Influence of hypercapnia on circulatory response to endotracheal intubation

: Effects of CO2 on circulatory responses to laryngoscopy and endotracheal intubation were investigated in 16 patients under constant depth of enflurane anesthesia (1.2MAC) at different levels of CO2 (normocapnia, PETCO2: 40mmHg or hypercapnia, PETCO2: 60mmHg). Patients were randomly divided into two groups; normocapnia group (n = 8) and hypercapnia group (n = 8). Although there was no significant difference in blood pressure response to laryngoscopy and endotracheal intubation between normocapnic and hypercapnic groups, heart rate response was significantly attenuated in hypercapnic group and the latent period between the start of laryngoscopy and the onset of increase in heart rate was significantly longer in hypercapnic group. Our results suggest that hypercapnia exerts inhibitory influence on heart rate responses to laryngoscopy and endotracheal intubation.