After obtaining Institutional Ethical Committee approval and written informed consent, 178 patients ASA I/II scheduled to undergo elective Knee orthopedic surgeries under spinal anesthesia in El Kasr Al-Aini Hospital, Cairo University were enrolled into this prospective randomized controlled study, excluding patients with age less than 18 and more than 60 years, Body mass index more than 30, uncooperative patients and those with known coagulopathy. The study adheres to CONSORT guidelines.
Patients were randomized using opaque sealed envelope after enrolment into two groups, ultrasound group (group US n = 89) and conventional group (group C n = 89). Numbers in the envelope were generated by a computer-generated randomization (www.randomization.com).
Upon arrival to the operating theatre, analgesia will be given in form of fentanyl IV (0.5 ug/kg) only for those in pain associated with positioning, measurements of the baseline hemodynamic parameters will be recorded. All patients will be monitored intra-operatively using: an ECG, non-invasive blood pressure, and pulse oximetry. An infusion of a crystalloid solution will be started as a bolus of 500 ml in 10 min.
In the two groups, Patients were helped to maintain a sitting position on a leveled trolley with their feet comfortably rested. A pillow was given to hug and patients were asked to sustain an arched posture with the help of an assistant to maintain positioning. Sedation was avoided before or during carrying out spinal anesthesia.
In group (C): After positioning, landmarks were palpated and a 4-point scale varying between easy, moderate, difficult and impossible, was used to assess the ease of palpation. After palpating spinous processes in the midline, an interspinous space was selected with preference of the anesthesiologist and a mark 1.5 cm lateral and caudal to the center of the selected space was identified to spot the paramedian access. Then with strict aseptic technique including scrubbing and preparing the skin with povidone iodine, a 2 mL of 1% lidocaine was used to infiltrate the skin. A 25G whitacre spinal needle was directed medially and slightly cephalad to access the space selected in the paramedian approach with no restriction for the angle of insertion or depth reached, but with simultaneous record of the data awaited in our hypothesis. After successful puncture flagged by free flow of cerebrospinal fluid (CSF), preferred dose of local anesthetic was injected for spinal anesthesia followed by aiding the patient for desired operative position and testing the block by cold discrimination till achievement of the preferred level. In case of failure, the patient was aided to set in-order to perform the matched technique (an US guided paramedian technique) as mentioned later on. And in case of repeated failure, general anesthesia was conducted.
In group (US): After palpation of the landmarks, then using the SIEMENS (Acuson S2000) ultrasound system. The curved array low frequency transducer (2–5 MHz) was used for the scan to allow for deeper acoustic visualization. Generous amount of US gel was applied to the skin over the lumbar and sacral regions for acoustic pairing. A (pre-intervention scan) was performed combined with optimization of the view by adjusting appropriate depth and gain. The transducer was positioned longitudinally 1–2 cm lateral and parallel to the spinous processes reflecting the long axis of the vertebral column, with its orientation marker directed cephalic, also tilted slightly medially during the scan, so that the US beam is insonated in a paramedian oblique sagittal plane. The sacrum was identified by scanning caudally while still maintaining unchanged angulation. It was identified as a flat hyperechoic band with an anechoic shadow anteriorly. The bony spinous process appeared as a hyperechoic white convex rim with a deep anechoic shadow. The concavity or gap between the sacrum and the lamina of L5 was the L5/S1 intervertebral space. Identification of the L3/L4 and L4/L5 intervertebral spaces was done consequently by counting upwards. Finally the transducer was positioned over the L3/L4 and L4/L5 intervertebral spaces.
This position of the transducer was marked on the patient’s back using a skin marking pen in order to ensure that the transducer was placed on the same position after sterilization made before the intervention, also to avoid the need to repeat the guide scan done to identify the L3/4 or L4/5 intervertebral space as described above. The transducer was prepared by smearing a thin layer of US gel on its outline and covering with a sterile-transparent dressing ensuring that no air was trapped between the outline and the transparent dressing. No gel was applied directly to the skin over the area scanned as there were no data demonstrating the safety of US gel on central neuroaxial structures, but it was replaced by saline as a substitute coupling agent. Fine adjustments to the settings mentioned before were required to excel the slight deterioration in the quality of the US image lacking the US gel on the skin. Local anesthetic (lignocaine 1%) 2–3 ml was infiltrated to the skin at the caudal end of the probe. The 25G whitacre spinal needle was inserted in plane of the US transducer from the caudal end while maintaining a long axis relation with its tip directed towards the targeted interlaminar space (L3/L4 or L4/L5) which was always maintained centered on the US image. The angle of needle insertion was adjusted according to the real-time US guidance. The needle was advanced to the interlaminar space, till visualizing the engagement with the ligamentum flavum followed by the dura. Once a free flow of CSF is determined, anesthetic management was continued as mentioned before, with the alternative of introducing the (conventional landmark technique) in case of failure.
Our primary outcome was the difference in number of puncture attempts (the separate insertion of the needle through the skin) between the 2 groups needed till successful dural puncture which was noted by free flow of CSF, secondary outcomes were Landmark palpation easiness score using a four point scale (16), the visibility of the ligamentum flavum-dura mater complex by the US using a four point numerical scale (17), duration of the anesthetic procedure(the time from the handling the needle till completion of injection), number of needle redirections and puncture attempts, the incidence of paraesthesia and backache, the incidence of failure of introducing spinal anesthesia using each of the study techniques, patient’s satisfaction score regarding the anesthetic technique using a three point scale 0–2 in which (0 = dissatisfied, 1 = somewhat satisfied, 2 = satisfied), and post dural puncture headache (incidence-onset-duration-severity).
The ease of landmark palpation (palpation of the iliac crests and spinous processes) was graded on a four point scale (16):
- Easy = light palpation of iliac crests, spinous processes identified sight.
- Moderate = light to deep palpation of iliac crests, light palpation of spinous processes.
- Difficult = deep palpation of iliac crests and spinous processes.
- Impossible = iliac crests or spinous processes could not be palpated.
The visibility of the ligamentum flavum-dura mater complex by the US was graded using a four point numerical scale (17) (0: not visible, 1: hardly visible, 2: well visible, 3: very well visible). Time for marking the anatomical access: in group C was defined as time from which the anesthesiologist start palpating to identify the landmarks till marking the skin, In group US it was defined as time from which the ultrasound probe is placed on the skin till the anesthesiologist declare that the markings is completed.
Sample size calculation was done using the comparison of number of puncture attempts till successful dural puncture, as it is the primary outcome of our study. As reported in previous publication (18), the mean ±SD of number of attempts in ultrasonographic guided approach was approximately 1.28±0.7 times, while in conventional technique it was approximately 1.98±1.66 times. Accordingly, we calculated that the minimum proper sample size will be 89 patient in each group to be able to detect a real difference of 0.7 times with 80% power at α = 0.05 level using Student’s t-test for independent samples. Sample size calculation was done using MedCalc statistical software version 16.2.1 for MS Windows, MedCalc bvba, US.
Data were described statistically in expressions of mean ± standard deviation (± SD), median and range, or frequencies (number of patients) and percentages when appropriate. Comparison of numerical variables between the study groups has been done using Student t test for independent samples in comparing 2 groups when normally distributed and Mann Whitney U test for independent samples when not normally distributed. In order to compare categorical data, Chi square (χ2) test has been performed. Same test has been used as an alternative when the expected frequency is less than 5. A probability value (p value) less than 0.05 is considered statistically significant. All statistical calculations were done using computer programs Microsoft Excel 2007 (Microsoft Corporation, NY, USA) and SPSS (Statistical Package for the Social Science; SPSS Inc., Chicago, IL, USA) version 15 for Microsoft Windows.