Letter to the Editor re: “Bicarbonate Values for Healthy Residents Living in Cities Above 1500 Meters of Altitude: A Theoretical Model and Systematic Review” by Ramirez-Sandoval et al. (High Alt Med Biol 2016;17:85-92)

The subject dealt with in “Bicarbonate values for healthy residents living in cities above 1500 meters of altitude: A theoretical model and systematic review” (Ramirez-Sandoval et al., 2016) is transcendental but has been dealt with before (Paulev and Zubieta-Calleja, 2005). We affirmed that the high actual bicarbonate concentration during the 1952–1953 polio epidemic in Denmark was obviously misleading, since it was the consequence rather than the cause, thus disqualifying it as an essential variable.

Our framework was based on the three variables in the Henderson–Hasselbalch equation: pH, pCO₂, and titratable hydrogen ion concentration difference (THID, a more precise term, instead of the previously known base excess [BE]). Since the pH at any altitude has to be the same as at sea level, around 7.4, and the THID likewise has to be zero at any altitude, the pCO₂ is the fundamental variable that changes at high altitude. This is why it is included in the tolerance to hypoxia formula (Zubieta-Calleja et al., 2013).

We applied correction factors to the interpretation of acid–base disorders near the summit of Mount Everest, challenging the analysis made in the interesting scientific article “Arterial Blood gases and oxygen content in climbers on Mount Everest” (Grocott et al., 2009), where sea level BE calculation was used. We showed that the acid–base status was nearly normal for the summit of Mount Everest, which made it possible to reach the summit and was not a misbalance as originally interpreted (Zubieta-Calleja et al., 2012).

Why is the venous total CO₂ used instead of the arterial PaCO₂? Venous samples are subject to misleading variations particularly at high altitude, giving false results due to peripheral vascular contraction and central vasodilation.

In table 1, it cannot be affirmed that “acclimatized residents” to the summit of Mt. Everest (8400 m) have a PaCO₂ of 17.3 mmHg and during “acute exposure” a PaCO₂ of 30.2 mmHg. How can acute exposure subjects present hypoventilation? Furthermore, in the city of La Paz (3600 m), both residents and newcomers—except those who have some difficulties in initial adaptation—have a PaCO₂ of 30 mmHg. In table 2, Lima, unexplainably, is affirmed to be at 1500 m instead of the usual 150 m. Table 3 shows La Paz, Bolivia, at 3640 m, but in reality it is between 3100 and 4100 m.

Newcomers to high altitude can present respiratory alkalosis, a transitory acid–base imbalance that has no “normal values.” Furthermore, this is not a long lasting effect as line 3 in page 5 suggests by affirming “many years.” The respiratory alkalosis is promptly corrected to a pH of 7.4 within hours or just in one or 2 days.

Citing the late Gustavo Zubieta-Castillo “The organic systems of human beings and all other species tend to adapt to any environmental change and circumstance, and never tend towards regression which would inevitably lead to death.” Hence to have reference bicarbonate values for newcomers is not useful and rather misleading.