Acute effects of a single dose of porcine surfactant on patients with the adult respiratory distress syndrome

Differential impact of ultrasonically nebulized versus tracheal-instilled surfactant on ventilation-perfusion (VA/Q) mismatch in a model of acute lung injury

In a model of acute lung injury, established by saline lavage of isolated perfused rabbit lungs, the effect of ultrasonic surfactant nebulization on gas exchange was compared with that of tracheal instillation, assessed by the multiple inert gas elimination technique (MIGET). Ultrasonic aerosolization provided particles with a mass median aerodynamic diameter of 4.5 microm (geometric SD, 2.3), the pulmonary deposition of which was monitored on-line by a laserphotometric technique. Under baseline conditions, a narrow unimodal distribution of ventilation and perfusion with shunt-flow ranging below 2% and absence of perfusion of low V A/Q (0.01 < V A/Q < 0.1) areas was noted throughout. This physiological V A/Q matching was not affected by lung deposition of 8.6 mg surfactant/kg body weight (bw), forwarded by 1 h ultrasonic nebulization. In contrast, tracheal bolus injection of 80 mg/ kg bw surfactant in control lungs provoked the appearance of low V A/Q areas (maximum approximately 13% of perfusion) and shunt flow (4 to 6%), in addition to marked ventilation-perfusion mismatch (broadening of perfusion and ventilation distribution) in the midrange V A/Q regions. The saline lavage procedure caused progressive development of shunt flow ( approximately 22%) and perfusion of low V A/Q areas ( approximately 7%), associated with severe V A/Q mismatch. "Rescue" tracheal instillation of 80 mg/kg bw surfactant in lavaged lungs reduced the shunt-flow to approximately 4%, but increased the perfusion of low V A/Q areas to 10 to 14%; V A/Q mismatch in the midrange V A/Q regions was not improved. Ultrasonic deposition of 8.8 mg surfactant/kg bw in the injured lungs reduced the shunt flow to approximately 7% and the perfusion of low V A/Q areas to < 2%, coincident with improvement of V A/Q matching in the midrange V A/Q areas. We conclude that low doses of ultrasonically delivered natural surfactant are similarly effective as "conventional" doses of tracheal-instilled surfactant in reducing shunt flow in an acute lung injury model, but exert more advantageous effects on ventilation perfusion matching.

Bronchopulmonary segmental lavage with Surfaxin (KL(4)-surfactant) for acute respiratory distress syndrome

We performed a trial to assess the safety and tolerability of sequential bronchopulmonary segmental lavage with a dilute synthetic surfactant (Surfaxin) in 12 adults with ARDS. Patients received one of three dosing regimens in which aliquots of Surfaxin were administered via a wedged bronchoscope to each of the 19 bronchopulmonary segments. Suctioning was performed 10-30 s after instillation of individual aliquots. Group 1 patients (n = 3) received one 30-ml aliquot of a 2.5-mg/ml concentration of Surfaxin in each segment, followed by a second 30-ml aliquot with a 10-mg/ml concentration. Group 2 patients (n = 4) received two 30-ml aliquots of the 2.5-mg/ml concentration followed by a third lavage with the 10-mg/ml concentration. Group 3 patients (n = 5) received therapy identical to that received by patients in Group 2 and were eligible for repeat dosing 6 to 24 h later. All patients tolerated the procedure. There were no serious adverse experiences ascribed to either the procedure or the surfactant. In the 96 h after treatment initiation, FI(O(2)) decreased from 0.80 to 0.52 and PEEP decreased from 10.3 to 7.6 cm H(2)O. Bronchoscopic "cleansing" of the lungs with dilute Surfaxin may offer a safe and feasible approach to improving outcomes in patients with ARDS. Wiswell TE, Smith RM, Katz LB, Mastroianni L, Wong DY, Willms D, Heard S, Wilson M, Hite RD, Anzueto A, Revak SD, Cochrane CG. Bronchopulmonary segmental lavage with Surfaxin (KL(4)-surfactant) for acute respiratory distress syndrome.

Effect of enteral feeding with eicosapentaenoic acid, gamma-linolenic acid, and antioxidants in patients with acute respiratory distress syndrome. Enteral Nutrition in ARDS Study Group

OBJECTIVES

Recent studies in animal models of sepsis-induced acute respiratory distress syndrome (ARDS) have shown that a low-carbohydrate, high-fat diet combining the anti-inflammatory and vasodilatory properties of eicosapentaenoic acid (EPA; fish oil), gamma-linolenic acid (GLA; borage oil) (EPA+GLA), and antioxidants improves lung microvascular permeability, oxygenation, and cardiopulmonary function and reduces proinflammatory eicosanoid synthesis and lung inflammation. These findings suggest that enteral nutrition with EPA+GLA and antioxidants may reduce pulmonary inflammation and may improve oxygenation and clinical outcomes in patients with ARDS.

DESIGN

Prospective, multicentered, double-blind, randomized controlled trial.

SETTING

Intensive care units of five academic and teaching hospitals in the United States.

PATIENTS

We enrolled 146 patients with ARDS (as defined by the American-European Consensus Conference) caused by sepsis/pneumonia, trauma, or aspiration injury in the study.

INTERVENTIONS

Patients meeting entry criteria were randomized and continuously tube-fed either EPA+GLA or an isonitrogenous, isocaloric standard diet at a minimum caloric delivery of 75% of basal energy expenditure x 1.3 for at least 4-7 days.

MEASUREMENTS AND MAIN RESULTS

Arterial blood gases were measured, and ventilator settings were recorded at baseline and study days 4 and 7 to enable calculation of PaO2/FIO2, a measure of gas exchange. Pulmonary neutrophil recruitment was assessed by measuring the number of neutrophils and the total cell count in bronchoalveolar lavage fluid at the same time points. Clinical outcomes were recorded. Baseline characteristics of 98 evaluable patients revealed that key demographic, physiologic, and ventilatory variables were similar at entry between both groups. Multiple bronchoalveolar lavages revealed significant decreases (approximately 2.5-fold) in the number of total cells and neutrophils per mL of recovered lavage fluid during the study with EPA+GLA compared with patients fed the control diet. Significant improvements in oxygenation (PaO2/FIO2) from baseline to study days 4 and 7 with lower ventilation variables (FIO2, positive end-expiratory pressure, and minute ventilation) occurred in patients fed EPA+GLA compared with controls. Patients fed EPA+GLA required significantly fewer days of ventilatory support (11 vs. 16.3 days; p = .011), and had a decreased length of stay in the intensive care unit (12.8 vs. 17.5 days; p = .016) compared with controls. Only four of 51 (8%) patients fed EPA+GLA vs. 13 of 47 (28%) control patients developed a new organ failure during the study (p = .015).

CONCLUSIONS

The beneficial effects of the EPA+GLA diet on pulmonary neutrophil recruitment, gas exchange, requirement for mechanical ventilation, length of intensive care unit stay, and the reduction of new organ failures suggest that this enteral nutrition formula would be a useful adjuvant therapy in the clinical management of patients with or at risk of developing ARDS.

Dextran restores albumin-inhibited surface activity of pulmonary surfactant extract

We examined the effect of dextran (molecular weight 71,000) in counteracting the surfactant inhibitory action of plasma albumin. The surface adsorption time of 0.5 mg/ml modified natural surfactant (MNS; porcine lung extract consisting of phospholipids and hydrophobic surfactant proteins) with 7.5 mg/ml albumin decreased from 681 to 143 s by addition of dextran at a concentration of 10 mg/ml (P < 0.01). The minimum surface tension of 2.0 mg/ml MNS with 30 mg/ml albumin decreased from over 21 mN/m to below 3 mN/m when dextran was added at a concentration of 10 mg/ml (P < 0.01). Surfactant-deficient newborn rabbits given 10 ml/kg of a liquid containing 2.0 mg/ml MNS with 30 mg/ml albumin had a mean tidal volume </=5 ml/kg after 5 min of mechanical ventilation, but, in those animals given the liquid containing 10 mg/ml dextran also, the volume was >13 ml/kg (P < 0.05). Although the underlying mechanism remains to be elucidated, we conclude that dextran restores the albumin-inhibited surface activity of MNS.

Dosing and delivery of a recombinant surfactant in lung-injured adult sheep

The purpose of this study was to evaluate a surfactant based on a recombinant surfactant protein-C (rSP-C) at three different doses (25, 100, and 200 mg lipid/kg) in the saline lavage adult sheep model of acute lung injury. All three doses resulted in significant improvements in gas exchange, although the 100 and 200 mg/kg doses were superior to the 25 mg/kg dose. There were no significant differences in effect of the 100 and 200 mg/kg doses. In addition, the physiologic efficacy and lobar surfactant distribution patterns were similar when two different surfactant delivery methods were compared. This comparison involved administering the surfactant directly into each lobe under bronchoscopic guidance, versus instilling the surfactant through an endotracheal tube into the lungs. However, the former technique took significantly longer to perform (24.5 +/- 3.3 min versus 11.6 +/- 2.5 min, p < 0.05) and required a skilled bronchoscopist. In conclusion, rSP-C surfactant was effective in improving gas exchange in this model of lung injury, although higher doses were required for optimal responses. The bronchoscopic administration technique produced results similar to those of the tracheal instillation method, but had some disadvantages that may limit the widespread clinical use of this technique in patients with lung injury.

Instillation of calf lung surfactant extract (calfactant) is beneficial in pediatric acute hypoxemic respiratory failure. Members of the Mid-Atlantic Pediatric Critical Care Network

OBJECTIVE

Prospective study of the efficacy of calf lung surfactant extract in pediatric respiratory failure.

DESIGN

Multi-institutional, prospective, randomized, controlled, unblinded trial.

SETTING

Eight pediatric intensive care units (ICU) of tertiary medical centers.

PATIENTS

Forty-two children with acute hypoxemic respiratory failure characterized by diffuse, bilateral pulmonary infiltrates, need for ventilatory support, and an oxygenation index of >7.

INTERVENTION

Instillation of intratracheal surfactant (80 mL/m2).

MEASUREMENTS AND MAIN RESULTS

Ventilator parameters, arterial blood gases, and derived oxygenation and ventilation indices were recorded before and at intervals after surfactant administration. Complications and outcome measures, including mortality, duration of mechanical ventilation, and length of pediatric ICU and hospital stay, were also examined. Patients who received surfactant demonstrated rapid improvement in oxygenation and, on average, were extubated 4.2 days (32%) sooner and spent 5 fewer days (30%) in pediatric intensive care than control patients. There was no difference in mortality or overall hospital stay. Surfactant administration was associated with no serious adverse effects.

CONCLUSIONS

Administration of calf lung surfactant extract, calfactant, appears to be safe and is associated with rapid improvement in oxygenation, earlier extubation, and decreased requirement for intensive care in children with acute hypoxemic respiratory failure. Further study is needed, however, before widespread use in pediatric respiratory failure can be recommended.

Acute Respiratory Distress Syndrome: Potential Pharmacologic Interventions

The mortality of the acute respiratory distress syndrome (ARDS) remains high despite advances in supportive care of ARDS and in the understanding of the pathogenesis. Numerous inflammatory mediators including reactive oxygen species, arachidonic acid metabolites, and growth factors, are present in the circulation of patients with or at risk for developing this syndrome and play a key pathophysiologic role in the development of lung injury. Pharmacologic therapy is being evaluated to: 1) support the failing lung by improving gas exchange; 2) interrupt the mediator-induced mechanisms of inflammation and injury. Although none of these experimental therapies has yet been proven to improve survival in well conducted prospective, randomized, double-blind, controlled clinical trials, many have demonstrated improvement in physiologic function. These results have helped lay the groundwork for future advances in this field.

Principles of surfactant replacement

Surfactant therapy is an established part of routine clinical management of babies with respiratory distress syndrome. An initial dose of about 100 mg/kg is usually needed to compensate for the well documented deficiency of alveolar surfactant in these babies, and repeated treatment is required in many cases. Recent experimental and clinical data indicate that large doses of exogenous surfactant may be beneficial also in conditions characterized by inactivation of surfactant, caused by, for example, aspiration of meconium, infection, or disturbed alveolar permeability with leakage of plasma proteins into the airspaces. The acute response to surfactant therapy depends on the quality of the exogenous material (modified natural surfactants are generally more effective than protein-free synthetic surfactants), timing of treatment in relation to the clinical course (treatment at an early stage of the disease is better than late treatment, and may reduce the subsequent need for mechanical ventilation), and mode of delivery (rapid instillation via a tracheal tube leads to more uniform distribution and is more effective than slow airway infusion). Treatment with aerosolized surfactant improves lung function in animal models of surfactant deficiency or depletion, but is usually associated with large losses of the nebulized material in the delivery system. Furthermore, data from experiments on immature newborn lambs indicate that treatment response may depend on the mode of resuscitation at birth, and that manual ventilation with just a few large breaths may compromise the effect of subsequent surfactant therapy. The widespread clinical use of surfactant has reduced neonatal mortality and lowered costs for intensive care in developed countries. The hydrophobic surfactant proteins SP-B and SP-C are probably essential for optimal biophysical and physiological activity of exogenous surfactants isolated from mammalian lungs, and the dose-effectiveness (in part reflecting resistance to inactivation) can be further improved by enrichment with SP-A. The development of new artificial surfactant substitutes, based on synthetic analogues of the native surfactant proteins, is an important challenge for future research.

[Recent developments in the treatment of pediatric acute respiratory distress syndrome]

Acute respiratory distress syndrome (ARDS) is a severe condition with a high mortality rate, despite conventional treatment using mechanical ventilation. Better understanding of the pathophysiology and awareness of important iatrogenic lung injury secondary to mechanical ventilation has led to new therapeutic principles. Mechanical ventilation strategy during ARDS is characterized by positive end-expiratory pressure, increase in the inspiratory time, high inspiratory oxygen concentration and, more recently, use of permissive hypercapnia. High frequency ventilation allows optimal lung recruitment under small tidal volume. The effectiveness of extracorporeal oxygenation techniques is demonstrated, but because of their cost and morbidity these therapies are rational only in patients who seem likely to die. Partial liquid ventilation and inhaled nitric oxide have great potential but require further studies. Intratracheal exogenous surfactant might be beneficial but controlled trials are needed to confirm the usefulness of this expensive therapy. Finally, a number of adjuncts to mechanical ventilation are currently available to minimize iatrogenic lung injury and improve the outcome. The role of these new treatments must be defined with randomized and controlled clinical trials using homogenous inclusion criteria.

Pharmacologic adjuncts to mechanical ventilation in acute respiratory distress syndrome

This article reviews pharmacologic approaches to treating acute respiratory distress syndrome (ARDS). The authors discuss the therapeutic effects of ketoconazole, antioxidants, corticosteroids, surfactant, ketanserin, pentoxifylline, bronchodilators, and almitrine in ARDS. Current animal data and proposed mechanics which may foster future pharmacologic therapies are also examined.

Effects of surfactant distribution and ventilation strategies on efficacy of exogenous surfactant

The effects of both surfactant distribution patterns and ventilation strategies utilized after surfactant administration were assessed in lung-injured adult rabbits. Animals received 50 mg/kg surfactant via intratracheal instillation in volumes of either 4 or 2 ml/kg. A subset of animals from each treatment group was euthanized for evaluation of the exogenous surfactant distribution. The remaining animals were randomized into one of three ventilatory groups: group 1 [tidal volume (VT) of 10 ml/kg with 5 cmH2O positive end-expiratory pressure (PEEP)]; group 2 (VT of 5 ml/kg with 5 cmH2O PEEP); or group 3 (VT of 5 ml/kg with 9 cmH2O PEEP). Animals were ventilated and monitored for 3 h. Distribution of the surfactant was more uniform when it was delivered in the 4 ml/kg volume. When the distribution of surfactant was less uniform, arterial PO2 values were greater in groups 2 and 3 compared with group 1. Oxygenation differences among the different ventilation strategies were less marked in animals with the more uniform distribution pattern of surfactant (4 ml/kg). In both surfactant treatment groups, a high mortality was observed with the ventilation strategy used for group 3. We conclude that the distribution of exogenous surfactant affects the response to different ventilatory strategies in this model of acute lung injury.

Lavage administration of dilute surfactants after acute lung injury in neonatal piglets

Exogenous surfactant therapy is not standard in the acute respiratory distress syndrome (ARDS) because of a lack of proven benefit. Nonuniform surfactant distribution after either bolus or aerosol administration may be an important factor limiting response. In a previous study of acute lung injury, we demonstrated that lavage administration of Exosurf (13.5 mg phospholipid/ml) was both effective and distributed uniformly in the lungs. Since the endogenous surfactant pool is much smaller than the typical dose of exogenous surfactant administered, we hypothesized that dilute surfactant preparations (4-4.5 mg phospholipid/ml) administered by lung lavage would be equally effective in reversing pulmonary dysfunction in a piglet model of acute lung injury. We compared three dilute surfactants: Infasurf (n = 5), KL4-Surfactant (n = 6), and Exosurf (n = 5) with controls (n = 6) and undiluted Exosurf (13. 5 mg phospholipid/ml; n = 6). All dilute surfactant preparations were effective in improving oxygenation and other parameters of pulmonary function. Surfactant administered by lavage resulted in uniform lung distribution. We conclude that dilute surfactants administered by lung lavage are effective in reversing pulmonary dysfunction after acute lung injury. We speculate that doses in the range of 20-40 mg phospholipid/kg may be adequate to improve lung function in ARDS when exogenously administered surfactant is uniformly distributed in the lung.

A theoretical study of surfactant and liquid delivery into the lung

A computational study is presented for the transport of liquids and insoluble surfactant through the lung airways, delivered from a source at the distal end of the trachea. Four distinct transport regimes are considered: 1) the instilled bolus may create a liquid plug that occludes the large airways but is forced peripherally during mechanical ventilation; 2) the bolus creates a deposited film on the airway walls, either from the liquid plug transport or from direct coating, that drains under the influence of gravity through the first few airway generations; 3) in smaller airways, surfactant species form a surface layer that spreads due to surface-tension gradients, i.e., Marangoni flows; and 4) the surfactant finally reaches the alveolar compartment where it is cleared according to first-order kinetics. The time required for a quasi-steady-state transport process to evolve and for the subsequent delivery of the dose is predicted. Following fairly rapid transients, on the order of seconds, steady-state transport develops and is governed by the interaction of Marangoni flow and alveolar kinetics. Total delivery time is approximately 24 h for a typical first dose. Numerical solutions show that both transit and delivery times are strongly influenced by the strength of the preexisting surfactant and the geometric properties of the airway network. Delivery times for follow-up doses can increase significantly as the level of preexisting surfactant rises.

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

The acute respiratory distress syndrome (ARDS) continues as a contributor to the morbidity and mortality of patients in intensive care units throughout the world, imparting tremendous human and financial costs. During the last 10 years there has been a decline in ARDS mortality without a clear explanation. The American-European Consensus Committee on ARDS was formed to re-evaluate the standards for the ICU care of patients with acute lung injury (ALI), with regard to ventilatory strategies, the more promising pharmacologic agents, and the definition and quantification of pathologic features of ALI that require resolution. It was felt that the definition of strategies for the clinical design and coordination of studies between centers and continents was becoming increasingly important to facilitate the study of various new therapies for ARDS.

Pharmacologic strategies in acute respiratory distress syndrome

Treatment of the acute respiratory distress syndrome includes both supportive measures and correction of the underlying cause. Various pharmacological interventions have been proposed to limit the severity of lung injury and enhance the healing process, including exogenous surfactant, inhaled vasodilators (mainly nitric oxide), corticosteroids, prostaglandin E1, antioxidants (N-acetylcysteine), ketoconazole and other substances. Some of these interventions are administered via the airways, for example inhaled nitric oxide or liquid ventilation with perfluorocarbons. Some have beneficial effects on surrogate end-points such as pulmonary gas exchange. However, in large prospective trials none of these pharmacological approaches have resulted in significantly improved survival in acute respiratory distress syndrome patients.

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

The acute respiratory distress syndrome (ARDS) continues as a contributor to the morbidity and mortality of patients in intensive care units throughout the world, imparting tremendous human and financial costs. During the last ten years there has been a decline in ARDS mortality without a clear explanation. The American-European Consensus Committee on ARDS was formed to re-evaluate the standards for the ICU care of patients with acute lung injury (ALI), with regard to ventilatory strategies, the more promising pharmacologic agents, and the definition and quantification of pathological features of ALI that require resolution. It was felt that the definition of strategies for the clinical design and coordination of studies between centers and continents was becoming increasingly important to facilitate the study of various new therapies for ARDS.

Nebulisation of surfactants in an animal model of neonatal respiratory distress

AIMS

To evaluate pulmonary deposition and gas exchange following nebulisation of two surfactants by either a jet or an ultrasonic nebuliser.

METHOD

After bronchoalveolar lavage (BAL), 19 rabbits were ventilated in four groups. Group A1 (n = 5) and A2 (n = 6) received Technetium-99m labelled Exosurf, and groups B1 (n = 4) and B2 (n = 4) received radiolabelled Survanta. Groups A1 and B1 received jet nebuliser therapy, whereas groups A2 and B2 received ultrasonic nebuliser. Pulmonary deposition, distribution, and blood gases were determined.

RESULTS

Pulmonary deposition as per cent of initial dose and mg lipid) was 0.28(0.10)% or 0.59(0.21) mg in group A1, 1.05(0.23)% or 2.21(0.48) mg in group A2, 0.08(0.02)% or 0.30(0.08) mg in group B1, and 0.09(0.02)% or 0.34(0.08) mg in group B2. Deposition in group A2 was greater than in other groups (p = 0.001). Group A2 showed a small improvement in blood gases.

CONCLUSIONS

Even the highest deposition--ultrasonic nebuliser with Exosurf--achieved limited clinical effect. The aerosol route is currently not effective for surfactant treatment.

Exogenous surfactant therapy in a patient with adult respiratory distress syndrome after near drowning

A 24-year-old woman developed adult respiratory distress syndrome (ARDS) after near-drowning due to attempted suicide. Conventional mechanical ventilation together with prone positioning and inhaled nitric oxide could not provide sufficient oxygenation. Surface tension data (gamma min = 27 dyn/cm, stability index = 0.341) from a lavage sample supported the hypothesis that the surfactant function of this patient was drastically reduced due to a washout effect by aspiration of fresh water. Porcine surfactant (Curosurf, 50 mg/kg for each lung) was instilled via fibreoptic bronchoscope. The partial arterial carbon dioxide pressure (paCO2) and fraction of inspired oxygen (FiO2) ratio as well as shunt fraction (Qs/Qt) improved impressively. When respiratory situation deteriorated again, surfactant application was repeated. Altogether, six bolus instillations of surfactant (total dose 300 mg/kg = 18,000 mg) were administered until the respiratory situation had stabilized and oxygenation could be maintained by conventional mechanical ventilation. The radiological findings did not show substantial amelioration. The patient developed septic shock and died 12 days after admission. Surfactant application apparently led to a significant improvement of the respiratory function. However, the outcome could not be influenced positively. The high cost of surfactant therapy prevents the more widespread early administration in patients at risk.

Exosurf enhances adenovirus-mediated gene transfer to alveolar type II cells

We assessed the role of surfactant replacement mixtures in the enhancement of adenovirus-mediated gene transfer to pulmonary epithelial cells both in vitro and in vivo. A549 cells, a pulmonary epithelium-derived adenocarcinoma cell line, were incubated with either media alone or media containing 10 microg phospholipid/ml Exosurf or Infasurf for 50 min followed by addition of a replication-deficient adenovirus (E1-deleted) expressing the luciferase reporter gene [AdCMV-Luc; 10 plaque-forming units (PFU)/cell] for 4 h. Pretreatment with Exosurf, but not Infasurf, at 37 degrees C, but not at 4 degrees C, enhanced luciferase activity in A549 cells 24 h later by 156% (P < 0.01). Intratracheal instillation of AdCMV-Luc (2 x 10(9) PFU) into rats resulted in luciferase expression mainly in alveolar macrophages and to a smaller extent in alveolar type II (ATII) cells 24 h later. However, when the AdCMV-Luc instillation was preceded by Exosurf (250 microl; 25 mg/ml), a 10-fold increase in ATII cell luciferase activity was noted. Preincubation of cultured ATII cells with Exosurf also enhanced their transfection by AdCMV-Luc by 515% (P < 0.001). The results of these studies provide a new strategy for targeting ATII cells for gene delivery.

Surfactant dysfunction develops in BALB/c mice infected with respiratory syncytial virus

Recent reports suggest an important role for pulmonary surfactant in maintaining the patency of narrow conducting airways. The hypothesis that surfactant dysfunction is an important factor in respiratory syncytial virus (RSV) infection was tested in a mouse model. Mice, inoculated with either a low or a high dose of RSV, were subjected to bronchoalveolar lavage (BAL), and the fluids were analyzed for percentage of inflammatory cells and concentrations of proteins and phospholipids. After concentration of the surfactant by centrifugation, its function was analyzed with a capillary surfactometer. RSV infection resulted in a dose-dependent disruption of surfactant function (p < 0.0001). BAL fluid supernatants were added to calf lung surfactant extract (CLSE) to examine whether surfactant inhibiting agents were present. Indeed, BAL fluid supernatants of RSV-infected mice disrupted the normal function of calf lung surfactant extract in a dose dependent way (p < 0.0001), indicating the presence of inhibitors. Protein concentrations were increased in BAL fluids of RSV-infected mice versus control mice (p < 0.0001), and were inversely related to surfactant function (r = -0.44, p = 0.0004), suggesting an inhibitory effect of proteins. Protein concentration also correlated with the percentage of inflammatory cells (r = 0.51, p = 0.004). Phospholipid concentrations were not affected by the RSV infection. The results of these studies strongly suggest that a disruption of pulmonary surfactant function, most likely due to inhibition from inflammatory proteins, is important for the pathophysiology of RSV infection.

Fatal pulmonary edema after nitric acid inhalation

We report a case of acute inhalation injury of nitric acid in a 56-year old white male. The patient presented conscious and dyspnoic at the emergency department after cleaning a copper chandelier with nitric acid. He had to be intubated 2 h after admission and mechanically ventilated because of fulminant respiratory insufficiency. As all sources of mechanical ventilation failed, extracorporeal membrane oxygenation had to be established 7 h after admission. With the additional use of surfactant and low dose inhalation therapy with nitric oxide (NO), the patient could be stabilised for 3 days and lung function improved temporarily. Despite all efforts the patient died at the fourth day from refactory respiratory failure. Pathologic examination revealed massive pulmonary edema without signs of inflammation. Thus, nitric acid inhalation induced pulmonary edema appears to be a most severe situation in which even most modern therapeutic interventions fail. As, in respect of recent literature and our case no promising therapy for nitric acid inhalation pulmonary edema is available, our efforts have to be directed towards prevention of nitric acid exposure.

Very low density lipoproteins stimulate surfactant lipid synthesis in vitro

Surfactant synthesis is critically dependent on the availability of fatty acids. One fatty acid source may be circulating triglycerides that are transported in VLDL, and hydrolyzed to free fatty acids by lipoprotein lipase (LPL). To evaluate this hypothesis, we incubated immortalized or primary rat alveolar pre-type II epithelial cells with VLDL. The cells were observed to surface bind, internalize, and degrade VLDL, a process that was induced by exogenous LPL. LPL induction of lipoprotein uptake significantly increased the rates of choline incorporation into phosphatidylcholine (PC) and disaturated PC, and these effects were associated with a three-fold increase in the activity of the rate-regulatory enzyme for PC synthesis, cytidylyltransferase. Compared with native LPL, a fusion protein of glutathione S-transferase with the catalytically inactive carboxy-terminal domain of LPL did not activate CT despite inducing VLDL uptake. A variant of the fusion protein of glutathione S-transferase with the catalytically inactive carboxy-terminal domain of LPL that partially blocked LPL-induced catabolism of VLDL via LDL receptors also partially blocked the induction of surfactant synthesis by VLDL. Taken together, these observations suggest that both the lipolytic actions of LPL and LPL-induced VLDL catabolism via lipoprotein receptors might play an integral role in providing the fatty acid substrates used in surfactant phospholipid synthesis.

Surfactant: current and potential therapeutic application in infants and adults

Exogenous surfactant administration is currently being evaluated for the Acute Respiratory Distress Syndrome (ARDS). Although surfactant supplementation is now a routine therapy for babies born with neonatal RDS, this treatment modality for adults does not appear to result in a predictable improvement in lung function as is noted in neonates. This article will review the basic abnormalities of the surfactant system in patients with ARDS and contrast them with the primary surfactant deficient state of nRDS. Various factors that have been shown to influence an individual's response to exogenous surfactant will the be outlined. Finally, potential treatment approaches for patients with ARDS utilizing exogenous surfactant will be proposed.

[Current aspects of acute respiratory distress syndrome in children]

Acute respiratory distress syndrome (ARDS) is a frequent condition in pediatric intensive care units. The mortality remains high despite advances in conventional mechanical ventilation and aetiological treatment. Several animal studies have documented lung injury during mechanical ventilation with high tidal volume, and clinical investigations have shown that in human ARDS, most ventilation is distributed to the small areas of remaining aerated lung resulting in overdistension of these areas and lung injury ("baby lung" theory). Nevertheless the usefulness of extrapulmonary gas exchange remains much debated. New ventilatory strategies have been developed in order to reduce ventilator-induced lung injury and to improve systemic oxygenation but multicentric randomized clinical trials are needed before these strategies can be validated.

Modified natural porcine surfactant inhibits superoxide anions and proinflammatory mediators released by resting and stimulated human monocytes

Pulmonary surfactant has a potential role in modulating inflammation in normal and injured lungs. In lung injury, monocytes become activated and participate in lung inflammation. We therefore, investigated the proinflammatory functions of stimulated human blood monocytes after an overnight preincubation period with modified natural porcine surfactant (Curosurf) (500-1000 micrograms/mL). Monocytes were stimulated either with phorbol myristate acetate (PMA), bacterial extract OM-85, lipopolysaccharide (LPS), or Ca2+ ionophore A23187. The present study shows that Curosurf significantly inhibits: 1) the production of superoxide anions stimulated with OM-85 (1 mg/mL, 30 min), but not with PMA (100 ng/mL, 30 min); 2) the release of cyclooxygenase metabolites prostaglandin E2 and thromboxane B2 stimulated with OM-85 (1 mg/mL, overnight); 3) the release of lipoxygenase metabolite leukotriene C4 stimulated with A23187 (10 microM, 10 min); 4) the release of the cytokine TNF-alpha stimulated overnight with either OM-85 (1 mg/mL) or LPS (10 micrograms/mL)) in a dose-dependent fashion. In addition, Curosurf decreases the spontaneous adherence of monocytes to plastic culture wells in a dose-dependent fashion. Experiments performed with staurosporine, an inhibitor of protein kinase C (PKC) indicate that, in contrast with PMA, the production of superoxide anions stimulated by OM-85 is not related to PKC activation. Consequently, we propose that the mechanism involved in the suppressive effects of Curosurf is PKC-independent. In summary, the present study provides experimental evidence that favors the anti-inflammatory role of modified natural porcine surfactant (Curosurf) in human monocytes in vitro.

[Value of surfactant in the treatment of acute respiratory distress syndrome in a child]

BACKGROUND

Adult respiratory distress syndrome has a high mortality rate, despite treatment including mechanical ventilation with positive end-expiratory pressure, increase of the inspiratory time and high inspiratory oxygen concentration. Exogenous surfactant, a well established treatment in premature newborns with neonatal respiratory distress syndrome has only been occasionally evaluated in adult respiratory distress syndrome.

CASE REPORT

A 3 year-old child suffered from adult respiratory distress secondary to respiratory syncytial virus infection. Both mechanical ventilation and inhaled nitric oxide failed to improve the respiratory distress. Two doses of intratracheal surfactant application immediately improved pulmonary functions, transiently after the first instillation on day 13 and definitely after the second one, on day 16.

CONCLUSION

Exogenous surfactant appeared to be useful for the survival of our patient but prospective evaluation of this treatment in adult respiratory distress syndrome is needed.

Betamethasone modulation of sphingomyelin hydrolysis up-regulates CTP:cholinephosphate cytidylyltransferase activity in adult rat lung

Glucocorticoids appear to play an integral role in stimulating surfactant synthesis by activating the rate-regulatory enzyme for phosphatidylcholine synthesis, CTP:cholinephosphate cytidylyltransferase (CT). The activity of liver CT, in vitro, has been shown to be inhibited by the sphingomyelin hydrolysis product, sphingosine. In order to investigate the mechanisms by which glucocorticoids alter CT activity, in vivo, we administered betamethasone (1 mg/kg intraperitoneally) sequentially to adult male rats for 5 days. Betamethasone increased CT activity 2-fold relative to control in whole lung. The hormone also increased membrane-bound activity, but did not affect cytosolic enzyme activity. Betamethasone modestly increased CT mRNA as determined by the reverse-transcription PCR and Southern analysis of PCR products, but did not alter the levels of immunoreactive enzyme in lung membranes as demonstrated by Western blotting. The hormone did, however, produce a nearly 3-fold increase in membrane-associated sphingomyelin, and co-ordinately a substantial decrease in the levels of sphingosine in lung membranes. Sphingosine, but not sphinganine, was a competitive, reversible inhibitor of lung CT with respect to the enzyme activator, phosphatidylglycerol. Betamethasone decreased the activities of the sphingomyelin hydrolases: acid sphingomyelinase by 33% and of alkaline ceramidase by 21%. The hormone also inhibited the generation of sphingosine from lysosphingomyelin in lung membranes. There was no significant effect of the hormone on serine palmitoyltransferase activity, the first committed enzyme for sphingolipid biosynthesis. Further, administration of L-cycloserine, an inhibitor of sphingosine formation, was shown to stimulate CT activity by 74% and increase disaturated phosphatidylcholine in alveolar lavage by 52% relative to control. These observations suggest that glucocorticoids up-regulate surfactant synthesis at the level of a key regulatory enzyme by significantly altering the availability of inhibitory metabolites resulting from sphingomyelin hydrolysis.

Transfusion-related acute lung injury treated with surfactant in a neonate

A term, male neonate suddenly developed respiratory distress and severe cyanosis while undergoing exchange transfusion for hyperbilirubinaemia. Transfusion-related acute lung injury was diagnosed. Because of persistent hypoxaemia despite aggressive treatment, two doses of surfactant were administered, resulting in marked improvement.

CONCLUSION

Transfusion-related acute lung injury may occur in neonates, and may be successfully treated by surfactant replacement.

Aerosolized surfactant in adults with sepsis-induced acute respiratory distress syndrome. Exosurf Acute Respiratory Distress Syndrome Sepsis Study Group

BACKGROUND

Patients with acute respiratory distress syndrome (ARDS) have a deficiency of surfactant. Surfactant replacement improves physiologic function in such patients, and preliminary data suggest that it may improve survival.

METHODS

We conducted a prospective, multicenter, double-blind, randomized, placebo-controlled trial involving 725 patients with sepsis-induced ARDS. Patients were stratified according to the risk of death at base line (indicated by their score on the Acute Physiological and Chronic Health Evaluation [APACHE III] index) and randomly assigned to receive either continuously administered synthetic surfactant (13.5 mg of dipalmitoylphosphatidylcholine per milliliter, 364 patients) or placebo (o.45 percent saline; 361 patients) in aerosolized form for up to five days.

RESULTS

The demographic and physiologic characteristics of the two treatment groups were similar at base line. The mean (+/- SD) age was 50 +/- 17 years in the surfactant group and 53 +/- 18 years in the placebo group, and the mean APACHE III scores at randomization were 70.4 +/- 25 and 70.5 +/- 25, respectively. Hemodynamic measures, measures of oxygenation, duration of mechanical ventilation, and length of stay in intensive care unit did not differ significantly in the two groups. Survival at 30 days was 60 percent for both groups. Survival was similar in the groups when analyzed according to APACHE III score, cause of death, time of onset and severity of ARDS, presence or absence of documented sepsis, underlying disease, whether or not there was a do-not-resuscitate order, and medical center. Increased secretions were significantly more frequent in the surfactant group; the rates of other complications were similar in the two groups.

CONCLUSIONS

The continuous administration of aerosolized synthetic surfactant to patients with sepsis-induced ARDS had no significant effect on 30-day survival, length of stay in the intensive care unit, duration of mechanical ventilation, or physiologic function.

Surfactant replacement therapy for adult respiratory distress syndrome in children

Surfactant replacement therapy may have a role in the treatment of ARDS in children. The current studies suggest that rapid instillation of exogenous surfactant is more effective than slow tracheal instillation or aerosolized delivery. Studies suggest that exogenous surfactant given early in the development of ARDS is more effective than therapy provided late in the course of the disease. Natural surfactants appear to be more effective than artificial surfactants due to the presence of SP-B and SP-C, which prevent inhibition of the exogenous surfactant by the protein leakage into the alveolus that is characteristic of ARDS. Exogenous surfactant replacement therapy appears to be safe and well tolerated. A surfactant that can be delivered by aerosol would be useful since this is more easily tolerated by the patients, requires less surfactant, and would be more cost effective when compared with tracheal instillation. Aerosolized surfactant could be given to patients who have not yet required mechanical ventilation, thus potentially preventing the progression of the acute lung injury to respiratory failure. The recent failure of a large multi-center trial of aerosolized Exosurf for the treatment of sepsis-related ARDS72 may have been due to the failure of the delivery system as opposed to the surfactant used in the trial; therefore, further research into aerosol delivery systems is needed. There may be different responses to exogenous surfactant therapy by patients with ARDS of different etiologies, such as aspiration pneumonia, sepsis, or trauma. Well-planned placebo-controlled trials will be required to determine these differences. The data supporting the role of surfactant replacement for the treatment of ARDS in children is growing. However, before widespread use of surfactant is considered, a multi-center, placebo-controlled trial will be required to establish the safety and efficacy of surfactant replacement in such patients.

Acute respiratory distress syndrome: diagnosis and management

This review will attempt to put together the voluminous studies and concepts that have been published during the past 25 years following the description of the acute respiratory distress syndrome (ARDS) regarding diagnosis and management. The initial discussion will focus on how to clinically diagnose ARDS based recommendations. This also gives the current definition of acute lung injury and when to call it ARDS. The radiographic and hemodynamic characteristics are discussed including oxygenation parameters. The management outlines the conventional as well as new therapies intended to improve survival of this devastating disease.

[Natural or artificial surfactants? Arguments in favour of natural surfactants]

The use of exogenous surfactant (ES) is an essential component for prevention and treatment of hyaline membrane disease (HMD). The ES available for clinical use are of two therapeutic classes: natural surfactants prepared from mammalian lung and artificial surfactants. The choice between these two classes of ES is controversial. In this overview, we present the arguments in favour of the preferential use of natural ES. The presence of hydrophobic specific proteins (SP-B and SP-C) provides to natural ES better surface tension properties than artificial ES. The in vitro greater efficacy of natural ES has been confirmed in vivo in experimental models of surfactant deficiency, human pharmacodynamic studies, and comparative clinical trials. Furthermore, the excellent clinical tolerance and harmlessness of natural ES has been firmly established. A meta-analysis of the comparative clinical trials between natural ES and one artificial ES (enrolling as many as 4400 babies treated for HMD) suggests that the use of natural ES compared to this artificial ES significantly reduces the neonatal mortality by 20%. In conclusion, all these arguments are in favor of the preferential use of natural ES for prevention and treatment of HMD.

Surfactant replacement therapy in acute respiratory distress syndrome from viral pneumonia

A modified natural surfactant was administered to a patient with life-threatening adult respiratory distress syndrome caused by viral pneumonia. Subsequently, there was a marked improvement in gas exchange. In order to assess the mechanism for improved oxygenation, computed tomography of the lungs was done. Quantitative analysis of the scans taken before and after surfactant administration indicates that improvement in gas exchange was largely due to the expansion of underinflated and collapsed lung areas. Although this is a single case report, it provides insight into the possible beneficial effect of instilled surfactant in severe respiratory distress from viral pneumonia.

Inhibitory effect of porcine surfactant on the respiratory burst oxidase in human neutrophils. Attenuation of p47phox and p67phox membrane translocation as the mechanism

Surfactant has been shown to inhibit the production of reactive oxygen intermediates by various cells including alveolar macrophages and peripheral blood neutrophils. Superoxide O2-. production by the respiratory burst oxidase in isolated plasma membranes prepared from PMA-treated human neutrophils was significantly attenuated by prior treatment with native porcine surfactant. The effect was concentration dependent with half-maximal inhibition seen at approximately 0.050 mg surfactant phospholipid/ml. Kinetic analyses of the membrane-bound enzyme prepared from neutrophils stimulated by PMA in the presence or absence of surfactant demonstrated that surfactant treatment led to a decrease in the maximal velocity of O2-. production when NADPH was used as substrate, but there was no effect on enzyme substrate affinity. Immunoblotting studies demonstrated that surfactant treatment induced a decrease in the association of two oxidase components, p47phox and p67phox, with the isolated plasma membrane. In contrast, surfactant treatment of the cells did not alter the phosphorylation of p47phox. A mixture of phospholipids (phosphatidylcholine and phosphatidylglycerol in a 7:3 ratio) showed similar inhibition of the PMA-induced O2-. generation. Taken together, these data suggest the mechanism of surfactant-induced inhibition of O2-. production by human neutrophils involves attenuation of translocation of cytosolic components of the respiratory burst oxidase to the plasma membrane. The phospholipid components of surfactant appear to play a significant role in this mechanism.

The effects of multiple small doses of exogenous surfactant on experimental respiratory failure induced by lung lavage in rats

AIM

To test the effect on pulmonary gas exchange and mechanics of multiple small doses of exogenous surfactant as an alternative to bolus delivery in experimental respiratory failure induced by lung lavage.

METHOD

After anesthesia, tracheostomy and constant volume ventilation, respiratory failure was induced by lung lavage in 20 rats. Animals were randomly assigned to an untreated control group or two experimental groups. Equal total doses of modified porcine surfactant (200 mg.kg-1 body weight), were given by tracheal instillation, either as a single bolus or in four (50 mg.kg-1 b.w.) fractional doses at 10-min intervals. Arterial pH and blood gases, and peak inspiratory pressure (PIP) were measured.

RESULTS

After lavage, a rapid decrease in arterial pH and PaO2, and an increase in PaCO2 and PIP were observed in all animals. In both surfactant-treated groups, PaO2 increased after surfactant instillation, and remained significantly higher than controls throughout the experiment. Arterial pH was significantly higher and PaCO2 significantly lower only in the single bolus group. In the multiple dose group, these levels were similar to those of controls.

CONCLUSION

In surfactant-depleted rats with respiratory failure, instillation of four fractional surfactant doses did not result in the same enhancement on gas exchange and PIP, in the following 60 min, as same total dose given by a single bolus.

Prevention and therapy of the adult respiratory distress syndrome

The complex pathophysiology of adult respiratory distress syndrome (ARDS) makes preventive and therapeutic concepts difficult. Ample experimental evidence indicates that ARDS can be prevented by blocking systemic inflammatory agents. Clinically, only heparin, for inhibition of coagulation phenomena, is presently used among this array of approaches. Corticosteroids have not proven to be beneficial in ARDS. Alternative antiinflammatory agents are being proposed and are under current clinical investigation (e.g. indomethacin, acetylcysteine, alpha 1-proteinase inhibitor, antitumor necrosis factor, interleukin 1 receptor antagonist, platelet-activating factor antagonists). Symptomatic therapeutic strategies in early ARDS include selective pulmonary vasodilation (preferably by inhaled vasorelaxant agents) and optimal fluid balance. Transbronchial surfactant application, presently tested in pilot studies, may be available for ARDS patients in the near future and may have acute beneficial effects on gas exchange, pulmonary mechanics, and lung hemodynamics; its impact on survival cannot be predicted at the present time. Strong efforts should be taken to reduce secondary nosocomial pneumonia in ARDS patients and thus avoid the vicious circle of pneumonia, sepsis from lung infection, and perpetuation of multiple organ dysfunction syndrome. Optimal respirator therapy should be directed to ameliorate gas-exchange conditions acutely but at the same time should aim at minimizing potentially aggravating side effects of artificial ventilation (barotrauma, O2 toxicity). Several new techniques of mechanical ventilation and the concept of permissive hypercapnia address these aspects. Approaches with extracorporeal CO2 removal and oxygenation are being used in specialized centers.

Postsurgical complications in older patients. The role of pharmacological intervention

The number of elderly patients undergoing surgery has been rapidly increasing during the last few years. Following surgical interventions, high rates of mortality and morbidity have been reported in the most advanced age groups. Nevertheless, perioperative evaluation and postoperative care are the major determinants of the overall outcome. Postsurgical complications are common in advanced age, since multiple pathology is often present in geriatric patients. Furthermore, the decreased efficiency of homeostatic mechanisms may facilitate the development of multiple organ failure (MOF), even as a consequence of apparently slight alterations in immune, cardiac or respiratory systems. Thus, prompt recognition and treatment of any complication often prevents the development of irreversible conditions. While cardiac and pulmonary complications account for 50% of early postoperative adverse events, infections, thromboembolism, renal failure, stress ulcers and coagulation disorders may occur well after surgical procedures. An important part of postoperative geriatric care is the diagnosis and correction of fluid, electrolyte and acid-base disturbances. These disturbances may manifest as mild, atypical signs, such as slight neuromuscular depression or delirium. Yet, they often constitute life-threatening conditions that should be rapidly and properly corrected. Finally, it should be remembered that, due to the frequent use of multiple drugs, elderly patients are at high risk of developing adverse drug reactions. Thus, the treatment of postoperative complications requires a strong rational effort to disentangle the combined effects of aging, drugs and pathology.

Exposure of the hydrophobic components of porcine lung surfactant to oxidant stress alters surface tension properties

We have tested the hypothesis that oxidation of lung surfactant results in loss of surface tension lowering function. Porcine lung surfactant was exposed to conditions known to cause lipid peroxidation (0.2 mM FeCl2 + 0.1 mM H2O2 or 5 microM CuCl2). Lipid peroxidation was verified by detection of conjugated dienes, thiobarbituric acid reactive substances, fluorescent products, hydroxy alkenals, and loss of unsaturated fatty acids. Exposed samples had significantly diminished surface tension lowering ability in vitro as measured in a bubble surfactometer. Samples exposed to FeCl2 + H2O2 had significantly diminished surface tension lowering ability in vivo as indicated by their reduced ability to improve lung compliance of surfactant-deficient fetal rabbits. Oxidation of phospholipid mixtures with surface tension lowering activity and containing unsaturated acyl groups resulted in partial loss of activity as determined in vitro. These results suggest that the effect of oxidants on lung surfactant function is due, in part, to effects on the phospholipid components and that acute pulmonary inflammation accompanied by oxygen radical production may result in surfactant lipid peroxidation and loss of surface tension lowering function.