Tissue Blood Flow During Remifentanil Infusion With Carbon Dioxide Loading

The aim of this study was to investigate the effect of changes in end-tidal carbon dioxide tension (ETCO₂) during remifentanil (Remi) infusion on oral tissue blood flow in rabbits. Eight male tracheotomized Japan White rabbits were anesthetized with sevoflurane under mechanical ventilation. The infusion rate of Remi was 0.4 μg/kg/min. Carbon dioxide was added to the inspired gas to change the inspired CO₂ tension to prevent changes in the ventilating condition. Observed variables were systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), heart rate (HR), common carotid artery blood flow (CCBF), tongue mucosal blood flow (TBF), mandibular bone marrow tissue blood flow (BBF), masseter muscle tissue blood flow (MBF), upper alveolar tissue blood flow (UBF), and lower alveolar tissue blood flow (LBF). The CCBF, TBF, BBF, UBF, and LBF values were increased, while MBF was decreased, under hypercapnia, and vice versa. The BBF, UBF, and LBF values were increased, while the MBF value was decreased, under hypercapnia during Remi infusion, and vice versa. The BBF, MBF, UBF, and LBF values, but not the CCBF and TBF values, changed along with ETCO₂ changes during Remi infusion.Key Words: Remifentanil, Oral tissue blood flow, Hypercapnia, Hypocapnia, End-tidal carbon dioxideThe oral region comprises mucosa and bone marrow, which include abundant vessels. Control of bleeding during oral and maxillofacial surgery is therefore important to establish a clear surgical field, to avoid blood transfusion, and to secure rapid postoperative recovery. Deliberate hypotension is a conventional method to reduce tissue blood flow during oral and maxillofacial surgery.^1–4 However, some reports pointed out that this technique may cause brain injury and other complications.^5,6Accordingly, we have researched another approach to control tissue blood flow in the oral region during general anesthesia. Handa et al⁷ reported that hypercapnia increases common carotid artery blood flow (CCBF) and mandibular bone marrow tissue blood flow (BBF), while it decreases masseter muscle tissue blood flow (MBF). Kemmochi et al⁸ reported that remifentanil (Remi) decreases CCBF and BBF without a substantial reduction of blood pressure. Koshika et al⁹ reported that Remi decreases tongue mucosal blood flow (TBF), BBF, MBF, upper alveolar tissue blood flow (UBF), and lower alveolar tissue blood flow (LBF) in a dose-dependent manner and that a Remi infusion at a rate of 0.2 μg/kg/min decreases oral tissue blood flow without a substantial reduction of heart rate (HR) and blood pressure. Based on these findings, we suppose that changes in tissue blood flow may be modified by changes in arterial carbon dioxide level during Remi infusion. However, there has been no report that investigates the effect of a combination of Remi infusion and the change in arterial carbon dioxide level on oral tissue blood flow. In this study, therefore, we investigated the effect of changes in end-tidal carbon dioxide tension (ETCO₂) during Remi infusion on oral tissue blood flow in rabbits.