2012
Volume 12, Number 3, pp. 103–112
Extremely high altitude hypoxic conditions during Mount Everest expeditions, residence at South Pole stations, in Tibet and among the Andes: Van Slyke equation modification is crucially important for acid–base measurements
Gustavo Zubieta-Calleja Jr,a Poul-Erik Paulev,b Jitendra N. Mehrishi c and Gustavo Zubieta-Castillo Sra
a High Altitude Pulmonary and Pathology Institute (IPPA), Av. Saavedra, 2302 La Paz, Bolivia
b Panum Institute, Department of Physiology, University of Copenhagen, Blegdamsvej 3b 12.5.29, 2200 Copenhagen, Denmark
c University of Cambridge, UK
The Van Slyke equation at sea level is used to calculate/monitor acid–base balance and changes, sometimes designated base excess or base deficit and, more recently, “titratable hydrogen ion difference” (THID). Sea level oxygen partial pressure, PaO2 (~95 mmHg) decreases exponentially with altitude; it is about half of the sea level value at 5,000 m (Everest Base Camp; PaO2: 47 mmHg) and only a third at the summit of Mt Everest (8,848 m; PaO2: 28 mmHg). On ascent above 1,500 m, hyperventilation is first experienced. The lower levels of oxygen sensed by the kidneys trigger erythropoietin production for increased RBCs-Hb, thereby compensating for a reduced quantity of inspired oxygen and also increasing the buffer capacity of blood. After reaching ~2,100 m altitude, the saturation of oxyhaemoglobin plummets. Hyperventilation increases the reduced alveolar PaO2at high altitude and alters the acid–base status, inducing changes in the mountaineer’s blood chemistry (CO2, bicarbonates, pH). Under hypoxic conditions at the very high (extreme) altitudes of Mt Everest (PaO2: 28 mmHg), using the Van Slyke equation for sea level conditions without corrections is invalid and, hence, inappropriate. Following our previous work on acid–base balance at high altitudes, we have modified the formula for extreme altitudes and incorporated an adaptation factor. Our modified Van Slyke equation (MVSE) used for recalculating THID at 8,400 m based on mountaineers’ arterial blood sampled (the Balcony, PaO2: 24.6 mmHg) provided true acid–base status, knowledge of which makes survival at such extreme altitude possible. MVSE should enable more accurate THID monitoring and, hence, better management of pathology in residents and visitors to Lhasa (Tibet), the Andes and the South Pole (which serving personnel typically reach after a 3 h flight; the barometric pressure is typically 168.71 kPa and the physiological altitude ~3,400 m) and will benefit Everest climbers suffering from acute mountain sickness (AMS) high altitude pulmonary oedema or high altitude cerebral oedema.
Keywords: acid–base, adaptation arterial blood, altitude, base deficit, base excess, Everest, oxygen requirement, respiration, South Pole, titratable hydrogen ion difference, THID, Van Slyke equation