Carlos R. Salvarezza
Condensation is any pathological process that increases the density of the lung parenchyma. This is a broad definition where pneumomias, atelectasis, fibrosis and tumors are included.
In this chapter, the abnormalities originating in pneumococcal pneumonia, in which a segment, a lobe or the entire lung lose their normal structure, will be considered as condensation syndrome. Other gram-positive and gram-negative bacteria can cause this syndrome.
The lung is basically made up of three compartments: vascular (capillaries), intersitial (collagen fibers and others) and air (alveoli).
The pulmonary capillaries are limited by an endothelium that rests on a basement membrane. Endothelial cells are linked together by less tight connections than epithelial cells. Diffusion of water, electrolytes, and small water-soluble molecules occurs through these junctions, but transfer of macromolecules is only possible under pathological conditions.
Endothelial cells are rich in filaments that are susceptible to being contracted by the effect of histamine, serotonin, and bradykinin, which consequently increases capillary permeability as the junctions open.
The interstitium is a compact space in which two areas can be differentiated: a very thin one constituted by the fusion of the basement membranes (sector responsible for gas exchange) and a wider one occupied by collagen and elastic fibers, monocytes, polymorphonuclear cells, lymphocytes, macrophages. and abundant interstitial cells.
The alveoli are made up of epithelial cells that support a basement membrane and are joined by closed connections. Pneumonocytes I occupy 96% of the alveolar surface and currently serve as mechanical support. The remaining 4% is made up of pneumonocytes II whose function is to synthesize the surfactant and transform into pneumonocytes I when they are destroyed. Alveolar macrophages are also located in their walls in the alveoli.
The hydrostatic pressure of the capillaries tends to displace the liquid from their interior towards the interstitial space.
Capillary oncotic pressure is around 24 mm Hg and tries to retain fluid and prevent it from reaching the interstitium.
The values of capillary hydrostatic pressure (it is calculated at 11 mm Hg) and interstitial (it would be below atmospheric pressure) and interstitial oncotic (approximately 20 mm Hg in the lung lymph) are unknown.
When the balance that regulates these pressures is broken, the fluid moves from the capillary to the interstitium (interstitial edema), and if the lymphatics are insufficient to drain it, it passes from the interstitium to the alveoli (alveolar edema).
In condensation, the first stage is that of an edema that fills the alveoli, similar to any other form of pulmonary edema, but that contains pneumococci. The alveoli are then occupied by red blood cells, fibrin, and a few polymorphonuclear cells. The small bronchi are covered by fibrin (red liver). The last period is the one that goes to resolution by reabsorption of the edema.
The most common cause of condensation is pneumococcus, an aerobic gram-positive bacterium of which 80 antigenic types are known. It is a habitual resident of the upper airways, and defects in the defense mechanisms of the respiratory system predispose to alveolar invasion.
Symptoms and signs
In 80% of cases, pneumonia begins acutely with hyperthermia, chills, general malaise, headaches, side stitch, dry cough. Then sputum is added, which can be mucopurulent, hemoptoic, or rusty.
For a condensation to be detected semiologically, it is necessary that its size exceeds 4 cm, that it be located close to the oracic surface, that its thickness is sufficient and that the bronchus corresponding to the condensation remains permeable.
The inspection may be negative or be observed tachypnea, facial flushing (slap sign), herpes. On palpation, local vibrations are increased in the area corresponding to condensation. In percussion the normal thoracic sound is modified and acquires the characteristics of submatidity or dullness. As for the auscultation, sub-crepitant and crackles are detected, which later disappear, and a bronchial sound is heard that replaces the respiratory sound.
The history and physical examination allow a presumptive diagnosis of condensation syndrome generated by bacteria.
Chest X-ray . A localized opacity is observed more frequently in the lower lobes, with a homogeneous density and imprecise limits. Occasionally an air bronchogram can be seen, which is the visualization of the bronchi due to the fact that the air contained within them contrasts with the opacity of the condensation.
Laboratory . Between 15,000 and 30,000 leukocytes per mm 3 are frequently observed on the blood count, with neutrophilia and an increased percentage of immature glanulocytes. Erythrocyte sedimentation is accelerated and in some patients it can reach up to 100 mm in the first hour. Blood culture, in turn, can isolate pneumococci in 30% of all patients.
Regarding the sputum examination, it should be remembered that pneumococci are habitual residents of the oropharyngeal cavity and that therefore their finding in the expectoration is of relative value to certify the etiological diagnosis.
Transcricothyroid puncture and pneumocentesis . The specimens obtained with these methophos are not contaminated and offer a high percentage of positivity. However, exceptionally it is necessary to indicate them in this pathology.