Accuracy of identification of intervertebral spaces through manual palpation by anaesthesiology trainees and comparison with ultrasound and c arm guidance imaging; a prospective observational study

Identification of intervertebral space level is an essential step in neuraxial block. The spinal cord terminates distally as conus medullaris at the level of the lower border of L1 in adults. The ideal site for spinal anaesthesia is below conus medullaris to avoid trauma to the spinal cord. Identification of the level of intervertebral space is important to have a safe neuraxial block avoiding damage to the spinal cord. Even for epidural analgesia, we need to accurately identify the intervertebral space level. If an epidural catheter is placed at the wrong levels, it leads to inaccurate catheter threading, and surgical response cannot be prevented.

Intervertebral spaces can be identified by palpation of landmark techniques like identifying intercristal line or tuffier’s line which corresponds to the line drawn between two iliac crests and traditionally corresponds to the level of the L4 vertebral body or L4 - L5 interspace. Inferior angle of scapula corresponds to T7 vertebral body.

The present study is conducted to identify accuracy among anaesthesiology trainees in identifying the level of intervertebral spaces by palpation in patients undergoing elective lower limb surgeries, where the identification by palpation may not be accurate, particularly in elderly patients with age-related degenerative changes of the spine and difficulty in positing due to associated osteoarthritis and fracture-related pain.  In previous studies, the accuracy in identifying intervertebral space by palpation of landmark technique by consultant anesthesiologists was found to be less when compared to ultrasound. In this study accuracy of identifying intervertebral space by palpation method by anaesthesiology residents having experience < 1 year, 1-2 years, 2-3 years, 3-4 years will be assessed and compared with ultrasound imaging and c-arm imaging to know the range of errors made by residents and if there is any difference with increasing level of experience among residents.

After shifting the patient to the operation theatre, the patient will be instructed and placed in the sitting position and a paper scale  will be sticked with a double adhesive tape in the paramedian position. Four anesthesiology residents with experience of 1year, 2years, 3years, 4years will be asked to palpate intervertebral spaces T9 - T10 and L3 - L4 and the corresponding numbers on the paper scale will be noted in R1, R2, R3, R4 columns in the data collection sheet. The quality of surface landmarks is graded according to the overall ease with which these landmarks could be palpated (4-point scale: visible, Felt easy, Felt with difficulty, Not felt). Investigator then identifies intervertebral spaces T9 - T10 and  L3 - L4 with a curvilinear ultrasound probe and the corresponding number on the paper scale is noted in the data collection sheet. With the patients in the supine position, a c-arm image in the anteroposterior plane is taken and the intervertebral spaces  T9 - T10 and  L3 - L4 identified and the corresponding numbers on the paper scale is noted in the data  collection sheet. All the palpatory readings will be compared with ultrasound and c-arm findings  in data collection sheet. With the c-arm being the gold standard, the intervertebral levels identified by the c-arm will be taken as zero. Palpatory and ultrasound markings are compared with the level of c-arm and if it is 1 mark cranial to c-arm marking it is taken as +1, if it is at the level of c-arm marking it is taken as 0 and if it is 1 mark caudal to c-arm marking it is taken as -1. Demographic data will be  recorded in the form of age, gender, height, weight, and BMI. The data collected will be entered into an Excel sheet. Statistical analysis will be done using SPSS software. Descriptive statistical analysis will be done using mean ± standard deviation for continuous variables and categorical variables will be expressed as frequency. The kappa coefficient will be used to assess the agreement between different methods of identification of intervertebral spaces.