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

Insights in pediatric ventilation: timing of intubation, ventilatory strategies, and weaning

PURPOSE OF REVIEW

Mechanical ventilation is a common intervention provided by pediatric intensivists. This fact notwithstanding, the management of mechanical ventilation in pediatrics is largely guided by a few pediatric trials along with careful interpretation and application of adult data.

RECENT FINDINGS

A low tidal volume, pressure limited approach to mechanical ventilation as established by the Acute Respiratory Distress Syndrome Network investigators, has become the prevailing practice in pediatric intensive care. Studies by these investigators suggest that high positive end expiratory pressure and recruitment maneuvers are not uniformly beneficial. High frequency oscillatory ventilation continues to be evaluated in an attempt to provide 'open lung' ventilation. Airway pressure release ventilation is a newer mode of ventilation that may combine the 'open lung' approach with spontaneous breathing. Prone positioning was demonstrated in a recent pediatric trial to have no effect on outcome, while calfactant was found to potentially improve outcomes in pediatric acute respiratory distress syndrome. Ventilator weaning protocols may not be as useful in pediatrics as in adults. Systemic corticosteroids decrease the incidence of post extubation stridor and may reduce reintubation rates.

SUMMARY

Mechanical ventilation with pressure limitation and low tidal volumes has become customary in pediatric intensive care units, and this lung protective approach will continue into the foreseeable future. Further investigation is warranted regarding use of high frequency oscillatory ventilation, airway pressure release ventilation, and surfactant to assist pediatric intensivists in application of these therapies.

Have changes in ventilation practice improved outcome in children with acute lung injury?

OBJECTIVES

To describe the changes that have occurred in mechanical ventilation in children with acute lung injury in our institution over the last 10-15 yrs and to examine the impact of these changes, in particular of the delivered tidal volume on mortality.

DESIGN

Retrospective study.

SETTING

University-affiliated children's hospital.

PATIENTS

The management of mechanical ventilation between 1988 and 1992 (past group, n = 79) was compared with the management between 2000 and 2004 (recent group, n = 85).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The past group patients were ventilated with a significantly higher mean tidal volume (10.2 +/- 1.7 vs. 8.1 +/- 1.4 mL.kg actual body weight, p < .001), lower levels of positive end-expiratory pressure (6.1 +/- 2.7 vs. 7.1 +/- 2.4 cm H2O, p = .007), and higher mean peak inspiratory pressure (31.5 +/- 7.3 vs. 27.8 +/- 4.2 cm H2O, p < .001) than the recent group patients. The recent group had a lower mortality (21% vs. 35%, p = .04) and a greater number of ventilator-free days (16.0 +/- 9.0 vs. 12.6 +/- 9.9 days, p = .03) than the past group. A higher tidal volume was independently associated with increased mortality (odds ratio 1.59; 95% confidence interval 1.20, 2.10, p < .001) and reduction in ventilation-free days (95% confidence interval -1.24, -0.77, p < .001).

CONCLUSIONS

The changes in the clinical practice of mechanical ventilation in children in our institution reflect those reported for adults. In our experience, mortality among children with acute lung injury was reduced by 40%, and tidal volume was independently associated with reduced mortality and an increase in ventilation-free days.

An early PEEP/FIO2 trial identifies different degrees of lung injury in patients with acute respiratory distress syndrome

RATIONALE

Current American-European Consensus Conference definitions for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are inadequate for inclusion into clinical trials due to the lack of standardization for measuring the oxygenation defect.

OBJECTIVES

We questioned whether an early assessment of oxygenation on specific ventilator settings would identify patients with established ARDS (persisting over 24 h).

METHODS

At the time of meeting ARDS criteria (Day 0) and 24 hours later (Day 1), arterial blood gases were obtained on standard ventilator settings, Vt 7 ml/kg predicted body weight plus the following positive end-expiratory pressure (PEEP) and Fi(O(2)) settings in sequence: (1) PEEP >or= 5 cm H(2)O and Fi(O(2)) >or= 0.5, (2) PEEP >or= 5 cm H(2)O and Fi(O(2)) 1.0, (3) PEEP >or= 10 cm H(2)O and Fi(O(2))>or=0.5, and (4) PEEP >or= 10 cm H(2)O and Fi(O(2)) 1.0.

MEASUREMENTS AND MAIN RESULTS

One hundred seventy patients meeting ARDS criteria (Pa(O(2))/Fi(O(2)) 128 +/- 33 mm Hg) were enrolled. Overall hospital mortality was 34.1%. The standard ventilator settings that best identified patients with established ARDS and predicted differences in intensive care unit (ICU) mortality were PEEP >or= 10 cm H(2)O and Fi(O(2)) >or= 0.5 at Day 1 (P = 0.0001). Only 99 (58.2%) patients continued to meet ARDS criteria (Pa(O(2))/Fi(O(2)), 155.8 +/- 29.8 mm Hg; ICU mortality, 45.5%), whereas 55 patients were reclassified as having ALI (Pa(O(2))/Fi(O(2)), 246.5 +/- 25.6 mm Hg; ICU mortality, 20%) and 16 patients as having acute respiratory failure (Pa(O(2))/Fi(O(2)), 370 +/- 54 mm Hg; ICU mortality, 6.3%) (P = 0.0001) on these settings.

CONCLUSIONS

Patients meeting current American-European Consensus Conference ARDS criteria may have highly variable levels of lung injury and outcomes. A systematic method of assessing severity of lung injury is required for enrollment of patients with ARDS into randomized controlled trials. Clinical trial registered with www.clinicaltrials.gov (NCT 00435110).

Mechanical ventilation in the management of acute respiratory distress syndrome

The occurrence of acute respiratory distress syndrome (ARDS), is now common in intensive care units throughout the world. The diagnosis of ARDS is based on a definition that includes bilateral pulmonary infiltrates on chest radiographs, impaired oxygenation, and the absence of clinical evidence of elevated left atrial pressure. ARDS is the clinical result of a group of diverse processes, which range from physical or chemical injury, to extensive activation of innate inflammatory response. All these processes damage the integrity of the alveolar-capillary barrier causing increased alveolar-capillary permeability and an influx of protein-rich fluid into the alveolar space. This alveolar flooding results in hypoxemia, inactivated surfactant, intrapulmonary shunt, and impaired alveolar ventilation. The treatment of acute respiratory distress syndrome is largely supportive in nature, keeping patients alive while allowing their lungs to heal, and minimizing further pulmonary insult. In 1994 the National Heart, Lung, and Blood Institute (NHLBI) established the ARDS Network for the conduct of clinical trials. This is a network, supported by the National Institutes of Health, that provided the infrastructure for well-designed, multicenter, randomized trials of therapies for ARDS. The first study from this group in 2001 produced landmark data demonstrating mortality improvements in ARDS with particular mechanical ventilation strategies. Specifically, low tidal volume mechanical ventilation was demonstrated to reduce mortality by 22%. Other strategies such as high positive end expiratory pressure and prone positioning have not been shown to reduce mortality. Clinicians who are involved in the care of patients with ARDS should have a basic understanding of mechanical ventilation and the evidence guiding the mechanical ventilation strategies of these patients. Until further evidence is published, providers should adopt the use of a volume and pressure limited approach to mechanical ventilation.

Acute lung injury and the acute respiratory distress syndrome: a clinical review

Acute respiratory distress syndrome and acute lung injury are well defined and readily recognised clinical disorders caused by many clinical insults to the lung or because of predispositions to lung injury. That this process is common in intensive care is well established. The mainstay of treatment for this disorder is provision of excellent supportive care since these patients are critically ill and frequently have coexisting conditions including sepsis and multiple organ failure. Refinements in ventilator and fluid management supported by data from prospective randomised trials have increased the methods available to effectively manage this disorder.

Physiology of mechanical ventilation

Mechanical ventilation, although essential in taking care of acute lung injury and widely used during surgical procedures worldwide, remains a highly debated field. Clinical trials in the last decade have shown convincingly that mechanical ventilation can result in additional mortality in patients with acute lung injury. This understanding has resulted in a resurged interest in mechanical ventilation, and especially in techniques and strategies to further improve mechanical ventilation. This article discusses physiological principles to improve the understanding of mechanical ventilation.

Mechanical ventilation in ARDS: a state-of-the-art review

Mechanical ventilation is an essential component of the care of patients with ARDS, and a large number of randomized controlled clinical trials have now been conducted evaluating the efficacy and safety of various methods of mechanical ventilation for the treatment of ARDS. Low tidal volume ventilation (</= 6 mL/kg predicted body weight) should be utilized in all patients with ARDS as it is the only method of mechanical ventilation that, to date, has been shown to improve survival. High positive end-expiratory pressure, alveolar recruitment maneuvers, and prone positioning may each be useful as rescue therapy in a patient with severe hypoxemia, but these methods of ventilation do not improve survival for the wide population of patients with ARDS. Although not specific to the treatment of ARDS, protocol-driven weaning that utilizes a daily spontaneous breathing trial and ventilation in the semirecumbent position have proven benefits and should be used in the management of ARDS patients.

Lung protective ventilatory strategies in acute lung injury and acute respiratory distress syndrome: from experimental findings to clinical application

This review addresses the physiological background and the current status of evidence regarding ventilator-induced lung injury and lung protective strategies. Lung protective ventilatory strategies have been shown to reduce mortality from adult respiratory distress syndrome (ARDS). We review the latest knowledge on the progression of lung injury by mechanical ventilation and correlate the findings of experimental work with results from clinical studies. We describe the experimental and clinical evidence of the effect of lung protective ventilatory strategies and open lung strategies on the progression of lung injury and current controversies surrounding these subjects. We describe a rational strategy, the open lung strategy, to accomplish an open lung, which may further prevent injury caused by mechanical ventilation. Finally, the clinician is offered directions on lung protective ventilation in the early phase of ARDS which can be applied on the intensive care unit.

Neutrophil apoptosis: a marker of disease severity in sepsis and sepsis-induced acute respiratory distress syndrome

Introduction

Apoptosis of neutrophils (polymorphonuclear neutrophils [PMNs]) may limit inflammatory injury in sepsis and acute respiratory distress syndrome (ARDS), but the relationship between the severity of sepsis and extent of PMN apoptosis and the effect of superimposed ARDS is unknown. The objective of this study was to correlate neutrophil apoptosis with the severity of sepsis and sepsis-induced ARDS.

Methods

A prospective cohort study was conducted in intensive care units of three tertiary hospitals in Porto Alegre, southern Brazil. Fifty-seven patients with sepsis (uncomplicated sepsis, septic shock, and sepsis-induced ARDS) and 64 controls were enrolled. Venous peripheral blood was collected from patients with sepsis within 24 hours of diagnosis. All surgical groups, including controls, had their blood drawn 24 hours after surgery. Control patients on mechanical ventilation had blood collected within 24 hours of initiation of mechanical ventilation. Healthy controls were blood donors. Neutrophils were isolated, and incubated ex vivo, and apoptosis was determined by light microscopy on cytospun preparations. The differences among groups were assessed by analysis of variance with Tukeys.

Results

In medical patients, the mean percentage of neutrophil apoptosis (± standard error of the mean [SEM]) was lower in sepsis-induced ARDS (28% ± 3.3%; n = 9) when compared with uncomplicated sepsis (57% ± 3.2%; n = 8; p < 0.001), mechanical ventilation without infection, sepsis, or ARDS (53% ± 3.0%; n = 11; p < 0.001) and healthy controls (69% ± 1.1%; n = 33; p < 0.001) but did not differ from septic shock (38% ± 3.7%; n = 12; p = 0.13). In surgical patients with sepsis, the percentage of neutrophil apoptosis was lower for all groups when compared with surgical controls (52% ± 3.6%; n = 11; p < 0.001).

Conclusion

In medical patients with sepsis, neutrophil apoptosis is inversely proportional to the severity of sepsis and thus may be a marker of the severity of sepsis in this population.

An automated method for measuring static pressure–volume curves of the respiratory system and its application in healthy lungs and after lung damage by oleic acid infusion

Elastic pressure/volume (PV) curves of the respiratory system have attracted increasing interest, because they may be helpful to optimize ventilator settings in patients undergoing mechanical ventilation. Clinically applicable methods need to be fast, use routinely available equipment, draw the inspiratory and expiratory PV curve limbs, separate the resistive and viscoelastic properties of the respiratory system from the elastic properties, and provide reproducible measurements. This paper presents a computer-controlled method for rapid measurements of static PV curves using a long inflation-deflation with pauses, and its evaluation in six pigs before and after lung damage caused by oleic acid. The method is fast, i.e. 20.5 +/- 1.9 s (mean +/- SD) in healthy lungs and 17.7 +/- 4.1 s in diseased lungs, this including inspiratory and expiratory pauses of 1.1 s duration. In addition the only equipment used was a clinical ventilator and a PC. For healthy and damaged lungs expiratory PV curve limbs were very reproducible and were at higher volume than the inspiratory limbs, indicating hysteresis. For damaged lungs inspiratory PV limbs were reproducible. For healthy lungs the inspiratory limbs were reproducible but only after the first inflation-deflation. It is possible that during the first inflation alveoli are recruited which are not derecruited on deflation, shifting the inspiratory limb of the PV curve. The paused long inflation-deflation technique provides a quick, automated measurement of static PV curves on both inspiratory and expiratory limbs using routinely available equipment in the intensive care unit.

Conventional mechanical ventilation in acute lung injury and acute respiratory distress syndrome

Acute lung injury and acute respiratory distress syndrome are inflammatory conditions involving a broad spectrum of lung injury from mild respiratory abnormality to severe respiratory derangement. Regardless of cause (direct or indirect lung injury), pulmonary physiology and mechanics are altered, leading to hypoxemic respiratory failure. the use of positive pressure ventilation itself may cause lung injury (ventilator-induced lung injury, or VILI). VILI may amplify preexisting injury, delay lung recovery, and result in adverse outcomes. This article examines the evidence supporting lung-protective ventilation strategies and addresses the methods, outcomes, and potential obstacles to implementation of such approaches.

The effect of positive end expiratory pressure on the respiratory profile during one-lung ventilation for thoracotomy

Summary In this randomised controlled trial we examined the effects of four different levels of positive end expiratory pressure (PEEP at 0, 5, 8 or 10 cmH(2)O), added to the dependent lung, on respiratory profile and oxygenation during one lung ventilation. Forty-six patients were recruited to receive one of the randomised PEEP levels during one lung ventilation. We did not find significant differences in lung compliance, intra-operative or postoperative oxygenation amongst the four different groups. However, the physiological deadspace to tidal volume ventilation ratio was significantly lower in the 8 cmH(2)O PEEP group compared with the other levels of PEEP (p < 0.0001). We concluded that the use of PEEP (< or =10 cmH(2)O) during one lung ventilation does not clinically improve lung compliance, intra-operative or postoperative oxygenation despite a statistically significant reduction in the physiological deadspace to tidal volume ratio.

The Role of CT-scan Studies for the Diagnosis and Therapy of Acute Respiratory Distress Syndrome

CT has provided new insights on the pathophysiology of acute respiratory distress syndrome (ARDS), demonstrating that ARDS does not affect the lung parenchyma homogeneously. These findings suggest that lung edema, as assessed by CT scan, should be included in the definition. Lung CT findings may provide a firm rationale for tailoring tidal volume during mechanical ventilation. Ideally, tidal volume should be proportional to the portion of the lung open to ventilation, as assessed by CT scan, rather than to the body weight. CT assessment of lung recruitability seems to be a prerequisite for a rational setting of positive end-expiratory pressure.

Acute lung injury: an indicator of serious systemic illness

The history of the acute respiratory distress syndrome (ARDS) parallels that of critical care. Descriptive and colorful names for the condition such as "shock lung," "post perfusion lung," and "traumatic wet lung" clearly communicate the reality that the pulmonary tissue is involved in a pathologic process. It is not difficult to speculate that the focus on the lung originated from the dramatic chest radiographs and gas exchange abnormalities frequently observed in association with the syndrome. However, a named condition does not necessarily dictate the therapeutic approach to it, and a review of some pertinent studies suggests the condition is in fact systemic in nature. Concurrent with this recognition, the need for markers of severity of illness has become more important. Rather than a process needing primarily pulmonary approaches to management, it now seems that ARDS is the result of systemic events with noticeable pulmonary manifestations, which may suffice as a clinical marker for severity of systemic inflammation. Because the pathophysiology has been described elsewhere, this article will focus on the clinical trials that are shaping our perception and management of the syndrome.

Ventilatory strategies and adjunctive therapy in ARDS

Acute respiratory distress syndrome, a diagnosis based on physiologic and radiological criteria, occurs commonly in critical care setting. A major challenge in evaluating therapies that may improve survival in ARDS is that it is not a single disease entity but, rather, numerous different diseases that result in endothelial injury, where the most obvious manifestation is within the lung resulting in pulmonary oedema. It has been shown that poor ventilatory technique that is injurious to the lungs can propagate systemic inflammatory response and adversely affect the mortality. The current data suggest that high tidal volumes with high plateau pressures are deleterious and a strategy of ventilation with lower tidal volumes and lower plateau pressure is associated with lower mortality. There may be a role for recruitment manoeuvres as well. Other forms of respiratory support still require further research. The present understanding of optimal ventilatory management and other adjunctive therapies are reviewed.

Limitations of clinical trials in acute lung injury and acute respiratory distress syndrome

PURPOSE OF REVIEW

To review the challenges and limitations of randomized clinical trials in acute respiratory distress syndrome, with special emphasis on those pertaining to ventilatory management.

RECENT FINDINGS

Superbly executed randomized trials of ventilatory strategy have garnered deserved attention from the critical care community and yet have illustrated the limitations of our current approach to clinical research in this area. Inexact definitions, incomplete mechanistic understanding of complex pathophysiology, inappropriate outcome variables, diverse therapeutic environments, lengthy data acquisition time and ethical constraints on trial design limit the applicability of randomized control trial methodology to acute respiratory distress syndrome and acute lung injury. As yet, clinical practice does not seem to have been greatly impacted by the implications of completed randomized controlled trials per se. Recent issues, both ethical and interpretive, regarding control group participants have raised troubling and theoretically important issues that are yet to be fully resolved.

SUMMARY

Without tighter definitions of the condition under treatment, more specific targets for interventions to act upon, stratification that recognizes key interactive elements, and cointerventions based on better mechanistic understanding, randomized controlled trials of new drugs, ventilatory strategy, and other management approaches in acute respiratory distress syndrome are likely to remain a blunt instrument for investigation. As valuable as they are for calling important therapeutic principles to attention and for helping to suggest general guidelines for care, the limitations of randomized controlled trials for treating the individual with acute respiratory distress syndrome must be acknowledged.

Lung-protective ventilation in neurosurgical patients

PURPOSE OF REVIEW

Concepts of ventilator-induced lung injury have revolutionized our approach to the ventilatory management of patients with acute lung injury and acute respiratory distress syndrome over the past 10 years. The extension of these principles to patients with brain injuries is challenging, as many of them are out of keeping with usual brain-protective management.

RECENT FINDINGS

Many patients with acute lung injury or acute respiratory distress syndrome and an acute brain injury may in fact be managed safely within the confines of a lung-protective strategy. Elevated levels of positive end-expiratory pressure in head-injured patients with acute lung injury or acute respiratory distress syndrome also appear to be safe, particularly when the level is set below that of the intracranial pressure, when patients have a low respiratory system compliance, or when positive end-expiratory pressure results in significant lung volume recruitment. Several novel therapies to minimize ventilator-induced lung injury are currently in the early stages of investigation in neurosurgical patients.

SUMMARY

In many patients with brain injuries and acute lung injury the goals of lung protection can be achieved without threatening cerebral perfusion. In patients with more refractory raised intracranial pressure the optimal balance between brain and lung is not well established. Further research is needed on lung-protective strategies in this vulnerable population.

Stretch-induced phosphorylation of focal adhesion kinase in endothelial cells: role of mitochondrial oxidants

Mechanical stretch activates a number of signaling pathways in endothelial cells, and it elicits a variety of functional responses including increases in the phosphorylation of focal adhesion kinase (FAK), a nonreceptor tyrosine kinase involved in integrin-mediated signal transduction. Stretch also triggers an increase in the generation of reactive oxygen species (ROS), which may function as second messengers in the signal transduction cascades that activate cellular responses to strain. Mitochondria represent an important source of ROS in the cell, and these organelles may release ROS in response to strain by virtue of their attachment to cytoskeletal proteins. We therefore tested whether cyclic stretch increases FAK phosphorylation at Tyr397 through a mitochondrial ROS signaling pathway in bovine pulmonary artery endothelial cells (BPAEC). Oxidant signaling, measured using 2′7′-dichlorofluorescin (DCFH), increased 152 ± 16% during 1.5 h of cyclic strain relative to unstrained controls. The mitochondrial inhibitors diphenylene iodonium (5 μM) or rotenone (2 μM) attenuated this increase, whereas l-nitroarginine (100 μM), allopurinol (100 μM), or apocynin (30 μM) had no effect. The antioxidants ebselen (5 μM) and dithiodidiethyldithiocarbamate (1 mM) inhibited the strain-induced increase in oxidant signaling, but Hb (5 μM) had no effect. These results indicate that strain induces oxidant release from mitochondria. Treatment with cytochalasin D (5 μM) abrogated strain-induced DCFH oxidation in BPAEC, indicating that actin filaments were required for stretch-induced mitochondrial ROS generation. Cyclic strain increased FAK phosphorylation at Tyr397, but this was abolished by mitochondrial inhibitors as well as by antioxidants. Strain-induced FAK phosphorylation was abrogated by inhibition of protein kinase C (PKC) with Ro-31-8220 or Gö-6976. These findings indicate that mitochondrial oxidants generated in response to endothelial strain trigger FAK phosphorylation through a signaling pathway that involves PKC.

Sepsis-induced lung injury in rats increases alveolar epithelial vulnerability to stretch

OBJECTIVE

Previous in vitro models have shown that cellular deformation causes dose-dependent injury and death in healthy rat alveolar epithelial cells (AECs). We compared the viability of AECs from septic rats with those from nonseptic rats after 1 hr of cyclic equibiaxial stretch. We hypothesized that sepsis would increase stretch-induced cell death.

DESIGN

Laboratory investigation.

SETTING

University research laboratory.

SUBJECTS

Thirty-seven male Sprague-Dawley rats weighing 240-260 g.

INTERVENTIONS

Anesthetized rats were subjected to cecal ligation and double puncture (2CLP) or sham laparotomy without cecal ligation or puncture (sham). After 24 or 48 hrs, AECs were isolated, seeded in custom wells, and maintained in culture for 48 hrs before study. AECs were stretched cyclically (15/min) to a 0%, 12%, 25%, or 37% change in surface area (DeltaSA) for 1 hr. Cell viability, phenotypic markers, and nuclear factor-kappaB intracellular localization were assessed using fluorescent immunocytochemistry.

MEASUREMENTS AND MAIN RESULTS

Phase and fluorescent images were evaluated for all studies. Response to stretch was the same at 24 and 48 hrs after 2CLP. Relative to sham, 2CLP significantly increased cell death at 25 and 37% DeltaSA (p<.003, analysis of variance). Relative to sham, 2CLP did not alter expression of type I or type II phenotypic markers. Nuclear factor-kappaB within the nuclear compartment was observed after 2CLP in unstretched cells and after 1 hr of cyclic stretch at 37% DeltaSA. In sham, nuclear factor-kappaB within the nuclear compartment was seen only after stretch.

CONCLUSIONS

AECs isolated from septic rats are more vulnerable to mechanical deformation injury than AECs from nonseptic animals.

A high positive end-expiratory pressure, low tidal volume ventilatory strategy improves outcome in persistent acute respiratory distress syndrome: a randomized, controlled trial

OBJECTIVE

It has been shown in a two-center study that high positive end-expiratory pressure (PEEP) and low tidal volume (LTV) improved outcome in ARDS. However, that study involved patients with underlying diseases unique to the study area, was conducted at only two centers, and enrolled a small number of patients. We similarly hypothesized that a ventilatory strategy based on PEEP above the lower inflection point of the pressure volume curve of the respiratory system (Pflex) set on day 1 with a low tidal volume would result in improved outcome in patients with severe and persistent acute respiratory distress syndrome (ARDS).

DESIGN

Randomized, controlled clinical trial.

SETTING

Network of eight Spanish multidisciplinary intensive care units (ICUs) under the acronym of ARIES (Acute Respiratory Insufficiency: España Study).

PATIENTS

All consecutive patients admitted into participating Spanish ICUs from March 1999 to March 2001 with a diagnosis of ARDS were considered for the study. If 24 hrs after meeting ARDS criteria, the Pao2/Fio2 remained < or =200 mm Hg on standard ventilator settings, patients were randomized into two groups: control and Pflex/LTV.

INTERVENTIONS

In the control group, tidal volume was 9-11 mL/kg of predicted body weight (PBW) and PEEP > or =5 cm H2O. In the Pflex/LTV group, tidal volume was 5-8 mL/kg PBW and PEEP was set on day 1 at Pflex + 2 cm H2O. In both groups, Fio2 was set to maintain arterial oxygen saturation >90% and Pao2 70-100 mm Hg, and respiratory rate was adjusted to maintain Paco2 between 35 and 50 mm Hg.

MEASUREMENTS AND MAIN RESULTS

The study was stopped early based on an efficacy stopping rule as described in the methods. Of 103 patients who were enrolled (50 control and 53 Pflex), eight patients (five in control, three in Pflex) were excluded from the final evaluation because the random group assignment was not performed in one center according to protocol. Main outcome measures were ICU and hospital mortality, ventilator-free days, and nonpulmonary organ dysfunction. ICU mortality (24 of 45 [53.3%] vs. 16 of 50 [32%], p = .040), hospital mortality (25 of 45 [55.5%] vs. 17 of 50 [34%], p = .041), and ventilator-free days at day 28 (6.02 +/- 7.95 in control and 10.90 +/- 9.45 in Pflex/LTV, p = .008) all favored Pflex/LTV. The mean difference in the number of additional organ failures postrandomization was higher in the control group (p < .001).

CONCLUSIONS

A mechanical ventilation strategy with a PEEP level set on day 1 above Pflex and a low tidal volume compared with a strategy with a higher tidal volume and relatively low PEEP has a beneficial impact on outcome in patients with severe and persistent ARDS.

Partial Liquid Ventilation in Adult Patients with Acute Respiratory Distress Syndrome

RATIONALE

Despite recent clinical trials demonstrating improved outcome in acute respiratory distress syndrome (ARDS), mortality remains high. Partial liquid ventilation (PLV) using perfluorocarbons has been shown to improve oxygenation and decrease lung injury in various animal models.

OBJECTIVE

To determine if PLV would have an impact on outcome in patients with ARDS.

METHODS

Patients with ARDS were randomized to (1) conventional mechanical ventilation (CMV; n=107), (2) "low-dose" perfluorocarbon (10 ml/kg; n=99), and (3) "high-dose" perfluorocarbon (20 ml/kg; n=105). Patients in all three groups were ventilated using volume ventilation, Vt <or= 10 ml/kg predicted body weight, rate <or= 25/min, inspiratory-to-expiratory ratio <or= 1:1, Fi(O(2)) >or= 0.5, and positive end-expiratory pressure >or= 13 cm H(2)O.

RESULTS

The 28-d mortality in the CMV group was 15%, versus 26.3% in the low-dose (p=0.06) and 19.1% in the high-dose (p=0.39) PLV groups. There were more ventilator-free days in the CMV group (13.0+/-9.3) compared with both the low-dose (7.4+/-8.5; p<0.001) and high-dose (9.9+/-9.1; p=0.043) groups. There were more pneumothoraces, hypoxic episodes, and hypotensive episodes in the PLV patients.

CONCLUSIONS

PLV at both high and low doses did not improve outcome in ARDS compared with CMV and cannot be recommended for patients with ARDS.

Mechanical Ventilation and Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome continues to be a high-mortality condition. The role of mechanical ventilation remains primarily a supportive modality. Recent research has elucidated the adverse impact of traditional ventilation strategies on development of the disease and, ultimately, mortality. The institution of low tidal volume ventilation has been the only intervention that has resulted in definitive improvement in survival. Animal and human investigations that culminated in the Acute Respiratory Distress Syndrome Network low tidal volume study are reviewed. Current controversies in the application of mechanical ventilation including the use of positive end-expiratory pressure, recruitment maneuvers, and high frequency oscillatory ventilation are also addressed.

Comparison of variable and conventional ventilation in a sheep saline lavage lung injury model*

OBJECTIVE

There has recently been considerable interest in alternative lung-protective ventilation strategies such as variable ventilation (VV). We aimed at testing VV in a large animal lung injury model and exploring the mechanism of improvement in gas exchange seen with VV.

DESIGN

Randomized, controlled comparative ventilation study.

SETTING

Research laboratory at a veterinary hospital.

SUBJECTS

Female sheep weighing 59.8 +/- 10.57 kg and excised calf lungs.

INTERVENTIONS

In a sheep saline lavage model of lung injury, we applied VV, whereby tidal volume (VT) and frequency (f) varied on each breath. Sheep were randomized into one of two groups (VV, n = 7; or control, n = 6) and ventilated for 4 hrs with all mean ventilation settings matched.

MEASUREMENTS AND MAIN RESULTS

Gas exchange, lung mechanics, and hemodynamic measures were recorded over the 4 hrs. VV sheep showed improvement in gas exchange (i.e., oxygenation and carbon dioxide elimination) and ventilation pressures (i.e., reduced mean and peak airway pressures) but control sheep did not. VV sheep also displayed lower-lung elastance and mechanical heterogeneity in comparison with control sheep from 2 to 4 hrs of ventilation. To study the mechanism behind improvements seen with VV, we examined the time course associated with the enhanced recruitment occurring during VV in eight saline-lavaged excised calf lungs. We found that the recruitment associated with a larger VT during VV lasted over 200 secs, nearly an order of magnitude greater than the average time interval between large VT deliveries during VV.

CONCLUSIONS

The application of VV in a large animal model of lung injury results in improved gas exchange and superior lung mechanics in comparison with CV that can be explained at least partially by the long-lasting effects of the recruitments occurring during VV.

High tidal volume and positive fluid balance are associated with worse outcome in acute lung injury

STUDY OBJECTIVES

Recent data have suggested that ventilatory strategy could influence outcomes from acute lung injury (ALI) and ARDS. We tested the hypothesis that infection/sepsis and use of higher tidal volumes than those applied in the ARDS Network (ARDSnet) study (> 7.4 mL/kg of predicted body weight) would worsen outcome in patients with ALI/ARDS.

DESIGN

International cohort, observational study.

SETTING

One hundred ninety-eight European ICUs participating in the Sepsis Occurrence in Acutely Ill Patients study.

PATIENTS OR PARTICIPANTS

All 3,147 adult patients admitted to one of the participating ICUs between May 1, 2002, and May 15, 2002.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Patients were followed up until death, hospital discharge, or for 60 days. Of the 3,147 patients, 393 patients (12.5%) had ALI/ARDS. ICU and hospital mortality was higher in patients with ALI/ARDS than those without ALI/ARDS (38.9% vs 15.6% and 45.5% vs 21.0%, respectively; p < 0.001). A multivariable logistic regression analysis with ICU outcome as the dependent factor showed that the independent risks for mortality were as follows: presence of cancer, use of tidal volumes higher than those used by the ARDSnet study, degree of multiorgan dysfunction, and higher mean fluid balance. Sepsis, septic shock, and oxygenation at the onset of ALI/ARDS were not independently associated with higher mortality rates.

CONCLUSIONS

In addition to comorbidities and organ dysfunction, high tidal volumes and positive fluid balance are associated with a worse outcome from ALI/ARDS.

Current issues in mechanical ventilation for respiratory failure

The morbidity and mortality associated with respiratory failure is, to a certain extent, iatrogenic. Mechanical ventilation, although the mainstay of treatment for respiratory distress syndrome, can result in physical trauma to lung tissue (ventilator-induced lung injury [VILI]). Strategies to alleviate VILI are often termed lung-protective strategies and are aimed at reducing overstretching and shear stresses associated with repetitive alveolar collapse and reopening. Lower tidal volumes during ventilation, maintenance of positive-end expiratory pressure, and high-frequency ventilation are the best-studied lung-protective strategies that appear to reduce VILI. Faster withdrawal from mechanical ventilation could also improve outcomes and lower the costs associated with care. To enhance the success of weaning from mechanical ventilation, the cooperative efforts of physicians and respiratory therapists are needed. These efforts involve the initiation of spontaneous-breathing trials, implementation of systematic weaning protocols, and optimization of individual patient interventions.

Alveolar recruitment in acute lung injury

Alveolar recruitment is one of the primary goals of respiratory care for acute lung injury. It is aimed at improving pulmonary gas exchange and, even more important, at protecting the lungs from ventilator-induced trauma. This review addresses the concept of alveolar recruitment for lung protection in acute lung injury. It provides reasons for why atelectasis and atelectrauma should be avoided; it analyses current and future approaches on how to achieve and preserve alveolar recruitment; and it discusses the possibilities of detecting alveolar recruitment and derecruitment. The latter is of particular clinical relevance because interventions aimed at lung recruitment are often undertaken without simultaneous verification of their effectiveness.

Tidal volume reduction in patients with acute lung injury when plateau pressures are not high

Use of a volume- and pressure-limited mechanical ventilation strategy improves clinical outcomes of patients with acute lung injury and acute respiratory distress syndrome (ALI/ARDS). However, the extent to which tidal volumes and inspiratory airway pressures should be reduced to optimize clinical outcomes is a controversial topic. This article addresses the question, "Is there a safe upper limit to inspiratory plateau pressure in patients with ALI/ARDS?" We reviewed data from animal models with and without preexisting lung injury, studies of normal human respiratory system mechanics, and the results of five clinical trials of lung-protective mechanical ventilation strategies. We also present an original analysis of data from the largest of the five clinical trials. The available data from each of these assessments do not support the commonly held view that inspiratory plateau pressures of 30 to 35 cm H2O are safe. We could not identify a safe upper limit for plateau pressures in patients with ALI/ARDS.

Acute respiratory distress syndrome: a historical perspective

Though well described even in ancient writings, the acute respiratory distress syndrome (ARDS) gained major medical attention with the availability of mechanical ventilation and establishment of intensive care units. In the 50 years since this beginning there have been remarkable advances in the understanding of the etiology, physiology, histology, and epidemiology of this often lethal complication of common human maladies. Until recently, improvements in outcome have mainly followed improvements in intensive care unit operation and their associated life support systems, and have not come through discoveries made in the course of prospective randomized trials. In spite of the remarkable increase in research focused on ARDS, there remain a large number of unanswered clinical questions that are potentially extremely important with regard to short-term morbidity as well as long-term outcome. The ARDS Clinical Trials Network study of tidal volume has proven that randomized trials in ARDS with positive results are possible even when using difficult primary outcome measures such as mortality or ventilator-free days. Therefore, the rich combination of new trial strategies, potential treatments, experienced investigators, and increasingly standardized routine care set the stage for rapid advances to be made in the short- and long-term outcomes of this devastating syndrome.

Ventilatory strategies in patients with sepsis and respiratory failure

Patients with sepsis may require mechanical ventilation due to the acute respiratory distress syndrome (ARDS). It has become increasingly accepted that mechanical ventilation can contribute to lung injury in these patients. The modern concept of ventilator-induced lung injury is described in the context of alveolar over-distention (volutrauma), alveolar de-recruitment (atelectrauma), and biochemical injury and inflammation to the lung parenchyma (biotrauma). To avoid over-distention lung injury, the tidal volume should be set at 6 mL/kg predicted body weight and plateau pressure should be limited to 30 cm H2O. This has been shown to afford a survival benefit. Although setting positive end-expiratory pressure (PEEP) to zero is likely harmful during mechanical ventilation of patients with ARDS, evidence is lacking for a survival benefit if a high PEEP level is set compared with a modest level of PEEP. Although adjunctive measures such as recruitment maneuvers, prone position, and inhaled nitric oxide may improve oxygenation, evidence is lacking that these measures improve survival.

Ventilatory Support of the Critically Ill Foal

Critically ill foals often have respiratory failure and benefit from respiratory support. Conventional mechanical ventilation using modem mechanical ventilators is easily adapted to foals. Establish-ing ventilator settings is a dynamic process aided by constant monitoring of blood gas values, end-tidal carbon dioxide, airway pressures, respiratory volumes, airway resistance, and respiratory compliance. Early weaning is as important as timely initiation of ventilation.

How to ventilate patients with acute lung injury and acute respiratory distress syndrome

PURPOSE OF REVIEW

The purpose of this paper is to review the mechanisms of ventilator-induced lung injury as a basis for providing the less damaging mechanical ventilation in patients with acute respiratory failure.

RECENT FINDINGS

In normal lungs, high tidal volume causes an immediate gene upregulation and downregulation. Although the importance of alveolar inflammatory reaction is well known, recent findings suggest the potential role of airway distension in causing ventilator-induced lung injury. The initial activation has been shown to occur in the airways, accounting for the damages induced by high peak flow. The healthier lung regions are more exposed to the injury, since they may be subjected to strain. Challenge with endotoxin enhances in a synergistic manner the pulmonary inflammation induced by mechanical ventilation. However, mechanical strain and endotoxin seem to trigger lung inflammation through two different pathways. Despite convincing experimental and clinical evidences of lung injury, the clinical implementation of low tidal volume ventilation is still limited and has not yet become part of standard clinical practice. Setting positive end-expiratory pressure remains an open problem because the ALVEOLI study did not provide any exhaustive answers, likely because of methodologic problems and, unphysiologic design.

SUMMARY

Gentle lung ventilation must be standard practice. Because stress and strain are the triggers of ventilator-induced lung injury, their clinical equivalents should be measured (transpulmonary pressure and the ratio between tidal volume and end-expiratory lung volume). For a rational application of positive end-expiratory pressure, the potential for recruitment in any single patient should be estimated.

Mathematical modelling to centre low tidal volumes following acute lung injury: a study with biologically variable ventilation

BACKGROUND

With biologically variable ventilation [BVV--using a computer-controller to add breath-to-breath variability to respiratory frequency (f) and tidal volume (VT)] gas exchange and respiratory mechanics were compared using the ARDSNet low VT algorithm (Control) versus an approach using mathematical modelling to individually optimise VT at the point of maximal compliance change on the convex portion of the inspiratory pressure-volume (P-V) curve (Experimental).

METHODS

Pigs (n = 22) received pentothal/midazolam anaesthesia, oleic acid lung injury, then inspiratory P-V curve fitting to the four-parameter logistic Venegas equation F(P) = a + b[1 + e-(P-c)/d]-1 where: a = volume at lower asymptote, b = the vital capacity or the total change in volume between the lower and upper asymptotes, c = pressure at the inflection point and d = index related to linear compliance. Both groups received BVV with gas exchange and respiratory mechanics measured hourly for 5 hrs. Postmortem bronchoalveolar fluid was analysed for interleukin-8 (IL-8).

RESULTS

All P-V curves fit the Venegas equation (R2 > 0.995). Control VT averaged 7.4 +/- 0.4 mL/kg as compared to Experimental 9.5 +/- 1.6 mL/kg (range 6.6 - 10.8 mL/kg; p < 0.05). Variable VTs were within the convex portion of the P-V curve. In such circumstances, Jensen's inequality states "if F(P) is a convex function defined on an interval (r, s), and if P is a random variable taking values in (r, s), then the average or expected value (E) of F(P); E(F(P)) > F(E(P))." In both groups the inequality applied, since F(P) defines volume in the Venegas equation and (P) pressure and the range of VTs varied within the convex interval for individual P-V curves. Over 5 hrs, there were no significant differences between groups in minute ventilation, airway pressure, blood gases, haemodynamics, respiratory compliance or IL-8 concentrations.

CONCLUSION

No difference between groups is a consequence of BVV occurring on the convex interval for individualised Venegas P-V curves in all experiments irrespective of group. Jensen's inequality provides theoretical proof of why a variable ventilatory approach is advantageous under these circumstances. When using BVV, with VT centred by Venegas P-V curve analysis at the point of maximal compliance change, some leeway in low VT settings beyond ARDSNet protocols may be possible in acute lung injury. This study also shows that in this model, the standard ARDSNet algorithm assures ventilation occurs on the convex portion of the P-V curve.

Bench-to-bedside review: adjuncts to mechanical ventilation in patients with acute lung injury

Mechanical ventilation is indispensable for the survival of patients with acute lung injury and acute respiratory distress syndrome. However, excessive tidal volumes and inadequate lung recruitment may contribute to mortality by causing ventilator-induced lung injury. This bench-to-bedside review presents the scientific rationale for using adjuncts to mechanical ventilation aimed at optimizing lung recruitment and preventing the deleterious consequences of reduced tidal volume. To enhance CO₂ elimination when tidal volume is reduced, the following are possible: first, ventilator respiratory frequency can be increased without necessarily generating intrinsic positive end-expiratory pressure; second, instrumental dead space can be reduced by replacing the heat and moisture exchanger with a conventional humidifier; and third, expiratory washout can be used for replacing the CO₂-laden gas present at end expiration in the instrumental dead space by a fresh gas (this method is still experimental). For optimizing lung recruitment and preventing lung derecruitment there are the following possibilities: first, recruitment manoeuvres may be performed in the most hypoxaemic patients before implementing the preset positive end-expiratory pressure or after episodes of accidental lung derecruitment; second, the patient can be turned to the prone position; third, closed-circuit endotracheal suctioning is to be preferred to open endotracheal suctioning.

Acute effects of upright position on gas exchange in patients with acute respiratory distress syndrome

Patients with acute respiratory distress syndrome (ARDS) have dorsal atelectasis of the lungs. This is probably caused by several mechanisms: compression on dependent lung zones, purulent secretions in alveoli, and upward shift of the diaphragm. An upright position (UP) of the patient (the whole body in a straight line at 40 to 45 degrees) can theoretically ameliorate these mechanisms. The objective was to evaluate whether there was an improvement of gas exchange during UP of ARDS patients and to evaluate the hemodynamic effects. A prospective interventional study was performed in the surgical and medical ICUs and the burn unit of the Ghent University Hospital, a tertiary care center. Included were ARDS patients with onset of ARDS within 48 hours before start of the study. Patients were excluded when there was hemodynamic instability or when the PaO2/FiO2 ratio deteriorated during the 2 hours preceding UP. After a 2-hour observation period in a semirecumbent position, patients were put in UP for 12 hours. Respiration and hemodynamic data were recorded at the start and end of the 2-hour observation period, and after 1, 4, and 12 hours in UP. Eighteen patients were included in the study. There was a significant increase of the PaO2/FiO2 ratio during UP (P < .001). Except for the need for volume resuscitation in 5 patients (27.8%), there was no significant change in the hemodynamic profile of the patients. Upright positioning of patients with ARDS, a relatively simple maneuver, resulted in an improvement of gas exchange and was tolerated hemodynamically relatively well during a 12-hour observation period.

Acute Respiratory Distress Syndrome

Acute lung injury is a syndrome diagnosed clinically and is one of the most common causes of respiratory failure seen in the intensive care unit. A consensus definition of this and its more severe form, acute respiratory distress syndrome (ARDS), has allowed for better consistency in determining the epidemiology and facilitates consistent clinical trial design to better find therapies to treat or prevent it. Patients who present with ARDS usually show signs of tachpnea or dyspnea and have underlying conditions that promote inflammatory responses. The pathogenesis involves an inflammatory insult that eventually destroys the pulmonary capillary vasculature as well as alveoli. Pathophysiologically, the patient with ARDS may progress through as many as 3 phases: exudative, proliferative, and fibrotic. Treatment options can be either nonpharmacologic or pharmacologic and are limited. Ventilator strategies such as low-tidal-volume ventilation have improved outcomes in these patients, while corticosteroid use is not as established to provide morbidity or mortality benefit. Other therapies have been investigated with inconclusive or disappointing results for the treatment of this fatal syndrome.

Adjunctive homeopathic treatment in patients with severe sepsis: a randomized, double-blind, placebo-controlled trial in an intensive care unit

BACKGROUND

Mortality in patients with severe sepsis remains high despite the development of several therapeutic strategies. The aim of this randomized, double-blind, placebo-controlled trial was to evaluate whether homeopathy is able to influence long-term outcome in critically ill patients suffering from severe sepsis.

METHODS

Seventy patients with severe sepsis received homeopathic treatment (n = 35) or placebo (n = 35). Five globules in a potency of 200c were given at 12h interval during the stay at the intensive care unit. Survival after a 30 and 180 days was recorded.

RESULTS

Three patients (2 homeopathy, 1 placebo) were excluded from the analyses because of incomplete data. All these patients survived. Baseline characteristics including age, sex, BMI, prior conditions, APACHE II score, signs of sepsis, number of organ failures, need for mechanical ventilation, need for vasopressors or veno-venous hemofiltration, and laboratory parameters were not significantly different between groups. On day 30, there was non-statistically significantly trend of survival in favour of homeopathy (verum 81.8%, placebo 67.7%, P= 0.19). On day 180, survival was statistically significantly higher with verum homeopathy (75.8% vs 50.0%, P = 0.043). No adverse effects were observed.

CONCLUSIONS

Our data suggest that homeopathic treatment may be a useful additional therapeutic measure with a long-term benefit for severely septic patients admitted to the intensive care unit. A constraint to wider application of this method is the limited number of trained homeopaths.

Acute respiratory distress syndrome: update on the latest developments in basic and clinical research

PURPOSE OF REVIEW

Acute lung injury/acute respiratory distress syndrome is a common, serious condition affecting a heterogeneous population of critically ill patients. Other than low tidal volume ventilation, no specific therapy has improved survival. Understanding the epidemiology, pathogenesis, and lessons to be learned from previous clinical trials is necessary for the development of new therapies and the rational design of studies assessing their efficacy.

RECENT FINDINGS

Acute lung injury/acute respiratory distress syndrome occurs in 6-8% of the general intensive care unit population, with a mortality of 32-45%. A recent epidemiologic study found that multi-organ dysfunction, use of tidal volumes higher than 6 ml/kg, and high mean fluid balance were independent risks for mortality. Although high levels of inflammatory mediators are also markers for acute respiratory distress syndrome development and death, short courses of high-dose steroids are not effective in acute cases. The latest theory of biotrauma proposes cellular mechanisms by which mechanical ventilation incites a local and systemic inflammatory response; protective lung ventilation with low tidal volumes can attenuate this inflammation and injury to distal organs. Endogenous surfactant function is clearly impaired, but no commercially available surfactant preparation has been shown to reduce mortality. Results of trials to determine efficacy of steroids in late cases and optimal fluid management are pending.

SUMMARY

The results of recent clinical trials have raised more questions. Further study of the inflammatory response, surfactant regulation, and the cellular impact of mechanical ventilation should help to develop new therapies, target patients most likely to benefit, and identify appropriate timing of intervention.

Protocols for lung protective ventilation

Protocols have a well-established role in clinical research and are increasingly being used to direct routine clinical care. In this article, we review the differing goals of research and clinical protocols and outline the similar process for their development. We use the mechanical ventilation protocol of the ARDS Network trial comparing small with traditional tidal volumes as an example. As a starting point for debate, we also suggest guiding principles and specific components of a protocol for high-frequency oscillatory ventilation.

Airway pressures, tidal volumes, and mortality in patients with acute respiratory distress syndrome

OBJECTIVE

To determine the usual practice for setting tidal volume and other ventilatory parameters in patients with acute respiratory distress syndrome (ARDS) in the late 1990s and to determine the independent effects of these practices on intensive care unit mortality.

DESIGN

Subanalysis of a prospective observational study. Multivariable logistic regression was used to analyze the effects of ventilatory management on mortality.

SETTING

A total of 361 intensive care units in 20 countries in March 1998.

PATIENTS

A total of 467 mechanically ventilated patients with ARDS.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The mean tidal volume used in the first week of ARDS was 8.8 mL/kg measured body weight, and there was great variability in these tidal volumes (sd = 2.0). Tidal volumes were significantly lower in patients with (n = 265) than without (n = 202) a recorded plateau pressure (8.6 vs. 9.1 mL/kg, p = .01). The overall intensive care unit mortality rate was 60.2%. In addition to the strong influence of organ failures and higher levels of inspired oxygen, late-onset ARDS (onset after >48 hrs of mechanical ventilation; odds ratio, 2.09) was independently associated with mortality. In addition, lower levels of positive end-expiratory pressure were independently associated with higher mortality (odds ratio, 0.91; 1 cm of H2O increments). Neither inspiratory pressures nor tidal volumes were independently associated with mortality, and there was no evidence of increased mortality with the use of lower inspiratory pressures.

CONCLUSIONS

This descriptive study demonstrated considerable interpatient variability in tidal volumes during the study period. In addition to traditional prognostic indicators, timing of ARDS onset and the use of low levels of positive end-expiratory pressure or no positive end-expiratory pressure during the first week may adversely influence outcome in ARDS patients.

Centromere DNA, proteins and kinetochore assembly in vertebrate cells

The centromere is a specialized region of the chromosome that is essential for faithful chromosome segregation during mitosis and meiosis in eukaryotic cells. It is the site at which the kinetochore, the functional nucleoprotein complex responsible for microtubule binding and chromosome movement, is assembled through complex molecular mechanisms. Herein, I review recent advances in our understanding of centromeric DNAs as sites for kinetochore assembly and the mechanisms underlying kinetochore assembly in vertebrate cells.

Progress in Postoperative ICU Management

The clinical case presented in this article illustrates how many of the more recent advances in the management of critically ill patients apply to current clinical practice. Simple cost-effective general measures (eg, optimal sterile precautions during procedures; hand washing; early goal-directed resuscitation with appropriate fluids, inotropes, and antibiotics; and surgical source control of infected foci) still should form the basis of clinical practice, however. There has been renewed interest in blood transfusion therapy and its associated risks. Lower tidal volume ventilation now is practiced almost universally in patients with ARDS, and several new selective pulmonary vasodilators have extended the armamentarium when taking care of these patients. High-frequency oscillatory ventilation and ECMO remain challenging options in patients with refractory hypoxemia. Appropriate patient selection is important when corticosteroid therapy is considered. Tight blood glucose control and monitoring improve outcome and should be part of ICU care of septic patients. The role of the PAC is controversial. Other techniques to measure cardiac output, hemodynamics, and perfusion are available and should be considered. Sedation and analgesia form an integral part of critical care. Because of its immediate and long-term risks, neuromuscular blockade should be used sparingly and only when all other options have been exhausted. Ongoing education regarding sedation protocols and the effect of sedation on outcome is needed among physicians and nurses caring for these patients.

Meta-analysis of controlled trials of ventilator therapy in acute lung injury and acute respiratory distress syndrome: an alternative perspective

OBJECTIVE

The role of protective ventilation in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) is controversial. Evidence was sought from published randomised trials for a consistent treatment effect of protective ventilation and any covariate modification.

DESIGN

Meta-analysis of protective ventilation trials in ALI/ARDS and meta-regression of covariates on treatment effect (log odds ratio), with respect to 28-day mortality. Heterogeneity impact on the meta-analysis was assessed by the H statistic (substantial impact, >1.5) and graphical analysis. Five trials with a total of 1,202 patients were considered.

MEASUREMENTS AND RESULTS

Average 28-day mortality was 0.40 in the treatment group (protective ventilation, n=605) vs. 0.46 in the control group (control ventilation, n=597). The treatment effect (odds ratio) was: fixed-effects, 0.71 (95% CI 0.56-0.91, p=0.006; heterogeneity, p=0.06) and random effects: 0.80 (95% CI 0.49-1.31, p=0.37). Heterogeneity impact (H statistic=1.50) was adjudged as modest. The treatment effect was significant and (a) favoured protective ventilation for a tidal volume less than 7.7 ml/kg predicted (treatment group) and a mean plateau pressure of 30 cmH(2)O or higher (control group) but was not influenced by plateau pressure 21-30 cmH(2)O (treatment group) and (b) depended upon plateau pressure difference greater than 5-7 cmH(2)O between protective ventilation and standard ventilation.

CONCLUSIONS

Overall treatment effect estimate favoured protective ventilation but did not achieve statistical significance. Protective ventilation depended upon threshold levels of tidal volume, plateau pressure, and plateau pressure difference.

Acute effects of tidal volume strategy on hemodynamics, fluid balance, and sedation in acute lung injury*

OBJECTIVE

To examine the effects of mechanical ventilation with a tidal volume of 6 mL/kg compared with 12 mL/kg predicted body weight on hemodynamics, vasopressor use, fluid balance, diuretics, sedation, and neuromuscular blockade within 48 hrs in patients with acute lung injury and acute respiratory distress syndrome.

DESIGN

Retrospective analysis of a previously conducted randomized, clinical trial.

SETTING

Two adult intensive care units at a tertiary university medical center and a large county hospital.

PATIENTS

One hundred eleven patients who were enrolled in the National Institutes of Health ARDS Network trial at the University of California, San Francisco.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Compared with 12 mL/kg predicted body weight, treatment with a tidal volume of 6 mL/kg predicted body weight had no adverse effects on hemodynamics. There were also no differences in the need for supportive therapies, including vasopressors, intravenous fluids, or diuretics. In addition, there were no differences in body weight, urine output, and fluid balance. Finally, there was no difference in the need for sedation or neuromuscular blockade between the two tidal volume protocols.

CONCLUSIONS

When compared with ventilation with 12 mL/kg predicted body weight, patients treated with the lung-protective 6 mL/kg predicted body weight tidal volume protocol had no difference in their supportive care requirements. Therefore, concerns regarding potential adverse effects of this protocol should not preclude its use in patients with acute lung injury or the acute respiratory distress syndrome.