Prospective, randomized, controlled clinical trial comparing traditional versus reduced tidal volume ventilation in acute respiratory distress syndrome patients

A description of intraoperative ventilator management and ventilation strategies in hypoxic patients

BACKGROUND

Hypoxia is a common finding in the anesthetized patient. Although there are a variety of methods to address hypoxia, it is not well documented what strategies are used by anesthesiologists when faced with a hypoxic patient. Studies have identified that lung protective ventilation strategies have beneficial effects in both oxygenation and mortality in acute respiratory distress syndrome. We sought to describe the ventilation strategies in anesthetized patients with varying degrees of hypoxemia as defined by the Pao(2) to fraction of inspired oxygen (Fio(2)) (P/F) ratio.

METHODS

We conducted a review of all operations performed between January 1, 2005, and July 31, 2009, using a general anesthetic, excluding cardiac and thoracic procedures, to assess the ventilation settings that were used in patients with different P/F ratios. Patients older than 18 years who received a general anesthetic were included. Four cohorts of arterial blood gases (ABGs) were identified with P/F >300, 300 > or = P/F > 200, 200 > or = P/F > 100, 100 > or = P/F. Using the standard predicted body weight (PBW) equation, we calculated the milliliters per kilogram (mL/kg PBW) with which the patient's lungs were being ventilated. Positive end-expiratory pressure (PEEP), peak inspiratory pressures (PIPs), Fio(2), oxygen saturation (Sao(2)), and tidal volume in mL/kg PBW were compared.

RESULTS

A total of 28,706 ABGs from 11,445 operative cases met criteria for inclusion. There were 19,679 ABGs from the P/F >300 group, 5364 ABGs from the 300 > or = P/F > 200 group, 3101 ABGs from the 200 > or = P/F > 100 group, and 562 ABGs from the 100 > or = P/F group identified. A comparison of ventilation strategies found statistical significance but clinically irrelevant differences. Tidal volumes ranged between 8.64 and 9.16 and the average PEEP varied from 2.5 to 5.5 cm H(2)O. There were substantial differences in the average Fio(2) and PIP among the groups, 59% to 91% and 22 to 29 cm H(2)O, respectively.

CONCLUSION

Similar ventilation strategies in mL/kg PBW and PEEP were used among patients regardless of P/F ratio. The results of this study suggest that anesthesiologists, in general, are treating hypoxemia with higher Fio(2) and PIP. The average Fio(2) and PIP were significantly escalated depending on the P/F ratio.

Clinical application of ventilator modes: Ventilatory strategies for lung protection

INTRODUCTION

Identification of the mortality reducing effect of lung protective ventilation using low tidal volumes and pressure limitation is one of the biggest advances in the application of mechanical ventilation. Yet studies continue to demonstrate low adoption of this style of ventilation. Critical care nurses in Australia and New Zealand have a high level of responsibility and autonomy for mechanical ventilation and weaning practices and therefore require in-depth knowledge of ventilator technology, its clinical application and the current evidence for effective ventilation strategies.

AIM

To present an overview of current knowledge and research relating to lung protective ventilation.

METHOD

A multidatabase literature search using the terms protective ventilation, open lung, high frequency oscillatory ventilation, airway pressure release ventilation, and weaning.

RESULTS

Based on clinical trials and physiological evidence lung protective strategies using low tidal volumes and moderate levels of PEEP have been recommended as strategies to prevent tidal alveolar collapse and overdistension in patients with ALI/ARDS. Evidence now suggests these strategies may also be beneficial in patients with normal lungs. Lung protective ventilation may be applied with either volume or pressure-controlled ventilation. Pressure-controlled ventilation allows regulation over injurious peak inspiratory pressures; however no study has identified the superiority of pressure-controlled ventilation over low tidal volume strategies using volume-control. Other lung protective ventilation strategies include moderate to high positive-end expiratory pressure, recruitment manoeuvres, high frequency oscillatory ventilation, and airway pressure release ventilation though definitive trials identifying consistently improved patient outcomes are still needed. No ventilation strategy can be more lung protective than the timely discontinuation of mechanical ventilation. Despite the above recommendations, evidence suggests the decision to commence weaning and attempt extubation continue to be delayed. Critical care nurses play a vital role in the recognition of patients capable of spontaneous breathing and ready for extubation. Organisational interventions such as weaning protocols as well as computerised weaning systems may have less effect when nurses are able to manage weaning processes effectively.

CONCLUSIONS

Lung protective ventilatory strategies are not consistently applied and weaning and extubation continue to be delayed. Critical care nurses need to establish a strong knowledge base to promote effective and appropriate management of patients requiring mechanical ventilation.

Positive end-expiratory pressure-induced functional recruitment in patients with acute respiratory distress syndrome

OBJECTIVE

In acute respiratory distress syndrome, alveolar recruitment improves gas exchange only if perfusion of the recruited alveolar units is adequate. To evaluate functional recruitment induced by positive end-expiratory pressure, we assessed pulmonary conductance for gas exchange based on lung diffusion for carbon monoxide and its components, including pulmonary capillary blood volume.

DESIGN

Prospective, randomized, crossover study.

SETTING

Medical intensive care unit of a university hospital.

PATIENTS

Sixteen patients with lung injury/acute respiratory distress syndrome as well as eight control patients under invasive ventilation and eight healthy volunteers.

INTERVENTIONS

Mechanical ventilation with two levels of positive end-expiratory pressure (5 and 15 cm H2O).

MEASUREMENTS AND MAIN RESULTS

Lung diffusion for carbon monoxide and lung volumes, arterial blood gas analysis, and pressure-volume curves. In patients with acute respiratory distress syndrome, high positive end-expiratory pressure induced a 23% mean lung diffusion for carbon monoxide increase (4.4 +/- 1.7 mm Hg . min vs. 3.6 +/- 1.4 mL . mm Hg . min). In control patients and in healthy volunteers, lung diffusion for carbon monoxide values were (median [interquartile range]) 5.5 [3.8-8.0] mm Hg . min and 19.6 [15.1-20.6] mL . mm Hg . min, respectively. Among patients with acute respiratory distress syndrome, eight showed a >20% lung diffusion for carbon monoxide increase (responders) when increasing positive end-expiratory pressure. In the other eight, lung diffusion for carbon monoxide decreased or showed a <5% increase (nonresponders) with high positive end-expiratory pressure. Compared with nonresponders, responders at low positive end-expiratory pressure had smaller lungs with higher capillary blood volume-to-lung-volume ratio, higher values of the lower inflection point, and significantly greater increases in pulmonary capillary blood volume with high positive end-expiratory pressure. High positive end-expiratory pressure increased PaO2/Fio2 only in the responders.

CONCLUSIONS

The functional response to positive end-expiratory pressure in patients with acute lung injury/acute respiratory distress syndrome seems better when the lungs are smaller and with a higher capillary blood-volume-to-lung-volume ratio. Lung diffusion for carbon monoxide measurement supplies additional information about functional lung recruitment, which is not synonymous with mechanical recruitment.

Acute lung injury after thoracic surgery

In this review, the authors discussed criteria for diagnosing ALI; incidence, etiology, preoperative risk factors, intraoperative management, risk-reduction strategies, treatment, and prognosis. The anesthesiologist needs to maintain an index of suspicion for ALI in the perioperative period of thoracic surgery, particularly after lung resection on the right side. Acute hypoxemia, imaging analysis for diffuse infiltrates, and detecting a noncardiogenic origin for pulmonary edema are important hallmarks of acute lung injury. Conservative intraoperative fluid administration of neutral to slightly negative fluid balance over the postoperative first week can reduce the number of ventilator days. Fluid management may be optimized with the assistance of new imaging techniques, and the anesthesiologist should monitor for transfusion-related lung injuries. Small tidal volumes of 6 mL/kg and low plateau pressures of < or =30 cmH2O may reduce organ and systemic failure. PEEP may improve oxygenation and increases organ failure-free days but has not shown a mortality benefit. The optimal mode of ventilation has not been shown in perioperative studies. Permissive hypercapnia may be needed in order to reduce lung injury from positive-pressure ventilation. NO is not recommended as a treatment. Strategies such as bronchodilation, smoking cessation, steroids, and recruitment maneuvers are unproven to benefit mortality although symptomatically they often have been shown to help ALI patients. Further studies to isolate biomarkers active in the acute setting of lung injury and pharmacologic agents to inhibit inflammatory intermediates may help improve management of this complex disease.

[Acute lung injury and acute respiratory distress syndrome--what should we know?]

Acutelunginjury (ALI) and its more severe form acute respiratory distress syndrome (ARDS) are syndromes with a spectrum of increasing severity of lung injury defined by physiologic and radiographic criteria. There are many clinical disorders as sociated with the development of ALI/ARDS and can be divided into those associated with direct or indirect lung injury. Early detection and protective lung ventilation strategy contribute to lowering the mortality rate.

What's new in critical care of the burn-injured patient?

The number of cases of mortality after burn injury continues to decline, in part because of advances in respiratory, fluid, and sepsis management. However, care needs to be exercised in the application of these new techniques and technologies, many of which have never been assessed or have been incompletely studied in patients who have burn injury. Use of any of these advances in critical care needs to be individualized for any given patient and altered based on the patient's response to therapy. Future advances in the critical care of burns will require multicenter prospective trials at dedicated burn centers to define the optimal therapy for the patient who has burn injury.

Effect of tidal volume in children with acute hypoxemic respiratory failure

OBJECTIVES

To determine if tidal volume (VT) between 6 and 10 ml/kg body weight using pressure control ventilation affects outcome for children with acute hypoxemic respiratory failure (AHRF) or acute lung injury (ALI). To validate lung injury severity markers such as oxygenation index (OI), PaO2/FiO2 (PF) ratio, and lung injury score (LIS).

DESIGN

Retrospective, January 2000-July 2007.

SETTING

Tertiary care, 20-bed PICU.

PATIENTS

Three hundred and ninety-eight endotracheally intubated and mechanically ventilated children with PF ratio <300. Outcomes were mortality and 28-day ventilator free days.

MEASUREMENTS AND MAIN RESULTS

Three hundred and ninety-eight children met study criteria, with 20% mortality. 192 children had ALI. Using >90% pressure control ventilation, 85% of patients achieved VT less than 10 ml/kg. Median VT was not significantly different between survivors and non-survivors during the first 3 days of mechanical ventilation. After controlling for diagnostic category, age, delta P (PIP-PEEP), PEEP, and severity of lung disease, VT was not associated with mortality (P > 0.1), but higher VT at baseline and on day 1 of mechanical ventilation was associated with more ventilator free days (P < 0.05). This was particularly seen in patients with better respiratory system compliance [Crs > 0.5 ml/cmH2O/kg, OR = 0.70 (0.52, 0.95)]. OI, PF ratio, and LIS were all associated with mortality (P < 0.05).

CONCLUSIONS

When ventilating children using lung protective strategies with pressure control ventilation, observed VT is between 6 and 10 ml/kg and is not associated with increased mortality. Moreover, higher VT within this range is associated with more ventilator free days, particularly for patients with less severe disease.

High levels of PEEP may improve survival in acute respiratory distress syndrome: A meta-analysis

OBJECTIVE

Positive end-expiratory pressure (PEEP) has been viewed as an essential component of mechanical ventilation in acute respiratory distress syndrome (ARDS) and acute lung injury (ALI). However, clinical trials have not yet convincingly demonstrated that high PEEP levels improve survival. The object of this study was to test a priori hypotheses that a small but clinically important mortality benefit of high PEEP did exist, especially in patients with greater overall severity of illness and differences in PEEP protocols might have affected the study results.

METHODS

Meta-analysis of randomized controlled trials comparing high versus low PEEP in ARDS/ALI. Studies were identified by search of MEDLINE (1950-2008) and other sources.

MEASUREMENTS AND MAIN RESULTS

Five studies including 2447 patients were identified. A pooled analysis showed a significant reduction in hospital mortality in favor of high PEEP (RR=0.89; 95% CI, 0.80-0.99; p=0.03). However, significant statistical and clinical heterogeneities such as differences in disease severity and ventilator protocols were found. The differences in PEEP protocols were not associated with differences in mortality rates. A logistic analysis suggested that the beneficial effect of high PEEP was greater in patients with higher ICU severity scores.

CONCLUSIONS

The statistical and clinical heterogeneities make proper interpretation of the results difficult. However, a small, but significant mortality benefit of high PEEP may exist. In addition, our analysis suggests the effects of high PEEP are greater in patients with higher ICU severity scores.

Low-tidal-volume ventilation as a strategy to reduce ventilator-associated injury in ALI and ARDS

One of the most hotly debated aspect of inhalation injury is the "best" method of mechanical ventilation. Mechanical ventilation protocols differ between both physicians and burn centers, and multiple different strategies for mechanical ventilation are currently being used to support the burn patient with inhalation injury. These strategies range from applying recent advances in acute respiratory distress syndrome to conventional mechanical ventilation to the use of alternative modes of ventilation such as the volumetric diffusive respirator. The articles in this section describe recent changes in philosophy with respect to mechanical ventilation, the various modes of ventilation being used to support the patient with inhalation injury, and the rationale behind each strategy.

Age bias in clinical trials in sepsis: how relevant are guidelines to older people?

Severe sepsis has a high mortality, and both incidence and mortality increases with increasing age. In recent years, several specific therapies have been recommended by guidelines to reduce mortality in severe sepsis. We review the age distribution in the key clinical trials on which these recommendations are made. Many therapeutic strategies have been evaluated, mainly in younger patients, with extrapolation of evidence toward the older population. Specific evidence of benefit in the elderly is present regarding treatment with activated protein C and ventilatory strategies. In view of the pharmacokinetic and pharmacodynamic differences in older people, and the higher incidence of comorbidity in the elderly, there is a need for clinical trials in severe sepsis to specifically include older patients.

Permissive hypercapnia

Mechanical ventilation using high tidal volume (VT) and transpulmonary pressure can damage the lung, causing ventilator-induced lung injury. Permissive hypercapnia, a ventilatory strategy for acute respiratory failure in which the lungs are ventilated with a low inspiratory volume and pressure, has been accepted progressively in critical care for adult, pediatric, and neonatal patients requiring mechanical ventilation and is one of the central components of current protective ventilatory strategies.

The design and interpretation of pilot trials in clinical research in critical care

BACKGROUND

Pilot trials are important to ensure that large randomized trials are rigorous, feasible, and economically justifiable. The objective of this review is to highlight the importance of randomized pilot trials and to describe key features of their design and interpretation using examples from critical care.

METHODS

We searched MEDLINE (1997-2007) and contacted experts to identify pilot randomized trials to exemplify and summarize their key methodologic features including objectives, sample size determination, outcomes, analysis, and reporting.

RESULTS

Pilot trials can have distinct and broad objectives. Investigators can predefine explicit criteria for determining their success. Surrogate outcome analyses are common in pilot trials, yet are usually underpowered to detect meaningful differences in clinically important end points and thus, should be cautiously interpreted. Pilot trials can facilitate successful conduct of large clinical trials by informing study design and streamlining protocol implementation.

RECOMMENDATIONS

We recommend that investigators define suitable objectives, determine sample size estimates, and select outcomes that will address their specific pilot trial objectives. Clinical effects documented in pilot trials should be reported with caution to avoid undue enthusiasm or pessimism about unstable estimates. Further methodologic work is required to identify optimal pilot trial design, indexing, and reporting.

Acute respiratory distress syndrome 40 years later: time to revisit its definition

OBJECTIVE

Acute respiratory distress syndrome is a common disorder associated with significant mortality and morbidity. The aim of this article is to critically evaluate the definition of acute respiratory distress syndrome and examine the impact the definition has on clinical practice and research.

DATA SOURCES

Articles from a MEDLINE search (1950 to August 2007) using the Medical Subject Heading respiratory distress syndrome, adult, diagnosis, limited to the English language and human subjects, their relevant bibliographies, and personal collections, were reviewed.

DATA SYNTHESIS

The definition of acute respiratory distress syndrome is important to researchers, clinicians, and administrators alike. It has evolved significantly over the last 40 years, culminating in the American-European Consensus Conference definition, which was published in 1994. Although the American-European Consensus Conference definition is widely used, it has some important limitations that may impact on the conduct of clinical research, on resource allocation, and ultimately on the bedside management of such patients. These limitations stem partially from the fact that as defined, acute respiratory distress syndrome is a heterogeneous entity and also involve the reliability and validity of the criteria used in the definition. This article critically evaluates the American-European Consensus Conference definition and its limitations. Importantly, it highlights how these limitations may contribute to clinical trials that have failed to detect a potential true treatment effect. Finally, recommendations are made that could be considered in future definition modifications with an emphasis on the significance of accurately identifying the target population in future trials and subsequently in clinical care.

CONCLUSION

How acute respiratory distress syndrome is defined has a significant impact on the results of randomized, controlled trials and epidemiologic studies. Changes to the current American-European Consensus Conference definition are likely to have an important role in advancing the understanding and management of acute respiratory distress syndrome.

Pressure characteristics of mechanical ventilation and incidence of pneumothorax before and after the implementation of protective lung strategies in the management of pediatric patients with severe ARDS

OBJECTIVE

To compare pressure characteristics of mechanical ventilation and their impact on pediatric patients with severe ARDS in the pre-protective lung strategy (PLS) and post-PLS eras.

METHODS

Medical records of 33 patients admitted to our pediatric ICU with ARDS from 1992 through 1994 (pre-PLS) and 52 patients with ARDS admitted from 2000 through 2003 (post-PLS) were retrospectively reviewed.

RESULTS

Patient age and gender distribution were identical in both eras. Fifty-five percent of the patients in the pre-PLS era had pneumothorax, compared to 17% in the post-PLS era (p < 0.05). Overall mortality rates for patients in the pre-PLS and post-PLS eras were 42% and 25%, respectively (p = 0.09; not significant). Mean duration of exposure to peak inspiratory pressure (PIP) values > 40 cm H2O was significantly longer in the pre-PLS era than in the post-PLS era. Pre-PLS patients with pneumothorax received mean maximum PIP of 72 +/- 17 cm H2O, mean maximum positive end-expiratory pressure (PEEP) of 20 +/- 5 cm H2O, and maximum mean airway pressure (MAP) of 46 +/- 8 cm H2O, while patients in the post-PLS era required mean maximum PIP of 42 +/- 2 cm H2O, mean maximum PEEP of 14 +/- 2 cm H2O, and maximum MAP of 30 +/- 6 cm H2O, respectively (p < 0.05 for all pressure parameters). There were no significant differences in mechanical ventilation pressure characteristics among patients who did not have pneumothorax during their course of management in both eras.

CONCLUSIONS

A significantly more aggressive use of ventilator pressure characteristics distinguished the pre-PLS era from the post-PLS era, and was found to be associated with a markedly higher incidence of pneumothorax. Outcome in both eras did not differ significantly, presumably due to insufficient statistical power.

Is there a best way to set tidal volume for mechanical ventilatory support?

Tidal breaths are an important component of mechanical ventilation. However, an inappropriate tidal volume setting can overstretch and injure the lung. Maximal stretch, tidal stretch, frequency of stretch, and rate of stretch are all implicated in such injury. Clinical trials have shown that limiting maximal and tidal stretch improves outcomes, even if gas exchange is partially compromised. Thus, current strategies should focus on limiting tidal and maximal stretch as much as possible.

[High PEEP vs. conventional PEEP in the acute respiratory distress syndrome: a systematic review and meta-analysis]

OBJECTIVE

To perform a systematic review and meta-analysis of the literature to evaluate the effects of high PEEP versus conventional PEEP on mortality and on the risk of barotrauma in patients with the acute respiratory distress syndrome (ARDS).

SOURCE OF DATA

Computer search of Medline, Embase, CINAHL, CANCERLIT, Pascal-Biomed, ACP Journal Club, Cochrane library (CDSR, DARE, CCTR), ISI Proceedings, Current Contents, and Web of Science, as well as manual search of selected references.

SELECTION OF STUDIES

Controlled random clinical trials published after NAECC (1994) that evaluated the effect of two levels of PEEP and that reported the mortality and incidence of barotrauma in the series.

DATA EXTRACTION

By two investigators working independently, with discrepancies resolved by group consensus. Contingency tables were elaborated and the RRs with corresponding confidence intervals were obtained for each study.

RESULTS

Four articles were selected for the meta-analysis of mortality and three for the meta-analysis of barotrauma. No effects of PEEP level on mortality were found (RR 0.73, 95% CI: 0.49 to 1.10) or on the incidence of barotrauma (RR 0.50, 95% CI: 0.14 to 1.73). However, an analysis of the studies in which PEEP was individualized in function of Pflex showed a significant decrease in mortality (RR 0.59, 95% CI: 0.43 to 0.82) (p=0.001)

CONCLUSIONS

The use of high or conventional PEEP in function of oxygenation does not affect mortality or the incidence of barotrauma in patients with ARDS. However, there might be a decrease in mortality associated to high PEEP individualized in function of the pulmonary mechanics of each patient.

Ventilation strategies and adjunctive therapy in severe lung disease

Respiratory failure caused by severe lung disease is a common reason for admission to the pediatric and neonatal intensive care units. Efforts to decrease morbidity and mortality have fueled investigations into innovative methods of ventilation, kinder gentler ventilation techniques, pharmacotherapeutic adjuncts, and extracorporeal life support modalities. This article discusses the rationale for and experience with some of these techniques.

Why are clinicians not embracing the results from pivotal clinical trials in severe sepsis? A bayesian analysis

BACKGROUND

Five pivotal clinical trials (Intensive Insulin Therapy; Recombinant Human Activated Protein C [rhAPC]; Low-Tidal Volume; Low-Dose Steroid; Early Goal-Directed Therapy [EGDT]) demonstrated mortality reduction in patients with severe sepsis and expert guidelines have recommended them to clinical practice. Yet, the adoption of these therapies remains low among clinicians.

OBJECTIVES

We selected these five trials and asked: Question 1--What is the current probability that the new therapy is not better than the standard of care in my patient with severe sepsis? Question 2--What is the current probability of reducing the relative risk of death (RRR) of my patient with severe sepsis by meaningful clinical thresholds (RRR >15%; >20%; >25%)?

METHODS

Bayesian methodologies were applied to this study. Odds ratio (OR) was considered for Question 1, and RRR was used for Question 2. We constructed prior distributions (enthusiastic; mild, moderate, and severe skeptic) based on various effective sample sizes of other relevant clinical trials (unfavorable evidence). Posterior distributions were calculated by combining the prior distributions and the data from pivotal trials (favorable evidence).

MAIN FINDINGS

Answer 1--The analysis based on mild skeptic prior shows beneficial results with the Intensive Insulin, rhAPC, and Low-Tidal Volume trials, but not with the Low-Dose Steroid and EGDT trials. All trials' results become unacceptable by the analyses using moderate or severe skeptic priors. Answer 2--If we aim for a RRR>15%, the mild skeptic analysis shows that the current probability of reducing death by this clinical threshold is 88% for the Intensive Insulin, 62-65% for the Low-Tidal Volume, rhAPC, EGDT trials, and 17% for the Low-Dose Steroid trial. The moderate and severe skeptic analyses show no clinically meaningful reduction in the risk of death for all trials. If we aim for a RRR >20% or >25%, all probabilities of benefits become lower independent of the degree of skepticism.

CONCLUSIONS

Our clinical threshold analysis offers a new bedside tool to be directly applied to the care of patients with severe sepsis. Our results demonstrate that the strength of evidence (statistical and clinical) is weak for all trials, particularly for the Low-Dose Steroid and EGDT trials. It is essential to replicate the results of each of these five clinical trials in confirmatory studies if we want to provide patient care based on scientifically sound evidence.

Design of a new variable-ventilation method optimized for lung recruitment in mice

Variable ventilation (VV), characterized by breath-to-breath variation of tidal volume (Vt) and breathing rate (f), has been shown to improve lung mechanics and blood oxygenation during acute lung injury in many species compared with conventional ventilation (CV), characterized by constant Vt and f. During CV as well as VV, the lungs of mice tend to collapse over time; therefore, the goal of this study was to develop a new VV mode (VVN) with an optimized distribution of Vt to maximize recruitment. Groups of normal and HCl-injured mice were subjected to 1 h of CV, original VV (VVO), CV with periodic large breaths (CVLB), and VVN, and the effects of ventilation modes on respiratory mechanics, airway pressure, blood oxygenation, and IL-1β were assessed. During CV and VVO, normal and injured mice showed regional lung collapse with increased airway pressures and poor oxygenation. CVLB and VVN resulted in a stable dynamic equilibrium with significantly improved respiratory mechanics and oxygenation. Nevertheless, VVN provided a consistently better physiological response. In injured mice, VVO and VVN, but not CVLB, were able to reduce the IL-1β-related inflammatory response compared with CV. In conclusion, our results suggest that application of higher Vt values than the single Vt currently used in clinical situations helps stabilize lung function. In addition, variable stretch patterns delivered to the lung by VV can reduce the progression of lung injury due to ventilation in injured mice.

Alterations to surfactant precede physiological deterioration during high tidal volume ventilation

Lung injury due to mechanical ventilation is associated with an impairment of endogenous surfactant. It is unknown whether this impairment is a consequence of or an active contributor to the development and progression of lung injury. To investigate this issue, the present study addressed three questions: Do alterations to surfactant precede physiological lung dysfunction during mechanical ventilation? Which components are responsible for surfactant's biophysical dysfunction? Does exogenous surfactant supplementation offer a physiological benefit in ventilation-induced lung injury? Adult rats were exposed to either a low-stretch [tidal volume (Vt) = 8 ml/kg, positive end-expiratory pressure (PEEP) = 5 cmH2O, respiratory rate (RR) = 54–56 breaths/min (bpm), fractional inspired oxygen (FiO2) = 1.0] or high-stretch (Vt = 30 ml/kg, PEEP = 0 cmH2O, RR = 14–16 bpm, FiO2 = 1.0) ventilation strategy and monitored for either 1 or 2 h. Subsequently, animals were lavaged and the composition and function of surfactant was analyzed. Separate groups of animals received exogenous surfactant after 1 h of high-stretch ventilation and were monitored for an additional 2 h. High stretch induced a significant decrease in blood oxygenation after 2 h of ventilation. Alterations in surfactant pool sizes and activity were observed at 1 h of high-stretch ventilation and progressed over time. The functional impairment of surfactant appeared to be caused by alterations to the hydrophobic components of surfactant. Exogenous surfactant treatment after a period of high-stretch ventilation mitigated subsequent physiological lung dysfunction. Together, these results suggest that alterations of surfactant are a consequence of the ventilation strategy that impair the biophysical activity of this material and thereby contribute directly to lung dysfunction over time.

Mechanical ventilation with lower tidal volumes does not influence the prescription of opioids or sedatives

Introduction

We compared the effects of mechanical ventilation with a lower tidal volume (V_T) strategy versus those of greater V_T in patients with or without acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) on the use of opioids and sedatives.

Methods

This is a secondary analysis of a previously conducted before/after intervention study, which consisting of feedback and education on lung protective mechanical ventilation using lower V_T. We evaluated the effects of this intervention on medication prescriptions from days 0 to 28 after admission to our multidisciplinary intensive care unit.

Results

Medication prescriptions in 23 patients before and 38 patients after intervention were studied. Of these patients, 10 (44%) and 15 (40%) suffered from ALI/ARDS. The V_T of ALI/ARDS patients declined from 9.7 ml/kg predicted body weight (PBW) before to 7.8 ml/kg PBW after the intervention (P = 0.007). For patients who did not have ALI/ARDS there was a trend toward a decline from 10.2 ml/kg PBW to 8.6 ml/kg PBW (P = 0.073). Arterial carbon dioxide tension was significantly greater after the intervention in ALI/ARDS patients. Neither the proportion of patients receiving opioids or sedatives, or prescriptions at individual time points differed between pre-intervention and post-intervention. Also, there were no statistically significant differences in doses of sedatives and opioids. Findings were no different between non-ALI/ARDS patients and ALI/ARDS patients.

Conclusion

Concerns regarding sedation requirements with use of lower V_T are unfounded and should not preclude its use in patients with ALI/ARDS.

Advances in critical care for the nephrologist: acute lung injury/ARDS

Acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) are a major cause of acute respiratory failure in the critically ill patient. ALI and ARDS are characterized by the acute onset of severe hypoxemia and bilateral pulmonary infiltrates in the absence of clinical evidence for left atrial hypertension. These conditions are differentiated from one another by the ratio of the partial pressure of oxygen in the arterial blood to the inspired fraction of oxygen; ARDS requires a more severe oxygenation defect. ALI and ARDS may occur in association with a number of clinical disorders, including sepsis, pneumonia, aspiration, trauma including inhalational injury, and blood transfusions. The mortality rate remains high, in the range of 25% to 40%. The pathophysiology of ALI/ARDS involves resident lung cells, including endothelial and epithelial cells, as well as neutrophils, monocytes/macrophages, and platelets. When ALI/ARDS is complicated by acute kidney injury, mortality increases substantially. Several supportive and pharmacologic therapies have been tested in clinical trials. Of these, a low tidal volume, lung protective ventilation strategy is the only strategy that has been demonstrated in a large, multicenter randomized clinical trial to reduce mortality for patients with ALI/ARDS. Based on a recent randomized trial, a conservative fluid management strategy reduces the duration of mechanical ventilation without increasing the incidence of renal failure. Pharmacologic strategies and other ventilator management strategies have not been successful to date; however, several randomized, placebo controlled treatment trials are ongoing.

Surviving Sepsis Campaign: international guidelines for management of severe sepsis and septic shock: 2008

OBJECTIVE

To provide an update to the original Surviving Sepsis Campaign clinical management guidelines, "Surviving Sepsis Campaign Guidelines for Management of Severe Sepsis and Septic Shock," published in 2004.

DESIGN

Modified Delphi method with a consensus conference of 55 international experts, several subsequent meetings of subgroups and key individuals, teleconferences, and electronic-based discussion among subgroups and among the entire committee. This process was conducted independently of any industry funding.

METHODS

We used the Grades of Recommendation, Assessment, Development and Evaluation (GRADE) system to guide assessment of quality of evidence from high (A) to very low (D) and to determine the strength of recommendations. A strong recommendation (1) indicates that an intervention's desirable effects clearly outweigh its undesirable effects (risk, burden, cost) or clearly do not. Weak recommendations (2) indicate that the tradeoff between desirable and undesirable effects is less clear. The grade of strong or weak is considered of greater clinical importance than a difference in letter level of quality of evidence. In areas without complete agreement, a formal process of resolution was developed and applied. Recommendations are grouped into those directly targeting severe sepsis, recommendations targeting general care of the critically ill patient that are considered high priority in severe sepsis, and pediatric considerations.

RESULTS

Key recommendations, listed by category, include early goal-directed resuscitation of the septic patient during the first 6 hrs after recognition (1C); blood cultures before antibiotic therapy (1C); imaging studies performed promptly to confirm potential source of infection (1C); administration of broad-spectrum antibiotic therapy within 1 hr of diagnosis of septic shock (1B) and severe sepsis without septic shock (1D); reassessment of antibiotic therapy with microbiology and clinical data to narrow coverage, when appropriate (1C); a usual 7-10 days of antibiotic therapy guided by clinical response (1D); source control with attention to the balance of risks and benefits of the chosen method (1C); administration of either crystalloid or colloid fluid resuscitation (1B); fluid challenge to restore mean circulating filling pressure (1C); reduction in rate of fluid administration with rising filing pressures and no improvement in tissue perfusion (1D); vasopressor preference for norepinephrine or dopamine to maintain an initial target of mean arterial pressure > or = 65 mm Hg (1C); dobutamine inotropic therapy when cardiac output remains low despite fluid resuscitation and combined inotropic/vasopressor therapy (1C); stress-dose steroid therapy given only in septic shock after blood pressure is identified to be poorly responsive to fluid and vasopressor therapy (2C); recombinant activated protein C in patients with severe sepsis and clinical assessment of high risk for death (2B except 2C for postoperative patients). In the absence of tissue hypoperfusion, coronary artery disease, or acute hemorrhage, target a hemoglobin of 7-9 g/dL (1B); a low tidal volume (1B) and limitation of inspiratory plateau pressure strategy (1C) for acute lung injury (ALI)/acute respiratory distress syndrome (ARDS); application of at least a minimal amount of positive end-expiratory pressure in acute lung injury (1C); head of bed elevation in mechanically ventilated patients unless contraindicated (1B); avoiding routine use of pulmonary artery catheters in ALI/ARDS (1A); to decrease days of mechanical ventilation and ICU length of stay, a conservative fluid strategy for patients with established ALI/ARDS who are not in shock (1C); protocols for weaning and sedation/analgesia (1B); using either intermittent bolus sedation or continuous infusion sedation with daily interruptions or lightening (1B); avoidance of neuromuscular blockers, if at all possible (1B); institution of glycemic control (1B), targeting a blood glucose < 150 mg/dL after initial stabilization (2C); equivalency of continuous veno-veno hemofiltration or intermittent hemodialysis (2B); prophylaxis for deep vein thrombosis (1A); use of stress ulcer prophylaxis to prevent upper gastrointestinal bleeding using H2 blockers (1A) or proton pump inhibitors (1B); and consideration of limitation of support where appropriate (1D). Recommendations specific to pediatric severe sepsis include greater use of physical examination therapeutic end points (2C); dopamine as the first drug of choice for hypotension (2C); steroids only in children with suspected or proven adrenal insufficiency (2C); and a recommendation against the use of recombinant activated protein C in children (1B).

CONCLUSIONS

There was strong agreement among a large cohort of international experts regarding many level 1 recommendations for the best current care of patients with severe sepsis. Evidenced-based recommendations regarding the acute management of sepsis and septic shock are the first step toward improved outcomes for this important group of critically ill patients.

Sepsis: from bench to bedside

Sepsis is a syndrome related to severe infections. It is defined as the systemic host response to microorganisms in previously sterile tissues and is characterized by end-organ dysfunction away from the primary site of infection. The normal host response to infection is complex and aims to identify and control pathogen invasion, as well as to start immediate tissue repair. Both the cellular and humoral immune systems are activated, giving rise to both anti-inflammatory and proinflammatory responses. The chain of events that leads to sepsis is derived from the exacerbation of these mechanisms, promoting massive liberation of mediators and the progression of multiple organ dysfunction. Despite increasing knowledge about the pathophysiological pathways and processes involved in sepsis, morbidity and mortality remain unacceptably high. A large number of immunomodulatory agents have been studied in experimental and clinical settings in an attempt to find an efficacious anti-inflammatory drug that reduces mortality. Even though preclinical results had been promising, the vast majority of these trials actually showed little success in reducing the overwhelmingly high mortality rate of septic shock patients as compared with that of other critically ill intensive care unit patients. Clinical management usually begins with prompt recognition, determination of the probable infection site, early administration of antibiotics, and resuscitation protocols based on "early-goal" directed therapy. In this review, we address the research efforts that have been targeting risk factor identification, including genetics, pathophysiological mechanisms and strategies to recognize and treat these patients as early as possible.

Usual care as the control group in clinical trials of nonpharmacologic interventions

We discuss the pros and cons of including usual care as a control arm in clinical trials of nonpharmacologic interventions. Usual care is a term used to describe the full spectrum of patient care practices in which clinicians have the opportunity (which is not necessarily seized) to individualize care. The decision to use usual care as the control arm should be based on the nature of the research question and the uniformity of usual-care practices. The use of a usual-care arm in a two-arm trial should be considered for trials of investigational drugs or devices, for trials that propose to test interventions that lie well outside usual-care practices, or for trials where the research question per se is to compare a strategy against usual care. Examples of the latter include pragmatic effectiveness trials of clinical pathways or protocolized-care versus usual-care practices. Randomized intervention trials can be safely conducted and monitored using two treatments that lie within the range of usual-care practices if both approaches are considered prudent and good care for the target population.

What type of monitoring has been shown to improve outcomes in acutely ill patients?

OBJECTIVE

Lack of evidence that some monitoring systems can improve outcomes has raised doubts about their use in the intensive care unit (ICU). The objective of this study was to determine which monitoring techniques have been shown to improve outcomes in ICU patients.

DESIGN

Comprehensive literature review.

METHODS

We conducted a highly sensitive search, up to June 2006, in the Cochrane Central Register of Controlled Trials (CENTRAL) and MedLine, for prospective, randomized controlled trials (RCTs) conducted in adult patients in the ICU and the operating room (major surgical procedures) and focusing on the impact of monitoring on outcome.

MEASUREMENTS AND RESULTS

Of 4,175 potential articles, 67 evaluated the impact of monitoring in acutely ill adult patients. There were 40 studies related to hemodynamic monitoring, 17 to respiratory monitoring, and 10 to neurological monitoring. Seven studies were classified in two different categories. Positive non-mortality outcomes were observed in 17 of 40 hemodynamic studies, 11 of 17 respiratory, and in all 10 neurological studies. Mortality was evaluated in 31 hemodynamic studies, but a beneficial impact was demonstrated in only 10. For respiratory monitoring, 7 studies evaluated mortality, but only 3 of them showed an improved outcome. We found no neurological monitoring studies that assessed mortality.

CONCLUSION

There is no broad evidence that any form of monitoring improves outcomes in the ICU and most commonly used devices have not been evaluated by RCT. This review puts into perspective the recent negative studies on the use of the pulmonary artery catheter in the acutely ill.

Surviving Sepsis Campaign: international guidelines for management of severe sepsis and septic shock: 2008

OBJECTIVE

To provide an update to the original Surviving Sepsis Campaign clinical management guidelines, "Surviving Sepsis Campaign guidelines for management of severe sepsis and septic shock," published in 2004.

DESIGN

Modified Delphi method with a consensus conference of 55 international experts, several subsequent meetings of subgroups and key individuals, teleconferences, and electronic-based discussion among subgroups and among the entire committee. This process was conducted independently of any industry funding.

METHODS

We used the GRADE system to guide assessment of quality of evidence from high (A) to very low (D) and to determine the strength of recommendations. A strong recommendation indicates that an intervention's desirable effects clearly outweigh its undesirable effects (risk, burden, cost), or clearly do not. Weak recommendations indicate that the tradeoff between desirable and undesirable effects is less clear. The grade of strong or weak is considered of greater clinical importance than a difference in letter level of quality of evidence. In areas without complete agreement, a formal process of resolution was developed and applied. Recommendations are grouped into those directly targeting severe sepsis, recommendations targeting general care of the critically ill patient that are considered high priority in severe sepsis, and pediatric considerations.

RESULTS

Key recommendations, listed by category, include: early goal-directed resuscitation of the septic patient during the first 6 hrs after recognition (1C); blood cultures prior to antibiotic therapy (1C); imaging studies performed promptly to confirm potential source of infection (1C); administration of broad-spectrum antibiotic therapy within 1 hr of diagnosis of septic shock (1B) and severe sepsis without septic shock (1D); reassessment of antibiotic therapy with microbiology and clinical data to narrow coverage, when appropriate (1C); a usual 7-10 days of antibiotic therapy guided by clinical response (1D); source control with attention to the balance of risks and benefits of the chosen method (1C); administration of either crystalloid or colloid fluid resuscitation (1B); fluid challenge to restore mean circulating filling pressure (1C); reduction in rate of fluid administration with rising filing pressures and no improvement in tissue perfusion (1D); vasopressor preference for norepinephrine or dopamine to maintain an initial target of mean arterial pressure > or = 65 mm Hg (1C); dobutamine inotropic therapy when cardiac output remains low despite fluid resuscitation and combined inotropic/vasopressor therapy (1C); stress-dose steroid therapy given only in septic shock after blood pressure is identified to be poorly responsive to fluid and vasopressor therapy (2C); recombinant activated protein C in patients with severe sepsis and clinical assessment of high risk for death (2B except 2C for post-operative patients). In the absence of tissue hypoperfusion, coronary artery disease, or acute hemorrhage, target a hemoglobin of 7-9 g/dL (1B); a low tidal volume (1B) and limitation of inspiratory plateau pressure strategy (1C) for acute lung injury (ALI)/acute respiratory distress syndrome (ARDS); application of at least a minimal amount of positive end-expiratory pressure in acute lung injury (1C); head of bed elevation in mechanically ventilated patients unless contraindicated (1B); avoiding routine use of pulmonary artery catheters in ALI/ARDS (1A); to decrease days of mechanical ventilation and ICU length of stay, a conservative fluid strategy for patients with established ALI/ARDS who are not in shock (1C); protocols for weaning and sedation/analgesia (1B); using either intermittent bolus sedation or continuous infusion sedation with daily interruptions or lightening (1B); avoidance of neuromuscular blockers, if at all possible (1B); institution of glycemic control (1B) targeting a blood glucose < 150 mg/dL after initial stabilization ( 2C ); equivalency of continuous veno-veno hemofiltration or intermittent hemodialysis (2B); prophylaxis for deep vein thrombosis (1A); use of stress ulcer prophylaxis to prevent upper GI bleeding using H2 blockers (1A) or proton pump inhibitors (1B); and consideration of limitation of support where appropriate (1D). Recommendations specific to pediatric severe sepsis include: greater use of physical examination therapeutic end points (2C); dopamine as the first drug of choice for hypotension (2C); steroids only in children with suspected or proven adrenal insufficiency (2C); a recommendation against the use of recombinant activated protein C in children (1B).

CONCLUSION

There was strong agreement among a large cohort of international experts regarding many level 1 recommendations for the best current care of patients with severe sepsis. Evidenced-based recommendations regarding the acute management of sepsis and septic shock are the first step toward improved outcomes for this important group of critically ill patients.

Is the mortality higher in the pulmonary vs the extrapulmonary ARDS? A meta analysis

BACKGROUND AND AIM

ARDS can occur from the following two pathogenetic pathways: a direct pulmonary injury (ARDSp); and an indirect injury (ARDSexp). The predisposing clinical factor can influence the pathogenesis and clinical outcome of ARDS. This metaanalysis was aimed at evaluating whether there is any difference in mortality between the two groups.

METHODS

We searched the MEDLINE, EMBASE, and CINAHL databases for relevant studies published from 1987 to 2007, and included studies that have reported mortality in the two groups of ARDS. We calculated the odds ratio (OR) and 95% confidence interval (CI) to assess mortality in patients with ARDSp vs patients with ARDSexp and pooled the results using three different statistical models.

RESULTS

Our search yielded 34 studies. In all, the studies involved 4,311 patients with 2,330 patients in the ARDSp group and 1,981 patients in the ARDSexp group. The OR of mortality in ARDSp group compared to the ARDSexp group was 1.11 (95% CI, 0.88 to 1.39), as determined by the random-effects model; 1.04 (95% CI, 0.92 to 1.18), as determined by the fixed-effects model; and 1.04 (95% CI, 0.92 to 1.18), as determined by the exact method, indicating that mortality is similar in the two groups. The mortality was no different whether the studies were classified as prospective (OR, 1.15; 95% CI, 0.87 to 1.51) or retrospective (OR, 1.01; 95% CI, 0.61 to 1.69); small (OR, 1.11; 95% CI, 0.77 to 1.60) or large (OR, 1.1; 95% CI, 0.82 to 1.49); or observational (OR, 1.10; 95% CI, 0.82 to 1.49) or interventional (OR, 0.97; 95% CI, 0.79 to 1.19). There was methodological and statistical heterogeneity (I(2), 50.9%; 95% CI, 21.3 to 66.2%; chi(2) statistic, 67.22; p = 0.0004).

CONCLUSIONS

The results of this study suggest that there is no difference in mortality between these two groups. Further studies should focus on specific etiologies within the subgroups rather than focusing on the broader division of ARDSp and ARDSexp.

High tidal volume is associated with the development of acute lung injury after severe brain injury: an international observational study

OBJECTIVE

Although a significant number of patients with severe brain injury develop acute lung injury, only intracranial risk factors have previously been studied. We investigated the role of extracranial predisposing factors, including hemodynamic and ventilatory management, as independent predictors of acute lung injury in brain-injured patients.

DESIGN

Prospective multicenter observational study.

SETTING

Four European intensive care units in university-affiliated hospitals.

PATIENTS

Eighty-six severely brain-injured patients enrolled in 13 months.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

All patients with severe brain injury (Glasgow Coma Scale score <9) were studied for 8 days from admission. Ventilatory pattern, respiratory system compliance, blood gas analysis, and hemodynamic profile were recorded and entered in a stepwise regression model. Length of stay in the intensive care unit, ventilator-free days, and mortality were collected. Eighteen patients (22%) developed acute lung injury on day 2.8 +/- 1. They were initially ventilated with significantly higher tidal volume per predicted body weight (9.5 +/- 1 vs. 10.4 +/- 1.1), respiratory rate, and minute ventilation and more often required vasoactive drugs (p < .05). In addition to a lower Pao2/Fio2 (odds ratio 0.98, 95% confidence interval 0.98-0.99), the use of high tidal volume (odds ratio 5.4, 95% confidence interval 1.54-19.24) and relatively high respiratory rate (odds ratio 1.8, 95% confidence interval 1.13-2.86) were independent predictors of acute lung injury (p < .01). After the onset of acute lung injury, patients remained ventilated with similar tidal volumes to maintain mild hypocapnia and had a longer length of stay in the intensive care unit and fewer ventilator-free days (p < .05).

CONCLUSIONS

In addition to a lower Pao2/Fio2, the use of high tidal volume and high respiratory rate are independent predictors of acute lung injury in patients with severe brain injury. In this patient population, alternative ventilator strategies should be considered to protect the lung and guarantee a tight CO2 control.

Effects of reduced tidal volume ventilation on pulmonary function in mice before and after acute lung injury

We investigated the influence of load impedance on ventilator performance and the resulting effects of reduced tidal volume (Vt) on lung physiology during a 30-min ventilation of normal mice and 10 min of additional ventilation following lavage-induced injury at two positive end-expiratory pressure (PEEP) levels. Respiratory mechanics were regularly monitored, and the lavage fluid was tested for the soluble E-cadherin, an epithelial cell adhesion molecule, and surfactant protein (SP) B. The results showed that, due to the load dependence of the delivered Vt from the small-animal ventilator: 1) uncontrolled ventilation in normal mice resulted in a lower delivered Vt (6 ml/kg at 3-cmH2O PEEP and 7 ml/kg at 6-cmH2O PEEP) than the prescribed Vt (8 ml/kg); 2) at 3-cmH2O PEEP, uncontrolled ventilation in normal mice led to an increase in lung parenchymal functional heterogeneity, a reduction of SP-B, and an increase in E-cadherin; 3) at 6-cmH2O PEEP, ventilation mode had less influence on these parameters; and 4) in a lavage model of acute respiratory distress syndrome, delivered Vt decreased to 4 ml/kg from the prescribed 8 ml/kg, which resulted in severely compromised lung function characterized by increases in lung elastance, airway resistance, and alveolar tissue heterogeneity. Furthermore, the low Vt ventilation also resulted in poor survival rate independent of PEEP. These results highlight the importance of delivering appropriate Vt to both the normal and injured lungs. By leaving the Vt uncompensated, it can significantly alter physiological and biological responses in mice.

Arteriovenous CO2 removal improves survival compared to high frequency percussive and low tidal volume ventilation in a smoke/burn sheep acute respiratory distress syndrome model

OBJECTIVES AND SUMMARY BACKGROUND: Low tidal volume ventilation (LTV) has improved survival with acute respiratory distress syndrome (ARDS) by reducing lung stretch associated with volutrauma and barotrauma. Additional strategies to reduce lung stretch include arteriovenous carbon dioxide removal (AVCO2R), and high frequency percussive ventilation (HFPV). We performed a prospective, randomized study comparing these techniques in our clinically relevant LD100 sheep model of ARDS to compare survival, pathology, and inflammation between the 3 ventilator methods.

METHODS

Adult sheep (n = 61) received smoke inhalation (48 breaths) and a 40% third-degree burn. After ARDS developed (Pao2/FiO2 <200), animals were randomized. In experiment 1, animals were killed at 48 hours after randomization. Hemodynamics, pulmonary function, injury scores, myeloperoxidase (MPO) in lung tissues and neutrophils, IL-8 in lung tissues, and apoptosis were evaluated. In experiment 2, the end point was survival to 72 hours after onset of ARDS or end-of-life criteria with extension of the same studies performed in experiment 1.

RESULTS

There were no differences in hemodynamics, but minute ventilation was lower in the AVCO2R group and Paco2 for the HFPV and AVCO2R animals remained lower than LTV. Airway obstruction and injury scores were not different among the 3 ventilation strategies. In experiment 1, lung tissue MPO and IL-8 were not different among the ventilation strategies. However, in experiment 2, lung tissue MPO was significantly lower for AVCO2R-treated animals (AVCO2R < HFPV < LTV). TUNEL staining showed little DNA breakage in neutrophils from experiment 1, but significantly increased breakage in all 3 ventilator strategies in experiment 2. In contrast, AVCO2R tissue neutrophils showed significant apoptosis at 72 hours post-ARDS criteria as measured by nuclear condensation (P < 0.001). Survival 72 hours post-ARDS criteria was highest for AVCO2R (71%) compared with HFPV (55%) and LTV (33%) (AVCO2R vs. LTV, P = 0.05).

CONCLUSIONS

Significantly more animals survived AVCO2R than LTV. In experiment 2, Lung MPO was significantly lower for AVCO2R, compared with LTV (P < 0.05). This finding taken together with the TUNEL and neutrophil apoptosis results, suggested that disposition of neutrophils 72 hours post-ARDS criteria was different among the ventilatory strategies with neutrophils from AVCO2R-treated animals removed chiefly through apoptosis, but in the cases of HFPV and LTV, dying by necrosis in lung tissue.

Low-tidal-volume ventilation in the acute respiratory distress syndrome

A 55-year-old man who is 178 cm tall and weighs 95 kg is hospitalized with community-acquired pneumonia and progressively severe dyspnea. His arterial oxygen saturation while breathing 100% oxygen through a face mask is 76%; a chest radiograph shows diffuse alveolar infiltrates with air bronchograms. He is intubated and receives mechanical ventilation; ventilator settings include a tidal volume of 1000 ml, a positive end-expiratory pressure (PEEP) of 5 cm of water, and a fraction of inspired oxygen (FiO₂) of 0.8. With these settings, peak airway pressure is 50 to 60 cm of water, plateau airway pressure is 38 cm of water, partial pressure of arterial oxygen is 120 mm Hg, partial pressure of carbon dioxide is 37 mm Hg, and arterial blood pH is 7.47. The diagnosis of the acute respiratory distress syndrome (ARDS) is made. An intensive care specialist evaluates the patient and recommends changing the current ventilator settings and implementing a low-tidal-volume ventilation strategy.

Lung protective ventilation strategy for the acute respiratory distress syndrome

BACKGROUND

Patients with acute respiratory distress syndrome and acute lung injury require mechanical ventilatory support. Acute respiratory distress syndrome and acute lung injury are further complicated by ventilator-induced lung injury. Lung-protective ventilation strategies may lead to improved survival.

OBJECTIVES

To assess the effects of ventilation with lower tidal volume on morbidity and mortality in patients aged 16 years or older affected by acute respiratory distress syndrome and acute lung injury. A secondary objective was to determine whether the comparison between low and conventional tidal volume was different if a plateau airway pressure of greater than 30 to 35 cm H20 was used.

SEARCH STRATEGY

In our original review, we searched databases from inception until 2003. In this updated review, we searched The Cochrane Central Register of Controlled Trials (CENTRAL), (The Cochrane Library 2006, Issue 3). We updated our search of MEDLINE, EMBASE, CINAHL and the Web of Science from 2003 to 2006. We also updated our search of intensive care journals and conference proceedings; databases of ongoing research, reference lists and 'grey literature' from 2003 to 2006.

SELECTION CRITERIA

We included randomized controlled trials comparing ventilation using either lower tidal volume (Vt) or low airway driving pressure (plateau pressure 30 cm H2O or less), resulting in tidal volume of 7 ml/kg or less versus ventilation that uses Vt in the range of 10 to 15 ml/kg, in adults (16 years old or older).

DATA COLLECTION AND ANALYSIS

We independently assessed trial quality and extracted data. Wherever appropriate, results were pooled. We applied fixed- and random-effects models.

MAIN RESULTS

We found one new study in this update for a total of six trials, involving 1297 patients, which were eligible for inclusion. Mortality at day 28 was significantly reduced by lung-protective ventilation: relative risk (RR) 0.74 (95% confidence interval (CI) 0.61 to 0.88); hospital mortality was reduced: RR 0.80 (95% CI 0.69 to 0.92); overall mortality was not significantly different if a plateau pressure less than or equal to 31 cm H2O in control group was used: RR 1.13 (95% CI 0.88 to 1.45). There was insufficient evidence about morbidity and long term outcomes.

AUTHORS' CONCLUSIONS

Clinical heterogeneity, such as different lengths of follow up and higher plateau pressure in control arms in two trials, make the interpretation of the combined results difficult. Mortality is significantly reduced at day 28 and at the end of hospital stay. The effects on long-term mortality are unknown, although the possibility of a clinically relevant benefit cannot be excluded.

Airway pressure release and biphasic intermittent positive airway pressure ventilation: are they ready for prime time?

Airway pressure release ventilation and biphasic positive airway pressure ventilation are being used increasingly as alternative strategies to conventional assist control ventilation for patients with acute respiratory distress syndrome (ARDS) and acute lung injury. By permitting spontaneous breathing throughout the ventilatory cycle, these modes offer several advantages over conventional strategies to improve the pathophysiology in these patients, including gas exchange, cardiovascular function, and reducing or eliminating the need for heavy sedation and paralysis. Whether these surrogate outcomes will translate into better patient outcomes remains to be determined. The purpose of this review is to summarize the rationale behind the use of these ventilatory strategies in ARDS, the clinical experience with the use of these modes, and their future applications in trauma patients.