An attempt to validate the modification of the American-European consensus definition of acute lung injury/acute respiratory distress syndrome by the Berlin definition in a university hospital

Purpose

The Berlin definition for acute respiratory distress syndrome (ARDS) is a new proposal for changing the American-European consensus definition but has not been assessed prospectively as yet. In the present study, we aimed to determine (1) the prevalence and incidence of ARDS with both definitions, and (2) the initial characteristics of patients with ARDS and 28-day mortality with the Berlin definition.

Methods

We performed a 6-month prospective observational study in the ten adult ICUs affiliated to the Public University Hospital in Lyon, France, from March to September 2012. Patients under invasive or noninvasive mechanical ventilation, with PaO₂/FiO₂ <300 mmHg regardless of the positive end-expiratory pressure (PEEP) level, and acute onset of new or increased bilateral infiltrates or opacities on chest X-ray were screened from ICU admission up to discharge. Patients with cardiogenic pulmonary edema were excluded. Patients were further classified into specific categories by using the American-European Consensus Conference and the Berlin definition criteria. The complete data set was measured at the time of inclusion. Patient outcome was measured at day 28 after inclusion.

Results

During the study period 3,504 patients were admitted and 278 fulfilled the American-European Consensus Conference criteria. Among them, 18 (6.5 %) did not comply with the Berlin criterion PEEP ≥ 5 cmH₂O and 20 (7.2 %) had PaO₂/FiO₂ ratio ≤200 while on noninvasive ventilation. By using the Berlin definition in the remaining 240 patients (n = 42 mild, n = 123 moderate, n = 75 severe), the overall prevalence was 6.85 % and it was 1.20, 3.51, and 2.14 % for mild, moderate, and severe ARDS, respectively (P > 0.05 between the three groups). The incidence of ARDS amounted to 32 per 100,000 population per year, with values for mild, moderate, and severe ARDS of 5.6, 16.3, and 10 per 100,000 population per year, respectively (P < 0.05 between the three groups). The 28-day mortality was 35.0 %. It amounted to 30.9 % in mild, 27.9 % in moderate, and 49.3 % in severe categories (P < 0.01 between mild or moderate and severe, P = 0.70 between mild and moderate). In the Cox proportional hazard regression analysis ARDS stage was not significantly associated with patient death at day 28.

Conclusions

The present study did not validate the Berlin definition of ARDS. Neither the stratification by severity nor the PaO₂/FiO₂ at study entry was independently associated with mortality.     

Effect of acute lung injury and acute respiratory distress syndrome on outcome in critically ill trauma patients

OBJECTIVE: Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are known to be associated with increased mortality and costs in trauma patients. We estimated the independent impact of these conditions on mortality and cost, beyond the severity of injury with which they are correlated. DESIGN: One-year prospective cohort. PATIENTS AND SETTING: All trauma patients admitted to the intensive care unit in a level I center were evaluated daily for ALI/ARDS using the American-European Consensus Conference definition. MEASUREMENTS AND MAIN RESULTS: The main outcome measures were hospital mortality and costs. Logistic regression was used to model hospital mortality in relation to the presence of ALI and ARDS, adjusting for trauma severity (Injury Severity Score), Acute Physiology Score, and age. Hospital costs were modeled using multivariable linear regression. Of the 1,296 trauma patients surviving beyond the first day, 4% experienced ALI (defined as Pao2/Fio2 of 201-300 mm Hg) and 12% had ARDS (Pao2/Fio2 < or = 200 mm Hg). The crude relative risk of mortality was 2.24 (95% confidence interval, 0.92-5.45) in patients with ALI and 3.84 (95% confidence interval, 2.41-6.13) in patients with ARDS compared with those without ALI/ARDS. However, there was no association of mortality with ALI (relative risk, 0.99; 95% confidence interval, 0.29-3.36) or with ARDS (relative risk, 1.23; 95% confidence interval, 0.63-2.43) after adjustment for age, Injury Severity Score, and Acute Physiology Score. Among patients of comparable age, severity score, and length of stay, median cost was 20% to 30% higher for those with ALI/ARDS. CONCLUSIONS: There is no additional mortality associated with ALI/ARDS above and beyond the factors that can be measured at intensive care unit admission. Therefore, mortality in trauma patients is explained by injury severity at admission and is not affected by the subsequent occurrence of ALI/ARDS. Nonetheless, ALI/ARDS was associated with increased intensive care unit stay and hospital cost, independent of trauma severity.     

Plasma levels of the three endothelial-specific proteins von Willebrand factor, tissue factor pathway inhibitor, and thrombomodulin do not predict the development of acute respiratory distress syndrome

Objective: To determine if the plasma levels of three endothelial-specific proteins, von Willebrand factor (vWF), tissue factor pathway inhibitor (TFPI) and thrombomodulin (TM) may be useful in predicting the development of acute respiratory distress syndrome (ARDS).¶Design: Blood samples were obtained from normal healthy volunteers and on the first day from patients at risk for ARDS and those with ARDS. Daily sequential measurements of vWF and TFPI were performed in two patients.¶Setting: Normal subjects were employees at Saint Louis University Hospital, St. Louis, Missouri. Patients at risk and those with ARDS were patients admitted to the medical and surgical floors and the intensive care units at St. Louis University Hospital.¶Patients and participants: Plasma levels of vWF, TFPI and TM were measured in 27 normals, and on day 1 in 15 patients at risk for ARDS and 18 patients with ARDS from different etiologic factors.¶Measurements and results: Plasma levels of vWF were significantly elevated in the at-risk (p < 0.01) and ARDS group (p < 0.001) as compared to normals but did not differ significantly between the two groups (p > 0.05). Plasma levels of TFPI were not significantly different between the normal and the at-risk group (p > 0.05); however, they were significantly elevated in ARDS as compared with at-risk and normal groups (p < 0.001). Levels of TM were significantly increased in the at-risk group as compared to normals (p < 0.01) but were not significantly different from the ARDS group (p > 0.05). Eight patients at risk progressed to develop ARDS. A vWF level of > 300 % in patients at risk was 62 % sensitive and 71 % specific for predicting the development of ARDS with a positive predictive value of only 34 %. TFPI levels were normal in 7 of the 8 patients who developed ARDS. A TM level of > 100 ng/ml in patients at risk was 50 % sensitive and 57 % specific with a positive predictive value of merely 8 % for development of ARDS. There was no significant difference in the mean plasma levels of the three proteins on day 1 in patients at risk who developed ARDS as compared with those who did not develop ARDS. There was also no difference in mean plasma levels of the three proteins in patients with ARDS from sepsis as compared with ARDS from other etiologies. Plasma levels of vWF and TFPI correlated significantly.¶Conclusion: Plasma levels of vWF, TFPI and TM did not appear to serve as useful markers for predicting ARDS in patients at risk.     

Current definitions of acute lung injury and the acute respiratory distress syndrome do not reflect their true severity and outcome

Background: Despite intensive research, there are no universally accepted clinical definitions for acute lung injury (ALI) or the acute respiratory distress syndrome (ARDS). A recent joint American-European Consensus Conference on ARDS formally defined the difference between ALI and ARDS based on the degree of oxygenation impairment. However, this definition may not reflect the true prevalence, severity and prognosis of these syndromes. Methods: During a 22-month period, 56 consecutive mechanically ventilated patients who met the American-European Consensus definition for ARDS [arterial oxygen tension/fractional inspired oxygen (PaO₂/FIO₂≤ 200 mmHg regardless of the level of positive end-expiratory pressure (PEEP), bilateral pulmonary infiltrates, and no evidence of left heart failure] were admitted into the intensive care units (ICU) of the Hospital del Pino, Las Palmas, Spain, and prospectively studied. The diagnosis of ALI and ARDS was made by a PEEP-FIO₂ trial, 24 h after patients met the Consensus inclusion criteria. Patients were classified as having ALI_{–24 h} if the PaO₂/FIO₂ was > 150 mmHg with PEEP = 5 cmH₂O, and ARDS_{–24 h} if the PaO₂ /FIO₂ was ≤ 150 mmHg with PEEP ≥ 5 cmH₂O. Results: Overall mortality was 43 % (24 of 56). However, 24 h after inclusion, PaO₂ response to PEEP 5 cmH₂O allowed the separation of our patients into two different groups: 31 patients met our ALI_{–24 h} criteria (PaO₂/FIO₂ > 150 mmHg) and their mortality was 22.6 %; 25 patients met our ARDS_{–24 h} criteria (PaO₂/FIO₂≤ 150 mmHg) and their mortality was 68 % (p = 0.0016). The differences in the respiratory severity index during the first 24 h of inclusion, PaO₂/FIO₂ ratio at baseline and at 24 h, maximum plateau airway pressure, maximum level of PEEP, and number of organ system failures during the ICU stay were statistically significant. Conclusions: Since the use of PEEP in the American-European Consensus criteria for ARDS is not mandatory, that definition does not reflect the true severity of lung damage and outcome. Our data support the need for guidelines based on a specific method of evaluating oxygenation status before the American-European Consensus definition is adopted. Received: 18 April 1999 Final revision received: 30 June 1999 Accepted: 9 July 1999     

A universal definition of ARDS: the PaO2/FiO2 ratio under a standard ventilatory setting—a prospective, multicenter validation study

Purpose

The PaO₂/FiO₂ is an integral part of the assessment of patients with acute respiratory distress syndrome (ARDS). The American-European Consensus Conference definition does not mandate any standardization procedure. We hypothesized that the use of PaO₂/FiO₂ calculated under a standard ventilatory setting within 24 h of ARDS diagnosis allows a more clinically relevant ARDS classification.

Methods

We studied 452 ARDS patients enrolled prospectively in two independent, multicenter cohorts treated with protective mechanical ventilation. At the time of ARDS diagnosis, patients had a PaO₂/FiO₂ ≤ 200. In the derivation cohort (n = 170), we measured PaO₂/FiO₂ with two levels of positive end-expiratory pressure (PEEP) (≥5 and ≥10 cmH₂O) and two levels of FiO₂ (≥0.5 and 1.0) at ARDS onset and 24 h later. Dependent upon PaO₂ response, patients were reclassified into three groups: mild (PaO₂/FiO₂ > 200), moderate (PaO₂/FiO₂ 101–200), and severe (PaO₂/FiO₂ ≤ 100) ARDS. The primary outcome measure was ICU mortality. The standard ventilatory setting that reached the highest significance difference in mortality among these categories was tested in a separate cohort (n = 282).

Results

The only standard ventilatory setting that identified the three PaO₂/FiO₂ risk categories in the derivation cohort was PEEP ≥ 10 cmH₂O and FiO₂ ≥ 0.5 at 24 h after ARDS onset (p = 0.0001). Using this ventilatory setting, patients in the validation cohort were reclassified as having mild ARDS (n = 47, mortality 17 %), moderate ARDS (n = 149, mortality 40.9 %), and severe ARDS (n = 86, mortality 58.1 %) (p = 0.00001).

Conclusions

Our method for assessing PaO₂/FiO₂ greatly improved risk stratification of ARDS and could be used for enrolling appropriate ARDS patients into therapeutic clinical trials.     

Regional distribution of gas and tissue in acute respiratory distress syndrome. II. Physiological correlations and definition of an ARDS Severity Score

Objectives: (a) To assess whether differences in lung morphology observed in patients with adult respiratory distress syndrome (ARDS) are associated with differences in cardiorespiratory parameters, lung mechanics, and outcome. (b) To propose a new ARDS Severity Score to identify patients with a high mortality risk. Design: Prospective study over a 53-month period. Setting: Fourteen-bed surgical intensive care unit of a university hospital. Patients and participants: Seventy-one consecutive patients with early ARDS. Measurements and results: Cardiorespiratory parameters were measured using a Swan-Ganz catheter, the pressure-volume (PV) curve was measured using the gross syringe method, and fast spiral computed tomography (CT) was performed. Patients with diffuse attenuations (n = 16) differed from patients with lobar attenuations (n = 26) regarding: (a) mortality rate (75 % vs. 42 %, p = 0.05), (b) incidence of primary ARDS (82 % vs. 50 %, p = 0.03), (c) respiratory compliance (47 ± 12 vs. 64 ± 16 ml per cmH₂O^–1 p = 0.04), and (d) lower inflexion point (8.4 ± 2.0 vs. 4.6 ± 2.0 cmH₂O, p = 0.001). A third group of patients with patchy attenuations (n = 29) had a mortality rate of 41 %, a respiratory compliance of 56 ± 18 ml per cmH₂O^–1 and a lower inflexion point of 6.3 ± 2.7 cmH₂O. The bedside chest radiograph accurately assessed lung morphology in only 42 % of the patients. In contrast to the scores based on the bedside chest radiograph, a new ARDS Severity Score based on CT lung morphology and cardiorespiratory parameters identified a subgroup of patients with a high mortality rate (≥ 60 %). Conclusions: In patients with ARDS, differences in lung morphology are associated with differences in outcome and lung mechanics. A new ARDS Severity Score based on CT lung morphology and cardiorespiratory parameters accurately identified patients with the most severe forms of ARDS and a mortality rate above 60 %. Received: 12 May 1999 Final revision received: 9 February 2000 Accepted: 10 April 2000     

Pulmonary function and health-related quality of life in a sample of long-term survivors of the acute respiratory distress syndrome

Objective: We performed a follow-up cohort analysis in order to delineate the correlation between pulmonary function (PF) and health-related quality of life (HRQL) in patients after ARDS.¶Design: Follow-up cohort study.¶Setting: A 20-bed ICU of a university teaching hospital.¶Patients: A cohort of 50 long-term survivors of ARDS.¶Measurements and results: Measurements of PF (FVC, FEV₁, TLC, D_LCO) and HRQL (SF-36 Health Status Questionnaire) were made 5.5 years (median value) after discharge from the ICU. Impairments in PF (defined as PF results below 80 % of the predicted value) were frequent but generally mild. Twenty patients had a single PF impairment (with limitations in FEV1/FVC ratio in 12 patients being the most common), four patients had two (with D_LCO and FEV1/FVC ratio impairment the most common) and three patients had pathologic results in three PF tests (FEV₁/FVC ratio, TLC and capillary pO₂ during exercise in one case, FVC, TLC and capillary pO₂ during exercise in the second patient and FVC, TLC and D_LCO in the third). Compared to normal controls, survivors of ARDS showed impairments in all SF-36 health dimensions (p < 0.001). Patients with multiple (> 1) PF impairments described the lowest HRQL with major limitations in all SF-36 categories (p < 0.037) including physical and mental summary scores (36.5 vs 46.9, p = 0.037 and 31.3 vs 51.4, p = 0.003) when compared to patients with no or only one PF impairment.¶Conclusions: Long-term survivors of ARDS have a significant reduction in HRQL and the presence of multiple PF impairments is associated with maximal decrements in HRQL.     

Trauma scoring systems explained

Objective: To list, describe and classify the extant trauma scoring systems found in the English language literature from the vantage of utility to emergency medicine. Each system is illustrated by a table and a hypothetical case study. Data Sources: Medline citations provided the data. The systems are classified as physiological, anatomical and combined trauma scoring systems. Results: We reviewed the Glasgow Coma Scale, the Paediatric Glasgow Coma Scale, the Trauma Score and Revised Trauma Score, the Circulation, Respiration, Abdominal/Thoracic, Motor and Speech Scale, the Acute Physiology and Chronic Health Evaluation System, Abbreviated Injury Scale, the Injury Severity Score, the Anatomical Profile, A Severity Characterization of Trauma, Revised Trauma Score and Injury Severity Score and its revisions, the Paediatric Trauma Score and the Drug-Rock Injury Severity Score. Conclusions: This compendium should help emergency physicians become familiar with trauma scoring systems which evaluate the extent and severity of injuries, facilitate inter-institutional comparisons and facilitate trauma research.     

Volume-dependent compliance in ARDS: proposal of a new diagnostic concept

Objective: Adaptation of ventilator settings to the individual's respiratory system mechanics requires information about the pressure-volume relationship and the change of compliance which is dependent on inflated volume. Unfortunately, established methods of obtaining this information are invasive and time-consuming, and, therefore, not well suited for clinical routine. We propose a new standardized diagnostic concept based on the recently developed slice method. This multiple linear regression method (MLR) determines volume-dependent respiratory system compliance (C_SLICE) within the tidal volume (V_T) during ongoing mechanical ventilation. The impact of a ventilator strategy, recommended by a consensus conference, on the course of compliance within V_T was investigated in patients with the acute respiratory distress syndrome (ARDS) or acute lung injury (ALI).¶Design: Prospective observational study.¶Setting: Intensive care unit of a university hospital.¶Patients: 14 ARDS patients, 2 patients with ALI.¶Interventions: None.¶Measurements and results: After measurement of flow and airway pressure and calculation of tracheal pressure, C_SLICE was determined. The resulting course of C_SLICE within V_T was estimated using a mathematical algorithm. C_SLICE data were compared to those obtained by standard MLR. We found decreasing C_SLICE mainly in the upper part of V_T in all patients. In 7 patients, we found an additional increasing C_SLICE mainly in the lower part of V_T.¶Conclusions: C_SLICE was not constant in patients with ARDS/ALI whose lungs were ventilated according to consensus conference recommendations. The proposed diagnostic concept may serve as a new tool to obtain a standardized estimation of respiratory system compliance within V_T non-invasively without interfering with ongoing mechanical ventilation.     

Early markers of acute respiratory distress syndrome development in severe trauma patients

PURPOSE: The aim of the study was to identify early risk factors for development of acute respiratory distress syndrome (ARDS) in severe trauma patients. MATERIALS AND METHODS: This was a prospective observational study of 693 severe trauma patients (Injury Severity Score >or=16 and/or Revised Trauma Score or=2) of long bone fractures, and with chest injuries (rib/sternal fracture [ICD-9 code 807] and hemo/pneumothorax [ICD-9 code 860/861]). Patients with ARDS required more colloids (P = .005) and red blood cell units (P = .02) than patients without ARDS during the first 24 hours. Multivariate analysis showed that ARDS was related to chest trauma diagnosis (ICD-9 code 807) (odds ratio [OR], 3.85), femoral fracture (OR, 3.16), APACHE II score (OR, 1.05), and blood transfusion during resuscitation (OR, 1.32). CONCLUSIONS: Risk of ARDS development is related to the first 24-hour admission variables, including severe physiologic derangements and specific ICD-9-classified injuries. Blood transfusion may play an independent role.     

Partial liquid ventilation with surfactant: effects on gas exchange and lung pathology in surfactant-depleted piglets

Objective: To evaluate the effects of 24 h partial liquid ventilation (PLV) with and without surfactant (S) treatment on gas exchange and lung injury in a newborn animal model of S deficiency.¶Design: A prospective, controlled, in vivo animal laboratory study.¶Setting: Research laboratory in a university setting.¶Subjects: Twenty-four pathogen-free, male piglets (mean weight 1.9 kg, age 1–3 days).¶Interventions: The animals were randomised in four groups: PLV with FC-77 combined with conventional ventilation (PLV/CV) versus S + PLV/CV and PLV combined with high frequency oscillatory ventilation (PLV/HFOV) versus S + PLV/HFOV. The piglets were anaesthetised, intubated and instrumented with vascular catheters. Thirty minutes after lung injury had been induced with repeated saline lavage, S animals received natural S. Thirty minutes after surfactant substitution PLV with FC-77 was started. The oxygenation index (OI), PaO₂/FIO₂ ratio, PaCO₂ and the ventilatory efficacy index were determined before and during PLV. After 24 h the lungs were removed for histopathological examination.¶Measurements and main results: Within 60 min after the initiation of PLV, all animals demonstrated improvements of the OI and PaO₂/FIO₂ ratio compared to the values after lung injury. However, at 18 and 24 h of PLV, the OI and PaO₂/FIO₂ ratio were significantly worse in the S + PLV/CV and S + PLV/HFOV groups compared to the groups without S. PaCO₂ was higher at 18 and 24 h when S was used in PLV/HFOV (p < 0.05). A semi-quantitative lung injury score revealed most severe lung damage in the S + PLV/HFOV group.¶Conclusion: The combination of S and PLV with FC-77 led to an impaired gas exchange and did not further protect the animal from lung injury.     

Angiotensin II formation and endothelin clearance in ARDS patients in supine and prone positions

Objective: In patients with acute respiratory distress syndrome (ARDS), the prone position may enhance oxygenation by changing ventilation/perfusion ratio. In this study, we investigated whether the prone position affects the net balance between pulmonary endothelin (ET-1) and angiotensin II (Ang II) production and clearance, two metabolic functions of lung endothelial cells.¶Setting: Anaesthesiological intensive care unit of a university hospital.¶Patients: Ten ARDS patients (Murray score > 2.5) were studied in both the supine position (SP) and the prone position (PP).¶Measurements and design: Blood samples were taken simultaneously from the patient in SP for assessment of mixed venous and arterial ET-1 and Ang II concentrations, and plasma renin concentration (PRC). This was repeated after 60 min in SP, immediately after turning the patient into PP, and 60 min thereafter. Net arterial/mixed venous ET-1 clearances and net Ang II formations were calculated.¶Results: arterial oxygen tension increased from SP to PP by an average of 60 mmHg, about 20 %. Arterial ET-1 concentrations of ARDS patients were 1.57 ± 1.1 pg/ml (mean ± SD) and within the range of healthy persons. Net ET-1 clearances were negative in SP, indicating pulmonary release of ET-1, and did not change in PP. Arterial Ang II concentrations (73 ± 56 pg/ml) as well as PRC (126 ± 85 pg/ml) were markedly elevated. Net transpulmonary Ang II formation did not change.¶Conclusion: Acute changes of oxygenation in ARDS patients by positioning do not induce any short-term effects on pulmonary ET-1 net clearance or Ang II net formation.     

Regional distribution of gas and tissue in acute respiratory distress syndrome. III. Consequences for the effects of positive end-expiratory pressure

Objective: To determine whether differences in lung morphology assessed by computed tomography (CT) affect the response to positive end-expiratory pressure (PEEP).¶Design: Prospective study over a 53-month period.¶Setting: Fourteen-bed surgical intensive care unit of a university hospital.¶Patients and participants: Seventy-one consecutive patients with early adult respiratory distress syndrome (ARDS).¶Measurements and results: Fast spiral thoracic CT was performed at zero end-expiratory pressure (ZEEP) and after implementation of PEEP 10 cmH₂O. Hemodynamic and respiratory parameters were measured in both conditions. PEEP-induced overdistension and alveolar recruitment were quantified by specifically designed software (Lungview). Overdistension occurred only in the upper lobes and was significantly correlated with the volume of lung, characterized by a CT attenuation ranging between –900 and –800 HU in ZEEP conditions. Cardiorespiratory effects of PEEP were similar in patients with primary and secondary ARDS. PEEP-induced alveolar recruitment of the lower lobes was significantly correlated with their lung volume (gas + tissue) at functional residual capacity. PEEP-induced alveolar recruitment was greater in the lower lobes with “inflammatory atelectasis” than in the lower lobes with “mechanical atelectasis.” Lung morphology as assessed by CT markedly influenced the effects of PEEP: in patients with diffuse CT attenuations PEEP induced a marked alveolar recruitment without overdistension, whereas in patients with lobar CT attenuations PEEP induced a mild alveolar recruitment associated with overdistension of previously aerated lung areas. These results can be explained by the uneven distribution of regional compliance characterizing patients with lobar CT attenuations (compliant upper lobes and stiff lower lobes) contrasting with a more even distribution of regional compliances observed in patients with diffuse CT attenuations.¶Conclusions: In patients with ARDS, the cardiorespiratory effects of PEEP are affected by lung morphology rather than by the cause of the lung injury (primary versus secondary ARDS). The regional distribution of the loss of aeration and the type of atelectasis –“mechanical” with a massive loss of lung volume, or “inflammatory” with a preservation of lung volume – characterizing the lower lobes are the main determinants of the cardiorespiratory effects of PEEP.     

Association of PEEP with two different inflation volumes in ARDS patients: effects on passive lung deflation and alveolar recruitment

Objective: To assess the effects of the association of positive end-expiratory pressure (PEEP) with different inflation volumes (V_T's) on passive lung deflation and alveolar recruitment in ARDS patients.¶Design: Clinical study using PEEP with two different V_T's and analyzing whether passive lung deflation and alveolar recruitment (Vrec) depend on end-inspired (EILV) or end-expired (EELV) lung volume in mechanically ventilated ARDS patients.¶Setting: Medical intensive care unit in a university hospital.¶Patients and participants: Six mechanically ventilated consecutive supine patients with ARDS.¶Interventions: Time-course of thoracic volume decay during passive expiration and Vrec were investigated in six ARDS patients ventilated on PEEP with baseline V_T (V_T,b) and 0.5V_T (0.5V_T,b), and on zero PEEP (ZEEP) with V_T,b. Time constants of the fast (τ ₁) and slow (τ ₂) emptying compartments, as well as resistances and elastances were also determined.¶Measurements and results: (a) the bi-exponential model best fitted the volume decay in all instances. The fast compartment was responsible for 84 ± 7 (0.5V_T,b) and 86 ± 5 % (V_T,b) on PEEP vs 81 ± 6 % (V_T,b) on ZEEP (P:ns) of the exhaled V_T, with τ ₁ of 0.50 ± 0.13 and 0.58 ± 0.17 s vs 0.35 ± 0.11 s, respectively; (b) only τ ₁ for V_T,b on PEEP differed significantly (P < 0.02) from the one on ZEEP, suggesting a slower initial emptying; (c) for the same PEEP, Vrec was higher with a higher volume (V_T,b) than at a lesser one (0.5V_T,b), reflecting the higher V_T.¶Conclusions: In mechanically ventilated ARDS patients: (a) the behavior of airway resistance seems to depend on the degree of the prevailing lung distension; (b) alveolar recruitment appears to be more important when higher tidal volumes are used during mechanical ventilation on PEEP; (c) PEEP changes the mechanical properties of the respiratory system fast-emptying compartment.     

The ALIEN study: incidence and outcome of acute respiratory distress syndrome in the era of lung protective ventilation

Purpose

While our understanding of the pathogenesis and management of acute respiratory distress syndrome (ARDS) has improved over the past decade, estimates of its incidence have been controversial. The goal of this study was to examine ARDS incidence and outcome under current lung protective ventilatory support practices before and after the diagnosis of ARDS.

Methods

This was a 1-year prospective, multicenter, observational study in 13 geographical areas of Spain (serving a population of 3.55 million at least 18?years of age) between November 2008 and October 2009. Subjects comprised all consecutive patients meeting American-European Consensus Criteria for ARDS. Data on ventilatory management, gas exchange, hemodynamics, and organ dysfunction were collected.

Results

A total of 255 mechanically ventilated patients fulfilled the ARDS definition, representing an incidence of 7.2/100,000?population/year. Pneumonia and sepsis were the most common causes of ARDS. At the time of meeting ARDS criteria, mean PaO₂/FiO₂ was 114?±?40?mmHg, mean tidal volume was 7.2?±?1.1?ml/kg predicted body weight, mean plateau pressure was 26?±?5?cmH₂O, and mean positive end-expiratory pressure (PEEP) was 9.3?±?2.4?cmH₂O. Overall ARDS intensive care unit (ICU) and hospital mortality was 42.7% (95%CI 37.7?C47.8) and 47.8% (95%CI 42.8?C53.0), respectively.

Conclusions

This is the first study to prospectively estimate the ARDS incidence during the routine application of lung protective ventilation. Our findings support previous estimates in Europe and are an order of magnitude lower than those reported in the USA and Australia. Despite use of lung protective ventilation, overall ICU and hospital mortality of ARDS patients is still higher than 40%.     

Prehospital Care of Burn Patients and Trajectories on Survival

We sought to identify factors associated with the prognosis and survival of burn patients by analyzing data related to the prehospital treatment of burn patients transferred directly to the burn unit from the accident site. We also aimed to assess the role of prehospital physicians and paramedics providing care to major burn patients. This study included adult burn patients with severe burns treated between 2006 and 2010. Prehospital patient records and clinical data collected during treatment were analyzed, and the Injury Severity Scale (ISS) was calculated. Patients were grouped into two cohorts based on the presence or absence of a physician during the prehospital phase. Data were analyzed with reference to survival by multivariable regression model. Specific inclusion criteria resulted in a sample of 67 patients. The groups were comparable with regard to age, gender, and injury etiology. Patients treated by prehospital physicians (group 1, n = 49) were more severely injured than patients treated by paramedics (group 2, n = 18) in terms of total burn surface area (%TBSA) (32% vs. 17%, p = 0.033), ISS (25 vs. 8, p < 0.000), and inhalation injuries (51% vs. 16%, p = 0.013), and presented with a higher pulse rate, lower systolic blood pressure, and lower median pH. Age, gender, %TBSA, and ISS were significantly associated with survival in both groups. Survival at 30 days was associated with age, gender, the amount of intravenous fluids (in liters) received during the first 24 hours, and the final %TBSA. Variables found to be independently associated by multivariable regression model with 30 day mortality were age, female gender, and final TBSA. We identified prehospital prognostic factors affecting patient outcomes. Based on the results from this study, our current EMS system is capable of identifying seriously injured burn patients who may benefit from physician attendance at the injury scene.     

Distribution of pulmonary blood flow in the perfluorocarbon-filled lung

Objective: Partial liquid ventilation (PLV) improves gas exchange in animal studies of lung injury. Perfluorocarbons (PFCs) are heavy liquids and are therefore preferentially delivered to the most dependent areas of lung. We hypothesised that improved oxygenation during PLV might be the consequence of a redistribution of pulmonary blood flow away from poorly ventilated, dependent alveoli, leading to improved ventilation/perfusion (V/Q) matching. This study investigated whether partially filling the lung with PFC would result in a redistribution of pulmonary blood flow.¶Design: Prospective experimental study.¶Setting: Hospital research institute laboratory.¶Participants: Six anaesthetised pigs without lung injury.¶Interventions: Animals were anaesthetised and ventilated (gas tidal volume 12 ml/kg, PEEP 5, FIO₂ 1.0, rate 16). Whilst the pigs were maintained in the supine position, regional pulmonary blood flow was measured during conventional gas ventilation and repeated during PLV. Flow to regions of lung was determined by injection of radioactive microspheres (Co⁵⁷, Sn¹¹³, Sc⁴⁶). Measurements were performed with ventilation held at end-expiratory pressure and, in two PLV animals only, repeated with ventilation held at peak inspiratory pressure.¶Results: During conventional gas ventilation, blood flow followed a linear distribution with the highest flow to the most dependent lung. In the lung partially filled with PFC a diversion of blood flow away from the most dependent lung was seen (p = 0.007), resulting in a more uniform distribution of flow down the lung (p = 0.006). Linear regression analysis (r ² = 0.75) also confirmed a difference in distribution pattern. On applying an inspiratory hold to the liquid-containing lung, blood flow was redistributed back towards the dependent lung.¶Conclusions: Partially filling the lung with PFC results in a redistribution of pulmonary blood flow away from the dependent region of the lung. During PLV a different blood flow distribution may be seen between inspiration and expiration. The clinical significance of these findings has yet to be determined.     

Risk factors for ventilator-associated pneumonia in trauma patients with torso injury: a retrospective single-center study

ObjectiveWe aimed to identify the risk factors for ventilator-associated pneumonia in patients admitted to critical care after a torso injury.MethodsWe retrospectively evaluated 178 patients with torso injury aged >15 years who were intubated in the emergency room and placed on a mechanical ventilator after intensive care unit (ICU) admission, survived for >48 hours, had thoracic and/or abdominal injuries, and had no end-stage renal disease. We compared clinico-laboratory variables between ventilator-associated pneumonia (n = 54, 30.3%) and non-ventilator-associated pneumonia (n = 124, 69.7%) groups. Risk factors for ventilator-associated pneumonia were assessed using multivariable logistic regression analysis.ResultsVentilator-associated pneumonia was associated with a significantly longer stay in the ICU (11.3 vs. 6.8 days) and longer duration of mechanical ventilation (7 vs. 3 days). Injury Severity Score (adjusted odds ratio [AOR]: 1.048; 95% confidence interval [CI]: 1.008–1.090), use of vasopressors (AOR: 2.541; 95% CI: 1.121–5.758), and insertion of a nasogastric tube (AOR: 6.749; 95% CI: 2.397–18.999) were identified as independent risk factors of ventilator-associated pneumonia.ConclusionVentilator-associated pneumonia in patients with torso injury who were admitted to the ICU was highly correlated with Injury Severity Score, use of vasopressors, and insertion of a nasogastric tube.     

Probability of survival,early critical care process,and resource use in trauma patients

Background

Trauma Injury Severity Score is a frequently used prediction model for mortality. However, few studies have assessed the probability of survival (Ps) and early resource use after trauma. We studied the impact of Ps on early critical care or costs to test its applicability to efficient trauma care.

Methods

The relationship between Ps in 8207 trauma patients and patients' demographics, organ injured, comorbidities, use of critical care, and total charges during the initial 48 hours was analyzed using multiple regression analyses.

Results

Significant differences were observed among study variables across different Ps. A large variability in total charges was observed and explained by critical care, which Ps was significantly associated with.

Conclusions

Trauma Injury Severity Score offers a tool for estimating resource use and might improve monitoring of early trauma care quality. Measuring the combined effect of Trauma Injury Severity Score and injured organs would refine the methodology for evaluating the trauma care system.     

Prognostic value of the pulmonary dead-space fraction during the first 6 days of acute respiratory distress syndrome

BACKGROUND: The ratio of pulmonary dead space to tidal volume (VD/VT) in acute respiratory distress syndrome (ARDS) is reported to be between 0.35 and 0.55. However, VD/VT has seldom been measured with consideration to the evolving pathophysiology of ARDS. METHODS: We made serial VD/VT measurements with 59 patients who required mechanical ventilation for > or = 6 days. We measured VD/VT within 24 h of the point at which the patient met the American-European Consensus Conference criteria for ARDS, and we repeated the VD/VT measurement on ARDS days 2, 3, and 6 with a bedside metabolic monitor during volume-regulated ventilation. We analyzed the changes in VD/VT over the 6-day period to determine whether VD/VT has a significant association with mortality. RESULTS: VD/VT was significantly higher in nonsurvivors on day 1 (0.61 +/- 0.09 vs 0.54 +/- 0.08, p < 0.05), day 2 (0.63 +/- 0.09 vs 0.53 +/- 0.09, p < 0.001), day 3 (0.64 +/- 0.09 vs 0.53 +/- 0.09, p < 0.001), and day 6 (0.66 +/- 0.09 vs 0.51 +/- 0.08, p < 0.001). CONCLUSION: In ARDS a sustained VD/VT elevation is characteristic of nonsurvivors, so dead-space measurements made beyond the first 24 hours may have prognostic value.