Total Positive End-expiratory Pressure Research Articles

Impact of tracheostomy tube modalities on ventilatory mechanics: a bench study

PurposeTracheostomized patients often present with muscle weakness, altered consciousness, or swallowing difficulties. Hence, the literature is scarce regarding the challenging management of tracheostomy weaning. There is a need to strengthen the understanding of respiratory mechanisms with the different tracheostomy tube modalities that compose this weaning pathway. We aimed to evaluate the impact of these modalities on the work of breathing (WOB), total positive end-expiratory pressure (PEEPtot), and tidal volume (VT).MethodsWith a three-dimensional (3D) printed head mimicking human upper airways, we added a tracheal extension, and pierced to allow insertion of a size 7.0 tracheostomy cannula. The whole was connected to an artificial lung. Three lung mechanics were simulated (normal, obstructive and restrictive). We compared five different tracheostomy tube modalities to a control scenario in which the tube was capped and the cuff was deflated.ResultsA marginal difference was observed on the WOB within conditions with a slight increase + 0.004 [95% CI (0.003–0.004); p < 0.001] when the cuff was inflated in the normal and restrictive models and a slight decrease in the obstructive model. The highest PEEPtot that was reached was + 1 cmH2O [95% CI (1–1.1); p < 0.001] with high-flow therapy (HFT) with the cuff inflated in the obstructive model. We observed a statistically significant reduction in VT [up to − 57 mL 95% CI (− 60 to − 54); p < 0.001] when the cuff was inflated, in both the normal and obstructive models.ConclusionsOur results support the use of conditions that involve cuff deflation. Intermediate modalities with the cuff deflated produced similar results than cannula capping.

Plateau Pressure and Driving Pressure in Volume- and Pressure-Controlled Ventilation: Comparison of Frictional and Viscoelastic Resistive Components in Pediatric Acute Respiratory Distress Syndrome.

To examine frictional, viscoelastic, and elastic resistive components, as well threshold pressures, during volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) in pediatric patients with acute respiratory distress syndrome (ARDS). Prospective cohort study. Seven-bed PICU, Hospital El Carmen de Maipú, Chile. Eighteen mechanically ventilated patients less than or equal to 15 years old undergoing neuromuscular blockade as part of management for ARDS. None. All patients were in VCV mode during measurement of pulmonary mechanics, including: the first pressure drop (P1) upon reaching zero flow during the inspiratory hold, peak inspiratory pressure (PIP), plateau pressure (P PLAT ), and total positive end-expiratory pressure (tPEEP). We calculated the components of the working pressure, as defined by the following: frictional resistive = PIP-P1; viscoelastic resistive = P1-P PLAT ; purely elastic = driving pressure (ΔP) = P PLAT -tPEEP; and threshold = intrinsic PEEP. The procedures and calculations were repeated on PCV, keeping the same tidal volume and inspiratory time. Measurements in VCV were considered the gold standard. We performed Spearman correlation and Bland-Altman analysis. The median (interquartile range [IQR]) for patient age was 5 months (2-17 mo). Tidal volume was 5.7 mL/kg (5.3-6.1 mL/kg), PIP cm H 2 O 26 (23-27 cm H 2 O), P1 23 cm H 2 O (21-26 cm H 2 O), P PLAT 19 cm H 2 O (17-22 cm H 2 O), tPEEP 9 cm H 2 O (8-9 cm H 2 O), and ΔP 11 cm H 2 O (9-13 cm H 2 O) in VCV mode at baseline. There was a robust correlation (rho > 0.8) and agreement between frictional resistive, elastic, and threshold components of working pressure in both modes but not for the viscoelastic resistive component. The purely frictional resistive component was negligible. Median peak inspiratory flow with decelerating-flow was 21 (IQR, 15-26) and squared-shaped flow was 7 L/min (IQR, 6-10 L/min) ( p < 0.001). P PLAT , ΔP, and tPEEP can guide clinical decisions independent of the ventilatory mode. The modest purely frictional resistive component emphasizes the relevance of maintaining the same safety limits, regardless of the selected ventilatory mode. Therefore, peak inspiratory flow should be studied as a mechanism of ventilator-induced lung injury in pediatric ARDS.

Product of driving pressure and respiratory rate for predicting weaning outcomes.

ObjectiveClinicians cannot precisely determine the time for withdrawal of ventilation. We aimed to evaluate the performance of driving pressure (DP)×respiratory rate (RR) to predict the outcome of weaning.MethodsPlateau pressure (Pplat) and total positive end-expiratory pressure (PEEPtot) were measured during mechanical ventilation with brief deep sedation and on volume-controlled mechanical ventilation with a tidal volume of 6 mL/kg and a PEEP of 0 cmH2O. Pplat and PEEPtot were measured by patients holding their breath for 2 s after inhalation and exhalation, respectively. DP was determined as Pplat minus PEEPtot. The rapid shallow breathing index was measured from the ventilator. The highest RR was recorded within 3 minutes during a spontaneous breathing trial. Patients who tolerated a spontaneous breathing trial for 1 hour were extubated.ResultsAmong the 105 patients studied, 44 failed weaning. During ventilation withdrawal, DP×RR was 136.7±35.2 cmH2O breaths/minute in the success group and 230.2±52.2 cmH2O breaths/minute in the failure group. A DP×RR index >170.8 cmH2O breaths/minute had a sensitivity of 93.2% and specificity of 88.5% to predict failure of weaning.ConclusionsMeasurement of DP×RR during withdrawal of ventilation may help predict the weaning outcome. A high DP×RR increases the likelihood of weaning failure.Statement: This manuscript was previously posted as a preprint on Research Square with the following link: https://www.researchsquare.com/article/rs-15065/v3 and DOI: 10.21203/rs.2.24506/v3

Ventilated Patients With COVID-19 Show Airflow Obstruction

Objective:Many patients with coronavirus disease 2019 (COVID-19) need mechanical ventilation secondary to acute respiratory distress syndrome. Information on the respiratory system mechanical characteristics of this disease is limited. The aim of this study is to describe the respiratory system mechanical properties of ventilated COVID-19 patients.Design, Setting, and Patients:Patients consecutively admitted to the medical intensive care unit at the University of Iowa Hospitals and Clinics in Iowa City, USA, from April 19 to May 1, 2020, were prospectively studied; final date of follow-up was May 1, 2020.Measurements:At the time of first patient contact, ventilator information was collected including mode, settings, peak airway pressure, plateau pressure, and total positive end expiratory pressure. Indices of airflow resistance and respiratory system compliance were calculated and analyzed.Main Results:The mean age of the patients was 58 years. 6 out of 12 (50%) patients were female. Of the 21 laboratory-confirmed COVID-19 patients on invasive mechanical ventilation, 9 patients who were actively breathing on the ventilator were excluded. All the patients included were on volume-control mode. Mean [±standard deviation] ventilator indices were: resistive pressure 19 [±4] cmH2O, airway resistance 20 [±4] cmH2O/L/s, and respiratory system static compliance 39 [±16] ml/cmH2O. These values are consistent with abnormally elevated resistance to airflow and reduced respiratory system compliance. Analysis of flow waveform graphics revealed a pattern consistent with airflow obstruction in all patients.Conclusions:Severe respiratory failure due to COVID-19 is regularly associated with airflow obstruction.

Comparative effects of flow vs. volume-controlled one-lung ventilation on gas exchange and respiratory system mechanics in pigs

BackgroundFlow-controlled ventilation (FCV) allows expiratory flow control, reducing the collapse of the airways during expiration. The performance of FCV during one-lung ventilation (OLV) under intravascular normo- and hypovolaemia is currently unknown. In this explorative study, we hypothesised that OLV with FCV improves PaO2 and reduces mechanical power compared to volume-controlled ventilation (VCV). Sixteen juvenile pigs were randomly assigned to one of two groups: (1) intravascular normovolaemia (n = 8) and (2) intravascular hypovolaemia (n = 8). To mimic inflammation due to major thoracic surgery, a thoracotomy was performed, and 0.5 μg/kg/h lipopolysaccharides from Escherichia coli continuously administered intravenously. Animals were randomly assigned to OLV with one of two sequences (60 min per mode): (1) VCV–FCV or (2) FCV–VCV. Variables of gas exchange, haemodynamics and respiratory signals were collected 20, 40 and 60 min after initiation of OLV with each mechanical ventilation mode. The distribution of ventilation was determined using electrical impedance tomography (EIT).ResultsOxygenation did not differ significantly between modes (P = 0.881). In the normovolaemia group, the corrected expired minute volume (P = 0.022) and positive end-expiratory pressure (PEEP) were lower during FCV than VCV. The minute volume (P ≤ 0.001), respiratory rate (P ≤ 0.001), total PEEP (P ≤ 0.001), resistance of the respiratory system (P ≤ 0.001), mechanical power (P ≤ 0.001) and resistive mechanical power (P ≤ 0.001) were lower during FCV than VCV irrespective of the volaemia status. The distribution of ventilation did not differ between both ventilation modes (P = 0.103).ConclusionsIn a model of OLV in normo- and hypovolemic pigs, mechanical power was lower during FCV compared to VCV, without significant differences in oxygenation. Furthermore, the efficacy of ventilation was higher during FCV compared to VCV during normovolaemia.

Neuromuscular blockers in the acute respiratory distress syndrome: A meta-analysis.

BackgroundThe effects of neuromuscular blocking agents (NMBAs) on adult patients with acute respiratory distress syndrome (ARDS) remain unclear. We performed a meta-analysis of randomized controlled trials (RCTs) to evaluate its effect on mortality.MethodsWe searched the Cochrane (Central) database, Medline, Embase, the Chinese Biomedical Literature Database (SinoMed), WanFang data and ClinicalTrials from inception to June 2019, with language restriction to English and Chinese. We included published RCTs and eligible clinical trials from ClinicalTrials.gov that compared NMBAs with placebo or usual treatment in adults with ARDS. We pooled data using random-effects models. The primary outcome was mortality. The secondary outcomes were the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO2/FIO2), total positive end expiratory pressure (PEEP), plateau pressure (Pplat), days free of ventilator at day 28, barotrauma and ICU-acquired weakness.ResultsWe included 6 RCTs (n = 1557). Compared with placebo or usual treatment, NMBAs were associated with lower 21 to 28-day mortality (RR 0.72, 95% CI 0.53–0.97, I2 = 59%). NMBAs significantly improved oxygenation (Pao2:Fio2 ratios) at 48 hours (MD 27.26 mm Hg, 95% CI 1.67, 52.84, I2 = 92%) and reduced the incidence of barotrauma (RR 0.55, 95% CI 0.35, 0.85, I2 = 0). However, NMBAs had no effect on oxygenation (Pao2:Fio2 ratios) (MD 18.41 mm Hg, 95% CI -0.33, 37.14, I2 = 72%) at 24 hours. We also found NMBAs did not affect total PEEP, plateau pressure, days free of ventilation at day 28 and ICU-acquired weakness.ConclusionsIn patients with moderate-to-severe ARDS, the administration of NMBAs could reduce 21 to 28-day mortality and barotrauma, and improve oxygenation at 48 hours, but have no significant effects on 90-day/ICU mortality, days free of ventilation at day 28 and the risk of ICU-acquired weakness. Further large-scale, high-quality RCTs are needed to confirm our findings. Registration: PROSPERO (ID: CRD 42019139656).

How to measure respiratory mechanics during controlled mechanical ventilation

Bedside measurement of respiratory mechanics allows to closely monitor the lung function in critically ill patients. The two fundamental parameters describing the respiratory system mechanics are resistance and compliance. Resistance of the respiratory system describes the opposition to gas flow during inspiration. During volume-controlled ventilation, resistance can be calculated as the ratio between the peak to plateau pressure drop and the resulting flow rate. Compliance describes the elastic property of the respiratory system, comprising the lung and the chest wall. It is the ratio between a change in volume (i.e. tidal volume) and the corresponding change in pressure, calculated as the difference between plateau pressure and total positive end-expiratory pressure, measured by end-inspiratory and end-expiratory manual occlusion, respectively. In this review, we describe how to measure respiratory mechanics at the bedside, starting from the physiological background of the equation of motion of the respiratory system. (Intensive care)

Effects of neuromuscular blockers on transpulmonary pressures in moderate to severe acute respiratory distress syndrome.

To investigate whether neuromuscular blocking agents (NMBA) exert beneficial effects in acute respiratory distress syndrome (ARDS) by reason of their action on respiratory mechanics, particularly transpulmonary pressures (P L). A prospective randomised controlled study in patients with moderate to severe ARDS within 48h of the onset of ARDS. All patients were monitored by means of an oesophageal catheter and followed up for 48h. Moderate ARDS patients were randomised into two groups according to whether they were given a 48-h continuous infusion of cisatracurium besylate or not (control group). Severe ARDS patients did not undergo randomisation and all received cisatracurium besylate per protocol. The changes during the 48-h study period in oxygenation and in respiratory mechanics, including inspiratory and expiratory P L and driving pressure, were assessed and compared. Delta P L (∆P L) was defined as inspiratory P L minus expiratory P L. Thirty patients were included, 24 with moderate ARDS and 6 with severe ARDS. NMBA infusion was associated with an improvement in oxygenation in both moderate and severe ARDS, accompanied by a decrease in both plateau pressure and total positive end-expiratory pressure. The mean inspiratory and expiratory P L were higher in the moderate ARDS group receiving NMBA than in the control group. In contrast, there was no change in either driving pressure or ∆P L related to NMBA administration. NMBA could exert beneficial effects in patients with moderate ARDS, at least in part, by limiting expiratory efforts.

Intrinsic positive end-expiratory pressure during ventilation through small endotracheal tubes during general anesthesia: incidence, mechanism, and predictive factors

Study ObjectiveTo assess the safety of mechanical ventilation and effectiveness of extrinsic positive end-expiratory pressure (PEEP) (PEEPe) in improving peripheral oxygen saturation (SpO2) during direct microlaryngeal laser surgery; to assess the incidence, amount, and nature (dynamic hyperinflation or airflow obstruction) of ensuing intrinsic PEEP (PEEPi); and to find a surrogate PEEPi indicator. DesignQuasiexperimental. SettingS. Raffaele Hospital (Milano), November 2009 to December 2010. PatientsFifty-two adults scheduled for direct microlaryngeal laser surgery. Exclusion criterion is pregnancy. InterventionsTwenty-one percent O2 mechanical ventilation through 4.5- to 5.5-mm internal diameter endotracheal tubes; in 29 patients, after measurement of PEEPi, an identical amount of PEEPe was added; and PEEPi. MeasurementsSpO2, peak (Pawpeak) and plateau (Pawplateau) airway pressure, and end-expiratory carbon dioxide were measured every 5 minutes. Respiratory compliance (Crs) was computed. PEEPi was measured (end-expiratory occlusion method). Main ResultsPEEPi ≥5 cm H2O occurred in 14 patients (27%) after intubation, in 16 (30%) at the beginning, and in 14 (27.3%) at the end of surgery. Thirty-one patients (59.4%) exhibited PEEPi ≥5 cm H2O on at least 1 time point. PEEPi at the beginning of surgery was positively correlated with Pawplateau, Crs, tidal volume, and body mass index. Body mass index was the only predictor for the occurrence of PEEPi ≥5 cm H2O. At the beginning of surgery, the Pawplateau receiver operating characteristic curve predicting PEEPi ≥5 cm H2O had area under the receiver operating characteristic curve of 0.85; best cutoff value of 15.5 cm H2O (sensitivity, 88.9%; specificity, 75%; correctly classified cases, 86.1%). When PEEPe was applied, in 23 cases (82.1%), total PEEP equaled PEEPe+ PEEPi; in 3 (10.7%), it was lower; and in 2 (7.1%), it was higher. Application of PEEPe increased SpO2 (P< .05) and Crs (P< .05). ConclusionsDuring ventilation through small endotracheal tubes, PEEPi (mostly due to dynamic hyperinflation) is common. Hemodynamic complications, barotrauma, and O2 desaturation (reversible with PEEPe) are rare. Pawplateau provided by ventilators is useful in suspecting and monitoring the occurrence of PEEPi and allows detection of lung overdistension as PEEPe is applied.

Monitoring of total positive end-expiratory pressure during mechanical ventilation by artificial neural networks

Ventilation treatment of acute lung injury (ALI) requires the application of positive airway pressure at the end of expiration (PEEPapp) to avoid lung collapse. However, the total pressure exerted on the alveolar walls (PEEPtot) is the sum of PEEPapp and intrinsic PEEP (PEEPi), a hidden component. To measure PEEPtot, ventilation must be discontinued with an end-expiratory hold maneuver (EEHM). We hypothesized that artificial neural networks (ANN) could estimate the PEEPtot from flow and pressure tracings during ongoing mechanical ventilation. Ten pigs were mechanically ventilated, and the time constant of their respiratory system (τRS) was measured. We shortened their expiratory time (TE) according to multiples of τRS, obtaining different respiratory patterns (Rpat). Pressure (PAW) and flow (V'AW) at the airway opening during ongoing mechanical ventilation were simultaneously recorded, with and without the addition of external resistance. The last breath of each Rpat included an EEHM, which was used to compute the reference PEEPtot. The entire protocol was repeated after the induction of ALI with i.v. injection of oleic acid, and 382 tracings were obtained. The ANN had to extract the PEEPtot, from the tracings without an EEHM. ANN agreement with reference PEEPtot was assessed with the Bland-Altman method. Bland Altman analysis of estimation error by ANN showed -0.40±2.84 (expressed as bias±precision) and ±5.58 as limits of agreement (data expressed as cmH2O). The ANNs estimated the PEEPtot well at different levels of PEEPapp under dynamic conditions, opening up new possibilities in monitoring PEEPi in critically ill patients who require ventilator treatment.

Physiological Effects of the Open Lung Approach in Patients with Early, Mild, Diffuse Acute Respiratory Distress Syndrome: An Electrical Impedance Tomography Study.

To test the hypothesis that in early, mild, acute respiratory distress syndrome (ARDS) patients with diffuse loss of aeration, the application of the open lung approach (OLA) would improve homogeneity in lung aeration and lung mechanics, without affecting hemodynamics. Patients were ventilated according to the ARDS Network protocol at baseline (pre-OLA). OLA consisted in a recruitment maneuver followed by a decremental positive end-expiratory pressure trial. Respiratory mechanics, gas exchange, electrical impedance tomography (EIT), cardiac index, and stroke volume variation were measured at baseline and 20 min after OLA implementation (post-OLA). Esophageal pressure was used for lung and chest wall elastance partitioning. The tomographic lung image obtained at the fifth intercostal space by EIT was divided in two ventral and two dorsal regions of interest (ROIventral and ROIDorsal). Fifteen consecutive patients were studied. The OLA increased arterial oxygen partial pressure/inspired oxygen fraction from 216 ± 13 to 311 ± 19 mmHg (P < 0.001) and decreased elastance of the respiratory system from 29.4 ± 3 cm H2O/l to 23.6 ± 1.7 cm H2O/l (P < 0.01). The driving pressure (airway opening plateau pressure - total positive end-expiratory pressure) decreased from 17.9 ± 1.5 cm H2O pre-OLA to 15.4 ± 2.1 post-OLA (P < 0.05). The tidal volume fraction reaching the dorsal ROIs increased, and consequently the ROIVentral/Dorsal impedance tidal variation decreased from 2.01 ± 0.36 to 1.19 ± 0.1 (P < 0.01). The OLA decreases the driving pressure and improves the oxygenation and lung mechanics in patients with early, mild, diffuse ARDS. EIT is useful to assess the impact of OLA on regional tidal volume distribution.

Gas exchange and lung mechanics in patients with acute respiratory distress syndrome: Comparison of three different strategies of positive end expiratory pressure selection

PurposeThe purpose of the study was to compare gas exchange and lung mechanics between different strategies to select positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS). MethodsIn 20 consecutive ARDS patients, 3 PEEP selection strategies were evaluated. One strategy was based on oxygenation using the ARDS network PEEP/fraction of inspired oxygen (Fio2) table; and two were based on lung mechanics, either PEEP titrated to reach a plateau pressure of 28 to 30 cm H2O as in the ExPress trial or best respiratory compliance method during a derecruitment maneuver. Gas exchange, airway pressures, stress index (SI), and end-expiratory transpulmonary pressure (Ptpe) and end-inspiratory transpulmonary pressure (Ptpi) values were assessed. Data are expressed as median (interquartile range [IQR]). ResultsLower total PEEP levels were observed with the use of the PEEP/Fio2 table (8.7 [6-10] cm H2O); intermediate PEEP levels, with the Best Compliance approach (13.0 [10.2-13.8] cm H2O); and higher PEEP levels, with the ExPress strategy (16.5 [15.0-18.5] cm H2O) (P < .01). Pao2/Fio2 ratio was lower with the PEEP/Fio2 table. Oxygenation with Best Compliance approach and ExPress strategy was not different with lower plateau pressure in the former (23 [20-25] vs 30 [29-30] cm H2O; P < .01). Paco2 was slightly higher with the ExPress method than the others 2 strategies. Negative Ptpe was observed in 35% of the patients with the PEEP/Fio2 table, in 15% applying the Best Compliance, and in only 1 case with the ExPress method. Higher SI and Ptpi, with lower lung compliance, were obtained with ExPress strategy. ConclusionsUsing a best respiratory compliance approach resulted in better oxygenation levels without risk of overdistension according to SI and Ptpi, achieving a mild risk of lung collapse according to Ptpe.

Assessment of respiratory system compliance with electrical impedance tomography using a positive end-expiratory pressure wave maneuver during pressure support ventilation: a pilot clinical study.

IntroductionAssessment of respiratory system compliance (Crs) can be used for individual optimization of positive end-expiratory pressure (PEEP). However, in patients with spontaneous breathing activity, the conventional methods for Crs measurement are inaccurate because of the variable muscular pressure of the patient. We hypothesized that a PEEP wave maneuver, analyzed with electrical impedance tomography (EIT), might be suitable for global and regional assessment of Crs during assisted spontaneous breathing.MethodsAfter approval of the local ethics committee, we performed a pilot clinical study in 18 mechanically ventilated patients (61 ± 16 years (mean ± standard deviation)) who were suitable for weaning with pressure support ventilation (PSV). For the PEEP wave, PEEP was elevated by 1 cmH2O after every fifth breath during PSV. This was repeated five times, until a total PEEP increase of 5 cmH2O was reached. Subsequently, PEEP was reduced in steps of 1 cmH2O in the same manner until the original PEEP level was reached. Crs was calculated using EIT from the global, ventral and dorsal lung regions of interest. For reference measurements, all patients were also examined during controlled mechanical ventilation (CMV) with a low-flow pressure-volume maneuver. Global and regional Crs(low-flow) was calculated as the slope of the pressure-volume loop between the pressure that corresponded to the selected PEEP and PEEP +5 cmH2O. For additional reference, Crs during CMV (Crs(CMV)) was calculated as expired tidal volume divided by the difference between airway plateau pressure and PEEP.ResultsRespiratory system compliance calculated from the PEEP wave (Crs(PEEP wave)) correlated closely with both reference measurements (r = 0.79 for Crs(low-flow) and r = 0.71 for Crs(CMV)). No significant difference was observed between the mean Crs(PEEP wave) and the mean Crs(low-flow). However, a significant bias of +17.1 ml/cmH2O was observed between Crs(PEEP wave) and Crs(CMV).ConclusionAnalyzing a PEEP wave maneuver with EIT allows calculation of global and regional Crs during assisted spontaneous breathing. In mechanically ventilated patients with spontaneous breathing activity, this method might be used for assessment of the global and regional mechanical properties of the respiratory system.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-014-0679-6) contains supplementary material, which is available to authorized users.

A multicenter study of respiratory multiple index in predicting weaning from mechanical ventilation in patients with acute exacerbation of chronic obstructive pulmonary disease

To study the result of respiratory multiple index(compliance, respiratory rate, oxygenation, pressure, CROP) in predicting weaning from mechanical ventilation in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). A prospective study was conducted. Two hundred and fifteen patients weaning from mechanical ventilation with AECOPD in intensive care unit (ICU) of five tertiary hospitals from September 2010 to October 2012 were enrolled. All of the AECOPD patients were troubled with respiratory failure and received non-invasive mechanical ventilation for more than 24 hours. They were conscious and cooperative at the time of extubation, and passed the spontaneous breathing trial (SBT) for 30 minutes. Before weaning, the maximal inspiratory pressure (PImax), the peak airway pressure (Ppeak), the total positive end expiratory pressure (PEEPtot), tidal volume (VT) and respiratory frequency (f) were recorded; the arterial partial pressure of oxygen (PaO₂) and arterial partial pressure of carbon dioxide (PaCO₂) were detected; the effective compliance of the respiratory system (Crs) and alveolar oxygen pressure(PAO₂) were calculated. The above indexes were substituted into the formula: CROP= Crs × 1/f × PaO₂/PAO₂× PImax to get the value of CROP. Successful weaning from mechanical ventilation was defined if there was no indication for intubation within 72 hours. The receiver operating characteristic curve (ROC curve) was drawn to analyze the predict value of CROP on result of weaning from mechanical ventilation in patients with AECOPD. In 215 patients, 182 patients successfully weaned from mechanical ventilation, and 33 failed. There were no significant differences in gender, age and the acute physiology and chronic health evaluation II (APACHEII) score between the successfully weaned patients and the failed. Before weaning from mechanical ventilation, PaCO₂ in failed group was significantly higher than that in successful group (60.69 ± 10.47 mm Hg vs. 51.24 ± 8.81 mm Hg, P<0.05), the CROP was significantly lowered (10.286 ± 1.392 ml × breath⁻¹ ×min⁻¹ vs. 58.746 ± 7.283 ml×breath⁻¹×min⁻¹, P<0.01), and the duration of mechanical ventilation was prolonged (10.28 ± 3.94 days vs. 6.21 ± 2.87 days, P<0.05). The best critical value of CROP which could predict the result of weaning from mechanical ventilation was 13.521 ml×breath⁻¹×min⁻¹. CROP≥ 13.521 ml×breath⁻¹×min⁻¹ had a specificity of 91.9% and sensitivity of 87.9% in predicting extubation succeed. The positive predicted value was 0.97, and the negative predicted value was 0.58; Odds ratio (OR)<1, which confirmed that CROP was a strong and independent predictor of extubation. For the AECOPD patients received mechanical ventilation, most extubation parameter was limited. Complex parameter of CROP has higher specificity and sensitivity, and has important value in predicting extubation outcome. When CROP ≥ 13.521 ml×breath⁻¹×min⁻¹, the successful rate is high, otherwise the rate is low.

The effect of neuromuscular blocking agents on prognosis of patients with acute respiratory distress syndrome: a meta analysis

To determine the effects of neuromuscular blocking agent (NMBA) on prognosis of patients with acute respiratory distress syndrome (ARDS). PubMed database, the Cochrane Library, EMBASE, Excepta Media, CBM, CNKI and other sources were used for retrieving the pertinent literature. All randomized controlled trials (RCTs) on NMBA treating ARDS patients were enrolled. The Cochrance Collaboration's software RevMan 5.0 was used for data analysis. Two authors independently extracted data and assessed study quality using standardized instruments. Three studies were included in the final analysis, providing a sample of 431 patients. The combined results demonstrated a decrease in 28 days mortality [Peto odds ratio (OR) =0.57, 95% confidence interval (95%CI) 0.37-0.88, P=0.01] and lower incidence of barotrauma (OR=0.42, 95%CI 0.20-0.91,P=0.003) after NMBA treatment for patients with ARDS as compared with control group. The incidence of acquired neuromyopathy was similar between NMBA group and control group (OR=1.20, 95%CI 0.67-2.14, P=0.54). As compared with the control group at 48 hours, there was no statistical difference in ventilator parameters including total positive end expiratory pressure (PEEP, OR=0.09, 95%CI -0.50-0.68, P=0.77) and plateau pressure (Pplat, OR=0.62, 95%CI -0.32-1.57, P=0.20). There was no heterogeneity (P>0.1, I (2)<50%). At 120 hours after NMBA treatment, the total PEEP was significantly lower than that of control group (OR=-1.22, 95%CI -2.39 to -0.04, P=0.04), and the difference in Pplat showed statistical difference compared with the control group (OR=-2.61, 95%CI -4.50 to -0.73, P=0.007). Early administration of NMBA for ARDS patients results in a significant reduction in 28 days mortality, and it improves outcome.

Computer simulation allows goal-oriented mechanical ventilation in acute respiratory distress syndrome

IntroductionTo prevent further lung damage in patients with acute respiratory distress syndrome (ARDS), it is important to avoid overdistension and cyclic opening and closing of atelectatic alveoli. Previous studies have demonstrated protective effects of using low tidal volume (VT), moderate positive end-expiratory pressure and low airway pressure. Aspiration of dead space (ASPIDS) allows a reduction in VT by eliminating dead space in the tracheal tube and tubing. We hypothesized that, by applying goal-orientated ventilation based on iterative computer simulation, VT can be reduced at high respiratory rate and much further reduced during ASPIDS without compromising gas exchange or causing high airway pressure.MethodsARDS was induced in eight pigs by surfactant perturbation and ventilator-induced lung injury. Ventilator resetting guided by computer simulation was then performed, aiming at minimal VT, plateau pressure 30 cmH2O and isocapnia, first by only increasing respiratory rate and then by using ASPIDS as well.ResultsVT decreased from 7.2 ± 0.5 ml/kg to 6.6 ± 0.5 ml/kg as respiratory rate increased from 40 to 64 ± 6 breaths/min, and to 4.0 ± 0.4 ml/kg when ASPIDS was used at 80 ± 6 breaths/min. Measured values of arterial carbon dioxide tension were close to predicted values. Without ASPIDS, total positive end-expiratory pressure and plateau pressure were slightly higher than predicted, and with ASPIDS they were lower than predicted.ConclusionIn principle, computer simulation may be used in goal-oriented ventilation in ARDS. Further studies are needed to investigate potential benefits and limitations over extended study periods.

Open lung ventilation does not increase right ventricular outflow impedance: An echo-Doppler study*

Ventilation according to the open lung concept (OLC) consists of recruitment maneuvers, followed by low tidal volume and elevated positive end-expiratory pressure (PEEP). Elevated PEEP is associated with an increased right ventricular afterload. We investigated the effect of OLC ventilation on right ventricular outflow impedance during inspiration and expiration in patients after cardiac surgery using transesophageal echo-Doppler. A prospective, single-center, crossover, randomized, controlled clinical study. Cardiothoracic intensive care unit of a university hospital. Twenty-eight patients scheduled for elective cardiac surgery with cardiopulmonary bypass. In the intensive care unit, each patient was ventilated for approximately 30 mins according to both OLC and conventional ventilation. During OLC ventilation, recruitment maneuvers were applied until PaO2/FiO2 was >375 torr (50 kPa); during conventional ventilation no recruitment maneuvers were performed. Transesophageal echo-Doppler measurements were performed at end-inspiration and end-expiration in a steady-state condition, 20 mins after initiation of a ventilation strategy. Mean acceleration of flow was determined in the long axis of the pulmonary artery in a transverse axis view. During OLC ventilation, a total PEEP of 14 +/- 4 cm H2O was applied vs. 5 cm H2O during conventional ventilation. Mean acceleration during expiration was comparable between groups. During inspiration, OLC ventilation did not cause a decrease of mean acceleration compared with expiration, whereas this did occur during conventional ventilation. Despite the use of elevated PEEP levels, ventilation according to OLC does not change right ventricular outflow impedance during expiration and decreases right ventricular outflow impedance during inspiration.

Comparaison de deux stratégies d'utilisation de la pression expiratoire positive au cours du syndrome de détresse respiratoire aiguë. Étude ExPress. Présentation du protocole de l'étude

The best strategy for setting positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS) remains controversial. High levels of PEEP could protect the lung by avoiding the opening-closing phenomenon but might, on the other hand, increase the risk of overdistension and the deleterious hemodynamic consequences of positive intrathoracic pressure. The ExPress study is a multicenter randomized controlled trial comparing the effects on mortality of two strategies for setting PEEP in patients with ARDS. The same tidal volume (6 ml/kg) is used in the two strategies. The “maximal alveolar recruitment” strategy is aimed to optimize alveolar recruitment with a high level of PEEP. In this arm, PEEP is set to maintain plateau pressure close to the maximal currently recommended value of 30 cmH 2O. In the “minimal alveolar distension” arm, the goal is to maximally decrease alveolar distension by using low to moderate levels of PEEP (total PEEP between 5 and 9 cm H 2O). The goals for oxygenation and alveolar ventilation are the same in the two arms. Precise guidelines are used to titrate sedation and to conduct weaning. The main efficacy criteria is mortality on day 28. The protocol of the study plans to include 800 patients, recruited in 37 ICU.

Open lung ventilation does not increase right ventricular afterload in cardiac surgery patients

Open lung ventilation (OLV) consists of recruitment maneuvers, followed by low tidal volume and elevated positive end-expiratory pressure (PEEP). Elevated PEEP is associated with an increased right ventricular (RV) afterload. We investigated the effect of OLV on RV afterload during inspiration and expiration in patients after cardiac surgery using Doppler echocardiography. In 28 patients scheduled for cardiac surgery, two ventilation strategies were applied in a randomized cross-over design. During OLV, recruitment maneuvers were applied until PaO2/FiO2 > 375 Torr was achieved (reflecting an open lung) and were maintained by the use of sufficient levels of PEEP. The tidal volume was 4–6 ml/kg. During conventional mechanical ventilation (CMV) the ventilation was with a low tidal volume (6–8 ml/kg) with 5 cmH2O PEEP, without recruitment maneuvers. The acceleration time (Acmean) of the pulmonary artery was measured with transesophageal echocardiography in a long-axis view of the pulmonary artery during end-inspiration and end-expiration. The total PEEP in the OLV group was 14 ± 4 compared with 5 ± 1 cmH2O in the CMV group. During expiration, the Acmean of both ventilation strategies was comparable. Inspiration caused a significant decrease of Acmean compared with expiration during CMV (Table ​(Table1).1). Surprisingly, this did not occur during OLV. Table 1 We conclude that despite the use of 'relatively' high PEEP, OLV with low tidal volume does not increase RV afterload during inspiration and expiration.

Intrinsic positive end-expiratory pressure in Acute Respiratory Distress Syndrome (ARDS) Network subjects

We tested the hypothesis that subjects randomized to the 6 mL/kg predicted body weight tidal volume study group of the National Institutes of Health Acute Respiratory Distress Syndrome (ARDS) Network study had higher levels of intrinsic positive end-expiratory pressure (PEEP) than subjects randomized to the 12 mL/kg predicted body weight tidal volume study group. Secondary analysis of a subgroup from a randomized controlled trial. Hospitals located in San Francisco, CA, and Seattle, WA. Eighty-four patients enrolled in the ARDS Network tidal volume trial in San Francisco, CA, and Seattle, WA, with records of measurement of intrinsic PEEP. None. Intrinsic PEEP was assessed a median of six times over the first 48 hrs of ARDS Network protocol ventilation in study subjects, with no significant difference in number of measurements between subjects randomized to the tidal volume protocol of 6 mL/kg compared with 12 mL/kg. We found that intrinsic PEEP was higher among subjects randomized to the 6 mL/kg protocol, with a median intrinsic PEEP of 1.3 cm H2O (interquartile range, 0-3.1 cm H2O), compared with a median intrinsic PEEP of 0.5 cm H2O (interquartile range, 0-1.5 cm H2O) among subjects randomized to 12 mL/kg (p = .029). There was no difference in total PEEP between the study groups. In a subgroup of ARDS Network subjects, intrinsic PEEP was statistically significantly higher in subjects randomized to the 6 mL/kg protocol than those in the 12 mL/kg study group. The amount of intrinsic PEEP was very low in both study groups, and difference of median intrinsic PEEP between the groups was <1 cm H2O. It is unlikely that the difference in intrinsic PEEP between the study groups was clinically important in the ARDS Network study of low tidal volume ventilation.