鎮静下での気管支鏡検査における呼吸状態の検討 Respiratory Monitoring in Patients Undergoing Bronchoscopy Under Sedation

背景と目的.気管支鏡検査を受ける患者の多くは不安を抱き,検査中の鎮静を希望する.しかし,鎮静は呼吸抑制による合併症の危険がある.鎮静下での気管支鏡検査において,呼吸状態をモニターする方法としての経皮CO_2測定の有用性を検証した.方法.研究の対象患者は88名(男性52名,女性36名)で,平均年齢は67.1歳であった.気管支鏡検査はミダゾラム静脈内投与による鎮静下で行った.鎮静前後で動脈血ガス分析を行った.検査中,患者には酸素投与を行い,血圧,心電図,経皮酸素飽和度(SpO_2;パルスオキシメーター),経皮CO_2分圧(PtcCO_2)をモニターした.結果.鎮静前のPaCO_2の平均は42.8mmHgであった.PaCO_2の上昇の平均は4.9mmHgであった.PaCO_2の上昇は女性でより大きかった.年齢,体重,体重あたりのミダゾラム量,呼吸機能などとPaCO_2の変化量との間に相関は認めなかった.PaCO_2とPtcCO_2との間には,強い相関がみられた.重篤な合併症は起こらなかったが,予想外のPaCO_2の上昇を認めた症例があった.今回の対象患者の内,高度にSpO_2が低下するか15mmHg以上のPaCO_2の上昇を認めたケースでは,気管支喘息か閉塞性睡眠時無呼吸症候群が基礎疾患として認められた.結論.鎮静下での気管支鏡検査では呼吸抑制が起こる.PtcCO_2の測定は検査中の低換気を知るには有用で,経皮モニターは非侵襲的に持続的なPtcCO_2測定が可能であり,有用な機器である.

Background and Aim. The majority of patients who undergo bronchoscopy feel anxiety and discomfort. Therefore, most of them prefer to be sedated during this procedure. However, sedation has the risk of complications caused by respiratory depression. The aim of this study was to evaluate the usefulness of transcutaneous CO_2 pressure (PtcCO_2) measurement as a tool for monitoring respiratory condition during flexible bronchoscopy under sedation. Methods. We studied 88 consecutive patients who underwent bronchoscopy. They consisted of 52 men and 36 women of mean age 67.1 years. Bronchoscopy was performed under sedation with intravenous midazolam. Arterial blood gas analysis was done before and during the sedation. During the procedure, patients were given supplemental oxygen and we monitored blood pressure, electrocardiogram, pulse oximetric saturation (SpO_2) and PtcCO_2. Results. The mean baseline PaCO_2 value was 42.8mmHg. Mean change in PaCO_2 measurement from the baseline was 4.9mmHg. Mean increase of PaCO_2 was larger in women than in men. Age, body weight, midazolam dosage per body weight and the pulmonary functional factors which we examined, were all unrelated to the degree of PaCO_2 change. In this examination, PtcCO_2 values demonstrated a high degree of correlation with PaCO_2. Serious complications did not happen in any case in this study, but there were a few cases that showed unexpectedly high PaCO_2 elevation. In this investigation, patients with more than a 15 mmHg elevation of PaCO_2 from the baseline value or critical decrease of SpO_2, had bronchial asthma or obstructive sleep apnea syndrome. Conclusion. Flexible bronchoscopy performed under sedation may cause respiratory depression. PtcCO_2 measurement is useful to non-invasively and continuously evaluate hypoventilation during this procedure.