手術房麻醉人員之麻醉廢氣暴露濃度評估

Personnel Exposure to Waste Sevoflurane and Nitrous Oxide during General Anesthesia with Cuffed Endotracheal Tube

背景：根據相關研究報告顯示，麻醉廢氣可能危害手術房麻醉人員的健康，為降低麻醉廢氣造成的健康風險，美國職業安全衛生研究所(US-NIOSH)對常用的麻醉氣體訂定其暴露容許濃度，其中N20的平均容許濃度為25 ppm，而其他揮發性麻醉劑（如sevoflurane, isoflurane, desflurane, enflurane and halothane)建議最高容許濃度為2 ppm。方法：為評估國內麻醉人員對麻醉廢氣的暴露狀況，本研究使用抽氣式霍氏紅外光譜儀(extractive FTIR)量測麻醉人員於手術過程中麻醉廢氣的暴露情形；本研究中，麻醉過程對病人的誘導採靜脈注射，而麻醉維持則利用具有袖帶之氣管內管(cuffed endotracheal tube)將11/min的N2O、11/min的02和2.5％的sevoflurane (SEV)導進病人的呼吸系統。結果：在正常的麻醉過程，麻醉人員對N20的平均暴露濃度為31.5 ppm，而對SEV最高暴露濃度值僅為1.45 ppm；然而，在催醒前麻醉機器管路的迫淨，造成N20與SEV的暴露濃度分別提高至751 ppm與26 ppm。另外，氣管內管袖帶之不完全充氣、麻醉機器廢氣管路與醫院排氣系統間的接頭脫落，皆造成麻醉廢氣濃度的嚴重升高。結論：為避免N20的健康危害，在麻醉過程中應盡量減少其使用；同時，(1)麻醉機器管路的迫淨、(2)氣管內管袖帶之不完全充氣與(3)麻醉機器廢氣管路與醫院排氣系統間的接頭脫落等三種不當操作應避免發生，以維護手術房內人員的健康。

Background: Waste anesthetic gases may have adverse effects on the health of operating room personnel. To reduce the risk of exposure, the United States National Institute of Occupational Safety and Health (US-NIOSH) recommends a time-weighted average (TWA) of 25 ppm (part-per-million) for nitrous oxide (N2O) and a ceiling of 2 ppm for sevoflurane (SEV). This study investigated the concentrations of these two gases in the atmosphere of operating room to which the working personnel (anesthetists) were exposed during anesthetic practice. Methods: An extractive Fourier transform infrared (FTIR) spectrometer, with an optical path length of 10 meters, was used to monitor the concentrations of waste general anesthetics in the operating rooms. The FTIR in application could simultaneously determine the concentrations of several gases in a near real-time manner, which helped to accurately obtain the varying concentrations of gases in different anesthetic condition. The sampling Teflon tube of the FTIR was conveniently installed in the breathing zone of the anesthetic personnel to obtain the personal exposure concentrations of N2O and SEV. Results: Nitrous oxide (N2O) and sevoflurane (SEV) concentrations for five surgeries in four different operating rooms were determined. In normal condition during maintenance, the SEV concentrations as measured were less than 2 ppm but the average N2O concentration was greater than 25 ppm. In addition, in three abnormal or specific conditions, the N2O and SEV concentrations increased dramatically. Firstly, at the end of maintenance (right before emergence), peak concentrations of 751 ppm for N2O and 26 ppm for SEV were measured. These unusually high concentrations resulted from flushing the tubing of the anesthetic machine to speed up the emergence of wakefulness of the patient from anesthesia. Secondly, when the cuff of the endotracheal tube was not well inflated or unserviceable, peak concentrations of 631 ppm for N2O and 32 ppm for SEV were measured. Thirdly, malfunction of or loose connection (or disconnection) between the anesthetic machine and the exhaust venting system of operating theater almost doubled the N2O and SEV concentrations. Conclusions: To decrease the exposure of the operating personnel to waste anesthetics, minimization of the use of N2O is recommended. Besides, the three extraordinary conditions as disclosed in this study were tubing flushing, illy managed endotracheal tube cuff and disconnection of scarvenging system, the first of which sometimes is unavoidable but the last two of which should be avoided.