The decreasing incidence and mortality of acute respiratory distress syndrome after injury: a 5-year observational study

Prognostic factors for development of acute respiratory distress syndrome following traumatic injury - a systematic review and meta-analysis

PURPOSE

To summarise the prognostic associations between various clinical risk factors and the development of the acute respiratory distress syndrome (ARDS) following traumatic injury.

METHODS

We conducted this review in accordance with the PRISMA and CHARMS guidelines. We searched six databases from inception through December 2020. We included English language studies describing the clinical risk factors associated with the development of post-traumatic ARDS, as defined by either the American-European Consensus Conference or the Berlin definition. We pooled adjusted odds ratios for prognostic factors using the random effects method. We assessed risk of bias using the QUIPS tool and certainty of findings using GRADE methodology.

RESULTS

We included 39 studies involving 5 350 927 patients. We identified the amount of crystalloid resuscitation as a potentially modifiable prognostic factor associated with the development of post-traumatic ARDS (adjusted odds ratio [aOR] 1.19 for each additional liter of crystalloid administered within first 6 h after injury, 95% CI 1.15 to 1.24, high certainty). Non-modifiable prognostic factors with a moderate or high certainty of association with post-traumatic ARDS included increasing age, non-Hispanic white race, blunt mechanism of injury, presence of head injury, pulmonary contusion, or rib fracture; and increasing chest injury severity.

CONCLUSION

We identified one important modifiable factor, the amount of crystalloid resuscitation within the first 24 h of injury, and several non-modifiable factors associated with development of post-traumatic ARDS. This information should support the judicious use of crystalloid resuscitation in trauma patients and may inform the development of a risk-stratification tools.

Attributable mortality of acute respiratory distress syndrome: a systematic review, meta-analysis and survival analysis using targeted minimum loss-based estimation

BACKGROUND

Although acute respiratory distress syndrome (ARDS) is associated with high mortality, its direct causal link with death is unclear. Clarifying this link is important to justify costly research on prevention of ARDS.

OBJECTIVE

To estimate the attributable mortality, if any, of ARDS.

DESIGN

First, we performed a systematic review and meta-analysis of observational studies reporting mortality of critically ill patients with and without ARDS matched for underlying risk factor. Next, we conducted a survival analysis of prospectively collected patient-level data from subjects enrolled in three intensive care unit (ICU) cohorts to estimate the attributable mortality of critically ill septic patients with and without ARDS using a novel causal inference method.

RESULTS

In the meta-analysis, 44 studies (47 cohorts) involving 56 081 critically ill patients were included. Mortality was higher in patients with versus without ARDS (risk ratio 2.48, 95% CI 1.86 to 3.30; p<0.001) with a numerically stronger association between ARDS and mortality in trauma than sepsis. In the survival analysis of three ICU cohorts enrolling 1203 critically ill patients, 658 septic patients were included. After controlling for confounders, ARDS was found to increase the mortality rate by 15% (95% CI 3% to 26%; p=0.015). Significant increases in mortality were seen for severe (23%, 95% CI 3% to 44%; p=0.028) and moderate (16%, 95% CI 2% to 31%; p=0.031), but not for mild ARDS.

CONCLUSIONS

ARDS has a direct causal link with mortality. Our findings provide information about the extent to which continued funding of ARDS prevention trials has potential to impart survival benefit.

PROSPERO REGISTRATION NUMBER

CRD42017078313.

Noninvasive ventilation with a helmet in patients with acute respiratory failure caused by chest trauma: a randomized controlled trial

Noninvasive ventilation (NIV) is beneficial in acute respiratory failure (ARF) caused by chest trauma; however, NIV-related complications affect the efficacy. We evaluated whether NIV with helmet decreases the incidence of complications and improves its effects in a single center. Patients with ARF after chest trauma were randomized to receive NIV with helmet or face mask. The primary outcome was the rate of NIV-related complications. Secondary outcomes were PaO₂/FiO₂, patient’s tolerance, intubation rate, length of intensive care unit (ICU) stay, and ICU mortality. The trial was terminated early after an interim analysis with 59 patients. The incidence of complications was lower in the helmet group [10% (3/29) vs 43% (13/30), P = 0.004], and PaO₂/FiO₂s were higher at 1 h and at the end of NIV (253.14 ± 64.74 mmHg vs 216.06 ± 43.86 mmHg, 277.07 ± 84.89 mmHg vs 225.81 ± 63.64 mmHg, P = 0.013 and 0.012) compared with them in face mask group. More patients reported excellent tolerance of the helmet vs face mask after 4 h of NIV [83% (24/29) vs 47% (14/30), P = 0.004] and at the end of NIV [69% (20/29) vs 30% (9/30), P = 0.03]. Differences in intubation rate, ICU stay, and mortality were non-significant (P = 0.612, 0.100, 1.000, respectively). NIV with helmet decreased NIV-related complications, increased PaO₂/FiO₂, and improved tolerance compared with NIV with face mask in patients with chest trauma.

Trial registration: Registered in the Chinese Clinical Trial Registry (ChiCTR1900025915), a WHO International Clinical Trials Registry Platform (http://www.chictr.org.cn/searchprojen.aspx).

Predictors of postinjury acute respiratory distress syndrome: Lung injury persists in the era of hemostatic resuscitation

BACKGROUND

Acute respiratory distress syndrome (ARDS) following trauma is historically associated with crystalloid and blood product exposure. Advances in resuscitation have occurred over the last decade, but their impact on ARDS is unknown. We sought to investigate predictors of postinjury ARDS in the era of hemostatic resuscitation.

METHODS

Data were prospectively collected from arrival to 28 days for 914 highest-level trauma activations who required intubation and survived more than 6 hours from 2005 to 2016 at a Level I trauma center. Patients with ratio of partial pressure of oxygen to fraction of inspired oxygen of 300 mmHg or less during the first 8 days were identified. Two blinded expert clinicians adjudicated all chest radiographs for bilateral infiltrates in the first 8 days. Those with left-sided heart failure detected were excluded. Multivariate logistic regression was used to define predictors of ARDS.

RESULTS

Of the 914 intubated patients, 63% had a ratio of partial pressure of oxygen to fraction of inspired oxygen of 300 or less, and 22% developed ARDS; among the ARDS cases, 57% were diagnosed early (in the first 24 hours), and 43% later. Patients with ARDS diagnosed later were more severely injured (ISS 32 vs. 20, p = 0.001), with higher rates of blunt injury (84% vs. 72%, p = 0.008), chest injury (58% vs. 36%, p < 0.001), and traumatic brain injury (72% vs. 48%, p < 0.001) compared with the no ARDS group. In multivariate analysis, head/chest Abbreviated Injury Score scores, crystalloid from 0 to 6 hours, and platelet transfusion from 0 to 6 hours and 7 to 24 hours were independent predictors of ARDS developing after 24 hours.

CONCLUSIONS

Blood and plasma transfusion were not independently associated with ARDS. However, platelet transfusion was a significant independent risk factor. The role of platelets warrants further investigation but may be mechanistically explained by lung injury models of pulmonary platelet sequestration with peripheral thrombocytopenia.

LEVEL OF EVIDENCE

Prognostic study, level IV.

Nationwide cohort study of independent risk factors for acute respiratory distress syndrome after trauma

Background

The primary objective of this study was to evaluate the effect of specific direct and indirect factors that accounted, in trauma patients, for the development of acute respiratory distress syndrome (ARDS) and mortality in patients with ARDS.

Methods

We performed a retrospective cohort study of patients from the National Trauma Data Bank. Multilevel mixed-effects logistic regression was used with the development of ARDS as the primary and mortality in patients with ARDS as the secondary outcome measures. We compared trauma patients with versus without thoracic (direct) and extrathoracic (indirect) risk factors, using patient demographics, physiologic, and anatomic injury severity as covariates. Subset analysis was performed for patients with trauma-induced lung contusion (TILC) and for patients with minor (Injury Severity Score [ISS] ≤15) injury.

Results

A total of 2 998 964 patients were studied, of whom 28 597 developed ARDS. From 2011 to 2014, the incidence of ARDS decreased; however, mortality in patients with ARDS has increased. Predictors of ARDS included direct thoracic injury (TILC, multiple rib fractures, and flail chest), as well as indirect factors (increased age, male gender, higher ISS, lower Glasgow Coma Scale motor component score, history of cardiopulmonary or hematologic disease, and history of alcoholism or obesity). Patients with ARDS secondary to direct thoracic injury had a lower risk of mortality compared with patients with ARDS due to other mechanisms.

Discussion

Despite the decreasing incidence of trauma-induced ARDS, mortality in patients with ARDS has increased. Direct thoracic injury was the strongest predictor of ARDS. Knowing specific contributors to trauma-induced ARDS could help identify at-risk patients early in their hospitalization and mitigate the progression to ARDS and thereby mortality.

Level of evidence

Prognostic study, level III.

Thoracic trauma now and then: A 10 year experience from 16,773 severely injured patients

Background and purpose

Thoracic trauma remains to be a relevant injury to the polytraumatised patient. However, literature regarding how far changes in clinical guidelines for pre- and in-hospital trauma management and diagnostic procedures affect the outcome of multiple injured patients with severe chest injury during a long-term observation period is sparse.

Methods

Multiple traumatised patients (age≥16y) documented in the TraumaRegister DGU^® (TR-DGU) from January 1^st 2005 to December 31^st 2014 with severe chest trauma (AIS≥3) were included in this study. Demographic data, the pattern of injury, injury severity, radiographic emergency procedures, indication for intubation, duration of mechanical ventilation, emergency surgery, occurrence of complications and mortality were evaluated per year and over time.

Results

A total of 16,773 patients were analysed. The use of whole body computer tomography increased (p<0.001), while the incidence of plain x-rays decreased (p<0.001). Furthermore, incidence of AIS_Thorax = 3 graded injuries increased (p<0.001) while AIS_Thorax = 4 decreased (p<0.001). Both, rate of patients being intubated at the time of ICU admission decreased (p<0.001) and the time of mechanical ventilation decreased (p<0.001). Additionally, need for emergency surgery, lung failure, sepsis, and multi organ failure all decreased (p<0.001). However, mortality remained unchanged.

Interpretation

Severity of severe chest trauma and associated complications decreased while diagnostics and treatment improved over time. However, mortality remained unchanged. Our results are in line with those expected in the context of the incidence of CT diagnostics, which has increased parallel to the clinical outcome Thus, our data demonstrate a positive trend in the treatment of patients with severe chest trauma.

Permissive Hypotension and Trauma: Can Fluid Restriction Reduce the Incidence of ARDS?

Emergency care, including the resuscitation of patients involved in traumatic events, has evolved over the years. A prior practice of utilizing large volumes of crystalloids has been found to contribute to complications such as coagulopathy, fluid overload, and adult respiratory distress syndrome (ARDS). In contrast, permissive hypotension is a method of fluid restriction that allows for low blood pressure and mean arterial pressure during the resuscitation period. When permissive hypotension occurs and fluids are restricted in trauma patients, the incidence of ARDS can be reduced significantly with improvement in patient outcomes. Using evidence, nurse practitioners in the emergency department have an important role in evaluating and updating protocols such as permissive hypotension.

Thoracic trauma severity contributes to differences in intensive care therapy and mortality of severely injured patients: analysis based on the TraumaRegister DGU®

Background

Thoracic trauma is a relevant source of comorbidity throughout multiply-injured patient care. We aim to determine a measurable influence of chest trauma’s severity on early resuscitation, intensive care therapy, and mortality in severely injured patients.

Methods

Patients documented between 2002 and 2012 in the TraumaRegister DGU®, aged ≥ 16 years, injury severity score (ISS) ≥ 16 are analyzed. Isolated brain injury and severe head injury led to exclusion. Subgroups are formed using the Abbreviated Injury Scale_Thorax.

Results

Twenty-two thousand five hundred sixty-five patients were predominantly male (74%) with mean age of 45.7 years (SD 19.3), blunt trauma (95%), mean ISS 25.6 (SD 9.6). Overall mean intubation period was 5.6 days (SD 10.7). Surviving patients were discharged from the ICU after a mean of about 5 days following extubation. Thoracic trauma severity (AIS_Thorax ≥ 4) and fractures to the thoracic cage significantly prolonged the ventilation period. Additionally, fractures extended the ICU stay significantly. Suffering from more than one thoracic injury was associated with a mean of 1–2 days longer intubation period and longer ICU stay. Highest rates of sepsis, respiratory, and multiple organ failure occurred in patients with critical compared to lesser thoracic trauma severity.

Conclusion

Thoracic trauma severity in multiply-injured patients has a measurable impact on rates of respiratory and multiple organ failure, sepsis, mortality, time of mechanical ventilation, and ICU stay.

Incidence, risk factors, and mortality associated with acute respiratory distress syndrome in combat casualty care

BACKGROUND

The overall incidence and mortality of acute respiratory distress syndrome (ARDS) in civilian trauma settings have decreased over the past four decades; however, the epidemiology and impact of ARDS on modern combat casualty care are unknown. We sought to determine the incidence, risk factors, resource utilization, and mortality associated with ARDS in current combat casualty care.

METHODS

This was a retrospective review of mechanically ventilated US combat casualties within the Department of Defense Trauma Registry (formerly the Joint Theater Trauma Registry) during Operation Iraqi Freedom/Enduring Freedom (October 2001 to August 2008) for ARDS development, resource utilization, and mortality.

RESULTS

Of 18,329 US Department of Defense Trauma Registry encounters, 4,679 (25.5%) required mechanical ventilation; ARDS was identified in 156 encounters (3.3%). On multivariate logistic regression, ARDS was independently associated with female sex (odds ratio [OR], 2.62; 95% confidence interval [CI], 1.21-5.71; p = 0.02), higher military-specific Injury Severity Score (Mil ISS) (OR, 4.18; 95% CI, 2.61-6.71; p < 0.001 for Mil ISS ≥25 vs. <15), hypotension (admission systolic blood pressure <90 vs. ≥90 mm Hg; OR, 1.76; 95% CI, 1.07-2.88; p = 0.03), and tachycardia (admission heart rate ≥90 vs. <90 beats per minute; OR, 1.53; 95% CI, 1.06-2.22; p = 0.02). Explosion injury was not associated with increased risk of ARDS. Critical care resource utilization was significantly higher in ARDS patients as was all-cause hospital mortality (ARDS vs. no ARDS, 12.8% vs. 5.9%; p = 0.002). After adjustment for age, sex, injury severity, injury mechanism, Mil ISS, hypotension, tachycardia, and admission Glasgow Coma Scale score, ARDS remained an independent risk factor for death (OR, 1.99; 95% CI, 1.12-3.52; p = 0.02).

CONCLUSIONS

In this large cohort of modern combat casualties, ARDS risk factors included female sex, higher injury severity, hypotension, and tachycardia, but not explosion injury. Patients with ARDS also required more medical resources and were at greater risk of death compared with patients without ARDS. Thus, ARDS remains a significant complication in current combat casualty care.

LEVEL OF EVIDENCE

Prognostic/epidemiologic study, level III.

Acute Respiratory Distress Syndrome Incidence, but Not Mortality, Has Decreased Nationwide: A National Trauma Data Bank Study

Acute respiratory distress syndrome (ARDS) incidence is reported to have decreased in recent years. However, no large-scale study to date has exclusively examined ARDS in the critically injured. We sought to examine the national incidence of ARDS and its associated outcomes exclusively in adult trauma patients. The National Trauma Data Bank (NTDB) was queried to evaluate the incidence of ARDS and associated outcomes over a 6-year study period (2007–2012). Included patients were ≥18 years old, with at least one ventilator day, and complications recorded. ARDS-associated outcomes and complications were also analyzed. Mean age increased over the study period (48.1–51.4 years, P < 0.003). ARDS incidence decreased from 21.5 to 8.5 per cent (P < 0.001). Length of stay (LOS), intensive care unit LOS (ICU LOS), and ventilator days decreased over time. Mortality increased from 21.3 to 24.9 per cent (P < 0.002). Incidence of pneumonia and acute kidney injury increased marginally (39.5–40.9% and 11.4–12.3%, respectively). Sepsis trended down from 2007 to 2010, after which comparable NTDB data were not available. ARDS incidence in mechanically ventilated adult trauma patients has decreased significantly in recent years. We theorize this is likely attributable to improved critical care strategies. Unlike ARDS incidence, mortality in this patient population has not improved despite these advancements.

Reducing acute respiratory distress syndrome occurrence using mechanical ventilation

The standard treatment for acute respiratory distress syndrome (ARDS) is supportive in the form of low tidal volume ventilation applied after significant lung injury has already developed. Nevertheless, ARDS mortality remains unacceptably high (> 40%). Indeed, once ARDS is established it becomes refractory to treatment, and therefore avoidance is key. However, preventive techniques and therapeutics to reduce the incidence of ARDS in patients at high-risk have not been validated clinically. This review discusses the current data suggesting that preemptive application of the properly adjusted mechanical breath can block progressive acute lung injury and significantly reduce the occurrence of ARDS.

Misclassification of acute respiratory distress syndrome after traumatic injury: The cost of less rigorous approaches

BACKGROUND

Adherence to rigorous research protocols for identifying adult respiratory distress syndrome (ARDS) after trauma is variable. To examine how misclassification of ARDS may bias observational studies in trauma populations, we evaluated the agreement of two methods for adjudicating ARDS after trauma: the current gold standard, direct review of chest radiographs and review of dictated radiology reports, a commonly used alternative.

METHODS

This nested cohort study included 123 mechanically ventilated patients between 2005 and 2008, with at least one PaO2/FIO2 less than 300 within the first 8 days of admission. Two blinded physician investigators adjudicated ARDS by two methods. The investigators directly reviewed all chest radiographs to evaluate for bilateral infiltrates. Several months later, blinded to their previous assessments, they adjudicated ARDS using a standardized rubric to classify radiology reports. A κ statistics was calculated. Regression analyses quantified the association between established risk factors as well as important clinical outcomes and ARDS determined by the aforementioned methods as well as hypoxemia as a surrogate marker.

RESULTS

The κ was 0.47 for the observed agreement between ARDS adjudicated by direct review of chest radiographs and ARDS adjudicated by review of radiology reports. Both the magnitude and direction of bias on the estimates of association between ARDS and established risk factors as well as clinical outcomes varied by method of adjudication.

CONCLUSION

Classification of ARDS by review of dictated radiology reports had only moderate agreement with the current gold standard, ARDS adjudicated by direct review of chest radiographs. While the misclassification of ARDS had varied effects on the estimates of associations with established risk factors, it tended to weaken the association of ARDS with important clinical outcomes. A standardized approach to ARDS adjudication after trauma by direct review of chest radiographs will minimize misclassification bias in future observational studies.

LEVEL OF EVIDENCE

Diagnostic study, level II.

Differences in degree, differences in kind: characterizing lung injury in trauma

BACKGROUND

Acute lung injury following trauma remains a significant source of morbidity and mortality. Although multiple trauma studies have used hypoxemia without radiographic adjudication as a surrogate for identifying adult respiratory distress syndrome (ARDS) cases, the differences between patients with hypoxemia alone and those with radiographically confirmed ARDS are not well described in the literature. We hypothesized that nonhypoxemic, hypoxemic, and ARDS patients represent distinct groups with unique characteristics and predictors.

METHODS

Laboratory, demographic, clinical, and outcomes data were prospectively collected from 621 intubated, critically injured patients at an urban Level 1 trauma center from 2005 to 2013. Hypoxemia was defined as PaO2/FIO2 ratio of 300 or lower. ARDS was adjudicated using Berlin criteria, with blinded two-physician consensus review of chest radiographs. Group comparisons were performed by hypoxemia and ARDS status. Logistic regression analyses were performed to separately assess predictors of hypoxemia and ARDS.

RESULTS

Of the 621 intubated patients, 64% developed hypoxemia; 46% of these hypoxemic patients developed ARDS by chest radiograph. Across the three groups (no hypoxemia, hypoxemia, ARDS), there were no significant differences in age, sex, or comorbidities. However, there was an increase in severity of shock, injury, and chest injury by group, with corresponding trends in transfusion requirements and volume of early fluid administration. Outcomes followed a similar stepwise pattern, with pneumonia, multiorgan failure, length of intensive care unit stay, number of ventilator days, and overall mortality highest in ARDS patients. In multiple logistic regression, early plasma transfusion, delayed crystalloid administration, body mass index, and head and chest injury were independent predictors of hypoxemia, while head and chest injury, early crystalloid infusion, and delayed platelet transfusion were independent predictors of ARDS.

CONCLUSION

Hypoxemia and ARDS exist on a spectrum of respiratory dysfunction following trauma, with increasing injury severity profiles and resuscitation requirements. However, they also represent distinct clinical states with unique predictors, which require directed research approaches and targeted therapeutic strategies.

LEVEL OF EVIDENCE

Prognostic and epidemiologic study, level III.

Burn intensive care

As a result of continuous development in the treatment of burns, the LD50 (the burn size lethal to 50% of the population) for thermal injuries has risen from 42% total body surface area (TBSA) during the 1940s and 1950s to more than 90% TBSA for young thermally injured patients. This vast improvement in survival is due to simultaneous developments in critical care, advancements in resuscitation, control of infection through early excision, and pharmacologic support of the hypermetabolic response to burns. This article reviews these recent advances and how they influence modern intensive care of burns.

Benchmarking outcomes in the critically injured burn patient

OBJECTIVE

To determine and compare outcomes with accepted benchmarks in burn care at 6 academic burn centers.

BACKGROUND

Since the 1960s, US morbidity and mortality rates have declined tremendously for burn patients, likely related to improvements in surgical and critical care treatment. We describe the baseline patient characteristics and well-defined outcomes for major burn injuries.

METHODS

We followed 300 adults and 241 children from 2003 to 2009 through hospitalization, using standard operating procedures developed at study onset. We created an extensive database on patient and injury characteristics, anatomic and physiological derangement, clinical treatment, and outcomes. These data were compared with existing benchmarks in burn care.

RESULTS

Study patients were critically injured, as demonstrated by mean % total body surface area (TBSA) (41.2 ± 18.3 for adults and 57.8 ± 18.2 for children) and presence of inhalation injury in 38% of the adults and 54.8% of the children. Mortality in adults was 14.1% for those younger than 55 years and 38.5% for those aged 55 years and older. Mortality in patients younger than 17 years was 7.9%. Overall, the multiple organ failure rate was 27%. When controlling for age and % TBSA, presence of inhalation injury continues to be significant.

CONCLUSIONS

This study provides the current benchmark for major burn patients. Mortality rates, notwithstanding significant % TBSA and presence of inhalation injury, have significantly declined compared with previous benchmarks. Modern day surgical and medically intensive management has markedly improved to the point where we can expect patients younger than 55 years with severe burn injuries and inhalation injury to survive these devastating conditions.

Impact of distinct definitions of acute lung injury on its incidence and outcomes in Brazilian ICUs: prospective evaluation of 7,133 patients*

OBJECTIVES

Evaluation of prevalence and outcomes of acute lung injury in a large cohort of critically ill patients in Brazil and comparison of predictive receiver operating characteristic curve mortality of American European Consensus conference definition with new Berlin definition of acute respiratory distress syndrome.

DESIGN

A 15-month prospective, multicenter, observational study.

SETTING

Fourteen medical ICUs in Espirito Santo, a state of Brazil.

PATIENTS

Mechanically ventilated patients who fulfilled American European Consensus conference criteria of acute lung injury or Berlin definition of acute respiratory distress syndrome.

INTERVENTIONS

Clinical and respiratory data were collected for 7 consecutive days and on the 14 and 28 days. Twenty-eight day mortality, hospital mortality, and predictive receiver operating characteristic curve mortality were calculated.

MEASUREMENTS AND MAIN RESULTS

Of 7,133 patients, 130 patients (1.8%) fulfilled criteria for acute lung injury (American European Consensus conference) or acute respiratory distress syndrome (Berlin definition). Median time for diagnosis was 2 days (interquartile range, 0-3 d). Main risk factors were pneumonia (35.3%) and nonpulmonary sepsis (31.5%). Mean age was 44.2 ± 15.9 years, and 61.5% were men. Mean Acute Physiology and Chronic Health Evaluation II score was 20.7 ± 7.9. Mean PaO2/FIO2 was 206 ± 61.5, significantly lower in nonsurvivors on day 7 (p = 0.003). Mean mechanical ventilation time was 21 ± 15 days. Length of ICU stay was 26.4 ± 18.7 days. Twenty-eight-day mortality was 38.5% (95% CI, 30.1-46.8); hospital mortality was 49.2% (95% CI, 40.6-57.8). Predictive 28-day mortality area under the receiver operating characteristic curve for American European Consensus conference definition was 0.5625 (95% CI, 0.4783-0.6467) and for the Berlin definition 0.5664 (95% CI, 0.4759-0.6568; p = 0.9510).

CONCLUSIONS

In our population, prevalence of acute lung injury was low, most cases were diagnosed 2 days after ICU admission, and Berlin definition was not different from American European Consensus conference definition in predicting mortality. There are still several problems with the global epidemiology, definition, and mortality predictive indices that should be added to the classification of this still lethal syndrome to improve its predictive mortality power in the future.

Early application of airway pressure release ventilation may reduce mortality in high-risk trauma patients: a systematic review of observational trauma ARDS literature

BACKGROUND

Adult respiratory distress syndrome is often refractory to treatment and develops after entering the health care system. This suggests an opportunity to prevent this syndrome before it develops. The objective of this study was to demonstrate that early application of airway pressure release ventilation in high-risk trauma patients reduces hospital mortality as compared with similarly injured patients on conventional ventilation.

METHODS

Systematic review of observational data in patients who received conventional ventilation in other trauma centers were compared with patients treated with early airway pressure release ventilation in our trauma center. Relevant studies were identified in a PubMed and MEDLINE search from 1995 to 2012 and included prospective and retrospective observational and cohort studies enrolling 100 or more adult trauma patients with reported adult respiratory distress syndrome incidence and mortality data.

RESULTS

Early airway pressure release ventilation as compared with the other trauma centers represented lower mean adult respiratory distress syndrome incidence (14.0% vs. 1.3%) and in-hospital mortality (14.1% vs. 3.9%).

CONCLUSION

These data suggest that early airway pressure release ventilation may prevent progression of acute lung injury in high-risk trauma patients, reducing trauma-related adult respiratory distress syndrome mortality.

LEVEL OF EVIDENCE

Systematic review, level IV.

Noninvasive ventilation in chest trauma: systematic review and meta-analysis

PURPOSE

Single studies of Noninvasive Ventilation (NIV) in the management of acute respiratory failure in chest trauma patients have produced controversial findings. The aim of this study is to critically review the literature to investigate whether NIV reduces mortality, intubation rate, length of stay and complications in patients with chest trauma, compared to standard therapy.

METHODS

We performed a systematic review and meta-analysis of randomized controlled trials, prospective and retrospective observational studies, by searching PubMed, EMBASE and bibliographies of articles retrieved. We screened for relevance studies that enrolled adults with chest trauma who developed mild to severe acute respiratory failure and were treated with NIV. We included studies reporting at least one clinical outcome of interest to perform a meta-analysis.

RESULTS

Ten studies (368 patients) met the inclusion criteria and were included for the meta-analysis. Five studies (219 patients) reported mortality and results were quite homogeneous across studies, with a summary relative risk for patients treated with NIV compared with standard care (oxygen therapy and invasive mechanical ventilation) of 0.26 (95 % confidence interval 0.09-0.71, p = 0.003). There was no advantage in mortality of continuous positive airway pressure over noninvasive pressure support ventilation. NIV significantly increased arterial oxygenation and was associated with a significant reduction in intubation rate, in the incidence of overall complications and infections.

CONCLUSIONS

These results suggest that NIV could be useful in the management of acute respiratory failure due to chest trauma.

Prediction of pulmonary morbidity and mortality in patients with femur fracture

BACKGROUND

We aimed to determine the effect of femur fractures on mortality, pulmonary complications, and adult respiratory distress syndrome (ARDS). In addition, we aimed to compare the effect of femur fractures with other major musculoskeletal injuries and to determine the effect of timing to surgery on these complications.

METHODS

All patients were identified from the trauma registries of two Level I trauma centers. Outcomes were defined at mortality in hospital, pulmonary complications, and ARDS in hospital. Regression analysis was used to determine the effect of femur fractures, while controlling for age, Abbreviated Injury Scales, Glasgow Coma Scale, and systolic blood pressure at presentation. We compared femur fractures with other major musculoskeletal injuries in similar models. Within the patients with femur fracture, time to surgery (< 8 hours, 8 hours to 24 hours, and > 24 hours) was evaluated using similar regression analysis.

RESULTS

Of the total 90,510 patients, 3,938 (4.35%) died in the hospital, 2,055 (2.27%) had a pulmonary complication, and 285 (0.31%) developed ARDS. Femur fracture is statistically predictive of mortality (odds ratio [OR], 1.606; 95% confidence interval [CI], 1.288-2.002) and pulmonary complications (OR, 1.659; 95% CI, 1.329-2.070), when controlling for other injury factors. This was comparable with the effect of pelvic fracture and other major musculoskeletal injuries. Femur fracture had a strong relationship with ARDS (OR, 2.129; 95% CI, 1.382-3.278). Patients treated in the 8 hours to 24 hours window had the lowest mortality risk (OR, 0.140; 95% CI, 0.052-0.375), and there was a trend to increased risk of ARDS in a delay to surgery of > 24 hours.

CONCLUSIONS

Femur fractures are a major musculoskeletal injury and increase the risk of mortality and pulmonary complications as much as any other musculoskeletal injuries. There is a unique relationship between ARDS and femur fractures, and this must be considered carefully in treatment planning for these patients.

Impact of plasma transfusion in trauma patients who do not require massive transfusion

BACKGROUND

For trauma patients requiring massive blood transfusion, aggressive plasma usage has been demonstrated to confer a survival advantage. The aim of this study was to evaluate the impact of plasma administration in nonmassively transfused patients.

STUDY DESIGN

Trauma patients admitted to a Level I trauma center (2000-2005) requiring a nonmassive transfusion (<10 U packed RBC [PRBC] within 12 hours of admission) were identified retrospectively. Propensity scores were calculated to match and compare patients receiving plasma in the first 12 hours with those who did not.

RESULTS

The 1,716 patients (86.1% of 1,933 who received PRBC transfusion) received a nonmassive transfusion. After exclusion of 31 (1.8%) early deaths, 284 patients receiving plasma were matched to patients who did not. There was no improvement in survival with plasma transfusion (17.3% versus 14.1%; p = 0.30) irrespective of the plasma-to-PRBC ratio achieved. However, the overall complication rate was significantly higher for patients receiving plasma (26.8% versus 18.3%, odds ratio [OR] = 1.7; 95% CI, 1.1-2.4; p = 0.016). As the volume of plasma increased, an increase in complications was seen, reaching 37.5% for patients receiving >6 U. The ARDS rate specifically was also significantly higher in patients receiving plasma (9.9% versus 3.5%, OR = 3.0; 95% CI, 1.4-6.2; p = 0.004]. Patients receiving >6 U plasma had a 12-fold increase in ARDS, a 6-fold increase in multiple organ dysfunction syndrome, and a 4-fold increase in pneumonia and sepsis.

CONCLUSIONS

For nonmassively transfused trauma patients, plasma administration was associated with a substantial increase in complications, in particular ARDS, with no improvement in survival. An increase in multiple organ dysfunction, pneumonia, and sepsis was likewise seen as increasing volumes of plasma were transfused. The optimal trigger for initiation of a protocol for aggressive plasma infusion warrants prospective evaluation.

ACS trauma centre designation and outcomes of post-traumatic ARDS: NTDB analysis and implications for trauma quality improvement

BACKGROUND

Several authors have examined the relationship between outcomes following severe trauma and American College of Surgeons (ACS) trauma centre designation. Little is known, however, about the association between ACS level and outcomes following complications of trauma.

METHODS

The National Trauma Databank (NTDB, v. 5.0) was queried to identify adult (age > or =18) trauma patients developing post-traumatic ARDS, who were admitted to either ACS level 1 or level 2 trauma centres from 2000 to 2004. Patients transferred between institutions and injuries following burns were excluded. Univariate analysis was used to assess differences between those patients admitted to ACS level 1 and level 2 facilities. Adjusted mortality was derived using logistic regression analysis.

RESULTS

A total of 902 adult trauma patients with ARDS after 48 h of mechanical ventilation were identified from the NTDB. Five hundred and thirty six patients were admitted to a level 1 ACS verified centre and 366 to a level 2 facility. Univariate analysis revealed no statistical differences in clinical and demographic characteristics between the two groups. On univariate comparison, patients admitted to level 1 facilities had longer mean hospital and ICU length of stay and higher hospital related charges than level 2 counterparts. Patients admitted to a level 1 centre were, however, significantly more likely to achieve discharge to home. Using multivariate logistic regression, ACS level designation was shown to have no statistical effect on mortality. Hypotension on admission and age greater than 55 were the only independent predictors of mortality.

CONCLUSION

ACS trauma centre designation level is not an independent predictor of mortality following post-traumatic ARDS.

Analysis of clinical risk factors associated with the prognosis of severe multiple-trauma patients with acute lung injury

BACKGROUND

Several clinical risk factors have been reported to be associated with the prognosis of acute lung injury (ALI). However, these studies have included a general trauma patient population, without singling out the severely injured multiple-trauma patient population.

OBJECTIVES

To identify the potential risk factors that could affect the prognosis of ALI in multiple-trauma patients and investigate the prognostic effects of certain risk factors among different patient subpopulations.

METHODS

In this retrospective cohort study, severely injured multiple-trauma patients with early onset of ALI from several trauma centers were studied. Potential risk factors affecting the prognosis of ALI were examined by univariate and multivariate logistic analyses.

RESULTS

There were 609 multiple-trauma patients with ALI admitted to the emergency department and emergency intensive care unit during the study period. The nine risk factors that affected prognosis, as indicated by the unadjusted odds ratios with 95% confidence intervals, were the APACHE II (Acute Physiology and Chronic Health Evaluation II) score, duration of trauma, age, gastrointestinal hemorrhage, pulmonary contusion, disseminated intravascular coagulation (DIC), multiple blood transfusions in 6 h, Injury Severity Score (ISS), and aspiration of gastric contents. Specific risk factors also affected different patient subpopulations in different ways.

CONCLUSIONS

Patients older than 65 years and with multiple (> 10 units) blood transfusions in the early stage after multiple trauma were found to be independent risk factors associated with deterioration of ALI. The other factors studied, including pulmonary contusion, APACHE II score ≥ 20, ISS ≥ 16, gastrointestinal hemorrhage, and aspiration of gastric contents, may predict the unfavorable prognosis of ALI in the early stage of trauma, with their effects attenuating in the later stage. Duration of trauma ≥ 1 h and the presence of DIC may also indicate unfavorable prognosis during the entire treatment period.

A 6-year review of total parenteral nutrition use and association with late-onset acute respiratory distress syndrome among ventilated trauma victims

AIM

To establish whether total parenteral nutrition (TPN) for ventilated trauma victims is associated with late-onset acute respiratory distress syndrome (ARDS) independent of ventilation and transfusion parameters.

METHOD

Intensive care unit data over 6 years from a level I centre regarding all trauma victims > or = 16 years old who underwent mechanical ventilation within the first 48 h of admission were examined. Patients were prospectively followed for late ARDS. Variables were examined for significant changes over time and independent associations with late ARDS were determined.

RESULTS

Of 2346 eligible patients among whom 404 (17.2%) were exposed to TPN, 192 (8.2%) met criteria for late ARDS. The incidence of late ARDS among those exposed to TPN was 28.7% (116/404) compared with 3.9% (76/1942) among those not so exposed. Adjustments for potential confounding associated risk factors were made.

CONCLUSIONS

TPN administration is independently associated with late ARDS, and its use among critically ill trauma victims should be carefully scrutinised.

Predefined massive transfusion protocols are associated with a reduction in organ failure and postinjury complications

INTRODUCTION

Massive transfusion (MT) protocols have been shown to improve survival in severely injured patients. However, others have noted that these higher fresh frozen plasma (FFP):red blood cell (RBC) ratios are associated with increased risk of organ failure. The purpose of this study was to determine whether MT protocols are associated with increased organ failure and complications.

METHODS

Our institution's exsanguination protocol (TEP) involves the immediate delivery of products in a 3:2 ratio of RBC:FFP and 5:1 for RBC:platelets. All patients receiving TEP between February 2006 and January 2008 were compared with a cohort (pre-TEP) of all patients from February 2004 to January 2006 that (1) went immediately to the operating room and (2) received MT (>or=10 units of RBC in first 24 hours).

RESULTS

Two hundred sixty-four patients met inclusion (125 in the TEP group, 141 in the pre-TEP). Demographics and Injury Severity Score were similar. TEP received more intraoperative FFP and platelets but less in first 24 hours (p < 0.01). There was no difference in renal failure or systemic inflammatory response syndrome, but pneumonia, pulmonary failure, open abdomens, and abdominal compartment syndrome were lower in TEP. In addition, severe sepsis or septic shock and multiorgan failure were both lower in the TEP patients (9% vs. 20%, p = 0.011 and 16% vs. 37%, p < 0.001, respectively).

CONCLUSIONS

Although MT has been associated with higher organ failure and complication rates, this risk appears to be reduced when blood products are delivered early in the resuscitation through a predefined protocol. Our institution's TEP was associated with a reduction in multiorgan failure and infectious complications, as well as an increase in ventilator-free days. In addition, implementation of this protocol was followed by a dramatic reduction in development of abdominal compartment syndrome and the incidence of open abdomens.

The impact of clinical risk factors in the conversion from acute lung injury to acute respiratory distress syndrome in severe multiple trauma patients

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are different stages of the same disease, the aggravated stage of ALI leading to ARDS. Patients with ARDS have higher hospital mortality rates and reduced long-term pulmonary function and quality of life. It is, therefore, important to prevent ALI converting to ARDS. This study evaluated 17 risk factors potentially associated with the conversion from ALI to ARDS in severe multiple trauma. The results indicate that the impact of pulmonary contusion, APACHE II score, gastrointestinal haemorrhage and disseminated intravascular coagulation may help to predict conversion from ALI to ARDS in the early phase after multiple-trauma injury. Trauma duration, in particular, strongly impacted the short- and long-term development of ALI. Being elderly (aged > or = 65 years) and undergoing multiple blood transfusions in the early phase were independent risk factors correlated with secondary sepsis, deterioration of pulmonary function and transfusion-related acute lung injury due to early multiple fluid resuscitation.

Haemorrhagic shock therapy

BACKGROUND

Severe injury is often associated with haemorrhagic shock and this is the most common cause of preventable mortality after injury. Care of the injured patient in shock involves an overlapping continuum of care beginning during the prehospital phase of care and extending through the interventional and critical care phases.

OBJECTIVE

This study aimed to review emerging therapies in the treatment of haemorrhagic shock.

METHODS

A review of recent clinical articles (1996 - 2007) examining therapeutic measures for haemorrhagic shock treatment was undertaken.

CONCLUSIONS

Although the mainstay of therapy continues to be obtaining haemostasis and restoring tissue perfusion, a multitude of novel strategies are emerging, including advanced haemostatic agents, hypertonic resuscitation and massive transfusion protocols, as well as blood substitutes and an improved understanding of damage control principles, thereby allowing increased survival and improved outcomes in the severely injured patient with major haemorrhage.

The analysis of risk factors of impacting mortality rate in severe multiple trauma patients with posttraumatic acute respiratory distress syndrome

OBJECTIVE

We hypothesize that not all of the traditional risk factors of impacting mortality rate in commonly traumatic populations with posttraumatic acute respiratory distress syndrome (ARDS) are independently associated with those patient populations identified with severe multiple trauma. Rather, we postulate that there may exist significantly different impacting degrees of specific risk factors in stratified patients (surviving beyond 24 and 96 hours)--more severe multiple trauma with higher injury score and long-term mechanical ventilation as well.

METHODS

This is a retrospective cohort study regarding trauma as a single cause for emergency intensive care unit admission. Twenty-two items of potential risk factors of impacting mortality rate were calculated by univariate and multivariate logistic analyses to find distinctive items in these severe multiple trauma patients.

RESULTS

The unadjusted odds ratio and 95% confidence intervals of mortality rate were found to be associated with 6 (out of 22) risk factors, namely, (1) Acute Physiology and Chronic Health Evaluation II score, (2) duration of trauma factor, (3) aspiration of gastric contents, (4) sepsis, (5) pulmonary contusion, and (6) duration of mechanical ventilation. Significant results also appeared in stratified patients.

CONCLUSIONS

Impact of pulmonary contusion and Acute Physiology and Chronic Health Evaluation II score contributing to prediction of mortality may exist in the early phase after trauma. Sepsis is still a vital risk factor referring to systemic inflammatory response syndrome, infection, secondary multiple organ dysfunction, etc. Discharging trauma factors as early as possible becomes the critical therapeutic measure. Aspiration of gastric contents in emergency intensive care unit admission could lead to incremental mortality rate due to aspiration pneumonia. Long-standing mechanical ventilation should be constrained because it is likely to cause severe refractory complications.

Leukoreduction is Associated with a Decreased Incidence of Late Onset Acute Respiratory Distress Syndrome after Injury

Transfusions are known to be associated with Acute Respiratory Distress Syndrome (ARDS). Transfusion of leukoreduced products may be associated with a decreased incidence of late posttraumatic ARDS (late ARDS). Data from ventilated and transfused trauma patients were analyzed. Key variables in the first 48 hours of admission were studied for their associations with late ARDS and examined for changes over the 6 year study period. Late ARDS developed in 244 of the 1488 patients studied (16.4%). The incidence in patients given nonleukoreduced (NLR) product was 30.4 per cent (75/247) versus 13.6 per cent (169/1241) for patients not exposed [2.77 (2.02–3.73), P < 0.001]. Exposure to NLR products (50.9% in 2000 vs 1.9% in 2005) and incidence of ARDS (26.3% in 2000 vs 6.3% in 2005) significantly decreased. Treatment variables independently associated with late ARDS were NLR product exposure, Total Parenteral Nutrition exposure, Peak Inspiratory Pressure ≥ 30 mm Hg, fluid balance ≥ 2 liters at 48 hours, and transfusion of ≥ 10 units of any product. NLR product exposure has an association with an increased incidence of late onset posttraumatic ARDS which is independent of large volume transfusions. Leukoreduction should be routinely included in an overall treatment strategy to furthermore mitigate this complication in critically ill trauma patients.

The presence of the adult respiratory distress syndrome does not worsen mortality or discharge disability in blunt trauma patients with severe traumatic brain injury

PURPOSE

To evaluate the prevalence of the acute respiratory distress syndrome (ARDS) among blunt trauma patients with severe traumatic brain injury (TBI) and to determine if ARDS is associated with higher mortality, morbidity and worse discharge outcome.

METHODS

Blunt trauma patients with TBI (head abbreviated injury score (AIS)> or =4) who developed predefined ARDS criteria between January 2000 and December 2004 were prospectively collected as part of an ongoing ARDS database. Each patient in the TBI+ARDS group was matched with two control TBI patients based on age, injury severity score (ISS) and head AIS. Outcomes including complications, mortality and discharge disability were compared between the two groups.

RESULTS

Among 362 TBI patients, 28 (7.7%) developed ARDS. There were no differences between the two groups with respect to age, sex, ISS, Glasgow coma score (GCS), head, abdomen and extremity AIS. The TBI+ARDS group had significantly more patients with chest AIS> or =3 (57.1% versus 32.1%, p=0.03). There was no difference with respect to overall mortality between the TBI+ARDS group (50.0%) and the TBI group (51.8%) (OR 0.79: 95% CI 0.31-2.03, p=0.63). There was no significant difference with respect to discharge functional capacity between the two groups. There were significantly more overall complications in the TBI+ARDS group (42.9%) compared to the TBI group (16.1%) (OR 3.66: 95% CI 1.19-11.24, p=0.02). The TBI+ARDS group had an overall mean intensive care unit (ICU) length of stay of 15.6 days, versus 8.4 days in the TBI group (p<0.01). The TBI+ARDS group had significantly higher hospital charges than the TBI group ($210,097 versus $115,342, p<0.01).

CONCLUSION

The presence of ARDS was not associated with higher mortality or worse discharge disability. It was, however, associated with higher hospital morbidity, longer ICU and hospital length of stay.

Prevention and treatment of post-traumatic acute respiratory distress syndrome

Post-Traumatic Acute Respiratory Distress Syndrome (ARDS) is a major cause of morbidity and mortality in the acutely injured patient. The American-European Consensus Conference Report established the most widely accepted definition of ARDS in 1994. In recent years it appears the incidence and impact of the disease are on the decline. This article reviews strategies to prevent and treat post-traumatic ARDS. Well-accepted, proven strategies include lung protective ventilation strategies, as well as conservative transfusion and crystalloid resuscitation policies and the adoption of leukoreduction techniques. Other modalities including hypertonic saline resuscitation, use of albumin and diuretics, positive end expiratory pressure, high-frequency ventilation, prone positioning, recruitment maneuvers, extracorporeal membrane oxygenation, corticosteroids, exogenous surfactant, and inhaled nitric oxide are also reviewed.

Abdominal insufflation for control of bleeding after severe splenic injury

BACKGROUND

To date, there is no rapid method to control intracavitary bleeding without an operation. Over 70% of trauma deaths from uncontrollable internal bleeding occur early after injury before an operation is feasible. Abdominal insufflation (AI) by carbon dioxide has been shown to reduce the rate of bleeding after intra-abdominal injury in pigs. The concept was proven in highly lethal models of severe vascular and liver injuries. Similar injuries in humans would result in immediate exsanguination and low likelihood for any intervention. We hypothesized that AI would similarly reduce bleeding in a model of moderate but persistent bleeding from a splenic injury. This model represents a clinically relevant scenario of continuous bleeding, which does not kill the patient immediately but may ultimately result in death if not managed early.

METHODS

A new model of splenic injury was applied on 19 pigs, randomized to standard resuscitation (SR, N = 10) or standard resuscitation with AI to 20 cm H2O (SRAI, N = 9). For 30 minutes, the pigs were bled and the hemodynamics recorded. At 30 minutes, the abdomen was opened and free blood was collected and measured. Outcomes were blood loss, mean arterial pressure, hemoglobin, lactate levels, and arterial blood gases at the end of the experiment.

RESULTS

All pigs survived to the end of the experiment. Blood loss was lower (1,114 +/- 486 mL vs. 666 +/- 323 mL, p = 0.03) and final mean arterial pressure higher (64 +/- 12 mm Hg vs. 54 +/- 8 mm Hg, p = 0.04) in SRAI when compared with those in SR animals. Heart rate, arterial blood gases, oxygen saturation, hemoglobin, and lactate levels were similar in the two groups, except there was a more acidotic pH among SRAI animals (7.27 +/- 0.06 vs. 7.47 +/- 0.21, p = 0.02).

CONCLUSIONS

AI is a novel method to control intra-abdominal bleeding temporarily. With proper portable instruments and first-responder training, this is a technique that can potentially be used in the field to save lives from intra-abdominal exsanguination.

The decreasing incidence of late posttraumatic acute respiratory distress syndrome: the potential role of lung protective ventilation and conservative transfusion practice

BACKGROUND

A reduction in the incidence of posttraumatic Acute Respiratory Distress Syndrome (ARDS) has been demonstrated. It is hypothesized that ventilation strategies and restrictive transfusion policies are contributory. The purpose of this study is to examine the changes in ventilation and transfusion parameters over time and their associations with late posttraumatic ARDS.

METHODS

The surgical intensive care unit and blood bank databases from a Level I center during a 6-year period were analyzed. All mechanically ventilated trauma patients were screened for ARDS with onset after 48 hours of admission (late ARDS). Demographic, injury, resuscitation, ventilation parameters, and transfusion data were extracted. Variables were analyzed for significant changes during the duration of the study, and independent associations with ARDS were determined.

RESULTS

There were 2,346 eligible patients and 192 (8.2%) of them met criteria for late ARDS. There was a significant decrease in the incidence of late ARDS by year (14.9% in 2000 to 3.8% in 2005). When comparing the first and second half of the study, there was a significant decrease in the percentage of patients transfused with packed red blood cells (49.0% versus 40.7%), patients with a peak inspiratory pressure > or = 30 mm Hg (64.9% versus 50.1%), and patients ventilated with a tidal volume/kg > or = 10 mL/kg (39.6% versus 21.8%). Early transfusions, peak inspiratory pressure > or = 30 mm Hg, and fluid balance > or = 2 L in the first 48 hours of admission were independently associated with ARDS.

CONCLUSIONS

The increasing use of restrictive transfusion policies and ventilation strategies that potentially limit elevations in early peak inspiratory pressures are associated with a decreased incidence of late posttraumatic ARDS.

New developments in fluid resuscitation

Hemorrhagic shock is the leading cause of death in civilian and military trauma. Effective hemorrhage control and optimal resuscitation are the main goals in the management of severely injured patients. This article addresses the changing trends in fluid resuscitation in regards to who, when, and how. Much of these changing trends are caused by the recognition that the current method of resuscitation with crystalloid fluids may not be optimal and may even have detrimental consequences. This article summarizes a number of studies that have evaluated the cellular toxicities of commonly used resuscitation fluids, to highlight the need for the development of new fluids.

Severe respiratory failure: advanced treatment options

BACKGROUND

Severe respiratory failure (including acute lung injury and acute respiratory distress syndrome) continues to be associated with significant mortality and morbidity in patients of all ages.

OBJECTIVE

To review the laboratory and clinical data in support of and future directions for the advanced treatment of severe respiratory failure.

DATA SOURCES

MEDLINE/PubMed search of all relevant primary and review articles.

DATA SYNTHESIS

Our understanding of lung pathophysiology and the role of ventilator-induced lung injury through basic science investigation has led to advances in lung protective strategies for the mechanical ventilation support of patients with severe respiratory failure. Specific modalities reviewed include low-tidal volume ventilation, permissive hypercapnia, the open lung approach, recruitment maneuvers, airway pressure release ventilation, high-frequency oscillatory ventilation, prone positioning, and extracorporeal life support. The pharmacologic strategies (including corticosteroids, surfactant, and nitric oxide) investigated for the treatment of severe respiratory failure are also reviewed.

CONCLUSION

In patients with severe respiratory failure, an incremental approach to the management of severe hypoxemia requires implementation of the strategies reviewed, with knowledge of the evidence base to support these strategies.

Regional differences in nitric oxide-mediated vasorelaxation in porcine pulmonary arteries

BACKGROUND

Several previous investigations have shown improved oxygenation when ventilator-treated patients with acute lung injury are turned prone. In a previous human study, we demonstrated higher Ca(2+)-dependent nitric oxide synthase (NOS) activity in dorsal than in ventral parts of the lung. The current investigation was designed to determine whether Ca(2+)-dependent NOS activity was different in dorsal and ventral porcine lung regions. In addition, possible differences in vascular responses to nitroprusside or secondary to acetylcholine- or bradykinin-stimulated NO production were studied in dorsal and ventral pulmonary arteries.

METHODS

In the study, 20 pigs were used. Lung biopsies and pulmonary arterial rings were harvested from ventral and dorsal lung regions. NOS activity was determined by citrulline assay in the presence and absence of the calcium chelator ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EDTA) to discriminate between Ca(2+)-dependent and Ca(2+)-independent NOS activity. In organ baths, in submaximally contracted arterial rings, vasorelaxation induced by acetylcholine, bradykinin and nitroprusside was measured.

RESULTS

Ca(2+)-dependent NOS activity was higher in dorsal parts (87.2 +/- 9.1 citrulline units) than in ventral parts (62.2 +/- 10.1 citrulline units, P < 0.05) of porcine lung. There was a greater relaxation in dorsal than in ventral pulmonary arterial rings induced by both acetylcholine and bradykinin. Nitroprusside relaxed both sites equally.

CONCLUSIONS

Our results show that endothelial-derived NO is an important factor influencing the differences between dorsal and ventral lung regions in vasorelaxing activity in porcine pulmonary arteries. This finding provides an explanation for the improved oxygenation when patients with severe acute lung insufficiency are turned prone.