Hypobaric L5-S1 Study

Condition(s) studied

Investigational drug(s) / intervention(s)

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.

Study 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.

Eligibility

Primary outcome measure(s)

• Rate of successful spinal anesthesia — Assessed from time of spinal injection to surgery completion
  "Successful spinal anesthesia" is defined as the completion of surgery without conversion to general anesthesia, administration of supplemental opioids or surgical local anesthetic infiltration in the operating room to manage surgical pain.
• Most cranial dermatomal level of sensory anesthesia achieved before surgery — Assessed every 5 minutes for the first 30 minutes after spinal injection
  A pinprick test using an 18G(gauge) blunt-tipped needle (BD Blunt Fill needle) will be performed on non-dependent and dependent sides to detect sensory loss over the torso and lower limbs. Sensation to pinprick testing in each dermatome will be categorized as normal ("sharp" sensation), analgesia ("dull" sensation), or anesthesia ("no" sensation). The most cephalad/cranial (upper) sensory block level of analgesia and anesthesia will be recorded based on the dermatomal map.
• Time to reach the most cranial dermatomal level of sensory anesthesia before surgery — Assessed from time of spinal injection to surgery commencement
  The most cranial dermatomal level of sensory anesthesia will be determined based on the pinprick test.
• Time to reach sensory anesthesia at level of T10 or higher before surgery, on the operative limb — Assessed from time of spinal injection to surgery commencement
  The dermatomal level of sensory anesthesia will be determined based on the pinprick test.
• Time to reach sensory anesthesia at level of L1 or higher before surgery, on the operative limb — Assessed from time of spinal injection to surgery commencement
  The dermatomal level of sensory anesthesia will be determined based on the pinprick test.
• Time to recovery of normal sensation at T10 or lower (also defined as duration of sensory analgesia at T10 or higher) in both lower limbs — Assessed at the end of surgery and every 30 minutes in the post-anesthesia care unit (PACU) or inpatient ward until a return of normal sensation in the T10 dermatome has been documented
  The dermatomal level of sensory anesthesia will be determined based on the pinprick test.
• Time to normal sensation at L1 or lower (also defined as duration of sensory analgesia at L1 or higher) in both lower limbs — Assessed at the end of surgery and every 30 minutes in the PACU or inpatient ward until a return of normal sensation in the L2 dermatome has been documented on the day of surgery.
  The dermatomal level of sensory anesthesia will be determined based on the pinprick test.
• Time to recovery of normal sensation at L2 or lower in both lower limbs — Assessed at the end of surgery and every 30 minutes in the PACU or inpatient ward until a return of normal sensation in the L2 dermatome has been documented on the day of surgery.
  The dermatomal level of sensory anesthesia will be determined based on the pinprick test.
• Time to achieve complete motor block at hip, knee, ankle, and toes — Assessed every 5 minutes for the first 30 minutes after spinal injection
  The development of motor block will be assessed by assessing the ability to actively flex and extend at the hip, ankle, knee, and toes. This will be scored as either 1 (movement present and observed) or 0 (movement absent) at each joint on both lower extremities.
• Time to regain ability to move hip, knee, ankle, and toes; and a score of 0 on the modified Bromage scale — Assessed at the end of surgery and every 30 minutes in the PACU or inpatient ward until full motor recovery has been achieved in both lower limbs on the day of surgery.
  Modified Bromage scale scores: 0 - Able to move hip, knee, ankle and toes 1. \- Unable to move hip, able to move knee, ankle and toes 2. \- Unable to move hip and knee, able to move ankle and toes 3. \- Unable to move hip, knee and ankle, able to move toes 4. \- Unable to move hip, knee, ankle, or toes

Trial sites (1)

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