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Zubieta-Calleja G.,High Altitude Pathology Institute IPPA | Zubieta-Castillo G.,High Altitude Pathology Institute IPPA | Zubieta-Calleja L.,High Altitude Pathology Institute IPPA | Ardaya-Zubieta G.,High Altitude Pathology Institute IPPA | And 2 more authors.
Indian Journal of Clinical Biochemistry | Year: 2011

As the oxygen tension of inspired air falls with increasing altitude in normal subjects, hyperventilation ensues. This acute respiratory alkalosis, induces increased renal excretion of bicarbonate, returning the pH back to normal, giving rise to compensated respiratory alkalosis or chronic hypocapnia. It seems a contradiction that so many normal people at high altitude should permanently live as chronic acid-base patients. Blood gas analyses of 1,865 subjects at 3,510 m, reported a P aCO 2 (arterial carbon dioxide tension ± SEM) = 29.4 ± 0.16 mmHg and pH = 7.40 ± 0.005. Base excess, calculated with the Van Slyke sea level equation, is -5 mM (milliMolar or mmol/l) as an average, suggesting chronic hypocapnia. THID, a new term replacing "Base Excess" is determined by titration to a pH of 7.40 at a P aCO 2 of 5.33 kPa (40 mmHg) at sea level, oxygen saturated and at 37°C blood temperature. Since our new modified Van Slyke equations operate with normal values for P aCO 2 at the actual altitude, a calculation of THID will always result in normal values-that is, zero. © 2010 Association of Clinical Biochemists of India. Source

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