Surfactant replacement therapy in late-stage adult respiratory distress syndrome

Short reports

Surfactant replacement therapy in late-stage adult respiratory distress

syndrome

In four adult patients with late-stage acute respiratory distress syndrome (ARDS), a single dose of the artificial surfactant ALEC was given by intrabronchial instillation. There was no sustained clinical improvement, but bronchoalveolar lavage measurements indicated that phosphatidylcholine (PC) at 24 h after treatment had increased up to 4 4 fold and phosphatidylglycerol up to 34 7 fold. However, PC relative to total phospholipid remained below normal, and protein contamination relative to PC remained above normal. Thus, therapeutic formulations and regimens to achieve greater and more sustained supplementation of PC may be required in patients with late-stage ARDS. Lancet

1994; 343: 1009-11

The benefit of surfactant replacement therapy in infant respiratory distress syndrome provoked interest in its potential in acute respiratory distress syndrome (ARD S).1,2 Surfactant replacement therapy can reduce the severity of injury and improve oxygenation in models of ARDS.2 Treatment soon after onset may transiently improve oxygenation in some patients,3-6 but there have been no reports at a late-stage of ARDS. Protein contamination appears to be the major contributory factor to surfactant dysfunction early in ARDS, whereas phospholipid deficiency is more evident later. We describe the effects of surfactant therapy in four patients at a late stage of ARDS and the in-vivo concentrations of surfactant supplementation achieved.

main bronchi via a fibreoptic bronchoscope. The clinical effect of therapy was determined by changes in arterial blood gases, thoracic compliance, and lung function measurements before and 0-5, 1, 2, 4, 8, 24, and 48 h after treatment. Bronchoalveolar lavage (BAL) samples were obtained from the lungs before and at 24 h after treatment. A measured amount of aspirated fluid was sent for microbiological screening and the remainder was centrifuged to sediment the cells, and the supernatant decanted for phospholipid and protein analysis and stored at - 70°C. Total BAL cells were counted in an improved Neaubauer chamber, and differential counts were made by counting at least 300 cells in cytocentrifuge preparations stained with May-Grunwald Giemsa. The results for each cell type were expressed as a percentage of the total BAL cells and as the number per mL of BAL fluid.

Phospholipids were analysed as described.8 Total phospholipid calculated by reference to standards. The results were expressed qualitatively as the proportion of each phospholipid class relative to the total phospholipid in the BAL sample, and quantitatively as the amount per mL in the original BAL sample. Total protein in the BAL supernatants was measured with the Bio-Rad protein assay kit. Albumin, as an indicator of leakage of proteins from plasma, was assayed by nephelometry with rabbit anti-human albumin (Dako). The results were expressed as ug/mL BAL fluid and as contamination ratios of total protein or albumin to PC (the major surfactant phospholipid). Normal ranges for BAL measurements were obtained from BAL samples from healthy non-smoking volunteers.8

was

The hypoxaemia scores (Pa02/Fi02 ratios) of the patients before ALEC therapy were severely impaired at 49, 51, 78 and 47, respectively. There was a transient improvement in arterial oxygenation after therapy in patient 4 (pretreatment Pa02 5 kPa rising to 9 kPa 60 min after therapy), maintained

Trials of artificial surfactant were done with ethical committee approval in a 9-year-old boy and a 16-year-old girl (patients 1 and 2) who developed ARDS after road-traffic accidents in which they had multiple injuries, and in two women aged 22 and 21 years (patients 3 and 4) who developed ARDS at 28 and 35 weeks of pregnancy, respectively. In patient 3, ARDS developed after an appendicectomy followed by an anaphylactic reaction to intravenous cefuroxine. ARDS developed in patient 4 after pre-eclampsia at 35 weeks. Caesarean sections were done in both patients, and live infants delivered. All four patients fulfilled the criteria for diagnosis of severe ARDS: widespread diffuse shadowing on chest radiographs indicative of high-permeability pulmonary oedema; severe hypoxaemia (Pa02 < 75 mm Hg (PaO2 < 10 kPa]atFiO 0-5); pulmonary artery occlusion pressure below 15 mm Hg; and decreased total thoracic compliance (< 13 mL/cm H2O). All were at a late stage of ARDS having remained ventilator-dependent with no sustained improvement in lung function despite mechanical ventilation for 17,16,19, and 16 days, respectively. All had alterations in pulmonary surfactant composition. They were given the artificial lung-expanding

compound (ALEC; 70% synthetic dipalmitoyl phosphatidylcholine [PC] and 30% phosphatidylglycerol [PG] mainly unsaturated, extracted from eggs; Britannia Pharmaceuticals, Redhill, Surrey, UK) as a crystalline suspension in sterile 0-9% saline.’ Each patient received 3-2gALEC in 50 mL saline (average 75 mgkg) instilled in two equal volumes into the right and left 1009

only for 24 h, and without improvement in thoracic compliance or lung function. She continued to deteriorate and died 13 days later. No clinical improvement was seen in the remaining three patients who survived for a further 18, 20 and 10 days, respectively. Before treatment, all four patients had low levels of PG, both quantitatively and qualitatively (table) compared with our normal ranges.8 There was no quantitative deficiency in PC or in total phospholipid, but all patients had a qualitative deficiency in PC caused by an increase in the relative amount of the non-surfactant phospholipid sphingomyelin. 24 h after therapy, BAL concentrations of PC (ug/mL) had increased in three patients 4-4, 2-4, and 13 fold compared with pre-treatment levels, whereas PG (ng/mL) had increased 25-3,20 0,93, and 34 7 fold. The proportion of PC relative to phospholipid remained below the lower limit of normal in all, but PG proportions and levels per mL increased to above the normal range in three. The proportion of contaminating sphingomyelin remained above normal in two patients. BAL albumin was increased before treatment in only one patient (table). The contamination index of albumin relative to PC was increased only in this case; these values decreased after therapy, but did not fall to normal. By contrast, total protein, indicative of protein contamination from a variety of sources, was increased in all four patients before treatment. The contamination index of total protein relative PC was also increased. One or both of these measurements decreased after treatment in patients 1, 2, and 3 but fell to within the normal range only in patient 3, which indicates that the therapeutic phospholipid supplementation was insufficient to counteract the excessive protein contamination of the surfactant system in three patients. All four patients had increases in neutrophil counts compared with controls (table). After therapy, a decrease in neutrophils per mL was seen in patient 3 and in neutrophil percentage count in patient 4. Two patients had reduced counts of macrophages per mL before therapy, which rose to within or above the normal range after treatment (patients 1 and 4). Patient 4, who showed a transient improvement in oxygenation after therapy, had the lowest count of neutrophils before treatment and was the only patient with a notable decrease in the percentage of neutrophils after treatment. She was also the only patient who showed no evidence of residual PC supplementation at 24 h after treatment, even though she had the highest relative supplementation of PG. Our findings suggest that a single dose of instilled therapeutic surfactant is insufficient to achieve maintained clinical benefit in patients with late-stage ARDS. Our patients had a qualitative deficiency in the proportion of PC relative to total phospholipid in their alveolar lining-fluid due to increased contamination by sphingomyelin. BAL protein was also increased but albumin was increased in only one patient, which suggests that the contaminants were derived more from tissue damage than plasma exudation. Protein contamination can impair the functional ability of normal surfactant to lower surface tension, and this impairment can be counteracted to a variable degree by increasing the proportion of the most highly surface active to

components.9 Dipalmitoyl-PC, the major phospholipid component and surface active component of surfactant, is not suitable for therapy in its pure form because additional components are required to accelerate adsorption and spreading of the surface film of phospholipid, and to stabilise the film to 1010

efficacy during repeated cycles of expansion compression.1.2 In normal surfactant, these are provided mainly by apopoteins. Tubular properties myelin, consisting of multi-lamellar aggregates of phospholipids, the hydrophilic apoprotein SpA, and the hydrophobic SpB and SpC, is the most highly surface active fraction of normal surfactant.2 However, therapeutic surfactants are usually depleted of hydrophilic proteins to

maintain functional and

reduce the risk of immunosensitisation. ALEC contains excess unsaturated PG compared with a natural surfactant to reduce the gel-to-liquid transition temperature of PC and aid its liquefaction at room or body temperature. PG deficiency is one of the most striking abnormalities of surfactant composition in ARDS. Before treatment, all our patients were deficient in PG, with excessive protein and sphingomyelin contamination of the surfactant system. 24 h after ALEC therapy, PG concentrations were increased above normal. ALEC contains more PC (23 fold) than PG, but PC supplementation at 24 h was less evident than PG supplementation. Isotopic tracer studies have indicated that after intratracheal administration the approximate half-life (50% clearance) of PC and PG from the air spaces of normal lungs is 4-3 and 30 h, respectively.’ The absolute rate of clearance from the lungs cannot be accurately measured because much surfactant phospholipid is recycled via type II cells. Our observations are consistent with more rapid clearance of PC from the airspaces compared with PG. Thus, patients with late-stage ARDS appear to retain the capacity for PC clearance despite extensive lung damage. However, the fact that some increased PC was detectable in BAL at 24 h in three of our four patients suggests that the normal clearance rate of PC may be reduced. The patient without increased PC in BAL at 24 h was the only one who showed a transient improvement in oxygenation after therapy, suggesting that her capacity for PC recycling from the airspaces may have been less impaired. Despite therapy, the proportions of PC relative to total phospholipid remained below normal at 24 h in all four patients, which suggests that multiple doses may be required to achieve sufficient supplementation for clinical response. Most therapeutic surfactants lack certain components found in normal surfactant, but they may interact with components in vivo to generate a mixture with functional properties influenced by the final composition.10 However, patients with ARDS develop SpA and SpB deficiency as well as phospholipid deficiency.2 Thus, formulations for use in ARDS may need to be improved. The BAL neutrophilia, which indicates persistent inflammation in ARDS, suggests that treatment with anti-inflammatory drugs may also be needed to avoid surfactant damage by oxidants and proteolytic enzymes. We thank the British Lung Foundation and the Clinical Research Committee of the Royal Brompton National Heart and Lung Hospitals for grants that supported this study, Britannia Pharmaceuticals for providing ALEC, and Mrs Joanna Harwood for her help in preparing the

manuscript. References 1 2

3

Jobe A, Ikegami M. State of the art: surfactant for the treatment of respiratory distress syndrome. Am Rev Respir Dis 1987; 136: 1256-75. Lewis JF, Jobe AH. Surfactant and the adult respiratory distress syndrome. Am Rev Respir Dis 1993; 147: 218-33. Richman PS, Spragg RG, Robertson B, Merritt TA, Curstedt T. The adult

respiratory distress syndrome: first trials with surfactant replacement. Eur Respir Dis 1989; 2 (suppl 3): 109-11s.

4 Lachmann B. Animal models and clinical pilot studies of surfactant replacement in adult respiratory distress syndrome. Eur Respir J 1989; 2 (suppl 3):98-103s. 5 Nosaka S, Sakai T, Yonekura M, Yoshikawa K. Surfactant for adults with respiratory failure. Lancet 1990; 336: 947-48. 6 Wiedemann H, Baughman R, de Boisblanc B, et al. A multicenter trial in human sepsis-induced ARDS of an aerosolized synthetic surfactant (Exosurf). Am Rev Respir Dis 1992; 145 (suppl): A184. 7 Morley CJ. The use of artificial surfactant (ALEC) in the prophylaxis of neonatal respiratory distress syndrome. Eur Respir J 1989; 3 (suppl): 81-86s. 8 Hughes DA, Haslam PL. Effect of smoking on the lipid composition of lung lining fluid and relationship between immunostimulatory lipids, inflammatory cells and foamy macrophages in extrinsic allergic alveolitis. Eur Respir J 1990; 3: 1128-39. 9 Seeger W, Grube C, Günther A, Schmidt R. Surfactant inhibition by plasma proteins: differential sensitivity of various surfactant preparations. Eur Respir J 1993; 6: 971-77. 10 Ikegami M, Ueda T, Absolom D, Baxter C, Rider E, Jobe AH. Changes in exogenous surfactant in ventilated preterm lamb lungs. Am Rev Respir Dis 1993; 148: 837-44.

Cell Biology Unit, National Heart and Lung Institute, London SW3 6LY, UK (P L Haslam MRCPath, D A Hughes PhD, C S Baker MSc); and Adult Intensive Care Unit, Royal Brompton National Heart and Lung Hospital, London (P D MacNaughton MD, T W Evans FRCP)

Correspondence to: Dr Patricia L Haslam

attack (1). Degree of stenosis, measured angiographically in 23 and by carotid duplex in 2, was 50-69% in 10,70-89% in 8, and 90% or greater in 7. 10 subjects had more than 50% contralateral carotid stenosis. Antiplatelet and anticoagulant treatment was aspirin in 21, aspirin and heparin in 2, warfarin in 1, and nil in 1. 24 patients with prosthetic cardiac valves inserted at least 1 month previously were also studied (mean age 60-8 [15’2]; 9 female). 3 had had a stroke or transient ischaemic attack at some time. 5 were in atrial fibrillation. 6 had a mitral prosthesis and 18 an aortic prosthesis. 11 had a pig xenograft (8 Carpentier Edwards, 3 Wessex), and 14 had mechanical valves (8 StarrEdwards, 5 St-Jude). All patients with mechanical valves were on warfarin or heparin. 2 patients with pig xenografts took low-dose aspirin, but none was taking anticoagulants. 20 normal volunteers in sinus rhythm with no clinical embolic source and normal carotid doppler readings were also recruited (mean age 57-5 [12’6]; 12 female). Recordings were made for 20 min from each middle cerebral artery at a depth of 44-52 mm with a sample volume of 10 mm by transcranial pulsed-doppler ultrasound with a 2 MHz probe fixed in position by head-strap (TC2000 S, EME Ltd, Germany). The doppler signal was recorded on computer to allow subsequent off-line analysis of individual time-frames of the 128-point fast Fourier transform. Maximum relative power amplitude (RPA) was recorded for each embolic signal. Background RPA in the absence of an embolic signal was measured from the doppler spectrum of the previous or next cardiac cycle, averaged from three frames at the same point in the cycle at the same velocity. Relative intensity increase (in dB) of each embolic signal was calculated from: 10 x log

ischaemic

(maximum RPA of embolic signal/RPA in absence of embolic

Detection of asymptomatic cerebral embolic signals with doppler ultrasound

Can asymptomatic cerebral emboli be detected? With transcranial doppler ultrasonography of the middle cerebral artery, short-duration high-intensity asymptomatic embolic signals were detected in 6 of 25 patients with carotid stenosis and in 9 of 24 with prosthetic cardiac valves, but not in 20 normal controls. In carotid stenosis the signals were usually unilateral and ipsilateral to the stenosis. Embolic signals were significantly more common in patients with mechanical valves than with pig xenografts (8/13 vs 1/11). With mechanical valves embolic signals were usually bilateral. Detection of asymptomatic emboli may allow identification of and preventive treatment in at-risk patients. Lancet 1994; 343: 1011-12

of ultrasound reflected at any interface is proportional to the density difference between the two materials. Low-density air-bubbles are therefore easily detected in blood as high-intensity signals, which can be heard and seen on the spectral display.l The density difference is much less for more common embolic materials; however, in animal models, atheroma, fat, platelet, and thrombus emboli as small as 200-400 um can be detected with doppler ultrasound. 2,3The lower limit of detection was set by an inability to make smaller emboli rather than by the detection technique. Initial studies suggest similar embolic signals can be detected in humans.4-6

The

amount

We applied the technique to two groups of patients at risk of embolic stroke. 25 patients with symptomatic carotid stenosis

(mean [SD] age 64-3 [8’3] years; 7 female) presented with amaurosis or retinal infarction (8), transient cerebral ischaemia (7), non-disabling stroke (9), and both amaurosis fugax and transient

fugax

signal). Duration of high-intensity signal was calculated from the number of frames (each 5 ms) over which an intensity of more than 4 dB persisted. Recordings were analysed by an observer unaware of the diagnosis; recordings from controls and patients were interspersed. Embolic signals were identifiedz.2,4 by short-duration unidirectional high-intensity signals visible in the doppler spectrum accompanied by a characteristic "clicking" sound. Random fluctuations in the background signal are associated with intensity increases of up to 3 dB.7 Therefore an intensity threshold of 4 dB was used to identify embolic signals. No embolic signals were detected in controls. 6 of the 25 carotid stenosis patients showed embolic signals. In the subjects with embolic signals, mean (SD) number of signals was 2-17 (1-77) per 20 min (median 2, range 1-4). Signals were unilateral in 6 cases, and bilateral in 1 in whom there was a symptomatic contralateral internal-carotid stenosis of 50° o. Signals occurred on the symptomatic side in 5 of the 6 subjects. The sixth patient had symptoms ipsilateral to an internal-carotid artery occlusion in the presence of a 70% contralateral stenosis; an embolic signal was detected in the middle cerebral artery ipsilateral to this stenosis. In 9 of the 24 patients with prosthetic cardiac valves embolic signals were detected, bilaterally in 8. They were more common in patients with mechanical valves than with tissue valves (8/13 [61 %] vs 1/11 [900], Fisher’s test, In those subjects with embolic signals, mean p<0’02). number of signals (mean of both sides) in patients with mechanical valves was 17-6 (28-3; median 8, 1 -5-86) per 20 min. In the only patient with a pig xenograft who had embolic signals, only 1 signal was detected during recordings from both sides. Embolic signals detected in cardiac-valve patients, compared with those in carotidartery patients, had a higher relative intensity increase

(mean [SD] 7-85 [1’40] vs 5.17 [1’03] dB; !7test, p < 0-0001) and a longer duration: 49-2 (21-8) versus 14-0 (10-4) ms; (p < 00001). Typical embolic signals are shown in the figure. 18 recordings were analysed by two independent observers; 7 of the tapes contained embolic signals according to the first observer. There was complete 1011