Predictive Value of an Ultrasound Model of Measurement of the Dural Sac Volume on the Sensory Level Obtained by Spinal Anesthesia
Description:
Sensory block extent may be difficult to predict in spinal anesthesia. Many factors
influencing the intrathecal spread have been identified. Among the most important factors is
the lumbosacral cerebrospinal fluid (CSF) volume and the dimensions of the dural sac. One
study using magnetic resonance imaging (MRI) reported significant correlations between CSF
volume and sensory block levels following spinal anesthesia. However, unlike ultrasound
imaging, MRI can be difficult to obtain in the surgical setting. Although ultrasound imaging
of the lumbar spine may not directly determine the CSF volume, multilevel measurements of the
transverse area and length of the dural sac by ultrasound imaging followed by a geometrical
calculation of its volume could help predict the extent of the intrathecal spread.
Methods: Patients scheduled for elective surgery under spinal anesthesia will be considered
for this study. Ultrasound imaging will be achieved in a non-sterile manner with the patient
in the sitting position. Spinal imaging will be performed using a low frequency probe. Focus
and gain will be optimized. The first images will be made to identify the inter-laminar
spaces from T11 to S1. At each level, the area of the dural sac will be measured in short
axis using an adjustable ruler built-in the ultrasound monitor. The middle of the
inter-laminar spaces will be marked on the patient’s skin and the length of the dural sac
will be defined as the distance between the middle of T11-12 and L5-S1. The total volume will
be geometrically calculated. The L3-L4 space will be localized by triangulation and marked on
the patient’s skin as the optimal puncture site for spinal anesthesia. The optimal puncture
angle will also be determined.
After placement of standard non-invasive monitoring, spinal anesthesia will be performed
using 27-G Pencan needle. After aspiration of CSF, a solution of hyperbaric bupivacaine and
fentanyl will be injected over a period of 15 seconds. The dose of bupivacaine will be
determined by the attendant anaesthesiologist. The aspiration of CSF will be repeated at the
end of the injection. Subsequently, the patient will be placed in supine position.
The extent of sensory block will be assessed by loss of pinprick sensation (using a #5.88 Von
Frey filament) and loss of cold sensation to ice every 10 minutes until the same sensory
level is observed in two consecutive assessments for a minimum period of 30 minutes. The
extent of the block will be assessed bilaterally from caudal to cranial direction in the
mid-clavicular line beginning at L3. The investigators will consider the peak sensory level
as the uppermost blocked dermatome.
Total amount of crystalloids administered, incidence of significant hypotension and
bradycardia will be recorded. Time to perform ultrasound measurements and time to discharge
will also be noted. Resolution of the motor block will be assessed using the Bromage score at
3.5 hour, 4 and 4.5 hour following the injection of bupivacaine.
Condition:
Spinal Anesthesia
Treatment:
Geometrical calculation of dural sac volume
Start Date:
September 2012
Sponsor:
Centre hospitalier de l’Université de Montréal (CHUM)
For More Information:
https://clinicaltrials.gov/show/NCT01624844