Ron Howard.
The High Altitude Diagram shows the relationship between the blood’s acidity (pH), respiration component (PCO2), and metabolism component (Base Excess) for a selected High Altitude. It is the Sea Level Diagram developed for use at the Local High Altitude to provide the appropriate values for the PCO2 and Altitude Base Excess (ABE).
Hypoxemic Threshold: Specific receptors in the Carotid Body detect low PaO2 levels (hypoxemia) to stimulate ventilation and lower the PCO2. The threshold varies with individuals but above 1500 meters (4920 feet)1, people are normally Altitude-Adapted with a low PCO2. This is the threshold altitude chosen for this high altitude diagram.
Notes:
Adaptation: In 1925 Barcroft claimed that around 4500 meters (or 14,800 ft): “All dwellers at high altitude are persons of impaired physical and mental powers”.2 However, this claim was disputed and more than 200 million people live at altitudes above 2,500 meters.3 Indeed, at moderately high altitude people are normally Altitude-Adapted and healthy with a decreased risk of postoperative pneumonia4 and a prolonged life-expectancy.5,6
Normal Values: The pH remains normal (pH = 7.4) because Metabolic acidosis balances the low PCO2 (Respiratory alkalosis). Both are appropriate for the altitude and neither of them requires treatment, i.e., Altitude Base Excess is normal (0 mMol/L).7 Because the exact values depend on altitude, the appropriate altitude diagram is essential when assessing a patient, planning the treatment, and observing progress. The original Sea-Level Zones8 have been relocated to suit the altitude.9 “Base Excess” is an appropriate part of the name because it is familiar when evaluating metabolic progress and treatment.
Diagram Explanation:
A pH of 7.4 with a PCO2 of 27 mmHg (3.6 kPa) is normally reported as respiratory alkalosis fully compensated by metabolic acidosis (Standard Base Excess of -7 mMol/L). However, for an Altitude-Adapted person living at 4,500 meters (14,760 ft) the same values are normal.
Observe the diagram here to see both versions. The abnormality at Sea Level moves to the central, normal location on the High Altitude version. This provides the target for therapy. The relationship to all of the abnormal zones is now preserved which helps when recognizing compensation or additional abnormalities.
Acknowledgement:
I am deeply indebted to Iván Solarte MD, MHPE. Full Professor, School of Medicine, Pontificia Universidad Javeriana, Respiratory Medicine Unit, Hospital Universitario San Ignacio. Bogotá Colombia. He persuaded me to modify the original sea-level version. Neither of us appreciated the magnitude of this undertaking; it occupied me for several weeks. In addition to his stimulus, he provided diagrams and equations, as well as several helpful ideas and corrections.
References:
1 Zubieta-Calleja G,Jr, Paulev PE, Mehrishi JN, and Zubieta-Calleja G,Sr. 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. Journal of Biological Physics and Chemistry 2012; 12:103-112.
2 Barcroft J. The Respiratory function of the blood. Part I. Lessons from high altitudes. 1925; Cambridge University Press, Cambridge, UK.
3 Zubieta-Calleja G, Zubieta-Calleja L, Ardaya-Zubieta G, and Paulev PE. Do Over 200 Million Healthy Altitude Residents Really Suffer from Chronic Acid–Base Disorders? Indian J Clin Biochem 2011; 26(1):62–65.
4 West JB. High Life. Association of Hospital Altitude and Postoperative Infectious Complications After Major Operations. Aasen DM, Wiedel C, Maroni P, Cohen ME, Meng X, and Meguid RA. High Altitude Medicine & Biology 2019; Dec:421-426. (http://doi.org/10.1089/ham.2019.0062)
5 Ezzati M, Horwitz MEM, Thomas DSK, Friedman AB, Roach R, Clark T, Murray CJL, Honigman B. Altitude, life expectancy and mortality from ischaemic heart disease, stroke, COPD and cancers: national population-based analysis of US counties. J Epidemiol Community Health 2012; 66:e17–e17.
6 Zubieta-Calleja GR, Zubieta-DeUrioste NA. Extended longevity at high altitude: Benefits of exposure to chronic hypoxia. BLDE University Journal of Health Sciences 2017; 2:2:80-90.
7 Acevado LE, Solarte I. Gasimetria arterial en adultos jovenes a nivel de Bogata. Acta Médica Colombiana 1984; 9:1-14.
8 Schlichtig R, Grogono AW, Severinghaus JW. “Human PaCO2 and standard base excess compensation for acid-base imbalance.” Critical Care Medicine 1998; 26:1173-1179.
9 Paulev PE, and Zubieta-Calleja GR. “Essentials in the Diagnosis of Acid-Base Disorders and their High Altitude Application”. J Physiol Pharmacol 2005; 56 Suppl 4:155-70.