Effects of prolonged controlled mechanical ventilation on diaphragmatic function in healthy adult baboons.

OBJECTIVE: To study diaphragmatic strength and endurance after a prolonged period of mechanical ventilation. DESIGN: Prospective animal study. SETTING: Animal research laboratory. SUBJECTS: Seven uninjured adult baboons (Papio cynocephalus) were anesthetized with ketamine, sedated, paralyzed, and mechanically ventilated. Animals were monitored with pulmonary arterial and peripheral arterial catheters. INTERVENTIONS: Mechanical ventilation was provided for 11 days with an FIO2 of 0.21 and tidal volume of 15 mL/kg. Pulmonary function tests, including lung volumes, arterial blood gases, and chest radiographs were also monitored. Nursing care procedures included frequent turning, chest physiotherapy, and endotracheal suction. Antacids and prophylactic antibiotics (intravenous penicillin, topical polymyxin B, and gentamicin sulfate) were administered. In three animals, fishhook electrodes were surgically placed around both phrenic nerves on both day 0 and after 11 days of mechanical ventilation for diaphragmatic stimulation. On day 0, the electrodes were removed after phrenic nerve stimulation studies were performed. After 11 days of mechanical ventilation, animals were electively killed and full autopsy performed. MEASUREMENTS AND MAIN RESULTS: Hemodynamic and pulmonary function parameters were measured at baseline and every day during the 11 days of mechanical ventilation. Diaphragmatic strength and endurance were measured on days 0 and 11. Diaphragmatic endurance was determined by an inspiratory resistive loading protocol. There were no significant changes in hemodynamics, lung volumes, or gas exchange during the period of mechanical ventilation. On day 7, the chest radiographs showed patchy lobar atelectasis in six animals, which cleared by day 11 in all but two of the animals. Lung pathology showed mild, focal pneumonitis. By day 11, maximum transdiaphragmatic pressure had decreased by 25% from day 0 and diaphragmatic endurance had decreased by 36%. CONCLUSIONS: Eleven days of mechanical ventilation and neuromuscular blockade in healthy baboons resulted in nonsignificant changes in hemodynamics, oxygenation, and/or lung function. However, significant impairment in diaphragmatic endurance and strength were seen. Based on these results, it is likely that prolonged mechanical ventilation by itself impairs diaphragmatic function independent of underlying lung disease.

Elastase activity in bronchoalveolar lavage fluid from oxygen-exposed, Pseudomonas-infected baboons.

The adult respiratory distress syndrome is a major cause of morbidity and mortality in critical care patients. Lung injury in this syndrome is frequently associated with lung infection. The combined insults result in an influx of neutrophils and damage to the pulmonary epithelium. We investigated whether active neutrophil elastolytic activity was present in the bronchoalveolar fluid in baboons with mild or moderate hyperoxic lung injury and infection. Group A (N = 7) was exposed for 6 days to FIO2 = 0.8 and then inoculated by intratracheal bolus with Pseudomonas aeruginosa strain DGI-R130 (PA); the FIO2 was reduced to 0.5. Group B (N = 6) was exposed to similar concentrations of inspired oxygen but inoculated with buffered saline. Antibiotics included parenteral penicillin and topical gentamicin and polymyxin B. All 3 were given continuously in group B but stopped 24 h prior to PA inoculation in group A. Bronchoalveolar lavage fluid was collected 1 week before oxygen administration, when the FIO2 was reduced (day 6 or 7) and prior to necropsy (day 11). Hemodynamic, pulmonary function, microbiological, and biochemical variables were studied. Injured, infected animals (group A) had significant elevations of mean pulmonary artery pressure and decreases in total lung capacity and PaO2 compared both to baseline and to group B at day 11. At autopsy, group A had significant increases of bronchoalveolar lavage fluid (BALF) neutrophils and bacterial pathogens. Elastase levels in BALF (equal to 0 at baseline) rose to 136 +/- 98 ng/ml in group A vs. 6 +/- 14 ng/ml in group B. The elastase was inhibited by inhibitors of serine proteases including ones specific for neutrophil elastase. On Sephacryl S-300 chromatography the elastase activity eluted near human alpha 2-macroglobulin and separated from other proteolytic activity. These studies demonstrate a significant level of elastase in BALF from injured, infected baboons compared to injured, uninfected animals.

O2- and pneumonia-induced lung injury. II. Properties of pulmonary surfactant.

Pulmonary surfactant was isolated from the lavage fluids of animals during the course of exposure to 100% O2, 80% O2, 40% O2, or 80% O2 plus 10(8) Pseudomonas aeruginosa instilled intratracheally and analyzed for its phospholipid composition. After 4-5 days of exposure to 100% O2, disaturated phophatidylcholine (DSPC) decreased to 87% of control, whereas the ratio of phosphatidylglycerol to phosphatidylinositol (PG/PI) was 37% of control. Longer periods of ventilation with 100% O2 resulted in DSPC falling to less than 40% of control. The injury was not reversed by reducing the O2 to 50%; rather, a progressive deterioration ensued. Acute respiratory failure (ARF) induced by 5 days of bacterial infection was very similar to that seen after 5 days of exposure to 100% O2. Ventilation with 80% O2 for 6 days resulted in smaller changes in DSPC but with differences in PG/PI comparable to those seen with 100% O2 or infection. We conclude that the ability of the type II cell to synthesize surfactant of normal composition is significantly impaired in these models of ARF. The earliest index of biochemical modification is the substantial change in PG/PI, which may be predictive of early lung injury. Further exacerbation of the injury could result in the reduction of DSPC content, with subsequent changes in lung mechanics and gas exchange.

Bacteriologic diagnosis of nosocomial pneumonia following prolonged mechanical ventilation.

Cultures of tracheal secretions, bronchoalveolar lavage (BAL), protected specimen brushes (PSB), and direct lung aspirates were compared with cultures of lung homogenates and histologic findings in 35 baboons after 7 to 10 days of intubation and mechanical ventilation. Six animals received no antibiotics, while the remainder were treated with a variety of prophylactic regimens of intravenous and topical agents. Bacterial contamination at each culture site was expressed as a "bacterial index" (BI), obtained as the sum of the logarithmic concentrations of individual species. In the absence of antibiotics, pneumonias occurred in all animals and were polymicrobial; 56% of organisms in lung tissue were members of the normal upper respiratory tract flora, while 44% were gram-negative bacilli with a mean total bacterial index of 13.94/g. Lobar tissue BI values greater than 6.0/g were found in 77% of lobes containing pneumonias judged by histologic criteria to be moderate or severe in extent, whereas only 7% of lobes with lesser inflammatory changes had similar BI values. The BI values of BAL were linearly related to tissue values, whether the BAL was performed of the same lobe cultured or a different lobe. BAL recovered 74% of all species present in lung tissue compared to 41% by PSB and 56% for needle aspirates. False positive specimens were found with similar frequency with these 3 procedures. Tracheal aspirates revealed 78% of organisms found in lung tissue, but 14 of 35 (40%) of species isolated were not present in lung tissue. BAL provides the best reflection of the lung's bacterial burden, both quantitatively and qualitatively, in the setting of prolonged intubation and ventilation.

Prevention of nosocomial pneumonia using topical and parenteral antimicrobial agents.

The efficacy of antimicrobial agents applied topically in the oropharynx and trachea with and without intravenous antibiotics in preventing bacterial pneumonias during prolonged (7 to 10 days) mechanical ventilation was studied in 35 baboons, 30 of which had acute lung injury induced by either oleic acid or hyperoxia. In 12 animals receiving no antibiotics, only topical application of polymyxin B (PB), or only intravenous penicillin and gentamicin (IV PCN/GM), moderate or severe pneumonia was found in 81% of lobes examined at necropsy; no lobes were sterile. Pneumonias were polymicrobial in the absence of antibiotics, due to PCN-sensitive organisms in the topical PB group, and due to gram-negative bacilli in the IV PCN/GM group. Combinations of topical PB or GM or both plus IV PCN were highly efficacious in preventing pneumonia in 23 animals as only 15% of the lobes contained moderate to severe pneumonia and 52% of lobes were sterile. In these groups, histologically evident pneumonias were associated with low concentrations of bacteria in lung tissue, principally gram-negative bacilli resistant to the topical agent being used. Resistance to PB appeared to be solely due to selection of intrinsically resistant species, whereas resistance to GM may have developed through additional mechanisms as well. Although this approach to pneumonia prevention is clearly efficacious in this animal model, clinical studies are needed to define the frequency and significance of microbial resistance in human subjects.

One hundred percent oxygen lung injury in adult baboons.

Healthy adult baboons exposed to 100% oxygen for 5 to 7 days maintained on continuous mechanical ventilation develop severe bilateral noncardiogenic pulmonary edema that resembles in many aspects the human adult respiratory distress syndrome (ARDS). In the present study, we evaluated the effects of hyperoxia for 5 to 6 days in 8 baboons to compare changes in abnormalities in bronchoalveolar lavage fluid (BALF) biochemical markers, hemodynamic measurements, and pulmonary function tests in order to find early predictors of lung injury. All animals had bilateral alveolar infiltrates, severe hypoxemia, and progressive deterioration of pulmonary function tests. Diffuse alveolar damage and mild-moderate pneumonias were found and were associated with low-grade bacterial infection. Total lung capacity, diffusing capacity for carbon monoxide, pulmonary static compliance, and oxygenation were significantly impaired after Day 5; BALF proteins, elastase, and total polymorphonuclear leukocytes increased significantly at least 24 h before (Day 4) any abnormalities in chest radiographs, pulmonary function tests, and hemodynamic measurements were detected. We conclude that exposure to 100% oxygen in this model causes marked gas exchange, hemodynamic, biochemical, cytologic, radiographic, and pathologic changes similar to those noted in patients with ARDS. Bronchoalveolar lavage abnormalities precede hemodynamic and gas exchange abnormalities.

Induction of acute pulmonary inflammation. A differential effect of C5 and the 200,000 molecular weight form of trypsin-activated C5 (C5').

A series of studies was performed in which Syrian golden hamsters were injected intratracheally with 25 to 200 micrograms of highly purified human C5 or the 200,000 molecular weight form of trypsin-activated C5 (C5'). Bronchoalveolar lavage (BAL) was performed 4 h after intratracheal injection, the recovered white cells were counted and differentiated, and the BAL fluid was assayed for in vitro neutrophil chemotactic activity. A significant increase in BAL neutrophils and total BAL cell numbers was evident at 4 h after C5' instillation. In contrast, highly purified native C5 induced no evidence of pulmonary inflammation, even at the highest injection doses studied. Kinetic experiments indicated that hamsters receiving an intratracheal injection of 60 micrograms of C5' per animal demonstrated rapid pulmonary neutrophil infiltration that persisted for 120 to 168 h. Control hamsters receiving intratracheal injections of phosphate-buffered saline (PBS) or 60 micrograms of highly purified C5 did not demonstrate significant neutrophil infiltration. Lung pathology studies revealed neutrophilic alveolitis with intraalveolar and intracapillary neutrophil infiltration in the C5'-treated animals. The BAL fluid obtained from C5'-treated, but not from C5-treated or control hamsters, contained chemotactic factors for neutrophils, which appeared to be unrelated to C5. From these studies we conclude that C5', the 200,000 molecular weight form of protease-activated C5, is capable of mediating an acute inflammatory response in the hamster lung in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluid balance and the adult respiratory distress syndrome.

This study examined the effect of fluid balance on survival in ARDS. Of the 213 patients entered into a prospective data collection study, we evaluated 113 patients who met strict criteria for ARDS. Multiple variables were analyzed for as long as 14 days after intubation including cardiac output, pulmonary capillary wedge pressure, mean blood pressure, intake minus output (I-O), cumulative intake minus output (cum I-O), and change in weight (delta wt). We found significant differences in cum I-O and delta wt between survivors and nonsurvivors on almost every day. Survivors lost weight and had a significantly lower cum I-O compared with nonsurvivors. Logistic regression was used to determine if delta wt and cum I-O could predict survival. Patients who lost 3 kg or more weight had a much higher survival than did those who gained 3 kg or more weight (67 and 0%, respectively, on Day 14). Similar results were obtained using comparably low and high values for cum I-O. The logistic regression equations demonstrated that weight loss and low cumulative I-O correlated with improved survival. Although cause and effect relationships are difficult to determine from these types of analyses, they can be used to formulate prospective studies and predict survival in patients.

Bacterial infection and acute lung injury in hamsters.

Bacterial pneumonia is a common complication of lung injury that can be an important determinant of outcome. We studied experimental lung injury produced in hamsters by injecting 20 mg/kg paraquat (PQ) intraperitoneally; control animals received saline vehicle. Three days later, Pseudomonas aeruginosa (PAO1), 10(8) organisms in 0.25 ml, or saline, 0.25 ml, was inoculated intratracheally. Lung and systemic antibacterial defenses were studied at death 24 h later. Paraquat alone produced focal interstitial pneumonitis and neutrophilic alveolitis, and resulted in a 12% (3 of 26) mortality. PAO1 alone caused focal pneumonias and no deaths. Animals receiving both agents (PAO1/PQ) had extensive diffuse alveolar damage characterized by alveolar hemorrhage, edema, influx of neutrophils, and vasculitis; 50% (16 of 32) died within 96 h of PQ injection. Mean lung counts of PAO1 at death were 7.6 X 10(4) colony forming units/g in PAO1 and 2.8 X 10(7) in PAO1/PQ animals (p less than 0.05). PAO1 colony counts in liver were increased nearly 100-fold in PAO1/PQ animals (p less than 0.05). Half-time of clearance of P. aeruginosa from the blood was prolonged in PAO1 and in PAO1/PQ animals (p less than 0.05) but not in PQ animals. Phagocytosis of Staphylococcus aureus by leukocytes lavaged from the lung was not impaired in any group compared with that in control animals, but intracellular killing was impaired in PAO1 and PAO1/PQ but not in PQ animals. Paraquat injury impairs lung antibacterial defenses by uncertain mechanisms. Superinfection of PQ-injured lungs by PAO1 appears responsible for defects in intrapulmonary and systemic antibacterial defenses.

Incidence, site, and outcome of infections in patients with the adult respiratory distress syndrome.

Bacterial infection in the adult respiratory distress syndrome (ARDS) is associated with the occurrence of multiple organ failures and death. We studied 108 infections in 129 patients with ARDS and evaluated the organisms responsible, the body sites involved, and the outcomes of therapy. Gram-negative bacilli represented 57% of the microbial pathogens and gram-positive cocci 36%. Only 7% of infections were caused by other organisms (fungi, viruses, Pneumocystis, Legionella). Gram-negative organisms were more common in the lung, abdomen, and pleura. Bacteremia was more common in abdominal infections (11 of 17, 67%) than in infections at other sites (18 of 65, 28%), (p less than 0.01); ;9 patients were bacteremic from clinically undetected sites. Ten of 17 (59%) patients with abdominal infections survived compared with 7 of 56 (13%) patients with lung infections (p less than 0.001). A retrospective review of in vitro organism susceptibility and the antibiotics administered revealed that the patients who received adequate antibiotic therapy did not have a higher survival rate (20 of 69, 29%) than those who received inadequate antibiotic therapy (3 of 13, 23%). These data suggest that further investigation of infections in patients with ARDS is required and that emphasis should be placed on pathogenesis, prevention, and host responses.

Recovery from paraquat pneumonitis.

New Zealand white rabbits were evaluated for recovery from paraquat induced pneumonitis six weeks after the last exposure. The animals were exposed to a respirable aerosol of 100 ml distilled water or 250 mg paraquat in 100 ml distilled water. Blood gases, breathing frequency, and body weights were recorded before and at regular intervals after exposure. Groups included control and two paraquat exposures (separated by a five day interval). Morphometric and pathological measurements were made at death either three days or 42 days after the second exposure. The animals killed three days after the second exposure showed hypoxia, decreased breathing frequency, decreased body weight, increased A-aO2 gradient, decreased per cent macrophages in bronchoalveolar lavage fluid, increased per cent neutrophils in bronchoalveolar lavage fluid, increased lung weight, and reduced lung volume compared with animals allowed to recover. None of these measures differed between control animals and animals allowed to recover, except that animals exposed to paraquat had significantly increased lung volume and lung weights. Pathological changes noted three days after two exposures were no longer found six weeks after exposure. It is concluded that rabbits exposed to paraquat aerosol develop a severe pneumonitis that resolves if exposure is stopped and recovery time is allowed; physiological abnormalities remain, however.

Steroid pretreatment does not prevent paraquat pneumonitis in rabbits.

Rabbits exposed to paraquat develop interstitial pneumonitis. A sublethal dose of paraquat (PQ) solution (250 mg/100 ml) was aerosolized by ultrasonic nebulization for one hour to rabbits in a closed vented chamber on two occasions with a five-day interval between exposures. Groups studied included saline-exposed (N = 4); saline-exposed, methylprednisolone (MP) treated (1 mg/kg daily IM starting one day prior to the first exposure and then throughout the exposure period until sacrifice at day 8) (N = 4); PQ-exposed (N = 6); and PQ-exposed, MP treated (N = 6). Controls and MP controls gained weight and showed no abnormalities of respiratory rate. PQ and PQ-MP animals lost weight (average -0.35 kg) and had decreased breathing frequency (average decrease, 80-90 BPM). Blood gases showed minimal changes in all groups, although some individuals had hypoxemia and an increased alveolar-arterial oxygen pressure quotient [P (A-a) O2]. Bronchoalveolar lavage at sacrifice showed a marked increase in the percent of neutrophils in PQ and PQ-MP animals that correlated with pathology scores (R = 0.83). The P(A-a)O2 correlated with both the percent of neutrophils in lavage and the pathology score. Total cells recovered from a 100 ml lavage were comparable in all groups (approximately 3 X 10(7) cells). Steroid did not prevent the development of pathologic change.

Lipid metabolism in rabbits exposed to paraquat aerosol.

In order to examine the effects of paraquat on pulmonary lipid metabolism rabbits were exposed to double distilled water by aerosol, or 250 mg paraquat in double distilled water. One hour prior to sacrifice, a group of rabbits were injected with [2-14C]-acetate. The levels of phospholipids, fatty acids, cholesterol, and triglycerides were determined as were their 14C-contents in the lung, bronchoalveolar lavage fluid, serum, and liver. The serum of paraquat-exposed animals contained significantly increased levels of phospholipids, cholesterol, and triglycerides. Liver, lung, and bronchoalveolar lavage contained less than or equal to control levels of phospholipids, cholesterol, and triglycerides. Percent of palmitate in the hepatic fatty acid profile was slightly increased in liver but not in lung. The source of the increased lipids in the serum is unknown.

Intravenous aminophylline in the treatment of acute bronchospastic exacerbations of chronic obstructive pulmonary disease.

Often chronic obstructive pulmonary disease (COPD) patients treated for acute exacerbations receive intravenous (IV) aminophylline in addition to inhaled bronchodilators that may raise serum levels of theophylline into the toxic range. A double-blind, randomized study of 52 men with COPD who came to the emergency department for treatment of exacerbations was initiated to establish the efficacy and safety of this common practice. After history and physical examination, patients were treated with 28% oxygen by Venturi mask and 0.3 cc metaproterenol sulfate in 2.5 cc saline by nebulizer; an IV line was started and patients received either aminophylline or D5W. Measurements included baseline and two-hour serum theophylline levels, pulmonary function tests, and symptom questionnaires. Mean values from the entire group showed decreases in respiratory rate, cardiac rate, and pulsus paradoxus, and increases in forced expiratory volume in one second (FEV1) and vital capacity (VC) over a two-hour treatment period (P less than .01). Despite the increase in serum theophylline in the treatment group, the demographic, clinical, pulmonary function, and outcome data were found to have no statistically significant differences when compared to control patients. The data were then analyzed according to serum theophylline levels. Theophylline level greater than 20 micrograms/mL occurred in 15 patients with no untoward effects; premature ventricular contractions (PVCs) were no more frequent in this group than in those with lower serum theophylline levels. A theophylline level greater than 10 micrograms/mL after two hours of treatment resulted in the following differences, which were not statistically significant: mean FEV1 response less than or equal to 10 micrograms/mL vs greater than 10 micrograms/mL, 20% vs 28%; mean VC change, 17% vs 30%; or mean emergency department returns in one week, 0.1 vs 0.26. In our experience, oxygen and inhaled metaproterenol are effective treatment for exacerbations of COPD.

Clinical comparison of albuterol, isoetharine, and metaproterenol given by aerosol inhalation.

The clinical effectiveness of albuterol, isoetharine, and metaproterenol administered by aerosol inhalation at manufacturer-recommended doses was compared. A double-blind, placebo-controlled, crossover comparison of albuterol 280 micrograms, isoetharine 680 micrograms, and metaproterenol 1300 micrograms was conducted in 10 adult men with reversible, chronic pulmonary obstruction. FEV1 (forced expiratory volume at one second), FEF25-75 (forced expiratory flow rate from 25 to 75% of vital capacity), and FVC (forced vital capacity) were determined periodically for six hours after drug administration. Bronchodilator effects, adverse effects, and cost of treatments were compared. Theophylline therapy was unaltered during the study, and serum theophylline concentration was determined periodically to control for its effect on pulmonary function. Serum theophylline concentration was not used as a covariate since it resulted in minimal change in the pulmonary-function measures. The mean maximum percent change from baseline for FEV1 for each drug was superior to placebo; there were no differences among drugs. Comparing area under the curve of mean percent change in FEV1 versus time, albuterol and metaproterenol produced changes that were greater than placebo but not different from each other or isoetharine. For FEF25-75 and FVC, albuterol and metaproterenol, respectively, were superior. No pattern of adverse effects was identifiable among the four treatments. The average wholesale cost of albuterol products was approximately 1.7 times the cost of metaproterenol products. Under the conditions of this study, metaproterenol was superior to isoetharine and therapeutically equivalent to and less expensive than albuterol.