de Gray L, Rush E M, Jones J G
Department of Anaesthesia, Ipswich Hospital NHS Trust, UK.
Anaesthesia. 1997 Jul;52(7):630-5. doi: 10.1111/j.1365-2044.1997.153-az0159.x.
A new noninvasive method was used to evaluate gas exchange in 12 patients undergoing thoracotomy for a variety of surgical procedures. A plot of inspired oxygen partial pressure versus oxygen saturation was analysed to calculate the independent contribution of shunt and intermediate ventilation/perfusion ratio which occurs during general anaesthesia for thoracotomy. A model based on the inspired to arterial oxygen difference involving the shunt equation was used to show how the relationship between inspired oxygen partial pressure and oxygen saturation could be used to derive two parameters of oxygen exchange, the virtual shunt and an index of low ventilation/perfusion ratio. In all cases, there was a very good fit of the data to the model. Thoracotomy caused a mean increase in shunt from 13.8% to 20.8% and a worsening ventilation/perfusion ratio from 0.5 to 0.2, the magnitude of which depended on the underlying pathology. In two patients, the ventilation/perfusion ratio decreased to less than 0.1. The method enables the prediction of oxygen saturation at different inspired oxygen partial pressures and allows the two components of gas exchange to be isolated using simple routine measurements of inspired oxygen and pulse oximetry.
一种新的非侵入性方法被用于评估12例因各种外科手术而接受开胸手术患者的气体交换情况。分析吸入氧分压与氧饱和度的关系图，以计算开胸手术全身麻醉期间分流和中间通气/灌注比的独立贡献。基于涉及分流方程的吸入动脉氧分压差的模型，用于展示吸入氧分压与氧饱和度之间的关系如何用于推导氧交换的两个参数，即虚拟分流和低通气/灌注比指数。在所有病例中，数据与模型拟合良好。开胸手术导致分流平均从13.8%增加到20.8%，通气/灌注比从0.5恶化到0.2，其幅度取决于潜在病理情况。在两名患者中，通气/灌注比降至低于0.1。该方法能够预测不同吸入氧分压下的氧饱和度，并允许使用吸入氧和脉搏血氧饱和度的简单常规测量来分离气体交换的两个组成部分。
