The American-European Consensus Conference on ARDS, part 2. Ventilatory, pharmacologic, supportive therapy, study design strategies and issues related to recovery and remodeling

Combined effects of prone positioning and airway pressure release ventilation on gas exchange in patients with acute lung injury

BACKGROUND

Prone positioning has been shown to improve oxygenation in 60-70% of patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Another way to improve matching of ventilation to perfusion is the use of partial ventilatory support. Preserving spontaneous breathing during mechanical ventilation has been shown to improve oxygenation in comparison with controlled mechanical ventilation. However, no randomized studies are available exploring the effects of preserved spontaneous breathing on gas exchange in combination with prone positioning. Our aim was to determine whether the response of oxygenation to the prone position differs between pressure-controlled synchronized intermittent mandatory ventilation with pressure support (SIMV-PC/PS) and airway pressure release ventilation with unsupported spontaneous breathing (APRV).

METHODS

We undertook a prospective randomized intervention study in a medical-surgical adult intensive care unit of a university hospital. Of 45, 33 ALI patients (acute lung injury) within 72 h after initiation of mechanical ventilation, and in whom the prone position was applied according to a predefined strategy, were included in the study. After initial stabilization the patients were randomized to receive either SIMV-PC/PS or APRV with predefined general ventilatory goals (PEEP, tidal volume, inspiratory pressure and PaCO2-level). The protocol for prone positioning was the same for both treatment arms. Prone positioning was triggered by finding a PaO2/FiO2-ratio below 200 mmHg evaluated twice per day. The duration of each prone episode was 6 h.

RESULTS

The first two episodes of prone positioning were analyzed. Gas exchange was measured before and at the end of prone positioning. Of the 45 patients enrolled, 33 were turned prone once and 28 twice. No significant differences were detected in baseline characteristics. Changes in oxygenation were analyzed in response to the first and second prone episodes 5 h and 24 h after randomization and initiation of SIMV-PC/PS or APRV respectively. Before the first prone episode the PaO2/FiO2-ratio was significantly better (P = 0.02) in the APRV-group (median; interquartile range) (162; 108-192 mmHg) than in the SIMV-PC/PS-group (123; 78-154 mmHg). The response in oxygenation to the first prone episode was similar in both groups: PaO2/FiO2-ratio increased 39.5; 17.75-77.5 mmHg in the SIMV-PC/PS-group and 75.0; 9.0-125.0 mmHg in the APRV-group (P = 0.49). Before the second prone episode, the PaO2/FiO2-ratio was comparable (SIMV-PC/PS 130.5; 61.0-161.0 mmHg vs. APRV 134; 98.3-175.0 mmHg). Improvement in oxygenation was significantly (P = 0.02) greater in the APRV group (82; 37.0-141.0 mmHg) than in the SIMV-PC/PS group (50; 24.0-68.8 mmHg) during the second prone episode. General ventilatory and hemodynamic variables and use of sedatives were similar in both groups during the study.

CONCLUSIONS

APRV during prone positioning is feasible in the treatment of ALI patients. APRV after 24 h appears to enhance improvement in oxygenation in response to prone positioning.

Treatment with bovine surfactant in severe acute respiratory distress syndrome in children: a randomized multicenter study

OBJECTIVE

To determine whether bovine surfactant given in cases of severe pediatric acute respiratory distress syndrome (ARDS) improves oxygenation.

DESIGN

Single-center study with 19 patients, followed by a multicenter randomized comparison of surfactant with a standardized treatment algorithm. Primary endpoint PaO(2)/FIO(2) at 48 h, secondary endpoints: PaO(2)/FIO(2) at 2, 4, 12, and 24 h, survival, survival without rescue, days on ventilator, subgroups analyzed by analysis of variance to identify patients who might benefit from surfactant.

SETTING

Multicenter study in 19 reference centers for ARDS.

PATIENTS

Children after the 44th postconceptional week and under 14 years old, admitted for at least 4 h, ventilated for 12-120 h, and without heart failure or chronic lung disease. In the multicenter study 35 patients were recruited; 20 were randomized to the surfactant group and 15 to the nonsurfactant group. Decreasing recruitment of patients led to a preliminary end of this study.

INTERVENTIONS

Administration of 100 mg/kg bovine surfactant intratracheally under continuous ventilation and PEEP, as soon as the PaO(2)/FIO(2) ratio dropped to less than 100 for 2 h (in the pilot study increments of 50 mg/kg as long as the PaO(2)/FIO(2) did not increase by 20%). A second equivalent dose within 48 h was permitted.

RESULTS

In the pilot study the PaO(2)/FIO(2) increased by a mean of 100 at 48 h (n=19). A higher PaO(2)/FIO(2) ratio was observed in the surfactant group 2 h after the first dose (58 from baseline vs. 9), at 48 h there was a trend towards a higher ratio (38 from baseline vs. 22). The rate of rescue therapy was significantly lower in the surfactant group. Outcome criteria were not affected by a second surfactant dose (n=11). A significant difference in PaO(2)/FIO(2) in favor of surfactant at 48 h was found in the subgroup with an initial PaO(2)/FIO(2) ratio higher than 65 and in patients without pneumonia. CONCLUSIONS. Surfactant therapy in severe ARDS improves oxygenation immediately after administration. This improvement is sustained only in the subgroup of patients without pneumonia and that with an initial PaO(2)/FIO(2) ratio higher than 65

The safety of the open lung approach in neurosurgical patients

A recent randomized controlled trial in patients with ARDS showed the beneficial effect of mechanical ventilation according to the so called Open Lung Approach, consisting of low tidal volumes and elevated PEEP settings after performing recruiting maneuvers. However, neurosurgical patients were excluded from this and other ARDS trials due to concerns of intracranial deterioration. In this report, we present the clinical data of eleven patients with known intracranial pathology and concomitant ARDS which was treated according to the Open Lung concept. The mean oxygenation index (paO2/FiO2) increased from 132 +/- 88 to 325 +/- 64 measured 24 hours after initiation of Open Lung ventilation (p < 0.001). Mean PEEP level after the first recruiting maneuver was 14.9 +/- 3.2 mmHg. Comparison of mean and peak ICP values over 24 hours of time before and after the first recruitment maneuver revealed a non-significant decline in ICP despite a moderate increase in mean paCO2. Although two patients needed additional ICP treatment, no patient had to be withdrawn from Open Lung ventilation. In our series, Open Lung ventilation in neurosurgical patients with ARDS was a safe method to improve oxygenation. Careful ICP monitoring provided, there is no reason to withhold this modern ARDS treatment in the neurosurgical intensive care unit.

Inhaled nitric oxide for acute hypoxemic respiratory failure in children and adults

BACKGROUND

Acute hypoxemic respiratory failure affects all age groups and may result from a number of systemic diseases. It continues to be associated with high mortality and morbidity. Initial studies examining the effect of inhaled nitric oxide in respiratory failure demonstrated transient improvement in oxygenation but did not examine mortality or other significant morbidity outcomes.

OBJECTIVES

To systematically examine randomized controlled trials addressing the effect of inhaled nitric oxide, compared with placebo inhaled gas, on mortality and morbidity in patients with acute hypoxemic respiratory failure.

SEARCH STRATEGY

Randomized controlled trials were identified from electronic databases: The Cochrane Central Register of Controlled Trials (CENTRAL) (Issue 2, 2002;MEDLINE (January 1966-August 2002); EMBASE (1980-March 2001); CINAHL (1982-July 2002), as well as from bibliographies of retrieved articles. Relevant journals and conference proceedings were hand searched and authors published in this field were contacted for knowledge of unpublished ongoing trials.

SELECTION CRITERIA

Randomized controlled trials comparing inhaled nitric oxide with maximal conventional therapy and inhaled placebo, in either children or adults with acute hypoxemic respiratory failure.

DATA COLLECTION AND ANALYSIS

Qualitative assessment of each trial was made and analyses performed according to statistical methods in Review Manager MetaView 4.1. A sub-group analysis was performed to assess the impact of inhaled nitric oxide at varied doses.

MAIN RESULTS

Five randomized controlled trials were evaluated, assessing 535 patients with acute hypoxemic respiratory failure (Age range not provided). Lack of data prevented assessment of all outcomes. There was no significant difference of nitric oxide on mortality in trials without cross-over (RR 0.98, 95%CI 0.66,1.44). Published evidence from one study demonstrated nitric oxide to transiently improve oxygenation in the first 72 hours of treatment. Limited data demonstrated no significant difference in ventilator-free days between treatment and placebo groups, and no specific dose of nitric oxide was significantly advantageous over another. Other clinical indicators of effectiveness, such as duration of hospital and intensive care stay, were inconsistently reported. There were no significant complications directly attributable to this treatment.

REVIEWER'S CONCLUSIONS

Nitric oxide did not demonstrate any statistically significant effect on mortality and transiently improved oxygenation in patients with hypoxemic respiratory failure. Lack of data prevented assessment of other clinically relevant end points. If further trials comparing inhaled nitric oxide with an inhaled placebo are to proceed, they should be stratified for primary disease, assess the impact of other combined treatment modalities for respiratory failure, and must specifically evaluate clinically relevant outcomes, before any benefit of inhaled nitric oxide for respiratory failure can be excluded.

Invited review: lung edema clearance: role of Na(+)-K(+)-ATPase

Acute hypoxemic respiratory failure is a consequence of edema accumulation due to elevation of pulmonary capillary pressures and/or increases in permeability of the alveolocapillary barrier. It has been recognized that lung edema clearance is distinct from edema accumulation and is largely effected by active Na(+) transport out of the alveoli rather than reversal of the Starling forces, which control liquid flux from the pulmonary circulation into the alveolus. The alveolar epithelial Na(+)-K(+)-ATPase has an important role in regulating cell integrity and homeostasis. In the last 15 yr, Na(+)-K(+)-ATPase has been localized to the alveolar epithelium and its contribution to lung edema clearance has been appreciated. The importance of the alveolar epithelial Na(+)-K(+)-ATPase function is reflected in the changes in the lung's ability to clear edema when the Na(+)-K(+)-ATPase is inhibited or increased. An important focus of the ongoing research is the study of the mechanisms of Na(+)-K(+)-ATPase regulation in the alveolar epithelium during lung injury and how to accelerate lung edema clearance by modulating Na(+)-K(+)-ATPase activity.

High frequency oscillatory ventilation in adult patients with acute respiratory distress syndrome--a retrospective study

BACKGROUND

At present there are limited data about the effects of high frequency oscillatory ventilation (HFOV) in adult patients with acute respiratory distress syndrome (ARDS). This study evaluates efficacy of HFOV in such patients.

METHODS

Sixteen ARDS patients, mean age 38.2 years (range 18-76), that underwent HFOV between 1997 and 2001 were enrolled in the study and evaluated in retrospect. FIo2, arterial blood gases, mean airway pressure (mean Paw), blood pressure, heart rate and central venous pressure were recorded by 4, 8, 12, 24, 48 and 72 h of HFOV and compared to conventional mechanical ventilation (CMV) at baseline (4 h prior to HFOV).

RESULTS

On admission to the ICU, mean Simplified Acute Physiology score (SAPS II) was 40.3 (SD 12.6). Main causes of ARDS were pneumonia (9/16) and burn injuries (4/16). At baseline the patients had severe ARDS as noted by a mean lung injury score (LIS) of 3.2 (SD 0.3) and Pao2/FIo2 ratio 12.2 (SD 3.2) kPa. Within 4 h of HFOV, Pao2/FIo2 increased to 17.3 (SD 5.9) kPa (P = 0.016). Throughout HFOV, Pao2/FIo2 was significantly higher than at baseline. There were no significant changes in haemodynamic parameters. Ending HFOV after 6.6 (SD 3.2) days, survivors (n = 11) significantly reduced their Sequential Organ Failure Assessment Score (SOFA) compared to baseline. Survival at 3 months was 68.8%.

CONCLUSION

HFOV effectively improves oxygenation without haemodynamic compromise. During HFOV, the SOFA score may predict outcome.

Impact of low pulmonary vascular pressure on ventilator-induced lung injury

OBJECTIVE

To study the impact of low pulmonary vascular pressure on ventilator-induced lung injury.

DESIGN

Randomized prospective animal study.

SUBJECTS

Isolated perfused rabbit heart-lung preparation.

SETTINGS

Animal research laboratory in a university hospital.

INTERVENTIONS

Twenty isolated sets of normal lungs were perfused (constant flow, 0.3 L/min; left atrial pressure, 6 mm Hg), ventilated for 20 min (pressure control ventilation, 15 cm H2O; baseline period), and then randomized into three groups. Group A (control, n = 7) was perfused and ventilated as previously described during three consecutive 20-min periods. In group B (high airway pressure/normal left atrial pressure, n = 7), pressure control ventilation was 20, 25, and 30 cm H2O during each period. Group C (high airway pressure/low left atrial pressure, n = 6) was ventilated as group B but, in contrast to groups A and B, left atrial pressure was reduced to 1 mm Hg.

MEASUREMENTS AND MAIN RESULTS

The rate of edema formation (WGR, weight gain per minute normalized for initial lung weight) and the ultrafiltration coefficient (Kf) were measured during and after each period and their changes from baseline [DeltaWGR (edema formation index) and DeltaKf (vascular permeability index)] calculated to compare groups. The incidence and timing of vascular failure were compared. Vascular failure was considered to be present if all the following conditions were met: pulmonary hypertension, accelerated weight gain, and occurrence of fluid leak from the lungs. At the end of the study, DeltaWGR (g.g.min(-1)) was higher in group C (0.54 +/- 0.17) than in groups B (0.08 +/- 0.04) and A (0.00 +/- 0.01; p<.05), as well as in group B compared with A (p <.05). Similar differences between groups (p <.05) were found for DeltaK (g x min(-1) x cm H2O(-1) x 100 g(-1)): C, 7.24 +/- 2.36; B, 1.40 +/- 0.49; A, 0.01 +/- 0.03. Vascular failure was not observed in groups A and B but occurred in all but one preparation in group C (p <.05; C vs. A and B).

CONCLUSION

Reducing left atrial pressure results in more severe ventilator-induced lung injury. These results suggest that lung blood volume modulates cyclic tidal lung stress.

Detection of porcine oleic acid-induced acute lung injury using pulmonary acoustics

To evaluate the utility of monitoring the sound-filtering characteristics of the respiratory system in the assessment of acute lung injury (ALI), we injected a multifrequency broadband sound signal into the airway of five anesthetized, intubated pigs, while recording transmitted sound over the trachea and on the chest wall. Oleic acid injections effected a severe lung injury predominantly in the dependent lung regions, increasing venous admixture from 6 +/- 1 to 54 +/- 8% (P < 0.05) and reducing dynamic respiratory system compliance from 19 +/- 0 to 12 +/- 2 ml/cmH(2)O (P < 0.05). A two- to fivefold increase in sound transfer function amplitude was seen in the dependent (P < 0.05) and lateral (P < 0.05) lung regions; no change occurred in the nondependent areas. High within-subject correlations were found between the changes in dependent lung sound transmission and venous admixture (r = 0.82 +/- 0.07; range 0.74-0.90) and dynamic compliance (r = -0.87 +/- 0.05; -0.80 to -0.93). Our results indicate that the acoustic changes associated with oleic acid-induced lung injury allow monitoring of its severity and distribution.

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.

Controlled versus assisted mechanical ventilation

On the basis of currently available data, it can be suggested that maintained spontaneous breathing during mechanical ventilation should not be suppressed even in patients with severe pulmonary dysfunction if no contraindications, such as increased intracranial pressure, are present. Improvements in pulmonary gas exchange, systemic blood flow, and oxygen supply to tissues, which have been observed when spontaneous breathing was allowed during ventilatory support, are reflected in the clinical improvement in the patient's condition, as indicated by significantly fewer days with ventilation, earlier extubation, and shorter stays in the intensive care unit. The positive effects of spontaneous breathing have been documented only for some of the available partial ventilatory support modalities. If ventilatory modalities are limited to those whose positive effects have been documented, then partial ventilatory support can be used as a primary modality even in patients with severe pulmonary dysfunction. Whereas controlled mechanical ventilation followed by weaning with partial ventilatory support modalities has been the earlier standard in ventilation therapy, this approach should be reconsidered in view of the available data.

Reduced tidal volumes and lung protective ventilatory strategies: where do we go from here?

Three major determinants of lung injury associated with mechanical ventilation have been clearly identified: high pressure/high volume, the shear forces caused by intratidal collapse and decollapse leading to barotrauma/volotrauma/biotrauma. The lung protective strategy aims to reduce the impact of all three determinants. A groundbreaking study showed that reduced tidal volume is less dangerous than high tidal volume, but the researchers did not apply "full" lung protective strategy and did not take into account the shear forces. "Full" protective lung strategy was tested in only one study and in a limited number of patients. Several physiologic studies strongly suggest the advantages of the lung protective strategy.

Multiple organ failure still a major cause of morbidity but not mortality in blunt multiple trauma

BACKGROUND

Multiple organ failure (OF/MOF) was found to be the major complication after blunt multiple trauma during the last 25 years and was correlated with a high mortality rate. Recently, several publications reported a decreased ARDS-related mortality, but there is little information about mortality rates from posttraumatic MOF. The purpose of this study was to describe the development of MOF-related death after blunt multiple trauma during the last 25 years.

METHODS

Blunt multiple trauma patients with an Injury Severity Score (ISS) > 15 points were included in this evaluation. According to the year of trauma, the population was divided into five groups: years 1975-1980 (n = 317), years 1981-1985 (n = 308), years 1986-1990 (n = 246), years 1991-1997 (n = 368), and years 1998-1999 (n = 122). Main outcome measurements were death, cause of death, and length of ICU stay. Patients dying within the first 24 hours after trauma were excluded. All data indicated in the Results section are presented as mean +/- SEM. Continuous variables were compared by ANOVA. Ordinal variables were analyzed by chi2 contingency table analysis and, if significant, subsequently by Fisher's exact test (two-tailed test, p < 0.05).

RESULTS

Mean ISS remained unchanged between 1975-1980 (ISS 29 +/- 1) and 1998-1999 (ISS 31 +/- 1) (p = 0.56). During the observation period, the mean age increased from 33 +/- 1 years (1975-1980) to 40 +/- 2 years (1998-1999) (p = 0.03). The overall incidence of OF/MOF slightly increased from 25.6% (1975-1980) to 33.6% (1998-1999) (p = 0.1). Length of ICU stay was not different between 1975-1980 (LOS: 14 +/- 1 d) and 1998-1999 (LOS: 19 +/- 2 d) (p = 1.0). The overall mortality decreased significantly, from 28.7% (1975-1980) to 13.9% (1998-1999) (p < 0.001). While the mortality due to severe head injuries remained unchanged (1975-1980, 8.2%; 1998-1999, 9.0%) (p = 0.85), mortality due to OF/MOF decreased significantly (p < 0.001), from 18.0% (1975-1980) to 4.1% (1998-1999). The age of patients dying from OF/MOF increased significantly (p = 0.04) during the observation period, from 44 +/- 3 years (1975-1980) to 63 +/- 6 years (1998-1999).

CONCLUSION

Although MOF incidence remains unchanged, there is a significant fall in MOF-related mortality in patients with severe trauma, and death from single organ failure is virtually absent. Severe brain injury is now the leading cause of death in patients with severe multiple injuries admitted to the ICU.

Procalcitonin versus interleukin-6 levels in bronchoalveolar lavage fluids of trauma victims with severe lung contusion

OBJECTIVE

To examine whether measurement of procalcitonin (PCT) in comparison with interleukin-6 is a reliable marker to score the extent of lung contusion in bronchoalveolar lavage (BAL) fluids in polytrauma patients.

DESIGN

Prospective, nonrandomized, observational study.

SETTING

Twelve-bed intensive care unit in a 1,100-bed primary care university hospital.

PATIENTS

Fourteen trauma victims presenting with severe lung contusion and acute lung injury or acute respiratory distress syndrome were enrolled in the study.

INTERVENTIONS

Bronchoscopy with collection of lavage fluid and serum blood samples. Samples were obtained on days 1 and 2 after severe chest trauma, and lung contusion was assessed by computed tomography scan.

MEASUREMENTS AND MAIN RESULTS

PCT was detectable in BAL fluids of all 14 patients. A significant correlation for PCT serum and BAL levels was found on day 2 (p =.0063). For PCT, no significant correlations (Spearman rank) were found to the lung injury score (p =.93), the abbreviated injury scale-lung (p =.33), or the sepsis-related organ failure assessment score-lung (p =.38). Also, for interleukin-6 there was no significant correlation to the lung injury score (p =.62), abbreviated injury scale-lung (p =.45), or the sepsis-related organ failure assessment score-lung (p =.54).

CONCLUSIONS

PCT and interleukin-6 BAL levels cannot be considered as reliable parameters to assess the extent of lung contusion.

Cardiac variability in critically ill adults: influence of sepsis

OBJECTIVE

To evaluate, in critically ill adults, factors associated with impaired sympathovagal balance.

DESIGN

One-month inception cohort study.

SETTING

Twenty-six-bed medical intensive care unit of a teaching hospital.

PATIENTS

Critically ill adults with an expected duration of intensive care unit stay of > or =48 hrs were enrolled. Patients with permanent arrhythmia or cardiac pacing were not included.

INTERVENTIONS

None.

MEASUREMENT AND MAIN RESULTS

Sympathovagal balance was assessed on the day after intensive care unit admission by the low-frequency/high-frequency ratio obtained from spectral components of heart rate signal: overall variability, low frequency, and high frequency.

RESULTS

Forty-one patients, 13 with sepsis and 28 without sepsis, were assessed. Predictors of low-frequency/high-frequency ratio with the automatic interaction detection method were sepsis and age. Binary logit analysis adjusted for age showed that sepsis remained a strong and independent factor of a low-frequency/high-frequency ratio of <1.50, with an odds ratio of 3.63 (95% confidence interval, 1.47-9.01, p =.005). Use of mechanical ventilation, catecholamines, or sedation did not add any information. The use of the low-frequency/high-frequency ratio in diagnosing sepsis may be supported by a likelihood ratio for low frequency/high frequency <1 at 6.47.

CONCLUSIONS

This work suggests that impaired cardiac variability and notably sympathovagal balance (i.e., a low-frequency/high-frequency ratio <1.0) may be a diagnostic test for sepsis.

An extracorporeal membrane oxygenation-based approach to cardiogenic shock in an older population

BACKGROUND

We investigated the efficacy of an integrated system of advanced supportive care based on extracorporeal membrane oxygenation (ECMO) in older patients with an estimated mortality of more than 90% to establish whether its use is justifiable.

METHODS

Treatment was provided by cardiac surgeons and critical care physicians and included the following key elements: (1) ECMO, (2) early application of continuous venovenous hemofiltration, (3) inhaled nitric oxide, (4) maintenance of perfusion pressure with norepinephrine, (5) maintenance of pulmonary blood flow by ventricular filling with intravenous colloids, (6) avoidance of early postoperative anticoagulation, (7) frequent use of transesophageal echocardiography, and (8) low tidal volume ventilation. Demographic features, intraoperative details, postoperative course, ECMO weaning rate, morbidity, survival to hospital discharge, and the quality of life of survivors were recorded.

RESULTS

Seventeen consecutive patients (median age, 69 years) with refractory cardiogenic shock were studied. The median duration of ECMO was 86 hours (20 to 201 hours). Eleven patients (65%) were successfully weaned from ECMO. Seven patients (41%) survived to discharge. The major causes of morbidity were bleeding and leg ischemia. All patients who survived to discharge were alive and well at follow-up (median, 21 months) and reported a satisfactory quality of life.

CONCLUSIONS

An ECMO-based approach can be used with acceptable results in the treatment of refractory cardiogenic shock, even in older patients.

Airway pressure release ventilation: theory and practice

Airway pressure release ventilation (APRV) is a relatively new mode of ventilation, that only became commercially available in the United States in the mid-1990s. Airway pressure release ventilation produces tidal ventilation using a method that differs from any other mode. It uses a release of airway pressure from an elevated baseline to simulate expiration. The elevated baseline facilitates oxygenation, and the timed releases aid in carbon dioxide removal. Advantages of APRV include lower airway pressures, lower minute ventilation, minimal adverse effects on cardio-circulatory function, ability to spontaneously breathe throughout the entire ventilatory cycle, decreased sedation use, and near elimination of neuromuscular blockade. Airway pressure release ventilation is consistent with lung protection strategies that strive to limit lung injury associated with mechanical ventilation. Future research will probably support the use of APRV as the primary mode of choice for patients with acute lung injury.

Acute lung injury: pathophysiology, assessment and current therapy

Acute respiratory distress syndrome (ARDS) is a clinically defined entity describing the severity of diffuse alveolar injury caused by direct or indirect injury to the lung. Pathophysiology, clinical course and outcome of ARDS depend on the underlying cause, the severity of the disease and co-morbidities. Pulmonary function tests show restrictive lung disease, which is characterised by a reduction in lung compliance and functional residual capacity, resulting in marked ventilation-perfusion inequality. Current ventilator strategies aim to minimise ventilator-induced lung injury by targeting mechanical ventilation between the lower and upper inflection point of the pressure volume curve. This includes recruitment manoeuvres and the use of high PEEP to open the atelectatic lung and the use of permissive hypercapnia and the limitation of peak inspiratory pressure below 35 cm H2O to avoid overinflation. The clinical benefit of newer modes of ventilatory support such as inverse ratio ventilation, high frequency oscillatory ventilation, surfactant replacement, prone positioning and inhaled nitric oxide has yet to be determined in children.

Nebulized prostacyclin (PGI2) in acute respiratory distress syndrome: impact of primary (pulmonary injury) and secondary (extrapulmonary injury) disease on gas exchange response

OBJECTIVES

To examine the hypothesis that the response to inhaled prostacyclin (PGI2 on oxygenation and pulmonary hemodynamics may be related to different morphologic features that are supposed to be present in acute respiratory distress syndrome (ARDS) originating from pulmonary (primary ARDS [ARDS(PR)]) and from extrapulmonary disease (secondary ARDS [ARDS(SEC)]).

DESIGN

Prospective, nonrandomized interventional study.

SETTING

Multidisciplinary intensive care unit, secondary care center.

PATIENTS

Fifteen consecutive, mechanically ventilated patients with ARDS and severe hypoxemia, defined as PaO2/FIO2 of <150 torr at the time of admission.

INTERVENTIONS

After an initial stable period of at least 60 mins, patients received nebulized PGI2 in 15-min steps; the drug was titrated to find the dose with the best improvement of PaO2, starting with 2 ng/kg/min up to an allowed maximum dose of 40 ng/kg/min.

MEASUREMENTS AND MAIN RESULTS

Blood gas, gas exchange, and hemodynamic measurements were performed at the following time points: a) baseline; b) during the optimal or maximum dose of PGI2; and c) 1 hr after withdrawal of the drug. Patients underwent a computed tomographic (CT) scan using a basal CT section to compute the mean CT numbers and the density histogram. Patients were considered responders to PGI2 if an increase in PaO2 of > or =7.5 torr or an increase in PaO2/FIO2 ratio of > or =10% occurred. For the group as a whole, mean pulmonary artery pressure decreased from 32 +/- 1 to 29 +/- 1 mm Hg during PGI2 nebulization, whereas pulmonary vascular resistance decreased 1 hr after withdrawal of nebulization from 177 +/- 18 to 153 +/- 16 dyne x sec/cm5; oxygenation did not change significantly. Eight patients responded to PGI2 nebulization on oxygenation (all were in the ARDS(SEC) subgroup), whereas seven did not (all but one were in the ARDS(PR) subgroup). Among the physiologic variables examined to assess any difference between the two ARDS groups at time of PGI2 nebulization, there was a significant difference concerning the mean CT density number, which was -445 +/- 22 Hounsfield Units in the ARDS(SEC) group and -258 +/- 16 Hounsfield Units in the ARDS(PR) group. In patients presenting with an ARDS(PR), PGI2 induced a reduction in PaO2/FIO2 and a reduction in PaO2 from 87 +/- 2 to 79 +/- 2 torr, whereas in patients with an ARDS(SEC) there was an increase in PaO2/FIO2 and in PaO2 from 76 +/- 4 to 84 +/- torr with a decrease in mean pulmonary artery pressure.

CONCLUSIONS

Based on the data from this study, the clinical recognition of the two types of the syndrome together with the CT number frequency distribution analysis may be associated with a prediction of the PGI2 nebulization response on oxygenation.

Combined-modality therapy with inhaled nitric oxide and exogenous surfactant in term infants with acute respiratory failure

OBJECTIVE

To report cases of neonates successfully treated with both exogenous surfactant and inhaled nitric oxide (INO).

DESIGN

Retrospective chart review of full term infants treated between January and May 1999 in the neonatal intensive care unit of The Children's Hospital at Strong, University of Rochester, Rochester, New York.

PATIENTS

Three full-term infants treated with surfactant and INO were identified. Each infant had severe acute respiratory failure (as a result of severe aspiration syndromes) and a clinical diagnosis of pulmonary hypertension and parenchymal lung disease in the absence of congenital malformations.

INTERVENTIONS

One infant received INO (20-40 ppm) followed by exogenous surfactant (100mg/kg); the other two received surfactant followed by INO.

MAIN RESULTS

All three infants exhibited a favorable response to treatment with these agents in terms of improved arterial oxygenation as summarized by oxygenation index and all survived to discharge home without referral for extracorporeal membrane oxygenation.

CONCLUSIONS

No adverse interactions were observed related to INO plus surfactant therapy. The responses of these critically ill infants were consistent with the hypothesis that the actions of INO in dilating the pulmonary microvasculature and of exogenous surfactant in stabilizing and recruiting alveoli are complementary and may lead to additive clinical benefits. These case results suggest that more extensive clinical studies are warranted for combined-modality therapy with INO and exogenous surfactant in patients with the acute respiratory distress syndrome.

Excellent coronary perfusion pressure during cardiopulmonary resuscitation is not good enough to ensure long-term survival with good neurologic outcome: a porcine case report

PURPOSE

To report a case of cerebral ischemia confirmed by magnetic resonance imaging after successful cardiopulmonary resuscitation (CPR) complicated by acute respiratory injury.

MATERIALS AND METHODS

After 4 min of cardiac arrest, followed by 3 min of basic life support CPR, a female pig weighing 38 kg received every 5 min vasopressin (0.4, 0.4 and 0.8 U/kg). After 22 min of cardiac arrest, including 18 min of CPR, one defibrillation attempt employing 100 J resulted in return of spontaneous circulation. Neurological evaluation was performed 24 and 96 h after successful CPR. Magnetic resonance imaging was carried out 4 days after CPR using a clinical 1.5 T scanner. The magnetic resonance imaging protocol consisted of fast spinecho T2-weighted, as well as spinecho T1-weighted imaging of the brain.

RESULTS

CPR with vasopressin resulted in excellent coronary perfusion pressure ranging between 35 and 60 mm Hg throughout CPR. Eight minutes after initiation of chest compressions, bleeding out of the tracheal tube occurred. This was later confirmed as originating from bilateral bloody pulmonary infiltrations, resulting in acute respiratory injury in the post-resuscitation phase. Ninety-six hours after successful CPR, magnetic resonance imaging revealed bilateral diffuse cerebral vasogenic edema.

CONCLUSION

Although excellent coronary perfusion pressure renders a return of spontaneous circulation more likely, complications such as acute respiratory injury in the post-resuscitation phase have to be managed carefully in order to ensure good neurological recovery from cardiac arrest.

Multiple organ dysfunction in ulcerative colitis

OBJECTIVE

The mortality rate in severe ulcerative colitis (UC) is commonly attributed to major colonic complications or surgical procedures. Early recognition of the severity of the colitis, intensive medical treatment, and prompt surgery have all contributed to improving its outcome over the past 40 yr. Recently, we have observed some fatal cases of severe UC in which death was related to multiple organ dysfunction syndrome (MODS). This complication, associated with a very high mortality rate, may occur in several acute critical diseases, both infectious and noninfectious, but has so far not been reported in UC. The aim of this study was to evaluate the prevalence and outcome of MODS in severe UC.

METHODS

The records of 180 consecutive patients admitted to the Gastrointestinal Unit, University of Rome for an acute severe attack of UC during the period 1976-1998 were retrospectively analyzed. Severity of UC was defined according to the criteria of Truelove and Witts. MODS was defined according to the original criteria of the American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference 1992. All patients were on a standard intensive regimen consisting of total parenteral nutrition and hydrocortisone 100 mg q.i.d. Colectomy was performed according to the timing of the Oxford intensive regimen.

RESULTS

Of these 180 severe UC patients, 11 (6.1%) experienced clinical and laboratory features of MODS. The lung was involved in five patients, the kidney in three, the liver in seven, the central nervous system in three, the hematological system in three, and the pancreas in one. MODS was preceded by toxic megacolon in five patients and by so-called "impending megacolon" in four, whereas in two patients no previous complications of UC were observed. MODS developed during the first attack of colitis in seven patients and during relapse in four. The overall mortality rate was 12/180 (6.6%). Of the 12 patients who died, eight (72.7%) had MODS.

CONCLUSIONS

These data indicate that UC must be included among the causes of MODS. In our referral center for inflammatory bowel diseases, MODS was responsible for the majority of UC cases with a fatal outcome. The timely identification of signs of MODS should prompt admission to an intensive care unit and emergency surgery.

Pathophysiology and implications for treatment of acute respiratory distress syndrome

Acute respiratory distress syndrome is a complex group of signs and symptoms caused by direct or indirect lung injury. In spite of decades of research, it is still associated with a high mortality rate. Pathogenesis of this disease is related to alveolar endothelial and epithelial cell injury and associated release and sequestration of inflammatory mediators and cells, including cytokines and neutrophils, respectively. Pharmacologic interventions have been largely unsuccessful, and ventilation strategies to support oxygenation while limiting ventilator associated lung injury have not demonstrated any significant reductions in the mortality rate. However, novel therapies are in development, based on the knowledge of the pathologic processes of acute respiratory distress syndrome. In this article an overview of the disease process and mediator involvement is presented, followed by a review of pharmacologic and ventilation treatments currently in use or under study.

Acute lung injury and acute respiratory distress syndrome in sepsis and septic shock

Sepsis remains the leading cause of ARDS, and ARDS is still an often fatal condition. With our expanding knowledge of the pathobiologic mechanisms and the relationship between these two entities, early recognition, treatment, and prevention of sepsis may prevent or hasten recovery from ARDS. Understanding the biologic markers involved in the complex inflammatory response of sepsis and acute lung injury offers the possibility of future investigations to target treatment based on these mediators.

Non-cardiogenic pulmonary oedema in vascular surgery

Non-cardiogenic pulmonary oedema, an early manifestation of the adult respiratory disease syndrome, is a serious complication following major vascular surgery. Hypovolaemia, ischaemia-reperfusion injury, massive blood transfusion, transient sepsis and transient endotoxaemia are insults responsible for initiating the process in vascular surgical patients. Free radicals, cytokines and humoral factors released secondary to the above insults activate neutrophils and facilitate their interaction with the endothelium. Activated neutrophils marginate through the endothelium where they are responsible for tissue injury by the release of free-radicals and proteases. The lungs are a large reservoir of neutrophils and bear a significant part of the injury. Conventional therapy includes treating the underlying condition and providing respiratory support. A better understanding of the pathophysiology of this process has led to new experimental treatment options. Novel therapeutic interventions have included the use of compounds to scavenge free radicals, anti-cytokine antibodies, extracorporeal lung support, nitric oxide and artificial surfactant therapy. The multifactorial nature of this process makes it unlikely that a single "magic bullet" will solve this problem. It is more likely that a combination of preventative, prophylactic and therapeutic modalities may reduce the mortality of this condition.