml, and 6 ml) and viscosity (watery, thick, and gel-like). A laboratory model was designed to replicate a human trachea. Thick secretions had the highest percentage of mean recovery representative of evacuation efficiency of SSs (mean recovery of 86%). The suction pressure of 30 mmHg had the highest overall mean of secretion recovery (83%) across all viscosity types and amounts. This study demonstrated that higher viscosity secretions were easier to evacuate than lower viscosity secretions when 30-mmHg suction pressure was applied. Management of secretion viscosity may assist in secretion removal and delay VAP development. With increased understanding of the molecular structure of SSs, there is the potential that clinicians will be able to manipulate secretion viscoelastic properties to maximize evacuation efficiency of the secretions. Further research is needed to identify safe suction pressures for optimal evacuation of SSs in human subjects.

Strategies for prophylaxis and treatment for aspiration

The absolute incidence of aspiration is difficult to define because of its relatively low occurrence and difficulty in diagnosis. The gastric volume predisposing to aspiration is larger than 30 ml. Fasting times for fluids have reduced; however, a large meal may require 9 hours of preoperative fasting. Preoperative carbohydrate-enriched beverages may attenuate postoperative catabolism. Aspiration occurs most frequently during induction and laryngoscopy. Awake fibre-optic intubation may be a suitable alternative in high-risk cases for aspiration. The role of cricoid pressure in anaesthesia needs re-evaluation as radiological and clinical evidence suggest that it may be ineffective and may impede intubation and ventilation. Chemoprophylaxis does not reduce the severity of aspiration pneumonitis as gastric bile is unaffected by these agents and induces a worse pneumonitis than gastric acid. Patients may be discharged home 2 hours after aspirating provided they are clinically unaffected and have postoperative surveillance.

Inflation of a pressure-limited cuff inside a model trachea

A theory of the elastic behaviour of thin rubber films is developed to describe inflation of pressure-limited tracheal tube cuffs (a) outside and (b) inside rigid cylindrical model tracheas. At each stage, assumptions and results were successfully checked against experiment. The theory predicts cylinder wall versus intracuff pressure. This allows, for any suitable cuff (of which there are many), the determination of a single intracuff pressure that ensures a satisfactory seal, for any diameter within the human adult range, the wall pressure staying below some chosen safety limit.

Gastroesophageal reflux and aspiration of gastric contents in anesthetic practice

General anesthesia may predispose patients to aspiration of gastroesophageal contents because of depression of protective reflexes during loss of consciousness. In addition, some patients may be at increased risk of pulmonary aspiration because of retention of gastric contents caused by pain, inadequate starvation, or gastrointestinal pathology resulting in reduced gastric emptying and gastroesophageal reflux. Despite increasing knowledge of the problems associated with aspiration, the relatively small incidence and associated mortality rates in the perioperative period do not appear to have changed markedly over the last few decades. In this review article, the physiological factors associated with an increased risk of gastroesophageal reflux and aspiration are considered together with some of the methods that are used to prevent aspiration. In particular, preoperative starvation, the use of drugs designed to increase gastric pH, recent developments in airway devices, and appropriate application of cricoid pressure are critically appraised.

The prevention of pulmonary aspiration with control of tracheal wall pressure using a silicone cuff

A prospective open randomized controlled study was performed to assess the ability of Euromedical ILM endotracheal tube cuff (silicone cuff) to prevent pulmonary aspiration. The inflation characteristics of this silicone cuff enables the control of tracheal wall pressure. The silicone cuffed tube was shortened and an adjustable flange was used to convert it to a cuffed tracheostomy tube. Twelve patients requiring a tracheostomy on a four-bed intensive care unit (ICU) in a district general hospital received either a silicone or a Shiley cuffed tracheostomy tube. Tracheal wall pressures of both cuffs were maintained at 30 cm H2O with a constant pressure inflation device. Blue food dye was instilled once daily into the subglottic space through a fine catheter above the cuff. There were six patients in the Shiley group and six patients in the silicone cuff group. Dye leaked to the trachea in six (100%) of the Shiley group compared with none (0%) of the silicone cuff group (P = 0.001). This study confirms the effectiveness of this silicone cuff at preventing aspiration and the high incidence of leakage with the conventional high-volume low-pressure tracheostomy tube cuff.

Pulmonary aspiration and lung injury

Lung injury after aspiration, although very rare, is a feared and potentially devastating sequela after anaesthesia. This paper summarizes the most recent studies in aspiration lung injury focusing on its clinical epidemiology, new insights in its pathophysiology and innovative concepts in its prevention and therapy.

Prevention of tracheal aspiration using the pressure-limited tracheal tube cuff

A new design of tracheal tube cuff, the pressure-limited cuff, used with a constant-pressure inflation system, was compared with a high-volume low-pressure cuffed tracheal tube for leakage of dye placed in the subglottic space into the trachea. Patients requiring ventilation on the intensive care unit were randomly allocated into two groups, one for each type of cuff, and blue food dye was instilled daily via a fine catheter above the cuff into the subglottic space. There were eight patients in the high-volume low-pressure group and seven in the pressure-limited cuff group. Dye leaked into the trachea in seven (87%) of the high-volume low-pressure group compared with none (0%) of the pressure-limited cuff group (p < 0.01). This study demonstrates that the pressure-limited cuffed tracheal tube, in combination with a constant-pressure inflation device, prevents leakage of fluid into the lungs that occurs with high-volume low-pressure cuffs in the critically ill, intubated patient.