Predictive Value of Ultrasound Measurement of the Dural Sac Volume on the Sensory Level in Spinal Anesthesia
Condition: Spinal Anesthesia
Study type: Interventional

Summary: 
      The purpose of this study is to investigate whether the dural sac volume as determined by a
      geometrical calculation following multilevel measurements of its transverse area and length
      by ultrasound imaging, correlates with the intrathecal spread of a single dose of hyperbaric
      bupivacaine in a non-obstetrical population.
    

Detailed 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.
    

Intervention name(s): Geometrical calculation of dural sac volume
Intervention type(s): Other
Intervention description(s): Geometrical calculation of the lumbar dural sac volume following multilevel measurements by ultrasound imaging before spinal anesthesia
Intervention model: Single Group Assignment
Masking: None (Open Label)
Keywords: ultrasound