Our study was performed in 33 nonconsecutive patients (17 men and 16 women; mean age, 57 ± 14 years) who were admitted to our ICU with a diagnosis of pulmonary embolism. In 21 of them (64 percent), the diagnosis of pulmonary embolism was initially made on the basis of the presence of multiple, large segmental defects on the perfusion lung scintigram. According to McNeil, in patients who showed “multiple large (segmental or greater) perfusion defects, pulmonary embolism is very likely.” Subsequently, the diagnosis was confirmed in these patients by the clinical and scintigraphic evolution after anticoagulant or fibrinolytic therapy. In 12 patients (36 percent) with smaller or less defined segmental perfusion defects at lung scintigraphy, pulmonary arteriography was performed to prove the diagnosis.
Pulmonary embolism occurred after surgery in 15 patients, after a proven episode of leg thrombophlebitis in five patients, after a long period of immobilization due to a lower limb trauma in two patients, and in the presence of lymphoma in one patient; the pulmonary embolism was apparently primary in the remaining ten patients.
Out of 33 patients, 12 were smokers and had a clinical history of cough and phlegm expectoration for several months in the year. In seven out of these 12 patients, pulmonary arteriography was performed.
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All patients were treated with fibrinolytic or heparin therapy for three to ten days after diagnosis. Both treatments were followed by oral therapy with warfarin for a period of at least six months.
On the same day as admittance to our ICU, all patients underwent perfusion lung scintigraphy, a chest x-ray film, and gas exchange measurements while spontaneously breathing room air. These examinations were then repeated after 7, 30, and 180 days during therapy.
Berfusion Lung Scintigraphy
Lung perfusion scintigraphy was routinely performed by a rectilinear scanner equipped with a 5-inch crystal and a focusing collimator after intravenous injection of 3 mCi of “”To-labelled serum albumin microspheres. Anterior, right, and left lateral views were regularly obtained. The lateral chest views are essential for the visualization of the anatomic division of the lung at the segmental level, since the various lung segments (there are 18 lung segments normally visible on a perfusion lung scan) are adjacent in the lateral projections and may be easily identified when missing. Perfusion lung scans were read for the presence of perfusion defects (segmental or subsegmental). The ULSs, which were estimated on the lateral chest views, were graded in the following way: a score of 1 was assigned to each unperfused area with the size, shape, and location of a known lung segment; and a score of 0.5 was assigned to perfusion defects with subsegmental size, shape, and location or when a scnitigraphic region corresponding to a lung segment was poorly perfused. The number of ULSs was taken as an index of the severity of pulmonary embolism. The perfusion lung scintigraphic views were examined by three independent observers, and the degree of agreement was tested. The mean value of the three readings was used for further analysis. No significant differences were found among the three readers by variance analysis (F = 0.83; NS) in the evaluation of ULSs at perfusion lung scintigraphy.
Gas Exchange Parameters
Gas exchange and ventilation parameters were measured by a computerized system which allowed the determination of alveolar gas concentrations. This system calculated gas exchange and ventilation parameters on a breath-by-breath basis. Briefly, the patient in a semirecumbent position breathed through a mouthpiece into a Hans-Rudolph valve (34-ml dead space), connected to a pneumotachograph (Fleisch No. 3) for flow and volume measurements. Respiratory gases were analyzed by a respiratory mass spectrometer (Varian MAT 3). The computerized system calculated end-tidal pressures of oxygen, carbon dioxide, and nitrogen. Blood gas analysis was performed by the standard electrode method Instrumentation Laboratory 1302) to obtain the Pa02 and PaC02.
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The P(A-a)Oz and P(a-A)COz were then calculated. The program also computed Ve and Vd/Vt percent, according to the Enghoff equation. The validation of the computer program has been reported elsewhere. Moreover, values for Pa02 were corrected for hyperventilation by adjusting for the level of PaC02, according to Mays diagram. The measured PaOz was thus standardized to a PaC02 of 40 mm Hg to obtain Pa02st by the following formula:
Pa02st = ([PaC02 x 1.66] -I- PaO,) – 66.4