Rosenbaum Abraham, Breen Peter H
Department of Anesthesiology, UCI Medical Center, University of California, Irvine, Building 53, Room 227, 101 The City Drive South, Orange, CA 92868, USA.
J Clin Monit Comput. 2007 Jun;21(3):137-46. doi: 10.1007/s10877-006-9065-5. Epub 2007 Mar 16.
Measurement of oxygen uptake (Vo2) should help detect non-steady state critical events and metabolic derangement during anesthesia. Vo2 requires measurement of respiratory relative humidity (RH) and temperature (T). We have developed a fast response T and humidity sensor (HS), which uses tiny wet and dry thermometers to determine RH by psychrometry, where low RH causes evaporation to decrease wet T below dry T. In laboratory bench studies, we determined that >/=5 l/min gas flow through the HS is required for valid psychrometry function. This study demonstrates that monitoring of flow through the HS enhances the accuracy of RH measurement and interpretation.
Phase One: Laboratory bench validation; We designed a special bench setup for the validation of metabolic gas exchange compared to precise ethanol combustion. Phase 2: Clinical study; During mechanical ventilation of 6 anesthetized surgical patients, airway flow was used to successfully select valid wet T and dry T during inspiration and expiration, from which respective RH's were calculated using principles of psychrometry.
The average (+/-SD) percent error for airway Vco2 (compared to the stoichiometric value) was -1.84 +/- 2.69% (Table 2). The average (+/-SD) percent error for airway Vo2 was 0.91 +/- 3.10%. Average RQ was 0.649 +/- 0.017. For all patients, average inspired RH was 36.1 +/- 11.8% (range of 17-52%), which differed significantly from expiration (103 +/- 9%). Among the 6-8 consecutive breaths for each patient, average standard deviations of expired RH were only 0.6%.
We conclude that airway flow monitoring enhances the interpretation and accuracy of the fast-response HS measurements during inspiration and expiration, allowing for the determination of Vo2 in patients during anesthesia.
测量氧摄取量（Vo2）应有助于检测麻醉期间的非稳态关键事件和代谢紊乱。Vo2需要测量呼吸相对湿度（RH）和温度（T）。我们开发了一种快速响应的T和湿度传感器（HS），它使用微小的干湿温度计通过干湿球湿度计法来确定RH，其中低RH会导致蒸发，使湿球温度低于干球温度。在实验室台架研究中，我们确定通过HS的气体流量≥5升/分钟是有效干湿球湿度计功能所必需的。本研究表明，监测通过HS的流量可提高RH测量和解释的准确性。
第一阶段：实验室台架验证；我们设计了一种特殊的台架装置，用于与精确的乙醇燃烧相比验证代谢气体交换。第二阶段：临床研究；在对6名麻醉手术患者进行机械通气期间，利用气道流量成功地在吸气和呼气期间选择有效的湿球温度和干球温度，并根据干湿球湿度计原理计算各自的RH。
气道Vco2的平均（±标准差）百分比误差（与化学计量值相比）为-1.84±2.69%（表2）。气道Vo2的平均（±标准差）百分比误差为0.91±3.10%。平均呼吸商为0.649±0.017。对于所有患者，平均吸入RH为36.1±11.8%（范围为[X]17 - 52%），与呼气时（103±9%）有显著差异。在每位患者连续6 - 8次呼吸中，呼出RH的平均标准差仅为0.6%。
我们得出结论，气道流量监测可提高快速响应HS在吸气和呼气期间测量的解释和准确性，从而能够在麻醉期间测定患者体内的Vo2。
