Experimental pulmonary fat embolism: effects on pulmonary function by reserpine pretreatment

Effect of reserpine on N-methylthiobenzamide-induced pulmonary edema: role of lung norepinephrine and hypothermia

N-Methylthiobenzamide (NMTB) is a pneumotoxin which causes pulmonary edema and hydrothorax in rodents. Reserpine has been shown to attenuate the pneumotoxicity induced by NMTB. Some of that evidence suggests that the protection afforded by reserpine occurs independently of its capacity to reduce peripheral 5-hydroxytryptamine (5-HT). We therefore investigated 2 other pharmacologic properties of reserpine, namely: (1) its capacity to reduce lung norepinephrine (NE); and (2) its capacity to induce hypothermia, in order to more fully understand its mechanism of protection. Pretreatment of mice or rats with 6-hydroxydopamine at a dose which reduced lung NE by approximately 80% did not affect the pneumotoxic response to NMTB. Thus a decrease in lung NE probably does not account for reserpine's protective effect. An investigation of reserpine's effects on core temperature revealed that mice dosed with a combination of reserpine + NMTB presented with core temperatures lower than mice treated with either compound alone. Mice placed in a cold environment (2 degrees C) and dosed with NMTB presented with hypothermia and an attenuated toxic response to NMTB. Thus a reserpine-induced hypothermia could be allowing for a reduction of NMTB metabolism and consequent diminution of toxicity. These observations suggest that reserpine's capacity to protect animals against NMTB-induced pulmonary edema may in part be due to its capacity to induce hypothermia.

Intravascular coagulation associated with the adult respiratory distress syndrome

In seven of 30 consecutive patients with the adult respiratory distress syndrome, disseminated intravascular coagulation (DIC) developed. Increasing respiratory dysfunction characterized by decreased effective static compliance and increased hypoxemia coincided with the development of DIC. Patients in whom DIC developed were characterized by a high incidence of bleeding, gangrene of the extremities, renal dysfunction, mortality and autopsy evidence of fibrin microthrombi in the lungs, kidney and skin. In 12 of 23 patients who did not meet the criteria for DIC, the platelet count decreased by at least 50 per cent of the initial values at some time during their illness. Fibrin microthrombi were found in the lungs in the majority of the patients subjected to autopsy. These data support the concept that depostion of platelet on damaged pulmonary capillary endothelium may be more common in the adult respiratory distress syndrome than the DIC syndrome.

The role of hypovolemic stress in the production of fat embolism in rabbits. 2. Changes in arterial blood gas levels and static compliance

The purpose of this study was to assess the possible role of hypovolemia as a factor in the production of impaired pulmonary function in pulmonary fat embolizaiton. Iv vivo static lung compliance was measured by inflating the lungs with known volumes of air and recording the transpulmonary pressure, monitoring intraesophageal pressure as an index of intrapleural pressure. Arterial blood was drawn from the central artery of the ear. Embolization was produced by the intravenous injection of homologous fat cells either as the sole experimental procedure or in conjunction with hypovolemic shock. Two types of shock were studied. In one, 20 percent of the blood volume was removed, producing hypovolemia associated with hemodilution, and in the other a tourniquet was applied to induce hypovolemia and hemoconcentration. The results indicate that embolization is associated with significantly greater impairment of pulmonary function if it develops on a background of shock than if it occurs in an otherwise healthy animal. These pathophysiologic findings parallel the results of a morphologic study.

The role of hypovolemic stress in the production of fat embolism in rabbits. 1. Morphologic alterations of the lungs

In rabbits, an experimental model of fat embolism was produced that simulates the course of events in the clinical situation. Small doses of fat-cell suspension (0.075 ml/kg of body weight), prepared by collagenase treatment of homologous adipose tissue, were injected intravenously. Concomitantly, hypovolemia was produced in two animal groups by either withdrawing 20 percent of the estimated blood volume or by application of a hind-limb ischemic tourniquet for 90 minutes. The presence of pathoanatomic characteristics typical of fat embolism was evaluated by recording lung/body weights, macroscopic appearance, and semiquantitative microscopic estimation in the lungs of edema, hemorrhage, atelectasis, intravascular coagulation, and leukocytic thrombi. Mean indices of lung/body weight were higher in all animals receiving injections of fat-cell suspension, as compared to controls. The score for microscopic generalized pulmonary damage was significantly higher in rabbits exposed to both fat-cell injections and hypovolemia than in controls or after fat-cell injections alone. It is concluded that hypovolemia enhances the development of fat embolism in rabbits subjected to small doses of fat-cell suspension.

[Pulmonary microembolism: pulmonary hemodynamics following trauma and hemorrhage (author's transl]

Standardized bone trauma by means of open osteotomy is performed on both hind legs of 16 out of 24 anaesthetised mongrels. During the following 6 hours the most important parameters of blood coagulation and the serum lipids are estimated at regular intervals. Subsequently in a number of the animals 50% of the total blood volume is withdrawn continuously over a period of one hour. All animals without the preceding trauma survive the hemorrhage. The animals in the trauma group die on the average 42 minutes after the beginning of the hemorrhage. The trauma causes an acute decrease in total platelet count (GTZ) to 40% of the pretraumatic value. During an initial phase of hypercoagulability there is a formation of reversible microaggregations containing platelets and fibrin, caused by an increased turnover of coagulation factors. Secondary fibrinolysis develops in the traumatised animals. A further increase in coagulation is caused by the following hemorrhage. In combination with decreased and inhibited fibrinolysis, a disseminated intravascular coagulation state is found and results in irreversible pulmonary microthrombosis. Massive pulmonary fat deposits cannot be found histologically in spite of an increase in serum triglycerid levels to 35% above the pretraumatic values. In dogs great amounts of fat are filtered by the glomeruli and are demonstrable in the tubular epithelium. Histological examinations show a marked disseminated pulmonary microthrombosis of platelets, fibrin and fat in those animals with trauma and hemorrhage. Only the accompanying hypovolemia produces the characteristic histologic changes of the so-called Pulmonary Microembolism Syndrome.