Prone positioning attenuates and redistributes ventilator-induced lung injury in dogs

Relationship between gas exchange response to prone position and lung recruitability during acute respiratory failure

PURPOSE

To clarify whether the gas exchange response to prone position is associated with lung recruitability in mechanically ventilated patients with acute respiratory failure.

METHODS

In 32 patients, gas exchange response to prone position was investigated as a function of lung recruitability, measured by computed tomography in supine position.

RESULTS

No relationship was found between increased oxygenation in prone position and lung recruitability. In contrast, the decrease of PaCO(2) was related with lung recruitability (R(2) 0.19; P = 0.01). Patients who decreased their PaCO(2) more than the median value (-0.9 mmHg) had a greater lung recruitability (19 +/- 16 vs. 8 +/- 6%; P = 0.02), higher baseline PaCO(2) (48 +/- 8 vs. 41 +/- 11 mmHg; P = 0.07), heavier lungs (1,968 +/- 829 vs. 1,521 +/- 342 g; P = 0.06) and more non-aerated tissue (1,009 +/- 704 vs. 536 +/- 188 g; P = 0.02) than those who did not.

CONCLUSIONS

During prone position, changes in PaCO(2), but not in oxygenation, are associated with lung recruitability which, in turn, is associated with the severity of lung injury.

Effect of recruitment and body positioning on lung volume and oxygenation in acute lung injury model

The mechanism of oxygenation improvement after recruitment manoeuvres or prone positioning in acute lung injury or acute respiratory distress syndrome is still unclear. We tried to determine the mechanism responsible for the effects of recruitment manoeuvres or prone positioning on lung aeration using a whole lung computed tomography scan in an oleic acid induced acute lung injury canine model. Twelve adult mongrel dogs were allocated into either the supine group (n=6) or the prone group (n=6). After the establishment of acute lung injury, three recruitment manoeuvres were performed at one-hour intervals. Haemodynamic and ventilatory variables, arterial blood gas analyses and CT scans of the whole lung were obtained 90 minutes after oleic acid injection and five minutes before and after each recruitment manoeuvre. Recruitment manoeuvres in the supine position improved oxygenation (P=0.025) that correlated with increase of the poorly- and well-aerated dorsal (dependent) lung volume (r=0.436, P=0.016). Prone positioning increased oxygenation (P=0.004) that also correlated with increase of the poorly- and well-aerated dorsal (nondependent) lung volume (r=0.787, P<0.001). However, the recruitment manoeuvre in the prone position had no effect on oxygenation despite an increase in ventral (dependent) lung volume. The increase in PaO2 after recruitment manoeuvres in the supine position or after prone positioning is related to the increase of the poorly- and well-aerated dorsal lung.

Propagation prevention: a complementary mechanism for "lung protective" ventilation in acute respiratory distress syndrome

OBJECTIVE

To describe the clinical implications of an often neglected mechanism through which localized acute lung injury may be propagated and intensified.

DATA EXTRACTION AND SYNTHESIS

Experimental and clinical evidence from the medical literature relevant to the airway propagation hypothesis and its consequences.

CONCLUSIONS

The diffuse injury that characterizes acute respiratory distress syndrome is often considered a process that begins synchronously throughout the lung, mediated by inhaled or blood-borne noxious agents. Relatively little attention has been paid to possibility that inflammatory lung injury may also begin focally and propagate sequentially via the airway network, proceeding mouth-ward from distal to proximal. Were this true, modifications of ventilatory pattern and position aimed at geographic containment of the injury process could help prevent its generalization and limit disease severity. The purposes of this communication are to call attention to this seldom considered mechanism for extending lung injury that might further justify implementation of low tidal volume/high positive end-expiratory pressure ventilatory strategies for lung protection and to suggest additional therapeutic measures implied by this broadened conceptual paradigm.

Positive end-expiratory pressure alters the severity and spatial heterogeneity of ventilator-induced lung injury: an argument for cyclical airway collapse

PURPOSE

Ventilator-induced lung injury (VILI) is a recognized complication of mechanical ventilation. Although the specific mechanism by which mechanical ventilation causes lung injury remains an active area of study, both alveolar overdistension and cyclical airway collapse and recruitment have been suggested as contributing causes. We hypothesized that mechanical ventilation in the absence of positive end-expiratory pressure (PEEP) causes VILI to be more severe and regionally variable as compared with PEEP = 8 cm H(2)O.

MATERIALS AND METHODS

To test this hypothesis, anesthetized, supine rabbits were mechanically ventilated with an end-inspiratory pressure of 28 cm H(2)O and either 0 or 8 cm H(2)O PEEP for 4 hours. Regional lung injury was determined by histologic scoring.

RESULTS

In the absence of PEEP, lung injury was regionally variable and greatest in the dorsal-caudal lung. This regional injury heterogeneity was abolished by the addition of PEEP = 8 cm H(2)O.

CONCLUSIONS

These results suggest that VILI is regionally heterogeneous and spatially correlates with regions in which cyclical airway collapse and recruitment is most likely to occur.

The effect of prone positioning in acute respiratory distress syndrome or acute lung injury: a meta-analysis. Areas of uncertainty and recommendations for research

OBJECTIVE

To compare the effects of ventilation in prone and in supine position in patients with acute lung injury/acute respiratory distress syndrome (ALI/ARDS).

DESIGN

Meta-analysis of randomised controlled trials.

DATA SOURCES

BioMedCentral, PubMed, CINAHL, and Embase (to November 2007), with additional information from authors.

MEASUREMENTS AND RESULTS

From selected randomised controlled trials comparing positioning in ALI/ARDS we extracted data concerning study design, disease severity, clinical outcomes, and adverse events. Five trials including 1,372 patients met the inclusion criteria for mortality analysis; one trial was added to assess the effects on acquisition of ventilator-associated pneumonia (VAP). The included trials were significantly underpowered and enrolled patients with varying severity. Prone positioning duration and mechanical ventilation strategy were not standardised across studies. Using a fixed-effects model, we did not find a significant effect of prone positioning (proning) on mortality (odds ratio 0.97, 95% confidence interval 0.77-1.22). The PaO(2)/FiO(2) ratio increased significantly more with proning (weighted means difference 25 mmHg, p < 0.00001). Proning was associated with a non-significant 23% reduction in the odds of VAP (p=0.09), and with no increase in major adverse airway complications: OR 1.01, 95% CI 0.71-1.43. Length of intensive care unit stay was marginally and not significantly increased by proning.

CONCLUSIONS

Prone position is not associated with a significant reduction in mortality from ALI/ARDS despite a significant increase in PaO(2)/FiO(2), is safe, and tends to decrease VAP. Published studies exhibit substantial clinical heterogeneity, suggesting that an adequately sized study optimising the duration of proning and ventilation strategy is warranted to enable definitive conclusions to be drawn.

Spatial and temporal heterogeneity of ventilator-associated lung injury after surfactant depletion

Volutrauma and atelectrauma have been proposed as mechanisms of ventilator-associated lung injury, but few studies have compared their relative importance in mediating lung injury. The objective of our study was to compare the injury produced by stretch (volutrauma) vs. cyclical recruitment (atelectrauma) after surfactant depletion. In saline-lavaged rabbits, we used high tidal volume, low respiratory rate, and low positive end-expiratory pressure to produce stretch injury in nondependent lung regions and cyclical recruitment in dependent lung regions. Tidal changes in shunt fraction were assessed by measuring arterial Po(2) oscillations. After ventilating for times ranging from 0 to 6 h, lungs were excised, sectioned gravitationally, and assessed for regional injury by evaluation of edema formation, chemokine expression, upregulation of inflammatory enzyme activity, and alveolar neutrophil accumulation. Edema formation, lung tissue interleukin-8 expression, and alveolar neutrophil accumulation progressed more rapidly in dependent lung regions, whereas macrophage chemotactic protein-1 expression progressed more rapidly in nondependent lung regions. Temporal and regional heterogeneity of lung injury were substantial. In this surfactant depletion model of acute lung injury, cyclical recruitment produced more injury than stretch.

Efficacy of prone ventilation in adult patients with acute respiratory failure: a meta-analysis

PURPOSE

The use of prone ventilation in acute respiratory failure has been investigated by several randomized controlled trials in the recent past. To date, there has been no systematic review or meta-analysis of these trials.

MATERIAL AND METHODS

Systematic literature search was performed between 1966 and July 2006 to identify randomized trials evaluating prone ventilation. Outcome measures included mortality, changes in oxygenation, incidence of pneumonia, duration of mechanical ventilation, intensive care unit (ICU) and hospital stay, cost-effectiveness, and adverse effects including pressure sores, endotracheal tube, or intravascular catheter complications.

RESULTS

Prone ventilation was not associated with reduction in mortality, but improvement in oxygenation was statistically significant (mean difference, 21.2 mm Hg; P < .001). There was no significant difference in incidence of pneumonia, ICU stay, and endotracheal tube complications. There was a trend toward an increased incidence of pressure sores in prone ventilated patients (odds ratio = 1.95; 95% confidence interval, 0.09-4.15; P = .08). The data on other outcomes were not suitable for meta-analysis.

CONCLUSIONS

The use of prone ventilation is associated with improved oxygenation. It is not associated with a reduction in mortality, pneumonia, or ICU stay and may be associated with an increased incidence of pressure sores.

Pediatric acute lung injury

Among ventilated children, the incidence of acute lung injury (ALI) was 9%; of that latter group 80% developed the acute respiratory distress syndrome (ARDS). The population-based prevalence of pediatric ARDS was 5.5 cases/100.000 inhabitants. Underlying diseases in children were septic shock (34%), respiratory syncytial virus infections (16%), bacterial pneumonia (15%), near-drowning 9%, and others. Mortality ranged from 18% to 27% for ALI (including ALI-non ARDS and ARDS) and from 29% to 50% for ARDS. Mortality was only 3%-11% in children with ALI-non ARDS. As risk factors, oxygenation indices and multi-organ failure have been identified. New insights into the pathophysiology (for example the interplay between intraalveolar coagulation/fibrinolysis and inflammation and the genetic polymorphism for the angiotensin-converting enzyme) offer new therapeutic options. Lung protective mechanical ventilation with optimal lung recruitment is the mainstay of supportive therapy. New therapeutic modalities refer to corticosteroid and surfactant treatment. Well-designed follow up studies are needed.

Prone position to treat bronchopleural fistula in post-operative acute lung injury

OBJECTIVE

Prone position is used to treat patients with acute lung injury or acute respiratory distress syndrome because it improves gas exchange and respiratory mechanics. When broncho-pleural fistula occurring, the clinical impact of prone position is limited; however, its use could be tried when the fistula is small or other potential treatments are not possible.

METHODS

A 45-year-old man with oesophageal cancer submitted to a total oesophagectomy with intrathoracic transposition of the stomach developed post-operatively respiratory failure and pneumothorax, which were worsened by unilateral pleural rupture and severe subcutaneous emphysema produced after an attempt to introduce through anterior chest wall a second drainage tube.

RESULTS

Prone position associated with lung protective strategy was implemented during 16-18 h daily and after the change of position PaO2/FiO2 increased of 35% and PaCO2-PetCO2 decreased about 40%; at 4th day under treatment, the subcutaneous emphysema and pneumothorax could not be detected either clinically or radiologically. On the 6th day the lung lesion could not be observed under the CT-scan.

CONCLUSIONS

In a patient that underwent a major thoracic surgery the addition of prone positioning to protective lung ventilation rendered possible not only the healing of the acute lung injury, but also the quick repair of a lung rupture owing to a thoracic drainage attempt.

[The prone position in acute respiratory distress syndrome: a critical systematic review]

OBJECTIVE

To do a critical systematic review regarding effects of prone positioning (PP) in patients with acute respiratory distress syndrome (ARDS).

METHODS

A systematic review (Highwire, Medline, Cochrane Library from 1976 to 2004), using the keywords: prone position, acute respiratory distress syndrome, allowed us to include the human studies on PP in ARDS patients, independantly of their objectives or their type of protocol. To appreciate the studies validity, we scored the quality evidence of the studies in order to grade our conclusions.

RESULTS AND CONCLUSION

The qualitative analysis of the 58 included studies (1,500 patients returned prone, 4,000 episodes of PP) led to the following main conclusions: 1) the PP improves oxygenation in the majority of ARDS patients (level of evidence I); 2) the PP improves the pulmonary haemodynamics without altering the systemic haemodynamics (level of evidence III); 3) the PP enhances the recruitment maneuvers (level of evidence III); 4) because there are no formal predictive criteria for response to the PP, a "trial of PP" or better two PP trials are necessary to look for the responders; 5) the PP should be performed as early as possible in the course of severe ARDS; 6) the optimal duration of PP is 18 to 23 hours daily, and it should be continued until improvement of arterial oxygenation, or loss of the positive effect of PP on arterial oxygenation or evidently patient's death.

Lung and 'end organ' injury due to mechanical ventilation in animals: comparison between the prone and supine positions

Introduction

Use of the prone position in patients with acute lung injury improves their oxygenation. Most of these patients die from multisystem organ failure and not from hypoxia, however. Moreover, there is some evidence that the organ failure is caused by increased cell apoptosis. In the present study we therefore examined whether the position of the patients affects histological changes and apoptosis in the lung and 'end organs', including the brain, heart, diaphragm, liver, kidneys and small intestine.

Methods

Ten mechanically ventilated sheep with a tidal volume of 15 ml/kg body weight were studied for 90 minutes. Five sheep were placed in the supine position and five sheep were placed in the prone position during the experiment. Lung changes were analyzed histologically using a semiquantitative scoring system and the extent of apoptosis was investigated with the TUNEL method.

Results

In the supine position intra-alaveolar hemorrhage appeared predominantly in the dorsal areas, while the other histopathologic lesions were homogeneously distributed throughout the lungs. In the prone position, all histological changes were homogeneously distributed. A significantly higher score of lung injury was found in the supine position than in the prone position (4.63 ± 0.58 and 2.17 ± 0.19, respectively) (P < 0.0001). The histopathologic changes were accompanied by increased apoptosis (TUNEL method). In the supine position, the apoptotic index in the lung and in most of the 'end organs' was significantly higher compared with the prone position (all P < 0.005). Interestingly, the apoptotic index was higher in dorsal areas compared with ventral areas in both the prone and supine positions (P < 0.003 and P < 0.02, respectively).

Conclusion

Our results suggest that the prone position appears to reduce the severity and the extent of lung injury, and is associated with decreased apoptosis in the lung and 'end organs'.

Does gas exchange response to prone position predict mortality in hypoxemic acute respiratory failure?

OBJECTIVE

To determine whether gas exchange response to a first prone position session can predict patient outcome in hypoxemic acute respiratory failure.

METHODS

Data from a previous multicenter randomized controlled trial were retrospectively analyzed for relationship between PaO(2)/FIO(2) ratio and PaCO(2) changes during the first 8-h prone position session to day 28 mortality rate; 370 prone position sessions were analyzed. Arterial blood gas was measured in supine position before proning and in prone position at the end of the session. Gas exchange improvement was defined as increase in the PaO(2)/FIO(2) ratio of more than 20% (PaO(2)R) or decrease in PaCO(2) of more than 1 mmHg (PaCO(2)R).

MAIN RESULTS

The 28-day mortality rate was 26.5% in PaO(2)R-PaCO(2)R, 31.7% in PaO(2)R-PaCO(2)NR, 38.9% in PaO(2)NR-PaCO(2)R, and 43% in PaO(2)NR-PaCO(2)NR (log-rank 14.02, p = 0.003). In a Cox proportional hazards model the gas exchange response was a significant predictor to patient outcome with a 82.5% increase in risk of death in the case of PaO(2)NR-PaCO(2)R or PaO(2)NR-PaCO(2)NR, relative to the gas exchange improvement response (odds ratio 1.825). However, after adjusting for the difference in oxygenation between day 2 and day 1 the gas exchange response does no longer reach significance.

CONCLUSION

In patients with hypoxemic acute respiratory failure initial improvement in gas exchange in the first PP session was associated with a better outcome, but this association disappeared when the change in oxygenation from day 1 to day 2 was taken into account, suggesting that underlying illness was the most important predictor of mortality in this patient population.

Atelectasis Causes Alveolar Injury in Nonatelectatic Lung Regions

RATIONALE

Many authors have suggested that the mechanism by which atelectasis contributes to injury is through the repetitive opening and closing of distal airways in lung regions that are atelectatic. However, neither the topographic nor mechanistic relationships between atelectasis and distribution of lung injury are known.

OBJECTIVES

To investigate how atelectasis contributes to ventilator-induced lung injury.

METHODS

Surfactant depletion was performed in anesthetized rats that were then allocated to noninjurious or injurious ventilation for 90 min.

MEASUREMENTS

Lung injury was quantified by gas exchange, compliance, histology, wet-to-dry weight, and cytokine expression, and its distribution by histology, stereology, cytokine mRNA expression, in situ hybridization, and immunohistochemistry. Functional residual capacity, percent atelectasis, and injury-induced lung water accumulation were measured using gravimetric and volumetric techniques.

MAIN RESULTS

Atelectasis occurred in the dependent lung regions. Injurious ventilation was associated with alveolar and distal airway injury, while noninjurious ventilation was not. With injurious ventilation, alveolar injury (i.e., histology, myeloperoxidase protein expression, quantification, and localization of cytokine mRNA expression) was maximal in nondependent regions, whereas distal airway injury was equivalent in atelectatic and nonatelectatic regions.

CONCLUSIONS

These data support the notion that lung injury associated with atelectasis involves trauma to the distal airways. We provide topographic and biochemical evidence that such distal airway injury is not localized solely to atelectatic areas, but is instead generalized in both atelectatic and nonatelectatic lung regions. In contrast, alveolar injury associated with atelectasis does not occur in those areas that are atelectatic but occurs instead in remote nonatelectatic alveoli.

Effects of endothelin receptor antagonism on acute lung injury induced by chlorine gas

OBJECTIVE

To test the hypothesis that the endothelin system is involved in chlorine gas-induced lung injury.

DESIGN

Experimental study.

SETTING

Academic research laboratory.

SUBJECTS

Twenty-four domestic juvenile pigs.

INTERVENTIONS

Anesthetized, ventilated pigs were exposed to chlorine gas (400 parts per million in air) for 20 mins and then randomly allocated to four groups (n=6 in each group). The tezosentan pretreatment group received the dual endothelin receptor antagonist tezosentan 20 mins before and hyperoxic gas (Fio2 0.6) after chlorine gas exposure. The tezosentan postinjury treatment group received hyperoxic gas after chlorine gas exposure and tezosentan 60 mins later. Animals in the oxygen group received hyperoxic gas after chlorine gas exposure. Pigs in the fourth group (air) were ventilated with room air (Fio2 0.21) throughout the experiment.

MEASUREMENTS AND MAIN RESULTS

Hemodynamics, gas exchange, lung mechanics, and plasma endothelin-1 were evaluated for 6 hrs. Chlorine gas exposure induced an increase in circulating endothelin-1 by 90% (p<.05). The acute chlorine gas-induced rise in pulmonary vascular resistance was partly blocked by tezosentan pretreatment (p<.001). Tezosentan postinjury treatment also decreased pulmonary vascular resistance to levels significantly lower than in the air and oxygen groups (p<.001). Recovery of peak airway pressure was better in the tezosentan-treated groups than in the air group. There were significant linear relationships between circulating endothelin-1 and pulmonary vascular resistance (r=.47, p<.001) and endothelin-1 and peak airway pressure (r=.41, p<.001). These relationships were modified by tezosentan.

CONCLUSIONS

Tezosentan modified chlorine gas-induced pulmonary dysfunction, indicating that the endothelin system is involved in this mode of acute lung injury.

The contribution of biophysical lung injury to the development of biotrauma

Patients with severe acute respiratory distress syndrome who die usually succumb to multiorgan failure as opposed to hypoxia. Despite appropriate resuscitation, some patients' symptoms persist on a downward spiral, apparently propagated by an uncontained systemic inflammatory response. This phenomenon is not well understood. However, a novel hypothesis to explain this observation proposes that it is related to the life-saving ventilatory support used to treat the respiratory failure. According to this hypothesis, mechanical ventilation per se, by altering both the magnitude and the pattern of lung stretch, can cause changes in gene expression and/or cellular metabolism that ultimately can lead to the development of an overwhelming inflammatory response-even in the absence of overt structural damage. This mechanism of injury has been termed biotrauma. In this review we explore the biotrauma hypothesis, the causal relationship between biophysical injury and organ failure, and its implications for the future therapy and management of critically ill patients.

Prone position augments recruitment and prevents alveolar overinflation in acute lung injury

RATIONALE

Mechanical ventilation in the prone position may be an effective means of recruiting nonaerated alveolar units and minimizing ventilation-induced lung injury.

OBJECTIVES

To evaluate and quantify regional lung volume alterations when patients with lobar or diffuse acute lung injury (ALI) were turned prone after a recruitment maneuver.

METHODS

In 21 patients with ALI, a recruitment maneuver was applied in the supine position followed by a multislice spiral computed tomography (CT) scan; then, patients were turned prone and a second CT scan was performed.

MAIN RESULTS

Both the recruitment maneuver and prone position resulted in improved oxygenation in patients with lobar ALI. Prone position also resulted in increased respiratory system compliance and decreased Pa(CO(2)) in lobar ALI. In lobar ALI, the proportion of overinflated and nonaerated areas declined, whereas the proportion of well-aerated areas increased in the prone position. The decrease in overinflated areas was observed mainly in the ventral areas. The dorsal regions showed a decrease in nonaerated areas and an increase in well-aerated areas. Recruitment maneuver and prone position improved oxygenation but had no effect either on Pa(CO(2)) or on the respiratory system compliance of patients with diffuse ALI. These patients responded to prone position with a decrease in nonaerated areas.

CONCLUSIONS

Prone position recruited the edematous lung further than recruitment maneuvers and reversed overinflation, resulting in a more homogeneous distribution of aeration. The effects of the prone position were more pronounced in patients with lobar ALI.

A multicenter trial of prolonged prone ventilation in severe acute respiratory distress syndrome

RATIONALE

Ventilation in the prone position for about 7 h/d in patients with acute respiratory distress syndrome (ARDS), acute lung injury, or acute respiratory failure does not decrease mortality. Whether it is beneficial to administer prone ventilation early, and for longer periods of time, is unknown.

METHODS

We enrolled 136 patients within 48 h of tracheal intubation for severe ARDS, 60 randomized to supine and 76 to prone ventilation. Guidelines were established for ventilator settings and weaning. The prone group was targeted to receive continuous prone ventilation treatment for 20 h/d.

RESULTS

The intensive care unit mortality was 58% (35/60) in the patients ventilated supine and 43% (33/76) in the patients ventilated prone (p = 0.12). The latter had a higher simplified acute physiology score II at inclusion. Multivariate analysis showed that simplified acute physiology score II at inclusion (odds ratio [OR], 1.07; p < 0.001), number of days elapsed between ARDS diagnosis and inclusion (OR, 2.83; p < 0.001), and randomization to supine position (OR, 2.53; p = 0.03) were independent risk factors for mortality. A total of 718 turning procedures were done, and prone position was applied for a mean of 17 h/d for a mean of 10 d. A total of 28 complications were reported, and most were rapidly reversible.

CONCLUSION

Prone ventilation is feasible and safe, and may reduce mortality in patients with severe ARDS when it is initiated early and applied for most of the day.

Adjuncts to Mechanical Ventilation in ARDS

Since its first description, acute respiratory distress syndrome has been characterized by abnormal physiologic and gas exchange properties of the lungs. Many adjunctive therapies have been developed to reduce the stresses of mechanical ventilation on already damaged lungs. We examined the mechanism of action and the latest clinical trial information of several adjunctive therapies including prone positioning, nitric oxide, extracorporeal membrane oxygenation, arterial venous carbon dioxide removal, and liquid ventilation. While all of these therapies have demonstrated short-term improvements in arterial blood gases and in the limitation of lung injury, none have shown an evidence-based survival benefit.

Prone positioning improves oxygenation in post-traumatic lung injury--a prospective randomized trial

BACKGROUND

In a prospective randomized trial the effect of prone positioning on the duration of mechanical ventilation was evaluated in multiple trauma patients and was compared with patients ventilated in supine position.

METHOD

Multiple trauma patients of the intensive care units of two university hospitals were considered eligible if they met the criteria for acute lung injury or the acute respiratory distress syndrome. Patients in the prone group (N = 21) were kept prone for at least eight hours and a maximum of 23 hours per day. Prone positioning was continued until a PaO2:FiO2 ratio of more than 300 was present in prone as well as supine position over a period of 48 hours. Patients in the supine group (N = 19) were positioned according to standard care guidelines.

RESULTS

The duration of ventilatory support did not differ significantly (30 +/- 17 days in the prone group and 33 +/- 23 days in the supine group). Worst case analysis (death and deterioration of gas exchange) displayed ventilatory support for 41 +/- 29 days in the prone group and 61 +/- 35 days in the supine group (p = 0.06). The PaO2:FiO2 ratio increased significantly more in the prone group in the first four days (p = 0.03). The prevalence of Acute Respiratory Distress Syndrome (ARDS) following acute lung injury (p = 0.03) and the prevalence of pneumonia (p = 0.048) were reduced also. One patient in the prone and three patients in the supine group died due to multi organ failure (p = 0.27).

CONCLUSIONS

Intermittent prone positioning was not able to reduce the duration of mechanical ventilation in this limited number of patients. However the oxygenation improved significantly over the first four days of treatment, and the prevalence of ARDS and pneumonia were reduced.

Rekrutierungsmanöver bei Patienten mit Lungenversagen

Recruitment maneuvers have been proposed as an adjunct to mechanical ventilation to re-expand collapsed lung regions. Although, in most patients recruitment maneuvers improve gas exchange a controversial discussion on recruitment maneuvers remains. This article reviews the physiological and patho-physiological backgrounds of recruitment maneuvers. The different recruitment maneuvers and possible monitoring are discussed as well as the influence of recruitment on other organs. Furthermore, we discuss whether recruitment maneuvers are useful if patients with acute lung injury or acute respiratory distress syndrome are ventilated with a lung-protective strategy.

Comparison of prone positioning and high-frequency oscillatory ventilation in patients with acute respiratory distress syndrome*

OBJECTIVE

Both prone position and high-frequency oscillatory ventilation (HFOV) have the potential to facilitate lung recruitment, and their combined use could thus be synergetic on gas exchange. Keeping the lung open could also potentially be lung protective. The aim of this study was to compare physiologic and proinflammatory effects of HFOV, prone positioning, or their combination in severe acute respiratory distress syndrome (ARDS).

DESIGN

: Prospective, comparative randomized study.

SETTING

A medical intensive care unit.

PATIENTS

Thirty-nine ARDS patients with a Pao2/Fio2 ratio <150 mm Hg at positive end-expiratory pressure > or =5 cm H2O.

INTERVENTIONS

After 12 hrs on conventional lung-protective mechanical ventilation (tidal volume 6 mL/kg of ideal body weight, plateau pressure not exceeding the upper inflection point, and a maximum of 35 cm H2O; supine-CV), 39 patients were randomized to receive one of the following 12-hr periods: conventional lung-protective mechanical ventilation in prone position (prone-CV), HFOV in supine position (supine-HFOV), or HFOV in prone position (prone-HFOV).

MEASUREMENTS AND MAIN RESULTS

Prone-CV (from 138 +/- 58 mm Hg to 217 +/- 110 mm Hg, p < .0001) and prone-HFOV (from 126 +/- 40 mm Hg to 227 +/- 64 mm Hg, p < 0.0001) improved the Pao2/Fio2 ratio whereas supine-HFOV did not alter the Pao2/Fio2 ratio (from 134 +/- 57 mm Hg to 138 +/- 48 mm Hg). The oxygenation index ({mean airway pressure x Fio2 x 100}/Pao2) decreased in the prone-CV and prone-HFOV groups and was lower than in the supine-HFOV group. Interleukin-8 increased significantly in the bronchoalveolar lavage fluid (BALF) in supine-HFOV and prone-HFOV groups compared with prone-CV and supine-CV. Neutrophil counts were higher in the supine-HFOV group than in the prone-CV group.

CONCLUSIONS

Although HFOV in the supine position does not improve oxygenation or lung inflammation, the prone position increases oxygenation and reduces lung inflammation in ARDS patients. Prone-HFOV produced similar improvement in oxygenation like prone-CV but was associated with higher BALF indexes of inflammation. In contrast, supine-HFOV did not improve gas exchange and was associated with enhanced lung inflammation.

Posição prona

A posição prona é uma manobra utilizada para combater a hipoxemia nos pacientes com síndrome do desconforto respiratório agudo. Apesar de hoje ser considerada um modo eficaz de melhorar a oxigenação, os mecanismos fisiológicos que levam à melhora da função respiratória ainda não estão completamente esclarecidos. O objetivo principal desta revisão é discutir os aspectos fisiológicos e clínicos da posição prona na síndrome do desconforto respiratório agudo.

Cellular stress failure in ventilator-injured lungs

The clinical and experimental literature has unequivocally established that mechanical ventilation with large tidal volumes is injurious to the lung. However, uncertainty about the micromechanics of injured lungs and the numerous degrees of freedom in ventilator settings leave many unanswered questions about the biophysical determinants of lung injury. In this review we focus on experimental evidence for lung cells as injury targets and the relevance of these studies for human ventilator-associated lung injury. In vitro, the stress-induced mechanical interactions between matrix and adherent cells are important for cellular remodeling as a means for preventing compromise of cell structure and ultimately cell injury or death. In vivo, these same principles apply. Large tidal volume mechanical ventilation results in physical breaks in alveolar epithelial and endothelial plasma membrane integrity and subsequent triggering of proinflammatory signaling cascades resulting in the cytokine milieu and pathologic and physiologic findings of ventilator-associated lung injury. Importantly, though, alveolar cells possess cellular repair and remodeling mechanisms that in addition to protecting the stressed cell provide potential molecular targets for the prevention and treatment of ventilator-associated lung injury in the future.

High-frequency oscillatory ventilation and adjunctive therapies: Inhaled nitric oxide and prone positioning

OBJECTIVE

To review the use of high-frequency oscillatory ventilation (HFOV) with adjunctive therapies (inhaled nitric oxide [iNO] and prone positioning [PP]) in adult patients with acute respiratory distress syndrome (ARDS).

DATA SOURCES

Published studies evaluating the use of iNO, PP, and HFOV in adult patients with ARDS.

DATA SUMMARY

Despite ongoing preclinical and clinical research, the therapeutic armamentarium for ARDS remains limited. Although a pressure- and volume-limited strategy aimed at mitigating ventilator-associated lung injury has demonstrated mortality benefit, patients with severe ARDS may still develop life-threatening hypoxemia. As a result, various salvage therapies aimed at improving oxygenation, including HFOV, iNO, and PP alone or in combination, have been evaluated in patients with refractory ARDS. Although the few preclinical and clinical trials of combination therapy to date have shown promising improvements in oxygenation and other physiological variables, with few adverse clinical events, the impact on survival awaits the performance of large randomized trials.

CONCLUSIONS

There is limited clinical data to recommend the widespread use of combination therapy in patients with ARDS. In the subset of patients with life-threatening hypoxemia from refractory ARDS, combination therapy is safe and may be considered for salvage therapy. More rigorous randomized, controlled trials are needed to help delineate the therapeutic role of combination therapy in adults with ARDS.

Prone position delays the progression of ventilator-induced lung injury in rats: Does lung strain distribution play a role?*

OBJECTIVE

To investigate if prone position delays the progression of experimental ventilator-induced lung injury, possibly due to a more homogeneous distribution of strain within lung parenchyma.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Animal laboratory of a university hospital.

SUBJECTS

Thirty-five Sprague Dawley male rats (weight 257 +/- 45 g).

INTERVENTIONS

Mechanical ventilation in either supine or prone position and computed tomography scan analysis.

MEASUREMENTS

: Animals were ventilated in supine (n = 15) or prone (n = 15) position until a similar ventilator-induced lung injury was reached. To do so, experiments were interrupted when respiratory system elastance was 150% of baseline. Ventilator-induced lung injury was assessed as lung wet-to-dry ratio and histology. Time to reach lung injury was considered as a main outcome measure. In five additional animals, computed tomography scans (GE Light Speed QX/I, thickness 1.25 mm, interval 0.6 mm, 100 MA, 100 Kv) were randomly taken at end-expiration and end-inspiration in both positions, and quantitative analysis was performed. Data are shown as mean +/- sd.

MEASUREMENTS AND MAIN RESULTS

Similar ventilator-induced lung injury was reached (respiratory system elastance, wet-to-dry ratio, and histology). The time taken to achieve the target ventilator-induced lung injury was longer with prone position (73 +/- 37 mins vs. 112 +/- 42, supine vs. prone, p = .011). Computed tomography scan analysis performed before lung injury revealed that at end-expiration, the lung was wider in prone position (p = .004) and somewhat shorter (p = .09), despite similar lung volumes (p = .455). Lung density along the vertical axis increased significantly only in supine position (p = .002). Lung strain was greater in supine as opposed to prone position (width strain, 7.8 +/- 1.8% vs. 5.6 +/- 0.9, supine vs. prone, p = .029).

CONCLUSIONS

Prone position delays the progression of ventilator-induced lung injury. Computed tomography scan analysis suggests that a more homogeneous distribution of strain may be implicated in the protective role of prone position against ventilator-induced lung injury.

Inhaled and intravenous corticosteroids both attenuate chlorine gas-induced lung injury in pigs

BACKGROUND

The accidental release of chlorine gas is a constant threat in urban areas. The purpose of this randomized, blinded, controlled experiment was to examine the effects of post-injury administration of inhaled or intravenous corticosteroid in chlorine gas-injured pigs followed for 23 h.

METHODS

Anaesthetized, ventilated pigs (n = 24) in the prone position were exposed to chlorine gas (400 parts per million in air) (1160 mg/m3) for 15 min, then randomly allocated to receive inhaled budesonide (BUD) and intravenous placebo, intravenous betamethasone (BETA) and inhaled placebo or inhaled and intravenous placebo. Haemodynamics, gas exchange and lung mechanics were evaluated for 23 h after exposure to chlorine gas.

RESULTS

Airway and pulmonary artery pressures increased and arterial oxygenation fell sharply (from 13.5 +/- 0.8 to 6.7 +/- 0.9 kPa, P < 0.001) after chlorine gas exposure. These immediate changes were followed by a gradual improvement over 5-7 h to a stable level of dysfunction for the rest of the experiment in placebo animals. Arterial oxygen tension, pulmonary vascular resistance and airway pressure recovered faster and more completely in the budesonide and betamethasone groups than in the placebo group (P < 0.01). Lung wet weight to dry weight ratios were greater in the placebo group than in the budesonide and betamethasone groups (6.34 +/- 0.59 vs. 5.56 +/- 0.38 and 5.53 +/- 0.54, respectively, P < 0.05). There was a trend towards lower histological injury scores compared with placebo in animals that received budesonide (P = 0.05) or betamethasone (P = 0.07).

CONCLUSION

Treatment of chlorine gas lung injury with nebulized budesonide or intravenous betamethasone had similar positive effects on recovery of lung function.

Intercomparison of recruitment maneuver efficacy in three models of acute lung injury*

OBJECTIVE

To compare the relative efficacy of three forms of recruitment maneuvers in diverse models of acute lung injury characterized by differing pathoanatomy.

DESIGN

We compared three recruiting maneuver (RM) techniques at three levels of post-RM positive end-expiratory pressure in three distinct porcine models of acute lung injury: oleic acid injury; injury induced purely by the mechanical stress of high-tidal airway pressures; and pneumococcal pneumonia.

SETTING

Laboratory in a clinical research facility.

SUBJECTS

Twenty-eight anesthetized mixed-breed pigs (23.8 +/- 2.6 kg).

INTERVENTIONS

The RM techniques tested were sustained inflation, extended sigh or incremental positive end-expiratory pressure, and pressure-controlled ventilation.

PRIMARY MEASUREMENTS

Oxygenation and end-expiratory lung volume.

MAIN RESULTS

The post-RM positive end-expiratory pressure level was the major determinant of post-maneuver PaO2, independent of the RM technique. The pressure-controlled ventilation RM caused a lasting increase of PaO2 in the ventilator-induced lung injury model, but in oleic acid injury and pneumococcal pneumonia, there were no sustained oxygenation differences for any RM technique (sustained inflation, incremental positive end-expiratory pressure, or pressure-controlled ventilation) that differed from raising positive end-expiratory pressure without RM.

CONCLUSIONS

Recruitment by pressure-controlled ventilation is equivalent or superior to sustained inflation, with the same peak pressure in all tested models of acute lung injury, despite its lower mean airway pressure and reduced risk for hemodynamic compromise. Although RM may improve PaO2 in certain injury settings when traditional tidal volumes are used, sustained improvement depends on the post-RM positive end-expiratory pressure value.

Methods to prevent ventilator-associated lung injury: a summary

Mechanical ventilation can cause ventilator-associated lung injury (VALI). This may manifest itself in various forms such as pneumothorax or, at the most extreme level, multi-system organ failure. The exact mechanisms by which the injury occurs are not known but appear to involve the conversion of mechanical stimulation of alveolar membranes into intracellular signalling, with subsequent upregulation of inflammatory mediators that produce the damage. This has been termed biotrauma. Furthermore, disruption of alveolar-capillary membranes may allow the release of these mediators into the systemic circulation that underpins the systemic inflammatory response syndrome. Various protective ventilatory strategies may be employed in order to reduce the lung damage and shall be discussed in this paper.

Prone positioning in the patient who has acute respiratory distress syndrome: the art and science

Acute respiratory distress syndrome (ARDS) remains a significant contributor to the morbidity and mortality of patients in the ICU. A variety of treatments are used to support the lung of the patient who has ARDS and improve gas exchange during the acute injury phase. It seems, however, that the simple, safe, and noninvasive act of prone positioning of the critically ill patient who has ARDS may improve gas exchange while preventing potential complications of high positive end-expiratory pressure, volutrauma, and oxygen toxicity. This article provides the critical care nurse with the physiologic rationale for use of the prone position, indications and contraindications for use, safe strategies for prone positioning, and care techniques and monitoring methods of the patient who is in the prone position.

Ventilator-associated lung injury in patients without acute lung injury at the onset of mechanical ventilation

OBJECTIVE

Although ventilation with small tidal volumes is recommended in patients with established acute lung injury, most others receive highly variable tidal volume aimed in part at normalizing arterial blood gas values. We tested the hypothesis that acute lung injury, which develops after the initiation of mechanical ventilation, is associated with known risk factors for ventilator-induced lung injury such as ventilation with large tidal volume.

DESIGN

Retrospective cohort study.

SETTING

Four intensive care units in a tertiary referral center.

PATIENTS

Patients who received invasive mechanical ventilation for > or = 48 hrs between January and December 2001.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The main outcome of interest, acute lung injury, was assessed by independent review of daily digital chest radiographs and arterial blood gases. Ventilator settings, hemodynamics, and acute lung injury risk factors were extracted from the Acute Physiology and Chronic Health Evaluation III database and the patients' medical records. Of 332 patients who did not have acute lung injury from the outset, 80 patients (24%) developed acute lung injury within the first 5 days of mechanical ventilation. When expressed per predicted body weight, women were ventilated with larger tidal volume than men (mean 11.4 vs. 10.4 mL/kg predicted body weight, p <.001) and tended to develop acute lung injury more often (29% vs. 20%, p =.068). In a multivariate analysis, the main risk factors associated with the development of acute lung injury were the use of large tidal volume (odds ratio 1.3 for each mL above 6 mL/kg predicted body weight, p <.001), transfusion of blood products (odds ratio, 3.0; p < 0.001), acidemia (pH < 7.35; odds ratio, 2.0; p =.032) and a history of restrictive lung disease (odds ratio, 3.6; p =.044).

CONCLUSIONS

The association between the initial tidal volume and the development of acute lung injury suggests that ventilator-associated lung injury may be an important cause of this syndrome. Height and gender should be considered when setting up the ventilator. Strong consideration should be given to limiting large tidal volume, not only in patients with established acute lung injury but also in patients at risk for acute lung injury.

Acute respiratory distress syndrome, the critical care paradigm: what we learned and what we forgot

In the last several years, we definitely learned that the acute respiratory distress syndrome lung is small, nonhomogeneous, and that mechanical ventilation in this baby lung may cause physical damage as well as inflammatory reaction. The clinical benefit of the gentle lung treatment, based on a decrease of global/regional stress and strain into the lung, has been finally proved. However, we forgot the importance of lung perfusion and its distribution in this syndrome and, besides a low tidal volume, we still do not know how to handle the other variables of mechanical ventilation. Measurements of variables as transpulmonary pressure and end expiratory lung volume, for a rational setting of mechanical ventilation, should be introduced in routine clinical practice.

Barriers to providing lung-protective ventilation to patients with acute lung injury

OBJECTIVE

No studies have explored the barriers to implementing lung-protective ventilation in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Our objective was to identify barriers to using lung-protective ventilation in patients with ALI/ARDS.

DESIGN

Survey with content analysis of open-ended responses.

SETTING

Medical center.

PARTICIPANTS

Experienced intensive care unit nurses and respiratory therapists network identified through purposive sampling at hospitals from the ARDS Network, a National Institutes of Health-sponsored research consortium.

INTERVENTIONS

Survey.

RESULTS

Fifty-five surveys representing all ten ARDS Network sites were received. Twenty-seven (49%) of the respondents were intensive care unit nurses, 24 (44%) were respiratory therapists, and four did not indicate their profession. Clinicians had used lung-protective ventilation in a median of 20 (interquartile range, 10-50) patients with ALI/ARDS. Respondents identified physician willingness to relinquish control of ventilator, physician recognition of ALI/ARDS, and physician perceptions of patient contraindications to low tidal volumes as important barriers to initiating lung-protective ventilation. Important barriers to continuing patients on lung-protective ventilation were concerns over patient discomfort and tachypnea and concerns over hypercapnia, acidosis, and hypoxemia. Techniques for overcoming barriers were identified including specific ventilator setup recommendations, clinician education, and tools to assess patient discomfort.

CONCLUSIONS

Experienced bedside clinicians perceive important barriers to implementing lung-protective ventilation. Successful strategies to increase use of lung-protective ventilation should target these barriers.

The role of the lactate dehydrogenase and the effect of prone position during ventilator-induced lung injury

To examine the impact of lactate dehydrogenase (LDH) as an early marker of ventilator-induced lung injury (VILI) and the effect of prone position during the VILI, we ventilated 28 normal white rabbits (10 supine, 10 prone, 8 controls) for 6 hr or until PaO2/FIO2 ratio was<200 mmHg. We applied an identical injurious ventilatory pattern (peak inspiratory pressure of 35 cmH2O with a PEEP of 3 cmH2O, I:E ratio of 1:2, and FIO2 of 0.40) in the supine and prone group. VILI was assessed by oxygenation, gravimetric analysis and histologic grading. Serum levels of LDH progressively increased significantly during the VILI (supine and prone groups) as compared with controls. There was a significant negative correlation between oxygenation and LDH levels (r=-0.619, p<0.001). Wet weight/dry weight ratios (WW/DW) and histologic scores for dependent regions were significantly higher in the supine than the prone group. There were no differences in WW/DW and histologic scores for nondependent regions between the supine and prone group. These findings suggest that serum LDH levels might be an early marker of severity of lung injury. The prone position resulted in a less severe and more homogenous distribution of VILI.

Ventilatory management of acute respiratory distress syndrome: a consensus of two

OBJECTIVE

To synthesize the emerging body of experimental, observational, and clinical trial data into a practical guideline for safe and effective ventilatory management of acute respiratory distress syndrome.

DATA SOURCES

Relevant, peer-reviewed, scientific literature and personal observations from clinical practice.

STUDY SELECTION

Relevant experimental studies and high-impact observational and clinical trials of acute respiratory distress syndrome management.

DATA EXTRACTION

Detailed review of information contained in published scientific work.

DATA SYNTHESIS

Interactive discussions between the authors that culminated in our consensus view of appropriate management.

CONCLUSIONS

Prevention of ventilator-induced lung injury while accomplishing the essential life-supporting roles of mechanical ventilation is a complex undertaking that requires application of principles founded on a broad experimental and clinical database and on the results of well-executed clinical trials. At the bedside, execution of an effective lung-protective ventilation strategy remains an empirical process best guided by integrated physiology and a readiness to revise the management approach depending on the individual's response.

Evaluation of density area in dorsal lung region during prone position using transesophageal echocardiography

OBJECTIVE

To evaluate the changes of density area in the dorsal lung regions of acute respiratory distress syndrome patients during prone position using transesophageal echocardiography.

DESIGN

Retrospective clinical study.

SETTING

General intensive care unit in a university hospital.

PATIENTS

Ten patients with acute respiratory distress syndrome who underwent prone position therapy.

INTERVENTIONS

Density areas in the left dorsal lung region were observed using transesophageal echocardiography before and after patients were in the prone position for 2 hrs. In five patients, a pediatric transesophageal echocardiography probe was left in the esophagus and used for observation during the prone procedure.

MEASUREMENTS AND MAIN RESULTS

Changes of density area and PaO2/FiO2 were observed. The density areas decreased after prone position compared with those of preprone position (preprone 11.4 +/- 5.1 cm2, after prone 5.6 +/- 3.5 cm2, mean +/- sd, p <.01, respectively). There was also a significant correlation between the percentage change of density area and PaO2/FiO2 (r =.47, p <.05) after prone position. During prone position, the density area decreased; however, there was no correlation between the percent changes of density area and PaO2/FiO2.

CONCLUSION

It was possible to observe the change in density area during prone position using transesophageal echocardiography. The change of density area estimated with transesophageal echocardiography during prone position was useful to estimate the effectiveness of the procedure.

Early enteral nutrition in mechanically ventilated patients in the prone position

OBJECTIVE

To assess the tolerance of early enteral nutrition in critically ill patients receiving invasive mechanical ventilation in the prone position.

DESIGN

Prospective, comparative study.

SETTING

General intensive care unit in a university-affiliated hospital.

PATIENTS

A total of 71 consecutive patients receiving invasive mechanical ventilation with early nasogastric enteral nutrition were studied for 5 days while being treated continuously in the supine position (supine position group, n = 37) or with intermittent prone positioning for severe hypoxemia (prone position group, n = 34).

INTERVENTIONS

Inclusion occurred within 24 hrs of mechanical ventilation initiation. Daily 18-hr enteral nutrition via a 14F gastric tube was initiated. Prone position patients were turned every 6 hrs as long as PaO2/FiO2 remained at <150, with a FiO2 of 0.6 and positive end-expiratory pressure of 10; the head was slightly elevated. When supine, patients in both groups were semirecumbent. Residual gastric volume was measured every 6 hrs, and enteral nutrition was discontinued if it exceeded 250 mL or vomiting occurred.

MEASUREMENTS AND MAIN RESULTS

The groups were similar for age, sex, Simplified Acute Physiology Score II, mortality, and risk factors for enteral nutrition intolerance. At baseline, PaO2/FiO2 was lower in prone position patients than in supine position patients (127 +/- 55 vs. 228 +/- 102; p <.001). As compared with supine position patients, prone position patients had significantly greater residual gastric volumes on days 1, 2, and 4 and experienced more vomiting episodes (median, 1 [interquartile range, 0-2] vs. 0 [interquartile range, 0-1]; p <.05). Enteral nutrition was stopped in 82% of prone position patients and 49% of supine position patients (p <.01) so that daily enteral nutrition volumes were lower with prone position patients. In the prone position group, vomiting occurred more frequently in the prone than in the supine position (relative risk, 2.5; 95% confidence interval, 1.5-4.0; p <.001).

CONCLUSION

In critically ill patients receiving invasive mechanical ventilation in the prone position, early enteral nutrition is poorly tolerated. Prokinetic agents or transpyloric feeding and semirecumbency should be considered to enhance gastric emptying and to prevent vomiting in patients receiving mechanical ventilation in the prone position.

Assessment of lung perfusion impairment in patients with pulmonary artery-occlusive and chronic obstructive pulmonary diseases with noncontrast electrocardiogram-gated fast-spin-echo perfusion MR imaging

PURPOSE

To evaluate the ability of noncontrast electrocardiogram (ECG)-gated fast-spin-echo (FSE) perfusion MR images for defining regional lung perfusion impairment, as compared with technetium (Tc)-99m macroaggregated albumin (MAA) single-photon emission computed tomography (SPECT) images.

MATERIALS AND METHODS

After acquisition of ECG-gated multiphase FSE MR images during cardiac cycles at selected lung levels in nine healthy volunteers, 11 patients with pulmonary artery-occlusive diseases, and 15 patients with chronic obstructive pulmonary diseases (COPD), the subtracted perfusion-weighted (PW) MR images were obtained from the two-phase images of the minimum lung signal intensity (SI) during systole and the maximum SI during diastole, and were compared with SPECT images.

RESULTS

ECG-gated PW images showed uniform but posture-dependent perfusion gradient in normal lungs and visualized the various sizes of perfusion defects in affected lungs. These defect sites were nearly consistent with those on SPECT images, with a significant correlation for the affected-to-unaffected perfusion contrast (r = 0.753; P < 0.0001). These MR images revealed that the pulmonary arterial blood flow in the affected areas of COPD was relatively preserved as compared with pulmonary artery-occlusive diseases, and also showed significant decrease in blood flow, even in the areas with homogeneous perfusion on SPECT images in patients with focal pulmonary emphysema.

CONCLUSION

This noninvasive MR technique allows qualitative and quantitative assessment of lung perfusion, and may better characterize regional perfusion impairment in pulmonary artery-occlusive diseases and COPD.