DETERMINATION OF THE DISTANCE FROM SKIN TO THE EPIDURAL SPACE IN PARTURIENTS, AND CORRELATION WITH WEIGHT, BODY MASS INDEX, HEIGHT, AND AGE

Mahmood Tabatabai, MD, PHD

PURPOSE

The purpose of the study was to measure the distance between the skin and the epidural space in the lumbar area in parturients receiving epidural block during labor and delivery.

This information helps to prevent or minimize the incidence of inadvertent dural puncture and subsequent post dural puncture headache (PDPH).

PATIENTS AND METHODS

One hundred patients in labor and delivery were included in this study.

Epidural block was performed in Sitting Position at the interspace between the 3rd and 4th Lumbar Vertebras, using a graduated Tuohy needle gauge 17, and Loss of Resistance (LOR) technique. Correct needle entry into the epid space was further confirmed by the relief of labor pain upon injection of Lidocaine into the space.

The Distance between the skin and the epidural space was measured.

The relation of the Body Weight, Body Mass Index (BMI), Height, and Age with the Distance was ascertained using Pearson Correlation Coefficient (r) and Linear Regression Analysis.

P<0.05 was considered statistically significant.

EPIDURAL SPACE

Extends from Foramen Magnum to the 2nd sacral vertebra along the spinal cord dural sac.

EPIDURAL SPACE

EPIDURAL SPACE

ANATOMY OF THE EPIDURAL SPACE

ANATOMY OF THE EPIDURAL SPACE

EPIDURAL BLOCK, SITTING POSITION

EPIDURAL BLOCK, LATERAL DECUBITUS POSITION

EPIDURAL NEEDLE INSERTION

EPIDURAL INJECTION

EPIDURAL NEEDLES

EPIDURAL INJECTION OF THE LOCAL ANESTHETIC

1. Single injection 2. Continuous injection via the epidural

catheter

TECHNIQUE OF EPIDURAL BLOCK

1. Loss of Resistance Technique 2. Hanging Drop Technique

CONFIRMATION OF THE NEEDLE ENTRY INTO THE EPIDURAL SPACE

1. By Loss of Resistance after passing through the Ligamentum Flavum.

2 . Relief of labor pain after injection of the local anesthetic into the epidural space.

RELEVANT STATISTICS:

DESCRIPTIVE STATISTICS: MEAN, SD, SE, MEDIAN, MODE, ETC

PEARSON CORRELATION COEFFICIENT = RR VALUE VARIES FROM (+1) TO (-1)

EQUATION FOR A STRAIGHT LINE: Y=MX+B, WHERE M=SLOPE OF THE LINE, AND B= Y INTERCEPT

STATISTICAL SIGNIFICANCE IS SHOWN BY THE P VALUE:P<0.05 IS STATISTICALLY SIGNIFICANT, AND P<0.01 IS STATISTICALLY EXTREMELY SIGNIFICANT

95% CONFIDENCE INTERVAL (95% CI) = MEAN +/- (2 SE), WHERE SE = SD/SQUARE ROOT OF N, AND N IS THE NUMBER OF OBSERVATIONS

STRAIGHT LINE EQUATIONY = MX + B

0 50 100 150 2000

2

4

6

8

10

Wt (kg)

Dist

ance

(cm

)

RELEVANT STATISTICS:

DESCRIPTIVE STATISTICS: MEAN, SD, SE, MEDIAN, MODE, ETC

PEARSON CORRELATION COEFFICIENT = RR VALUE VARIES FROM (+1) TO (-1)

EQUATION FOR A STRAIGHT LINE: Y=MX+B, WHERE M=SLOPE OF THE LINE, AND B= Y INTERCEPT

STATISTICAL SIGNIFICANCE IS SHOWN BY THE P VALUE:P<0.05 IS STATISTICALLY SIGNIFICANT, AND P<0.01 IS STATISTICALLY EXTREMELY SIGNIFICANT

95% CONFIDENCE INTERVAL (95% CI) = MEAN +/- (2 SE), WHERE SE = SD/SQUARE ROOT OF N, AND N IS THE NUMBER OF OBSERVATIONS

WEIGHT VS DISTANCECORRELATION COEFFICIENT R = 0.7460, P<0.0001SLOPE = 0.044, P<0.0001Y = 0.044X + 1.442

0 50 100 150 2000

2

4

6

8

10

Wt (kg)

Dis

tanc

e (c

m)

BMI VS DISTANCER = 0.6958, P<0.0001

0 20 40 60 800

2

4

6

8

10

BMI

Dis

tanc

e (c

m)

HEIGHT VS DISTANCER = 0.2242, P<0.05

120 140 160 180 2000

2

4

6

8

10

Height (cm)

Dist

ance

(cm

)

AGE VS DISTANCER = 0.09907, P = 0.3268

0 10 20 30 40 500

2

4

6

8

10

Age (year)

Dis

tanc

e (c

m)

RELEVANT STATISTICS:

DESCRIPTIVE STATISTICS: MEAN, SD, SE, MEDIAN, MODE, ETC

PEARSON CORRELATION COEFFICIENT = RR VALUE VARIES FROM (+1) TO (-1)

EQUATION FOR A STRAIGHT LINE: Y=MX+B, WHERE M=SLOPE OF THE LINE, AND B= Y INTERCEPT

STATISTICAL SIGNIFICANCE IS SHOWN BY THE P VALUE:P<0.05 IS STATISTICALLY SIGNIFICANT, AND P<0.01 IS STATISTICALLY EXTREMELY SIGNIFICANT

95% CONFIDENCE INTERVAL (95% CI) = MEAN +/- (2 SE), WHERE SE = SD/SQUARE ROOT OF N, AND N IS THE NUMBER OF OBSERVATIONS

HOW TO FIND M AND B?

STRAIGHT LINE EQUATIONY = MX + B

WEIGHT VS DISTANCECORRELATION COEFFICIENT R = 0.7460, P<0.0001SLOPE = 0.044, P<0.0001Y = 0.044X + 1.442

0 50 100 150 2000

2

4

6

8

10

Wt (kg)

Dis

tanc

e (c

m)

Y = 0.044 X + 1.442

Example 1: The parturient weighs 100 kg. What is the estimated distance from the skin to the epidural space?

X = 100 kg, Y? Y = (0.044 x 100) + 1.442 = 4.4 + 1.442 =

5.842 cm

Y = 0.044 X + 1.442

Example 2: The parturient weighs 75 kg. What is the estimated distance from the skin to the epidural space?

X = 75 kg, Y? Y = (0.044 x 75) + 1.442 = 3.3 +

1.442 = 4.742 cm

POSTDURAL PUNCTURE HEADACHE (PDPH)

PDPH is believed to be due to the leakage of the CSF through a dural tear or defect, resulting in intracranial hypotension.

Usually it develops 12-72 hours after the epidural wet tap, though it may happen almost immediately.

Headache is usually bilateral, frontal, retro-orbital or occipital, and may extend into the neck. It may be associated with photophobia and nausea.

The hallmark of the PDPH is the association with the body position: intensified by sitting or standing up, and relieved or decreased by lying down flat.

TREATMENT OF PDPH

1. Conservative: Bed rest in supine position, oral and intravenous fluids, analgesics (acetaminophen, NSAIDS, opioids), caffeine sodium benzoate 500 mg in 1000 ml crystalloid solution, given intravenously.

2. Epidural blood patch: 15- 20 ml autologous blood injected at the initial site of the epidural block, or one level above or below. 10% of the patients may require a second epidural blood patch.

CONCLUSIONS

The body weight and the BMI appear to be the major determinants of the distance between the skin and the epidural space.

Caution has to be exercised during induction of epidural block to avoid dural puncture and wet tap, which may result in PDPH.

The results may be used as a guide in performing a safe epidural block and avoiding dural puncture.

THANK YOU FOR YOUR ATTENTION.

ABSTRACT

0 20 40 60 800

2

4

6

8

10

BMI

Dist

ance

(cm

)

120 140 160 180 2000

2

4

6

8

10

Height (cm)

Dist

ance

(cm

)

120 140 160 180 2000

2

4

6

8

10

Height (cm)

Dist

ance

(cm

)

0 10 20 30 40 500

2

4

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10

Age (year)

Dist

ance

(cm

)

INTRACRANIAL CONTENTS

Brain accounts for 80% of the volume Blood accounts for 12% of the volume CSF accounts for 8% of the volume

CEREBROSPINAL FLUID (CSF)

Volume: 150 ml in adults, and 50 ml in infants. CSF production: 21-23 ml per hour, or 500-550

ml per day in adults. CSF production is mainly by the choroid plexus

of the cerebral ventricles, and absorption mainly via the arachnoid villi into the cerebral venous sinuses.

BRAIN

Intracranial Pressure (ICP): 7-15 mm Hg Cerebral Perfusion Pressure (CPP) = MAP-ICP, or CPP = MAP-CVP Normally, CPP = 90 – 10 = 80 mm Hg In the systemic circulation: Driving Pressure = Mean Arterial Pressure (MAP) –

CVP Cerebral Blood Flow = 50 ml/100 gm/min Brain weight = 1400 gm

EPIDURAL SPACE

ABSTRACT

WEIGHT VS DISTANCE

BMI VS DISTANCE

AGE

RELEVANT STATISTICS:

DESCRIPTIVE STATISTICS: MEAN, SD, SE, MEDIAN, MODE, ETC

PEARSON CORRELATION COEFFICIENT = RR VALUE VARIES FROM (+1) TO (-1)

EQUATION FOR A STRAIGHT LINE: Y=MX+B, WHERE M=SLOPE OF THE LINE, AND B= Y INTERCEPT

STATISTICAL SIGNIFICANCE IS SHOWN BY THE P VALUE:P<0.05 IS STATISTICALLY SIGNIFICANT, AND P<0.01 IS STATISTICALLY EXTREMELY SIGNIFICANT

95% CONFIDENCE INTERVAL (95% CI) = MEAN +/- (2 SE), WHERE SE = SD/SQUARE ROOT OF N, AND N IS THE NUMBER OF OBSERVATIONS