McPherson Duncan, Adekanye Olukorede, Wilkes Antony R, Hall Judith E
Department of Anaesthesia and Intensive Care Medicine, University Hospital of Wales, Cardiff, UK.
Anesth Analg. 2009 Apr;108(4):1198-202. doi: 10.1213/ane.0b013e3181966451.
Predicting flow through an IV cannula is useful to clinicians if changes in flow are required and to guide selection of cannula. We sought the usefulness of manufacturers' quoted flows in predicting actual flow and to characterize that flow.
We built a vein model and inserted cannulae between 14 and 20-gauge. In the first experiment, we compared the manufacturer's quoted flows using deionized water, Hartmann's solution and Gelofusine. In the second experiment, we varied the pressure feeding the cannula and measured the resulting flow.
Flow through a cannula is not a simple ratio of the manufacturers' quoted flow rate, even controlling for fluid type and feeding pressure. Flow is neither fully laminar, nor fully turbulent in the range of rates we have measured and in the International Organization for Standardization test. The Reynolds number is often below 2000.
Flow through cannulae is not laminar at the upper range of clinically used flows, therefore Poiseuille's law is not useful in predicting flow and the effect of changing radius is less than commonly believed. The quoted maximum flows are also not useful. There are many conditions for laminar flow apart from Reynolds number. Further work would determine useful predictors of flow.
如果需要改变输液流速并指导套管的选择，预测静脉输液套管的流速对临床医生很有用。我们探究了制造商公布的流速在预测实际流速方面的有用性，并对该流速进行了表征。
我们构建了一个静脉模型，并插入了14至20号的套管。在第一个实验中，我们比较了使用去离子水、哈特曼溶液和贺斯（Gelofusine）时制造商公布的流速。在第二个实验中，我们改变了输送到套管的压力，并测量了由此产生的流速。
即使控制了液体类型和输送压力，通过套管的流速也不是制造商公布流速的简单比例。在我们测量的流速范围内以及在国际标准化组织的测试中，流速既不是完全层流，也不是完全湍流。雷诺数通常低于2000。
在临床使用流速的上限范围内，通过套管的流速不是层流，因此泊肃叶定律在预测流速方面无用，并且半径变化的影响小于通常认为的那样。公布的最大流速也无用。除了雷诺数之外，还有许多层流条件。进一步的研究将确定流速的有用预测指标。
