Ultrasonography Versus Palpation for Spinal Anesthesia in Obese Parturients Undergoing Cesarean Delivery
Phase: NA
Conditions: Anesthesia, Spinal, Cesarean Section, Spinal Ultrasound
Sponsor: Mansoura University

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Official Title:  
Ultrasonography Versus Palpation for Spinal Anesthesia in 
Obese Parturients Undergoing Cesarean Delivery 
 
ClinicalTrials.gov Identifier:  
NCT03792191 
 
Document Date: 
31/12/2018 
 
 

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Introduction: 
Neuraxial blocks (including single shot spinal, epidural, and combined 
spinal-epidural) 
are 
the 
most commonly used techniques 
for 
uncomplicated cesarean delivery to avoid the complications of general 
anesthesia such as airway and pulmonary complications.1 
Neuraxial anesthesia relies primarily on the visualization and 
palpation of the surface landmarks, which can be difficult in the setting of 
obesity, edema, and anatomical variation.2 
Obesity causes difficulty in the detection of anatomical landmarks 
during neuraxial blocks resulting in increased number of attempts, longer 
procedure time, higher incidence of vascular puncture, and higher failure 
rate.3 
Ultrasonography has been used to guide neuraxial blocks either as 
a prepuncture procedure or less commonly as a real-time technique. 
Ultrasonography is readily available, relatively safe, and has now been 
familiar for anesthesiologists being used in vascular access and various 
regional anesthetic techniques.4,5 
Prepuncture ultrasound scan has been utilized to identify the 
midline, locate the appropriate intervertebral space, detect the optimal 
angle for needle insertion, and measure the distance to the epidural space. 
This added information has increased the success rate of neuraxial block 
on the first attempt, increased patient comfort and satisfaction, and 
decreased the incidence of complications such as vascular puncture and 
backache.6,7 However, the use of ultrasonography for identification of 
spinal structures is complicated because the epidural and intrathecal 
spaces are a thin and deep structure and surrounded by bony structures 

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which impede the ultrasound beam. It also needs additional training and 
adds cost and time to the procedure.8 
In obese patients, there are multiple factors that affect image 
quality because of deep anatomic location of structures, the ultrasound 
beam travels a greater distance, resulting in beam attenuation. Also phase 
aberration of the sound field occurs because of uneven speed of sound in 
the irregularly-shaped adipose layers. This is due to differing speeds of 
sound in the overlying nonhomogeneous tissues above the focus of the 
transducer. Another factor that can affect the quality of the ultrasound 
image is reflection which is due to mismatch of acoustic impedance at the 
fat/muscle interface. When the ultrasound beam crosses a boundary 
between muscle layer and fat, a portion of energy is reflected back to the 
transducer because of different acoustic velocity between the two tissues.9 
Moreover, the real-time ultrasound guidance seems difficult and 
may need two physicians; one to hold the ultrasound probe and the other 
to perform the neuraxial block. Therefore, real-time ultrasound guided 
neuraxial blocks are not currently recommended for routine use.5 The first 
report of ultrasound utilization for epidural catheterization in the English 
literature was published by Cork et al. in 1980. There were very few 
reports on the topic until the last decade when increasing number of 
studies were performed due to the great innovation in ultrasound 
technology.2 Most of these studies were designed to validate the 
prepuncture technique and they used inconsistent imaging strategies and 
were not blinded.  
Several studies have examined the use of preprocedural 
ultrasonography for spinal anesthesia and compared it with the 
conventional 
landmark 
technique. 
Creaney 
et 
al 
have 
used 
ultrasonography to identify the lumbar spaces in parturients with poorly 

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defined landmarks presenting for cesarean delivery under spinal 
anesthesia and demonstrated that ultrasonography reduced the number of 
needle passes and did not prolong the whole procedure time.10 Ekinci et al 
compared ultrasonography with conventional landmark technique in 
parturients with impalpable anatomical landmarks.11 Real- time 
ultrasonography also was used to guide spinal anesthesia in patients with 
predicted difficult anatomy.12  
 
 
 

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Aim of the study: 
The aim of this study is to evaluate the efficacy of prepuncture 
ultrasonography to facilitate spinal anesthesia in obese parturients 
undergoing elective cesarean delivery compared with the conventional 
palpation technique.  
 
Outcomes of the study: 
The primary outcome will be the number of needle passes required to 
obtain free CSF flow. Secondary outcomes will be the number of skin 
punctures required to obtain free CSF flow, the success rate at the first 
needle pass, the success rate at the first skin puncture, the duration of the 
spinal procedure, patient satisfaction from the procedure, and the 
incidence of vascular puncture, paresthesia, failure to obtain CSF flow, 
and failed spinal block. 
 
Anticipated Duration of the study: 
18 months 
 
Type of the study: 
Prospective, randomized controlled, double-blind, 2-arm study. 
The study subjects and the investigators assessing the outcomes will be 
blinded to the study group. 
 
 

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Patients: 
The study will be conducted on parturients scheduled for elective 
cesarean delivery under spinal anesthesia at the Obstetric department of 
Mansoura University Hospitals.  
Inclusion Criteria:  
 American Society of Anesthesiologists physical status II-III 
parturients 
 Full term, singleton pregnancy 
 Body Mass Index ≥ 35 Kg/m2 
Exclusion Criteria:  
 Age < 19 
 Women presenting in labor 
 Contraindications to neuraxial anesthesia (Coagulopathy, increased 
intracranial pressure, or local skin infection) 
 Significant spinal deformities or previous spinal surgery 
 Preeclampsia 
 
 

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Methods: 
After obtaining written informed consent, the study subjects will be 
randomly assigned to 2 equal groups (ultrasonography and palpation 
groups) according to computer-generated codes using the permuted block 
randomization method with randomly selected block sizes of 4 and 6. The 
group allocation will be concealed in sequentially numbered, sealed 
opaque envelopes. 
Vascular access will be obtained then the subjects will be placed in 
the sitting position and standard monitors (electrocardiography, non-
invasive blood pressure, and pulse oximetry) will be applied. The subjects 
will be kept in the same position during identification of landmarks and 
during the spinal anesthesia procedure. The subjects will be examined for 
the ease of landmark palpation using a 4-point scale (1 = the spinous 
processes and the interspaces can be identified by light palpation; 2 = the 
spinous processes and the interspaces can be identified by deep palpation; 
3 = the spinous processes only can be identified by deep palpation, and 
the interspaces cannot be identified; 4 = neither the spinous processes nor 
the interspaces can be identified). The difficulty grade for each patient 
will be recorded.  
In the palpation group, a sham procedure will be performed to 
blind the subjects by sliding the ultrasound probe on the patient`s back 
while the ultrasound machine is in the freeze position. Conventional 
palpation technique will be performed: The midline will be identified by 
palpation of the spinous processes and the line connecting the iliac crests 
(Tuffier`s line) will be assumed to cross the L4 spine or L3-L4 interspace. 
Identification of 2 intervertebral spaces (L3-L4 and L2-L3) will be done 
and the widest/most easily palpable interspace will be chosen for needle 
puncture. In women with impalpable spines, the iliac crest or the crease at 

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the bottom of the spine will be used to determine the needle insertion 
point. 
In the ultrasonography group, a systematic 7–step approach will be 
performed using an 8-2 MHz curved array transducer (SonoAceR3®, 
Samsung Medison; Seoul, South Korea):  
1. The probe will be longitudinally placed on the bottom of the spine, 
with the probe mark pointing cephalad, to obtain the longitudinal view of 
the sacrum and the paramedian sagittal oblique view of the L5–S1 
interspace. 
2. The operator will count up the intervertebral levels to obtain the 
paramedian sagittal oblique view of theL3–L4 interspace. 
3. The probe will be rotated 90ºanticlockwise to obtain the transverse 
interlaminar view of the L3–L4 interspace, which will be used in the next 
steps. 
4. The skin will be marked with horizontal and vertical lines at the 
midpoints of the probe’s short and long sides, respectively; the 
intersection point of the 2 lines represents the needle insertion point. 
5. The angle of the probe obtaining the best sonographic image will be 
observed. 
6. The distance from the skin surface to the ventral aspect of the 
ligamentum flavum-dura mater complex will be measured; this will 
correspond to the depth of the epidural space. 
7. The probe will be moved 1 interspace cephalad to obtain the transverse 
interlaminar view of the L2–L3 interspace and steps 4 to 6 will be 
repeated. 
 
The interspace with the best sonographic image or the widest/ most easily 
palpable interspace will be chosen for the first attempt in the 

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ultrasonography and palpation groups, respectively. If the 2 spaces are of 
equal image quality or width/ease of palpation, the L3-L4 interspace will 
be first attempted. The puncture site will be infiltrated with 1-2 mL of 2% 
lidocaine. Spinal anesthesia will be performed with a 25- or 22-gauge 
spinal needle (a 22-gauge needle will be only used after a failed first 
attempt in subjects with tough ligaments) using a midline or paramedian 
approach according to the preference of the operator. The paramedian 
approach will be used in women having difficulty in flexing their spines 
and/or difficult interspaces; the puncture site is 1 cm lateral to and 0.5 cm 
below the midpoint of the interspace. After obtaining free cerebrospinal 
fluid (CSF) flow, 2.5 mL of 0.5% hyperbaric bupivacaine (12.5 mg) and 
fentanyl 15 μg will be intrathecally administered. After intrathecal 
injection, women will be placed supine with slight left lateral table tilt.  
A maximum of 11 passes (the first attempt and 10 redirections) of 
the spinal needle will be allowed for each skin puncture and a maximum 
of 6 skin punctures will be allowed to obtain free CSF flow. 
The number of performed needle passes (defined as any forward 
introduction of the spinal needle after its incomplete withdrawal, 
including the primary attempt) and skin punctures (defined as any 
separate skin puncture by the needle after its complete withdrawal, 
including the primary attempt) will be recorded. 
The occurrence of unintentional vascular puncture will be 
recorded. The actual duration of the procedure (from the start of the first 
skin puncture by the spinal needle to obtaining free CSF flow) will be 
recorded.   

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Patient satisfaction from the procedure will be assessed 
immediately after intrathecal injection using a five-point scale (1 = very 
unsatisfied, 2 = unsatisfied, 3 = fair, 4 = satisfied, 5 = very satisfied). 
The upper sensory level will be assessed using pin prick and 
surgery will start after attaining a level of T6 or higher. The level after 20 
minutes of intrathecal injection will be recorded; a level below T6 will be 
considered a failed spinal block and the patient will be managed as 
appropriate. 
 
 
 

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Sample Size Calculation: 
The primary outcome will be the number of needle passes required to 
obtain free CSF flow. In a pilot study performed on 20 obese parturients 
using the palpation technique, 8 ± 5 needle passes were required to 
successfully obtain free CSF flow. Assuming alpha = 0.05 and beta = 0.1 
(power = 90%) and using the 2-tailed Student t test, 133 subjects will be 
required in each group to detect a difference of 2 needle passes between 
groups which is considered to be the minimal clinically important 
difference. To allow for subject dropouts, 140 subjects will be assigned to 
each group. 
 
Statistical analysis: 
Data will be analyzed using the R software (R Core Team; R Foundation 
for Statistical Computing, Vienna, Austria). Continuous data will be 
tested for normality using the histogram and the Kolmogorov-Smirnov 
test. Normally distributed data will be presented as mean ± standard 
deviation and compared using the Student`s t test. Non-normally 
distributed data will be presented as median (range) and compared using 
the Mann-Whitney U test. Categorical data will be presented as number 
(percentage) and compared using the chi-square test or Fisher`s exact test. 
A P-value < 0.05 will be considered statistically significant.    
 
 
 

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9.  
Saranteas T. Limitations in Ultrasound Imaging Techniques in 
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elective cesarean delivery under spinal anesthesia : a randomized 
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planned cesarean delivery under spinal anesthesia for patients 
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