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Methods for evaluation of helium/oxygen delivery through non-rebreather facemasks

机译：通过非循环呼吸口罩评估氦气/氧气输送的方法

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Background Inhalation of low-density helium/oxygen mixtures has been used both to lower the airway resistance and work of breathing of patients with obstructive lung disease and to transport pharmaceutical aerosols to obstructed lung regions. However, recent clinical investigations have highlighted the potential for entrainment of room air to dilute helium/oxygen mixtures delivered through non-rebreather facemasks, thereby increasing the density of the inhaled gas mixture and limiting intended therapeutic effects. This article describes the development of benchtop methods using face models for evaluating delivery of helium/oxygen mixtures through facemasks. Methods Four face models were used: a flat plate, a glass head manikin, and two face manikins normally used in life support training. A mechanical test lung and ventilator were employed to simulate spontaneous breathing during delivery of 78/22 %vol helium/oxygen through non-rebreather facemasks. Based on comparison of inhaled helium concentrations with available clinical data, one face model was selected for measurements made during delivery of 78/22 or 65/35 %vol helium/oxygen through three different masks as tidal volume varied between 500 and 750?ml, respiratory rate between 14 and 30 breaths/min, the inspiratory/expiratory ratio between 1/2 and 1/1, and the supply gas flow rate between 4 and 15?l/min. Inhaled helium concentrations were measured both with a thermal conductivity analyzer and using a novel flow resistance method. Results Face models borrowed from life support training provided reasonably good agreement with available clinical data. After normalizing for the concentration of helium in the supply gas, no difference was noted in the extent of room air entrainment when delivering 78/22 versus 65/35 %vol helium/oxygen. For a given mask fitted to the face in a reproducible manner, delivered helium concentrations were primarily determined by the ratio of supply gas flow rate to simulated patient minute ventilation, with the inspiratory/expiratory ratio playing a secondary role. However, the functional dependence of helium concentration on these two ratios depended on the mask design. Conclusions Large differences in mask performance were identified. With continued refinement, the availability of reliable benchtop methods is expected to assist in the development and selection of patient interfaces for delivery of helium/oxygen and other medical gases.
机译：背景技术低密度氦气/氧气混合物的吸入已被用于降低阻塞性肺疾病患者的气道阻力和呼吸功，并将药物气雾剂输送到阻塞性肺区域。然而，最近的临床研究强调了夹带室内空气以稀释通过非循环呼吸器面罩输送的氦气/氧气混合物的可能性，从而增加了吸入气体混合物的密度并限制了预期的治疗效果。本文介绍了使用面部模型评估通过面罩输送氦/氧混合物的台式方法的发展。方法使用四种面部模型：平板，玻璃头人体模型和两个通常用于生命维持训练的面部模型。使用机械测试肺和呼吸机模拟通过非循环呼吸器面罩输送78/22％vol的氦气/氧气期间的自发呼吸。根据吸入的氦气浓度与现有临床数据的比较，当潮气量在500至750？ml之间变化时，选择了一种面部模型，用于通过三种不同的面罩输送78/22或65/35％vol的氦气/氧气时进行的测量，呼吸频率在14到30次呼吸/分钟之间，吸气/呼气比率在1/2到1/1之间，供气流速在4到15？l / min之间。吸入氦气的浓度可通过热导仪和新型流阻法进行测量。结果从生活支持培训中借用的面部模型与可用的临床数据具有相当好的一致性。将供气中的氦气浓度归一化后，在输送78/22％体积的氦气/氧气与65/35％体积的氦气/氧气时，室内空气的夹带程度没有差异。对于以可重现方式安装在面部上的给定面罩，输送的氦气浓度主要由供气流速与模拟患者分钟通气量之比确定，吸气/呼气比起次要作用。但是，氦气浓度对这两个比率的功能依赖性取决于掩模的设计。结论确定了口罩性能的巨大差异。随着不断的完善，可靠的台式方法有望帮助开发和选择用于输送氦气/氧气和其他医用气体的患者接口。

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