Jean-Christophe Richard

Prone Positioning in Severe Acute Respiratory Distress Syndrome

BACKGROUND Previous trials involving patients with the acute respiratory distress syndrome (ARDS) have failed to show a beneficial effect of prone positioning during mechanical ventilatory support on outcomes. We evaluated the effect of early application of prone positioning on outcomes in patients with severe ARDS. METHODS In this multicenter, prospective, randomized, controlled trial, we randomly assigned 466 patients with severe ARDS to undergo prone-positioning sessions of at least 16 hours or to be left in the supine position. Severe ARDS was defined as a ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (FiO2) of less than 150 mm Hg, with an FiO2 of at least 0.6, a positive end-expiratory pressure of at least 5 cm of water, and a tidal volume close to 6 ml per kilogram of predicted body weight. The primary outcome was the proportion of patients who died from any cause within 28 days after inclusion. RESULTS A total of 237 patients were assigned to the prone group, and 229 patients were assigned to the supine group. The 28-day mortality was 16.0% in the prone group and 32.8% in the supine group (P<0.001). The hazard ratio for death with prone positioning was 0.39 (95% confidence interval [CI], 0.25 to 0.63). Unadjusted 90-day mortality was 23.6% in the prone group versus 41.0% in the supine group (P<0.001), with a hazard ratio of 0.44 (95% CI, 0.29 to 0.67). The incidence of complications did not differ significantly between the groups, except for the incidence of cardiac arrests, which was higher in the supine group. CONCLUSIONS In patients with severe ARDS, early application of prolonged prone-positioning sessions significantly decreased 28-day and 90-day mortality. (Funded by the Programme Hospitalier de Recherche Clinique National 2006 and 2010 of the French Ministry of Health; PROSEVA ClinicalTrials.gov number, NCT00527813.).

Higher vs lower positive end-expiratory pressure in patients with acute lung injury and acute respiratory distress syndrome: systematic review and meta-analysis.

CONTEXT Trials comparing higher vs lower levels of positive end-expiratory pressure (PEEP) in adults with acute lung injury or acute respiratory distress syndrome (ARDS) have been underpowered to detect small but potentially important effects on mortality or to explore subgroup differences. OBJECTIVES To evaluate the association of higher vs lower PEEP with patient-important outcomes in adults with acute lung injury or ARDS who are receiving ventilation with low tidal volumes and to investigate whether these associations differ across prespecified subgroups. DATA SOURCES Search of MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials (1996-January 2010) plus a hand search of conference proceedings (2004-January 2010). STUDY SELECTION Two reviewers independently screened articles to identify studies randomly assigning adults with acute lung injury or ARDS to treatment with higher vs lower PEEP (with low tidal volume ventilation) and also reporting mortality. DATA EXTRACTION Data from 2299 individual patients in 3 trials were analyzed using uniform outcome definitions. Prespecified effect modifiers were tested using multivariable hierarchical regression, adjusting for important prognostic factors and clustering effects. RESULTS There were 374 hospital deaths in 1136 patients (32.9%) assigned to treatment with higher PEEP and 409 hospital deaths in 1163 patients (35.2%) assigned to lower PEEP (adjusted relative risk [RR], 0.94; 95% confidence interval [CI], 0.86-1.04; P = .25). Treatment effects varied with the presence or absence of ARDS, defined by a value of 200 mm Hg or less for the ratio of partial pressure of oxygen to fraction of inspired oxygen concentration (P = .02 for interaction). In patients with ARDS (n = 1892), there were 324 hospital deaths (34.1%) in the higher PEEP group and 368 (39.1%) in the lower PEEP group (adjusted RR, 0.90; 95% CI, 0.81-1.00; P = .049); in patients without ARDS (n = 404), there were 50 hospital deaths (27.2%) in the higher PEEP group and 44 (19.4%) in the lower PEEP group (adjusted RR, 1.37; 95% CI, 0.98-1.92; P = .07). Rates of pneumothorax and vasopressor use were similar. CONCLUSIONS Treatment with higher vs lower levels of PEEP was not associated with improved hospital survival. However, higher levels were associated with improved survival among the subgroup of patients with ARDS.

Unplanned extubation: risk factors of development and predictive criteria for reintubation.

OBJECTIVES To define patients at risk for unplanned extubation; to assess the influence of nursing workload on the incidence of unplanned extubation; and to determine predictive criteria for patients requiring reintubation. DESIGN A prospective, case-control study, with 10 and 15 mos of data collection. SETTING University medical intensive care department. PATIENTS In the first study, which lasted 10 mos, unplanned extubation occurred in 40 (14%) of 281 ventilated and intubated patients; 36 cases were sufficiently documented to be compared with 74 intubated and ventilated controls. In the second study, which lasted 15 mos, the reintubated patients (n=23) of a series of 62 unplanned extubation patients were compared with those who were not reintubated (n=39). INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS The following parameters were recorded: gender, age, main reason for admission, Simplified Acute Physiology Score II, route of intubation (oral or nasotracheal), tube diameter, ventilatory mode, FiO2, frequency and tidal volume delivered by the ventilator immediately before unplanned extubation, arterial blood gases performed 24 hrs before unplanned extubation, the presence of any sedation with, in this case, the last Ramsay score, the presence of hand restraints, the presence of weaning of ventilation, the accidental or deliberate nature of unplanned extubation, the Glasgow Coma Score at the time of unplanned extubation, the duration of ventilation before unplanned extubation, total duration of ventilation and stay in the intensive care unit, and the patients survival or death. The nursing workload was evaluated using a score derived from the Projet de Recherche en Nursing and adapted to intensive care. Unplanned extubation patients were more frequently intubated orally than controls (33.3% vs. 14.9%, respectively; p< .05). In the population of sedated patients, unplanned extubation patients were more frequently agitated than controls (60% vs. 19%, respectively; p < .05). The nursing workload did not differ between days with and days without unplanned extubation. Twenty-three (37%) of the 62 cases of documented unplanned extubation were reintubated. Predictive factors of reintubation are, in decreasing order of importance: Glasgow Coma Score of <11, accidental nature of unplanned extubation, and a PaO2/FiO2 ratio <200 torr (<26.7 kPa). CONCLUSIONS Patients at risk for unplanned extubation are characterized by oral intubation and insufficient sedation. In the department studied, and with the specific score used, we did not observe a relationship between the nursing workload and the incidence of unplanned extubation. A Glasgow Coma Score of <11, the accidental nature of unplanned extubation, and a PaO2/FiO2 ratio <200 torr (<26.7 kPa) are factors associated with a risk of reintubation.

Respective effects of end-expiratory and end-inspiratory pressures on alveolar recruitment in acute lung injury

ObjectiveA low tidal volume can induce alveolar derecruitment in patients with acute lung injury. This study was undertaken to evaluate whether this resulted mainly from the decrease in tidal volume per se or from the reduction in end-inspiratory plateau pressure and whether there is any benefit in raising the level of positive end-expiratory pressure (PEEP) while plateau pressure is kept constant. DesignProspective crossover study. SettingMedical intensive care unit of a university teaching hospital. PatientsFifteen adult patients ventilated for acute lung injury (Pao2/Fio2, 158 ± 34 mm Hg; lung injury score, 2.7 ± 0.6). InterventionsThree combinations were tested: PEEP at the lower inflection point with 6 mL/kg tidal volume, PEEP at the lower inflection point with 10 mL/kg tidal volume, and high PEEP with tidal volume at 6 mL/kg, keeping the plateau pressure similar to the preceding condition. Measurements and Main ResultsPressure-volume curves at zero PEEP and at set PEEP were recorded, and recruitment was calculated as the volume difference between both curves for pressures ranging from 15 to 30 cm H2O. Arterial blood gases were measured for all patients. For a similar PEEP at the lower inflection point (10 ± 3 cm H2O), tidal volume reduction (10 to 6 mL/kg) led to a significant derecruitment. A low tidal volume (6 mL/kg) with high PEEP (14 ± 3 cm H2O), however, induced a significantly greater recruitment and a higher Pao2 than the two other strategies. ConclusionAt a given plateau pressure (i.e., similar end-inspiratory distension), lowering tidal volume and increasing PEEP increase recruitment and Pao2.

Mechanical effects of airway humidification devices in difficult to wean patients.

ObjectiveTo evaluate the influence of airway humidification devices on the efficacy of ventilation in difficult to wean patients. DesignA prospective, randomized, controlled physiologic study. SettingA 22-bed medical intensive care unit in a university hospital. PatientsChronic respiratory failure patients. InterventionsPerformances of a heated humidifier and a heat and moisture exchanger were evaluated on diaphragmatic muscle activity, breathing pattern, gas exchange, and respiratory comfort during weaning from mechanical ventilation by using pressure support ventilation. Eleven patients with chronic respiratory failure were submitted to four pressure support ventilation sequences by using the heated humidifier and the heat and moisture exchanger at two different levels of pressure support ventilation (7 and 15 cm H2O). Measurement and Main ResultsCompared with the heated humidifier and regardless of the pressure support ventilation level used, the heat and moisture exchanger significantly increased all of the inspiratory effort variables (inspiratory work of breathing expressed in J/L and J/min, pressure time product, changes in esophageal pressure, and transdiaphragmatic pressure;p < .05) and dynamic intrinsic positive end-expiratory pressure (p < .05). Similarly, the heat and moisture exchanger produced a significant increase in Paco2 (p < .01) responsible for severe respiratory acidosis (p < .05), which was insufficiently compensated for despite a significant increase in minute ventilation (p < .05). This resulted in respiratory discomfort for all patients with the heat and moisture exchanger (p < .01). Adverse effects were partially counterbalanced by increasing the pressure support ventilation level with the heat and moisture exchanger by ≥8 cm H2O. ConclusionsThe type of airway humidification device used may negatively influence the mechanical efficacy of ventilation and, unless the pressure support ventilation level is considerably increased, the use of a heat and moisture exchanger should not be recommended in difficult or potentially difficult to wean patients with chronic respiratory failure.

Noninvasive proportional assist ventilation compared with noninvasive pressure support ventilation in hypercapnic acute respiratory failure

Objectives To compare short-term administration of noninvasive proportional assist ventilation (NIV-PAV) and pressure support ventilation (NIV-PSV). Design Prospective, crossover, randomized study. Setting Medicosurgical intensive care unit in a nonteaching hospital. Patients Twelve chronic obstructive pulmonary disease patients admitted for hypercapnic acute respiratory failure. Intervention NIV-PSV and NIV-PAV given in a randomized order after baseline evaluation in continuous positive airway pressure. Using a flow-triggering ventilator, NIV-PAV was adjusted using the runaway method and compared with NIV-PSV at similar peak inspiratory airway pressure. Measurements and Main Results Flow, airway pressure, and changes in esophageal pressure were measured and the tidal volume, the patient’s inspiratory work of breathing, and the esophageal pressure–time product were calculated. Arterial pH and Paco2 were measured and breathing comfort was assessed using a visual analogic scale. Peak inspiratory airway pressure (17 ± 3 cm H2O) and tidal volume were similarly increased with the two modalities with no change in respiratory rate. The change in esophageal pressure was similarly decreased (from 20 ± 8 cm H2O in continuous positive airway pressure to 12 ± 7 in NIV-PSV and 10 ± 5 cm H2O in NIV-PAV) as well as inspiratory muscle effort indexes. Arterial pH and Paco2 were similarly improved. Breathing comfort was significantly improved in NIV-PAV (+38 ± 38%) but not in NIV-PSV (+11 ± 23%). The tidal volume was more variable in NIV-PAV (89 ± 18%) than in NIV-PSV (15 ± 8%) and changes in tidal volume variability were significantly correlated (p = .02) with changes in breathing comfort. Conclusions In chronic obstructive pulmonary disease patients with hypercapnic acute respiratory failure, NIV-PAV was able to unload inspiratory muscles similarly to NIV-PSV but may be more comfortable than NIV-PSV.

Electrical impedance tomography compared to positron emission tomography for the measurement of regional lung ventilation: an experimental study

IntroductionElectrical impedance tomography (EIT), which can assess regional lung ventilation at the bedside, has never been compared with positron-emission tomography (PET), a gold-standard to quantify regional ventilation. This experiment systematically compared both techniques in injured and non-injured lungs.MethodsThe study was performed in six mechanically ventilated female piglets. In normal lungs, tidal volume (VT) was randomly changed to 6, 8, 10 and 15 ml/kg on zero end-expiratory pressure (ZEEP), then, at VT 10 ml/kg, positive end-expiratory pressure (PEEP) was randomly changed to 5, 10 and 15 cmH2O. Afterwards, acute lung injury (ALI) was subsequently created in three animals by injecting 3 ml/kg hydrochloric acid into the trachea. Then at PEEP 5 cmH2O, VT was randomly changed to 8 and 12 ml/kg and PEEP of 10 and 15 cmH2O applied at VT 10 ml/kg. EIT and PET examinations were performed simultaneously. EIT ventilation (VTEIT) and lung volume (VL) were measured in the anterior and posterior area of each lung. On the same regions of interest, ventilation (VPET) and aerated lung volume (VAatten) were determined with PET.ResultsOn ZEEP, VTEIT and VPET significantly correlated for global (VTEIT = VPET - 2E-13, R2 = 0.95, P < 0.001) and regional (VTEIT = 0.81VPET+7.65, R2 = 0.63, P < 0.001) ventilation over both conditions. For ALI condition, corresponding R2 were 0.91 and 0.73 (P < 0.01). Bias was = 0 and limits of agreement were -37.42 and +37.42 ml/min for global ventilation over both conditions. These values were 0.04 and -29.01 and +29.08 ml/min, respectively, for regional ventilation. Significant correlations were also found between VL and VAatten for global (VL = VAatten+1E-12, R2 = 0.93, P < 0.0001) and regional (VL = 0.99VAatten+0.92, R2 = 0.65, P < 0.001) volume. For ALI condition, corresponding R2 were 0.94 (P < 0.001) and 0.54 (P < 0.05). Bias was = 0 and limits of agreement ranged -38.16 and +38.16 ml for global ventilation over both conditions. These values were -0.24 and -31.96 to +31.48 ml, respectively, for regional ventilation.ConclusionsRegional lung ventilation and volume were accurately measured with EIT in healthy and injured lungs and validated by simultaneous PET imaging.

Extracorporeal life support for patients with acute respiratory distress syndrome: report of a Consensus Conference

The influenza H1N1 epidemics in 2009 led a substantial number of people to develop severe acute respiratory distress syndrome and refractory hypoxemia. In these patients, extracorporeal membrane oxygenation was used as rescue oxygenation therapy. Several randomized clinical trials and observational studies suggested that extracorporeal membrane oxygenation associated with protective mechanical ventilation could improve outcome, but its efficacy remains uncertain. Organized by the Société de Réanimation de Langue Française (SRLF) in conjunction with the Société Française d’Anesthésie et de Réanimation (SFAR), the Société de Pneumologie de Langue Française (SPLF), the Groupe Francophone de Réanimation et d’Urgences Pédiatriques (GFRUP), the Société Française de Perfusion (SOFRAPERF), the Société Française de Chirurgie Thoracique et Cardiovasculaire (SFCTV) et the Sociedad Española de Medecina Intensiva Critica y Unidades Coronarias (SEMICYUC), a Consensus Conference was held in December 2013 and a jury of 13 members wrote 65 recommendations to answer the five following questions regarding the place of extracorporeal life support for patients with acute respiratory distress syndrome: 1) What are the available techniques?; 2) Which patients could benefit from extracorporeal life support?; 3) How to perform extracorporeal life support?; 4) How and when to stop extracorporeal life support?; 5) Which organization should be recommended? To write the recommendations, evidence-based medicine (GRADE method), expert panel opinions, and shared decisions taken by all the thirteen members of the jury of the Consensus Conference were taken into account.

What has been learnt from P/V curves in patients with acute lung injury/acute respiratory distress syndrome

Mechanical impairment of the respiratory system was recognised soon after the description of acute respiratory distress syndrome. The analysis of the pressure/volume (P/V) curve of the respiratory system contributed a lot to the understanding of the pathophysiology of acute lung injury and formed the basis for lung protection. The lower and upper inflection points were regarded as points of interest to avoid cyclic derecruitment and overdistension and to optimise ventilatory settings. However, because of the heterogeneity of lung injury, reducing the mechanical properties of the whole respiratory system to a single curve is a schematic approach, which makes interpretation difficult. New data suggest that alveolar re-inflation occurs along the whole P/V curve that can, therefore, be considered as a recruitment curve. The lower inflection point has no relationship with alveolar opening and closure and does not indicate the positive end-expiratory pressure needed to prevent alveolar collapse. The shape of the P/V curve gives information about the extension and the homogeneity of lung injury, indicating the possibility of lung recruitment. The upper inflection point, classically seen as the beginning of overdistension, may also indicate the end of recruitment. The pressure/volume curve offers the unique opportunity of evaluating alveolar recruitment/derecruitment at the bedside that can be helpful for the identification of optimal ventilatory settings and makes the curve a valuable tool for the ventilatory management of acute lung injury.

Clinical review: Bedside assessment of alveolar recruitment

Recruitment is a dynamic physiological process that refers to the reopening of previously gasless lung units. Cumulating evidence has led to a better understanding of the rules that govern both recruitment and derecruitment during mechanical ventilation of patients with acute respiratory distress syndrome. Therefore not only the positive end-expiratory pressure, but also the tidal volume, the inspired oxygen fraction, repeated tracheal suctioning as well as sedation and paralysis may affect recruitment of acute respiratory distress syndrome lungs that are particularly prone to alveolar instability. In the present article, we review the recently reported data concerning the physiological significance of the pressure–volume curve and its use to assess alveolar recruitment. We also describe alternate techniques that have been proposed to assess recruitment at the bedside. Whether recruitment should be optimized remains an ongoing controversy that warrants further clinical investigation.