Abstract
Incorrect needle placement during an epidural block causes medical complications such as dural puncture or spinal cord injury. We propose a system combining an optical coherence tomography imaging probe with an automatic identification algorithm to objectively identify the epidural needle-tip position and thus reduce complications during epidural needle insertion. Eight quantitative features were extracted from each two-dimensional optical coherence tomography image during insertion of the needle tip from the skin surface to the epidural space. 847 in vivo optical coherence tomography images were obtained from three anesthetized piglets. The area under the receiver operating characteristic curve was used to quantify the discriminative ability of each feature. We found a combination of six image features-mean value of intensity, mean value with depth, entropy, mean absolute deviation, root mean square, and standard deviation-showed the highest differentiating performance with the shortest processing time. Finally, differentiation of the needle tip inside or outside the epidural space was automatically evaluated using five classifiers: k-nearest neighbor, linear discriminant analysis, quadratic discriminant analysis, linear support vector machines, and quadratic support vector machine. We adopted an 8-fold cross-validation strategy with five classifications. Quadratic support vector machine classification showed the highest sensitivity (97.5%), specificity (95%), and accuracy (96.2%) among the five classifiers. This study provides an intelligent method for objective identification of the epidural space that can increase the success rate of epidural needle insertion.
Highlights
Epidural blockade is an effective anaesthesia and analgesia technique which is widely applied in neuraxial anaesthesia, labour analgesia, and acute and chronic pain therapy
Only 282 OCT images were selected in each trajectory path, including those for the muscle, ligamentum flavum (LF), and epidural space (ES) tissues; it corresponds to 10 images acquired per 1 mm distance
The light scattering from the LF is stronger than that in muscle; this may be because the LF tissue is mainly comprised of elastin, which is far denser than muscle tissue
Summary
Epidural blockade is an effective anaesthesia and analgesia technique which is widely applied in neuraxial anaesthesia, labour analgesia, and acute and chronic pain therapy. Epidural blockade procedures are estimated to account for 10% of all anaesthetic procedures worldwide. The epidural space (ES) is located between the ligamentum flavum (LF) and the dura mater and has a thickness ranging from 2 to 6 mm. The loss of resistance (LOR) method with air or saline is the standard method for epidural administration [1]. LOR is highly dependent on the operator’s experience, and learning to place the needle competently requires practice over an average of 60-90 epidural placement procedures [2]. The epidural technique using LOR is associated with a total failure rate of up to 10% [3,4]. Investigators have used optical reflectance [5,6], optical spectrum [7], ultrasound [8], and nerve stimulation [9] to improve the accuracy of needle placement
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