Incidence and mortality after acute respiratory failure and acute respiratory distress syndrome in Sweden, Denmark, and Iceland. The ARF Study Group

Epidemiology of acute lung injury and acute respiratory distress syndrome

PURPOSE OF REVIEW

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are diseases with a significant influence in the public health. A better knowledge of their epidemiology could help to improve the outcome of these diseases.

RECENT FINDINGS

Although the clinical criteria of the American-European Consensus Conference definitions for ALI and ARDS are simple, there is a risk of misclassification due to a poor reliability. Except for new emerging infectious diseases, such as severe acute respiratory syndrome, the etiology of ALI/ARDS has remained the same for several years. The only recent innovation is the hypothesis that pulmonary ARDS and extrapulmonary ARDS could be different clinical entities. In recent years, there has been a special interest in the study of genetic predisposition to development ALI/ARDS. Recent studies have estimated the incidence of these diseases to be between 15 and 34 cases per 100,000 inhabitants per year. This wide range could stem from differences in the methodology used to calculate the incidence or could be a true variation due to regional differences. Mortality rate of ALI/ARDS have remained steady for several years. Respiratory failure is the cause of the death in less than 20% of the patients.

SUMMARY

The epidemiology of ALI and ARDS has some issues to improve, such as the accuracy of the clinical criteria of ALI/ARDS. Future research must to include study of genetic polymorphisms of the mediators involve in the development of ALI/ARDS. Studies to define better the population at risk are necessary to estimate better their true incidence.

TEZOSENTAN COUNTERACTS ENDOTOXIN-INDUCED PULMONARY EDEMA AND IMPROVES GAS EXCHANGE

Sepsis-induced acute lung injury is still associated with high morbidity and mortality. The pathophysiology is complex, and markers of injury include increased extravascular lung water. To evaluate the effects of the novel dual endothelin receptor antagonist tezosentan on endotoxin-induced changes in extravascular lung water and gas exchange, 16 pigs were anaesthetized and catheterized. Twelve animals were subjected to 5 h of endotoxemia. After 2 h, six of these animals received a bolus of tezosentan 1 mg kg(-1) followed by a continuous infusion of 1 mg kg(-1) h(-1) to the end of the experiment at 5 h. Conventional pulmonary and hemodynamic parameters were measured. Extravascular lung water was determined in these pigs after 5 h of endotoxemia, as well as in the four additional nonendotoxemic sham animals. Tezosentan in the current dosage counteracted the deterioration of lung function caused by endotoxin, as measured by dead space, venous admixture, and compliance. In addition, pulmonary hypertension was attenuated. Tezosentan had a marked effect on the endotoxin-induced increase in extravascular lung water that was reduced to levels observed in nonendotoxemic sham animals. These results suggest that endothelin is involved in endotoxin-induced lung injury and the development of pulmonary edema. Dual endothelin receptor antagonism may be of value in the treatment of sepsis-related acute lung injury.

Randomized controlled trial of aerosolized prostacyclin therapy in children with acute lung injury

OBJECTIVES

To investigate whether aerosolized prostacyclin improves oxygenation in children with acute lung injury.

DESIGN

Double-blind, randomized, and placebo-controlled trial.

SETTING

Pediatric intensive care unit at a university hospital.

PATIENTS

Fourteen children with acute lung injury defined by the criteria of an American-European Consensus Conference.

INTERVENTIONS

Aerosolized prostacyclin (epoprostenol sodium) by stepwise increments of different doses (10, 20, 30, 40, and 50 ng x kg x min) vs. aerosolized normal saline (placebo).

MEASUREMENTS AND MAIN RESULTS

Before the start of the study, and before and after each dose of prostacyclin/placebo, the following variables were measured: arterial blood gases, heart rate, mean arterial blood pressure, and ventilator settings required. Changes in oxygenation were measured by calculation of the oxygenation index (mean airway pressure x 100 x Pao2/Fio2). After treatment with aerosolized prostacyclin, there was a significant 26% (interquartile range, 3%, 35%) improvement in oxygenation index at 30 ng x kg x min compared with placebo (p =.001). The response to prostacyclin was not the same in all children. We saw an improvement of > or = 20% in eight of 14 children (i.e., responders), and the number needed to treat was 1.8 (95% confidence interval, 1.2-3.2). No adverse effects were observed.

CONCLUSIONS

Aerosolized prostacyclin improves oxygenation in children with acute lung injury. Future trials should investigate whether this treatment will positively affect outcome.

Regulation of regional lung perfusion by nitric oxide

Improved oxygenation has previously been shown in patients with acute lung injury when ventilated in prone position. We hypothesized that this was due to higher regional production of nitric oxide in dorsocaudal lung regions. We measured nitric oxide synthase mRNA expression and nitric oxide production by citrulline assay in ventral and dorsal lung tissue from patients. In volunteers, regional lung perfusion in prone and supine postures was assessed by single photon emission computed tomography using (99m)Tc macroaggregated albumin before and after inhibition of nitric oxide synthase by N(G)-monomethyl-L-arginine infusion. Nitric oxide synthase mRNA expression and nitric oxide production were significantly higher in dorsal compared with ventral lung regions. In supine posture, lung perfusion was shifted to ventral parts during nitric oxide synthase inhibition, whereas in the prone posture lung perfusion remained unchanged. Our results suggest a role for endogenous nitric oxide in regulation of regional pulmonary perfusion.

Screening of ARDS patients using standardized ventilator settings: influence on enrollment in a clinical trial

OBJECTIVES

The American-European consensus conference (AECC) definition for acute respiratory distress syndrome (ARDS) requires a PaO(2)/F(I)O(2)< or =200 mmHg, regardless of ventilator settings. We report the results of using standardized ventilator settings to screen and enroll ARDS patients in a clinical trial of high-frequency oscillatory ventilation (HFOV), including the impact on study enrollment, and potential effects on study outcome.

DESIGN

Prospective cohort study.

SETTING

Intensive care units in two teaching hospitals. PARTICIPANTS. A consecutive sample of 41 patients with early ARDS by AECC criteria (baseline PaO(2)/F(I)O(2)< or =200) who met all other inclusion/exclusion criteria for the HFOV trial.

INTERVENTIONS

Patients were placed on standardized ventilator settings (tidal volume 7-8 ml/kg, PEEP 10 cmH(2)O, F(I)O(2) 1.0), and the PaO(2)/F(I)O(2) was reassessed after 30 min.

RESULTS

Seventeen patients (41.5%) had PaO(2)/F(I)O(2) ratios that remained < or =200 mmHg [Persistent ARDS; PaO(2)/F(I)O(2)=94+/-36 (mean+/-SD)] and went on to inclusion in the HFOV study; however, in 24 patients (58.5%) the PaO(2)/F(I)O(2) was >200 mmHg [Transient ARDS; PaO(2)/F(I)O(2)=310+/-74] and these patients were ineligible for the HFOV study. The ICU mortality was significantly greater (52.9 vs 12.5%; p=0.01) in the Persistent ARDS patients.

CONCLUSIONS

The use of these standardized ventilatory significantly impacted the PaO(2)/F(I)O(2) ratio and therefore the ARDS prevalence and trial enrollment. These results have effects on the evaluation of the current ARDS literature and conduct of clinical trials in ARDS and hence consideration should be given to the use of standardized ventilatory settings in future ARDS trials.

Implementing effective ventilator practice at the bedside

PURPOSE OF REVIEW

New data on the efficacy of low tidal volume ventilation for acute lung injury, noninvasive ventilation for chronic obstructive pulmonary disease exacerbation, weaning from mechanical ventilation, and prevention of ventilator-associated pneumonia provide, for perhaps the first time in respiratory care, compelling evidence for clinicians to change practice. However, experience from every other field in medicine suggests that there will be significant barriers to changing clinical practice at the bedside. Studies on implementation of effective practice in medicine shows that a multifaceted, team-oriented approach incorporating reminders, efficient use of non-physician personnel, protocols, and education is required to change clinical practice. Limited data on current practice of mechanical ventilation suggest that it deviates from recommended practice. Unfortunately, there are no studies exploring community-based implementation of mechanical ventilation guidelines and only a few studies to inform clinicians as to why ventilator practice may be difficult to change. As the evidence base grows for effective critical care practice, so does the responsibility to translate practices that improve outcome from research journals to patients' bedsides. Strategies for doing this are presented in the review.

Hyperosmolarity enhances the lung capillary barrier

Although capillary barrier deterioration underlies major inflammatory lung pathology, barrier-enhancing strategies are not available. To consider hyperosmolar therapy as a possible strategy, we gave 15-minute infusions of hyperosmolar sucrose in lung venular capillaries imaged in real time. Surprisingly, this treatment enhanced the capillary barrier, as indicated by quantification of the capillary hydraulic conductivity. The barrier enhancement was sufficient to block the injurious effects of thrombin, TNF-alpha, and H2O2 in single capillaries, and of intratracheal acid instillation in the whole lung. Capillary immunofluorescence indicated that the hyperosmolar infusion markedly augmented actin filament formation and E-cadherin expression at the endothelial cell periphery. The actin-depolymerizing agent latrunculin B abrogated the hyperosmolar barrier enhancement as well as the actin filament formation, suggesting a role for actin in the barrier response. Furthermore, hyperosmolar infusion blocked TNF-alpha-induced P-selectin expression in an actin-dependent manner. Our results provide the first evidence to our knowledge that in lung capillaries, hyperosmolarity remodels the endothelial barrier and the actin cytoskeleton to enhance barrier properties and block proinflammatory secretory processes. Hyperosmolar therapy may be beneficial in lung inflammatory disease.

Comparison of 3 Methods of Detecting Acute Respiratory Distress Syndrome: Clinical Screening, Chart Review, and Diagnostic Coding

• Background Although the incidence of acute respiratory distress syndrome has been studied, few researchers have prospectively assessed the search tool used to identify cases.

• Methods For 5 months, all patients admitted to a medical intensive care unit in a teaching hospital were evaluated daily to determine whether criteria for acute respiratory distress syndrome were met, and physicians’ progress notes and discharge summaries for these prospectively identified patients were reviewed for mention of the syndrome. Discharge forms were reviewed for the codes (International Classification of Diseases, Ninth Revision) specific to acute respiratory distress syndrome (518.82 or 518.85).

• Results Of 314 patients admitted, 65 prospectively met the criteria for acute respiratory distress syndrome. Of these 65 patients, 31 had acute respiratory distress syndrome mentioned in their progress notes, and 4 of the 31 were subsequently assigned a code of 518.82 or 518.85. Patients with a physician’s notation for acute respiratory distress syndrome in their charts had a higher mortality (22/31 [71%]) than did the patients with no such notation (10/34 [29%]). This difference could not be accounted for by differences in length of stay, mean age, score on Acute Physiology and Chronic Health Evaluation III, or number of days in the unit before meeting the criteria.

• Conclusions The incidence of acute respiratory distress syndrome is underestimated when based on either diagnostic coding or physicians’ notes without testing of the accuracy of coding. Both physicians and medical record coding specialists may require training in use of terms related to acute respiratory distress syndrome.

High-frequency ventilation versus conventional ventilation for treatment of acute lung injury and acute respiratory distress syndrome

BACKGROUND

High-frequency ventilation is often used to treat patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) but the effect of this treatment on clinical outcomes has not been well established.

OBJECTIVES

The objective of this review is to examine the effect of high-frequency ventilation compared with conventional ventilation as a therapy for ALI or ARDS in children (1 to 17 years old) and adults in order to quantify its effect on patient outcome (mortality, morbidity and other relevant outcomes).

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, issue 4, 2002), MEDLINE (1966 to October Week 5, 2002), EMBASE (1980 to Week 51, 2002), World Wide Web (www.controlled-trials.com, ARDS clinical network), and used Cited Reference Search (Web of Science 1988 to 2002, for specific reference lists of articles). We also contacted authors from each included trial, as well as manufacturers of high-frequency ventilators and other researchers in the field.

SELECTION CRITERIA

Randomized controlled clinical trials of children and adults comparing treatment using high-frequency ventilation with conventional ventilation for patients diagnosed with ALI or ARDS.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trial quality and extracted data. Study authors were contacted for additional information.

MAIN RESULTS

Two trials met the inclusion criteria for this review. One trial recruited children (including some children less than one year old) (n = 58) and the other recruited adults (n = 148). Both trials used a high-frequency oscillatory ventilator as the intervention and included variable use of lung-volume recruitment strategies. The intervention groups showed a trend towards lower 30 day mortality (children relative risk (RR) 0.83, 95% confidence interval (CI) 0.43 to 1.62; adults RR 0.72, 95% CI 0.50 to 1.03), although neither study showed a statistically significant difference. Similarly, there was no statistically significant difference between the intervention and control groups for 'Total length of ventilator days' (WMD) -2.00, 95% CI -18.36 to 14.36; and WMD 2.00, 95% CI -6.55 to 10.55 for the child and adult trials respectively). The studies used only proxies to measure long-term quality of life. There was a statistically significant reduction in the risk of requiring supplemental oxygen amongst survivors at 30 days in the paediatric study (RR 0.36, 95% CI 0.14 to 0.93).

REVIEWER'S CONCLUSIONS

There is not enough evidence to conclude whether high-frequency ventilation reduces mortality or long-term morbidity in patients with ALI or ARDS; further trials are needed.

Bench-to-bedside review: beta2-Agonists and the acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a devastating constellation of clinical, radiological and pathological signs characterized by failure of gas exchange and refractory hypoxia. Despite nearly 30 years of research, no specific pharmacological therapy has yet proven to be efficacious in manipulating the pathophysiological processes that underlie this condition. Several in vitro and in vivo animal or human studies suggest a potential role for β₂-agonists in the treatment of ARDS. These agents have been shown to reduce pulmonary neutrophil sequestration and activation, accelerate alveolar fluid clearance, enhance surfactant secretion, and modulate the inflammatory and coagulation cascades. They are also used widely in clinical practice and are well tolerated in critically ill patients. The present review examines the evidence supporting a role for β₂-agonists as a specific pharmacological intervention in patients with ARDS.

Impact of positive end-expiratory pressure on the definition of acute respiratory distress syndrome

OBJECTIVE

We examined whether PEEP during the first hours of ARDS can induce such a change in oxygenation that could mask fulfillment of the AECC criteria of a PaO(2)/FIO(2) </= 200 essential for ARDS diagnosis.

DESIGN AND SETTING

Observational, prospective cohort in two medical-surgical ICU in teaching hospitals.

PATIENTS

48 consecutive patients who met AECC criteria of ARDS on 0 PEEP (ZEEP) at the moment of diagnosis.

MEASUREMENTS AND RESULTS

PaO(2)/FIO(2) and lung mechanics were recorded on admission (0 h) to the ICU on ZEEP, and after 6, 12, and 24 h on PEEP levels selected by attending physicians. Lung Injury Score (LIS) was calculated at 0 and 24 h. PaO(2)/FIO(2) rose significantly from 121+/-45 on ZEEP at 0 h, to 234+/-85 on PEEP of 12.8+/-3.7 cmH(2)O after 24 h. LIS did not change significantly (2.34+/-0.53 vs. 2.42+/-0.62). These variables behaved similarly in pulmonary and extrapulmonary ARDS, and in survivors and nonsurvivors. After 24 h only 18 patients (38%) still had a PaO(2)/FIO(2) of 200 or lower. Their mortality was similar to that in the remaining patients (61% vs. 53%).

CONCLUSIONS

The use of PEEP improved oxygenation such that one-half of patients after 6 h, and most after 24 h did not fulfill AECC hypoxemia criteria of ARDS. However, LIS remained stable in the overall series. These results suggest that PEEP level should be taken into consideration for ARDS diagnosis.

Epidemiology and outcome of acute lung injury in European intensive care units. Results from the ALIVE study

OBJECTIVES

To re-examine the epidemiology of acute lung injury (ALI) in European intensive care units (ICUs).

DESIGN AND SETTING

A 2-month inception cohort study in 78 ICUs of 10 European countries.

PATIENTS

All patients admitted for more than 4 h were screened for ALI and followed up to 2 months.

MEASUREMENTS AND MAIN RESULTS

Acute lung injury occurred in 463 (7.1%) of 6,522 admissions and 16.1% of all mechanically ventilated patients; 65.4% cases occurred on ICU admission. Among 136 patients initially presenting with "mild ALI" (200< PaO2/FiO2 < or =300), 74 (55%) evolved to acute respiratory distress syndrome (ARDS) within 3 days. Sixty-two patients (13.4%) remained with mild ALI and 401 had ARDS. The crude ICU and hospital mortalities were 22.6% and 32.7% (p<0.001), and 49.4% and 57.9% (p=0.0005), respectively, for mild ALI and ARDS. ARDS patients initially received a mean tidal volume of 8.3+/-1.9 ml/kg and a mean PEEP of 7.7+/-3.6 cmH2O; air leaks occurred in 15.9%. After multivariate analysis, mortality was associated with age (odds ratio (OR) =1.2 per 10 years; 95% confidence interval (CI): 1.05-1.36), immuno-incompetence (OR: 2.88; Cl: 1.57-5.28), the severity scores SAPS II (OR: 1.16 per 10% expected mortality; Cl: 1.02-1.31) and logistic organ dysfunction (OR: 1.25 per point; Cl: 1.13-1.37), a pH less than 7.30 (OR: 1.88; Cl: 1.11-3.18) and early air leak (OR: 3.16; Cl: 1.59-6.28).

CONCLUSIONS

Acute lung injury was frequent in our sample of European ICUs (7.1%); one third of patients presented with mild ALI, but more than half rapidly evolved to ARDS. While the mortality of ARDS remains high, that of mild ALI is twice as low, confirming the grading of severity between the two forms of the syndrome.

Acute lung injury and the acute respiratory distress syndrome

Although ALI/ARDS mortality rates have improved over the last several decades, they remain high, particularly in the geriatric patient population. Although considerable progress has been made in understanding the pathogenesis of the disease, a large number of promising treatments have proven unsuccessful. One exception has been in the area of ventilator management, where a strategy of protective ventilation with low tidal volumes has demonstrated a significant mortality benefit. Basic research continues to help advance our understanding of this complex syndrome and identify interesting new directions of investigation. The results of several large, randomized trials of new ventilatory and pharmacologic strategies currently underway may help identify successful methods of treating this important disease.

Acute respiratory distress syndrome: an audit of incidence and outcome in Scottish intensive care units

This prospective audit of incidence and outcome of the acute respiratory distress syndrome was conducted as part of the national audit of intensive care practice in Scotland. All patients with acute respiratory distress syndrome in 23 adult intensive care units were identified using the diagnostic criteria defined by the American-European Consensus Conference. Daily data collection was continued until death or intensive care unit discharge. Three hundred and sixty-nine patients were diagnosed with acute respiratory distress syndrome over the 8-month study period. The frequency of acute respiratory distress syndrome in the intensive care unit population was 8.1%; the incidence in the Scottish population was estimated at 16.0 cases.100,000(-1).year(-1). Intensive care unit mortality for acute respiratory distress syndrome was 53.1%, with a hospital mortality of 60.9%. In our national unselected population of critically ill patients, the overall outcome is comparable with published series (Acute Physiology and Chronic Health Evaluation II standardised mortality ratio = 0.99). However, mortality from acute respiratory distress syndrome in Scotland is substantially higher than in recent other series suggesting an improvement in outcome in this condition.

Aerosolized surfactant and dextran for experimental acute respiratory distress syndrome caused by acidified milk in rats

BACKGROUND

Inhibition of pulmonary surfactant by plasma-derived proteins is an important pathogenetic factor of acute respiratory distress syndrome (ARDS). Inhalation of aerosolized surfactant may be suitable for early treatment of ARDS. However, requirement of a high dose is a drawback. Because dextran reverses surfactant inhibition, we examined whether dextran improves the therapeutic effects of aerosolized surfactant in rats with experimental ARDS.

METHODS

Acidified milk (pH 1.8, 1.5 ml kg(-1)) was injected into the trachea of the rats ventilated with pure oxygen using 2.45 kPa peak inspiratory pressure and 0.74 kPa positive end-expiratory pressure. When PaO2 decreased to <13 kPa, the rats were assigned to four groups: control group (n = 8), receiving no material; D-only group (n = 6), receiving aerosolized dextran for 45 min; S-only group (n = 8), receiving aerosolized modified natural surfactant (MNS) for 30 min; and S-plus-D group (n = 9), receiving aerosolized MNS for 30 min followed by aerosolized dextran for 15 min.

RESULTS

In the control group and D-only groups, the mean PaO2 remained at <10 kPa for 180 min. In the S-only and S-plus-D groups, the PaO2 increased to 50 kPa (P < 0.01 vs. untreated). The PaO2 of the surfactant-only group gradually decreased to <17 kPa at 180 min, whereas the PaO2 of the S-plus-D group was maintained at >38 kPa for 180 min (P < 0.01 vs. S-only group).

CONCLUSION

Inhalation of aerosolized dextran potentiates the effects of aerosolized surfactant by prolonging the therapeutic response.

Effect of age on the development of ARDS in trauma patients

STUDY OBJECTIVES

The purpose of this study was to determine the independent effect of age on the risk of developing ARDS in patients with trauma.

DESIGN

Prospective cohort study.

SETTING

Level I trauma center.

MEASUREMENTS AND RESULTS

A total of 4,020 consecutive trauma patients who were > 12 years of age were identified through the Harborview Medical Center Trauma Registry over a 3-year period. During this time, 484 of the trauma patients (12%) developed ARDS, as identified by the Harborview Medical Center ARDS Registry. Patients who developed ARDS were, on average, older (mean [+/- SD] age, 44.0 +/- 18.8 vs 40.2 +/- 20.0 years, respectively; p < 0.0001) and had higher injury severity scores (23.7 +/- 11.3 vs 18.0 +/- 10.3, respectively; p < 0.0001) than trauma patients who did not develop ARDS. The maximum unadjusted odds ratio for developing ARDS was 2.93 (95% confidence interval, 1.91 to 4.50) for the group 60 to 69 years of age compared to the group 13 to 19 years of age. Patients aged > or = 80 years had an equal risk of developing ARDS compared to those age 13 to 19 years.

CONCLUSIONS

Age demonstrated a complex relationship with risk for ARDS development. Older patients showed increasingly higher risks for ARDS development up to 60 to 69 years of age, when the risk for ARDS declined. We concluded that older patients are at significantly greater risk of developing ARDS when compared to younger patients, while the oldest patients may be at less risk.

Sublethal hyperoxia impairs pulmonary innate immunity

Supplemental oxygen is often required in the treatment of critically ill patients. The impact of hyperoxia on pulmonary host defense is not well-established. We hypothesized that hyperoxia directly impairs pulmonary host defense, beyond effects on alveolar wall barrier function. C57BL/6 mice were kept in an atmosphere of >95% O(2) for 4 days followed by return to room air. This exposure does not lead to mortality in mice subsequently returned to room air. Mice kept in room air served as controls. Mice were intratracheally inoculated with Klebsiella pneumoniae and followed for survival. Alveolar macrophages (AM) were harvested by bronchoalveolar lavage after 4 days of in vivo hyperoxia for ex vivo experiments. Mortality from pneumonia increased significantly in mice exposed to hyperoxia compared with infected mice in room air. Burden of organisms in the lung and dissemination of infection were increased in the hyperoxia group whereas accumulation of inflammatory cells in the lung was impaired. Hyperoxia alone had no impact on AM numbers, viability, or ability to phagocytize latex microbeads. However, following in vivo hyperoxia, AM phagocytosis and killing of Gram-negative bacteria and production of TNF-alpha and IL-6 in response to LPS were significantly reduced. AM surface expression of Toll-like receptor-4 was significantly decreased following in vivo hyperoxia. Thus sublethal hyperoxia increases Gram-negative bacterial pneumonia mortality and has a significant adverse effect on AM host defense function. Impaired AM function due to high concentrations of supplemental oxygen may contribute to the high rate of ventilator-associated pneumonia seen in critically ill patients.

A practice survey on vasopressor and inotropic drug therapy in Scandinavian intensive care units

BACKGROUND

This practice survey was performed to analyse the indications for use of vasopressor/inotropic drugs, preferred drugs and doses as well as concomitant monitoring and desired haemodynamic target values in Scandinavian ICUs. An internet-based reporting system was implemented.

METHODS

A total of 223 ICUs were identified in the Scandinavian countries and invited to participate in a one-day point-prevalence study. An internet-based database was constructed and a practice survey protocol designed to identify haemodynamic monitoring, indications for vasopressor/inotropic drug-therapy, fluids used for volume loading, pretreatment circulatory state, actual and targeted haemodynamic variables. Patients were eligible for the study if on vasopressor/inotropic drug-therapy for more than 4 h.

RESULTS

A total of 114 ICUs participated. A total of 114 adult patients matched the inclusion criteria. Sixty-seven per cent of the patients had received vasopressor/inotropic drug-treatment for >24 h and 32% received more than one drug. Arterial hypotension (92%) and oliguria (50%) were most common indications. Fluid loading prior to therapy was reported in 87% of patients. Dopamine (47%) and noradrenaline (44%) were the most commonly used drugs followed by dobutamine (24%). No other drug exceeded 6%. Non-catecholamine drugs were rarely used even in cardiac failure patients. Invasive arterial pressure was monitored in 95% of patients, pulmonary artery catheters were used in 19%. Other cardiac output monitoring techniques were used in 8.5% of the patients.

CONCLUSION

Dopamine and noradrenaline seem to be the most commonly used inotropic/vasopressor drugs in Scandinavia. Traditional indications for inotropic/vasopressor support as hypotension and oliguria seem to be most common. Invasive monitoring was used in almost all patients, whereas a limited use of pulmonary artery catheters was noted. The internet-based reporting system proved to be an efficient tool for data collection.

Incidence of acute lung injury in the United States

OBJECTIVE

Recent estimates of acute respiratory distress syndrome (ARDS) incidence have varied from 1.3 to 22 per 100,000 person years (105 person.years); the incidence of acute lung injury (ALI) has varied from 17.9 to 34 cases per 105 person.years. Potential reasons for this wide range include differences in the definition of the syndrome, in the populations sampled, and in the assumptions made to estimate incidence. We hypothesized that careful, prospective, protocol-driven case identification that included the milder hypoxemia criterion for ALI would yield incidence numbers greater than previously reported.

DESIGN

Prospective cohort study with extrapolation to the U.S. population.

SETTING

National Heart, Lung, and Blood Institute-sponsored ARDS Network composed of 20 hospitals.

PATIENTS

As part of the National Institutes of Health-sponsored ARDS network, 20 hospitals prospectively identified patients with ALI from 1996 to 1999. Screening logs from this study were used to estimate ALI rates per intensive care unit (ICU) bed per year. We used the registry and data from the American Hospital Association to estimate the incidence of ALI in the United States.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The ALI per ICU bed incidence in the ARDS network registry varied from 0.7 to 5.8 cases of ALI per ICU bed per year with an average of 2.2 cases of ALI per ICU bed per year. We tested the robustness of the incidence estimate by performing a variety of sensitivity analyses. When we used the conservative assumptions that the ARDS network screening logs were complete at each of the participating hospitals and that ALI cases are limited to academic hospitals with > or =20 adult ICU beds, the incidence of ALI in adults in the United States is 22.4 cases per 105 person.years. Under the less conservative assumption that ALI cases occurred only at hospitals with > or =20 ICU beds, regardless of their academic status, the incidence of ALI in the United States is estimated at 64.2 cases per 105 person.years.

CONCLUSIONS

Based on this analysis, which used prospective clinical trial screening data and conservative assumptions about where patients with ALI are cared for, the incidence of ALI in the United States appears to be higher than previously reported.

Acute respiratory distress syndrome after kidney transplantation: epidemiology, risk factors, and outcomes

OBJECTIVE

To determine the rate of the acute respiratory distress syndrome (ARDS) after kidney transplantation and to identify risk factors associated with the development of ARDS after kidney transplantation and outcomes for patients diagnosed with ARDS in this setting.

DESIGN

Retrospective analysis of the national registry for end-stage renal disease in the United States.

PATIENTS

We studied all patients who underwent kidney transplantation between July 1, 1994 and June 30, 1998 and identified patients diagnosed with ARDS. The diagnosis of ARDS was based on coding of patients records. We also compared the rate of ARDS after kidney transplantation with the rate of ARDS in the remainder of the U.S. population based on the results of the National Hospital Discharge Survey for 1997.

MEASUREMENTS AND MAIN RESULTS

During the study period, 42,190 kidney transplantations were performed in the United States and ARDS was diagnosed in 86 of these subjects (0.2%) resulting in an annualized rate of ARDS of 51.0 cases per 100,000 patients per year. The rate of ARDS after kidney transplantation was significantly higher than the reported rate of ARDS in the U.S. population (p <.050). Demographic factors, indications for transplantation, comorbid illness, antigen mismatch, cytomegalovirus status, and development of rejection did not correlate with the development of ARDS. Of the immunosuppressive agents (e.g., cyclosporine, FK-506, mycophenolate mofetil, azathioprine, OKT-3, antilymphocyte globulin), only the use of antilymphocyte globulin when used to treat rejection was linked with an increased risk for ARDS (odds ratio: 3.85; 95% confidence interval: 1.36 to 10.87). Subjects with graft failure were 2.70 (95% confidence interval: 1.33 to 5.52) times more likely to develop ARDS. The 28-day mortality in subjects with ARDS was 52.1%. The 3-yr survival after kidney transplantation was 88.9% in those without ARDS compared with 57.8% in persons with ARDS (p <.001).

CONCLUSIONS

Although ARDS is a rare event after kidney transplantation, undergoing renal transplantation increases the risk for ARDS. Among patients receiving kidney transplants, graft failure and the use of antilymphocyte globulin for rejection are associated with the development of ARDS. Patients who develop ARDS after kidney transplantation face significant mortality.

Epidemiology of acute lung injury

OBJECTIVE

To review the epidemiology of acute lung injury (ALI) with particular emphasis on its effect on public health.

DATA SOURCES

Published studies on the definitions, incidence, and outcomes of ALI.

DATA SUMMARY

ALI is a syndrome of acute hypoxemic respiratory failure that is not primarily cardiac in origin. The diagnostic criteria for the syndrome have not been well studied for their reliability or validity. The lack of a gold standard for the diagnosis of ALI is a challenge to clinical investigation. Recent data on the incidence of ALI (20-50 cases/105 person-years) indicate that it is more common than previous estimates for the incidence of acute respiratory distress syndrome (3-8 cases/105 person-years). There is conflicting evidence as to whether the mortality rate in the broader patient population with ALI is different from the mortality rate in acute respiratory distress syndrome. Mortality attributable to and associated with ALI in the United States is comparable to HIV infection, breast cancer, and asthma. Morbidity from impaired cognitive function, functional status, and psychiatric complications has been reported in survivors of ALI.

CONCLUSIONS

Recent studies of the epidemiology of ALI have reported higher incidence rates for this syndrome than previously described. The mortality and morbidity rates associated with ALI are considerable, with significant impact on public health.

Future research directions in acute lung injury: summary of a National Heart, Lung, and Blood Institute working group

Acute lung injury (ALI) and its more severe form, the acute respiratory distress syndrome (ARDS), are syndromes of acute respiratory failure that result from acute pulmonary edema and inflammation. The development of ALI/ARDS is associated with several clinical disorders including direct pulmonary injury from pneumonia and aspiration as well as indirect pulmonary injury from trauma, sepsis, and other disorders such as acute pancreatitis and drug overdose. Although mortality from ALI/ARDS has decreased in the last decade, it remains high. Despite two major advances in treatment, low VT ventilation for ALI/ARDS and activated protein C for severe sepsis (the leading cause of ALI/ARDS), additional research is needed to develop specific treatments and improve understanding of the pathogenesis of these syndromes. The NHLBI convened a working group to develop specific recommendations for future ALI/ARDS research. Improved understanding of disease heterogeneity through use of evolving biologic, genomic, and genetic approaches should provide major new insights into pathogenesis of ALI. Cellular and molecular methods combined with animal and clinical studies should lead to further progress in the detection and treatment of this complex disease.

Epidemiology and outcome of acute respiratory failure in intensive care unit patients

OBJECTIVES

To summarize the prevalence of various forms of acute respiratory failure in acutely ill patients and review the major factors involved in the outcome of these patients.

DATA SOURCES AND SELECTION

MEDLINE search for published studies reporting the prevalence or outcome for patients with acute respiratory failure and cited reference studies and abstracts from a recent international meeting in the intensive care medicine field.

DATA SYNTHESIS AND EXTRACTION

From the selected articles, information was obtained regarding the prevalence of acute respiratory failure, including acute respiratory distress syndrome and acute lung injury as defined by the North American-European Consensus Conference, the outcome, and the factors influencing mortality rates in this population of patients.

CONCLUSIONS

The prevalence of acute respiratory failure varies according to the definition used and the population studied. Nonsurvivors of acute respiratory distress syndrome die predominantly of respiratory failure in <20% of cases. The relatively high mortality rates of acute lung injury/acute respiratory distress syndrome are primarily related to the underlying disease, the severity of the acute illness, and the degree of organ dysfunction.

Decreased GSSG reductase activity enhances cellular zinc toxicity in three human lung cell lines

Cellular reduced glutathione (GSH) levels have been identified as an essential determinant in zinc-induced cytotoxicity. However, cytotoxic effects of zinc have also been observed without depletion of GSH stores. In a previous study, the intracellular activity of GSSG reductase (GR) has come into focus (Walther et al. 2000, Biol Trace Elem Res 78:163-177). In the present paper we have tried to address this issue more deeply by inhibiting the activity of cellular GR without any appreciable decreases of cellular glutathione. In three pulmonary cell lines, GR activity was inhibited in a dose-dependent manner by the alkylating agent carmustine (BCNU), a known inhibitor of GR. Cells were pretreated with BCNU for 14 h, followed by exposure to various concentrations of zinc chloride. Then we determined the incorporation of radiolabelled methionine (to assess protein synthesis), and measured the GSH and oxidized glutathione (GSSG) levels. Additionally, GR activity of controls was measured. IC(50) values for zinc-induced inhibition of methionine incorporation, as well as GSH contents, was strongly correlated to the decreased GR activity. These results firmly suggest that GR is an important factor in the event chain of zinc cytotoxicity. Together with the results from our previously cited study where impaired regeneration of GSH levels were accompanied by a decrease in total cellular glutathione (GSH + GSSG) we conclude that GSSG itself is an important effector in zinc cytotoxicity.

Adjusting positive end-expiratory pressure and tidal volume in acute respiratory distress syndrome according to the pressure-volume curve

BACKGROUND

Management of acute respiratory distress syndrome (ARDS) patients implies the selection of the adequate ventilatory parameters, essentially PEEP and tidal volume (Vt), to prevent ventilator-induced lung injury. These parameters should be reset as the lung injury evolves. Among the different methods proposed for the adjustment of the ventilator, the measurement of the P-V curve has emerged as a useful, although debated, tool. Our aim has been to study the relationship between the different inflection points of the P-V curve in ARDS patients, and to assess the changes in the empiric PEEP and Vt (PEEP(emp), V(temp) following its use.

METHODS

P-V curves were measured in 27 patients (lung injury score [LIS] >or= 2, 69 measurements) by means of the low-flow continuous inflation method.

RESULTS

A lower inflection point (LIP) was found in all patients and, although it correlated with the PEEP(emp), there was only a fair concordance, so the PEEP was modified in 80% of the cases. The expiratory inflection point (EIP) was significantly lower than the LIP (6.3 +/- 1.7 vs. 8.1 +/- 3.2, P = 0.008). An upper inflection point was observed in 16 measurements (23%) and the Vt was reset in 20% of the cases. Both PEEP and Vt were readjusted on 10 occasions (14%). Only the EIP was significantly higher on the first 3 days of mechanical ventilation. The LIS was correlated with all the inflection points. There were no differences for any parameter independent of the cause of the ARDS (pulmonary/extrapulmonary).

CONCLUSIONS

The quasi-static measurement of the P-V curve is a simple method, easy to interpret, for objective adjustment of the ventilatory parameters in ARDS patients as the lung injury evolves. The implementation of this strategy may vary the empiric clinical practice. The role of the EIP for the evaluation of the severity of lung injury deserves further investigation.

Contributions to the epidemiology of acute respiratory failure

Recently, incidence ranges for acute respiratory failure (ARF), acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) in adults were reported and found to be 77.6–88.6, 17.9–34.0, and 12.6–28.0 cases/100 000 population per year, respectively. Mortality rates of approximately 40% were reported for patients with acute respiratory failure, and similar or slightly lower rates for those with ALI and ARDS. Some experts believe that there is a trend toward lower mortality rates in ALI and ARDS, but this suggestion has not been scientifically validated. Additional organ failures, but not oxygenation indices, appear to be crucial with regard to predicting outcome. Finally, it has remained uncertain whether there exists seasonal variability with respect to the frequency of various forms of respiratory failure.

Outcome after acute respiratory failure is more dependent on dysfunction in other vital organs than on the severity of the respiratory failure

INTRODUCTION

The incidence and outcome of acute respiratory failure (ARF) depend on dysfunction in other organs. As a result, reported mortality in patients with ARF is derived from a mixed group of patients with different degrees of multiorgan failure. The main goal of the present study was to investigate patient outcome in single organ ARF.

PATIENTS AND METHOD

From 1 January 2000 to 1 July 2002, all adult patients (>16 years) in the intensive care unit (ICU) at Haukeland University Hospital were scored daily using the Sequential Organ Failure Assessment (SOFA) score for organ failure. ARF was defined by the SOFA criteria: ratio of arterial oxygen tension to fractional inspired oxygen, with a value < 26.6 kPa (200 mmHg) in more than one recording during the ICU stay (SOFA score 3 or 4). Patients with ARF alone and in combination with other severe organ failure (SOFA score 3 or 4) were included. Survival was recorded on discharge from the ICU, at hospital discharge and at 90 days after ICU discharge.

RESULTS

During the period of study, 832 adult patients were treated and 529 (63.0%) had ARF. The ICU, hospital and 3-month mortality rates were lowest in single organ ARF (3.2, 14.7 and 21.8%, respectively), with increasing mortality with each additional organ failure. When ARF occurred with four or five additional organ failures, the 3-month mortality rate was 75%. No significant differences in mortality were found between early and late ARF.

CONCLUSION

The prognosis for ICU patients with single organ ARF is good, both in the short and long terms. The high overall mortality rate observed is caused by dysfunction in other organs.

Science review: mechanisms of ventilator-induced injury

Acute respiratory distress syndrome (ARDS) and acute lung injury are among the most frequent reasons for intensive care unit admission, accounting for approximately one-third of admissions. Mortality from ARDS has been estimated as high as 70% in some studies. Until recently, however, no targeted therapy had been found to improve patient outcome, including mortality. With the completion of the National Institutes of Health-sponsored Acute Respiratory Distress Syndrome Network low tidal volume study, clinicians now have convincing evidence that ventilation with tidal volumes lower than those conventionally used in this patient population reduces the relative risk of mortality by 21%. These data confirm the long-held suspicion that the role of mechanical ventilation for acute hypoxemic respiratory failure is more than supportive, in that mechanical ventilation can also actively contribute to lung injury. The mechanisms of the protective effects of low tidal volume ventilation in conjunction with positive end expiratory pressure are incompletely understood and are the focus of ongoing studies. The objective of the present article is to review the potential cellular mechanisms of lung injury attributable to mechanical ventilation in patients with ARDS and acute lung injury.

Incidence, clinical course, and outcome in 217 patients with acute respiratory distress syndrome

OBJECTIVE

To assess prospectively acute respiratory distress syndrome incidence, etiologies, physiologic and clinical features, and mortality and its predictors in four intensive care units in Argentina.

DESIGN

Prospective inception cohort.

SETTING

Four general intensive care units in teaching hospitals.

PATIENTS

All consecutive adult patients admitted between January 3, 1999, and January 6, 2000, that met the criteria of the American-European Consensus Conference for acute respiratory distress syndrome.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 235 patients developed acute respiratory distress syndrome, and 217 survived for >24 hrs; these were further analyzed. Main risk factors were: sepsis (44%, including 65 pneumonia cases), shock (15%), trauma (11%), gastric aspiration (10%), and other (34%). At admission, nonsurvivors had significantly higher Acute Physiology and Chronic Health Evaluation II, Sequential Organ Failure Assessment and McCabe scores, and lower oxygenation and pH. During the first week, Pao2/Fio2, Sequential Organ Failure Assessment, pH, base excess, and driving pressure consistently discriminated between survivors and nonsurvivors. Hospital mortality was 58%. One third of patients died early. Main causes of death were multiple organ dysfunction syndrome, sepsis, and septic shock; refractory hypoxemia was uncommon. Factors independently associated with mortality were organ dysfunctions on day 3, Pao2/Fio2 on day 3, and McCabe score.

CONCLUSIONS

Acute respiratory distress syndrome was a frequent syndrome in this cohort. Sepsis was its leading cause, and pneumonia was the most common single diagnosis. Mortality was high but similar to most recent series that included serious comorbidities. Independent predictors of death 72 hrs after admission emphasize the importance of both extrapulmonary and pulmonary factors together with preexisting severe illnesses.

Ventilator treatment in the Nordic countries. A multicenter survey

BACKGROUND

A 1-day point prevalence study was performed in the Nordic countries to identify ventilator-treatment strategies in the region.

MATERIAL AND METHODS

On 30 May 30 2001 all mechanically ventilated patients in 27 intensive care units (ICUs) were registered via the internet. The results are shown as medians (25th, 75th percentile).

RESULTS

One hundred and eight patients were included (69% male) with new simplified acute physiology score (SAPS) 48 (37,57) and 4.5 d (2,11) of ventilator treatment. The most frequent indication for ventilator treatment was acute respiratory failure (73%). Airway management was by endotracheal tube (64%), tracheostomy (32%) and facial mask (4%). Pressure regulated ventilator modes were used in 86% of the patients and spontaneous triggering was allowed in 75%. The tidal volume was 7 ml/kg (6,9), peak inspiratory pressure 22 cmH2O (18,26) and positive end-expiratory pressure (PEEP) 6 cmH2O (6,9). FiO2 was 40% (35,50), SaO2 97% (95-98), PaO2 11 kPa (10,13), PaCO2 5.4 kPa (4.7,6.3), pH 7.43 (7.38,7.47) and BE 2.0 mmol/l (- 0.5,5). The PaO2/FiO2 ratio was 220 mmHg (166,283). The peak inspiratory pressure (r=0.37), mean airway pressure (r=0.36), PEEP (r=0.33), tidal volume (r=0.22) and SAPS score (r=0.19) were identified as independent variables in relation to the PaO2/FiO2 ratio.

CONCLUSION

The vast majority of patients were ventilated with pressure-regulated modes. Tidal volume was well below what has been considered conventional in recent large trials. Correlations between the parameters of gas exchange, respiratory mechanics, ventilator settings and physiological status of the patients was poor. It appears that blood gas values are the main tool used to steer ventilator treatment. These results may help to design future interventional studies of ventilator treatment.

Classification for coding procedures in the intensive care unit

BACKGROUND

There is no commonly accepted coding system for non-operative procedures in general, including intensive care unit (ICU) procedures. In order to create a classification of codes for ICU procedures, a system developed at the University Hospital of Bergen was evaluated in four Nordic countries.

METHODS

Classification codes were constructed using seven main groups of related procedures that were given a letter from A to G. Within each group major procedures were given a number from 00 to 99, with the possibility of up to 10 subclassifications within each procedure. A simple questionnaire regarding the use of coding general ICU procedures and some specific procedures was sent to 171 ICUs in Sweden, Finland, Denmark, and Norway. They were also asked to give their comments on the new classification coding system, which was attached.

RESULTS

One hundred and fifty-four questionnaires were returned (response rate 90%). Some or most of the ICU procedures were registered in the ICUs (82.2%). However 38% did not use any coding system and 24% used a specific internal system. The new classification coding system was well received, and was given a mean value of 7.5 using a VAS scale from 0 to 10 (best). Most ICUs would consider using this system if introduced at a national level.

CONCLUSION

Most Nordic ICUs do register some or most of the procedures performed. Such procedures are however, registered in very different ways, using several different systems, and are often home-made. The new classification system of ICU procedures was well rated.

Statistical evaluation of ventilator-free days as an efficacy measure in clinical trials of treatments for acute respiratory distress syndrome

OBJECTIVE

Trials of potential new therapies in acute lung injury are difficult and expensive to conduct. This article is designed to determine the utility, behavior, and statistical properties of a new primary end point for such trials, ventilator-free days, defined as days alive and free from mechanical ventilation. Describing the nuances of this outcome measure is particularly important because using it, while ignoring mortality, could result in misleading conclusions.

DESIGN

To develop a model for the duration of ventilation and mortality and fit the model by using data from a recently completed clinical trial. To determine the appropriate test statistic for the new measure and derive a formula for power. To determine a formula for the probability that the test statistic will reject the null hypothesis and mortality will simultaneously show improvement. To plot power curves for the test statistic and determine sample sizes for reasonable alternative hypotheses.

SETTING

Intensive care units.

PATIENTS

Patients with acute respiratory distress syndrome or acute lung injury as defined by the American-European Consensus Conference.

MAIN RESULTS

The proposed model fit the clinical data. Ventilator-free days were improved by lower tidal volume ventilation, but the improvement was mostly caused by the improved mortality rate, so trials that expected similar effects would only have modest increase in power if they used ventilator-free days as their primary end point rather than 28-day mortality. Similar results were obtained using the model in two groups segregated by low or high Acute Physiology and Chronic Health Evaluation score. On the other hand, if patients are divided into two groups on the basis of the lung injury score, both the duration of ventilation and mortality are lower in the low lung injury score group. A trial of a treatment that had a similar clinical effect would have a large increase in power, allowing for a reduction in the required sample size.

CONCLUSIONS

Use of ventilator-free days as a trial end point allows smaller sample sizes if it is assumed that the treatment being tested simultaneously reduces the duration of ventilation and improves mortality. It is unlikely that a treatment that led to higher mortality could lead to a statistically significant improvement in ventilator-free days. This would be especially true if the treatment were also required to produce a nominal improvement in mortality.

Race and gender differences in acute respiratory distress syndrome deaths in the United States: an analysis of multiple-cause mortality data (1979- 1996)

OBJECTIVE

Acute respiratory distress syndrome (ARDS) is a devastating clinical disorder that affects critically ill patients with a wide variety of underlying illnesses. Presently, there is limited population-based information concerning both the impact of ARDS on mortality, and the effects of race and gender on national ARDS mortality rates. In this study, we have attempted to evaluate trends over an 18-yr period in deaths associated with ARDS in the United States.

DESIGN

Case series.

PATIENTS

The Multiple-Cause Mortality Files compiled by the National Center for Health Statistics from 1979-1996 contains information on 38,263,780 decedents. We identified 333,004 decedents who had ARDS.

MEASUREMENTS AND MAIN RESULTS

We calculated age-adjusted annual ARDS mortality rates. The annual age-adjusted mortality rate for ARDS initially increased from 1979 (5.0 deaths per 100,000 individuals) to 1993 (8.1 deaths per 100,000 individuals). From 1993 to 1996, the mortality rate for ARDS decreased significantly to 7.4 deaths per 100,000 individuals. Annual ARDS mortality rates have been continuously higher for men when compared with women and for African-Americans when compared with white decedents and decedents of other racial backgrounds. When decedents were stratified by race and gender, African-American men had the highest ARDS mortality rates in comparison to all other subgroups (mean annual mortality rate of 12.8 deaths per 100,000 African-American men).

CONCLUSIONS

Although the annual ARDS mortality rate is slowly declining in the United States, significant race and gender differences in ARDS mortality exist.

Severe ARDS may cause right heart failure with extreme hepatomegaly but without hepatic failure

A young trauma patient developed severe adult respiratory distress syndrome (ARDS), right heart failure, hepatic congestion and an extreme hepatomegaly but no hepatic failure. The patient needed 100% oxygen during ventilatory support for 80 days and was weaned from the ventilator after more than 100 days. The hepatomegaly gradually disappeared. Four months after the injury, the anatomical shape of the lungs, heart and liver were normalized. This case illustrates that severe ARDS may cause right heart failure and extreme hepatomegaly due to venous congestion in the liver and spleen, but without hepatic failure.

Pharmacology of acute lung injury

The acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a clinical syndrome that affects both medical and surgical patients. To date, despite improved understanding of the pathogenesis of ALI/ARDS, pharmacological modalities have been unsuccessful in decreasing mortality. However, several pharmacological agents for ARDS are in development and have shown great promise. In addition to the anti-inflammatory category including late corticosteroids, inhaled nitric oxide, alveolar surfactant, and vasodilators are being evaluated. Replacements of anticoagulation mediators have also suggested beneficial effects on the patient outcome. This article provides an overview of pharmacological treatments of ALI/ARDS.

Incidence of ARDS in an adult population of northeast Ohio

STUDY OBJECTIVES

To assess the incidence of the ARDS in a well-defined adult population.

DESIGN

Kaiser Permanente of northeast Ohio, a health maintenance organization, uses the Cleveland Clinic Foundation as its only tertiary care center. In an ongoing prospective assessment in the Cleveland Clinic ICUs, we identified adult Kaiser Permanente patients with ARDS between 1996 and 1999. ARDS was defined according to the 1994 American-European Consensus Conference criteria. The denominator in the incidence calculation was the adult members of Kaiser Permanente of each year of the study period, and the numerator was the new adult ARDS patients in this particular year. The cause of ARDS, the mortality, and the cause of death were retrospectively identified, as well as other characteristics of the study population.

RESULTS

ARDS was diagnosed in 66 patients during the 3-year study period. The incidence per 100,000 population was 11.4 in 1996, 19.8 in 1997, and 14.4 in 1998; the overall incidence was 15.3/100,000/yr. The mean PaO(2)/fraction of inspired oxygen (+/- SD) was 110.8 +/- 37.8, the mean APACHE II was 23.4 +/- 6.9, and the mean ICU stay was 12.0 +/- 9.5 days. The most common cause of ARDS was direct lung injury (75.8%), and the most common cause of death was septic shock (53.8%).

CONCLUSION

The incidence of ARDS in an adult population in northeast Ohio was 15.3/100,000/yr, a number that is slightly higher but comparable to recent estimates reported by other researchers.

Acute respiratory distress syndrome epidemiology and pathophysiology

Acute respiratory distress syndrome is a devastating syndrome of lung injury following known risk factors, with a persistently high mortality. A consensus conference definition of ARDS has been adopted by clinical researchers, but potential problems remain. ARDS may represent more than one entity, and radiographic and mechanical differences between pulmonary versus extrapulmonary initiated ARDS have been described. There is increasing recognition of inflammatory mediators in the pathophysiology of acute lung injury. Surfactant abnormalities contribute to the associated lung dysfunction. A growing body of evidence supports the presence of VILI and a potential mechanism for developing MOSF, and has led to new management strategies. The importances of apoptosis to the repair process, and mechanisms that may lead to persistent fibrosis, such as the activation of the coagulant pathway with fibrin deposition, are increasingly recognized.

The epidemiology of acute respiratory failure in critically ill patients(*)

STUDY OBJECTIVES

To describe the risk factors for the development of and mortality resulting from acute respiratory failure (ARF) in a large patient population.

DESIGN

A substudy of a prospective, multicenter, observational cohort study, which was designed to validate the sequential organ failure assessment score.

SETTING

Forty ICUs in 16 countries.

PATIENTS

All critically ill patients who were admitted to one of the participating ICUs during a 1-month period were observed until the end of their hospital course.

MEASUREMENTS AND RESULTS

Of the 1,449 patients who were enrolled into the study, 458 (32%) were admitted to an ICU with ARF, as defined by a PaO(2)/fraction of inspired oxygen ratio of < 200 mm Hg and the need for respiratory support. Patients who presented with ARF were older than the other patients (63 vs 57 years, respectively; p < 0.001) and more commonly had an infection (47% vs 20%, respectively; p < 0.001). The length of ICU stay was longer (6 vs 4 days, respectively; p < 0.001) and the ICU mortality rate was more than double (34% vs 16%, respectively; p < 0.001) in ARF patients compared to non-ARF patients. Of the 991 patients who were admitted to an ICU without ARF, 352 (35%) developed ARF later during the ICU stay. The independent risk factors for the development of ARF were infection developing in the ICU (odds ratio [OR], 7.59; 95% confidence interval [CI], 5.08 to 11.33) or present on ICU admission (OR, 2.3; 95% CI, 1.68 to 3.16), the presence of neurologic failure on ICU admission (OR, 2.73; 95% CI, 1.90 to 3.91), and older age (OR, 1.70; 95% CI, 1.30 to 2.22). Of all 810 patients with ARF, 253 (31%) died. The independent risk factors for death were multiple organ failure following ICU admission, history of hematologic malignancy, chronic renal failure or liver cirrhosis, the presence of circulatory shock on ICU admission, the presence of infection, and older age.

CONCLUSIONS

The present study stresses that ARF is common in the ICU (56% of all patients) and that a number of extrapulmonary factors are related to the risk of development of ARF and to mortality rate in these patients.

The pulmonary physician in critical care. 5: Acute lung injury and the acute respiratory distress syndrome: definitions and epidemiology

An understanding of the epidemiology of ALI/ARDS and the effects of treatment have been hampered by the lack of a uniform definition of the syndrome. Various definitions have been proposed, and these are reviewed with particular attention to how changes in definition have affected our understanding of the natural history and treatment options for the condition.

Incidence and mortality of acute lung injury and the acute respiratory distress syndrome in three Australian States

To determine the incidence and 28-d mortality rate for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) using the 1994 American-European Consensus Conference definitions, we prospectively screened every admission to all 21 adult intensive care units in the States of South Australia, Western Australia, and Tasmania (total population older than 15 yr of age estimated as 2,941,137), between October 1 and November 30, 1999. A total of 1,977 admissions were screened of which 168 developed ALI and 148 developed ARDS, which represents a first incidence of 34 and 28 cases per 100,000 per annum, respectively. The respective 28-d mortality rates were 32% and 34%. The most common predisposing factors for ALI were nonpulmonary sepsis (31%) and pneumonia (28%). Although the incidences of ALI and ARDS are higher and the mortality rates are lower than those reported from studies in other countries, multicenter international studies are required to exclude methodological differences as the cause for this finding.

Clinical developments for treating ARDS

Acute respiratory distress syndrome (ARDS), is characterised by capillary permeability and pulmonary oedema formation and may complicate a variety of medical and surgical illnesses. As a self-perpetuating state of inflammatory derangement, acute lung injury (ALI)/ARDS is manifest clinically as rapid development of radiographic infiltrates, severe hypoxaemia and reduced lung compliance. Over the years, researchers have made significant progress in elucidating the pathophysiology of this complex syndrome. Therapies targeting specific pathophysiologic steps in the development or persistence of this syndrome are in various stages of laboratory and clinical testing. Results to date have shown nitric oxide (NO) to improve oxygenation in the majority of patients but fail to improve mortality. Surfactant replacement has had limited success in adults, but new formulations and delivery methods may prove beneficial. Several inflammatory mediator-targeted therapies have progressed successfully through early clinical evaluation. Among these, neutrophil elastase inhibitors have shown the most promise and are currently undergoing Phase III trials. Other mediator-targeted therapies, such as prostaglandin E1, IL-10 and platelet activating factor antagonists, have not been found efficacious in large clinical trials of ARDS. However, these therapies, along with coagulation modulators, may have a favourable impact on ARDS by improving outcomes in sepsis, the greatest risk factor for developing this condition. In the interim, supportive care through improvements in mechanical ventilation are beneficial, while specific fluid balance and nutrition strategies may prove advantageous.

Surfactant alteration and replacement in acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a frequent, life-threatening disease in which a marked increase in alveolar surface tension has been repeatedly observed. It is caused by factors including a lack of surface-active compounds, changes in the phospholipid, fatty acid, neutral lipid, and surfactant apoprotein composition, imbalance of the extracellular surfactant subtype distribution, inhibition of surfactant function by plasma protein leakage, incorporation of surfactant phospholipids and apoproteins into polymerizing fibrin, and damage/inhibition of surfactant compounds by inflammatory mediators. There is now good evidence that these surfactant abnormalities promote alveolar instability and collapse and, consequently, loss of compliance and the profound gas exchange abnormalities seen in ARDS. An acute improvement of gas exchange properties together with a far-reaching restoration of surfactant properties was encountered in recently performed pilot studies. Here we summarize what is known about the kind and severity of surfactant changes occurring in ARDS, the contribution of these changes to lung failure, and the role of surfactant administration for therapy of ARDS.