Alternative approaches to ventilator-associated pneumonia prevention.

Ventilator-associated pneumonia (VAP), which develops in patients receiving mechanical ventilation, is the most common nosocomial infection in patients with acute respiratory failure. The major mechanism of lower respiratory tract colonization is aspiration of bacteria-colonized secretions from the oropharynx into the lower airways. The hydrostatic pressure of the secretions that collect in the subglottic space, which is the area above the endotracheal tube (ETT) cuff, or aerosolization of bacteria from the secretions collected within the respiratory tubing may facilitate the leakage into the lower airways. Ideally, the elimination of the mechanisms responsible for aspiration would decrease the incidence of VAP. Several preventive measures have been tested in clinical trials with little success.Here we present the results of our efforts to develop novel approaches for the prevention of VAP. Specifically, we found that keeping ventilated patients in a lateral position, which eliminates gravitational forces, is feasible and possibly advantageous. Additionally, several novel medical devices have been recently developed to prevent bacterial biofilm formation from the ETT and breathing tubing. These devices include coated ETTs, mucus shavers and mucus slurpers. Prevention of ETT bacterial colonization showed decreased bacterial colonization of the respiratory circuit and of the lower respiratory tract in laboratory studies and clinical trials. Future large studies should be designed to test the hypothesis that VAP can be prevented with these novel strategies. While there is a current focus on the use of respiratory devices to prevent biofilm formation and microaspiration, it is important to remember that lower respiratory tract colonization is multifactorial. Prevention of VAP cannot be achieved solely by eliminating bacterial biofilm on respiratory devices, and more comprehensive care of the intubated patient needs to be implemented.

New approaches for the prevention of airway infection in ventilated patients. Lessons learned from laboratory animal studies at the National Institutes of Health.

Despite early diagnosis and appropriate antibiotic therapy, ventilator-associated pneumonia (VAP) remains the leading cause of death from hospital-acquired infection in ventilator-dependent patients. Strategies to prevent bacterial colonization of the trachea and lungs are the key to decrease mortality, hospital length of stay, and cost. It is well established that the VAP can result from entry of infected oropharyngeal/gastric secretions into the lower airways. Aspiration may occur during 1) intubation, 2) mechanical ventilation through leakage around the tracheal tube cuff, 3) suctioning of the tracheal tube when bacteria can detach from the biofilm within the tube, or 4) areosolization of bacterial biofilm during mechanical ventilation through the tracheal tube or the ventilator circuit biofilm. From experimental studies in sheep, we drew 3 relevant conclusions: 1) The tracheal tube and neck should be oriented horizontal/below horizontal to prevent aspiration of colonized secretions and subsequent bacterial colonization of the lower respiratory tract. 2) Continuous aspiration of subglottic secretions (CASS) can lower bacterial colonization of the respiratory tract, but at the price of severe tracheal mucosal damage at the level of the suction port. 3) Coating the interior of the tracheal tube with bactericidal agents can prevent bacterial colonization of the tube surface and of the entire respiratory circuit, during 24 hours of mechanical ventilation.

Bacterial colonization of the respiratory tract following tracheal intubation-effect of gravity: an experimental study.

OBJECTIVE: To explore the role of the horizontal orientation of endotracheal tube and neck on bacterial colonization of the respiratory tract in anesthetized sheep on mechanical ventilation, without use of antibiotics. DESIGN: Prospective animal study. SETTING: National Institutes of Health research laboratory. SUBJECTS: Anesthetized, paralyzed, and ventilated sheep. INTERVENTIONS: Sheep were randomized into five groups and managed as follows: Group IS contained sheep that were not intubated and were immediately killed. Group HU4 contained six sheep that were mechanically ventilated for 4 hrs, with head and endotracheal tube elevated 30 degrees from horizontal. Group HU72 contained seven sheep that were prone, mechanically ventilated for 72 hrs, and managed the same as group HU4. Groups G and Gf each contained seven sheep that were prone on a lateral body rotation device, mechanically ventilated for 72 hrs, with neck and endotracheal tube horizontal. Group Gf received nasogastric enteral feeding. MEASUREMENTS AND MAIN RESULTS: At the end of the study, sheep were examined postmortem, and a total of 11 tissue samples were taken from the trachea, the five lobar bronchi, and the five lobar parenchyma, for qualitative and quantitative culture. Group HU72 had significant decrease in Pao2/Fio2 and heavy bacterial colonization in all sheep. Groups G and Gf retained excellent lung function; lung bacterial colonization was no different from the IS group. CONCLUSIONS: The horizontal orientation of the endotracheal tube and neck, through lateral body rotation, showed no altered airway colonization and maintained excellent gas exchange and lung function in our animal model.

Intratracheal pulmonary ventilation keeps tracheal tubes clean without impairing mucociliary transport.

BACKGROUND: Intratracheal pulmonary ventilation (ITPV) is a form of tracheal gas insufflation through a reverse thrust catheter that facilitates expiration and enhances CO2 removal. Tracheas of sheep mechanically ventilated for 3 days with gas delivered through the reverse-thrust catheter remained free of secretions, without suctioning. It was hypothesized that: 1) The expiratory flow from the lungs, combined with continuous cephalad flow from the reverse-thrust catheter keeps endotracheal tubes clean; and 2) tracheal mucus velocity is not impaired by ITPV. METHODS: A model trachea connected to a test lung and to a ventilator, via an 8-mm endotracheal tube, was used. Inspiratory and expiratory peak flow velocities and the movement of mucus in the model trachea and in the endotracheal tube were measured during conventional mechanical ventilation and ITPV. Tracheal mucus velocity was measured radiographically, using tantalum discs as markers, in seven intubated sheep ventilated for one hour with volume-controlled ventilation, and with ITPV. One millilitre Evans Blue dye was introduced into the trachea, to visualize mucus transport into the endotracheal tube. RESULTS: Peak expiratory flow velocity exceeded peak inspiratory flow velocity by 100% during ITPV. During volume-controlled ventilation, flow velocities were equal. During ITPV, there was slow, then rapid cephalad movement of mucus in the model trachea, 0.5 cm distal to the tip of the endotracheal tube, the velocity increasing once mucus entered the endotracheal tube. During volume-controlled ventilation, no movement of mucus was found. Baseline tracheal mucus velocity was equal during volume-controlled ventilation and ITPV. Secretions stained with Evans Blue dye entered the endotracheal tube and were rapidly expelled from within the endotracheal tubes during ITPV; only traces of mucus were found in two sheep during volume-controlled ventilation. CONCLUSION: The enhanced expiratory flow during ITPV expels secretions from the endotracheal tube through entraining of mucus at the tip of the endotracheal tube. Tracheal mucus velocity is not influenced by ITPV.

The mechanical ventilator: a potentially dangerous tool.

Mechanical ventilation is an important therapeutic technique for patients with respiratory failure. Nonetheless, it can be potentially dangerous, worsening by itself pre-existing lesions and producing new ones. The author carefully reviews the results of a number of long term studies in large animals, which highlight the factors causing ventilator-induced lung injury. When the pathology is not manageable with non invasive approach, invasive mechanical ventilation should be tailored to the patient to avoid iatrogenic damage.

A standardized method of oleic acid infusion in experimental acute respiratory failure.

UNLABELLED: Commonly, acute respiratory failure (ARF) in laboratory animals is induced through the intravenous infusion of oleic acid (OA). The methods by which OA is infused, and the methods by which droplets are generated, differ greatly among investigators. The resulting ARF, and the distribution of the underlying pulmonary pathology, are not highly reproducible. A method was developed that generated a reproducible, known spectrum of OA microdroplets. This method was applied to infuse a known volume of OA into the vena cava superior (VCS) in sheep, to induce ARF. In vitro studies were conducted in an observation chamber filled with saline or plasma. The distal end was cut off a 7F Swan Ganz catheter. The catheter was immersed in an observation chamber. Through one of the channels OA was infused at a low flow rate while saline was infused at variable high flow rates through a second channel. The size and the distribution spectrum of the so generated OA droplets were determined from flash photographic studies. The distribution and the size of the microdroplets depended on the media in the observation chamber, and on the saline infusion rate. In vivo studies were conducted in six anesthetized and ventilated sheep. We chose in our in vivo studies a saline flow rate of 126 mL/min and at an OA flow rate of 3 mL/min, that generated OA microdroplets 125 +/- 32 microm SD in size. OA microdroplets were generated in situ in the VCS and where then embolized into small pulmonary vessels. A total dose of 0.06 mL/kg of OA was administered in three separate doses of 0.02 mL/kg, each 10 min apart. The evolving ARF was manifested by a progressive deterioration in arterial blood gases, and a uniform opacification of all lung fields on chest X-ray films. At autopsy the lungs were diffusely consolidated. CONCLUSION: A method was developed to standardize the infusion of OA in laboratory animals that resulted in diffuse involvement of the all lungs, with a predictable and reproducible severe acute respiratory failure.

A comparison of intratracheal pulmonary ventilation to conventional ventilation in a surfactant deficient animal model.

OBJECTIVE: To compare intratracheal pulmonary ventilation (ITPV) with conventional ventilation in a rabbit model of surfactant deficiency. DESIGN: A prospective randomized animal study. SETTING: The Children's National Medical Center Research Animal Facility in Washington, DC. SUBJECTS: Adult male New Zealand white rabbits (n = 20), weighing 1.4-4.2 kg. INTERVENTIONS: After anesthesia and catheter placement, rabbits were tracheotomized, paralyzed, and placed on the conventional ventilator. We determined pulmonary functions at baseline. We washed surfactant out of the lungs by using serial bronchoalveolar lavages. Pulmonary function studies were determined after completion of the bronchoalveolar lavages and were used as an indication of severity of lung injury. Animals were randomized into two groups: We placed ten animals on ITPV, using the ITPV reverse thruster catheter designed by Kolobow and a prototype ITPV ventilator designed at Children's National Medical Center; we placed ten animals on conventional ventilation using the Sechrist iv-100 ventilator. Arterial blood gases were drawn every 15 mins, and the ventilator settings were adjusted to the minimal level that would maintain arterial blood gases in the following ranges: pH 7.35-7.45, PaCO2 30-40 torr (3.995.33 kPa), PaO2 50-70 torr (6.66-9.33 kPa). Animals were ventilated with the randomized ventilation techniques for 4 hrs. MEASUREMENTS AND MAIN RESULTS: Peak inspiratory pressure, mean airway pressure, and positive end-expiratory pressure were measured at the distal end of the endotracheal tube. We recorded these variables plus respiratory rate at baseline and every 30 mins for a total of 4 hrs of ventilation. Lung compliance did not differ between groups at the postlavage study period (ITPV, 0.56+/-0.13 mL/cm H2O/kg; conventional 0.49+/-0.15 mL/cm H2O/kg). At the end of the 4 hr study period, peak inspiratory pressure (ITPV, 26.2+/-4.6 cm H2O; conventional, 32.4+/-5.04 cm H2O, p = .007) and positive end-expiratory pressure (ITPV, 3.9+/-1.96 cm H2O; conventional, 6.3+/-1.42 cm H2O, p = .005) were lower in the ITPV ventilation group. Peak inspiratory pressure was significantly lower in the ITPV group by 2 hrs into the study. CONCLUSION: In this model of surfactant deficiency lung injury, ventilation and oxygenation were achieved at significantly lower ventilator settings using ITPV compared with conventional ventilation. Long-term studies are needed to determine whether this reduction in ventilation is maintained, and if so, if lung injury is reduced.

Efficacy of tracheal gas insufflation in spontaneously breathing sheep with lung injury.

Tracheal gas insufflation (TGI) decreases dead space (V D) and can be combined with continuous positive airway pressure (CPAP) to decrease minute volume (VE) and effort of breathing. In 11 anesthetized sheep, we induced acute lung injury (ALI) through oleic acid (OA) infusion and studied the effects of TGI combined with CPAP (CPAP-TGI) at different TGI flows and with catheters of different designs. Sheep were randomized to two groups: Group A (n = 7) was placed on CPAP and CPAP-TGI at 10 and 15 L/min of insufflation flow delivered through a reverse thrust catheter (RTC). Group B (n = 4) was placed on CPAP and CPAP-TGI at a flow of 10 L/min delivered through a RTC, and through a straight flow catheter (SFC). Compared with CPAP alone, CPAP-TGI resulted in significantly lower VD, VE, pressure time product, and work of breathing. We found no additional benefit from TGI flow of 15 L/min, compared with 10 L/min, and no statistically significant difference between the SFC and the RTC. In conclusion, TGI can be combined with CPAP in this model of ALI to reduce ventilation and effort of breathing.

Intratracheal pulmonary ventilation at low airway pressures in a ventilator-induced model of acute respiratory failure improves lung function and survival.

STUDY OBJECTIVE: The pulmonary parenchyma in patients with acute respiratory failure (ARF) is commonly not involved in a homogenous disease process. Conventional mechanical ventilation (MV) at elevated positive end-expiratory pressure (PEEP) and peak inspiratory pressure (PIP) aims at recruiting collapsed or nonventilated lung units. Invariably, those pressures are also transmitted to the healthiest regions, with possible extension of the disease process (barotrauma). During intratracheal pulmonary ventilation (ITPV), a continuous flow of fresh gas is delivered directly at the carina, bypassing the dead space proximal to the catheter tip. In healthy sheep, it allows lowering tidal volume (VT) to as low as 1.0 mL/kg, at respiratory rates (RR) up to 120 breaths/min, while maintaining normocapnia. In a model of ventilator-induced lung injury, we wished to explore whether ITPV, applied at low VT and low PEEP and tailored to ventilate the healthiest regions of the lungs, could provide adequate oxygenation and alveolar ventilation, without any attempt to recruit lungs. DESIGN: Randomized study in sheep. SETTING: Animal research laboratory. PARTICIPANTS: We induced ARF in 12 sheep following 1 to 2 days of MV at a PIP of 50 cm H2O, except that 5 to 8% of lungs were kept on apneic oxygenation of 5 cm H2O, sparing those regions from the injury process. INTERVENTIONS: Sheep were randomized to volume-controlled MV (control group) (n = 6) with VT of 8 to 12 mL/kg, PEEP of 5 to 10 cm H2O, or to ITPV (n = 6) at PEEP of 3 to 5 cm H2O, VT of 2.5 to 4 mL/kg, PIP of <20 cm H2O, at RRs sufficient to sustain normocapnia. MEASUREMENTS AND RESULTS: Hemodynamic status in the ITPV group progressively improved, and all six sheep were weaned to room air within 83+/-54 h. Sheep in the control group had progressively deteriorating conditions and all animals died after a mean of 50+/-39 h. Barotrauma and postmortem histopathologic changes were more pronounced in the control group. CONCLUSION: In this model of ventilator-induced lung injury, low PEEP-low VT ventilation with ITPV sustained normocapnia and prevented further lung injury, allowing weaning to room air ventilation.

Cardiopulmonary bypass through peripheral cannulation with percutaneous decompression of the left heart in a model of severe myocardial failure.

Prolonged closed chest cardiopulmonary bypass for severe total biventricular myocardial dysfunction requires invasive decompression of the left heart. The authors have developed an elongated helical coil that is permanently attached to the distal 8-10 cm of a flow directed Swan-Ganz catheter. When properly positioned, the helical coil kept the pulmonary artery (PA) and the tricuspid valves open, and allowed closed chest retrograde decompression of the left heart. The authors have evaluated the merits of closed chest cardiopulmonary bypass with decompression of the left heart in this manner in four sheep subjected to 30 min of warm global myocardial ischemia, along with induced ventricular fibrillation. All sheep developed severe global myocardial failure, with no left ventricular (LV) ejection. The authors have shown that pulmonary blood flow during cardiopulmonary bypass was reversed from the left heart, across the lungs, and into the right heart. The wedge pressure never exceeded 12 mmHg at any time, attesting to good decompression during periods of total ventricular failure, during partial recovery with some LV ejection, and after good recovery of LV function, followed by weaning from bypass after 44, 67, and 78 h of such support. One sheep could not be weaned from bypass, even after 5 days of CPBP. Lung function in all sheep remained unimpaired throughout, and there was no wound bleeding. The authors conclude that in this model of total myocardial failure, and while on closed chest CPBP, at all times and with all degrees of myocardial dysfunction, excellent LV decompression with the helical coil catheter was attained.

Intratracheal pulmonary ventilation and continuous positive airway pressure in a sheep model of severe acute respiratory failure.

STUDY OBJECTIVES: Previously we have shown that optimal pulmonary gas exchange can be sustained at normal airway pressures in a model of severe acute respiratory failure (ARF), using intratracheal pulmonary ventilation (ITPV), with weaning to room air. In an identical model of ARF, we have now explored whether ITPV, combined with continuous positive airway pressure (CPAP), can sustain adequate ventilation, with weaning to room air. DESIGN: Randomized study in sheep. SETTING: Animal research laboratory at the National Institutes of Health. INTERVENTIONS: ARF was induced in 12 sheep, using mechanical ventilation at peak inspiratory pressure of 50 cm H2O, but excluding 5 to 8% of lungs. Sheep were then randomized into two groups: the CPAP-ITPV group (n=6), in which ITPV was combined with a novel CPAP system; and a control group (n=6) in which the same CPAP circuit was used, but without ITPV. MEASUREMENTS AND RESULTS: All sheep in the CPAP-ITPV group were weaned to room air in 38.7+/-14 h. PaO2/fraction of inspired oxygen (FIO2) progressively increased from 108.8+/-43 to 355.7+/-93.1; PaCO2 remained within normal range; respiratory rate (RR) ranged from 18 to 120 breaths/min, and tidal volume (VT) was as low as 1.1 mL/kg. All sheep in the control group (CPAP alone) developed severe respiratory acidosis and hypoxemia after 4.8+/-4 h. PaO2/FIO2 decreased from 126.6+/-58.2 to 107.2+/-52.5 mm Hg, with a final PaCO2 of 166.8+/-73.3 mm Hg. CONCLUSIONS: All sheep treated with CPAP-ITPV maintained good gas exchange without hypercapnia at high RR and at low VT, with weaning to room air. All control animals treated with CPAP alone developed severe hypercapnia, respiratory acidosis, and severe hypoxemia, and were killed.

Clearance of mucus from endotracheal tubes during intratracheal pulmonary ventilation.

BACKGROUND: Intratracheal pulmonary ventilation (ITPV) is a form of tracheal gas insufflation in which all gas emerges in a cephalad direction from the tip of a reverse-thrust catheter positioned within an endotracheal tube. In vitro experiments have shown that this rapid gas flow, with 5 ml/h of normal saline added to the gas flow, continuously removes tracheal secretions from within the endotracheal tube. The authors evaluated its effectiveness to remove mucus in long-term studies in sheep. METHODS: Fourteen healthy sheep were tracheally intubated and ventilated for 3 days with ITPV or with volume-controlled ventilation. Measurements were made of the total amount of secretions within the endotracheal tubes (weight gain), the protein content within the endotracheal tubes, and the increase in resistance to constant air flow. The structure of the airways was examined grossly and histologically. Three additional sheep were ventilated for 24 h with ITPV, and Evans Blue dye was added to the saline to assess the distribution of the infused saline. RESULTS: There was significantly less mucus in endotracheal tubes of sheep ventilated with ITPV than with conventional ventilation, as shown by minimal weight gain (0.70 +/- 0.14 g vs. 2.44 +/- 0.81 g; P < 0.001), lower protein content (14.09 +/- 10.79 mg vs. 294.99 +/- 153.06 mg; P < 0.001), and lower resistance to constant air flow (6.15 +/- 0.54 cm H2O x 1(-1) x s(-1) vs. 15.34 +/- 5.28 cm H2O x 1(-1) x s(-1); P < 0.001). Results of gross and histological examinations of the tracheas of animals in both groups were similar, and the tracheas were well preserved. More than 95% of the instilled saline was recovered during ITPV. Only traces of Evans Blue dye were found near the tip of the endotracheal tubes. CONCLUSION: Intratracheal pulmonary ventilation makes it possible to keep the endotracheal tubes of sheep ventilated for 3 days free of mucus without suctioning.

Tracheal mucus velocity remains normal in healthy sheep intubated with a new endotracheal tube with a novel laryngeal seal.

BACKGROUND: Tracheal mucus velocity (TMV), an index of mucociliary clearance, is reduced markedly in patients intubated with standard endotracheal tubes (ETTs) with high-compliance low-pressure (hi-lo) cuffs. The authors developed a new ultra-thin walled ETT in which the inflatable cuff is replaced with a no-pressure seal, positioned at the level of the larynx. The seal consists of 12 to 20 toroidal layers of thin polyurethane film ("gills") at the level of the vocal cords and prevents both air leak and fluid aspiration. The authors hypothesized that ETTs with the new laryngeal seal may impair TMV less than ETTs with inflated hi-lo cuffs do. METHODS: The TMV was measured in seven healthy female sheep by radiographically tracking the motion of small discs of tantalum inserted into the trachea through a bronchoscope. The TMV was measured in spontaneously breathing sheep before intubation (baseline) and after intubation with either a hi-lo ETT (control group) or after intubation with a new ETT with gills (study group). Four to six weeks later, the studies were repeated, but the sheep that were previously in the control group served as the study group, and those in the study group served as controls. RESULTS: Baseline TMV did not differ in the two groups. In the control group, TMV decreased significantly (by 67%) from baseline. In the study group, TMV did not differ significantly from baseline and remained steady during 3 h of intubation. CONCLUSIONS: The TMV does not change in sheep intubated with new ETTs with gills. The new ETT's may help promote a normal mucociliary clearance in patients who require ventilation.

Reduced airway resistance and work of breathing during mechanical ventilation with an ultra-thin, two-stage polyurethane endotracheal tube (the Kolobow tube).

OBJECTIVES: To compare dynamic pulmonary function studies using the ultrathin walled Kolobow endotracheal tube, with conventional endotracheal tubes of similar external diameter on rabbits during mechanical ventilation. To test the hypothesis that the increased internal diameter of the Kolobow tube will result in decreased airway resistance and work of breathing. DESIGN: Controlled animal study. SETTING: Institutional animal research facility. SUBJECTS: Adult female Dutch Belted rabbits (n = 6), weighing 1.4 to 1.6 kg. INTERVENTIONS: The animals were initially intubated with a conventional endotracheal tube (2.5-mm internal diameter; 3.6-mm outer diameter); they were paralyzed and placed on a mechanical ventilator. Ventilatory settings were adjusted to obtain standard arterial blood gases: pH of 7.35 to 7.45; PaCO2 of 35 to 40 torr (4.7 to 5.3 kPa), and PaO2 of 90 to 100 torr (12.0 to 13.3 kPa). After the stabilization period, pulmonary function tests (PFTs) were measured (period 1), the conventional endotracheal tube was replaced with a Kolobow tube, and PFTs were measured again and recorded (period 2). While continuously monitoring tidal volume, the peak inspiratory pressure was decreased to match the tidal volume measured during ventilation with the conventional endotracheal tube. Once the desired tidal volume was reached, PFTs were recorded (period 3). Flows were unchanged during the experiment and the length of the endotracheal tubes was the same for both the conventional and the Kolobow tube. MEASUREMENTS AND MAIN RESULTS: Mean values of the airway resistance and work of breathing from periods 1 and 3 were compared using the Student's t-test. There was a 59% decrease in total airway resistance (p = .001) and 45% decrease in the work of breathing (p = .0006). CONCLUSIONS: The use of the ultrathin walled Kolobow endotracheal tube resulted in significant decreases in airway resistance and work of breathing, which has the potential for improving the ventilatory mechanics in very small premature newborns.

Evaluation of a new thin-walled endotracheal tube for use in children.

Conventional endotracheal tubes have high intrinsic resistive properties due to their high outer-to-inner diameter ratio. This has significant disadvantages in the treatment of the small neonatal or pediatric patient as work of breathing increases with decreasing internal radius. Diagnostic and therapeutic procedures, including suctioning, may be very difficult in patients with small endotracheal tubes. We therefore measured airway resistance and pressure differential during simulated mechanical ventilation using proximal and distal endotracheal tube flow transducers. Conventional and new, ultrathin-walled endotracheal tubes reinforced with flat stainless steel or a novel, crush-proof nickel-titanium alloy were compared using fixed ventilator settings. Ventilation through the ultrathin-walled tubes resulted in a significantly reduced airway resistance (p < or = 0.01). These new ultrathin-walled endotracheal tubes showed flow characteristics typical of much larger conventional endotracheal tubes: the 3.2-mm internal diameter had an airway resistance (Raw) of 36, while a standard 2.5-mm internal diameter endotracheal tube had a Raw of 146. Both endotracheal tubes have identical external diameters of 3.6 mm. We conclude that ultrathin-walled endotracheal tubes could have a significant role in the treatment of the ventilated child by facilitating interactive ventilation and maintenance of airway patency and may make procedures such as fiberoptic endoscopy and intrapulmonary ventilation using reverse-thrust catheters possible in the small child.

New ultrathin-walled endotracheal tube with a novel laryngeal seal design. Long-term evaluation in sheep.

BACKGROUND: A new endotracheal tube (ETT) was fabricated and tested in sheep. It had no tracheal cuff; airway seal was achieved at the level of the glottis through a no-pressure seal made of "gills"; the laryngeal portion was oval-shaped; and the wall thickness was reduced to 0.2 mm. METHODS: Sheep were tracheally intubated either with a standard tube or with the new tube, and their lungs were mechanically ventilated for 1 or 3 days. Air leak was recorded at different peak inspiratory pressures (PIPs). Liquid seepage into the trachea was assessed using an indicator dye. Tracheolaryngeal lesions were scored grossly and histologically. RESULTS: There was no air leak up to 40 cmH2O of PIP, in either group, in short- and long-term studies. Methylene blue leaked across the cuff in two sheep with standard ETTs. No dye leaked across the gills with the new ETTs. In the new ETT group, the trachea appeared better preserved, grossly and histologically, than in the standard ETT group at both 1 and 3 days (P < 0.05). At day 1, the larynx and vocal cords appeared grossly less injured in the new ETT group (P < 0.05), whereas there was no difference at day 3. Histology did not show significant difference on vocal cords, epiglottis, and larynx between the two groups at any time. CONCLUSIONS: The novel, no-pressure seal design of the new ETT is highly effective in preventing air leak and aspiration. It causes no significant tracheal injury.

Design and development of ultrathin-walled, nonkinking endotracheal tubes of a new "no-pressure" laryngeal seal design. A preliminary report.

BACKGROUND: Endotracheal tubes (ETTs) of conventional design and manufacture greatly increase the air-flow resistance of the upper airways. This increase in upper-airway resistance can lead to a significant increase in the work of breathing and may necessitate the use of assisted mechanical ventilation. Current ETTs are relatively stiff and contribute greatly to patient discomfort. The inflatable cuffs now mounted onto the ETTs function well in short-term use but impart significant morbidity when used over longer periods. These issues were addressed by the designing of a low-resistance ETT. METHODS: Using new techniques, we developed ultrathin-walled, wire reinforced ETTs of conventional configuration and ETTs the oropharyngeal-section diameter of which was a few millimeters larger than the diameter of the tracheal section. The wall thickness was a constant 0.20 mm. The wire reinforcement was stainless steel flat wire or superelastic nickel-titanium alloy. The superelastic nickel-titanium alloy reinforcement made those ETTs crush-proof; after forceful manual compression, recovery was complete. To obtain a seal with the upper airways, we first shaped a short section of the oropharyngeal section of the ETT from round to oval (or egg-shaped) to conform better to the larynx. We then attached to this segment numerous soft, pliable, 0.025-0.075-mm-thick rings of polyurethane to occlude voids for potential air leaks from within the larynx. RESULTS: In vitro pressure-flow studies showed a decrease by as much as four- or fivefold in air-flow resistance in the adult ETT range, effectively increasing the internal diameter by 2.3-3.7 mm, compared with conventional ETTs of the same outside diameter. In vivo studies for 24 h in sheep showed no air leaks at airway pressures to 30 cmH2O and minimal leak at greater pressures. The gross appearance of the trachea was normal. CONCLUSIONS: Although the new tubes appear to offer advantages to those currently used, testing in humans is required to assess the clinical utility of the tube-cuff design.