Dry spinal tap during real-time ultrasound-guided paramedian spinal injection with patient in the lateral decubitus position: A single-centre retrospective study.

Background: Real-time ultrasound-guided (USG) spinal injection is generally performed via the paramedian sagittal oblique (PMSO) ultrasound window.

Objective: The aim of this retrospective study was to draw attention to the occurrence of 'dry tap' during real-time USG spinal injection.

Design: Single-centre retrospective study.

Setting: University teaching hospital, Hong Kong, China.

Patients: Data from 113 patients (aged 69.2 ± 18.0 years and BMI 22.3 ± 3.6 kg m-2) of American Society of Anesthesiologists physical status 1 to 3 scheduled for surgery under neuraxial blockade between 2007 to 2017 were reviewed.

Interventions: Real-time USG spinal injections or combined spinal-epidural (CSE) using the PMSO ultrasound window with the patient in the lateral decubitus position and the spinal needle inserted from the nondependent side were studied.

Main Outcome Measures: 'Dry tap' was defined as a failure of cerebrospinal fluid (CSF) to efflux from the hub of the needle, within 3 min, with the spinal needle visualised sonographically within the thecal sac. 'Slow CSF efflux' was defined as efflux of CSF within 1 to 3 min. Irrespective of whether it was a 'dry tap' or 'slow CSF efflux', the planned dose of local anaesthetic was injected through the spinal needle.

Results: The combined incidence of 'dry tap' and 'slow CSF efflux' was 23.8% (27/113) with an individual incidence for each event of 9.7% (11/113) and 14.2% (16/113), respectively. Under the conditions of this study, successful spinal anaesthesia developed in all patients.

Conclusion: 'Dry tap' occurs in 9.7% of cases during real-time USG spinal injection using the PMSO ultrasound window, with the patient in the lateral decubitus position and the spinal needle inserted from the nondependent side.

Trial Registration: ChiCTR-IOR-1800019011, Chinese Clinical Trials Registry (www.chictr.org.cn).