Ultrasound-Guided vs. Landmark-Guided Lumbar Puncture for Obese Patients in the Emergency dEpartment
Kathy Kimpel, MD
Published June 26, 2024
Probetrotters | Medical Education
Study Design
This study was a randomized controlled trial.
Objective
In obese patients, the traditional landmark guided lumbar puncture (LP) using the superior iliac crests and palpating the spinous processes can be extremely difficult. The objective of this study is to compare the success rate, incidence of injury, and postoperative complications of ultrasound guided LP versus the traditional landmark guided LP in obese patients.
Methods
- From January 2018 to June 202, sixty patients with suspected subarachnoid hemorrhage, intracranial infection, and intraventricular hemorrhage, whom needed an LP to confirm the diagnosis, were selected in Shingling Hospital of China Medical University. They were randomly assigned to two groups by the order of their enrollment: Group A (Landmark-guided group, n=30) and Group B (Ultrasound-guided group, n= 30). The physicians performing the LPs were all attending physicians with > 5 years of experience. Subjects’ age, gender, BMI, and interspace levels were recorded, as well as post-procedure assessments including time it took to perform the LP, the number of bloody CSF samples, pain scale, complications, and patient satisfaction. Data was analyzed using SPSS software.
What are some possible flaws in the methods used?
- The sample size was quite small, only 30 patients in each group. Additionally, it was performed at only a single site (Shingling Hospital), which could affect the external validity of the study.
- It is unclear how much variability there was in the skill and experience of the different attending physicians performing the LPs, as the only criteria they had to meet was >5 years of practice.
- According to the inclusion criteria, the subjects only needed to meet the BMI criteria of 28 kg/m2. The methods did not include pair matching or any other way of ensuring that both groups had a similar median BMI. If one group had a median BMI of 30 and another of 40 that could call into question the validity of the results.
- Many of the outcome measures were esubjective including VAS pain scale (0-10) and satisfaction scale.
Results
In the ultrasound guided group, LPs were performed faster and there were less LP attempts. The ultrasound group had a statistically significant higher first puncture success rate (p<0.05) and less bloody CSF samples (p<0.05), less intraprocedural sciatic nerve irritation and less post procedural paresthesia (not statistically significant). In the ultrasound group, the post-procedure VAS (pain score) was lower (p<0.05), and the overall satisfaction was higher (p<0.05). Additionally, between the two groups there was no significant different in age, gender, BMI, interspace level, and pre-procedure pain score, lending higher internal validity to the study.
Discussion
The LP is a crucial procedure in the emergency department, and generally has a high success rate. However, in certain cases such as obese patients, it can be difficult and require repeated attempts. Repeat attempts can lead to bloody samples, pain, and lower patient satisfaction. This study has showed that for obese patients, ultrasound guidance can improve LP success rate, shorten the time of the LP procedure reduce the number of LP attempts, reduce pain, and decrease the amount of traumatic, bloody taps. The study further found that the paramedic approach and curvilinear probe was superior to the midline approach and linear probe. The amount of subcutaneous fat present did not affect the ability of ultrasound to detect markers, unlike with palpation in the traditional landmark technique. All 30 patients in the ultrasound group were successfully punctured compared to 27/30 in the landmark group, with 86.7% first puncture success rate in ultrasound vs 50% in the landmark group (p<0.05). Performing LPs under ultrasound guidance can also avoid post-procedure complications such as penetration of blood vessels and nerves and reduce post-procedure back pain. Overall, when performing LPs in obese patients, ultrasound guidance increases LP success, makes LPs faster, improves first puncture success rate, and decreases post-procedure complications.
Take Home Points
- Performing LPs on obese patients using the traditional landmark technique can be very difficult because of the extra subcutaneous fat.
- Ultrasound can improve LP success rates, decrease the amount of traumatic bloody taps in obese patients.
- There is also evidence from this study to suggest that ultrasound guided LPs have few post-procedure complications, less post-procedure back pain, and higher patient satisfaction in obese patients.
- Based on this study, emergency physicians should use ultrasound guidance for LPs in obese patients whose landmarks may be difficult to palpate.
Study Limitations
- Small sample size (60 patients total, 30 in each group).
- The study was performed at a single hospital Lin China (Shengjing Hospital), which calls into question the external validity of the study. Can this study apply to patients in US hospitals?
- The sutdy did not account for variability in skill between the emergency physicians performing the LPs.
- The VAS pain scan and patient satisfaction scores were subjective as opposed to objective measurements, making them subject to bias.
- There was no way to blind either the patients, the emergency physicians, or the researchers, which could have led to further bias in the study.
Does this study influence your practice?
Yes, it most certainly dose! For obese patients in which I cannot confidently palpate any of the landmarks including the iliac crests or spinous processes, I will use ultrasound for my LPs.
Read the full study here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9086450/