Per Berggren

Gas exchange and lung morphology after surfactant replacement in experimental adult respiratory distress syndrome induced by repeated lung lavage

Severe respiratory insufficiency was induced in adult guinea pigs by repeated lung lavage. The animals were then ventilated for 75 min with 100% O2, insumation pressure 28/68 cmH2O (2.7/0.6–0.8 kPa), frequcnry 30/min, and 33% inspiration time. One group of animals (I) was treated with protein‐depleted porcinr surfactant, prepared by a combination of sucrose‐gradient centrifugation, heating to 90°C, and chloroform/methanol extraction. Another group (II) received the phospholipid fraction of porcine surfactant, isolared from minced lungs by chloroform/methanol extraction and liquid‐gel chromatography. Surfactant was administered in two 1‐ml doses (lipid concentration 90 mg/ml) instilled via the tracheal cannula about 15 and 45 min after the lavage procedure. Non‐treated, lavaged animals served as controls. After 75 min of ventilation, control values for Pao2 and Paco2 were 13.3 ± 6.8 and 6.8 ± 2.3 kPa (mean ± s.d.), respectively. The corresponding values in Group I of surfactant‐treated animals were 52.9 ± 7.7 and 4.4 ±1.I kPa, in Group II 53.5 ± 7.3 and 4.8 ±1.3 kPa (P<0.02–0.002). The two groups of surfactant‐treated animals also had significantly improved alveolar air expansion in histological sections, as reflected by increased alveolar volume density (0.67 ± 0.05 and 0.62 ± 0.11 vs. 0.45 ± 0.08 in controls; P<0.002). The benefits of surfactant replacement in this experimental model were thus similar to those previously observed in animal models of neonatal surfactant deficiency as well as in babies with respiratory distress syndrome (RDS). Our data suggest that surfactant replacement might have a therapeutic effect also in clinical adult RDS.

Physiological Activity of Pulmonary Surfactant with Low Protein Content: Effect of Enrichment with Synthetic Phospholipids

A natural surfactant with low protein content (1%) was prepared by a sequence of cold centrifugation, heating to 90 degrees C, sucrose-gradient centrifugation, and extraction with chloroform:methanol. Some of the material was enriched with dipalmitoylphosphatidylcholine (DPPC) and unsaturated phosphatidylglycerol (PG) to relative concentrations of 56% and 10%, respectively. The in vitro physical properties of these preparations were evaluated with pulsating bubble and Wilhelmy balance and their in vivo activity with experiments on artificially ventilated premature newborn rabbits, delivered on day 27 of gestation. The animals were kept in body plethysmographs at 37 degrees C and ventilated artificially with a standardized sequence of insufflation pressures: 25, 20, and 15 cm H2O. The lungs were fixed by vascular perfusion and the alveolar expansion evaluated morphometrically in histologic sections. Enrichment of surfactant with DPPC and PG resulted in lower minimal surface tension during surface compression but did not further improve lung compliance or the alveolar expansion pattern. Treatment with nonenriched surfactant at a phospholipid concentration of 100 mg/ml (individual dose = 200 mg/kg) caused a markedly increased lung compliance at all insufflation pressure levels (p vs. controls less than .01). Our data indicate that pulmonary surfactant remains physiologically active after removal of most of its protein components and that enrichment with DPPC and PG reduces the in vitro minimal surface tension without adding to the in vivo efficacy.

Combined effects of surfactant substitution and prolongation of inspiration phase in artificially ventilated premature newborn rabbits.

Summary: Premature newborn rabbits, delivered by hysterotomy on day 27 of gestation, were tracheotomized at birth, kept in body plethysmographs, and subjected to pressure-generated ventilation at a working pressure of 25 cm H2O, 100% O2, and frequency 40/min. Thirty-seven animals received 50 μl of heterologous surfactant (phospholipid content 40 mg/ml) via the tracheal cannula before onset of artificial ventilation, eight were ventilated with a positive end-expiratory pressure (PEEP) of 6 cm H2O, and 44 served as controls. All animals were ventilated in a randomized sequence of 2-min periods with 20, 40, 60, or 80% inspiration time. After the experiment the trachea was clamped at end-inspiration and the lungs fixed by immersion in formalin. Plethysmograph recordings of tidal volume revealed that lung-thorax compliance was low in control animals, even at inspiration time 80% (mean ± S.E. = 0.17 ± 0.03 ml/cm H2O·kg). In animals treated with surfactant or PEEP, compliance was significantly improved at all ventilator settings. The highest mean compliance values, obtained at 60% inspiration time were 0.91 ± 0.07 and 0.73 ± 0.14 ml/cm H2O·kg in surfactant- and PEEP-treated animals, respectively. Compliance of surfactant-treated animals was significantly higher than that of PEEP-treated animals at inspiration time 40% (0.85 ± 0.07 versus 0.52 ± 0.13 ml/cm H2O·kg; P < 0.05). The relative volume of the alveolar compartment, determined morphometrically in histologic sections and expressed as the alveolar expansion index (Ia), was significantly higher in surfactant-treated animals than in controls (1.60 ± 0.12 versus 0.74 ± 0.06; P < 0.005), but not improved in animals ventilated with PEEP. In animals receiving surfactant, Ia increased with the duration of the inspiration phase, from 0.99 ± 0.10 at 20% to 1.95 ± 0.22 at 80% inspiration time. There was also histologic evidence of enhanced recruitment of aerated alveoli in surfactant-treated animals ventilated with prolonged inspiration time.Speculation: The air expansion of the premature neonatal lung can be enhanced to a significant degree by treatment with surfactant in combination with appropriate prolongation of the inspiration phase. Such a therapeutic regimen might be useful in the management of newborn infants with severe respiratory distress syndrome, requiring artificial ventilation; however, because excessive prolongation of the inspiration phase could have adverse effects on pulmonary hemodynamics and lead to hypoventilation with respiratory acidosis, the setting of the ventilator should be carefully adjusted with respect to the therapeutic response in patients with respiratory distress syndrome who are treated with supplementary surfactant.

Surfactant treatment and ventilation by high frequency oscillation in premature newborn rabbits: effect on survival, lung aeration, and bronchiolar epithelial lesions.

ABSTRACT: Premature rabbit neonates delivered at gestational age 27 days were ventilated by high frequency oscillation for 60 min with 100% O2, using a frequency of 7-8 Hz, 50% inspiration time and mean airway pressures of 6-8 cm H2O. Twenty-five animals received bovine surfactant (2 ml/kg body weight; phospholipid concentration 85-100 mg/ml) in the tracheal cannula before onset of ventilation, and 22 littermates served as controls. In the surfactant-treated group, average tidal volume was about 10 times larger than in controls, yet only 15% of the estimated dead space. Judged from ECG recordings, the treated animals also had a much higher survival rate: 96 versus 5% (p < 0.001). Morphometrically, mean alveolar volume density was increased in the surfactant-treated animals in comparison with controls: 0.65 ± 0.08 versus 0.37 ± 0.08 (x ± SD; p < 0.005). Bronchiolar epithelial lesions were found in all control animals and were severe in almost all cases. In the surfactant-treated group, epithelial lesions were absent in 12, mild in 11, and fairly prominent in two animals. We conclude that after treatment with surfactant, the premature newborn rabbit can be ventilated adequately with high frequency oscillation at comparatively low mean airway pressures and that surfactant replacement effectively reduces the development of epithelial lesions in conducting airways during high frequency oscillation.

Bubbles and Computer-Aided Image Analysis for Evaluation of Surfactant Inhibition

Surfactant (Curosurf, diluted to 5 mg/ml) was suspended in normal saline with 3 mM CaCl2 and mixed with different concentrations of albumin or fibrinogen. The samples were vortexed to generate microbubbles, and the equivalent circle diameter of these bubbles was determined with computer-aided image analysis. Bubbles in the original surfactant suspension had an average diameter of 27 microns after 2 min, and their size increased only little during a 15-min period of observation. The diameter of bubbles generated in the presence of albumin (4 or 40 mg/ml) or fibrinogen (4 mg/ml) was 4-5 times larger, indicating surfactant inhibition. We conclude that evaluation of microbubble stability with image analysis provides an objective and rapid assessment of surfactant inhibition, and we speculate that the method could also be used for quantification of surfactant activity in airway samples.

Effect of surfactant and specific antibody on bacterial proliferation and lung function in experimental pneumococcal pneumonia.

OBJECTIVE To investigate the effect of surfactant and specific antibody on bacterial proliferation in experimental pneumococcal pneumonia. METHODS Near-term newborn rabbits received a standard dose (10(7)) of type 3 pneumococci via the airways. Control animals were sacrificed 1 minute later. Other animals were ventilated for 5 hours and treated via the tracheal cannula with surfactant (Curosurf 200 mg/kg), a mixture of surfactant and a polyclonal antipneumococcal antibody, the antibody without surfactant, or saline. RESULTS There was a significant bacterial proliferation in lung tissue in all animals ventilated for 5 hours. Bacterial growth, expressed as log10 colony forming units (CFU) per gram of lung tissue was less prominent in animals treated with a mixture of surfactant and specific antibody than in animals treated with antibody alone (median, 7.51, range, 6.80--7.70 vs. median, 7.92, range, 7.07--8.50; P < 0.05). Dynamic lung-thorax compliance was improved with surfactant or surfactant plus antibody in comparison with saline or antibody alone. CONCLUSIONS The data suggest that the suppressive effect of the antibody on bacterial proliferation becomes evident only when surfactant is administered together with the antibody.

EXOSURF VERSUS CUROSURF; COMPARISON OF SURFACE PROPERTIES, RESISTANCE TO INHIBITION, AND PHYSIOLOGICAL EFFECTS IN PRETERM RABBITS

ExosurfR (Wellcome) and CurosurfR (Chiesi) are two widely used exogenous surfactants. We compared their physical and physiological properties by image analysis of microbubble stability in surfactant suspensions (1 mg/ml), mixed with various concentrations of albumin (0-40 mg/ml), and by evaluating lung structure and function in ventilated immature newborn rabbits receiving clinical treatment doses of either surfactant (Exosurf, 67.5 mg/kg; Curosurf, 160 mg/kg).Results: Bubbles in Curosurf were significantly smaller than those in Exosurf (diameter, mean±SEM: 19±2 vs. 106±19 μm;P <0.001). Both surfactants were inhibited by albumin ≥2 mg/ml, as reflected by in- creasing microbubble diameter, but Curosurf bubbles remained smaller than Exosurf bubbles at albumin concentrations ≤4 mg/ml. Lung-thorax compliance after 1 h was significantly greater in Curosurf-treated animals (mean±SEM: 0.62±0.05 ml/cmH2O.kg) than in littermates receiving Exosurf (0.45±0.01) or controls (0.44±0.06)(P <0.05). Airway epithelium of Curosurf-treated animals was mostly intact, whereas Exosurf-treated and control animals had widespread epithelial injury.Conclusions: Curosurf stabilizes microbubbles better than Exosurf, even in the presence of low concentrations of albumin. Curosurf is more effective than Exosurf when given in clinical treatment doses to ventilated immature rabbits.