Bicarbonate Values for Healthy Residents Living in Cities Above 1500 Meters of Altitude: A Theoretical Model and Systematic Review.

Plasma bicarbonate (HCO3-) concentration is the main value used to assess the metabolic component of the acid-base status. There is limited information regarding plasma HCO3- values adjusted for altitude for people living in cities at high altitude defined as 1500 m (4921 ft) or more above sea level. Our aim was to estimate the plasma HCO3- concentration in residents of cities at these altitudes using a theoretical model and compare these values with HCO3- values found on a systematic review, and with those venous CO2 values obtained in a sample of 633 healthy individuals living at an altitude of 2240 m (7350 ft). We calculated the PCO2 using linear regression models and calculated plasma HCO3- according to the Henderson-Hasselbalch equation. Results show that HCO3- concentration falls as the altitude of the cities increase. For each 1000 m of altitude above sea level, HCO3- decreases to 0.55 and 1.5 mEq/L in subjects living at sea level with acute exposure to altitude and in subjects acclimatized to altitude, respectively. Estimated HCO3- values from the theoretical model were not different to HCO3- values found in publications of a systematic review or with venous total CO2 measurements in our sample. Altitude has to be taken into consideration in the calculation of HCO3- concentrations in cities above 1500 m to avoid an overdiagnosis of acid-base disorders in a given individual.