Adult respiratory distress syndrome: current concepts

The role of complement in pregnancy-induced hypertensive disease

Preeclampsia is a pregnancy-induced hypertensive disease with an incidence of about 5% in primigravidas and, being common, it significantly contributes to maternal and neonatal morbidity and mortality. The primary cause remains unknown but might be immunologic, since immunologic aberrations are described in preeclampsia. Activation of the complement system in pregnancy-induced hypertensive disease has been discussed during the last 60 years. It is now strongly indicated that complement activation occurs in preeclampsia. The complement system is very potent and one of the major effector pathways of the process of inflammation. The pathological manifestations, endothelial damage and microvascular injury, and thereby the clinical findings in preeclampsia, may be explained by complement activation, resulting in the direct vascular effects of biological active complement components and complement-mediated activation of leukocytes, with release of potent inflammatory mediators. This new etiological hypothesis might give other options in therapy and prevention of pregnancy-induced hypertensive disease.

Increased susceptibility of aged rats to haemorrhage and intravascular hypercoagulation following endotoxin administered in a generalized Shwartzman regime

Ageing rats are known to have an increased incidence of myocardial fibrosis and dyspnoea caused by pulmonary intravascular coagulation. In order to determine whether endotoxin can be responsible for such responses in ageing rats we have exposed rats of differing ages (2 months, 16 months and 24 months) to single or repeated (two doses 24 h apart; generalized Shwartzman regime) intravenous doses of endotoxin (E. coli 0111 B4). Only the 2-year-old rats reacted adversely. Two doses of endotoxin produced death, with focal myocardial necrosis, haemorrhage and pulmonary and hepatic intravascular coagulation. The increased susceptibility of aged rats to the toxic effects of endotoxin explains some of the changes found in the tissues of old rats. The sporadic nature of both cardiac failure and dyspnoea as a cause of morbidity and mortality in ageing rats may be related to the need for two endotoxin episodes in a period of 24 h to provoke a generalized Shwartzman reaction, an occurrence likely to be relatively uncommon under natural conditions.

Immunotoxic effects of hexachlorobenzene on the pathogenesis of systemic, pneumonic and hepatic virus infections in the mouse

A quantitative histopathological method has been developed for the evaluation of the effects of hexachlorobenzene (HCB) on the pathogenesis of three virus infections in the mouse. Hexachlorobenzene was selected because a substantial amount of immunotoxicological data already exists with which we could compare our results. To establish the validity of the method a systemic virus infection (mouse cytomegalovirus, MCMV), a pneumonia causing virus (pneumonia virus of mice, PVM) and a hepatitis virus (mouse hepatitis virus, MHV) were used. We have compared the existing data with the actual pathological effects of hexachlorobenzene on virus disease processes, to gain a more realistic idea of the value of the risk assessment to be derived from extrapolating the in-vitro data in particular, to the in-vivo situation. The results show that the data derived from previous studies on the immunotoxicity of HCB were accurate in predicting the exacerbation of the viral hepatitis, especially in immunodeficient athymic 'nude' mice. It is proposed that this histopathological technique could be a useful technique in the evaluation of host resistance changes following exposure to potentially immunotoxic compounds, but caution will have to be exercised in interpretation in relation to human disease.

Reactive type II pneumocytes in bronchoalveolar lavage fluid from adult respiratory distress syndrome can be mistaken for cells of adenocarcinoma

A growing body of literature illustrates that bronchoalveolar lavage is a reliable and efficient means of diagnosing primary and secondary malignancies in the lung. Its safety in severely compromised patients often makes it preferable to other biopsy procedures. However, a variety of reparative and degenerative pulmonary disorders may result in cytologic alterations so severe that pneumocytes resemble cells of malignancy. We describe four patients with the adult respiratory distress syndrome from whom lavage fluid showed gland-like groups of malignant-appearing cells morphologically consistent with adenocarcinoma. Transbronchial biopsy sections in one case and lavage fluid electron microscopy in another showed that these pseudomalignant cells were reactive Type II pneumocytes with surface microvilli, cell junctions, and numerous cytoplasmic myelin figures. Careful clinicopathologic correlation is the best way to ensure accurate diagnosis in these cases.