Inter-individual variability of plasma PAF-acetylhydrolase activity in ARDS patients and PAFAH genotype

BACKGROUND

Platelet activating factor (PAF), a pro-inflammatory phospholipid, stimulates cytokine secretion from polymorphonuclear leukocytes expressing the transmembrane G-protein coupled PAF receptor. Elevated PAF levels are associated with acute respiratory distress syndrome (ARDS) and sepsis severity. The pro-inflammatory effects of PAF are terminated by PAF acetylhydrolase (PAF-AH).

OBJECTIVE

We sought to determine whether allelic variants in the human PAFAH gene (Arg92His, Ile198Thr, and Ala379Val) contribute to variability in PAF-AH activity in patient plasma obtained within 72 h of ARDS diagnosis.

RESULTS

Plasma PAF-AH activity (mean +/- SD) was higher in patients homozygous for the Arg92 allele compared to His92 allele carriers (2.21 +/- 0.77 vs. 1.64 +/- 0.68 U/min; P < 0.01; n = 31 and 21 respectively). Baseline plasma PAF-AH activity was higher among day 7 survivors vs. day 7 non-survivors (2.05 +/- 0.75 vs. 1.27 +/- 0.63, P = 0.05).

CONCLUSION

These data demonstrate an association between PAF-AH allelic variation, plasma activity, and outcome in ARDS.

Evidence of biological efficacy for prolonged glucocorticoid treatment in patients with unresolving ARDS

Acute respiratory distress syndrome (ARDS) is a disease of multifactorial etiology characterised by rapid development of severe diffuse and nonhomogenous inflammation of the pulmonary lobules causing life-threatening hypoxaemic respiratory failure. The current authors tested a therapeutic intervention on a previously defined pathophysiological model of ARDS. The model was defined by investigating, during the natural history of ARDS, the relationship among the three fundamental elements of a disease process pathogenesis, structural alterations, and functional consequences. In these studies, the present authors provided biological and morphological evidence indicating that ARDS patients failing to improve after 1 week of mechanical ventilation (unresolving ARDS) have intense and protracted (dysregulated) pulmonary and systemic inflammatory and neo-fibrogenetic activity. Nuclear factor-kappaB and the glucocorticoid receptor have diametrically opposed functions in regulating inflammation. This chapter will review recent data indicating that poor outcome in acute respiratory distress syndrome might be related in part to failure of the activated glucocorticoid receptors to downregulate the transcription of inflammatory cytokines despite elevated levels of circulating cortisol. In a small randomised study of patients with unresolving acute respiratory distress syndrome, the current authors have shown that prolonged glucocorticoid supplementation improved all aspects of glucocorticoid receptors function and enhanced glucocorticoid-mediated anti-inflammatory action by interfering with nuclear factor-kappaB activation.

Noninvasive vs. conventional mechanical ventilation in patients with chronic obstructive pulmonary disease after failure of medical treatment in the ward: a randomized trial

OBJECTIVE

We conducted a randomized prospective study comparing noninvasive positive pressure ventilation (NPPV) with conventional mechanical ventilation via endotracheal intubation (ETI) in a group of patients with chronic obstructive pulmonary disease who failed standard medical treatment in the emergency ward after initial improvement and met predetermined criteria for ventilatory support.

DESIGN AND SETTING

Prospective randomized study in a university hospital 13-bed general ICU.

PATIENTS

Forty-nine patients were randomly assigned to receive NPPV (n=23) or conventional ventilation (n=26).

RESULTS

both NPPV and conventional ventilation significantly improved gas exchanges. The two groups had similar length of ICU stay, number of days on mechanical ventilation, overall complications, ICU mortality, and hospital mortality. In the NPPV group 11 (48%) patients avoided intubation, survived, and had a shorter duration of ICU stay than intubated patients. One year following hospital discharge the NPPV group had fewer patients readmitted to the hospital (65% vs. 100%) or requiring de novo permanent oxygen supplementation (0% vs. 36%).

CONCLUSIONS

The use of NPPV in patients with chronic obstructive pulmonary disease and acute respiratory failure requiring ventilatory support after failure of medical treatment avoided ETI in 48% of the patients, had the same ICU mortality as conventional treatment and, at 1-year follow-up was associated with fewer patients readmitted to the hospital or requiring for long-term oxygen supplementation. An editorial regarding this article can be found in the same issue (http://dx.doi.org/10.1007/s00134-002-1503-3).

Predictors of failure of noninvasive positive pressure ventilation in patients with acute hypoxemic respiratory failure: a multi-center study

CONTEXT

In patients with hypoxemic acute respiratory failure (ARF), randomized studies have shown noninvasive positive pressure ventilation (NPPV) to be associated with lower rates of endotracheal intubation. In these patients, predictors of NPPV failure are not well characterized.

OBJECTIVE

To investigate variables predictive of NPPV failure in patients with hypoxemic ARF.

DESIGN

Prospective, multicenter cohort study.

SETTING

Eight Intensive Care Units (ICU) in Europe and USA.

PATIENTS

Of 5,847 patients admitted between October 1996 and December 1998, 2,770 met criteria for hypoxemic ARF. Of these, 2,416 were already intubated and 354 were eligible for the study.

RESULTS

NPPV failed in 30% (108/354) of patients. The highest intubation rate was observed in patients with ARDS (51%) or community-acquired pneumonia (50%). The lowest intubation rate was observed in patients with cardiogenic pulmonary edema (10%) and pulmonary contusion (18%). Multivariate analysis identified age > 40 years (OR 1.72, 95% CI 0.92-3.23), a simplified acute physiologic score (SAPS II) > or = 35 (OR 1.81, 95% CI 1.07-3.06), the presence of ARDS or community-acquired pneumonia (OR 3.75, 95% CI 2.25-6.24), and a PaO2:FiO2 < or = 146 after 1 h of NPPV (OR 2.51, 95% CI 1.45-4.35) as factors independently associated with failure of NPPV. Patients requiring intubation had a longer duration of ICU stay ( P < 0.001), higher rates of ventilator-associated pneumonia and septic complications ( P < 0.001), and a higher ICU mortality ( P < 0.001).

CONCLUSIONS

In hypoxemic ARF, NPPV can be successful in selected populations. When patients have a higher severity score, an older age, ARDS or pneumonia, or fail to improve after 1 h of treatment, the risk of failure is higher.

Effects of methylprednisolone on intracellular bacterial growth

Clinical studies have shown positive associations among sustained and intense inflammatory responses and the incidence of bacterial infections. Patients presenting with acute respiratory distress syndrome (ARDS) and high levels of proinflammatory cytokines, such as tumor necrosis factor alpha (TNF-alpha), interleukin 1 beta (IL-1 beta), and IL-6, have increased risk for developing nosocomial infections attributable to organisms such as Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter spp., compared to those patients with lower levels. Our previous in vitro studies have demonstrated that these bacterial strains exhibit enhanced growth extracellularly when supplemented with high concentrations of pure recombinant TNF-alpha, IL-1 beta, or IL-6. In addition, we have shown that the intracellular milieu of phagocytic cells that are exposed to supraoptimal concentrations of TNF-alpha, IL-1 beta, and IL-6 or lipopolysaccharide (LPS) favors survival and replication of ingested bacteria. Therefore, we hypothesized that under conditions of intense inflammation the host's micromilieu favors bacterial infections by exposing phagocytic cells to protracted high levels of inflammatory cytokines. Our clinical studies have shown that methylprednisolone is capable of reducing the levels of TNF-alpha, IL-1 beta, and IL-6 in ARDS patients. Hence, we designed a series of in vitro experiments to test whether human monocytic cells (U937 cells) that are activated with high concentrations of LPS, which upregulate the release of proinflammatory cytokines from these phagocytic cells, would effectively kill or restrict bacterial survival and replication after exposure to methylprednisolone. Fresh isolates of S. aureus, P. aeruginosa, and Acinetobacter were used in our studies. Our results indicate that, compared with the control, stimulation of U937 cells with 100-ng/ml, 1.0-microg/ml, 5.0-microg/ml, or 10.0-microg/ml concentrations of LPS enhanced the intracellular survival and replication of all three species of bacteria significantly (for all, P = 0.0001). Stimulation with < or =10.0 ng of LPS generally resulted in efficient killing of the ingested bacteria. Interestingly, when exposed to graded concentrations of methylprednisolone, U937 cells that had been stimulated with 10.0 microg of LPS were able to suppress bacterial replication efficiently in a concentration-dependent manner. Significant reduction in numbers of CFU was observed at > or =150 microg of methylprednisolone per ml (P values were 0.032, 0.008, and 0.009 for S. aureus, P. aeruginosa, and Acinetobacter, respectively). We have also shown that steady-state mRNA levels of TNF-alpha, IL-1 beta, and IL-6 in LPS-activated cells were reduced by treatment of such cells with methylprednisolone, in a concentration-dependent manner. The effective dose of methylprednisolone was 175 mg, a value that appeared to be independent of priming level of LPS and type of mRNA. We therefore postulate that a U-shaped relationship exists between the level of expression of TNF-alpha, IL-1 beta, and IL-6 within the phagocytic cells and their abilities to suppress active survival and replication of phagocytized bacteria.

Time-variant increase in methylprednisolone clearance in patients with acute respiratory distress syndrome: a population pharmacokinetic study

Methylprednisolone (MP) disposition was evaluated in 20 individuals who participated in an ongoing randomized, double-blind, placebo-controlled study designed to evaluate the efficacy of MP in the treatment of acute respiratory distress syndrome (ARDS). MP (1 mg/kg) was given as a loading infusion over 30 minutes followed by a 1 mg/kg/day continuous i.v. infusion. Patients were switched to oral MP upon restoration of oral intake. MP plasma concentrations (n = 110) were determined using a specific HPLC method. Population pharmacokinetic analysis was performed using nonlinear mixed-effects models, implemented in NONMEM, version V. MP plasma concentration data were described by a one-compartment open model with a time-dependent, non-linear increase in the clearance (CL) of MP during the course of therapy. Initial clearance of MP (CLo) in ARDS patients at the start of therapy increased to a maximal value (CLmax) after approximately 7 days. The estimate of CLmax was similar to the CL of MP in healthy individuals reported previously. Population mean estimates (+/- SE) of parameters in the model were as follows: CLo = 13.2 +/- 2.4 L/h, CLmax = 25.0 +/- 3.6 L/h, time of half-maximal increase in CL (T50) = 41.1 +/- 8.2 h, gamma (Hill coefficient) = 3.8 +/- 0.6, and volume of distribution (Vd) = 137 +/- 30.2 L. Disease progression indices and patient demographics were evaluated as covariates, and no significant correlation was found. Means (+/- SD) of plasma protein binding differed between healthy individuals (72% +/- 4%) and ARDS patients (46% +/- 11%) (p < 0.001). The pharmacokinetics of MP in ARDS patients has not been described previously.

Enhanced extracellular growth of Staphylococcus aureus in the presence of selected linear peptide fragments of human interleukin (IL)-1beta and IL-1 receptor antagonist

Replication of Staphylococcus aureus is significantly enhanced in the presence of recombinant interleukin (IL)-1beta. In this study, specific binding of IL-1beta to the surface of S. aureus significantly increased growth of S. aureus in the presence of IL-1beta and IL-1ra in a concentration-dependent manner. Although IL-1ra enhanced the growth of S. aureus, there was a significant reduction in IL-1beta-mediated growth enhancement of S. aureus when 25-fold excess amounts of IL-1ra (in comparison with the IL-1beta concentration) were present in the culture medium. Thus, IL-1beta may influence the growth of S. aureus through a receptor-mediated event. By using 5 linear peptides spanning limited regions of IL-1beta, the growth-promoting regions were localized to amino acid residues 118-147 and 208-240. These results build on the newly evolved concept of direct interactions between the soluble mediators of inflammation and infectious agents.

Noninvasive ventilation for treatment of acute respiratory failure in patients undergoing solid organ transplantation: a randomized trial

CONTEXT

Noninvasive ventilation (NIV) has been associated with lower rates of endotracheal intubation in populations of patients with acute respiratory failure.

OBJECTIVE

To compare NIV with standard treatment using supplemental oxygen administration to avoid endotracheal intubation in recipients of solid organ transplantation with acute hypoxemic respiratory failure.

DESIGN AND SETTING

Prospective randomized study conducted at a 14-bed, general intensive care unit of a university hospital.

PATIENTS

Of 238 patients who underwent solid organ transplantation from December 1995 to October 1997, 51 were treated for acute respiratory failure. Of these, 40 were eligible and 20 were randomized to each group.

INTERVENTION

Noninvasive ventilation vs standard treatment with supplemental oxygen administration.

MAIN OUTCOME MEASURES

The need for endotracheal intubation and mechanical ventilation at any time during the study, complications not present on admission, duration of ventilatory assistance, length of hospital stay, and intensive care unit mortality.

RESULTS

The 2 groups were similar at study entry. Within the first hour of treatment, 14 patients (70%) in the NIV group, and 5 patients (25%) in the standard treatment group improved their ratio of the PaO2 to the fraction of inspired oxygen (FIO2). Over time, a sustained improvement in PaO2 to FIO2 was noted in 12 patients (60%) in the NIV group, and in 5 patients (25%) randomized to standard treatment (P = .03). The use of NIV was associated with a significant reduction in the rate of endotracheal intubation (20% vs 70%; P = .002), rate of fatal complications (20% vs 50%; P = .05), length of stay in the intensive care unit by survivors (mean [SD] days, 5.5 [3] vs 9 [4]; P = .03), and intensive care unit mortality (20% vs 50%; P = .05). Hospital mortality did not differ.

CONCLUSIONS

These results indicate that transplantation programs should consider NIV in the treatment of selected recipients of transplantation with acute respiratory failure.

New rationale for glucocorticoid treatment in septic shock

Two recent small randomized trials evaluating a 5- to 12-day course of low dose hydrocortisone in patients with septic shock have reported a significant clinical improvement and a reduction in mortality. Recent studies indicate that an overaggressive and unregulated systemic inflammatory response is a major determinant of outcome in sepsis. In septic shock, nonsurvivors as opposed to survivors have over time: (1) significantly higher NF-kB activity in peripheral mononuclear cells, (2) persistent elevation in circulating inflammatory cytokine levels, and (3) elevated ACTH and cortisol levels. Current research recognizes that cytokines can cause a concentration-dependent resistance to endogenous glucocorticoids (GC). It is postulated that an excess of cytokine-induced transcription factors, such as NF-kB, may form complexes with activated glucocorticoid receptors (GCR), preventing GCR interaction with DNA. When T cells are incubated with a combination of cytokines, GC resistance is induced in a cytokine concentration-dependent fashion and reversed by removal of cytokines. Prolonged treatment with physiological doses of exogenous GCs may be necessary to compensate adequately for the inability of target organs to respond to endogenous cortisol and for the inability of the host to produce appropriately elevated levels of GCs. This hypothesis is supported by the laboratory findings of a recent randomized study of patients with unresolving acute respiratory disease.

Cytokines IL-1beta, IL-6, and TNF-alpha enhance in vitro growth of bacteria

We have previously reported that in acute respiratory distress syndrome (ARDS), nonsurvivors have persistent elevation in pulmonary and circulating proinflammatory cytokine levels over time and a high rate of nosocomial infections antemortem. In these patients, none of the proven or suspected nosocomial infections caused a transient or sustained increase in plasma proinflammatory cytokine levels above preinfection values. We hypothesized that cytokines secreted by the host during ARDS may favor the growth of bacteria. We conducted an in vitro study of the growth of three bacteria clinically relevant in nosocomial infections, evaluating their in vitro response to various concentrations of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6. We found that all three bacterial species showed concentration-dependent growth enhancement when incubated with one or more tested cytokines and that blockade by specific neutralizing cytokine MoAb significantly inhibited cytokine-induced growth. When compared with control, the 6-h growth response (cfu/ml) was maximal with IL-1beta at 1,000 pg for Staphylococcus aureus (36 +/- 16 versus 377 +/- 16; p = 0.0001) and Acinetobacter spp. (317 +/- 1,147 versus 1,124 +/- 147; p = 0.002) and with IL-6 at 1,000 pg for Pseudomonas aeruginosa (99 +/- 50 versus 509 +/- 50; p = 0.009). The effects of cytokines were seen only with fresh isolates and were lost with passage in vitro on bacteriologic medium without added cytokines. In this study we provide additional evidence for a newly described pathogenetic mechanism for bacterial proliferation in the presence of exaggerated and protracted inflammation.

Effects of cytokines and endotoxin on the intracellular growth of bacteria

Patients with unresolving acute respiratory distress syndrome (ARDS) have persistently elevated levels of proinflammatory cytokines in the lungs and circulation and increased rates of bacterial infections. Phagocytic cells hyperactivated with lipopolysaccharide (LPS), which induces high levels of proinflammatory cytokines in monocytic cells, are inefficient in killing ingested bacteria despite having intact phagocytic activity. On the other hand, phagocytic cells that are activated with an analogue of LPS that does not induce the expression of proinflammatory cytokines effectively ingest and kill bacteria. We hypothesized that in the presence of high concentrations of proinflammatory cytokines, bacteria may adapt and utilize cytokines to their growth advantage. To test our hypothesis, we primed a human monocytic cell line (U937) with escalating concentrations of the proinflammatory cytokines tumor necrosis factor alpha, interleukin-1beta (IL-1beta), and IL-6 and with LPS. These cells were then exposed to fresh isolates of three common nosocomial pathogens: Staphylococcus aureus, Pseudomonas aeruginosa, and an Acinetobacter sp. In human monocytes primed with lower concentrations of proinflammatory cytokines (10 to 250 pg) or LPS (1 and 10 ng), intracellular bacterial growth decreased. However, when human monocytes were primed with higher concentrations of proinflammatory cytokines (1 to 10 ng) or LPS (1 to 10 micrograms), intracellular growth of the tested bacteria increased significantly (P <0.0001). These results were reproduced with peripheral blood monocytes obtained from normal healthy volunteers. The specificity of the cytokine activity was demonstrated by neutralizing the cytokines with specific antibodies. Our findings provide a possible mechanism to explain the frequent development of bacterial infections in patients with an intense and protracted inflammatory response.

Epidemiology of ventilator-acquired pneumonia based on protected bronchoscopic sampling

We performed a prospective observational cohort study of the epidemiology and etiology of nosocomial pneumonia in 358 medical ICU patients in two university-affiliated hospitals. Protected bronchoscopic techniques (protected specimen brush and bronchoalveolar lavage) were used for diagnosis to minimize misclassification. Risk factors for ventilator-associated pneumonia were identified using multiple logistic regression analysis. Twenty-eight cases of pneumonia occurred in 358 patients for a cumulative incidence of 7.8% and incidence rates of 12.5 cases per 1, 000 patient days and 20.5 cases per 1,000 ventilator days. Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Hemophilus species made up 65% of isolates from the lower respiratory tract, whereas only 12.5% of isolates were enteric gram-negative bacilli. Daily surveillance cultures of the nares, oropharynx, trachea, and stomach demonstrated that tracheal colonization preceded ventilator-associated pneumonia in 93.5%, whereas gastric colonization preceded tracheal colonization for only four of 31 (13%) eventual pathogens. By multiple logistic regression, independent risk factors for ventilator- associated pneumonia were admission serum albumin <= 2.2 g/dl (odds ratio [OR] 5.9; 95% confidence interval [CI] 2.0-17.6; p = 0.0013), maximum positive end-expiratory pressure >= 7.5 cm H2O (OR, 4.6; 95% CI, 1.4 to 15.1; p = 0.012), absence of antibiotic therapy (OR, 6.7; 95% CI, 1.8 to 25.3; p = 0.0054), colonization of the upper respiratory tract by respiratory gram-negative bacilli (OR, 3.4; 95% CI, 1.1 to 10.1; p = 0.028), pack-years of smoking (OR, 2.3 for 50 pack-years; 95% CI, 1. 2 to 4.2; p = 0.012), and duration of mechanical ventilation (OR, 3. 4 for 14 d; 95% CI, 1.5 to 7.8; p = 0.0044). Several of these risk factors for ventilator-associated pneumonia appear amenable to intervention.

Procollagen types I and III aminoterminal propeptide levels during acute respiratory distress syndrome and in response to methylprednisolone treatment

Ineffective lung repair in patients with unresolving acute respiratory distress syndrome (ARDS) is accompanied by progressive fibroproliferation, inability to improve lung injury score (LIS), progressive multiple organ dysfunction syndrome (MODS), and an unfavorable outcome. Our aim was to investigate the relationship between fibrogenesis, pulmonary and extrapulmonary organ dysfunction, and outcome during the natural course of ARDS and in response to prolonged methylprednisolone treatment. We investigated 29 patients with ARDS. We obtained serial measurements of plasma and BAL procollagen aminoterminal propeptide type I (PINP) and type III (PIIINP) levels and components of the lung injury score (LIS) and MODS score. A reduction in LIS greater than one point from day 1 to day 7 of ARDS divided patients in improvers (group 1, n = 7) and nonimprovers (n = 22). Nonimprovers included those who were recruited (day 9 +/- 3 of ARDS) into a prospective, randomized, double-blind, placebo-controlled trial investigating prolonged methylprednisolone therapy in unresolving ARDS (group 2, n = 17), and those who died (all by day 10 of ARDS) prior to meeting eligibility criteria for the randomized trial (group 3, n = 5). On day 1 of ARDS, plasma PINP or PIIINP levels were elevated in all patients. By day 7 of ARDS, mean plasma PINP or PIIINP levels were unchanged in group 1 but increased significantly in group 2 (p = 0. 0002) and group 3 (p = 0.03). On day 7, patients with plasma PINP levels less than 100 ng/ml were 2.5 times more likely to survive (95% CI: 0.855-7.314), and patients with plasma PIIINP levels greater than 25 ng/ml were nine times more likely to die (95% CI: 1. 418-55.556). In group 2, patients taking placebo (n = 6) had no change in plasma PINP or PIIINP levels over time, while patients treated with methylprednisolone (n = 11) had a rapid and sustained reduction in mean plasma and bronchoalveolar lavage (BAL) PINP and PIIINP levels. By day 3 of treatment, mean plasma PINP and PIIINP levels (ng/ml) decreased from 100 +/- 9 to 45 +/- 8 (p = 0.0001) and 31 +/- 3 to 12 +/- 3 (p = 0.0008), respectively. After 8 to 15 d of methylprednisolone, mean BAL PINP and PIIINP levels (ng/ml) decreased from 63 +/- 25 to 6 +/- 23 (p = 0.002) and 42 +/- 5 to 10 +/- 3 (p = 0.003), respectively. Estimated partial correlation coefficients indicated that as plasma PINP and PIIINP levels decreased over the first 7 d of methylprednisolone treatment, positive end-expiratory pressure, creatinine, bilirubin, and temperature also decreased, while PaO2:FIO2 increased. In early ARDS, plasma PINP and PIIINP levels are elevated and continue to increase over time in those not improving. Among nonimprovers, those randomized to prolonged methylprednisolone treatment had a rapid and significant reduction in plasma and BAL aminoterminal propeptide levels and similar changes in lung injury and MODS scores. These findings provide additional evidence of an association between biological efficacy and physiologic response during prolonged methylprednisolone treatment of unresolving ARDS.

Pneumonia in acute respiratory distress syndrome. A prospective evaluation of bilateral bronchoscopic sampling

We evaluated the diagnostic yield of bilateral bronchoalveolar lavage (BAL) in patients with acute respiratory distress syndrome (ARDS) with suspected ventilator-associated pneumonia (VAP) and compared BAL results from contralateral sites. Ninety-four ARDS patients with suspected VAP underwent 172 bronchoscopies (344 BALs). BAL was processed for quantitative cultures, total cell count and subjected to microscopic analysis for cell differential, presence of intracellular organisms (ICO), and Gram stain. The diagnostic threshold for VAP was a growth of >= 10(4) cfu/ml in BAL culture. Most episodes (68%) had bilateral insignificant bacterial growth. Forty (43%) patients had one or more episodes of VAP. Thirty-three of the 55 (60%) positive bronchoscopies had significant growth in only one side, 18 were right BAL, and 15 were left BAL. Episodes with bilateral significant growth were more likely to be polymicrobial, to have a bacterial growth >= 10(5) cfu/ml in the BAL, and to possess a higher percentage of neutrophils and ICO. Among 65 microorganisms recovered in significant concentration, Pseudomonas aeruginosa occurred in 43% and S. aureus in 15%. Overall, Gram stain had a sensitivity of 54% and a specificity of 87%; and Giemsa stain (> 2% ICO) had a sensitivity of 46% and a specificity of 93%. Antibiotic treatment was modified by the results of BAL cultures in 50 (91%) episodes of pneumonia. In patients with ARDS and suspected VAP, bilateral BAL quantitative bacterial cultures had significant growth on one side only in 19% and in both sides in 13%.

A comparison of noninvasive positive-pressure ventilation and conventional mechanical ventilation in patients with acute respiratory failure

BACKGROUND AND METHODS

The role of noninvasive positive-pressure ventilation delivered through a face mask in patients with acute respiratory failure is uncertain. We conducted a prospective, randomized trial of noninvasive positive-pressure ventilation as compared with endotracheal intubation with conventional mechanical ventilation in 64 patients with hypoxemic acute respiratory failure who required mechanical ventilation.

RESULTS

Within the first hour of ventilation, 20 of 32 patients (62 percent) in the noninvasive-ventilation group and 15 of 32 (47 percent) in the conventional-ventilation group had an improved ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO2:FiO2) (P=0.21). Ten patients in the noninvasive-ventilation group subsequently required endotracheal intubation. Seventeen patients in the conventional-ventilation group (53 percent) and 23 in the noninvasive-ventilation group (72 percent) survived their stay in the intensive care unit (odds ratio, 0.4; 95 percent confidence interval, 0.1 to 1.4; P=0.19); 16 patients in the conventional-ventilation group and 22 patients in the noninvasive-ventilation group were discharged from the hospital. More patients in the conventional-ventilation group had serious complications (66 percent vs. 38 percent, P=0.02) and had pneumonia or sinusitis related to the endotracheal tube (31 percent vs. 3 percent, P=0.003). Among the survivors, patients in the noninvasive-ventilation group had shorter periods of ventilation (P=0.006) and shorter stays in the intensive care unit (P=0.002).

CONCLUSIONS

In patients with acute respiratory failure, noninvasive ventilation was as effective as conventional ventilation in improving gas exchange and was associated with fewer serious complications and shorter stays in the intensive care unit.

Effect of prolonged methylprednisolone therapy in unresolving acute respiratory distress syndrome: a randomized controlled trial

CONTEXT

No pharmacological therapeutic protocol has been found effective in modifying the clinical course of acute respiratory distress syndrome (ARDS) and mortality remains greater than 50%.

OBJECTIVE

To determine the effects of prolonged methylprednisolone therapy on lung function and mortality in patients with unresolving ARDS.

DESIGN

Randomized, double-blind, placebo-controlled trial.

SETTING

Medical intensive care units of 4 medical centers.

PARTICIPANTS

Twenty-four patients with severe ARDS who had failed to improve lung injury score (LIS) by the seventh day of respiratory failure.

INTERVENTIONS

Sixteen patients received methylprednisolone and 8 received placebo. Methylprednisolone dose was initially 2 mg/kg per day and the duration of treatment was 32 days. Four patients whose LIS failed to improve by at least 1 point after 10 days of treatment were blindly crossed over to the alternative treatment.

MAIN OUTCOME MEASURES

Primary outcome measures were improvement in lung function and mortality. Secondary outcome measures were improvement in multiple organ dysfunction syndrome (MODS) and development of nosocomial infections.

RESULTS

Physiological characteristics at the onset of ARDS were similar in both groups. At study entry (day 9 [SD, 3] of ARDS), the 2 groups had similar LIS, ratios of PaO2 to fraction of inspired oxygen (FIO2), and MODS scores. Changes observed by study day 10 for methylprednisolone vs placebo were as follows: reduced LIS (mean [SEM], 1.7 [0.1] vs 3.0 [0.2]; P<.001); improved ratio of PaO2 to FIO2 (mean [SEM], 262 [19] vs 148 [35]; P<.001); decreased MODS score (mean [SEM], 0.7 [0.2] vs 1.8 [0.3]; P<.001); and successful extubation (7 vs 0; P=.05). For the treatment group vs the placebo group, mortality associated with the intensive care unit was 0 (0%) of 16 vs 5 (62%) of 8 (P=.002) and hospital-associated mortality was 2 (12%) of 16 vs 5 (62%) of 8 (P=.03). The rate of infections per day of treatment was similar in both groups, and pneumonia was frequently detected in the absence of fever.

CONCLUSIONS

In this study, prolonged administration of methylprednisolone in patients with unresolving ARDS was associated with improvement in lung injury and MODS scores and reduced mortality.

Ventilator-associated pneumonia in patients with adult respiratory distress syndrome: CT evaluation

PURPOSE

To determine the diagnostic accuracy of computed tomography (CT) for pneumonia in patients with adult respiratory distress syndrome (ARDS).

MATERIALS AND METHODS

CT scans were obtained within 1 week of bronchoscopic sampling in 31 patients receiving mechanical ventilation for ARDS for more than 48 hours. Of 11 patients with pneumonia, five developed symptoms less than 11 days after the onset of ARDS (early ARDS). CT scans were rated for pneumonia independently by four radiologists who were unaware of the clinical diagnosis. Diagnostic accuracy was defined by means of the area under the receiver operating characteristic curve, or A2.

RESULTS

Diagnostic accuracy for pneumonia was fair (A2 = 0.69 +/- 0.04 [standard error]) owing to 70% true-negative ratings (vs 59% true-positive ratings). The generalizability coefficient was good (0.79). No single CT finding was significantly different for the presence of pneumonia. Nondependent opacities predominated in 10 (91%) of 11 patients with pneumonia and 12 (60%) of 20 without pneumonia. Nondependent opacities predominated in nine (56%) of 16 patients with early ARDS and 13 (87%) of 15 with late ARDS.

CONCLUSION

CT has fair diagnostic accuracy for ventilator-associated pneumonia in patients with ARDS owing primarily to identification of patients without pneumonia. No single CT sign was significantly different for pneumonia, but dependent atelectasis was more common in patients with early ARDS without pneumonia.

Effect of changing position on arterial oxygenation in a patient with agenesia of the left pulmonary artery

The effects of body position (supine, right and left lateral decubitus) on gas exchange were evaluated in a patient with agenesis of the left pulmonary artery, subjected to mechanical ventilation because of adult respiratory distress syndrome. Arterial blood gases were measured 60 min after each of the three positions was attained and showed that lying on the left side (i.e. the side of the impaired lung) produced higher arterial oxygen pressure (68.5 +/- 1.5 mm Hg) than lying on the opposite side (50.0 +/- 1.2 mm Hg); (p < 0.05). No significant differences in mean arterial carbon dioxide pressure were found. In contrast to unilateral lung diseases affecting the parenchyma, the position improving arterial oxygenation was the one in which the healthy lung was uppermost, in our patient with a unilateral perfusion defect.

Infections and the inflammatory response in acute respiratory distress syndrome

STUDY OBJECTIVE

Systemic inflammatory response syndrome (SIRS) and infections are frequently associated with the development and progression of acute respiratory distress syndrome (ARDS) and multiple organ dysfunction syndrome (MODS). We investigated, at onset and during the progression of ARDS, the relationships among (1) clinical variables and biological markers of SIRS, (2) infections defined by strict criteria, and (3) patient outcome. Biological markers of SIRS included serial measurements of inflammatory cytokines (IC)-tumor necrosis factor-alpha (TNF-alpha) and interleukins (IL) 1 beta, 2, 4, 6, and 8-in plasma and BAL fluid.

METHODS

We prospectively studied two groups of ARDS patients: 34 patients treated conventionally (group 1) and nine patients who received glucocorticoid rescue treatment for unresolving ARDS (group 2). Individual SIRS criteria and SIRS composite score were recorded daily for all patients. Plasma IC levels were measured by enzyme-linked immunosorbent assay on days 1, 2, 3, 5, 7, 10, and 12 of ARDS and every third day thereafter while patients received mechanical ventilation. Unless contraindicated, bilateral BAL was performed on day 1, weekly, and when ventilator-associated pneumonia was suspected. Patients were closely monitored for the development of nosocomial infections (NIs).

RESULTS

ICU mortality was similar among patients with and without sepsis on admission (54% vs 40%; p < 0.45). Among patients with sepsis-induced ARDS, mortality was higher in those who subsequently developed NIs (71% vs 18%; p < 0.05). At the onset of ARDS, plasma TNF-alpha, IL-1 beta, IL-6, and IL-8 levels were significantly higher (p < 0.0001) in nonsurvivors (NS) and in those with sepsis (p < 0.0001). The NS group, contrary to survivors (S), had persistently elevated plasma IC levels over time. In 17 patients, 36 definitive NIs (17 in group 1 and 19 in group 2) were diagnosed by strict criteria. No definitive or presumed NIs caused an increase in plasma IC levels above patients' preinfection baseline. Daily SIRS components and SIRS composite scores were similar among S and NS and among patients with and without sepsis-induced ARDS, were unaffected by the development of NI, and did not correlate with plasma IC levels.

CONCLUSIONS

Sepsis as a precipitating cause of ARDS was associated with higher plasma IC levels. However, NIs were not associated with an increase in SIRS composite scores, individual SIRS criteria, or plasma IC levels above patients' preinfection baseline. SIRS composite scores over time were similar in S and NS. SIRS criteria, including fever, were found to be nonspecific for NI. Irrespective of etiology of ARDS, plasma IC levels, but not clinical criteria, correlated with patient outcome. These findings suggest that final outcome in patients with ARDS is related to the magnitude and duration of the host inflammatory response and is independent of the precipitating cause of ARDS or the development of intercurrent NIs.

The role of the host defence response in the progression and outcome of ARDS: pathophysiological correlations and response to glucocorticoid treatment

The host defence response (HDR) to insults is similar regardless of the tissue involved and consists of an interactive network of simultaneously activated pathways that act in synergy to increase the host's chance of survival. Among this cascade of integrated pathways, three aspects of the HDR, inflammation, coagulation and tissue repair, are analysed separately to explain the histological and physiological changes occurring at the tissue level in unresolving acute respiratory distress syndrome (ARDS). Cellular responses in HDR are regulated by a complex interaction among cytokines, and cytokines have concentration-dependent biological effects. The degree of initial HDR may determine the progression of ARDS. On Day 1 of mechanical ventilation and over time, nonsurvivors of ARDS have significantly higher plasma and bronchoalveolar lavage inflammatory cytokine levels than survivors. In the absence of inhibitory signals, the continued production of HDR mediators prevents effective restoration of lung anatomy and function by sustaining inflammation with tissue injury, intra- and extravascular coagulation and proliferation of mesenchymal cells (fibroproliferation) with deposition of extracellular matrix resulting in fibrosis. Glucocorticoids inhibit the HDR cascade at virtually all levels; their gradual and generalized suppressive influence protects the host from overshooting. In patients with exaggerated HDR, however, cytokine elevation may cause a concentration-dependent resistance to glucocorticoids by reducing glucocorticoid receptor binding affinity. Recent clinical and experimental studies have shown that effective containment of the HDR in unresolving ARDS may be achieved only if glucocorticoid administration is prolonged. A double-blind randomized study is in progress to evaluate the role of prolonged glucocorticoid treatment in unresolving ARDS.

Noninvasive positive pressure ventilation in status asthmaticus

OBJECTIVE

In asthmatic patients with acute respiratory failure (ARF), placing an endotracheal tube is associated with a high rate of complications and results in increased airway resistance. In acute asthma, mask-continuous positive airway pressure (CPAP) decreases airway resistance and the work of breathing (WOB), but does not improve gas exchange. In COPD with ARF, adding intermittent positive pressure ventilation to mask-CPAP results in an additional improvement in WOB and is highly effective in correcting gas exchange abnormalities. In our medical ICU, noninvasive positive pressure ventilation (NPPV) is used as first-line interventional therapy in eligible patients with hypercapnic ARF. We report our experience with NPPV in 17 episodes of asthma and ARF over a 3-year period.

METHODS

A face mask was secured with head straps, avoiding a tight fit, and connected to a ventilator (PB-7200). Initial ventilatory settings included CPAP at 4 +/- 2 cm H2O to offset intrinsic positive end-expiratory pressure and pressure support ventilation (PSV) at 14 +/- 5 cm H2O aiming at a respiratory rate less than 25 breaths/min and an exhaled tidal volume of 7 mL/kg or more. PSV was then adjusted following arterial blood gas results.

RESULTS

Mean age was 35.4 +/- 11.3 years; 10 patients were female. The mean (+/- SE) for different physiologic values are reported at initiation, less than 2 h, 2 to 6 h, and 12 to 24 h into NPPV. pH was 7.25 +/- 0.01, 7.32 +/- 0.02 (p = 0.0012), 7.36 +/- 0.02 (p < 0.0001), and 7.38 +/- 0.02; PaCO2 was 65 +/- 2, 52 +/- 3(p = 0.002), 45 +/- 3(p < 0.0001), and 45 +/- 4; PaO2 fraction of inspired oxygen was 315 +/- 41, 403 +/- 47, 367 +/- 47, and 472 +/- 67 (p = 0.06); and respiratory rate was: 29.1 +/- 1, 22 +/- 1 (p < 0.0001), 20 +/- 1, and 17 +/- 1. NPPV was well tolerated, and only two patients required sedation. Initial delivered minute ventilation was 16 +/- 4 L/min. The mean (+/- SD) peak inspiratory pressure to ventilate in the NPPV-treated patients was 18 +/- 5 cm H2O and always less than 25 cm H2O. There was no complication or problem with expectorating of secretions. Oral intake (liquid diet) was preserved. Two patients required intubation (35 min and 89 h into NPPV) for worsening PaCO2. Duration of NPPV was 16 +/- 21 h. All patients survived. Length of hospital stay was 5 +/- 4 days.

CONCLUSIONS

In asthmatic patients with ARF, NPPV via a face mask appears highly effective in correcting gas exchange abnormalities using a low inspiratory pressure (< 25 cm H2O). A randomized study is in progress to assess fully the role of NPPV in status asthmaticus.

Noninvasive positive-pressure ventilation via face mask during bronchoscopy with BAL in high-risk hypoxemic patients

STUDY OBJECTIVE

The aim of this study was to assess the feasibility and safety of noninvasive positive-pressure ventilation (NPPV) via a face mask to aid in performing fiberoptic bronchoscopy (FOB) with BAL in immunosuppressed patients with gas exchange abnormalities that contraindicate using conventional unassisted FOB.

STUDY POPULATION

Eight consecutive immunosuppressed patients (40 +/- 14 years old) with suspected pneumonia entered the study. Entrance criteria included the following: (1) PaO2/fraction of inspired oxygen (FIo2) of 100 or less; pH of 7.35 or more; and (3) improvement in O2 saturation during NPPV before initiating FOB.

INTERVENTION

Patients had routine application of topical anesthesia to the nasopharynx. A full face mask was connected to a ventilator (Servo 900C; Solna, Sweden) set to deliver continuous positive airway pressure (CPAP) of 4 cm H2O, pressure support ventilation of 17 cm H2O, and 1.0 FIo2. The mask was secured to the patient with head straps. NPPV began 10 min before starting FOB and continued for 90 min or more after the procedure was completed. The bronchoscope was passed through a T-adapter and advanced through the nose. BAL was obtained by sequential instillation and aspiration of 5 to 25 mL aliquots of sterile saline solution through a bronchoscope wedged in a radiographically involved subsegment. Oxygen saturation, heart rate, respiratory rate, and arterial blood gases were monitored during the study.

RESULTS

NPPV significantly improved PaO2/FIo2 and O2 saturation. FOB with NPPV was well tolerated, and no patient required endotracheal intubation. A causative pathogen was identified by BAL in all patients. Six patients responded to treatment and survived hospital admission. Two patients died 5 to 7 days after FOB from unrelated complications of the underlying illness.

CONCLUSIONS

NPPV should be considered during bronchoscopy of immunosuppressed patients with severe hypoxemia.

Noninvasive positive-pressure ventilation in patients with acute respiratory failure

This article provides a systematic review of the literature on the application of noninvasive ventilation in various forms of hypercapnic and hypoxemic respiratory failures. A description of the underlying pathophysiology is followed by a review of physiologic data explaining the mechanisms of action of noninvasive ventilation. A critical review of clinical studies is presented with specific suggestions. The methodology of correctly implementing and monitoring noninvasive ventilation in patients with acute respiratory failure, critical to success, is detailed.

Differential diagnosis of fever and pulmonary densities in mechanically ventilated patients

Sepsis continues to represent a major threat to the recovery of mechanically ventilated patients and a serious challenge to physicians in charge of their care. Diagnosis of pneumonia is made difficult by numerous infectious and noninfectious conditions that may present in a clinically similar fashion. Clinical criteria are insensitive in identifying extrapulmonary sources of fever. Furthermore, several pathologic conditions may coexist in a single patient, making correct diagnosis and treatment even more difficult. A thorough understanding of the various causes of fever and pulmonary densities, other than pneumonia, is necessary to avoid misdiagnosis and inappropriate treatment. This understanding then allows a systematic approach to diagnosis using the most appropriate tests.

The role of gallium-67 scintigraphy in diagnosing sources of fever in ventilated patients

OBJECTIVE

To evaluate the diagnostic value of gallium-67 scintigraphy in febrile ventilated patients by correlating the findings of 67Ga scintigraphy to sources of fever and pulmonary density, as determined by a comprehensive protocolized diagnostic evaluation.

DESIGN

Prospective observational study.

PATIENTS

Thirty-two intubated patients on mechanical ventilation for > or = 3 days with fever (> or = 38.3 degrees C) and a new or progressive density on chest radiograph. Twenty patients (21 tests) had adult respiratory distress syndrome (ARDS).

INTERVENTION

Diagnostic evaluation for fever included bronchoscopy with protected specimen brushing and (protected) bronchoalveolar lavage (BAL); computed tomography (CT) of sinuses; cultures of blood, urine, and central lines; and CT of the abdomen in high-risk patients.

MEASUREMENTS AND RESULTS

Uptake of 67Ga was reported as either focal or diffuse pulmonary uptake and extrapulmonary uptake. The combined causes of fever were pneumonia (9), fibroproliferation of late ARDS (7), abdominal process (4), sinusitis (4), urinary tract infection (3), and others (6). Causes of the pulmonary densities were pneumonia (9), ARDS (13), atelectasis (7), congestive heart failure (3), and empyema (1). Marked and diffuse pulmonary uptake was found only in patients with ARDS; however, it was not useful in discriminating those patients with pulmonary fibroproliferation as the sole cause of fever (p = 0.167) from those with infection. 67Ga scintigraphy was inadequate for detecting pneumonia but valuable in identifying extrapulmonary sites of infection in patients with ARDS (p = 0.021).

CONCLUSIONS

67Ga scintigraphy should be considered only as an adjunct diagnostic test in the febrile, ventilated patient who has no obvious source of fever, despite a negative evaluation that includes testing for pneumonia, sinusitis, and urinary tract infection, conditions that are rarely detected by 67Ga scintigraphy.

Noninvasive positive pressure ventilation via face mask. First-line intervention in patients with acute hypercapnic and hypoxemic respiratory failure

OBJECTIVES

We have previously reported our experience with noninvasive positive pressure ventilation (NPPV) via face mask in a small group of selected patients with acute respiratory failure (ARF). NPPV was frequently effective (70% success rate) in correcting gas exchange abnormalities and in avoiding endotracheal intubation (ETI); NPPV also had a low rate of complications. We have evaluated the clinical application of NPPV as first-line intervention in patients with hypercapnic and short-term hypoxemic ARF. A dedicated respiratory therapist conducted an educational program with physicians-in-training rotating through the medical ICUs of a university medical center and supervised implementation of a simplified management protocol. Over 24 months, 164 patients with heterogeneous forms of ARF received NPPV. We report on the effectiveness of NPPV in correcting gas exchange abnormalities, in avoiding ETI, and associated complications, in different conditions precipitating ARF.

PATIENT POPULATION

One hundred fifty-eight patients completed the study. Forty-one had hypoxemic ARF, 52 had hypercapnic ARF, 22 had hypercapnic acute respiratory insufficiency (ARI), 17 had other forms of ARF, and 26 with advanced illness had ARF and refused intubation. Twenty-five percent of the patients developed ARF after extubation.

INTERVENTION

Mechanical ventilation was delivered via a face mask. Initial ventilatory settings were continuous positive airway pressure (CPAP) mode, 5 cm H2O, with pressure support ventilation of 10 to 20 cm H2O titrated to achieve a respiratory rate less than 25 breaths/min and an exhaled tidal volume of 7 mL/kg or more. Ventilator settings were adjusted following arterial blood gases (ABG) results.

RESULTS

The mean duration of NPPV was 25 +/- 24 h. When the 26 patients with advanced illness are excluded, NPPV was effective in improving or correcting gas exchange abnormalities in 105 patients (80%) and avoiding ETI in 86 (65%). Failure to improve ABG values was the reason for ETI in 20 of 46 (43%). The overall average predicted and actual mortality were 32% and 16%, respectively. Survival was 93% in non-intubated patients and 79% in intubated patients. NPPV was effective in lessening dyspnea throughout treatment in all but seven patients. Complications developed in 24 patients (16%). In patients with hypercapnic ARF, nonresponders had a higher PaCO2 at entrance (91.5 +/- 4.2 vs 80 +/- 1.5; p < 0.01). In patients with hypercapnic ARF and ARI, arterial blood gases response (pH and PaCO2) within 2 h of NPPV predicted success (p < 0.0001). None of the entrance parameters predicted need for ETI.

CONCLUSIONS

We conclude that application of NPPV in clinical practice is an effective and safe alternative to ETI in many hemodynamically stable patients with hypercapnic ARF and in those with hypoxemic ARF in whom the clinical condition can be readily reversed in 48 to 72 h. An educational and supervision program is essential to successfully implement this form of therapy.

Plasma and BAL cytokine response to corticosteroid rescue treatment in late ARDS

BACKGROUND

In late ARDS, a persistent and exaggerated inflammatory response causes recurrent injury to the alveolocapillary barrier and amplification of intra-alveolar fibroproliferation. When ARDS patients fail to improve, corticosteroid (CS) rescue treatment frequently leads to rapid improvements in lung function. We tested the hypothesis that response to CS treatment is related to suppressing the inflammatory response by comparing changes in lung function to inflammatory cytokine (IC) levels in the plasma and BAL.

METHODS

Blood samples were obtained on days 1, 3, 5, and 7 of ARDS, and on days -5, -3, 0 (initiation of treatment), +3, +5, +7, +10, and +14 of CS treatment. Bilateral BAL was obtained on day 1 of ARDS, before administration of CS treatment, and at weekly intervals. We analyzed changes in IC levels during CS treatment in relation to improvements in lung injury score (LIS), indices of endothelial permeability, and final outcome. We also analyzed data to identify timing to a significant reduction in plasma IC levels and predictors of response.

RESULTS

Nine patients entered the study. CS treatment was initiated 15 +/- 9 days into ARDS. Improvement in LIS (> 1-point reduction) was rapid (< 7 days) in five, delayed (< 14 days) in two, and absent in two. Baseline plasma and BAL IC levels in study patients were similar to a previously reported comparison group of 12 ARDS nonsurvivors. No significant changes in plasma and BAL IC levels were observed before CS administration. Following initiation of CS treatment, significant reductions in plasma tumor necrosis factor-alpha and interleukin 6 (IL-6) levels were seen by day 7 in both rapid and delayed responders (p = 0.03). IL-1 beta was significantly reduced by day 5 (p = 0.04) in rapid responders and by day 10 (p = 0.03) in delayed responders. In responders, improvement in LIS and BAL albumin paralleled reduction in plasma and BAL IC levels. At initiation of treatment, rapid responders had significantly lower tumor necrosis factor-alpha and IL-6 levels. Nonresponders had a significantly higher plasma IL-6 level on days 1 to 3 of ARDS (p = 0.004) and lower ratio of arteriolar oxygen tension to inspired oxygen concentration at initiation of treatment (p < 0.01).

CONCLUSIONS

In patients with late ARDS and a low likelihood of survival, prolonged corticosteroid rescue treatment was associated with a reduction in plasma and BAL IC levels and parallel improvements in indices of endothelial permeability and LIS.

Inflammatory cytokines in the BAL of patients with ARDS. Persistent elevation over time predicts poor outcome

BACKGROUND

Inflammatory cytokines (ICs) are important modulators of injury and repair. ICs have been found to be elevated in the BAL of patients with both early and late ARDS. We tested the hypothesis that recurrent injury to the alveolocapillary barrier and amplification of intra-alveolar fibroproliferation observed in nonresolving ARDS is related to a persistent inflammatory response. For this purpose, we obtained serial measurements of BAL IC and correlated these levels with lung injury score (LIS), BAL indexes of endothelial permeability (albumin, total protein [TP]), and outcome.

METHODS

We prospectively studied 27 consecutive patients with severe medical ARDS. Using enzyme-linked immunosorbent assay methods, levels of tumor necrosis factor-alpha (TNF-alpha) and interleukins (IL) 1 beta, 2, 4, 6, and 8 were measured at frequent intervals in both plasma and BAL. In 22 patients, bilateral BAL was obtained on day 1 of ARDS and at weekly intervals when possible. Right and left BALs were analyzed separately for IC levels, total cell count and differential, albumin, TP, and quantitative bacterial cultures.

RESULTS

On day 1 of ARDS, the 10 nonsurvivors had significantly higher (p = 0.0002) BAL TNF-alpha, IL-1 beta, IL-6, and IL-8 levels, which remained persistently elevated over time, indicating a continuous injury process. In contrast, the 12 survivors had a lesser elevation and a rapid reduction over time. Initial BAL IL-2 and IL-4 levels were significantly higher in patients with sepsis (p = 0.006); both increased over time in survivors and nonsurvivors. BAL levels of TNF-alpha, IL-1 beta, IL-6, and IL-8 correlated with BAL albumin and TP concentrations but not with LIS or ratio of arterial oxygen tension to inspired oxygen concentration. BAL: plasma ratios were elevated for all measured cytokines, suggesting a pulmonary origin. On day 1 of ARDS, nonsurvivors had significantly higher (p = 0.04) BAL: plasma ratios for TNF-alpha, IL-1 beta, IL-6, and IL-8. Over time, BAL:plasma ratios for TNF-alpha, IL-1 beta and IL-6 remained elevated in nonsurvivors and decreased in survivors.

CONCLUSIONS

Our findings indicate that an unfavorable outcome in ARDS is associated with an initial, exaggerated, pulmonary inflammatory response that persists unabated over time. Plasma IC levels parallel changes in BAL IC levels. The BAL:plasma ratio results suggest, but do not prove, a pulmonary origin for IC production. BAL TNF-alpha, IL-1 beta, and IL-8 levels correlated with BAL indices of endothelial permeability. In survivors, reduction in BAL IC levels over time was associated with a decline in BAL albumin and TP levels, suggesting effective repair of the endothelial surface. These findings support a causal relationship between degree and duration of lung inflammation and progression of fibroproliferation in ARDS.

The fibroproliferative phase of late adult respiratory distress syndrome

Tissue response to insults is similar regardless of the tissue involved, and occurs in two sequential and interconnected steps, inflammation and fibroproliferation. Adult respiratory distress syndrome (ARDS) is a disease characterized by acute onset of diffuse and severe inflammatory reaction of the lung parenchyma with loss of compartmentalization, resulting in protein rich exudative edema. Following tissue injury, a complex pattern of responses begins to repair the lung. Ineffective repair is evident histologically with extensive pulmonary fibroproliferation and clinically with fever (without a source of infection) and inability to improve lung function. We will review recent observations indicating that an exaggerated pulmonary inflammatory response plays a key role in the progression of ARDS. We will provide a unifying pathogenetic model of ARDS, showing how the evolution from acute to chronic inflammation explains the progression of histological, laboratory, clinical, and physiological findings seen during the course of unresolving ARDS.

Persistent elevation of inflammatory cytokines predicts a poor outcome in ARDS. Plasma IL-1 beta and IL-6 levels are consistent and efficient predictors of outcome over time

BACKGROUND

Inflammatory cytokines have been related to the development of adult respiratory distress syndrome (ARDS), shock, and multiple organ dysfunction syndrome (MODS). We tested the hypothesis that unfavorable outcome in patients with ARDS is related to the presence of a persistent inflammatory response. For this purpose, we evaluated the behavior of inflammatory cytokines during progression of ARDS and the relationship of plasma inflammatory cytokines with clinical variables and outcome.

METHODS

We prospectively studied 27 consecutive patients with severe medical ARDS. Plasma levels of tumor necrosis factor alpha (TNF-alpha) and interleukins (ILs) 1 beta, 2, 4, 6, and 8 were measured (enzyme-linked immunosorbent assay [ELISA] method) on days 1, 2, 3, 5, 7, 10, and 12 of ARDS and every third day thereafter while patients were receiving mechanical ventilation. Subgroups of patients were identified based on outcome, cause of ARDS, presence or absence of sepsis, shock, and MODS at the time ARDS developed. Subgroups were compared for levels of plasma inflammatory cytokines on day 1 of ARDS and over time.

RESULTS

Of the 27 patients, 13 survived ICU admission and 14 died (a mortality rate of 52%). Overall mortality was higher in patients with sepsis (86 vs 38%, p < 0.02). The mean initial plasma levels of TNF-alpha, IL-1 beta, IL-6, and IL-8 were significantly higher in nonsurvivors (p < 0.0001) and in those patients with sepsis (p < 0.0001). Plasma levels of IL-1 beta (p < 0.01) and IL-6 (p = 0.03) were more strongly associated with patient outcome than cause of ARDS (p = 0.8), lung injury score (LIS), APACHE II score, sepsis (p = 0.16), shock, or MODS score. Plasma levels of TNF-alpha, IL-1 beta, IL-6, and IL-8 remained significantly elevated over time (p < 0.0001) in those who died. Although it was the best early predictor of death (p < 0.001), plasma IL-2 > 200 pg/mL lost its usefulness after the first 48 h. A plasma IL-1 beta or IL-6 level > 400 pg/mL on any day in the first week of ARDS was associated with a low likelihood of survival.

CONCLUSIONS

Our findings indicate that unfavorable outcome in acute lung injury is related to the degree of inflammatory response at the onset and during the course of ARDS. Patients with higher plasma levels of TNF-alpha, IL-1 beta, IL-6, and IL-8 on day 1 of ARDS had persistent elevation of these inflammatory cytokines over time and died. Survivors had lesser elevations of plasma inflammatory cytokines on day 1 of ARDS and a rapid reduction over time. Plasma IL-1 beta and IL-6 levels were consistent and efficient predictors of outcome.

The pathogenesis of ventilator-associated pneumonia: I. Mechanisms of bacterial transcolonization and airway inoculation

Ventilator-associated pneumonia (VAP) is an infection of the lung parenchyma developing in patients on mechanical ventilation for more than 48 h. VAP is associated with a remarkably constant spectrum of pathogenic bacteria, most of which are aerobic Gram-negative bacilli (AGNB) and, to a lesser extent Staphyloccus aureus. Most authorities agree that VAP develops as a result of aspiration of secretions contaminated with pathogenic organisms, which appear to be endogenously acquired. These pathogens gain access to the distal airways by mechanical reflux and aspiration of contaminated gastric contents and also by repetitive inoculation of contaminated upper airway secretions into the distal tracheobronchial tree. Persistence of these organisms in the upper airways involves their successful colonization of available surfaces. Although exogenous acquisition can occur from the environment, the rapidity at which critically ill patients acquire AGNB in the upper airways in conjunction with the low rate of AGNB colonization of health-care workers exposed to the same environment favors the presence of endogenous proximate sources of AGNB and altered upper airway surfaces that are rendered receptive. Proximate sources of AGNB remain unclear, but potential sites harboring AGNB prior to illness include the upper gastrointestinal tract, subgingival dental plaque, and the periodontal spaces. Following illness or antibiotic therapy, competitive pressures within the oropharynx favor AGNB adherence to epithelial cells, which lead to oropharyngeal colonization. Similar dynamic changes in contiguous structures (oropharynx, trachea, sinuses, and the upper gastrointestinal tract) lead to the transcolonization of these structures with pathogenic bacteria. Following local colonization or infection, these structures serve as reservoirs of AGNB capable of inoculating the lower airways. As the oropharynx becomes colonized with AGNB, contaminated oropharyngeal secretions reach the trachea, endotracheal tube, and ventilator circuit. Contaminated secretions pooled above the endotracheal tube cuff gain access to the trachea and inner lumen of the endotracheal tube by traversing endotracheal tube cuff folds. Amorphic particulate deposits containing AGNB form along the endotracheal tube and are capable of being propelled into the distal airways by ventilator-generated airflow or by tubing manipulation. Bacteria embedded within this type of amorphous matrix are particularly difficult for the host to clear. If host defenses fail to clear the inoculum, then bacterial proliferation occurs, and the host inflammatory response progresses to bronchopneumonia.(ABSTRACT TRUNCATED AT 400 WORDS)

Diagnosis and differential diagnosis of ventilator-associated pneumonia

Clinical criteria, radiographic findings, and analysis of a tracheal aspirate are inaccurate for diagnosing ventilator-associated pneumonia (VAP). This article reviews both invasive and noninvasive diagnostic techniques, discusses microbiologic and microscopic analysis of lower airway secretions, and considers factors influencing the results of these tests. The differential diagnosis of fever and pulmonary densities in ventilated patients is discussed, and a systematic diagnostic approach for the evaluation of patients with suspected VAP is presented.

Noninvasive mechanical ventilation via face mask in patients with acute respiratory failure who refused endotracheal intubation

OBJECTIVE

To evaluate the response to noninvasive ventilation in a group of terminally ill patients with acute respiratory failure who refused endotracheal intubation.

DESIGN

Case series.

SETTING

Medical intensive care units (ICUs) in a university health science center.

PATIENTS

Eleven patients, nine with hypercapnic and two with hypoxemic acute respiratory failure. Mean age of patients was 64 yrs.

INTERVENTION

Mechanical ventilation was delivered via a face mask. The initial ventilatory setting was continuous positive airway pressure mode, with pressure-support ventilation of 10 to 20 cm H2O, titrated to achieve a respiratory rate of < 25 breaths/min and a tidal volume of 5 to 7 mL/kg. Ventilatory settings were adjusted based on results of arterial blood gases. Mean duration of mechanical ventilation was 44 hrs.

MEASUREMENTS AND MAIN RESULTS

Mechanical ventilation via face mask was effective in correcting gas exchange abnormalities in seven of 11 patients, all of whom survived and were discharged from the ICU. Four patients with hypercapnic acute respiratory failure died. Mechanical ventilation via face mask was effective in improving respiratory acidosis in three patients and had no effect in one patient. Two of the four patients could not be weaned from mechanical ventilation and opted for discontinuation of this method. Removal of the ventilator while retaining the mask for oxygen supplementation was a nontraumatic experience to the patient and family. Even when respiratory failure did not resolve, mechanical ventilation via face mask was effective in lessening dyspnea and allowed the patient to maintain autonomy and continuous verbal communication.

CONCLUSIONS

We conclude that mechanical ventilation via face mask offers an effective, comfortable, and dignified method of supporting patients with end-stage disease and acute respiratory failure.

New approaches in the diagnosis of nosocomial pneumonia

We have presented a review of the present literature on new modalities to diagnose nosocomial pneumonia. Procedures are now available that, when correctly used, can establish a diagnosis of pneumonia with a high degree of reliability. In our institution, reliance on bronchoscopic modalities has simplified management of patients with suspected VAP, by eliminating confusion and rationalizing antibiotic treatment. Invasive procedures, however, should be performed only if the results of cultures are consistently applied to treatment. As this field rapidly evolves, we hope that this review will provide the reader with a foundation to understand new developments.

Causes of fever and pulmonary densities in patients with clinical manifestations of ventilator-associated pneumonia

BACKGROUND

Ventilator-associated pneumonia, a leading cause of sepsis in patients with acute respiratory failure, is difficult to distinguish clinically from other processes affecting patients receiving mechanical ventilation. We conducted a prospective study of patients with suspected ventilator-associated pneumonia to identify the causes of fever and densities on chest radiographs and to evaluate the diagnostic yield and efficiency of tests used alone and in combination.

METHODS

The 50 patients entered into the study underwent a systematic diagnostic protocol designed to identify all potential causes of fever and pulmonary densities. Diagnoses responsible for fever were established by strict diagnostic criteria for 45 of the 50 patients. The prevalence of specific conditions and diagnostic yield of individual tests were used to formulate a simplified diagnostic protocol.

RESULTS

The diagnostic protocol identified 78 causes of fever (median 2 per patient). Infections were the leading causes of fever and pulmonary densities. Of the 45 patients with fever, 37 had one or more infections identified (67 sources). Most infections (84 percent) were one of four types:pneumonia, sinusitis, catheter-related infection, or urinary tract infection. Ventilator-associated pneumonia occurred in only 42 percent. All but nine infections (87 percent) were directly or indirectly related to insertion of a catheter or a tube. Concomitant infections were frequent (62 percent), particularly in patients with sinusitis (100 percent), catheter-related infections (93 percent), and pneumonia (74 percent). Of concomitant infections, 60 percent were caused by a different pathogen. Noninfectious causes of fever were more common in the 22 patients with adult respiratory distress syndrome. Histologically proved pulmonary fibroproliferation was the only cause of fever in 25 percent of patients with adult respiratory distress syndrome. Radiographic densities were caused by an infection in only 20 patients (19 pneumonia, 1 empyema). In more than 50 percent of the 25 patients without adult respiratory distress syndrome, congestive heart failure, and atelectasis were the sole causes of pulmonary densities, and fever always originated from an extrapulmonary site of infection. Used in combination, bronchoscopy with protected sampling, computed tomographic scan of the sinuses, and cultures of maxillary sinus aspirate, central intravenous or arterial lines, urine, and blood identified 58 of the 78 sources of fever (74 percent).

CONCLUSIONS

The observations in this study document the complex nature of acute respiratory failure and fever and underscore the need for accuracy in diagnosis. The frequent occurrence of multiple infectious and noninfectious processes justifies a systematic search for source of fever, using a comprehensive diagnostic protocol. A simplified diagnostic protocol was devised based on the diagnostic value of individual tests.

Corticosteroid rescue treatment of progressive fibroproliferation in late ARDS. Patterns of response and predictors of outcome

Pulmonary fibroproliferation (PFP) is directly or indirectly the leading cause of death in patients with late ARDS. We previously reported our experience using intravenous corticosteroids (IVC) in 8 patients with late ARDS and now have expanded our observation to a total of 25 patients with severe fibroproliferation (mean lung injury score [LIS] 3) and progressive respiratory failure (RF). Thirteen patients had open-lung biopsy before treatment. Patients were started on IVC treatment (IVCT) an average of 15 +/- 7.5 days into mechanical ventilation (MV). Significant physiologic improvement (SPI) to IVCT was defined as a reduction in LIS of greater than 1 point or an increase in PaO2:FIO2 ratio of greater than 100. We observed three patterns of response: rapid responders (RR) had an SPI by day 7 (n = 15); delayed responders (DR) had an SPI by day 14 (n = 6); nonresponders (NR) were without SPI by day 14 (n = 4). Overall the following significant mean changes were seen within 7 days of IVCT: LIS from 3 to 2 (p = 0.001), PaO2:FIO2 from 162 to 234 (p = 0.0004), PEEP from 11 to 6.8 cm H2O (p = 0.001), chest radiograph score from 3.8 to 3.0 (p = 0.009), and VE from 16 to 13.6 L/min (p = 0.01). Development of pneumonia was related to the pattern of response. Surveillance bronchoscopy was effective in identifying pneumonia in eight afebrile patients. Nineteen of 25 (76 percent) patients survived the ICU admission. Comparisons were made between survivors (S) and nonsurvivors (NS) and among the three groups of responders. At the time ARDS developed, no physiologic or demographic variable could discriminate between S and NS. At the time of IVCT, only liver failure was more frequent in nonsurvivors (p = 0.035). Histologic findings at open-lung biopsy and pattern of physiologic response clearly predicted outcome. The presence of preserved alveolar architecture (p = 0.045), myxoid type fibrosis (p = 0.045), coexistent intraluminal bronchiolar fibrosis (p = 0.0045), and lack of arteriolar subintimal fibroproliferation (p = 0.045) separated S from NS. ICU survival rate was 86 percent in responders and 25 percent in nonresponders (p = 0.03). Only one death resulted from refractory respiratory failure.

Late adult respiratory distress syndrome

Late adult respiratory distress syndrome (ARDS) refers to the clinical stage of ARDS when the lung attempts to repair the initial or persistent injury to the endothelial and epithelial lining of the respiratory units. Histologically, it is characterized by the replacement of damaged epithelial cells and the striking accumulation of mesenchymal cells (fibroproliferative phase) and their connective tissue products in the air spaces and walls of the intra-acinar microvessels. Unfortunately, this reparative process is frequently ineffective, leading directly or indirectly to the patient's death. Its evolution appears to be determined by the extent of initial insult to the lung and by the presence of a protracted inflammatory response. Continuous injury may result from persistent release of inflammatory cytokines in the lung. In late ARDS, injury to the endothelial surface appears to be the pathogenic mechanism behind persistent bronchoalveolar lavage neutrophilia and diffuse pulmonary uptake of gallium. Ineffective repair is characterized by progressive proliferation of myofibroblast and deposition of collagen in the alveoli, thereby producing worsening gas exchange and lung mechanics. Prolonged mechanical ventilation predisposes the patient to the development of pulmonary and extrapulmonary infections. Moreover, release of inflammatory cytokines from the lung with fibroproliferation causes fever and leukocytosis, making clinical distinction from pulmonary or extrapulmonary infections difficult, if not impossible. Anecdotal reports suggest that corticosteroid treatment may accelerate recovery in late ARDS.

Pneumonia and ARDS in patients receiving mechanical ventilation: diagnostic accuracy of chest radiography

This study was done to evaluate the diagnostic accuracy of bedside chest radiography for pneumonia, adult respiratory distress syndrome (ARDS), or both in patients receiving mechanical ventilation. The series consisted of 40 patients; diagnostic accuracy was defined as the area under the receiver operating characteristic curve. Overall diagnostic accuracy for ARDS was 0.84. Overall diagnostic accuracy for pneumonia was 0.52. Review of previous radiographs and knowledge of clinical data did not enhance diagnostic accuracy for ARDS or pneumonia. Diagnostic accuracy for pneumonia was minimally reduced when ARDS was present. There was an increase in false-negative results because the diffuse areas of increased opacity in ARDS obscured the radiographic features of pneumonia. The authors conclude that chest radiography is of limited value for the diagnosis of pneumonia in patients receiving mechanical ventilation. The high false-negative and false-positive ratings for pneumonia resulted in a low diagnostic accuracy. The high diagnostic accuracy for ARDS was primarily due to the well-defined radiographic appearance of ARDS and few false-positive ratings.

Diagnosis of ventilator-associated pneumonia

Ventilator-associated pneumonia is a frequent complication of mechanical ventilation, and it carries a significant added mortality. Proper recognition and treatment of pneumonia are associated with improved outcome. Clinical manifestations of pneumonia, chest radiograph findings, and routine analysis of the tracheal aspirate are inadequate, alone or in combination, in diagnosing pneumonia. This article discusses the methodologies that are presently available for diagnosing pneumonia in ventilated patients. Correct use of these techniques helps the clinician to establish a diagnosis with a high degree of reliability and facilitates the rational use of antibiotic treatment.