Effects of respiratory rate on venous-to-arterial CO(2) tension difference in septic shock patients undergoing volume mechanical ventilation

BACKGROUND: To explore the effects of the respiratory rate (RR) on the venous-to-arterial CO(2) tension difference (gapCO(2)) in septic shock patients undergoing volume mechanical ventilation. METHODS: Adult patients with septic shock underwent volume mechanical ventilation between October 2015 and October 2016. RR was started at 10 breaths/min, and 2 breaths/min were added every 60 min until 16 breaths/min was reached. At every point, central venous and arterial blood gas measurements were obtained simultaneously. RESULTS: In this study, gapCO(2) induced by hyperventilation significantly increased, while the central venous carbon dioxide pressure (PvCO(2)) and the partial pressure of CO(2) (PaCO(2)) in arteries decreased. The decreasing trend of the PaCO(2) was more obvious than that of the PvCO(2). HCO(3)(−) and ctCO(2) were markedly decreased, when the RR was increased (P < 0.05). Central venous oxygen saturation (S(cv)O(2)) had a decreasing trend between 14 (77.1 ± 8.3%) and 16 (75.2 ± 8.7%) breaths/min; however, the difference was not significant. CONCLUSIONS: In septic patients undergoing ventilation, respiratory alkalosis induced by hyperventilation caused an increase in the gapCO(2). Clinicians should cautiously interpret the gapCO(2) in hemodynamically stable ventilated septic shock patients and its relationship with low cardiac output and inadequate perfusion.