POSSIBLE DRY TAP, HYDRATE BEFORE THE LUMBAR PUNCTURE?

Background: Among bedside procedures, factors such as body mass index (BMI), prior spinal procedures, and complex spinal anatomy are known to affect the success of lumbar punctures (LP) [2, 3]. However, the phenomenon of a “dry tap,” where cerebrospinal fluid (CSF) cannot be obtained despite the needle tip being correctly positioned in the thecal sac, is well-documented in neuroradiology literature [4, 5]. This challenge is particularly prevalent in inpatient populations, who often have elevated Charlson scores and are typically at risk for dehydration [4, 6]. Addressing the issue of “dry tap” could enhance the success rate of inpatient bedside LPs.

Methods: As part of a quality improvement initiative, we analyzed 140 LP cases performed by the hospitalist Procedural Team (HPT) at a single large urban academic institution from April 13, 2023 until October 31, 2024. HPT comprises 5 hospitalists on on-call consult bases to perform or supervise trainees on bedside procedures, such as LP or paracentesis, for admitted medicine patients. LPs were performed without the use of ultrasound guidance. Procedures and outcomes were tracked in a HIPAA-compliant case log. Data including BMI, patient characteristics, outcome measures, and follow-up procedure documentation were obtained via manual chart review. The outcome “unsuccessful LP” was defined as no CSF obtained. A “dry tap” was defined as failure to obtain CSF despite apparent correct anatomical positioning and location. Complex spinal anatomy was defined if the patient had previous lumbar spine surgical history, scoliosis, or extensive degenerative change on radiographs.

Results: Of 140 total LP cases, the average and median BMI were 24.1 and 23.0. The overall success rate was 66% (93 cases), with successful cases having an average BMI of 22.5 and a median of 22.0. Unsuccessful cases (33.6%, 47 cases) had higher average and median BMIs of 27.5 and 27.0Among unsuccessful cases, 12 (25.5%) had complex spinal anatomy. Successful cases did not have logs of complex spinal anatomy.Among unsuccessful cases, 19 (40.4%) were completed by neuro-interventional radiology (IR), and 5 were repeated by HPT. Repeat LPs were deferred on the 23 cases due to clinical changes or patient refusal.15 (31.9%) unsuccessful cases had concerns about “dry tap”. Of these cases, 5 of 9 cases referred to IR yielded minimal CSF of 1 to 3 milliliters and 5 cases had successful repeat by HPT within five days following hydration.From total LP, Minor superficial bleeding complications were noted in 3 in successful cases and 5 in unsuccessful cases. No major complications including herniations and intra or epidural bleedings were noted.

Conclusions: We found that increased BMI and complex spinal anatomy were associated with higher rates of LP failure. Dry taps appeared associated with minimal CSF during IR repeats or improved CSF output when HPT repeated LPs after hydration. However, the successful repeat LP by HPT after hydration is limited in defining a true “dry tap,” as needle placement within the thecal sac could not be confirmed by imaging. For patients not at risk of volume overload, intravenous hydration before LP may improve success rates. Future studies exploring same-day IR attempts for failed bedside LPs could provide more robust insights about “dry tap”. We believe implementing a checklist that includes BMI assessment, reviewing spinal radiographs and history, and ensuring adequate hydration status before LP can aid in improving the success rate.