Effects of Methyiprednisolone on Experimental Pulmonary Injury F. W. CHENEY, JR., M.D.,* T. H. HUANG, M.D., PH.D.,t R. GRONKA, B.S.4

We studied the effects of methylprednisolone on pulmonary function of unanesthetized dogs with oleic acid induced pulmonary edema observed over a four day period. Methylprednisolone (30 mg/kg) was administered to 11 dogs three and 24 hours after pulmonary injury. Eleven animals were untreated after pulmonary injury and served as controls. There was no difference between the two groups until 72 hours after injury, when the venous admixture of the steroid treated animals was 11 + 3% (SD) compared to 22 + 8% (p < 0.001) in the untreated with respective Pao2 values of 76 + 6 torr and 64 + 8 torr (p < 0.001). Light microscopic examination of the lungs 96 hours after injury revealed a marked proliferation of Type II pneumocytes in the methylprednisolone treated animals. We concude that, in the oleic acid or fat embolism model of pulmonary injury, methylprednisolone significantly increases resolution of the pulmonary injury presumably by stimulation of active proliferation and maturation of Type II pneumocytes. O LEIC ACID PRODUCES a pathophysiologic picture

similar to that seen in the clinical syndrome of fat

embolism,1'10 which is one of the syndromes included in the human adult respiratory distress syndrome. The major features of this syndrome are hypoxemia, decreased lung compliance, and noncardiogenic pulmonary edema. Corticosteroids improve survival when administered prior to or after oleic acid pulmonary embolism in dogs3'8 and rats.19 As evidence is lacking that survival is due to improved pulmonary function, we studied the effects of methylprednisolone (SoluMedrol) on the course of pulmonary injury from a sublethal dose of oleic acid. Methods Twenty-two mongrel dogs (mean weight 25 ± 3 kg SD) were anesthetized with 30 mg/kg of pentobarbital * Professor, Department of Anesthesiology. t Assistant Professor, Department of Pathology. t Research Technologist, Department of Anesthesiology. Reprint requests: Frederick W. Cheney, M.D., Professor, Department of Anesthesiology RN-10, University of Washington School of Medicine, Seattle, Washington 98195. Submitted for publication: September 8, 1978. Supported by PHS grant #HL 20612 and the Upjohn Company,

Kalamazoo, Michigan.

From the Departments of Anesthesiology and Pathology, University of Washington School of Medicine,

Seattle, Washington

and, under sterile conditions, instrumented with triple lumen Swan-Ganz catheters and arterial lines. The Swan-Ganz catheters were placed via the external jugular vein and the arterial lines were placed in the forepaw. The distal tip of the pulmonary artery catheter was placed in the proximal pulmonary artery to avoid mixed venous blood sampling error15 and as a result, we were unable to make pulmonary artery wedge pressure measurements in most animals. The catheters were filled with heparin and secured with dressings so that the animals could not dislodge them. Penicillin (600,000 units) and streptomycin (0.5 g) were administered intramuscularly and the animals allowed to recover for 48 hours. No further antibiotics were administered. The animals were brought to the laboratory and control measurements of arterial and mixed venous blood gases, Hgb, vascular pressures, heart rate, and cardiac output (Qt) were done in unanesthetized state. USP oleic acid 0.06 ml/kg was then injected into the right atrium via the indwelling Swan-Ganz catheter. During injection of oleic acid, the animals did not show any obvious signs of discomfort except for occasional coughing. Measurements were repeated at two, four, 24, 48, 72, and 96 hours after the oleic acid

injection. The animals were divided into two groups: 1) 11 control dogs were untreated, 2) 11 steroid treated dogs received 30 mg/kg methylprednisolone intravenously three hours after oleic acid injection and again at 24 hours. After the 96 hour measurements, the animals were anesthetized with 30 mgm/kg pentobarbital, thoracotomy was performed, and the animals sacrificed by ligation of the main pulmonary artery. Samples for light microscopic examination were taken from both grossly normal and abnormal areas of the lung. The pulmonary veins were ligated at the hilum, the lungs removed and weighed. The right lung was weighed, 1 ml

0003-4932/79/0800/0236 $00.85 C) J. B. Lippincott Company

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METHYLPREDNISOLONE A]ND PULMONARY INJURY

of distilled water was added for each gram of lung weight, and the mixture homogenized in a blender. Hemoglobin of the mixture was measured. Weighed aliquots were heated at 800 in a vacuum oven for five days until weights on successive days were within 2-3% of each other. The final lung water/dry lung weight ratio was corrected for blood content of the lung. Histologic specimens were processed, embedded in paraffin, sections cut at 6 gm and stained with hematoxylin and eosin stains. Slides were then coded so that the pathologist was unaware of the treatment group to which the animal belonged. Cellular proliferation in the microscopic sections was scored according to the following criteria: - no proliferation + occasional plump cuboidal epithelial cells at the periphery of the necrotic areas 2+ Focal clusters of proliferating epithelial cells which do not form a continuous rim. 3+ A continuous rim of proliferating epithelial cells, less than 3 cells in width surrounding the periphery of the necrotic area 4+ A continuous rim of proliferating epithelial cells more than 3 cells in width surrounding the edge of the necrotic area The entire experiment was carried out with the animals breathing room air and awake or lightly sedated with 5-10 mg/kg thiamylal. If the animals dislodged one of the intravascular catheters, a new one was rapidly inserted with the animal sedated. Cardiac output was measured by the thermal dilution technique. Venous admixture (QVA/Qt) was measured during room

237

air breathing and calculated using the standard shunt equation.4 Arterial and mixed venous oxygen contents were calculated using the measured hemoglobin and hemoglobin saturation which was derived from blood gas values using a computer program developed by Ruiz et al.14 Statistical analysis was performed using the Student's unpaired t-test for comparisons between treated and untreated animals and the paired t-test for comparisons before and after oleic acid injection in each group. Results All 22 animals survived the 96 hour study period. In both groups, QVA/Qt increased (Fig. 1) and Pao2 decreased (Fig. 2) two hours after oleic acid injection as compared to control measurements. These changes persisted at about the same level for 48 hours in the steroid treated group and 72 hours in the untreated group. The major difference between groups was marked improvement in QVA/Qt (Fig. 1) and Pao2 (Fig. 2) at 72 hours in the treated animals. At 96 hours the QVA/Qt of the untreated animals began to return tooward pre-oleic acid levels although QVA/Qt was still sig.iificantly higher in the untreated animals at 96 hours as compared to the treated (Fig. 1). Administration of steroids three and 24 hours after lung injury had no immediate major effect on gas exchange. Venous admixture did not decrease significantly one hour following methylprednisolone compared to QVA/Qt measured prior to drug administration (Fig. 3). There was, however, a small but significant increase in Pao2 without a significant change in PacO2 one hour after the second administration of steroids (Fig. 4). Cardiac output de-

40 \ 30FIG. 1. Mean values for

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Ann. Surg. * August 1979

CHENEY, HUANG AND GRONKA

238

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Time (hours) untreated animals was at 48 hours when the steroid treated animals had a small but significantly higher Qt. In the untreated animals, mean pulmonary artery pressure (PAP) increased over preoleic acid values at two and four hours, then decreased so there was no

creased in both groups of animals immediately after administration ofoleic acid (Fig. 5) but 24 hours after oleic acid injection, Qt had returned to control levels in both treated and untreated animals. The only significant difference in cardiac output between treated and

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METHYLPREDNISOLONE AND PULMONARY INJURY

STEROID TREATED

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Time (hours) significant difference from control at 24 hours and for subsequent measurements (Table 1). Mean pulmonary artery pressure of untreated animals was slightly higher at 96 hours than the PAP of treated animals. There were essentially no differences in mean blood pressure, heart rate, Pac02, and pH between the two groups (Table 1).

Gross postmortem examination of the lungs in both groups showed congestion with focal areas of hemorrhage and necrosis. Edema fluid exuded from the cut surface of the lung. Both treated and untreated animals had significantly higher lung water/dry weight ratios than control values for normal dog (Table 2). There was no difference however, in lung water/dry weight ratios

D Untreated 2 Steroids 4FIG. 5. Mean values for cardiac output (Qt) + standard deviation before and after intravenous oleic acid. Solid bars: untreated. Stripped bars: steroids. *p < 0.05 between values for untreated and steroid treated.

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CHENEY, HUANG AND GRONKA

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August 1979

TABLE 1. Mean Values for Mean Pulmonary Artery Pressure (PAP), Paco2, Arterial pH, Mixed Venous Oxygen Tension (Pvd), Heart Rate (HR), and Mean Arterial Blood Pressure (BP) Prior to and After 0.06 mllkg Oleic Acid

PAP cm H2O

Paco2

(Torr)

pHa

Pvo,

(Torr) HR

BP (Torr)

Untreated Treated Untreated Treated Untreated Treated Untreated Treated Untreated Treated Untreated Treated

Control

2 Hours

17 4 14 4 35 2 36 4 7.38 ± .03 7.39 ± .04 39 ± 5 37 ± 3 99 ± 24 104± 27 110+ 20 114± 13

23 ± 5* 23 8 37 5 35 6 7.38 ± .04 7.37 ± .05 34 ± 4 33 + 6 102 ± 31 139 ± 26t 113 ± 16 117 ± 13

4 Hours

28 24 35 30 7.39 7.42 35 34 118 140 113 115

between treated and untreated (Table 2). Microscopic examination of the lung sections in both groups revealed extensive but patchy alveolar edema and hemorrhage. The alveolar space was filled with red blood cells and eosinophilic proteinaceous material. Where alveolar septae were necrotic, no nuclear profiles were discernable. Occasional polymorphonuclear leukocytes were noted within the alveolar septae, but there were none within the alveolar space. There was a variable degree of cellular proliferation, predominately epithelial cells at the periphery of necrotic and hemorrhagic areas. These cells were cuboidal to low cuboidal in shape, with abundant basophilic cytoplasm, presumably representing Type II (granular) pneumocytes. The degree of cellular proliferation was scored from 0 to 4+ as described in the Methods section. The most striking difference between treated and untreated animals was in the increased amount of cell proliferation in the treated animals. The mean cell proliferation score for the treated was 3.43 + 1.13 (SD) and for the untreated 2.0 + 1.0. The difference was significant (p < .05) when compared with the Student's unpaired t-test. A representative histologic section of the lung of an untreated animal (Fig. 6) is compared with that of a treated animal in Figure 7 and shows the marked increase in Type II cell proliferation in the treated. Discussion Animals treated with methylprednisolone in this study had markedly improved gas exchange 72 hours after lung injury compared to untreated animals. In' spite of the fact QVA/Qt was significantly lower in steroid treated animals at 96 hours, direct lung water measurements made at that time showed no difference between treated and untreated. This suggests that in vitro gravimetric measurements of lung water may not accurately reflect the gas exchanging capability of the lung in vivo. Other studies3 8 have shown that corticosteroids decrease mortality from oleic acid injury in

19 20 34 36 7.39 ± 7.39 ± 32 ± 35 ± 102± 83 ± 102± 83 ±

25 19 18 6 35 3 34 4 7.39 ± .03 7.42 ± .06 33 3 33 +5 122 44 104 ± 23 102 ± 12 98 ± 10*

14* 12 5 6* ± .04 ± .04* ±6 ±5 ± 36 ± 16* ± 14 ±9

Treated group received 30 mgm/kg methylprednisolone 3 and 25 hours after oleic acid injection. N = 11 in both groups.

48 Hours

24 Hours

*

p <