To observe the arterial and central venous blood gas changes in patients with normal cardiopulmonary function in Xining area to measure the reference values of central venous oxygen saturation (ScvO₂), central venous minus arterial carbon dioxide pressure (Pcv-aCO₂), and Pcv-aCO₂-to-arterial minus central venous oxygen content ratio (Pcv-aCO₂/Ca-cvO₂) in Xining area.

The clinical data of 64 volunteers who were hospitalized at Qinghai Provincial People's Hospital from April 1, 2019 to December 31, 2020 were collected. And the indexes of arterial and central venous blood gas analysis were also collected from volunteers without oxygen inhalation. The results of arterial and venous blood gas analysis among different regions/altitudes were compared.

The pH, partial pressure of carbon dioxide (PCO₂), partial pressure of oxygen (PO₂), Ca²⁺, lactic acid (Lac), HCO₃^-, base excess (BE), and saturation of peripheral oxygen (SO₂) differed significantly between venous blood and arterial blood of patients from Xining (P＜0.05 for all). The pH and PCO₂ in arterial blood of patients from Xining were significantly different from those in Kunming (P＜0.05 for all). The PCO₂, PO₂, BE, and SO₂ in arterial blood of patients from Xining were all significantly different from those in Tibet (P＜0.05 for all). The PCO₂, PO₂, and SO₂ in arterial blood of patients from Xining were significantly different from those in Los Angeles (P＜0.05 for all). The PCO₂, PO₂, and SO₂ in venous blood of patients from Xining were significantly different from those in Los Angeles (P＜0.05 for all). The Pcv-aCO₂ in Xining was (9±3) mmHg, which was significantly different from that at low altitude (6 mmHg; P＜0.05). The Pcv-aCO₂/Ca-cvO₂ in Xining was 1.864±0.792.

The arterial and central venous blood gas parameters in the population from medium altitude regions are not completely consistent with those from low altitude regions. ScvO₂ significantly decreases in the population from medium altitude regions.