Comparison of Conventional Landmark Guided Midline (Group C) Versus Pre-procedural Ultrasound Guided Paramedian at L5S1 (Group P) Technique for Spinal Anaesthesia

This will be a prospective, randomised, controlled study. All consented patients scheduled to undergo elective total knee or total hip arthroplasty under spinal anesthesia will be included in the study. A written informed consent will be obtained from all patients participating in the study. Patients with contraindications to spinal anesthesia (allergy to local anesthetic, coagulopathy, local infection and indeterminate neurological disease) will be excluded from the study.

The patients will be randomised using random number generating software (Research Randomizer Version 4.0 ) to undergo either conventional landmark-guided spinal anesthesia (Group C) or pre-procedural ultrasound-guided paramedian L5S1 spinal (Group P). Group allocation will be concealed by enclosing the codes in a sealed opaque envelope and will be seen by the attending anesthesiologist immediately before performing the procedure. Patients will be blinded as to their allocated study group.

In both groups, spinal anesthesia will be performed by one of three consultant anesthesiologists (FL, PL, GI), each having performed more than 75 neuraxial ultrasound scans prior to the study. On arrival to the anesthesia induction room baseline monitoring (non-invasive blood pressure, pulse oximetry and 3 lead ECG) and intravenous access will be established. The patients will be then positioned sitting on a level trolley with feet resting on a foot rest. They will be given a pillow to hug and requested to maintain an arched back posture with an assistant holding the patient to aid positioning.

In group C, the anesthesiologist will palpate the landmarks after positioning and graded the ease of palpation on a 4 point scale (easy, moderate, difficult or impossible) as described in previous studies.10 Strict asepsis will be followed throughout the procedure with anesthesiologist scrubbed prior to procedure, wearing mask and sterile gloves. The skin will be prepped with 2% Chlorhexidine (Chloraprep 3 ml applicator, CareFusion Corporation, San Diego, CA 92130,USA) following which 2-5 ml of 1% lidocaine will be used to infiltrate the skin. The anesthesiologist performing the spinal technique will be allowed to choose the appropriate needle length ( 90 or 119 mm 25 G Whitacre needle, Becton, Dickinson and Company, Franklin Lakes, New Jersey, 07417-1880, USA), gauge (25 or 22G), depth and angle of insertion. Hyperbaric bupivacaine will be used in both groups. After completion of spinal anesthetic injection, and positioning the patient in lateral decubitus, ultrasound will be used to identify the interspinous level at which the injection will be administered.

In group P, a portable ultrasound unit with a curved 2-5 MHz probe will be used for initial pre-procedural marking. A paramedian sagittal oblique view of the neuraxis will be obtained and the sacrum will be identified, following which the interlaminar space between L5 and S1 will be noted. At this interspace with the probe positioned to obtain the clearest ultrasound image of the anterior complex (ligamentum flavum dura complex- LFD) and posterior complex (posterior longitudinal ligament- PLL) possible, a skin marker will be used to mark the midpoint of the long border of the probe and the midpoints of the short borders of the probe. The medial angulation of the probe will also be noted to guide the insertion of the spinal needle. At the same horizontal level as the midpoint of the long border of the probe, the midpoint of the line drawn between the two short border midpoints of the probe will be used as paramedian insertion point for the spinal needle. A transverse median (TM) view at the same level will also be obtained and the midline will be marked. This marking will be used to aid the medial angulation of the spinal needle. Both PSO and TM views would be graded as good (both LFD and PLL visible), intermediate (either LFD or PLL visible) and poor (both LFD and PLL not visible).15 Following skin marking, care will be taken to make sure that the needle entry site will be free of ultrasound gel prior to needle insertion. In group P, the anesthesiologist will not palpate the landmarks for grading until the spinal injection is complete. Spinal anesthesia will be performed in the same aseptic manner as mentioned earlier.