Hypobaric L5-S1 Study

NCT ID: NCT06526156

Last Updated: 2025-11-20

Basic Information

• Recruitment Status: ACTIVE_NOT_RECRUITING
• Total Enrollment: 55 participants
• Study Classification: OBSERVATIONAL
• Study Start Date: 2024-07-22
• Study Completion Date: 2025-12-31

Brief Summary

Patients going through total hip or knee replacement (arthroplasty) have to be put under spinal anesthesia to prevent them from feeling any pain during surgery. Spinal anesthesia means having a small needle inserted between the bones of the lower lumbar spine (vertebrae). The choice of space used is decided by the anesthesiologist in charge of patient care. The space between these bones is often narrowed by arthritis or other age-related degenerative spine disease in patients having total hip or knee replacement surgery. The lowest L5-S1 (Lumbar 5- Sacral 1) space is the largest one and often least affected by arthritis, which makes it the easiest option. Despite this, it is not currently the most common space used for spinal anesthesia, because it is hard to find by palpation (feeling the bones through the skin), and because there is concern that local anesthetic will not always spread up high enough from this lowest space, which is needed for a successful spinal anesthesia. How far it spreads depends on the amount (dose) and density of local anesthetic given.

There are two types of local anesthetic: one called isobaric, which has the same density as CSF (Cerebro-Spinal Fluid), and another called hypobaric, which has lower density than CSF.

Isobaric local anesthetic spreads evenly throughout the CSF irrespective of patient positioning. However, a larger dose is required to achieve adequate anesthesia for surgery. Using larger doses, leads to a very long duration of sensory and motor block, far in excess of that required for surgical completion which leads to a slower recovery from anesthesia.

Hypobaric local anesthetic, on the other hand, floats in CSF like oil on water. This allows anesthesiologists to use a smaller dose while still being sure that it will spread high enough to achieve adequate anesthesia for surgery. The smaller doses in turn allow for faster recovery of normal movement and feeling in the legs of patients after surgery.

It has been observed that all of these dilemma can be solved by:

1. Using ultrasound imaging to find and mark the space, and

2. Injecting hypobaric local anesthetic.

The goal of this observational study is to determine the success rate of spinal anesthesia with a lower dose of hypobaric bupivacaine injected into the L5-S1 space, when done on total hip or knee arthroplasty patients at Toronto Western Hospital.

Detailed Description

Spinal anesthesia is the recommended type of anesthesia for total hip or knee arthroplasty, as it is associated with superior clinical outcomes compared to general anesthesia. However, many patients undergoing these surgical procedures have age-related spine disease, previous spine surgery, or other spinal deformities which make the injection of spinal anesthesia difficult.

One strategy is to administer the spinal anesthesia at the L5-S1 space: it is least affected by arthritic and degenerative changes, and as it is the largest intervertebral space, it has the lowest chance of causing spinal cord trauma.

However, administration of spinal anesthesia at the lowest lumbar intervertebral levels significantly decreases the odds of success of surgical anesthesia. This is due to the fact that the standard solution of 0.5% bupivacaine is isobaric with respect to the cerebrospinal fluid (CSF), leading to unpredictable distribution within the CSF and inconsistent extent of sensory block. It has been shown that an inordinately large dose of 25 mg (5 milliliter) of 0.5% bupivacaine is required to achieve the adequate extent of sensory loss, as opposed to more conventional doses of 12-15 mg (milligram). However, this leads to a very long duration of sensory and motor block, far in excess of that required for surgical completion. This delays patient discharge from the post-anesthetic recovery unit, mobilization, and recovery. This is at odds with the goals of modern total hip and knee arthroplasty, which emphasizes same-day mobilization, physiotherapy, and even same-day hospital discharge. Using lower doses of isobaric bupivacaine, on the other hand, increases the risk of inadequate or failed spinal anesthesia, requiring conversion to general anesthesia.

One strategy to address this dilemma, which has been employed with great success to date at the Toronto Western Hospital (TWH), is to use a solution of bupivacaine that is hypobaric relative to CSF. This promotes cranial distribution of bupivacaine within the CSF and blockade of the higher spinal nerve roots, thus ensuring adequate extent of sensory block, even when administering doses as low as 10 mg of bupivacaine. This hypobaric bupivacaine solution is prepared by mixing 2 mL(milliliter) of isobaric 0.5% bupivacaine with 1 mL of sterile water. The investigators have demonstrated the efficacy of this for successful surgical anesthesia of adequate, but not excessive, duration in a recently concluded observational study. Notably, two subjects in the cohort of 60 patients received spinal anesthesia at the L5-S1 level. Both patients had adequate sensory block height and duration for commencement and completion of surgery without need for anesthetic supplementation. The investigator(s) have performed spinal anesthesia at the L5-S1 level in many other patients over the last 3 years with the same dose of hypobaric bupivacaine and have not encountered failure to date.

The purpose of this observational study is to determine the success rate of spinal anesthesia with low-dose (10 mg) hypobaric bupivacaine injected into the L5-S1 space in patients undergoing total hip or knee arthroplasty surgery.

Conditions

Anesthesia; Anesthesia, Local

Study Design

• Observational Model Type: COHORT
• Study Time Perspective: PROSPECTIVE

Study Groups

Hypobaric L5-S1 Spinal Anesthesia

Will receive a dose of hypobaric (0.33%) bupivacaine, administered at the L5-S1 space.

Bupivacaine injection

Intervention Type: DRUG

A 3 mL hypobaric (0.33%) solution of bupivacaine, prepared by mixing 2 mL of isobaric (0.5%) bupivacaine with 1 mL of sterile water. Dural puncture will be performed using a 25 or 27G (gauge) spinal needle at the L5-S1 intervertebral space, and the 3 mL of 0.33% bupivacaine will be injected into the intrathecal space.

Interventions

Bupivacaine injection

A 3 mL hypobaric (0.33%) solution of bupivacaine, prepared by mixing 2 mL of isobaric (0.5%) bupivacaine with 1 mL of sterile water. Dural puncture will be performed using a 25 or 27G (gauge) spinal needle at the L5-S1 intervertebral space, and the 3 mL of 0.33% bupivacaine will be injected into the intrathecal space.

Intervention Type: DRUG

Other Intervention Names

Marcaine

Eligibility Criteria

Inclusion Criteria

• Patients undergoing elective unilateral total hip or knee arthroplasty under spinal anesthesia at TWH who are scheduled for inpatient overnight admission
• American Society of Anesthesiologists physical status class (ASA-PS) 1-3
• At least 20 years of age

Exclusion Criteria

• Refusal to participate
• Inability to communicate due to language barrier or cognitive impairment
• Height > 200 cm
• Weight >120 kg
• Body mass index (BMI) >45 kg/m^2
• Contraindication or allergy to amide-type local anesthetic
• Contraindication to spinal anesthesia at the L5-S1 space (e.g., infection at the injection site, existing coagulopathy, severe spinal stenosis at higher vertebral levels)
• Previous spinal surgery in the lumbosacral spine
• Spinal anesthesia performed in the operating room rather than the block room
• Spinal anesthesia that includes administration of intrathecal opioids (e.g., morphine, fentanyl)
• Pre-existing sensory or motor impairment in the lower extremities
• Inability to identify the L5-S1 space with ultrasonography

• Minimum Eligible Age: 20 Years
• Eligible Sex: ALL
• Accepts Healthy Volunteers: No

Sponsors

University Health Network, Toronto

OTHER

Sponsor Role: lead

Responsible Party

Responsibility Role: SPONSOR

Principal Investigators

Ki Jinn Chin, MBBS,MMed,FRCPC

Role: PRINCIPAL_INVESTIGATOR

UHN

Locations

Toronto Western Hospital

Toronto, Ontario, Canada

Countries

Canada

Other Identifiers

CAPCR# 24-5192

Identifier Type: OTHER

Identifier Source: secondary_id

24-5192

Identifier Type: -

Identifier Source: org_study_id