Gas exchange mechanism of orthodeoxia in hepatopulmonary syndrome

✍ Scribed by Federico P. Gómez; Graciela Martínez-Pallí; Joan A. Barberà; Josep Roca; Miquel Navasa; Robert Rodríguez-Roisin

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 176 KB
• Volume: 40
• Category: Article
• ISSN: 0270-9139
• DOI: 10.1002/hep.20358

✦ Synopsis

The mechanism of orthodeoxia (OD), or decreased partial pressure of arterial oxygen (PaO 2 ) from supine to upright, a characteristic feature of hepatopulmonary syndrome (HPS), has never been comprehensively elucidated. We therefore investigated the intrapulmonary (shunt and ventilation-perfusion [V ˙A/Q ˙] mismatching) and extrapulmonary factors governing PaO 2 in 20 patients with mild to severe HPS (14 males, 6 females; 50 ؎ 3 years old SE) at upright and supine, in random order. We set out a cutoff value for OD, namely a PaO 2 decrease >5% or >4 mm Hg (area under the receiver operating characteristic curve, 0.96 each). Compared to supine, 5 patients showed OD (PaO 2 change, ؊11% ؎ 2%, ؊7 ؎ 1 mm Hg, P < .05) with further V ˙A/Q ˙worsening (shunt ؉ low V ˙A/Q ˙mode increased from 19% ؎ 7% to 21% ؎ 7% of cardiac output [Q ˙T], P < .05), as opposed to 15 patients who did not (؉2% ؎ 2%, ؉1؎ 1 mm Hg) with V ˙A/Q ˙improvement (from 20% ؎ 4% to 16% ؎ 4% of Q ˙T, P < .01). Cardiac output was significantly lower in OD patients in both positions. Changes in extrapulmonary factors at upright, such as increased minute ventilation and decreased Q ˙T, were of similar magnitude in both subsets of patients. In conclusion, our data suggest that gas exchange response to OD in HPS points to a more altered pulmonary vascular tone inducing heterogeneous blood flow redistribution to lung zones with prominent intrapulmonary vascular dilatations. (HEPATOLOGY 2004;40:660 -666.) Abbreviations: HPS, hepatopulmonary syndrome; OD, orthodexia; PaO 2 ; partial pressure of arterial oxygen; Pv O 2, partial pressure of mixed venous oxygen; FEV, forced expiratory volume in one second.