Normal Tidal Volume Research Articles

Performance Evaluation of Selected N95 Respirators and Surgical Masks When Challenged with Aerosolized Endospores and Inert Particles

The objective of this study was to assess how the relative efficiency of N95 respirators and surgical masks might vary with different challenge aerosols, utilizing a standardized manikin head form as a surrogate to human participation. A Collision nebulizer aerosolized B. anthracis Sterne strain endospores and polystyrene latex (PSL) particles to evaluate 11 models of N95 respirators and surgical masks. An automated breathing simulator, calibrated to normal tidal volume and active breathing rate, mimicked human respiration. A manikin head form with N95 respirators or surgical masks, and manikin head form without N95 respirators or surgical masks were placed in the bioaerosol chamber. An AGI-30 sampler filled with phosphate buffered water was fitted behind the mouth of each manikin head form to collect endospore bioaerosol samples. PSL aerosols concentrations were quantified by an ARTI Hand Held Particle Counter. Geometric Mean (GM) relative efficiency of N95 respirators and surgical masks challenged with endospore bioaerosol ranged from 34–65%. In PSL aerosol experiments, GM relative efficiency ranged from 35–64% for 1.3 μm particles. GM filtration efficiency of all N95 and surgical N95 respirators filter media evaluated was ≥99% when challenged with particles ≥0.1 μm. GM filtration efficiency of surgical mask filter media ranged from 70–83% with particles ≥0.1 μm and 74–92% with 1.3 μm PSL particles. Relative efficiencies of N95 respirators and surgical masks challenged with aerosolized B. anthracis endospores and PSL were similar. Relative efficiency was similar between N95 respirators and surgical masks on a manikin head form despite clear differences in filtration efficiency. This study further highlights the importance of face seal leakage in the respiratory protection provided by N95 respirators, and demonstrates it on a human surrogate.

How absolute EIT reflects the dependence of unilateral lung aeration on hyper-gravity and weightlessness?

We studied the influence of three gravity levels (0, 1 and 1.8 g) on unilateral lung aeration in a left lateral position by the application of absolute electrical impedance tomography. The electrical resistivity of the lung tissue was considered to be a meaningful indicator for lung aeration since changes in resistivity have already been validated in other studies to be proportional to changes in lung volume. Twenty-two healthy volunteers were studied during parabolic flights with three phases of different gravity, each lasting ∼20–22 s. Spontaneous breathing at normal tidal volume VT and at increased VT was performed. During transition to hyper-gravity mean expiratory resistivities (±SD in Ωm) increased at normal VT in the upper (right) lung from 7.6 ± 1.5 to 8.0 ± 1.7 and decreased from 5.8 ± 1.2 to 5.7 ± 1.2 in the lower (left) lung. Inspiratory resistivity values are 8.3 ± 1.6 to 8.8 ± 1.8 (right) and 6.3 ± 1.3 to 6.0 ± 1.3 (left). At increased VT, the changes in resistivities at end-expiration were 7.7 ± 1.5 to 8.0 ± 1.7 (right) and 5.8 ± 1.2 to 5.7 ± 1.2 (left). Corresponding end-inspiratory values are 9.9 ± 1.9 to 10.0 ± 2.0 (right) and 8.6 ± 2.1 to 7.9 ± 2.0 (left). During weightlessness, the distortion in the lungs disappeared and both lungs showed a nearly identical aeration, which was between the levels displayed at normal gravity. The small increase in resistivity for the upper lung during transition to hyper-gravity from 1 to 1.8 g at increased VT suggests that the degressive part of the pressure–volume curve has already been reached at end-inspiration. The results for a left lateral position are in agreement with West's lung model which has been introduced for cranio-caudal gravity dependence in the lungs.

Prone positioning use to hasten veno-venous ECMO weaning in ARDS

Dear Editor, A 41-year-old overweight (body mass index 35 kg/m) woman was admitted from home to the intensive care unit (ICU) for acute respiratory distress with fever. Her medical history mainly included a neurosarcoidosis treated with corticosteroids, methotrexate and six courses of cyclophosphamide. The computed tomography scan revealed a diffuse alveolar–interstitial syndrome without any mediastinal adenopathy. She received an initial antibiotherapy (cephalosporine, rovamycin) after an examination for infectious diseases. No infectious process or cause for an acute exacerbation of pulmonary sarcoidosis was found in the bronchoalveolar lavage fluid, and antibiotherapy was stopped after 5 days. There was no acute cardiac dysfunction on echocardiography. No diagnosis was made and her respiratory state worsened. She required, after 6 days of evolution, invasive mechanical ventilation to treat an acute respiratory distress syndrome (ARDS). After 3 days of lung protective ventilation [normal tidal volume (Vt) 5 ml/kg, respiratory rate (RR) 30/min, positive end expiratory pressure (PEEP) 12 cmH2O, plateau pressure (PP) 30 cmH2O, static compliance (SC) 20 ml/cmH2O) with neuromuscular blockade, she remained with a severe ARDS [partial pressure of oxygen in the blood (PaO2)/fraction of inspired oxygen (FiO2) 85 mmHg]. Two 24-h sessions of prone positioning failed to improve the PaO2/FiO2. No evolutive infectious process was found, and corticosteroids were maintained at 1 mg/kg/day to treat the ARDS inflammatory process. Her respiratory function worsened (Vt 5 ml/kg, RR 35/min, PEEP 10 cmH2O, PP 30 cmH2O, SC 20 ml/cmH2O) with refractory hypoxia on arterial gasometry [FiO2 100 %, pH 7.45; partial pressure oxygen (PO2) 75 mmHg; PCO2 40 mmHg; HCO3 -

Predicted end-tidal sevoflurane concentration for insertion of a Laryngeal Mask Supreme

The single-use Laryngeal Mask Airway (LMA) Supreme is a new supraglottic airway device. It has been reported to be reliable and easy-to-use in clinical practice; however, the anaesthetic techniques for its insertion are not standardised. The purpose of this study was to determine the ED50 of end-tidal sevoflurane concentration for successful LMA Supreme insertion without the use of neuromuscular blockade. A prospective observational study. A single tertiary care surgical centre. Thirty-one consecutive elective patients scheduled for minor elective surgery under general anaesthesia. Patients were preoxygenated with 100% oxygen and anaesthetised using normal tidal volume inhalation of sevoflurane. The target sevoflurane concentration was determined using a modified Dixon's 'up-and-down' method (starting at 2.5% with 0.5% as the step size). After the predetermined end-tidal concentration had been established and maintained for 10 min, LMA Supreme insertion was attempted. The main outcome measure was the patient's response to LMA Supreme insertion, classified as either 'movement' or 'no movement'. The mean of the concentrations of seven cross-overs from 'movement' to 'no movement' was used to estimate the ED50. The estimated sevoflurane concentration for successful LMA Supreme insertion in 50% of adults was 3.03 ± 0.75% (95% confidence interval 2.3 to 3.7%). The values of the ET50 and ET95 obtained by logistic regression were 2.83 and 5.30%, respectively. Sevoflurane alone can provide acceptable conditions for insertion of the LMA Supreme in adults, at an estimated minimum alveolar anaesthetic concentration of 3% with minimal adverse effects.

Early application of high frequency oscillatory ventilation in ‘H1N1 influenza’ related ARDS is associated with better outcome: a retrospective study

Dear Editor, High frequency oscillatory ventilation (HFOV) is an accepted therapy for refractory hypoxemia in acute respiratory distress syndrome (ARDS). There is a paucity of data for use of HFOV for 2009 H1N1 influenza ARDS and whether early application of HFOV decreases mortality in this subgroup of patients with severe ARDS. We performed a retrospective analysis of 19 patients who received HFOV as a rescue therapy for 2009 H1N1 influenza with severe ARDS to study the outcome predictors. Deenanath Mangeshkar Hospital ethics committee has approved use of HFOV as a rescue therapy in severe ARDS and consent was obtained from next of kin. Inclusion criteria were the presence of severe ARDS (PaO2/FiO2 100) due to H1N1 influenza virus infection, the application of a maximal support of conventional mechanical ventilation (PEEP equal or greater than 12 cm H2O), and the use of HFOV as a rescue therapy. Patients who received HFOV treatment for less than 24 h were excluded from the analysis. Out of the 19 patients studied, 10 survived (52 %). Patients were divided into survivors and non-survivors Demographic variables, baseline gas exchange and ventilation variables were comparable. Average age and APACHE II score were 30.21 ± 9.60 years 13.25 ± 1.90, respectively. Average tidal volume and plateau pressure on conventional ventilation prior to initiation of HFOV were 6.12 ± 1.26 ml/kg of predicted body weight and 27.21 ± 3.85 cm H2O, respectively. In the whole cohort there was a significant improvement in PaO2/FiO2 at 24 h, after initiation of HFOV (77.89 ± 32.50 vs. 121.78 ± 37.94, p = 0.005). Earlier application of HFOV was the only significant independent predictor of survival (p = 0.045) on multivariate logistic regression analysis. Survival odds ratio was 7.05 (95 % CI, 1.04–47.78) for every day of reduced conventional ventilation. Cox regression analysis of survival rates adjusted for APACHE II score, oxygenation index and time from symptom onset to hospital contact indicated a decrease in survival with increasing duration of conventional ventilation (Fig. 1, Table 1). Our findings are in general agreement with the literature on ARDS in adults. Terragni et al. [1] has shown that even with a lung protective strategy, ventilator induced lung injury is possible. Matthias David et al., had suggested that, an increased conventional ventilation period of more then 3 days prior to HFOV was associated with higher mortality [2]. A recent meta-analysis had reaffirmed this suggestion [3]. However, Casper Bollen et al, [4] had suggested that prolonged conventional ventilation prior to HFOV is not associated with higher mortality. Patients in this case series, randomized to the HFOV group had received conventional ventilation at higher tidal volumes (9.30 ± 2.20 ml/kg of predicted body weight), prior to initiation of HFOV. Limiting the duration of volume controlled ventilation before HFOV may confer a benefit by pre-empting ventilator induced lung injury in these patients. A limitation of our case series is a small sample size. However, it may provide useful insight into management of severe ARDS related to

Techniques of preoxygenation in patients with ineffective face mask seal

Background:Ineffective face mask seal is the most common cause for suboptimal pre-oxygenation. Room air entrainment can be more with vital capacity (VC) breaths when the mask is not a tight fit.Aims:This study was designed to compare 5 min tidal volume (TV) breathing and eight VC breaths in patients with ineffective face mask seal.Methods:Twenty eight ASA I adults with ineffective face mask seal were randomized to breathe 100% oxygen at normal TV for 5 min (Group TV) and eight VC breaths (Group VC) in a cross over manner through circle system at 10 L/min. End tidal oxygen concentration (EtO2) and arterial blood gas analysis was performed to evaluate oxygenation with each technique.Statistical and Analysis:Data were analysed using SPSS statistical software, version 16. Friedman's two-way analysis of variance by ranks was used for non-parametric data.Results:Significant increase in EtO2 (median 90) and PaO2 (228.85) was seen in group TV when compared to group VC (EtO2 median 85, PaO2 147.65), P<0.05. Mean total ventilation volume in 1 min in group VC was 9.4±3.3 L/min and more than fresh gas flow (10 L/min) in seven patients. In group TV, the fresh gas flow (50 L/5 min) was sufficient at normal TV (mean total ventilation in 5 min 36.7±6.3 L/min).Conclusions:TV breathing for 5 min provides better pre-oxygenation in patients with ineffective mask seal with fresh gas flow of 10 L/min delivered through a circle system.

Abstract 19585: Tidal Volume and Minute Ventilation Measurement at High, Low, and Erratic Respiratory Rates by a Non-Invasive Respiratory Monitoring System

Introduction: Changes in minute ventilation (MV) &amp; tidal volume (TV) signal the beginning of respiratory compromise which often precedes cardiopulmonary arrest. Currently, respiratory monitoring in non-intubated patients lacks objective &amp; quantitative methodology for determining the adequacy of ventilation. A non-invasive, Respiratory Volume Measurement (RVM) system has been developed to measure MV, TV and respiratory rate (RR) continuously. Previous work has demonstrated clinically acceptable accuracy and precision of RVM monitoring across normal respiratory patterns and rates. Hypothesis: RVM monitoring accurately yields tidal volume &amp; minute ventilation across abnormal breathing rates, and erratic patterns. Methods: We studied 51 adult subjects (93 visits, 2252 tests) at low (4 - 6 bpm), normal (8 - 20 bpm), and high (30 - 40 bpm) respiratory rates and during erratic breathing. TV, RR and MV were measured simultaneously with an impedance-based RVM system (ExSpiron, Respiratory Motion, Inc., Waltham, MA) and a dry rolling seal spirometer (Morgan Scientific Inc., Haverhill, MA). Advanced data processing algorithms displayed a real time respiratory curve and calculated RVM measurements. Results: Throughout the range of 4 bpm to 40 bpm and during erratic breathing, RVM measurements are highly-correlated with spirometer measurements, with an average MV and TV correlation coefficient of 0.96, 95% CI 0.93 to 0.99 (Fig 1). Across all subjects, median correlation coefficients ranged from 0.91 to 0.99. Conclusions: High correlation (r = 0.96) between spirometric measurements and RVM signals concludes that the RVM system is capable of monitoring respiratory status during normal and erratic breathing, and at high and low breathing rates. As a passive, continuous, non-invasive system, RVM monitoring of non-intubated patients could provide earlier indications of respiratory decline potentially permitting interventions to prevent cardiopulmonary arrest.

Preliminary study of the internal margin of the gross tumor volume in thoracic esophageal cancer

PurposeTo measure the displacement of the tumor of the gross tumor volume (GTV) of thoracic esophageal cancer in the calm states of end-inspiration and end-expiration for determining the internal margin of the GTV (IGTV). MethodsTwenty-two patients with thoracic esophageal cancer who were unable to undergo surgery were identified in our hospital. The patients received radiotherapy. By using 16-slice spiral computed tomography (CT), we acquired the calm states of end-inspiration and end-expiration. The displacement and volume changes in tumor target volume were measured, and the changes were analyzed to determine if these were associated with the tidal volume and the location and length of the target volume V. In the end, we analyzed the displacement of tumor target volume and calculated the internal margin of the GTV by empirical formula. ResultsThe average tidal volume was 463.6ml. The average GTV at end-inspiration was 33.3ml and at end-expiration was 33.35ml. Three was not any significant between two groups (T=−0.034, P>0.05). The IGTV (X-axis direction) was 3.09mm for the right sector and 4.08mm for the left border; the IGTV (Z-axis direction) was 3.96mm for the anterior border and 2.83mm for the posterior border; and the IGTV (Y-axis direction) was 7.31mm for the upper boundary (head direction) and 10.16mm for the lower boundary (feet direction). The motion of the GTV showed no significant correlation with the tidal volume of patients and the length of the tumor, but in relation to the tumor location, the displacement of the lower thoracic and the middle thoracic target volumes occurred in the direction of the anterior and right, which were not significantly different (T=0.859, 0.229, P>0.05) The significant differences were observed for the other directions (P<0.05). ConclusionsBecause of respiratory and organ movements, the displacement of the tumor target volume was different in all directions. Therefore, we recommend that expansion of the planning target volume during clinical radiation treatment needs to include the displacement of the tumor target volume caused by respiratory and organ movements during each radiotherapy session.

Influence of end-expiratory level and tidal volume on gravitational ventilation distribution during tidal breathing in healthy adults

Our understanding of regional filling of the lung and regional ventilation distribution is based on studies using stepwise inhalation of radiolabelled tracer gases, magnetic resonance imaging and positron emission tomography. We aimed to investigate whether these differences in ventilation distribution at different end-expiratory levels (EELs) and tidal volumes (V (T)s) held also true during tidal breathing. Electrical impedance tomography (EIT) measurements were performed in ten healthy adults in the right lateral position. Five different EELs with four different V (T)s at each EEL were tested in random order, resulting in 19 combinations. There were no measurements for the combination of the highest EEL/highest V (T). EEL and V (T) were controlled by visual feedback based on airflow. The fraction of ventilation directed to different slices of the lung (VENT(RL1)-VENT(RL8)) and the rate of the regional filling of each slice versus the total lung were analysed. With increasing EEL but normal tidal volume, ventilation was preferentially distributed to the dependent lung and the filling of the right and left lung was more homogeneous. With increasing V (T) and maintained normal EEL (FRC), ventilation was preferentially distributed to the dependent lung and regional filling became more inhomogeneous (p<0.05). We could demonstrate that regional and temporal ventilation distribution during tidal breathing was highly influenced by EEL and V (T).

Why the Gray Zone May Shift within the Fog

To the Editor: We read the article by Cannesson1et al. and the accompanying editorial2with great interest, and praise the effort to better define the clinical utility and applicability of pulse pressure variation (PPV), not only as a tool to predict volume responsiveness but also to move away from a single-threshold value for conducting intraoperative volume optimization and perioperative goal-directed fluid therapy. We would like to make three points.First, the most commonly used index to assess volume responsiveness, by far in the United States, appears to be stroke volume variation (SVV). Although the area under the receiver-operating curve, in systematic reviews,3shows that both PPV and SVV have excellent sensitivity and specificity in patients who are mechanically ventilated with normal tidal volumes and in a regular sinus rhythm, the threshold values discriminating between fluid responders and nonresponders are not the same for these two parameters.3,4Thus, although strategies using the “gray zone approach” applied to PPV identify a range of values where volume responsiveness cannot reliably be predicted, this range may not be applicable when SVV is used for determining volume responsiveness. Although it is clear from the work of Joseph Erlanger, the father of the pulse pressure concept,5that pulse pressure in man is proportional to left ventricular stroke volume (depending both on arterial tone and cardiac contractility) it is plausible that variations in pulse pressure may also be proportional to variations in stroke volume. To the extent that PPV and SVV are affected differently by changes in arterial tone, given the same degree of volume responsiveness,4these values may lose their direct proportionality as vascular tone changes. Pinsky described the potential utility of a SVV-to-PPV ratio to reflect ventricular-arterial coupling that might be helpful when extrapolating PPV threshold data to SVV.6Overall, applying PPV's “gray zone” to SVV seems clinically appealing but may be misleading. The “gray zone” defined for PPV should not simply be applied to patients who are being optimized using stroke volume variation. The “gray zone” for SVV requires its own definition.Second, the paper does not address the issue of volume responsiveness versus needing to give volume or using a dynamic index to actively restrict fluids or to administer diuretics to patients under certain clinical circumstances. That is, not all patients who are volume responsive require volume therapy. Conversely, there may be untapped utility for SVV- and/or PPV-guided fluid restriction and diuretic use (consider patients with acute lung injury or acute respiratory distress syndrome).7The goal would be to identify patients with a PPV that is “too low” who, consequently, should receive restrictive fluid therapy or diuretics.Third, what is, perhaps, not considered by the author2is the fact that PPV goals may vary within individual patients across changing clinical settings in relatively short intervals of time, such as during single lung ventilation for thoracic surgery, laparoscopic pneumoperitoneum, and conditions of pathologic intraabdominal hypertension. For example, the goals for intraoperative PPV during esophagectomy vary during the case, such that the goal during the abdominal part of the procedure is fluid liberal and during the thoracic part of the procedure is fluid restrictive.8In summary, we praise Cannesson et al. 1for their work and we agree that there is a “gray zone” well represented by the picture in the editorial2(i.e. , the Golden Gate Bridge with fog going across the middle represents “a static view of dynamic indices”). We contend that PPV and SVV “gray zones” are probably better described as the view one gets of the Golden Gate Bridge, with fog going across the middle as one is driving along winding hilly roads. This is a “dynamic view of dynamic indices,” such that the gray zone changes at different times depending on one's changing vantage point, an analogy closer to clinical reality.

Alveolar Overdistension as a Cause of Lung Injury: Differences among Three Animal Species

This study analyses characteristics of lung injuries produced by alveolar overdistension in three animal species. Mechanical ventilation at normal tidal volume (10 mL/Kg) and high tidal volume (50 mL/Kg) was applied for 30 min in each species. Data were gathered on wet/dry weight ratio, histological score, and area of alveolar collapse. Five out of six rabbits with high tidal volume developed tension pneumothorax, and the rabbit results were therefore not included in the histological analysis. Lungs from the pigs and rats showed minimal histological lesions. Pigs ventilated with high tidal volume had significantly greater oedema, higher neutrophil infiltration, and higher percentage area of alveolar collapse than rats ventilated with high tidal volume. We conclude that rabbits are not an appropriate species for in vivo studies of alveolar overdistension due to their fragility. Although some histological lesions are observed in pigs and rats, the lesions do not appear to be relevant.

Influence of tidal volume on pulmonary gas exchange during general anaesthesia

Background and objective: General anaesthesia impairs respiratory function. The present studies were performed to compare arterial concentration of sevoflurane, oxygen and carbon dioxide in normal and overweight patients ventilated with increased tidal volume (VT), or normal tidal volume with and without PEEP. Methods: Prospective, randomised, clinical studies. ASA І and II abdominal surgery patients were randomly assigned to be ventilated with normal VT (NVT) with and without PEEP to 10 cmH2O or with increased VT (IVT) achieved by increasing inspired plateau pressure 0.04 cm H2O kg-1. Extra apparatus dead space was added to maintain PETCO2 at 4.5 kPa. Arterial oxygenation, sevoflurane tension (Pasevo, Fisevo, PETsevo), PaCO2, PETCO2, stroke volume, cardiac output, VT and airway pressure were measured. Results: The groups of patients compared were similar regarding gender, age, and BMI. Arterial oxygen and sevoflurane tension was generally higher in the IVT group (P < 0.05) whereas mean FiO2 and PETsevo did not differ between the groups. Arterial carbon dioxide was significantly lower with IVT than NVT ventilated without PEEP but in the presence of PEEP in the NVT group, the groups were similar. Cardiac output decreased significantly less in the IVT group compared to the NVT group with PEEP (5 and 33 % respectively). Conclusion: Isocapnic ventilation with larger tidal volumes maintained with added apparatus dead-space increases the arterial oxygen and sevoflurane tension as well as carbon dioxide elimination in normal and overweight patients, and in overweight patient also preserves cardiac output better than in the presence of PEEP. (Less)

Lumican Expression in Diaphragm Induced by Mechanical Ventilation

BackgroundDiaphragmatic dysfunction found in the patients with acute lung injury required prolonged mechanical ventilation. Mechanical ventilation can induce production of inflammatory cytokines and excess deposition of extracellular matrix proteins via up-regulation of transforming growth factor (TGF)-β1. Lumican is known to participate in TGF-β1 signaling during wound healing. The mechanisms regulating interactions between mechanical ventilation and diaphragmatic injury are unclear. We hypothesized that diaphragmatic damage by short duration of mechanical stretch caused up-regulation of lumican that modulated TGF-β1 signaling.MethodsMale C57BL/6 mice, either wild-type or lumican-null, aged 3 months, weighing between 25 and 30 g, were exposed to normal tidal volume (10 ml/kg) or high tidal volume (30 ml/kg) mechanical ventilation with room air for 2 to 8 hours. Nonventilated mice served as control groups.ResultsHigh tidal volume mechanical ventilation induced interfibrillar disassembly of diaphragmatic collagen fiber, lumican activation, type I and III procollagen, fibronectin, and α-smooth muscle actin (α-SMA) mRNA, production of free radical and TGF-β1 protein, and positive staining of lumican in diaphragmatic fiber. Mechanical ventilation of lumican deficient mice attenuated diaphragmatic injury, type I and III procollagen, fibronectin, and α-SMA mRNA, and production of free radical and TGF-β1 protein. No significant diaphragmatic injury was found in mice subjected to normal tidal volume mechanical ventilation.ConclusionOur data showed that high tidal volume mechanical ventilation induced TGF-β1 production, TGF-β1-inducible genes, e.g., collagen, and diaphragmatic dysfunction through activation of the lumican.

Risk factors for underuse of lung-protective ventilation in acute lung injury

PurposeWe assessed factors associated with underuse of lung-protective ventilation (LPV) in patients with acute lung injury (ALI). MethodsA secondary analysis of Acute Respiratory Distress Syndrome Clinical Trials Network trial data, 1999 to 2005, was conducted. Tidal volumes recorded before trial randomization were analyzed to determine receipt of LPV (tidal volume ≤6.5 mL/kg of predicted body weight [PBW]). ResultsOf 1385 participants, 430 (31.2%) received LPV. Average tidal volume was 7.65 ± 1.82 mL/kg PBW; measured tidal volumes were greater than “lung-protective” tidal volumes predicted by 6.5 mL/kg PBW (mean difference, 67 ± 108 mL; P < .0001). Multivariate predictors of LPV underuse were older age (odds ratio [OR] per SD year, 1.18; 95% confidence interval [CI], 1.02-1.38), white race (OR, 1.40; 95% CI, 1.05-1.88), shorter stature (OR per SD centimeter, 0.55; 95% CI, 0.48-0.63), lower Simplified Acute Physiology II Score (OR per SD, 0.78; 95% CI, 0.67-0.92), lower lung injury score (OR per SD, 0.83; 95% CI, 0.70-0.95), decreased serum bicarbonate (OR per SD mmol/L, 0.83; 95% CI, 0.71-0.97), shorter preenrollment intensive care unit stay (OR per SD day, 0.84; 95% CI, 0.73-0.98), and use of non–volume-controlled ventilation (OR, 3.07; 95% CI, 1.78-5.27). Setting tidal volumes to 450 mL (men) or 350 mL (women) would provide LPV to 80% of patients with ALI. ConclusionsSimple interventions could substantially improve adherence with LPV among patients with ALI and warrant prospective study.

Quantitative computed tomography in porcine lung injury with variable versus conventional ventilation: Recruitment and surfactant replacement*

Biologically variable ventilation improves lung function in acute respiratory distress models. If enhanced recruitment is responsible for these results, then biologically variable ventilation might promote distribution of exogenous surfactant to nonaerated areas. Our objectives were to confirm model predictions of enhanced recruitment with biologically variable ventilation using computed tomography and to determine whether surfactant replacement with biologically variable ventilation provides additional benefit in a porcine oleic acid injury model. Prospective, randomized, controlled experimental animal investigation. University research laboratory. Domestic pigs. Standardized oleic acid lung injury in pigs randomized to conventional mechanical ventilation or biologically variable ventilation with or without green dye labeled surfactant replacement. Computed tomography-derived total and regional masses and volumes were determined at injury and after 4 hrs of ventilation at the same average low tidal volume and minute ventilation. Hemodynamics, gas exchange, and lung mechanics were determined hourly. Surfactant distribution was determined in postmortem cut lung sections. Biologically variable ventilation alone resulted in 7% recruitment of nonaerated regions (p < .03) and 15% recruitment of nonaerated and poorly aerated regions combined (p < .04). Total and normally aerated regional volumes increased significantly with biologically variable ventilation, biologically variable ventilation with surfactant replacement, and conventional mechanical ventilation with surfactant replacement, while poorly and nonaerated regions decreased after 4 hrs of ventilation with biologically variable ventilation alone (p < .01). Biologically variable ventilation showed the greatest improvement (p < .003, biologically variable ventilation vs. all other groups). Hyperaerated regional gas volume increased significantly with biologically variable ventilation, biologically variable ventilation with surfactant replacement, and conventional mechanical ventilation with surfactant replacement. Biologically variable ventilation was associated with restoration of respiratory compliance to preinjury levels and significantly greater improvements in gas exchange at lower peak airway pressures compared to all other groups. Paradoxically, gas exchange and lung mechanics were impaired to a greater extent initially with biologically variable ventilation with surfactant replacement. Peak airway pressure was greater in surfactant-treated animals with either ventilation mode. Surfactant was distributed to the more caudal/injured lung sections with biologically variable ventilation. Quantitative computed tomography analysis confirms lung recruitment with biologically variable ventilation in a porcine oleic acid injury model. Surfactant replacement with biologically variable ventilation provided no additional recruitment benefit and may in fact be harmful.

Variable ventilation improves ventilation and lung compliance in preterm lambs

In adult animals, ventilation with variable tidal volume and rate improves lung mechanics, arterial oxygenation and ventilation compared to a monotonously controlled ventilation pattern. We assessed the physiological consequences of variable ventilation in the immature lung. Lambs delivered at 129 days (term = 150 days) were euthanised (n = 9) or anaesthetised, tracheostomised and suctioned prior to prophylactic intra-tracheal surfactant instillation (Curosurf(®), 100 mg/kg) and commencement of controlled ventilation (50 breaths/min, tidal volume 7.7 ± 0.8 mL/kg). Volume history was standardised at 20 min with two sustained (3 s) inflations to 30 cmH(2)O followed immediately by measurement of baseline dynamic lung mechanics (FlexiVent, Scireq, Canada). Ventilation was continued according to prior randomisation (variable or conventional ventilation). For variable ventilation (n = 9), breath-to-breath tidal volume and respiratory rate varied but intra-breath minute volume (MV) and average tidal volume were equivalent to the conventional ventilation group with fixed tidal volume and rate (n = 7). Lung mechanics and gas exchange were measured at intervals. Lambs were euthanised at 2 h. Inflammatory cell counts and protein from bronchoalveolar lavage fluid and lung tissue cytokine mRNA were quantified. At study completion, PaCO(2) (p = 0.026) and mean airway pressure (p = 0.002) were lower and pH (p = 0.047), ventilation efficiency index (p = 0.021) and dynamic compliance were higher (p = 0.003) in lambs on variable rather than conventional ventilation. However, oxygenation indices and post-mortem static compliances were not different between groups. Variable ventilation improves ventilation efficiency and in vivo lung compliance in the preterm lung, but unlike adult models, had no effect on arterial oxygenation.

Comparison of two mask holding techniques for two person bag-valve-mask ventilation: A cross-over simulation study

Purpose: Two-person bag-valve-mask (BVM) ventilation can provide a better seal and more effective ventilation. It is known that a mask holding technique using thenar eminence of both hands (Thenar technique) could results in less fatigue and be more comfortable than two-hand E-C technique for prolonged ventilation. However, evidence to support this hypothesis is limited. This study compared the fatigue of hands and ventilation parameters in two person BVM ventilation using two mask holding techniques. Materials and methods: The hospital providers who do not frequently use BVM in their practice were enrolled in the study. They all performed BVM holding on RespiTrainer™ for 5 min using both techniques 1 week apart after being randomized. An anesthesia ventilator substituted for bagging to unify the delivered volume. The pinch and grip power of both hands before and after the holding using each technique, average tidal volume (TV) and peak airway pressure (PAP) for 5 min were compared between groups using ANCOVA. Results: Twenty-one doctors and seven nurses participated in the study. The pinch power of both hands in E-C technique was significantly decreased after 5 min compared to Thenar technique (7.65 ± 1.83 kg vs. 8.37 ± 1.99 kg in left; 8.07 ± 2.00 kg vs. 8.56 ± 2.15 kg in right; p < 0.05, respectively). There were no differences in the grip powers of both hands between E-C and Thenar techniques (32.55 ± 9.65 kg vs. 31.96 ± 9.56 kg in left, 34.21 ± 10.35 kg vs. 33.32 ± 9.65 kg in right). The TV (E-C 554.1 ± 6.56 ml vs. Thenar 554.1 ± 6.26 ml) and PAP (E-C 12.93 ± 0.23 cmH2O vs. Thenar 12.98 ± 0.19 cmH2O) were not different. Conclusion: The E-C technique may induce more fatigue in the intrinsic muscles of the first web space of hands compared to the Thenar technique during 5 minutes of two person BVM ventilation. However, there was no significant difference in grip power loss and ventilation quantity between the two techniques.

Method for Evaluating the Relative Efficiency of Selected N95 Respirators and Surgical Masks to Prevent the Inhalation of Airborne Vegetative Cells by Healthcare Personnel

Aerosol droplet- and airborne-transmitted diseases are an important healthcare concern. The anthrax attacks of 2001, severe acute respiratory syndrome outbreaks in 2003 which resulted in transmission to numerous healthcare personnel (HCP) and concerns about smallpox as a bioterrorist agent have contributed to heightened concern about airborne infectious agents. Respirators and surgical masks can provide respiratory protection against such airborne diseases but their efficacy needs to be assessed. This study describes a method for quantitatively assessing the relative efficiency of respiratory protective equipment (RPE) when challenged with a bioaerosol. Five surgical masks, three N95 respirators and three surgical N95 respirators were evaluated. All are commercially available and used in US healthcare settings. Bacterial aerosols of vegetative Bacillus anthracis strain Sterne 34F2 (a surrogate for pathogenic B. anthracis) were generated with a six-jet Collison nebuliser. To mimic human respiratory breathing, an automated breathing simulator (ABS) calibrated to normal tidal volume and active breathing rate (500 mL/breath and 20 breath/min, respectively) was used. Respirators were placed on manikin head-forms designed for use in cardiopulmonary resuscitation training and used in our investigation as surrogates for HCP. The method showed that a Collison nebuliser could generate monodisperse bacterial aerosol to effectively test RPE total inward leakage. Also, the AGI-30 air samplers, combined with the ABS, provided an accurate method of quantifying RPE relative efficiency. For the 11 RPE this ranged from 34% to 69% with statistically significant differences between several RPE models. We conclude that neither RPE type nor brand name was an indicator of RPE relative efficiency.

A Two-handed Jaw-thrust Technique Is Superior to the One-handed “EC-clamp” Technique for Mask Ventilation in the Apneic Unconscious Person

Mask ventilation is considered a "basic" skill for airway management. A one-handed "EC-clamp" technique is most often used after induction of anesthesia with a two-handed jaw-thrust technique reserved for difficult cases. Our aim was to directly compare both techniques with the primary outcome of air exchange in the lungs. Forty-two elective surgical patients were mask-ventilated after induction of anesthesia by using a one-handed "EC-clamp" technique and a two-handed jaw-thrust technique during pressure-control ventilation in randomized, crossover fashion. When unresponsive to a jaw thrust, expired tidal volumes were recorded from the expiratory limb of the anesthesia machine each for five consecutive breaths. Inadequate mask ventilation and dead-space ventilation were defined as an average tidal volume less than 4 ml/kg predicted body weight or less than 150 ml/breath, respectively. Differences in minute ventilation and tidal volume between techniques were assessed with the use of a mixed-effects model. Patients were (mean ± SD) 56 ± 18 yr old with a body mass index of 30 ± 7.1 kg/m. Minute ventilation was 6.32 ± 3.24 l/min with one hand and 7.95 ± 2.70 l/min with two hands. The tidal volume was 6.80 ± 3.10 ml/kg predicted body weight with one hand and 8.60 ± 2.31 ml/kg predicted body weight with two hands. Improvement with two hands was independent of the order used. Inadequate or dead-space ventilation occurred more frequently during use of the one-handed compared with the two-handed technique (14 vs. 5%; P = 0.013). A two-handed jaw-thrust mask technique improves upper airway patency as measured by greater tidal volumes during pressure-controlled ventilation than a one-handed "EC-clamp" technique in the unconscious apneic person.

Targeting Aerosolized Drugs to the Conducting Airways Using Very Large Particles and Extremely Slow Inhalations

The site of deposition in the respiratory tract for aerosolized, inhaled therapeutic drugs depends on both the particles' aerodynamic size and the patient's breathing pattern. In 21 healthy subjects with normal lung function, we evaluated an extremely slow inhalation of a large 9.5-μm MMAD particle aerosol (ESI-9) for its ability to enhance the delivery of radiolabeled particles ((99m)Tc-labeled sulfur colloid) to the conducting airways. The regional deposition of the large particles (modified Pari-Boy jet nebulizer), inhaled at the extremely low rate of 0.080 Lps for 10 sec, was compared to the deposition of 5-μm MMAD particles inhaled during cyclic resting tidal breathing (TVB-5-) (mean 0.44 L and 0.46 Lps). Gamma scintigraphy gave an estimate of conducting airway deposition (% CAD) as a fraction of all deposited particles by multiplying the percent of activity in both lungs immediately postdeposition relative to the total deposition (i.e., lungs + mouth + esophagus + stomach) times the percent of activity cleared from the lungs over 24 h. % CAD for healthy subjects for the ESI-9 and TVB-5 maneuvers was 35% (±8%) and 27% (±11%), respectively, p = 0.004). The amount deposited within the oropharynx was 26% (±7%) and 37% (±11%), respectively, p < 0.001. Higher therapeutic value of a medication delivered to the conducting airways where the primary defect is associated with many diseases, and with fewer losses to the extrathoracic surfaces, may be obtained by using an "extremely slow inhalation and large particle" routine when compared to a normal tidal volume breathing associated with typical nebulizers.