Bench Assessment of Expiratory Valve Resistance of Current ICU Ventilators in Dynamic Conditions.

BACKGROUND: We hypothesized that the lack of benefit of setting a low versus a high PEEP in patients with ARDS may be due in part to differences in the dynamic behavior of the expiratory valve in ventilators. We tested this hypothesis by conducting a bench comparison of the dynamic behavior of expiratory valves on ICU ventilators currently in use. METHODS: We attached 7 ICU ventilators (C5, C6, Carescape, PB980, ServoU, V500, and V680) to the ASL 5000 lung model (passive condition with compliance 20 mL/cm H2O and resistance 5 cm H2O/L/s) and set in volume controlled mode (tidal volume 0.8 L, breathing frequency 10 breaths/min). Flow and pressure were measured just before the exhalation valve. At PEEP of 5, 10, and 15 cm H2O, the median instantaneous expiratory resistance, the time to valve opening, and the pressure time products above or below the values of PEEP (expressed in cm H2O × s) were determined. RESULTS: Median instantaneous expiratory resistance values differed between the ventilators and PEEP settings with a significant interaction: at PEEP 5 cm H2O, the median (interquartile range) expiratory resistance values were 3.9 (3.5-4.7), 3.0 (3.0-3.1), 20.9 (15.8-24.9), 27.4 (26.5-43.2), 13.8 (13.6-13.9), 4.4 (4.0-4.6), and 34.3 (33.7-33.8) cm H2O/L/s, for the C5, C6, Carescape, PB980, ServoU, V500, and V680, respectively. For all the PEEP settings, the corresponding times to valve opening were 0.080 (0.077-0.082), 0.082 (0.080-0.085), 0.110 (0.105-0.110), 0.100 (0.085-1.05), 0.072 (0.062-0.072), 0.145 (0.115-0.150), and 0.075 (0.070-0.080) s, respectively, and pressure-time products were 2.8 (2.1-7.4), 6.8 (6.7-7.3), 2.4 (2.1-2.4), 3.5 (2.7-3.6), 1.8 (1.8-2.1), 2.8 (2.7-2.9), and 5.7 (5.4-5.9) cm H2O × s, respectively. CONCLUSIONS: The resistance of active expiratory valves differed significantly between the 7 ICU ventilators tested.

A Comprehensive Bench Assessment of Automatic Tube Compensation in ICU Ventilators for Better Clinical Management.

BACKGROUND: Automatic tube compensation (ATC) unloads endotracheal tube (ETT) resistance. We conducted a bench assessment of ATC functionality in ICU ventilators to improve clinical management. METHODS: This study had 2 phases. First, we performed an international survey on the use of ATC in clinical practice, hypothesizing a rate of ATC use of 25%. Second, we tested 7 modern ICU ventilators in a lung model mimicking a normal subject (Normal), a subject with ARDS, and a subject with COPD. Inspiratory effort consisted of esophageal pressure over 30 consecutive breaths obtained in a real patient under weaning. A brand new 8-mm inner diameter ETT was attached to the lung model, and ATC was set at 100% compensation for the ETT. The 30 breaths were first run with ATC off and no ETT (ie, reference period), and then with ATC on and ETT (ie, active period). The primary end point was the difference in tidal volume (VT) between reference and active periods. We hypothesized that the VT difference should be equal to 0 in an ideally functioning ATC. VT difference was compared across ventilators and respiratory mechanics conditions using a linear mixed-effects model. RESULTS: The clinical use of ATC was 64% according to 644 individuals who responded to the international survey. The VT difference varied significantly across ventilators in all respiratory mechanics configurations. The divergence between VT difference and 0 was small but significant: the extreme median (interquartile range) values were -0.013 L (-0.019 to -0.002) in the COPD model and 0.056 L (0.051-0.06) in the Normal model. VT difference for all ventilators was 0.015 L (95% CI 0.013-0.018) in the ARDS model, which was significantly different from 0.021 L (95% CI 0.018-0.024) in the Normal model (P < .001) and 0.010 L (0.007-0.012) in the COPD model (P = .003). CONCLUSIONS: ATC is used more frequently in clinical practice than expected. In addition, VT delivery by ATC differed slightly though significantly between ventilators.

Voxel-wise assessment of lung aeration changes on CT images using image registration: application to acute respiratory distress syndrome (ARDS).

PURPOSE: (1) To improve the accuracy of global and regional alveolar-recruitment quantification in CT scan pairs by accounting for lung-tissue displacements and deformation, (2) To propose a method for local-recruitment calculation. METHODS: Recruitment was calculated by subtracting the quantity of non-aerated lung tissues between expiration and inspiration. To assess global recruitment, lung boundaries were first interactively delineated at inspiration, and then they were warped based on automatic image registration to define the boundaries at expiration. To calculate regional recruitment, the lung mask defined at inspiration was cut into pieces, and these were also warped to encompass the same tissues at expiration. Local-recruitment map was calculated as follows: For each voxel at expiration, the matching location at inspiration was determined by image registration, non-aerated voxels were counted in the neighborhood of the respective locations, and the voxel count difference was normalized by the neighborhood size. The methods were evaluated on 120 image pairs of 12 pigs with experimental acute respiratory distress syndrome. RESULTS: The dispersion of global- and regional-recruitment values decreased when using image registration, compared to the conventional approach neglecting tissue motion. Local-recruitment maps overlaid onto the original images were visually consistent, and the sum of these values over the whole lungs was very close to the global-recruitment estimate, except four outliers. CONCLUSIONS: Image registration can compensate lung-tissue displacements and deformation, thus improving the quantification of alveolar recruitment. Local-recruitment calculation can also benefit from image registration, and its values can be overlaid onto the original image to display a local-recruitment map. They also can be integrated over arbitrarily shaped regions to assess regional or global recruitment.

Bench Assessment of the Effect of a Collapsible Tube on the Efficiency of a Mechanical Insufflation-Exsufflation Device.

BACKGROUND: Collapsibility of upper airways may impair the efficacy of mechanical insufflation-exsufflation (MI-E) devices. The aim of this study was to determine the effect of a collapsible tube on peak expiratory flow (PEF) when using an MI-E device. METHODS: An MI-E device was attached to a lung simulator. Resistance was set at 5 and 20 cm H2O/L/s (R5, R20) for compliance settings of 20, 40, and 60 mL/cm H2O (C20, C40, C60). A series of 5 cycles were delivered at 3 pressures in the following order: +30/-30, +40/-40, and +50/-50 cm H2O for each compliance/resistance combination with and without the collapsible tube. Each respiratory mechanics profile was tested in random order. Pressure and flow were measured upstream of the MI-E device, and the primary outcome measure was PEF. The relationships of PEF to maximum expiratory pressure were compared with and without the collapsible tube using a linear regression model. RESULTS: For the C20-R5 condition, the effect of the collapsible tube on the intercept (-0.35 cm H2O) was not significant, but this was offset by a significant (and the largest) increase in slope (+0.12 L/s/cm H2O). For the C60-R20 condition, the effect of the collapsible tube on the slope (-0.003 L/s/cm H2O) was not significant, but this was offset by a significant (and the largest) increase of the intercept (+3.16 cm H2O) at 30 cm H2O expiratory pressure. For the other conditions, the collapsible tube significantly increased PEF at 30 cm H2O expiratory pressure, and the gap further increased above this pressure as the slope increased with the collapsible tube. CONCLUSIONS: The collapsible tube resulted in a higher PEF for all respiratory mechanics profiles tested.

The Cost-Effectiveness of Interventions to Increase Utilization of Prone Positioning for Severe Acute Respiratory Distress Syndrome.

OBJECTIVES: Despite strong evidence supporting proning in acute respiratory distress syndrome, few eligible patients receive it. This study determines the cost-effectiveness of interventions to increase utilization of proning for severe acute respiratory distress syndrome. DESIGN: We created decision trees to model severe acute respiratory distress syndrome from ICU admission through death (societal perspective) and hospital discharge (hospital perspective). We assumed patients received low tidal volume ventilation. We used short-term outcome estimates from the PROSEVA trial and longitudinal cost and benefit data from cohort studies. In probabilistic sensitivity analyses, we used distributions for each input that included the fifth to 95th percentile of its CI. SETTING: ICUs that care for patients with acute respiratory distress syndrome. SUBJECTS: Patients with moderate to severe acute respiratory distress syndrome. INTERVENTIONS: The implementation of a hypothetical intervention to increase the appropriate utilization of prone positioning. MEASUREMENTS AND MAIN RESULTS: In the societal perspective model, an intervention that increased proning utilization from 16% to 65% yielded an additional 0.779 (95% CI, 0.088-1.714) quality-adjusted life years at an additional long-term cost of $31,156 (95% CI, -$158 to $92,179) (incremental cost-effectiveness ratio = $38,648 per quality-adjusted life year [95% CI, $1,695-$98,522]). If society was willing to pay $100,000 per quality-adjusted life year, any intervention costing less than $51,328 per patient with moderate to severe acute respiratory distress syndrome would represent good value. From a hospital perspective, the intervention yielded 0.072 (95% CI, 0.008-0.147) more survivals-to-discharge at a cost of $5,242 (95% CI, -$19,035 to $41,019) (incremental cost-effectiveness ratio = $44,615 per extra survival [95% CI, -$250,912 to $558,222]). If hospitals were willing to pay $100,000 per survival-to-discharge, any intervention costing less than $5,140 per patient would represent good value. CONCLUSIONS: Interventions that increase utilization of proning would be cost-effective from both societal and hospital perspectives under many plausible cost and benefit assumptions.

Patient Mortality Is Associated With Staff Resources and Workload in the ICU: A Multicenter Observational Study.

OBJECTIVE: Matching healthcare staff resources to patient needs in the ICU is a key factor for quality of care. We aimed to assess the impact of the staffing-to-patient ratio and workload on ICU mortality. DESIGN: We performed a multicenter longitudinal study using routinely collected hospital data. SETTING: Information pertaining to every patient in eight ICUs from four university hospitals from January to December 2013 was analyzed. PATIENTS: A total of 5,718 inpatient stays were included. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We used a shift-by-shift varying measure of the patient-to-caregiver ratio in combination with workload to establish their relationships with ICU mortality over time, excluding patients with decision to forego life-sustaining therapy. Using a multilevel Poisson regression, we quantified ICU mortality-relative risk, adjusted for patient turnover, severity, and staffing levels. The risk of death was increased by 3.5 (95% CI, 1.3-9.1) when the patient-to-nurse ratio was greater than 2.5, and it was increased by 2.0 (95% CI, 1.3-3.2) when the patient-to-physician ratio exceeded 14. The highest ratios occurred more frequently during the weekend for nurse staffing and during the night for physicians (p < 0.001). High patient turnover (adjusted relative risk, 5.6 [2.0-15.0]) and the volume of life-sustaining procedures performed by staff (adjusted relative risk, 5.9 [4.3-7.9]) were also associated with increased mortality. CONCLUSIONS: This study proposes evidence-based thresholds for patient-to-caregiver ratios, above which patient safety may be endangered in the ICU. Real-time monitoring of staffing levels and workload is feasible for adjusting caregivers' resources to patients' needs.

Noninvasive quantitative assessment of pulmonary blood flow with 18F-FDG PET.

UNLABELLED: Pulmonary blood flow (PBF) is a critical determinant of oxygenation during acute lung injury (ALI). PET/CT with (18)F-FDG allows the assessment of both lung aeration and neutrophil inflammation as well as an estimation of the regional fraction of blood (FB) if compartmental modeling is used to quantify (18)F-FDG pulmonary uptake. The aim of this study was to validate the use of FB to assess PBF, with PET and compartmental modeling of (15)O-H2O kinetics as a reference method, in both control animals and animals with ALI. For the purpose of studying a wide range of PBF values, supine and prone positions and various positive end-expiratory pressures (PEEPs) and tidal volumes (V(T)s) were selected. METHODS: Pigs were randomized into 3 groups in which ALI was induced by HCl inhalation: pigs studied in the supine position with a low PEEP (5 ± 3 [mean ± SD] cm of H2O; n = 9) or a high PEEP (12 ± 1 cm of H2O; n = 8) and pigs studied in the prone position with a low PEEP (6 ± 3 cm of H2O; n = 9). Also included were a control group that did not have ALI (n = 6) and 2 additional groups (n = 6 each) that had a high V(T) to maintain a transpulmonary pressure of greater than or equal to 35 cm of H2O and that either received HCl inhalation or did not receive HCl inhalation. PBF and FB were measured with PET and compartmental modeling of (15)O-H2O and (18)F-FDG kinetics in 10 lung regions along the anterior-to-posterior lung dimension, and both were expressed in each region as a fraction of their values in the whole lung. RESULTS: PBF and FB were strongly correlated (R(2) = 0.9), with a slope of the regression line close to unity and a negligible intercept. The mean difference between PBF and FB was 0, and the 95% limits of agreement were -0.035 to 0.035. This good agreement between methods was obtained in both normal and injured lungs and under a wide range of V(T), PEEP, and regional PBF values (7-71 mL/kg, 0-15 cm of H2O, and 24-603 mL·min(-1)·100 mL of lung(-1), respectively). CONCLUSION: FB assessed with (18)F-FDG is a good surrogate for PBF in both normal animals and animals with ALI. PET/CT has the potential to be used to study ventilation, perfusion, and lung inflammation with a single tracer.

Bench assessment of a new insufflation-exsufflation device.

BACKGROUND: The Nippy Clearway is a new mechanical insufflation-exsufflation device used to assist cough. METHODS: We compared the peak expiratory flow (PEF) with the Nippy Clearway versus the CoughAssist in a bench experiment. The relationship between PEF and pressure at the airway opening during exsufflation (minimum expiratory PAO) was investigated under 6 combinations of compliance (30 or 60 mL/cm H2O) (C30 and C60) and resistance (0, 5, or 20 cm H2O/L/s) (R0, R5, and R20) over a 25-50 cm H2O range of set P(AO). The intercepts and slopes of the linear regression performed over PEF and P(AO) relationships were compared for both devices. RESULTS: For the C30R0, C30R5, and C60R5 conditions, the change in both the intercepts and slopes was significant with the Nippy Clearway, compared to the CoughAssist, averaging -2.96 L/s and -0.03 L/s/cm H2O, -1.46 L/s and 0.02 L/s/cm H2O, and -1.02 L/s and -0.04 L/s/cm H2O, respectively. As a result, at any minimum expiratory P(AO), PEF was significantly greater with the Nippy Clearway. For C30R20 and C60R20, the regression lines were similar for the Nippy Clearway and CoughAssist. CONCLUSIONS: In this bench study, PEF with the Nippy Clearway was greater than with the CoughAssist at low respiratory-system compliance.

Assessment of airway closure from deflation lung volume-pressure curve: sigmoidal equation revisited.

OBJECTIVE: To assess a sigmoidal equation for describing airway closure. DESIGN: Experimental study. SETTING: University laboratory. PARTICIPANTS: Eight piglets mechanically ventilated on zero end-expiratory pressure (ZEEP). INTERVENTIONS: Control and lung saline lavage. MEASUREMENTS AND RESULTS: Lungs were inflated up to transpulmonary pressure of 30 cmH(2)O at constant flow (0.12l s(-1)) then deflated at the same flow rate up to the point at which oesophageal pressure was constant, which was assumed to represent complete airway closure. The deflation volume-transpulmonary pressure curve was fitted to: (1) a sigmoidal equation focusing on inflexion point and pressure at maximal compliance increase and (2) an exponential equation above an inflexion point determined by eyeballing. Data deviate from the exponential equation at the point of airway closure onset. The zero-volume intercept was determined. Complete airway closure was reached at -8.3+/-3.5cmH(2)O in control conditions and at -1.3+/-3.7 cmH(2)O after lavage (p < 0.05). Between control and lavage, onset of airway closure was 3.0+/-1.9 vs. 6.0+/-2.8 cmH(2)O (p <0.05), inflexion point 3.2+/-1.8 vs. 7.7+/-2.6 cmH(2)O (p <0.001), pressure at maximal compliance increase -1.9+/-0.7 vs. -0.03+/-2.1cmH(2)O (p <0.05) and zero-volume intercept -1.5+/-1.4 vs. 0.3+/-2.3cmH(2)O (p <0.05). CONCLUSIONS: During mechanical ventilation airways stay open and close around ZEEP in control but are closed above ZEEP after lavage. Inflexion point might reflect onset of airways closure in control. Pressure at maximal compliance increase was not a marker of complete airways closure. In control and lavage, pressure at maximal compliance increase and zero-volume intercept were reasonably equivalent.

Quantitative assessment of regional alveolar ventilation and gas volume using 13N-N2 washout and PET.

UNLABELLED: Measurement of alveolar volume (Va) and regional ventilation (a) is crucial to understanding the pathophysiology of acute lung injury and ventilator-induced lung injury. PET has previously been used as a noninvasive, quantitative method to assess a, but formal validation of this technique in experimental lung injury is lacking. This study aims to validate Va and a regional assessment with PET, using inhaled (13)N-N(2) in pigs. METHODS: Two normal and 2 oleic acid-injured pigs were tracheotomized, mechanically ventilated, and studied in 5 different levels of ventilation by changing respiratory rate. In each experimental condition, lungs were washed-in and then washed-out with (13)N-N(2) through an open circuit in the ventilator. Using this method, multiframe images were acquired with a dedicated PET camera. Regions of interest (ROIs) were drawn on each lung. Regional time-activity curves during washout were generated for each ROI and fitted to a mono- and a bicompartmental model. Validation of this method was performed in 2 ways. First, regional values of predicted Va (Va(emission)) were compared with regional volume obtained independently from density analysis on a transmission scan (Va(trans)). Second, regional values of predicted a were summed in each animal during each experimental condition and compared with minute-ventilation values set on the ventilator. RESULTS: The bicompartmental model best fitted the experimental values in normal (94.7% [62.2%-100.0%] (median [interquartile range]) of the ROIs) as well as in injured animals (90.7% [81.6%-97.4%] of the ROIs) (P = 0.49). Va(emission) significantly correlated with Va(trans) (R(2) = 0.89, P < 0.001) but exceeded Va(trans) by 10%. Finally, a strongly and positively correlated with minute-ventilation in both normal (R(2) = 0.96, P < 0.001) and injured (R(2) = 0.96, P < 0.001) animals. CONCLUSION: Measurement of (13)N-N(2) washout using PET is accurate to assess regional alveolar volume and ventilation during experimental acute lung injury.