The intra-arterial route remains the gold standard for measuring blood pressure but is not free from potential error. A major source of inaccuracy is over- or underdamping of the pressure signal. In cases of underdamping, anaesthetists often inject a small amount of air into the tubing of the arterial line to achieve optimal damping. Fine-tuning the air bubble size appropriate for optimal damping can be technically difficult. Creating an air bubble in-line with the arterial pressure measurement system is also potentially dangerous since the constant gradual flushing or any rapid flushing of the line can carry the air into the artery causing embolisation [1].

There is an alternative technique of correcting underdamping that also uses air but may be safer and easier to use in achieving close to optimal damping. The only additional equipment required is a three-way stopcock, which has to be attached to the sidearm of the three-way stopcock already present in-line with the measurement line (Fig. 1). This technique avoids the in-line air bubble, but instead achieves damping through the air pocket in the sidearm of the measurement system, the size of which is adjustable by rotating both three-way stopcocks appropriately. The suggested method allows for a stepwise adjustment in four increments of the amount of air exposed to the fluid column inside the line, thereby varying the degrees of damping. See Figure 1: stopcock position 3 most closely achieved optimal damping. Position 1 shows significant underdamping with over-reading of systolic blood pressure and superimposed oscillations, while with position 4 overdamping and loss of the dicrotic notch is observed.

A limitation of this method is that it depends on either a three-way stopcock already being present in-line with the transducing pressure line to which the second three-way stopcock can be attached, or the pressure line allowing for a disconnection and insertion of a three-way stopcock. Arterial line measurement systems from some manufacturers include only a two-way stopcock within a line in which all components are secured together as a safety feature, thereby preventing any disconnections. These devices do not permit simultaneous pressure measurement and opening of a sidearm for our suggested damping method.

动脉内途径仍然是测量血压的金标准，但也存在潜在的错误。不准确的主要来源是压力信号的过阻尼或阻尼不足。在阻尼不足的情况下，麻醉师通常会向动脉管路中注入少量空气以实现最佳阻尼。微调适合最佳阻尼的气泡尺寸在技术上是困难的。在动脉压力测量系统内产生气泡也有潜在危险，因为持续逐渐冲洗或任何快速冲洗都会将空气带入动脉，导致栓塞 [ 1 ]。

还有一种校正欠阻尼的替代技术，它也使用空气，但在实现接近最佳阻尼时可能更安全、更容易使用。唯一需要的附加设备是三通旋塞，它必须连接到已经与测量线对齐的三通旋塞的侧臂上（图 1）。这种技术避免了在线气泡，而是通过测量系统侧臂中的气穴实现阻尼，气穴的大小可以通过适当旋转两个三通旋塞来调节。建议的方法允许以四个增量逐步调整暴露于管线内流体柱的空气量，从而改变阻尼程度。参见图 1：旋塞阀位置 3 最接近实现最佳阻尼。

这种方法的局限性在于，它依赖于已经存在与第二个三通旋塞可以连接的转换压力管线串联的三通旋塞，或者允许断开和插入的压力管线三通旋塞阀。一些制造商的动脉线路测量系统在一条线路中仅包括一个双向旋塞阀，其中所有组件都固定在一起作为安全功能，从而防止任何断开。对于我们建议的阻尼方法，这些设备不允许同时进行压力测量和侧臂的打开。