jcourse2-0612-p223-230

www.aana.com/aanajournalonline AANA Journal June 2012 Vol. 80, No. 3 223

AANA Journal CourseUpdate for Nurse Anesthetists

Evidence-Based Anesthesia: The Use of Preprocedural Ultrasonography During Labor to Facilitate Placement of an Epidural Catheter

CDR Dennis Spence, CRNA, PhD, NC, USNLCDR Ryan Nations, CRNA, MS, NC, USNLT Orlando Rivera, CRNA, MSN, NC, USNLT Shawn Bowdoin, RN, BSN, NC, USNLCDR Bradley Hazen, CRNA, MSN, NC, USNLT Robert Orgill, CRNA, MSN, NC, USNCAPT John Maye, CRNA, PhD, NC, USN

ObjectivesAt the end of this course, the learner should be able to:

1. Describe the limitations of traditional epidural catheter placement techniques and purported ben-efits of preprocedural ultrasonography to facilitate epidural catheter placement.

2. Describe the equipment, procedure, and spinal anatomy observed when performing preprocedural ultrasonography.

3. Apply findings from investigations of the use of preprocedural ultrasonography to facilitate epidural catheter placement in parturients to improve clini-cal practice.

4. Outline findings and limitations of studies on the use preprocedural ultrasonography in parturients.

5. Incorporate the use of preprocedural ultrasonogra-phy into clinical practice.

IntroductionA 30-year-old, 61-in-tall, 80-kg (body mass index, 33.3 kg/m2), ASA physical status 2, gravid 2, parity 1, parturient is admitted for an elective, repeated low transverse cesarean delivery for twins under combined spinal-epidural anesthe-sia. The patient has exaggerated lumbar lordosis, making it diffi cult to palpate an interspace. Multiple attempts by the student registered nurse anesthetist and staff Certifi ed Registered Nurse Anesthetist are unsuccessful. Preprocedural ultrasound scanning identifi es the ideal insertion point at L3-L4 and a depth of approximately 6 cm to the ligamentum fl avum. Original insertion points are found to be off midline by approximately 1.5 cm. The combined spinal-epidural catheter is placed on the fi rst attempt without redirection or reinsertion of the epidural needle. Adequate surgical anesthe-sia is obtained after injection of the spinal anesthetic.

The preceding clinical vignette demonstrates the

AANA Journal Course No. 32 (Part 2): AANA Journal course will consist of 6 successive articles, each with objectives for the reader and sources for additional reading. At the conclusion of the 6-part series, a fi nal examination will be published on the AANA website and in the AANA Journal. This educational activity is being presented with the understanding that any confl ict of interest on behalf of the planners and presenters has been reported by the author(s). Also, there is no mention of off-label use for drugs or products.

6 CE Credits*

2

Placement of an epidural catheter in parturients can be challenging because the anatomic changes of preg-nancy may make it difficult to palpate an ideal inser-tion point or detect loss of resistance. Preprocedural ultrasonography (U/S-P) is reported to facilitate place-ment of epidural catheters in parturients. U/S-P pro-vides information on the ideal insertion point, angle of needle insertion, and estimated depth to the epidural space. The purposes of this course are to describe the

technique, systematically review the literature, and discuss techniques for integrating U/S-P into practice. It provides evidence demonstrating that U/S-P is a useful adjunct for placement of epidural catheters in obstetrical patients, especially patients with presumed “difficult backs” or obesity.

Keywords: Epidural, labor, parturients, preprocedural, ultrasonography.

224 AANA Journal June 2012 Vol. 80, No. 3 www.aana.com/aanajournalonline

challenges of performing and teaching students how to administer neuraxial anesthetics to parturients. The anatomic changes of pregnancy may make it difficult to palpate an ideal insertion point. This problem is worsened in an obese parturient (body mass index [BMI], > 30 kg/m2)1,2 who may have an excess amount of adipose tissue overlying anatomic landmarks.2 Neuraxial place-ment is essentially a “blind” technique that relies on palpa-tion of an ideal interspace and tactile sensation of the loss of resistance to identify the epidural space. Preprocedural ultrasonography (U/S-P) is reported to facilitate place-ment of epidural catheters in parturients. U/S-P provides information on the optimal insertion point, angle of needle insertion, and estimated depth to the epidural space. In ad-dition, U/S-P has been reported to decrease the number of puncture attempts and increase the success rate in place-ment of epidural catheters in parturients.3-5 The purposes

of this course are to review and discuss current literature regarding the use of U/S-P to facilitate administration of neuraxial anesthetics and to present techniques for inte-grating U/S-P into practice.

Preprocedural Ultrasound Scanning Procedure in ParturientsUltrasonography is commonly used in the placement of peripheral nerve blocks or central venous catheters (see the notable review by Falyar6 on basic ultrasound prin-ciples). For many peripheral nerve blocks and central line placements, a high-frequency (10-15 MHz) linear probe is used to identify relevant structures and to observe the needle location in real time. However, when ultrasonog-raphy is used to facilitate placement of an epidural cath-eter during labor, it is not used in real time, but rather preprocedurally, to identify lumbar spine anatomy and to

Figure 1. Longitudinal Paramedian and Transverse Ultrasound PlanesPerform the longitudinal scan first by starting at 2-3 cm right of the spine at the level of the sacrum. Move the probe cephalad until the chosen interspace is identified. Note the sawtooth pattern, with the “teeth” represented by the articular processes and the space between the interspace. When performing the longitudinal scan, ensure the ligamentum flavum – dura (LF-D) unit is in the center of the screen. The articular processes should be to the left and right of center. When performing a scan in the transverse plane, make a skin mark in the middle of the top and side of the ultrasound probe (upper right image), and then connect the lines to mark the ideal inser-tion point. Note the angle of the probe that provides the brightest image of the LF-D; a good landmark is the “=” sign, represented by the LF-D on top and vertebral body on bottom in the image on the lower right.


estimate the ideal needle insertion point and depth to loss of resistance. The use of U/S-P can be challenging because the bony structures of the lumbar interspace create a very narrow viewing plane.7 In addition, the structures that need to be visualized are much deeper; therefore, a low-frequency (2-5 MHz) curved probe is required (Figure 1). The curved probe provides a wider field of view (acoustic window), and the lower frequency allows the sound waves to penetrate deeper into tissues. Unfortunately, because of the deeper tissue penetration, the image resolution is lower, and some structures may not be visualized.7

With U/S-P, 2 viewing planes are used: a longitudinal paramedian and a transverse plane (Figures 1 and 2). When compared with the transverse plane, the longitu-dinal paramedian plane allows for accurate identification of the interspaces and provides better image quality of the ligamentum flavum–dura (LF-D) unit,7,8 articular processes, spinal canal, and vertebral body.9 With exist-ing ultrasound equipment, it is difficult to discern the difference between the ligamentum flavum and posterior dura mater; thus, it is defined as a single unit, the LF-D. In the transverse plane, structures that can be visualized are the spinous process, articular processes, transverse process, LF-D, and vertebral body.

The longitudinal paramedian viewing plane can be used to estimate the midline of the interspace in the long axis by identifying the sawtooth pattern, with the “saws” rep-resenting the articular processes and the spaces between the teeth representing the lumbar interspaces (see Figure 1). Scanning in the longitudinal paramedian plane starts with the probe placed 2 to 3 cm to the left of the midline of the sacrum and slightly angled to target the center of the spinal canal. The probe is moved cephalad until the interspace chosen for needle placement is centered in the middle of the ultrasound screen (see Figures 1 and 2). A mark is placed on the skin at the midline of the interspace. Additional interspaces between L5-S1 and L1-L2 may also be marked, if desired. Next, the probe is turned perpen-

dicular to the long axis to obtain the transverse plane view. If the probe is overlying a spinous process, the spinous process may appear as a bright signal with a dark shadow spreading out from top to bottom, much like an upside down “v”. The probe is then moved caudad or cephalad to obtain the brightest image of the LF-D unit within the interspace. With a typical image, the LF-D unit will be identified as the first bright structure seen in the midline in a similar plane as the transverse processes, followed by a dark space, and then the vertebral body (see Figures 1 and 2). The ultrasound probe can be tilted slightly up or down to obtain the brightest image of the LF-D. The midline of the interspace should be centered in the middle of the screen; a mark should be placed on the skin on the center of the top and side of the ultrasound probe, and the lines should be connected with a skin marker (Figures 1 and 3). The intersection of these 2 lines represents the ideal inser-tion point. Note the angle at which the brightest image of the LF-D is identified; this will be the needle angle used when starting the procedure. The transverse image can be frozen and the built-in calipers used to estimate the ultra-sound depth from the skin to the posterior border of the LF-D. During placement of the epidural catheter during labor, when loss of resistance is obtained, a sterile skin marker can be used to make a mark on the epidural needle to note the needle depth. Later, the ultrasound depth and needle depth can be compared. Alternatively, the nearest 0.5-cm mark on the epidural needle can be noted and compared with the ultrasound depth. For a more detailed description of the procedure, see the Carvalho video clip10 and review article.7

Review of Literature• Search Strategy. The literature was systematically re-viewed to identify articles evaluating the efficacy of U/S-P to facilitate placement of neuraxial anesthetics in laboring parturients. MEDLINE and the Cochrane Collaboration databases were searched for articles published in English

Figure 2. Longitudinal and Transverse Plane Ultrasound ImagesAbbreviation: LF-D, ligamentum flavum–dura mater.


between the years 1980 and 2010. The MeSH search terms included preprocedural, ultrasonography, partu-rients, neuraxial, lumbar, learning curve, epidural, and anesthesia. All study designs were included. Reference lists of identified studies were hand searched until no new references were found. Articles were reviewed by two of us (D.S. and S.B.) for inclusion.

• Description of Studies. In the search, we identified 16 studies on 1,373 subjects: 1 systematic review,3 5 ran-domized controlled trials (RCTs),4,5,11-13 1 cohort study,14 1 case-control study,15 and 8 descriptive-correlational studies2,9,16-21 (Table).2-5,9,11,13-23 The only other relevant research was a learning curve study by Margarido et al22 to determine the amount of training needed to achieve competence in U/S-P. Of the 16 studies, 11 were pub-lished by research groups in Germany (N = 575)4,9,11-14 and Canada (N = 261).2,15,16,20,22 One other RCT was done by Vallejo et al,5 who found that U/S-P significantly decreased the failure rate of epidural anesthetics during labor that were administered by first-year anesthesia residents supervised by a staff anesthesiologist (N = 370).

A substantial number of studies have been published, many as RCTs.3-5,11-13 It should be noted, however, that a risk of publication bias, or “dominating center bias,”3

may exist because all but 1 of the RCTs were done by Grau et al,4,11-13 and a majority of the other studies were done by the research group of Carvalho et al.2,15,16,20,24 The Table is a synthesis table showing the results of the literature review.

The next section reviews results of the literature review; findings are organized according to study design (eg, descriptive-correlational, case-control and cohort, RCTs).

Results• Descriptive-Correlational, Case-Control, and Cohort Studies. Of the 16 studies identified in the literature search, 6 described how U/S-P can accurately estimate the depth to the epidural space and how the ultrasound depth correlates with needle depth when loss of resis-

tance is obtained.2,16-19,21 In 1980, Cork et al17 first de-scribed the U/S-P technique in parturients; these authors found a strong correlation (r = 0.980) between ultra-sound depth and needle depth. In 200716 and 2009,2 in-vestigators from Mount Sinai Hospital, Toronto, Canada, reported that U/S-P estimated ultrasound depth was strongly correlated with needle depth. Concordance cor-relation coefficients ranged from r = 0.7902 to r = 0.880,16 with lower correlations observed in obese parturients.2 Furthermore, in obese parturients, positive correlations were found between BMI and ultrasound depth (r = 0.435) and needle depth (r = 0.580). This finding sug-gests that as BMI increases, ultrasound depth and needle depth are greater.

Several of the studies in this review demonstrated that the ultrasound depth is an accurate estimate of the needle depth at which loss of resistance is obtained in parturi-ents. Mean ± SD differences between the ultrasound depth and needle depth range from 0.010 ± 0.35 cm16 to 0.3 ± 0.5 cm,2,17,18 with larger differences reported in obese par-turients.2 The ultrasound depth tends to underestimate the needle depth, especially in obese parturients, because of soft tissue compression with the probe.2 Balki et al25 demonstrated that the depth to the epidural space was deeper in obese parturients (BMI range, 33-86 kg/m2), with a mean needle depth of 6.6 ± 1.0 cm. In their study, Balki et al2 reported that loss of resistance was obtained at more than 8 cm in only 17% of parturients. In contrast, Arzola et al16 reported a mean ± SD needle depth to loss of resistance of 4.6 ± 0.72 cm in a sample of parturients with a BMI range of 22.2 to 42.5 kg/m2. These results indicate that in a majority of patients, a 10-cm epidural needle should be long enough to obtain loss of resistance.

U/S-P has been reported to increase the success of epidural placement. Arzola et al16 found that using U/S-P to identify the ideal insertion point resulted in no needle reinsertions in 91.8% of the parturients and no need to redirect the needle in 73.7% of parturients. In 96.7% of parturients, the epidural space was identified in 2 or

Figure 3. Skin Markings for Longitudinal and Transverse Scanning Planes


So

urc

e D

esig

n/s

amp

le

Res

ult

s C

on

clu

sio

n

Cor

k et

al17

D

C; N

= 3

6 (M

= 2

2; F

= 1

4)

UD

= 4

.45

[0.1

0] c

m; N

D =

4.5

0 [0

.10]

cm

; UD

:ND

, r =

0.9

80

U/S

-P s

cann

ing

may

be

bene

fici

al

Cur

rie18

D

C; N

=75

U

D =

4.1

3 (2

.9-7

.2) c

m; N

D =

4.3

5 (3

.2-7

.1) c

m; r

= 0

.960

U

/S-P

acc

urat

e es

timat

e of

dep

th t

o LO

R

Wal

lace

et

al19

D

C; N

= 3

6 ob

ese

part

urie

nts

ND

= 0

.216

+ 1

.017

cm

× U

D

U/S

-P r

elia

bly

pred

icts

ND

Gra

u et

al9

DC

; N =

60

LP im

age

qual

ity >

TP

LP

sup

erio

r im

age

qual

ity

Arz

ola

et a

l16

DC

; N =

61

UD

= 4

.66

[0.6

8] c

m; N

D =

4.6

5 [0

.72]

cm

; CC

C, r

= 0

.880

; TP

U/S

-P r

elia

ble

guid

e fo

r to

fac

ilita

te C

LE

inse

rtio

n po

int

succ

ess,

91.

8%; n

o ne

ed t

o re

dire

ct, 7

3.7%

pl

acem

ent

Bal

ki e

t al

2 D

C; N

= 4

6 ob

ese

part

urie

nts

UD

= 6

.3 [0

.8] c

m; N

D =

6.6

[1.0

] cm

; CC

C, r

= 0

.790

; U

/S-P

use

ful i

n ob

ese

part

urie

nts

inse

rtio

n po

int

succ

ess,

76.

1%; n

o ne

ed t

o re

dire

ct, 6

7.4%

Bor

ges

et a

l20

DC

; N =

100

LP

, 100

% im

ages

con

clus

ive/

typi

cal;

atyp

ical

TP

LF:

L1-

L2, 2

%;

LP b

est

imag

e qu

ality

L2

-L3,

1%

; L3-

L4, 3

.1%

; L4-

L5, 1

9.8%

; L5-

S1,

28.

8%

Tran

et

al21

D

C; N

= 2

0 LP

UD

to

ND

, r =

0.8

20

LP u

sefu

l to

estim

ate

ND

Gra

u et

al14

C

ohor

t; N

= 5

3 LF

det

ectio

n: p

regn

ant

vs p

ostp

artu

m, 6

6% v

s 91

%; U

D,

Vis

ibili

ty o

f LF

red

uced

in p

regn

ancy

5.

4 [0

.85]

vs

4.8

[0.7

3] c

m

Lee

et a

l15

Cas

e-co

ntro

l; A

DP

, N =

18;

C: N

= 1

8 A

bnor

mal

LF

sono

anat

omy

> in

AD

P g

roup

; OR

, 8.2

1; 9

5%

Cho

ose

inte

rspa

ce w

ith b

est

imag

e LF

C

I, 3.

07-2

2

Gra

u et

al11

R

CT;

U/S

-P, N

= 3

6; C

, N =

36

Att

empt

s: C

, 2.6

[1.4

] vs

U/S

-P, 1

.5 [0

.9];

punc

ture

site

s:

Ultr

asou

nd f

acili

tate

s pl

acem

ent

with

C

, 1.5

[0.7

] vs

U/S

-P, 1

.3 [0

.05]

; cat

hete

r ad

vanc

emen

t: C

, pr

esum

ed d

iffic

ult

plac

emen

t

1.

3 [0

.6] v

s U

/S-P

, 1.1

[0.4

]

Gra

u et

al27

R

CT;

U/S

-P-C

SE

, N =

40;

CS

E, N

= 4

0 Fi

rst-

atte

mpt

suc

cess

: U/S

-P-C

SE

: CS

E, 7

5% v

s 20

%;

U/S

-P f

acili

tate

s C

SE

pla

cem

ent

No.

of

inte

rspa

ces,

1.0

vs

1.17

5; r

= 0

.920

Gra

u et

al13

R

CT;

U/S

-P, N

= 1

50; C

, N =

150

P

unct

ure

atte

mpt

s: 1

.3 [0

.6] v

s 2.

2 [1

.1];

punc

ture

site

s:

U/S

-P f

acili

tate

CLE

pla

cem

ent

in p

artu

rient

s

1.

1 [0

.4] v

s 1.

3 [0

.6];

inco

mpl

ete

anal

gesi

a: 8

% v

s 2%

;

U

D, 5

.3 [0

.79]

vs

ND

, 5.1

[0.9

2] c

m

Gra

u et

al4

RC

T; U

/S-P

, N =

5; C

, N =

5

300

CLE

s pl

aced

in e

ach

grou

p: s

ucce

ss r

ate,

firs

t 10

CLE

s,

For

resi

dent

s, U

/S-P

hig

her

succ

ess

com

pare

d

U

/S-P

to

C, 8

6% ±

15%

vs

60%

± 1

6%; s

ucce

ss r

ate,

firs

t 60

w

ith p

alpa

tion

CLE

s, U

/S-P

to

C, 9

4% ±

9%

vs

84%

± 1

5%

Val

lejo

et

al5

RC

T; U

/S-P

, N =

189

; C, N

= 1

81

CLE

fai

lure

: U/S

-P t

o C

, 1.6

% v

s 5.

5%; p

unct

ure

atte

mpt

s,

U/S

-P im

prov

es s

ucce

ss o

f C

LE p

lace

men

t by

1

(1-6

) vs

2 (1

-6);

staf

f in

terv

entio

n, 2

8.6%

vs

35.4

%; C

CC

, fi

rst-

year

res

iden

ts

r =

0.9

40

Sch

nabe

l et

al3

Met

a-an

alys

is; i

nclu

ded

RC

Ts, c

ase-

P

unct

ure

atte

mpt

s: M

D, –

0.92

; No.

of

inte

rspa

ces:

MD

, –0.

2;

U/S

-P m

ay im

prov

e ef

fica

cy a

nd s

afet

y of

CLE

cont

rol,

and

coho

rt s

tudi

es, 1

966-

2009

ca

thet

er a

dvan

cem

ent:

MD

, –0.

51; P

DP

H R

R, 0

.28;

firs

t-at

tem

pt

plac

emen

t in

par

turie

nts

succ

ess

rate

, 71%

; firs

t in

ters

pace

suc

cess

rat

e, 8

8.3%

Mar

garid

o et

al22

18

ane

sthe

siol

ogis

ts

Com

pete

nce

to ID

inte

rspa

ce, 2

7% w

ith m

edia

n of

11

atte

mpt

s

>20

sup

ervi

sed

tria

ls t

o ac

hiev

e co

mpe

tenc

e

(r

ange

, 8-1

8); c

ompe

tenc

e to

ID in

sert

ion

poin

t/de

pth

to L

F, 0

%

Tab

le.

Syn

thes

is o

f O

bst

etri

cal A

nes

thes

ia P

rep

roce

du

ral U

ltra

son

og

rap

hy

Lite

ratu

reA

bbre

viat

ions

: AD

P, a

ccid

enta

l dur

al p

unct

ure;

C, c

ontr

ol g

roup

; CC

C, c

onco

rdan

ce c

orre

latio

n co

effi

cien

t; C

I, co

nfid

ence

inte

rval

; CLE

, con

tinuo

us lu

mba

r ep

idur

al; C

SE

, com

bine

d sp

i-na

l epi

dura

l; D

C, d

escr

iptiv

e-co

rrel

atio

nal s

tudy

; ID

, ide

ntify

; LF,

liga

men

tum

flav

um; L

OR

, los

s or

res

ista

nce;

LP,

long

itudi

nal p

aram

edia

n pl

ane;

MD

, mea

n di

ffere

nce;

ND

, nee

dle

dept

h;

OR

, odd

s ra

tio; P

DP

H, p

ostd

ural

pun

ctur

e he

adac

he; R

CT,

ran

dom

ized

con

trol

led

tria

l; R

R, r

elat

ive

risk;

TP,

tra

nsve

rse

plan

e; U

/S-P

, ultr

asou

nd; U

D, u

ltras

ound

dep

th.


fewer needle redirections. In contrast, lower success rates were found in obese parturients, in whom the estimated ideal insertion point resulted in no needle redirections in 76.1 % and no need to redirect the needle in 67.4%.2 These 2 studies demonstrated that identification of the ideal insertion point with U/S-P may help facilitate epi-dural catheter placement in parturients. It is important to point out that in both studies, all U/S-P scans were per-formed by the same experienced senior staff anesthesia provider and that all epidural catheters were placed by senior residents or fellows.

Image quality of the sonoanatomy (anatomy and struc-tures seen during ultrasound examination) was reported in several of the studies.2,9,16,20 Good image quality of the LF-D ranges from 67%2 to 100%,16 with lower image quality reported when parturients are obese.2 A limita-tion of several studies was that image quality was rated as good or poor, rather than measured on a Likert scale.2,16 Image quality in the longitudinal paramedian plane is higher when compared with the quality of images in the transverse plane.9,20 Borges et al20 reported the transverse plane has a higher incidence of atypical or inconclusive images of the LF-D compared with the longitudinal plane (atypical LF-D incidence, 19.8%-28.8%). The reduced image quality in the transverse plane may be due to ar-tifact; however, it may be a result of a residual shadow from the spinous process.20 Poor image quality of the LF-D may be an anatomic variation associated with diffi-cult epidural catheter placement and dural puncture. Lee et al15 found that the odds of a dural puncture were 8.21 times more likely with abnormal sonoanatomy of the LF-D (95% confidence interval, 3.07-22.0; P < .0001). Likewise, poor image quality may be due to increased soft tissue and edema in the lumbar interspaces, exaggerated lordosis, or loosening of connective tissue.14

• Randomized Controlled Trials. RCTs have consis-tently demonstrated that U/S-P significantly decreases the number of puncture attempts (defined as any ad-vancement of the epidural needle forward) and punc-ture sites (interspaces).5,11-13 U/S-P seems to decrease the number of puncture attempts by approximately 1 attempt5,11,13 and the number of puncture sites by 0.2 at-tempts.11,13 It is important to note that all but one5 RCT was published by Grau et al.4,11-13 With the exception of a learning curve study4 and the study by Vallejo et al,5 all ultrasound scans and epidural catheters were placed by the principal investigator in the reviewed studies.

Several studies reported that U/S-P resulted in de-creased pain during epidural catheter placement, de-creased patchy or failed epidural anesthetics, and de-creased pain scores. When compared with a control group, parturients who had U/S-P reported significantly lower pain during epidural catheter placement.11,13 Pain scores with epidural catheter placement during labor decreased from 0.313 to 1.0 cm11 on a 0 to 10 visual

analog scale when U/S-P was used. In 1 investigation of parturients with presumed difficult placement, no sig-nificant difference was found in the incidence of asym-metric, patchy, or failed epidural anesthesia.11 However, in another study, the incidence of incomplete analgesia was decreased by 6% when U/S-P was used in parturi-ents without presumed difficult epidural catheter place-ment.13 Vallejo et al5 found that when U/S-P was used, the epidural anesthetic failure rate (pain score > 3/10 after 3 boluses) decreased from 5.5% in the control group to 1.6% in the ultrasound group. No significant differ-ences in the numbers of accidental dural punctures or postdural puncture headaches or backache were reported in any of the RCTs.5,11-13

In 2003, Grau et al4 conducted an RCT to determine if the use of U/S-P hastened the learning curve of the first 60 lumbar epidural catheters placed by anesthe-sia residents. Residents in the ultrasound group were provided with information on the ideal insertion point, estimated angle, and estimated depth to the epidural space. The control group placed the epidural catheters in a conventional way using the loss of resistance technique without the use of preprocedural ultrasonography. All residents were alone when placing the epidural catheter. Successful placement was deemed to have occurred when there was adequate anesthesia with fewer than 3 attempts at a single level without changing epidural technique and a pain score less than 1 during the procedure. After the first 10 attempts, the ultrasound group had an initial success rate of 86% compared with the control group, which had a rate of 60%. During the next 50 epidural an-esthetics, the ultrasound group achieved a success rate of 94%, while the control group reached 84%. These results suggest that U/S-P increases the proficiency of epidural catheter placement during labor and points to the value of ultrasound imaging for teaching and learning obstetric regional anesthesia.

• Systematic Review. One systematic review and meta-analysis of published studies between 1966 and 2009 sought to assess the efficacy and safety of U/S-P.3

The investigators found the U/S-P pooled first attempt success rate to be 71% and the first interspace success rate to be 88.3%. Patients in the ultrasound groups re-quired approximately 1 fewer puncture attempts, 0.2 fewer puncture levels, and 0.5 fewer catheter advances. Patients in the ultrasound group experienced 0.28 times fewer postdural puncture headaches (95% confidence interval, 0.14-0.57; P = .0005). However, the incidence of back pain was not reduced (relative risk, 0.72; 95% con-fidence interval, 0.47-1.12; P = .15). Asymmetric, patchy, or failed epidural anesthesia rates were not analyzed. In addition, the data from the study by Vallejo et al5 were not included in the analysis. These results suggest that U/S-P may improve the efficacy and safety of epidural catheter placement in parturients. However, publication


and center bias may have influenced the results because Grau et al reported 84% of the data.

• Other Studies. Margarido et al22 conducted a learn-ing curve study to determine the amount of training needed to achieve competence in U/S-P. The investiga-tors’ power analysis determined that 18 anesthesiologists would be needed to conduct a learning curve analysis. Participants were provided with educational material and videos on ultrasound-facilitated epidural catheter placement (U/S-P) and attended a 45-minute lecture on U/S-P, followed by a demonstration on a live model and a 30-minute hands-on workshop in a small group setting. At 7 to 14 days later, the participants were evaluated individually on their ability to identify the interspace, estimate the ideal insertion point, and approximate the LF-D depth. They were given up to 20 attempts for each of these outcomes, with 2 minutes allowed for each attempt and up to 50 minutes per participant. The inves-tigators concluded that only 27% of participants obtained competence at determining the interspace, with a median of 11 attempts. At the end of the course, none were able to demonstrate competence in identifying the ideal inser-tion point or LF-D depth. These results suggest that some providers may require a substantial amount of practice before they are competent in performing U/S-P.

DiscussionResults of this review reveal that U/S-P may be effica-cious in decreasing the number of puncture attempts, interspace determinations, and catheter insertions when attempting to place an epidural catheter in a parturient. In addition, 1 study of anesthesia trainees suggested a reduced epidural failure rate when U/S-P was used.5 The reason for improved efficacy may be the placement of the epidural catheter in the midline, which allows for a more even spread of local anesthetic.

In a majority of the studies, epidural catheter place-ment was performed by an experienced anesthesia pro-vider with extensive experience with U/S-P.2,11,13,14,16,20 This is an important distinction, given the findings of Margarido et al,22 which suggest there is a substantial learning curve to obtain competence. Further research is needed to determine the amount of practice required to obtain competence in performance of U/S-P scanning to identify the interspace and ideal insertion point and estimate the LF-D ultrasound depth.

A frequent concern expressed by some anesthesia providers is that use of U/S-P will delay epidural catheter placement during labor. When performed by experienced anesthesia providers, U/S-P increases the total procedure duration by only 1 to 5 minutes.7,13 However, a study by Chin et al26 in 2011 found that the use of U/S-P resulted in a 2-fold increase in the first-attempt success rate for spinal anesthesia in nonobstetrical surgical patients with suspected difficult backs. In this Chin et al26 study, the

investigators noted the ultrasound scanning duration was partially offset by the shorter time needed for administra-tion of spinal anesthesia in the ultrasound group.

Some anesthesia providers also believe they do not need to use U/S-P to successfully place an epidural cath-eter during labor. We agree that a majority of parturients do not require U/S-P to facilitate successful epidural cath-eter placement. Nevertheless, in some cases of difficult placement of an epidural catheter during labor, U/S-P may increase the likelihood of successful placement.11 Parturients who are morbidly obese and have a potential difficult airway may benefit the most from U/S-P because they have higher rates of failed epidural anesthetics and need for cesarean delivery.1,27 However, RCTs of U/S-P in morbidly obese parturients are lacking.

Additional unanswered questions include whether ab-normal sonoanatomy or atypical images seen during the U/S-P examination are predictive of epidural anesthetic failure. As is evident in this review, the presence of ab-normal sonoanatomy was predictive of accidental dural puncture. However, it is not known if the presence of abnormal sonoanatomy is associated with increased epi-dural anesthetic failure rates. Future studies are needed to test the hypothesis that abnormal sonoanatomy is as-sociated with epidural anesthetic failure.

How can anesthesia providers incorporate the findings of this review into clinical practice? First, they should attempt to obtain experience with U/S-P in a controlled setting. At our facility, we frequently hold small group practice sessions in which didactic material is provided on the procedure, and anesthesia providers are able to practice performing ultrasound scans on volunteers with the guidance of an anesthesia provider experienced with the technique. During the teaching sessions, video clips10 and review articles7,8 are provided as educational resources, and readers are referred to a recent review article by Chin et al.8

Second, anesthesia providers should practice using U/S-P on parturients in whom difficulty inserting an epidural catheter is not expected, such as during an elec-tive cesarean delivery. This approach provides a more controlled setting in which to perform the ultrasound scanning and allows a trainee to compare the ultrasound depth with the needle depth. In a teaching institution, the following demonstrations should be considered when working with new anesthesia trainees: how to perform the procedure, how to identify the relevant anatomy and ideal insertion point, and how to estimate the depth to the LF-D. As the student gets closer to the estimated depth, staff can provide feedback as to what tactile sensa-tions should be felt when approaching the epidural space.

ConclusionThis course offers a state-of-the-science review and some practical tips on the use of U/S-P to facilitate epidural


catheter placement during labor. We suggest that this technique may improve the efficacy of epidural catheter placement during labor in certain populations; however, we also acknowledge areas where further research is needed. Anesthesia providers are encouraged to find ways to incorporate findings of this review into their clinical practice.

REFERENCES 1. Dresner M, Brocklesby J, Bamber J. Audit of the influence of body

mass index on the performance of epidural analgesia in labour and the subsequent mode of delivery. BJOG. 2006;113(10):1178-1181.

2. Balki M, Lee Y, Halpern S, Carvalho JC. Ultrasound imaging of the lumbar spine in the transverse plane: the correlation between esti-mated and actual depth to the epidural space in obese parturients. Anesth Analg. 2009;108(6):1876-1881.

3. Schnabel A, Schuster F, Ermert T, Eberhart LH, Metterlein T, Kranke P. Ultrasound guidance for neuraxial analgesia and anesthesia in obstetrics: a quantitative systematic review [published online ahead of print November 15, 2010]. Ultraschall Med. doi:10.1055/s-0029- 1245724.4.

4. Grau T, Bartusseck E, Conradi R, Martin E, Motsch J. Ultrasound imaging improves learning curves in obstetric epidural anesthesia: a preliminary study. Can J Anaesth. 2003;50(10):1047-1050.

5. Vallejo MC, Phelps AL, Singh S, Orebaugh SL, Sah N. Ultrasound decreases the failed labor epidural rate in resident trainees. Int J Obstet Anesth. 2010;19(4):373-378.

6. Falyar CR. Ultrasound in anesthesia: applying scientific principles to clinical practice. AANA J. 2010;78(4):332-340.

7. Carvalho JC. Ultrasound-facilitated epidurals and spinals in obstet-rics. Anesthesiol Clin. 2008;26(1):145-158.

8. Chin KJ, Karmakar MK, Peng P. Ultrasonography of the adult tho-racic and lumbar spine for central neuraxial blockade. Anesthesiology. 2011;114(6):1459-1485.

9. Grau T, Leipold RW, Horter J, Conradi R, Martin EO, Motsch J. Paramedian access to the epidural space: the optimum window for ultrasound imaging. J Clin Anesth. 2001;13(3):213-217.

10. Carvalho JC. Ultrasound-guided epidural anesthesia video tutorial. http://www.sonosite.com/education/anesthesiology/clinical-tutorials/guided-epidural/. Accessed June 8, 2011.

11. Grau T, Leipold RW, Conradi R, Martin E. Ultrasound control for presumed difficult epidural puncture. Acta Anaesthesiol Scand. 2001;45(6):766-771.

12. Grau T, Leipold RW, Conradi R, Martin E, Motsch J. Ultrasound imag-ing facilitates localization of the epidural space during combined spinal and epidural anesthesia. Reg Anesth Pain Med. 2001;26(1):64-67.

13. Grau T, Leipold RW, Conradi R, Martin E, Motsch J. Efficacy of ultrasound imaging in obstetric epidural anesthesia. J Clin Anesth. 2002;14(3):169-175.

14. Grau T, Leipold RW, Horter J, Conradi R, Martin E, Motsch J. The lumbar epidural space in pregnancy: visualization by ultrasonogra-phy. Br J Anaesth. 2001;86(6):798-804.

15. Lee Y, Tanaka M, Carvalho JC. Sonoanatomy of the lumbar spine in patients with previous unintentional dural punctures during labor epidurals. Reg Anesth Pain Med. 2008;33(3):266-270.

16. Arzola C, Davies S, Rofaeel A, Carvalho JC. Ultrasound using the transverse approach to the lumbar spine provides reliable landmarks for labor epidurals. Anesth Analg. 2007;104(5):1188-1192.

17. Cork RC, Kryc JJ, Vaughan RW. Ultrasonic localization of the lumbar epidural space. Anesthesiology. 1980;52(6):513-516.

18. Currie JM. Measurement of the depth to the extradural space using ultrasound. Br J Anaesth. 1984;56(4):345-347.

19. Wallace DH, Currie JM, Gilstrap LC, Santos R. Indirect sonographic guidance for epidural anesthesia in obese pregnant patients. Reg Anesth. 1992;17(4):233-236.

20. Borges BC, Wieczorek P, Balki M, Carvalho JC. Sonoanatomy of the lumbar spine of pregnant women at term. Reg Anesth Pain Med. 2009;34(6):581-585.

21. Tran D, Kamani AA, Lessoway VA, Peterson C, Hor KW, Rohling RN. Preinsertion paramedian ultrasound guidance for epidural anesthesia. Anesth Analg. 2009;109(2):661-667.

22. Margarido CB, Arzola C, Balki M, Carvalho JC. Anesthesiologists’ learning curves for ultrasound assessment of the lumbar spine. Can J Anaesth. 2010;57(2):120-126.

23. Grau T, Leipold RW, Fatehi S, Martin E, Motsch J. Real-time ultra-sonic observation of combined spinal-epidural anaesthesia. Eur J Anaesthesiol. 2004;21(1):25-31.

24. Margarido CB, Mikhael R, Arzola C, Balki M, Carvalho JC. The intercristal line determined by palpation is not a reliable anatomical landmark for neuraxial anesthesia [published online ahead of print December 3, 2010]. Can J Anaesth. 2011;58(3):262-266.

25. Balki M. Locating the epidural space in obstetric patients: ultrasound a useful tool: continuing professional development. Can J Anaesth. 2010;57(12):1111-1126.

26. Chin KJ, Perlas A, Chan V, Brown-Shreves D, Koshkin A, Vaishnav V. Ultrasound imaging facilitates spinal anesthesia in adults with difficult surface anatomic landmarks. Anesthesiology. 2011;115(1):94-101.

27. Weiss JL, Malone FD, Emig D, et al; for the FASTER Research Consortium. Obesity, obstetric complications and cesarean delivery rate: a population-based screening study. Am J Obstet Gynecol. 2004; 190(4):1091-1097.

AUTHORSCDR Dennis Spence, CRNA, PhD, NC, USN, is the chair, Research Educa-tion and Facilitation, Naval Medical Center San Diego, California. This manuscript was written while he was the clinical research director, Uni-formed Services University of the Health Sciences (USUHS), Nurse Anesthe-sia Program, Naval Medical Center San Diego. Email: [email protected].

LCDR Ryan Nations, CRNA, MS, NC, USN, is a staff nurse anesthetist at Naval Medical Center San Diego.

LT Orlando Rivera, CRNA, MSN, NC, USN,* is a staff nurse anesthe-tist at Naval Hospital Camp Pendleton, California.

LT Shawn Bowdoin, RN, BSN, NC, USN, is a student in the USUHS, Nurse Anesthesia Program.

LCDR Bradley Hazen, CRNA, MSN, NC, USN,* is a staff nurse anes-thetist at Naval Medical Center Portsmouth, Virginia.

LT Robert Orgill, CRNA, MSN, NC, USN,* is a staff nurse anesthetist at Naval Medical Center San Diego.

CAPT John Maye, CRNA, PhD, NC, USN, is the director of the Triser-vice Nursing Research Program, Bethesda, Maryland. This course was writ-ten when he was the research director for the USUHS, Nurse Anesthesia Program, Bethesda, Maryland.

*At the time this course was written, they were students in the USUHS, Nurse Anesthesia Program.

DISCLAIMERThe views expressed in this article are those of the authors and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.

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