High Volume Low Pressure Research Articles

Will the Taper Shaped Cuff Replace the Conventional High Volume-Low Pressured Cuff on Endotracheal Tube?

An effective tracheal seal plays an essential role in precluding aspiration and boosting efficiency with mechanical ventilation when endotracheal tube is inflated. High cuff pressure can cause damage to the tracheal wall and lead to serious complications such as tracheal stenosis. Endotracheal tube (ET) cuff pressures greater than 30 cmH2O may impede capillary blood flow in the tracheal wall, and ET cuff pressures greater than 50 cmH2O is considered high enough to completely block capillary blood flow.[1] Low volume high pressure cuff was used in early ETs but replaced by high volume low pressure (HVLP) cuff because the former causes mucosal injury along the lateral tracheal wall. HVLP cuffs appeared ideal because they are capable of producing a seal with low pressure. However, HVLP's large cuff diameter has emerged as a key issue as it is 1.5 to 2 times larger than the adult trachea. Longitudinal or oblique folds are developed upon inflation within the larger sized HVLP cuffs. The seal then becomes incomplete and allows secretions and air to leak as a result. Pulmonary aspiration of microorganism mass found in the oral cavity is considered one of leading causes of ventilator-associated pneumonia. In addition, over inflation of HVLP cuff can markedly increase cuff pressure, particularly around the folds and result in injury to the tracheal mucosa.[2] Low volume cuff tubes has recently drawn attention again while many researchers explored benefits of modified low volume low pressure (LVLP) cuff tubes. A taper-shaped cuff is designed to fit into the trachea at its narrow end and provides smaller cuff volume. This tapered cuff design is more effective in minimizing longitudinal folds when inflated, improving tracheal seal and preventing leakage of secretions and air even under high airway pressures, compared with conventional HVLP cuffs.[2,3] The transition from HVLP cuffs to taper-shaped cuffs is currently underway in endotracheal tubes. That is, the trend is moving back to low volume cuff tracheal tubes, which exert low pressure, in favor of better outcomes. Then we can have a question: Are tapered cuffs safe from pressure injury that is the most critical complication of low volume high pressure cuffs? While transmission of intracuff pressure to the tracheal wall depends on the cuff material, taper-shaped cuffs can transmit all the intracuff pressure to the tracheal wall.[4] In endoracheal position, the intracuff pressure of LVLP cuffs can be significantly increased by a slight change in inflating volume. In addition, the tapered cuff design provides smaller area of contact with the tracheal wall, compared to cylindrical shaped HVLP cuffs,[2] meaning that the extent of transmitted pressure is higher on the tracheal wall. It is therefore important to examine pressure changes with volume in tracheal tube cuff inflated. Special attention to pressure changes is also crucial in the tracheal tube cuff exposed to nitrous oxide for anesthesia because cuff pressure can significantly increase with increasing volume.[5] In case the taper-shaped cuff is not inflated adequately and develops an asymmetrical shape,

Impact of a Low-Pressure Polyurethane Adult Endotracheal Tube on the Incidence of Ventilator-Associated Pneumonia: A before and after Concurrence Study

Background. Ventilator-associated pneumonia (VAP) is a leading cause of morbidity and mortality in intensive care unit (ICU) patients, encompassing up to 15% of all hospital acquired infections. Our hospital implemented a facility-wide conversion from a low-volume high-pressure polyvinyl cuffed endotracheal tube (PV-cuffed ETT) to a high-volume low-pressure (HVLP) polyurethane-cuffed endotracheal tube (PU-cuffed ETT) in an effort to reduce the incidence of VAP. Methods. We completed an IRB approved, retrospective chart review comparing the number of episodes of VAP 12 months preceding and following the introduction of a new ETT. A diagnosis of VAP was made based upon the guidelines of our institution, consistent with the Center of Disease Control and Prevention definition. Results. The number of patients developing VAP the year after the ETT conversion reduced to 32 (16.3%) from 68 (24.7%) the year before the conversion (). The rate of VAP was reduced by 56% per ventilator day after the implementation of the PU-cuffed ETT (). No significant differences were observed in length of hospital stay, length of mechanical ventilation, or mortality before or after the conversion. Conclusions. We found that HVLP PU-cuffed ETTs were associated with a statistically significant reduction of VAP in the adult ICUs.

Manufacturing of biocompatible nonwoven structures by using spray atomization of dissolved polymers

The use of porous polymer materials for vascular prostheses demonstrates promising results. Fleece‐like nonwoven structures can be generated by atomization of dissolved polycarbonate urethanes. This article focuses on the manufacturing process for the fleece structures. The solution is atomized through a high volume low pressure nozzle. The solvent evaporates during time of flight to target, so that small fibers are formed from each drop of solution. By using different rotating molds and positioning systems, tubular shapes or open surfaces can be generated. The manufacturing process is described in detail. In a simple comparison with electrospinning, the process shows its superior throughput of material. Problems with the process and their possible solutions are shown. The influence of certain basic parameters on the generated nonwoven material is discussed. The manufactured structures are inspected for their mechanical properties and their permeability for water and blood. POLYM. ENG. SCI., 54:867–873, 2014. © 2013 Society of Plastics Engineers

Endotracheal tube with tapered-type cuff for preventing ventilator-associated pneumonia: a randomized clinical trial

The most common cause of ventilator-associated pneumonia (VAP) is aspiration of oral secretion through the endotracheal tube (ET). Subglottic suction drainage (SSD) has been recommended as a safety measure against aspiration due to its high effectiveness. Currently, two types of cuff shape - spindle and tapered - are predominant in high-volume, low-pressure (HVLP) ETs with SSD. However, the shape most suitable for preventing dripping onto the subglottis has not been determined. The purpose of this study was to determine whether an ET with tapered-type cuff can reduce the incidence of VAP.

Migration of polyurethane high-volume low-pressure cuffed endotracheal tubes after neck flexion and extension

To the Editor: In 2007 our hospital converted from standard polyvinyl high-pressure low-volume (HPLV) cuffed endotracheal tubes (ETT) to high-volume low-pressure (HVLP) polyurethane cuffed ETTs. HVLP ETTs feature cuffs that are longer, made of thinner material (10 lm), and inflate to a lower pressure, compared to traditional polyvinyl cuffed ETTs (Fig. 1) [1]. We have noticed the material of the HVLP polyurethane cuffs allows tube stem migration of 0.5 cm in either direction (up and down) while the cuff stays in place. The migration of ETTs towards the carina with neck flexion and away from the carina with neck extension has been documented only with HPLV ETTs [2–5]. The thinner material of HVLP cuffs may allow significant tracheal migration; we therefore conducted a prospective, IRB approved study to observe the mobility of these ETTs from their fixed position following flexion and extension of the neck. One hundred patients (50 males, 50 females) undergoing elective surgery, requiring routine intubation and general anesthesia, signed a written informed consent to participate in the study. All patients’ tracheas were initially intubated to a depth of 21 or 23 cm for women and men, respectively. A single anesthesiologist utilized a fiberoptic bronchoscope (Olympus LF-GP, Center Valley, PA, USA) and a standard metric ruler in centimeters to determine the actual tip to carina distances following intubation. The ETTs were then secured and held in place at the incisors by a second anesthesiologist. Following both flexion and extension of the neck, any ETT tip migration observed (fiber-optic evaluation) was recorded in centimeters by research personnel. Data are expressed as mean ± SD and (range) where appropriate. The Wilcoxon signed ranks test was used to calculate the displacements of the ETT. A P value of B0.05 was considered statistically significant. Flexion resulted in movement of the ETT tip inward (towards the carina) in 78 % of patients and extension moved the tip outward (away from the carina) in 81 % of patients. The average migratory distance (cm) of the ETT tip was 1.2 ± 1.0 (0–3.5) away from the carina following extension and 1.4 ± 1.4 (0–5) towards the carina after flexion (P \ 0.001 for flexion and extension). D. Mangar C. J. Sprenker R. A. Karlnoski R. K. Dodson E. M. Camporesi Florida Gulf-to-Bay Anesthesiology Associates, 1 Tampa General Circle Suite A327, Tampa, USA

Unilateral vocal cord paralysis following a short period of endotracheal intubation anesthesia

Unilateral vocal cord paralysis following a short period of endotracheal intubation anesthesia

Do lower cuff pressures reduce damage to the tracheal mucosa? A scanning electron microscopy study in neonatal pigs

Modern high volume-low pressure (HVLP) endotracheal tubes (ETT) cuffs can seal the trachea using baseline cuff pressures (CP) lower than peak inspiratory airway pressures (PIP). The aim of the study was to determine whether this technique reduces the damage to the tracheal mucosa compared to constant CP of 20 cmH(2)O. Eighteen piglets were intubated with an ID 4.0 mm HVLP cuffed ETT (Microcuff PET) and artificially ventilated with 20 cmH(2)O PIP and 5 cmH(2)O PEEP. Animals were randomly allocated to two groups of CP: group A (just seal; n = 9) and group B (20 cmH(2)O; n = 9), controlled constantly with a manometer during the following 4-h study period under sevoflurane anesthesia. After euthanasia, cuff position was marked in situ. Damage in the cuff region was evaluated with scanning electron microscopy (SEM) examination by grading of mucosal damage and by estimating percentage of intact mucosal area both by a blinded observer. Maximal CP to seal the trachea in group A ranged from 12 to 18 cmH(2)O (median: 14 cmH(2)O). Using a mixed effects model approach, the estimated mean effect of group B vs group A was an increase of 17.9% (SE 8.1%) higher proportion of pictures with an area of at least 5% intact mucosa (P = 0.042). Minimal sealing pressures with cyclic pressure changes from CP did not result in decreased damage to the tracheal mucosa compared to constant CP of 20 cmH(2)O in this short-term animal trial.

Effect of Lanz Pressure Regulating Valve on Self-sealing Mechanism and Air Leakage Across the Tracheal Tube Cuffs in a Benchtop Model

The aim of the present study was to investigate the effect of the Lanz system on air sealing by self-inflation in high volume-low pressure (HVLP) tube cuffs. In vitro tracheal air sealing was studied in HVLP tracheal tube cuffs (internal diameter [ID] 8.0mm) made from polyurethane ([PU] Seal Guard tracheal tube, Covidien, Athlone, Ireland) and from polyvinylchloride ([PVC] HiLo tracheal tube, Covidien) with and without Lanz pressure regulating valve. Tube cuffs were placed in a vertical 22 mm ID artificial trachea and inflated to 5, 10, 15, 20, 25, or 30 cm H2O cuff pressures. Pressure control ventilation with peak inspiratory pressures (PIPs) of 20 or 25 cm H2O was applied and air leakage was assessed spirometrically as the ratio of expiratory to inspiratory tidal volumes. Nonparametric Mann-Whitney test was applied to compare the air leakage with and without Lanz system for both cuff types at each cuff pressure and PIP (P < .05). The PVC tube cuffs with Lanz system resulted in significant air leakage at both 20 and 25 cm H2O PIP as compared to those without the Lanz system, especially at cuff pressures lower than the preset PIP (P < .05). Although PU tube cuffs with Lanz system showed reduced air sealing when compared with cuffs without Lanz, the difference was not statistically significant. Cuff pressure compensation with the Lanz system during cyclic respiratory pressure changes interferes with the self-sealing mechanism in HVLP tube cuffs at cuff pressures lower than PIP level. This results in larger air leak across tube cuffs particularly in tube cuffs made from PVC.

Preventing Ventilator-Associated Pneumonia - The Role of the Endotracheal Tube

The endotracheal tube, rather than the ventilator, is responsible for the vast majority of cases of ventilatorassociated pneumonia (VAP). Tracheal intubation should be avoided, or early extubation performed, if at all possible. With current high-volume low-pressure (HVLP) cuffs, pulmonary aspiration of microorganisms from the upper aerodigestive tract normally occurs and is frequently silent, until there is a clinical respiratory deterioration. Aspiration occurs by 3 mechanisms; channels within the HVLP cuff, in folding of the cuff upon movement and intermittent deflation of the cuff. This aspiration is the pivotal step in the development of VAP. The diagnosis of VAP is notoriously inaccurate and stifles the progress of research into prevention strategies. When treating bacteria present in the lung, the various paradigms of VAP diagnosis remain the only (and best) tools that we have to decide when the benefits of antibiotics outweigh the disadvantages. It is surprising, considering the accepted high mortality and cost of VAP, that until recently, there has been a massive under investment from industry in preventative technologies. New technologies should address the multiple factors implicated in the pathogenesis of VAP, including aspiration elimination by improved cuff designs. However, surrogate outcomes, such as pulmonary aspiration and tracheal colonisation (a more rigorous standard to aspire to), should be considered when evaluating preventative strategies. Pulmonary aspiration and/or tracheal colonisation by pathogenic organisms are undesirable and should be unacceptable. This review appraises the role of the endotracheal tube in both the development and prevention of VAP. Keywords: Agento, CASS, cuff, endotracheal, high volume low pressure, HILO EVAC, HVLP, Lotrach, low volume low pressure, LVLP, Microcuff, PneuX, sealguard, subglottic secretion drainage, taperguard, tube, ventilator-associated pneumonia

Mechanical influences on fluid leakage past the tracheal tube cuff in a benchtop model

High-volume low-pressure (HVLP) cuffs on endotracheal tubes do not fully protect the lower airway from leakage of potentially contaminated secretions down the longitudinal folds within the cuff. Here, our purpose was to evaluate potential effects of positive end-expiratory pressure (PEEP), inspiratory effort intensity, and tube characteristics on fluid leakage past the cuff. This benchtop study at a research laboratory used a tracheal tube inserted into an artificial Plexiglas trachea connected to a ventilator and lung model. Methylene blue was deposited above the tube cuff to simulate subglottic secretions. Five PEEP levels (0, 5, 10, 15, and 20 cmH₂O) were tested with volume-controlled ventilation and three simulated inspiratory effort levels with pressure-support ventilation. Several cuff materials and tube sizes were tested. The leakage occurrence rate ranged from 91% with zero PEEP to 8% with 15 and 20 cmH₂O PEEP and was indirectly proportional to the PEEP level with significant correlation (R² = 0.39, p < 0.001), an effect not explained by higher peak inspiratory pressure. Low, moderate, and high inspiratory effort intensities were associated with 38%, 46%, and 75% leakage rates, respectively (p = 0.024). Leakage flow was considerably less with polyurethane than with polyvinylchloride tubes (mean 0.5 versus 31.8 ml/h). Leakage increased with larger tube diameters. This benchtop study shows that PEEP and a polyurethane cuff prevent leakage past the endotracheal tube cuff, whereas greater inspiratory effort and larger tube diameters for given tracheal size induce or worsen leakage.

Massive Aspiration Past the Tracheal Tube Cuff Caused by Closed Tracheal Suction System

Aspiration past the tracheal tube cuff has been recognized to be a risk factor for the development of ventilator-associated pneumonia (VAP). This study investigated the effect of closed tracheal suctioning on aspiration of fluid past the tracheal tube cuff in an in vitro benchtop model. High-volume low pressure tube cuffs of 7.5 mm internal diameter (ID) were placed in a 22 mm ID artificial trachea connected to a test lung. Positive pressure ventilation (PPV) with 15 cm H₂O peak inspiratory pressure and 5 cm H₂O positive end-expiratory pressure (PEEP) was used. A closed tracheal suction system (CTSS) catheter (size 14Fr) was attached to the tracheal tube and suction was performed for 5, 10, 15, or 20 seconds under 200 or 300 cm H₂O suction pressures. Amount of fluid (mL) aspirated along the tube cuff and the airway pressure changes were recorded for each suction procedure. Fluid aspiration during different suction conditions was compared using Kruskal-Wallis and Mann-Whitney test (Bonferroni correction [α = .01]). During 10, 15, and 20 seconds suction, airway pressure consistently dropped down to -8 to -13 cm H₂O (P < .001) from the preset level. Fluid aspiration was never observed under PPV + PEEP but occurred always during suctioning. Aspiration along the tube cuff was higher with -300 cm H₂O than with -200 cm H₂O suction pressure (P < .001) and was much more during 15 and 20 seconds suction time as compared to 5 seconds (P < .001). Massive aspiration of fluid occurs along the tracheal tube cuff during suction with the closed tracheal suction system.

Tracheal fluid leakage in benchtop trials: comparison of static versus dynamic ventilation model with and without lubrication

Longitudinal folds in tracheal tube (TT) cuffs cause leakage of pooled secretions past the tube cuff, and the most common in vitro method to test the efficacy of a new tube is a benchtop model using an artificial rigid trachea. This study compared the potential of a static and dynamic ventilation benchtop model and cuff lubrication in testing the tracheal sealing properties of a given TT cuff. Static trial Six brands of 7.5 mm internal diameter (ID) cuffed TT (n = 8) with high volume-low pressure cuffs were inflated in an artificial trachea (18 mm ID) without and with lubrication. Dynamic trial The same tube cuffs, without lubrication, were subjected to positive pressure ventilation (PPV) + positive end-expiratory pressure (PEEP) of 5cmH(2)O or to PPV alone (without PEEP) or to PEEP alone (without PPV). Clear water (5 ml) was placed above the tube cuff, and fluid leakage (ml) was measured up to 60 min. Gel lubrication, PEEP alone and PPV + PEEP completely prevented fluid leakage across the tube cuffs in all six TT brands tested within 60 min when compared to the static unlubricated model (0% leak versus 100% leak; P < 0.01). Fluid leakage in the static unlubricated model and the PPV group was 1.38-4.76 ml and 0.23-4.47 ml, respectively. Gel lubrication, PEEP alone, and PPV + PEEP in the benchtop model had a much stronger protective effect than PPV alone on fluid leakage. Studies testing the fluid sealing efficiency of tube cuffs might be more conclusive in a static benchtop model without lubrication than in a dynamic model.

Integration of post-combustion capture and storage into a pulverized coal-fired power plant

Post-combustion CO 2 capture and storage (CCS) presents a promising strategy to capture, compress, transport and store CO 2 from a high volume–low pressure flue gas stream emitted from a fossil fuel-fired power plant. This work undertakes the simulation of CO 2 capture and compression integration into an 800 MW e supercritical coal-fired power plant using chemical process simulators. The focus is not only on the simulation of full load of flue gas stream into the CO 2 capture and compression, but also, on the impact of a partial load. The result reveals that the energy penalty of a low capture efficiency, for example, at 50% capture efficiency with 10% flue gas load is higher than for 90% flue gas load at the equivalent capture efficiency by about 440 kWh e/tonne CO 2. The study also addresses the effect of CO 2 capture performance by different coal ranks. It is found that lignite pulverized coal (PC)-fired power plant has a higher energy requirement than subbituminous and bituminous PC-fired power plants by 40.1 and 98.6 MW e, respectively. In addition to the investigation of energy requirement, other significant parameters including energy penalty, plant efficiency, amine flow rate and extracted steam flow rate, are also presented. The study reveals that operating at partial load, for example at half load with 90% CO 2 capture efficiency, as compared with full load, reduces the energy penalty, plant efficiency drop, amine flow rate and extracted steam flow rate by 9.9%, 24.4%, 50.0% and 49.9%, respectively. In addition, the effect of steam extracted from different locations from a series of steam turbine with the objective to achieve the lowest possible energy penalty is evaluated. The simulation shows that a low extracted steam pressure from a series of steam turbines, for example at 300 kPa, minimizes the energy penalty by up to 25.3%.

Infrared thermography-based visualization of droplet transport in liquid sprays

An infrared thermography-based technique for the characterization and visualization of liquid sprays was developed. The technique was tested on two atomizers: a high-speed rotary bell atomizer and a high volume low pressure air-assisted atomizer. The technique uses an infrared thermography-based measurement in which a uniformly heated background acts as a thermal radiation source, and an infrared camera as the receiver. The infrared energy emitted by the radiation source in traveling through the spray is attenuated by the presence of the droplets inside the spray. The infrared intensity is captured by the receiver showing the attenuation in the image as a result of the presence of the spray. The captured thermal image is used to study detailed macroscopic features of the spray flow field and the evolution of the paint droplets as they are transferred from the applicator to the target surface.

VOIDING FUNCTION IN WOMEN WITH ORTHOTOPIC NEOBLADDER DIVERSION

INTRODUCTION AND OBJECTIVE: To evaluate patients with orthotopic bladder substitution for benign causes in terms of indications, complications as well as the functional outcome. METHODS: Between April 1986 and January 2006, 73 patients (57males and16females) with mean age 41.5 years (29-56 years) underwent simple cystectomy and orthotopic bladder substitution for management of contracted bladders(62) or complex vesicovaginal fistulae (11) . The prostate and seminal vesicles were preserved in men with removal of a core of the prostate. Ileal W neobladders were applied for 37 patients and Urethral Hemi-Kock pouch for 36. . Patients were followed for a period ranged from 18 up to 243 months (mean 94.5 ± 43 months). All patients were evaluated for continence status. Pouchometry and urethral pressure profile were performed in 38 patients . Potency and fertility were verified in eligible male patients. Late sequalae after urinary diversion were assessed especially what is concerning upper tract function and configuration RESULTS: Poucho-prostatic anastomotic strictures were diagnosed in 11 men ( 19.3% ) and were managed endoscopically. Twelve patients (12.4%) developed chronic retention and were maintained on CIC. Out of the other 61 patients, 45 (73.8%) were continent day and night while 16 (26.2%) showed various degrees of nocturnal enuresis. Urodynamic studies showed high volume low pressure reservoirs in those patients with chronic retention and low urethral closure pressure in those with enuresis. Potency was preserved in 54 out of 61 eligible men(88.5%) and fertility in 9 out of 21(42.8%). Out of 138 evaluated renal units (8 patients had solitary kidney),122 showed stable kidney function and configuration. The other 16 units (11.6 % ) showed various degrees of deterioration due to obstruction ( 3), pyelonephritis (7) or chronic retention (6).Pouch stones were encountered in 12 cases (16.4% ). CONCLUSIONS: Simple cystectomy and orthotopic substitution is a viable option of management of benign bladder diseases . Relatively high incidence of chronic retention is anticipated necessitating regular follow-up for early diagnosis and management. Potency and fertility could be preserved in a good proportion of male patients.

Rapid pressure compensation by automated cuff pressure controllers worsens sealing in tracheal tubes

Cyclic redistribution of air within the cuff during respiratory pressure changes creates a self-sealing mechanism which allows tracheal sealing, despite tracheal airway pressure being above baseline cuff inflation pressure. The aim of the present study was to investigate the effect of continuous automated cuff pressure regulation on tracheal sealing during cyclic respiratory pressure changes. In vitro tracheal sealing was studied in four different high volume-low pressure (HVLP) tracheal tube cuffs size internal diameter 8.0 and 5.0 mm in combination with a conventional pressure manometer and two different automated pressure controllers (VBM Cuff Controller; Cuff Pressure Control Tracoe). Experiments were performed at 10, 15, 20, and 25 cm H(2)O cuff pressure during intermittent positive pressure ventilation with peak inspiratory pressures of 20 and 25 cm H(2)O. Air leakage was assessed spirometrically. Experiments were performed four times with each tube brand and size with two exemplars of each of the three cuff pressure controllers. Owing to immediate cuff pressure correction, tracheal sealing at cuff pressure below inspiratory pressure was reduced in most of the tracheal tube cuffs, except in those with reduced sealing characteristics when using the Pressure Control Tracoe compared with the conventional pressure manometer and the VBM Cuff Controller. Tracheal sealing with the Pressure Control Tracoe comparable with the other two devices was only achieved at cuff pressures of 20 and 25 cm H(2)O. Automated cuff pressure controllers with rapid pressure correction interfere with the self-sealing mechanism of high sealing HVLP tube cuffs and reduce their improved sealing characteristics.

Fabrication of Fracture-Free Nanoglassified Substrates by Layer-by-Layer Deposition with a Paint Gun Technique for Real-Time Monitoring of Protein−Lipid Interactions

New sensing materials that are robust, biocompatible, and amenable to array fabrication are vital to the development of novel bioassays. Herein we report the fabrication of ultrathin (ca. 5-8 nm) glass (silicate) layers on top of a gold surface for surface plasmon resonance (SPR) biosensing applications. The nanoglass layers are fabricated by layer-by-layer (LbL) deposition of poly(allylamine) hydrochloride (PAH) and sodium silicate (SiO(x)), followed by calcination at high temperature. To deposit these layers in a uniform and reproducible manner, we employed a high-volume, low-pressure (HVLP) paint gun technique that offers high precision and better control through pressurized nitrogen gas. The new substrates are stable in solution for a long period of time, and scanning electron microscopy (SEM) images confirm that these films are nearly fracture-free. In addition, atomic force microscopy (AFM) indicates that the surface roughness of the silicate layers is low (rms = 2 to 3 nm), similar to that of bare glass slides. By tuning the experimental parameters such as HVLP gun pressure and layers deposited, different surface morphology could be obtained as revealed by fluorescence microscopy and SEM images. To demonstrate the utility of these ultrathin, fracture-free substrates, lipid bilayer membranes composed of phosphorylated derivatives of phosphoinositides (PIs) were deposited on the new substrates for biosensing applications. Fluorescence recovery after photobleaching (FRAP) data indicated that these lipid components in the membranes were highly mobile. Furthermore, interactions of PtdIns(4,5)P2 and PtdIns(4)P lipids with their respective binding proteins were detected with high sensitivity by using SPR spectroscopy. This method of glass deposition can be combined with already well-developed surface chemistry for a range of planar glass assay applications, and the process is amenable to automation for mass production of nanometer thick silicate chips in a highly reproducible manner for label-free measurements.

The current science of gastric banding: an overview of pressure–volume theory in band adjustments

Background Laparoscopic adjustable gastric banding (LAGB) is a safe and effective bariatric operation for the treatment of morbid obesity. Optimized long-term weight loss and reduced complications may be facilitated by development of a standardized, accurate, band-fill measurement methodology for use in postoperative LAGB adjustments. Methods A summary of the primary in vitro, theoretical, and in vivo studies of pressure–volume theory relative to gastric banding was undertaken. Results LAGBs range in mechanisms of action from low-pressure/high-volume to high-pressure/low-volume. Use of both basic and dynamic pressure data obtained experimentally and clinically with a low-pressure/high-volume (LP/HV) band as a research tool revealed that intra-band pressures remained very low even when the band balloon was filled to its maximum fill volume; in contrast, when a high-pressure/low-volume (HP/LV) band was filled, it exhibited a pressure curve markedly steeper and of greater amplitude than that of the LP/HV band. Theoretical calculations of the differences between the bands in terms of the pressures they exerted on a bolus of food passing through a stoma found that the pressure created by the HP/LV band against the gastric wall was >100% higher than that applied by the LP/HV band; these mathematical results were verified by using invasive manometry in 35 patients undergoing band adjustment. In clinical testing, basic band pressure, band volume, and dynamic pressure data (that demonstrated esophageal motility patterns at the stoma during bolus passage) were gathered and correlated. As identified by intra-band pressure readings, a zone of disruptive peristaltic activity that obstructed bolus passage through the stoma was observed; slightly beneath this zone, it was hypothesized that successful patient adjustments might be carried out. The manometrically delineated measure of mean band pressure sufficient to exert a significant yet not disruptive restriction (i.e., 20 mm Hg; mean volume of 5.4 mL) was tested in 25 patients in follow-up. No patient required readjustment due to obstruction. Intra-band pressure, as opposed to band–fill-volume measurement, per se, was shown to produce a more accurate measurement of actual band (stoma) restriction in individual patients, and to identify a pressure “green zone” for effective restriction at adjustments. Discussion Ongoing scientific studies are needed to refine pressure–volume theory by using laboratory, theoretical, and clinical manometry to establish a reliable pressure-based algorithm for gastric band adjustment. Such an algorithm may lead to more consistent weight loss, fewer complications, and more compliant patients.

Ventilator-associated pneumonia and new airway technologies

Current endotracheal and tracheostomy tubes have high volume low pressure cuffs. These cuffs are ineffective at preventing the ongoing pulmonary aspiration of oropharyngeal and gastric contents. This ubiquitous complication of intubation is the most important cause of ventilator-associated pneumonia (VAP), the commonest and most devastating nosocomial infection in the Intensive Care Unit (ICU). Current tracheal tubes are made of relatively fixed curved PVC, and this produces forces on the airway tissues which is associated with laryngeal and tracheal injury. There is a need for the development of tracheal tube technologies to prevent aspiration injury and the reduce airway injury associated with mechanical ventilation of the critically ill. Given the costs associated with VAP there is currently a massive mismatch in what we spend on prevention.

Tracheal wall pressures in the clinical setting: comparing Portex Soft Seal and Lotrach cuffs

The tracheal wall pressure (TWP) exerted by a tracheal tube cuff should normally be kept between 20 and 30 cmH2O. This protects against mucosal injury whilst allowing ventilation without an audible air leak [1]. The Portex Soft Seal high-volume low-pressure (HVLP) cuff has a working intracuff pressure of 30 cmH2O, providing a safe TWP of the same value because there is no tension in the cuff wall material. There are, however, folds within the cuff wall that allow passage of subglottic fluid to the tracheobronchial tree below, increasing the risk of ventilator-associated pneumonia [2]. The Lotrach endotracheal tube was designed to prevent this leakage at an equivalent TWP to that of correctly inflated HVLP cuffs [3]. Each Lotrach cuff is individually calibrated to transmit only 30 cmH2O to the tracheal wall, yet because of the lack of folds in the cuff wall it has been shown to prevent of aspiration of subglottic contents [4]. Although extensively tested in benchtop models and pig tracheas, we wished to demonstrate that the Lotrach cuff had an identical sealing pressure, and therefore TWP, as the HVLP cuff in normal clinical practice.