title: Mechanisms of hypoxemia in patients with status asthmaticus requiring mechanical ventilation.
abstract: Eight consecutive patients (mean +/- SD age, 43 +/- 11 yr) with acute severe asthma (status asthmaticus) requiring assisted ventilation were studied within the first 24 to 48 h of admission, at maintenance FIO2 and while breathing 100% O2, using the multiple inert gas elimination technique. Ventilation-perfusion (VA/Q) inequality was characterized by a marked bimodal blood flow distribution (perfusion to normal and low VA/Q populations) in all but two patients, with a mean of 27.6 +/- 12.3% of the total perfusion present in the low VA/Q ratio units (between 0.1 and 0.005). As a result, the dispersion of pulmonary blood flow distribution (log SDQ) was severely abnormal (mean, 1.65 +/- 0.28; normal range, 0.3 to 0.6). No patient had a substantial shunt (VA/Q = 0) (mean value, 1.5 +/- 2.3%). The ventilation distribution was never bimodal, but the dispersion of the ventilation distribution (log SDV) was moderately elevated (1.01 +/- 0.24). High VA/Q areas (ventilation to VA/Q units between 10 and 100) were generally absent. While breathing 100% O2, PaO2, PvO2, and PaCO2 significantly rose, as did shunt and blood flow dispersion. Patients with life-threatening acute severe asthma treated by mechanical ventilation show: (1) the most abnormal gas exchange characteristics of the VA/Q spectrum observed to date in human asthma but essentially the same pattern as in patients with less severe disease; (2) a high level of hypoxic pulmonary vascular response; (3) a significant amount of shunt while breathing 100% O2, suggesting the presence of absorption atelectasis or redistribution of blood flow.
authors.affiliation: Department of Medicine, Facultat de Medicina, Universitat de Barcelona, Spain.
authors.forename: R
authors.initials: R
authors.lastname: Rodriguez-Roisin
authors.forename: E
authors.initials: E
authors.lastname: Ballester
authors.forename: J
authors.initials: J
authors.lastname: Roca
authors.forename: A
authors.initials: A
authors.lastname: Torres
authors.forename: P D
authors.initials: PD
authors.lastname: Wagner
mesh_terms: D000328:Adult; D001249:Asthma / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D006801:Humans; D000860:Hypoxia / Q000209:etiology / Q000503:physiopathology*; D008875:Middle Aged; D010100:Oxygen; D012119:Respiration; D012121:Respiration, Artificial; D013224:Status Asthmaticus / Q000150:complications / Q000503:physiopathology* / Q000628:therapy; D014692:Ventilation-Perfusion Ratio
chemical_list: D010100:Oxygen