Distributed strain sensing optical guidance for epidural anesthesia

Epidural anesthesia is the most diffused clinical practice described as a placement of a medical needle into an epidural space, an insertion of a catheter through the needle and an injection of anesthetic in order to numb the nerves. A skilled anesthesiologist penetrates the needle through tissue layers such as subcutaneous fat, interspinous ligament, intraspinous ligament, ligamentum flavum and reaches the target space. Currently, methods of positioning of the needle tip into the epidural space are based on subjective perception, which are not safe and accurate. In order to improve the effectiveness of the epidural space identification, this work proposes a sensorized optical fiber mounted externally on the needle. This medical device provides continuous and real-Time measurements with the help of an optical backscattered reflectometry. When the needle is exposed to strain variations during its advancement, the intensity of backscattered light changes. By correlating the spectrum with the reference one, strain patterns can be produced. Obtained data can detect the needle passage from one tissue to the other in a custom made phantom, which mimics a human spinal anatomy. Specifically, needle passage from the stiff ligamentum flavum to the soft epidural space results in a significant strain drop and a consequent increase, which is considered as a crucial indicator of epidural space identification. The proposed device is advantageous over existing optical guidance: it does not obstruct the flow of a liquid in the inner side of the needle; the needle from the tip to the tail performs as a sensor.