Spinal Anesthesia in Patients With Poorly-palpable Surface Landmarks
Spinal Anesthesia in Patients With Poorly-palpable Surface Landmarks
Anesthesia trainees can perform spinal anesthesia in patients who have poorly-palpable
 surface landmarks with fewer needle passes using an ultrasound-guided technique compared to
 the conventional surface landmark-guided technique.
Neuraxial blockade has traditionally been accomplished using a surface landmark-guided
 technique, in which the approximate location of the neuraxial midline, lumbar interspinous
 and interlaminar spaces are determined based on palpation of the intercristal line and the
 tips of the spinous processes. It is not surprising, therefore, that the technical difficulty
 of neuraxial blockade (usually measured in terms of the number of needle passes required for
 success) correlates with the quality of palpable surface landmarks.

 Reducing the technical difficulty of neuraxial blockade is desirable as multiple needle
 insertion attempts may increase the risk of complications such as post-dural puncture
 headache, paresthesiae, and epidural hematoma. Ultrasound (US) imaging of the spine can help
 in this regard by more precisely identifying landmarks, determining the intervertebral level,
 and measuring the depth to the epidural space. It has been shown to facilitate the
 performance of neuraxial block in the obstetric population, and our group has also
 demonstrated similar benefits in the older non-obstetric population. In a feasibility study
 of US-guided spinal anesthesia for total joint replacement surgery, achieved successful
 spinal anesthesia with a single needle insertion attempt in 84% of these patients, despite
 the fact that nearly half of them had poorly palpable surface landmarks.This compares well
 with large prospective cohort studies which report successful neuraxial blockade on the first
 needle insertion attempt in 61-64% of all patients. Investigators recently completed a
 randomized controlled trial in which 120 patients with difficult anatomical landmarks
 (defined as poorly palpable surface landmarks and a BMI>35 kgm-2, significant spinal
 deformity, or spinal surgery resulting in distortion or absence of surface landmarks)
 received spinal anesthesia performed by experienced anesthesiologists using either a
 conventional surface landmark-guided technique or an US-guided technique. There was a
 two-fold difference between the US-guided group and the control group in the first-attempt
 success rate (62% vs 32%, P<0.001), and the median number of needle passes required for
 success (6 vs 13, P=0.003).

 The main limitation of all clinical studies conducted to date on US-guided neuraxial block is
 that ultrasound imaging was performed solely by experienced operators; although in two
 studies the neuraxial block itself (but not the ultrasound scan) was performed by trainees.

 Investigators believe that the benefits of the US-guided technique can be realized when it is
 performed in its entirety by novices, e.g. anesthesia trainees. Investigators therefore
 designed this study to establish if novices are able to use the US-guided technique to
 facilitate the performance of spinal anesthesia in obese patients with poorly-palpable
 landmarks.
Inclusion Criteria:

 -  Patients presenting for elective total hip or knee replacement under spinal anesthesia
 who have poorly palpable or impalpable spinous processes

 -  BMI ≥ 35 kgm-2

 Exclusion Criteria:

 -  Inability or refusal to provide informed consent,

 -  Bleeding diathesis,

 -  Allergy to local anesthetics

 -  Contra-indication to spinal anesthesia