Power Doppler Ultrasonography in Localization of Epidural Catheter

Epidural anesthesia is a widely used method for pain relief which is useful in various settings. Identification of needle entry into the epidural space (EDS) is performed most using a loss of resistance (LOR) technique, which was described in 1921 by Sicard and Forestier, and has remained largely unchanged since. Hysterectomy operations anesthesia and analgesia rely heavily on proper needle placement technique. A noninvasive approach to confirm the correct position of the epidural needle prior to injection of local anesthetics into the epidural space, would thus be beneficial. Ultrasound (US) is a noninvasive approach increasingly used in anesthesia practice. The use of color flow Doppler (CFD) may further aid in defining the epidural space. The aim of current study is to detect and confirm site of epidural catheter in hysterectomy by using color flow doppler ultrasonography.

This study will be performed in the Fayoum University hospital. The study design will be prospective study. A detailed informed consent will be signed by the eligible patients .

female patients who undergoing an ultrasound guided for hysterectomy will be included in this review. The ultrasound guided epidural will be used in those in which an anticipated technical difficult landmark epidural space localization will be expected. These included those patients with diagnosis of obesity, defined as Body Mass Index (BMI) ≥35 kg/m2, and lumbar scoliosis, as well as those with poorly defined surface lumbar bone anatomy.

Demographic data, intervertebral level of insertion, dermatome level, and failure rate of epidural needle placement using CFD will be noted for each patient. Operation will be obtained via spinal epidural technique.

Sterile preparation and dropping of the area will be followed by placement of a curvilinear ultrasound transducer in a sterile sheath. The ultrasound will be used to identify the interspinous space. The epidural needle will be guided with the use of ultrasound direction by the use of an out of plane technique.

A two-hand technique will be used to manipulate the needle and ultrasound probe.

A 17-G Tuohy needle (Braun Medical, Inc., Melsungen,AG, Germany) will be advanced until loss of resistance to normal saline will be attained.

Confirmation of the epidural space with the use of CFD will be then obtained after injection of up to 10 mL of normal saline through the epidural needle.

A 21-G epidural catheter (B. Braun Medical, Inc.) will be then threaded into the epidural space.

A 22G, 50mm needle (SONOTAP,Pajunk,Geisingen,Germany will be then advanced until CSF is obtained.

Use of intrathecal local anesthetic will be then used as a bolus in the spinal space.

After loss of resistance to normal saline, the CFD function will be turned on to examine flow through the epidural needle tip.

The ultrasound probe was positioned in the transverse axis slightly below the epidural needle but still in the interspinous space .

Two-dimensional (2D) ultrasound images will be initially obtained after making adjustments on the ultrasound system.

These include an appropriate scanning depth (6-12 cm), using the "penetration" or "general" frequency range and adjusting the gain or the time gate compensation to improve image resolution.

The CFD function will be then turned on and then the window will be adjusted to be centered over the area of interest. The authors will adjust color baseline to enhance the qualitative depiction of flow. The authors also increased color gain to amplify the appearance of flow changes. The color gain was adjusted to a level that provided the best image while avoiding the display of random color speckles. The orientation and tilt of the ultrasound probe will be essential for optimal visualization of the CFD pattern.

The best views were obtained while the probe was tilted upwards, parallel to the lumbar spinous process orientation, in order to avoid shadow interference cast by the spinous process bony structure. This maneuver will optimize the 2D view by minimizing the shadowing caused by bony structures.

The color scale will be adjusted to maximize color flow while avoiding excessive aliasing.

The best images will be best seen with a color scale on the range of 12-20 without needing to adjust the baseline.

Sample size was calculated using G-Power©️ software version 3.1.7 (Institute of experimental psychology, Heinrich Heine University, Dusseldorf, Germany).Minimal sample size of patients was (60) patients. Effect size 0.47 Depending on previous research results. Two tailed type I error 0.05 and power of 80%.

Statistical analysis will be performed using SPSS version 24.0 (IBM, Armonk, NY, USA). Data will be tested for normality using the Kolmogorov-Smirnov test. Continuous variables are presented as mean ± standard deviation (SD) or median (interquartile range) as appropriate and categorical variables are presented as number of patients (%). Parametric continuous variables will be analyzed by unpaired t-test and non-parametric continuous variables will be analyzed by Mann-Whitney U test. For categorical variables, the Chi-square (X2) test or Fisher's exact test will be used as appropriate. Two-tailed p values of 0.05 will be considered statistically significant.

Eligibility Criteria:
Inclusion Criteria:

* Women who will have hysterectomy operation under epidural analgesia
* Women with the epidural catheter still in place
* American Society of Anesthesiologists (ASA) physical status I, II
* Age range from 30 and 70 years.

Exclusion Criteria:

* Patient refusal
* History of allergy to one of the study drugs.
* Any contraindication to regional anesthesia such as local infection or bleeding disorders