Sosis M B
Department of Anesthesiology, Rush Medical College, Chicago, IL, USA.
J Clin Anesth. 1996 Mar;8(2):110-2. doi: 10.1016/0952-8180(95)00193-x.
To predict the inspired concentrations achieved when nitrous oxide (N2O)/oxygen mixtures are administered to patients by way of a nasal cannula.
The method used for estimating the FiN2O is based on one employed to calculate the FiO2 obtained with a nasal cannula. We assume a tidal volume of 500 ml, a respiratory rate of 20 breaths per minute, an inspiratory time of 1 second, an expiratory time of 2 seconds, and an anatomic reservoir volume of 50 ml. The reservoir consists of the nose, the nasopharynx, and the oropharynx. Its volume is assumed to be one-third of the anatomic dead space. It is also assumed that during the last 0.5 second of expiration, there is negligible flow of expired respiratory gases. A 6 L/min flow from the cannula will completely fill the reservoir. The FiO2 or FiN2O is then calculated by assuming that during the 1 second inspiratory time period, the gases in the anatomic reservoir that are provided by the nasal cannula and a volume of air such that the sum of the components of the tidal volume equals 500 ml are inspired.
Research laboratory of a university-affiliated metropolitan medical center.
The calculated FiO2 values for 100% oxygen delivered by nasal cannula agree with those determined by others. The FiN2Os estimated were directly proportional to the cannula flow rate and the fraction of N2O delivered. At the maximum total flow rate considered, 6L/min flow, with 70% N2O (remainder O2) delivered to the nasal cannula, an FiN2O of only 0.21 was estimated due to the large volume of air inspired. The FiO2 under these conditions would only be 0.23.
Our analysis shows that the maximum FiN2O achievable by using a nasal cannula is limited to 0.21 even with a 6 L/min flow of 70% N2O for the defined respiratory parameters.
预测通过鼻导管向患者输送氧化亚氮（N₂O）/氧气混合气体时所达到的吸入浓度。
用于估算吸入氧化亚氮浓度（FiN₂O）的方法基于一种用于计算通过鼻导管获得的吸入氧浓度（FiO₂）的方法。我们假设潮气量为500毫升，呼吸频率为每分钟20次呼吸，吸气时间为1秒，呼气时间为2秒，以及解剖学死腔容积为50毫升。死腔包括鼻腔、鼻咽和口咽。其容积假定为解剖学死腔的三分之一。还假定在呼气的最后0.5秒内，呼出的呼吸气体流量可忽略不计。来自鼻导管的6升/分钟的流量将完全充满死腔。然后通过假设在1秒的吸气时间段内，由鼻导管提供的解剖学死腔内的气体以及一定体积的空气（使得潮气量各成分之和等于500毫升）被吸入，来计算FiO₂或FiN₂O。
一所大学附属大都市医疗中心的研究实验室。
通过鼻导管输送100%氧气时计算出的FiO₂值与其他人测定的值一致。估算出的FiN₂O与鼻导管流速和输送的N₂O分数成正比。在所考虑的最大总流速（6升/分钟流量）下，向鼻导管输送70% N₂O（其余为O₂）时，由于吸入的空气量较大，估算出的FiN₂O仅为0.21。在这些条件下FiO₂仅为0.23。
我们的分析表明，对于所定义的呼吸参数，即使以6升/分钟的流量输送70% N₂O，使用鼻导管所能达到的最大FiN₂O也限制在0.21。
