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Alveolar Dead Space as a Predictor of Severity of Pulmonary Embolism

2000; Wiley; Volume: 7; Issue: 6 Linguagem: Inglês

10.1111/j.1553-2712.2000.tb02033.x

1553-2712

Jeffrey D. Kline, Anita K. Kubin, Manish M. Patel, Edward J. Easton, Rawle A. Seupal,

Ultrasound in Clinical Applications

Abstract. Objective: To determine whether the alveolar dead space volume (V D alv), expressed as a percentage of the alveolar tidal volume (V D alv/V T alv), can predict the degree of vascular occlusion caused by pulmonary embolism (PE). Methods: Fifty‐three subjects with suspected PE were prospectively studied. Pulmonary embolism was diagnosed in 33 by high‐probability ventilation/perfusion (V/Q) scan (n = 19) or by pulmonary arteriography (PAG, n = 14). Pulmonary embolism was excluded by PAG in 20 subjects. The V D alv/V T alv was determined from volumetric capnography and arterial blood gas analysis, which permits measurement of the physiologic dead space, V D phys (mL) = [PaCO 2 — PeCO 2 )/PaCO 2 ]. tidal volume. Airway dead space (V D aw) was subtracted to yield the alveolar dead space [(V D phys — V D aw) = V D alv (mL)]; the percentage of alveolar volume occupied by alveolar dead space per breath = V D alv/V T alv · 100%. Percentage perfusion defect was determined from V/Q scans by a radiologist blinded to other data. Regression analysis was performed to show correlation between V D alv/V T alv and defect on V/Q scan or systolic pulmonary arterial pressure (SPAP). Results: For subjects with PE, the mean perfusion defect on lung scan was 38 ± 22%; the mean V D alv = 208 ± 115 mL, V T alv = 452 ± 251 mL, and V D alv/V T alv = 43 ± 18%. Regression of V D alv/V T alv vs perfusion defect yielded r 2 = 0.41. Regression of V D alv/V T alv vs pulmonary artery pressures yielded r 2 = 0.59. For subjects without PE, V D alv/V T alv = 27 ± 14% and V D alv = 89 ± 66 mL. Conclusions: The V D alv/V T alv correlates with the lung perfusion defect and the pulmonary artery pressures in subjects with PE. These findings show the potential for V D alv/V T alv to quantify the embolic burden of PE.