///2017 Abstract Details
2017 Abstract Details2019-08-02T15:54:53-06:00

An initial look at identification of L3-L4 interspace in parturients by palpation: Can we teach residents to be better than chance?

Abstract Number: SAT-58
Abstract Type: Original Research

Beth VanderWielen MD1 ; Philip Hess MD2; Laura Sorabella MD3; Justin Stiles MD4; Anasuya Vasudevan MD5; Nathan Liu MD6

Identification of the L3-L4 interspace is based on palpation of the intercristal line; however, published literature shows that this method is inaccurate (success rate 13-76%)(1). This may be because the intercristal line is based on radiographic imaging not landmark palpation. Ultrasound is a readily accessible tool that we hypothesized could provide real-time feedback to improve resident palpation skills.


We performed an observational, education-based study to improve resident’s ability to correctly identify the L3-L4 interspace. Residents were trained in a 2-week program using ultrasound via an online module and hands-on teaching on live models. The program taught intercristal line identification by correlating ultrasound imaging with palpation. After training, each resident was tested on five parturients by having to identify the L3-L4 interspace using palpation alone. The resident’s site was confirmed using ultrasound. Analyses were conducted using SAS 9.3.


A convenience sample of 18 CA-1 residents participated. The rate of correct identification was 65.8%. Fourteen percent of attempts were one level below, 16.5% attempts one level above, and 3.8% attempts two or more levels above the targeted L3/4 interspace. Residents improved their success significantly after their first attempt with ultrasound feedback (Figure 1). No statistical difference between age, height, weight or BMI was found amongst patients who had correct versus incorrect interspace identification.

We compared our results to 11 studies totaling 1701 patients where an experienced anesthesiologist attempted to identify a lumbar interspace. The average success (55.7%) was significantly less than our result (p=0.038). When focusing on OB patients with a similar BMI (mean 29.9 kg/m2) compared to our patients (mean 29.4 kg/m2), success rate was reduced to 39.7% (p<0.001 vs. our results).


Our study reflects the utility of ultrasound as an education tool to improve resident palpation skills. We had an overall success rate to 65.8% for new CA-1 residents within their first month of training, which exceeds the comparison data from experienced anesthesiologists, especially when OB comparison was used.

This preliminary study represents a novel, promising method of real-time ultrasound feedback to improve resident education of interspace palpation skills. What remains to be investigated is if our results are sustained on long-term follow-up.

1) Reg Anesth Pain Med. 2015;40:1-10

SOAP 2017