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Electron Microscopy in Quality Control of Equipment
Used in Regional Anesthesia
Andrés López, MD, Miguel Angel Reina, MD, Fabiola Machés, MD, Oscar de Leon Casasola, MD,
José Antonio De Andrés, MD, and Jorge Garcı́a Trapero, MD
We evaluate the use of the scanning electron microscopy to
study different materials used in regional anesthesia with the aim
of finding an alternative method for quality analysis of such items.
We study spinal needles, epidural catheters, and epidural filters
of different manufacturers and we verify differences between
products labeled with the same denomination. We find fissures,
broken tips, and faults in unused spinal needles. The characteristics of the catheters and microcatheters were observed. We
observed structural details from pores in epidural filters and the
mechanisms involved in the trapping of particles facilitated by
the presence of several numbers of pores randomly distributed in
layers within the filtering lamina.
Copyright 2002, Elsevier Science (USA). All rights reserved.
nesthesiologists give great relevance to the equipment used
in regional anesthesia to improve the safety of these techniques while reducing possible complications.1 However, the
information related to this equipment given by makers is occasionally incomplete and sometimes does not meet the needs of
anesthesiologists.2 This lack of information may be a factor to
be considered when evaluating complications derived from
these techniques.
Scanning electron microscopy (SEM) gives the opportunity
to observe with significant precision regional anesthetic tools
such as needles, catheters, and filters, among others.3-5 Observations made under SEM show differences between items made
by different companies that have been given equal denomination.1 Therefore, it would not be incorrect to think that such
items did not pass the same quality controls nor did they comply with the same standards.
A
Methods
When using SEM, nonmetallic objects must be stained with
heavy metal salts to enhance contrast. The samples to be observed are coated with a gold microfilm by circulating 20 A
electrical current through a gold electrode, within a vaporiza-
From the Department of Anesthesiology and Critical Care, Hospital
General de Móstoles, Madrid, Spain; Department of Anesthesiology and
Critical Care, Hospital Madrid Monteprı́ncipe, Madrid, Spain; Department
of Anesthesiology and Critical Care Medicine, Roswell Park Cancer
Institute, Buffalo, NY; and Department of Anesthesiology and Critical
Care, Hospital General Universitario, Valencia, Spain.
Address reprint requests to Andrés López, Department of Anesthesiology and Critical Care, Hospital de Móstoles, Rı́o Júcar s/n Móstoles
(28935), Madrid, Spain.
Copyright 2002, Elsevier Science (USA). All rights reserved.
1084-208X/02/0604-0002$35.00/0
doi:10.1053/trap.2002.123511
172
tion chamber SCD 004 Balzers Sputter Coater (Balzers, Bal Tec
AG, Fürstentum, Lichtenstein) regulated to 0.1 millibar vacuum. Metallic objects such as spinal needle samples do not
need to undergo this process, but if gold microfilm coating is
used in them, the presence of non-metallic debri on their surface could be better detected. In our study, we used a JEOL JSM
6400 Scanning Microscope, Tokyo, Japan.
Spinal Needles
We observed under SEM 200 spinal needles that had not been
used previously; they all were 25G and had a pencil-point tip.
We divided them in 5 groups of 40 units each, chosen from 2
lots and 5 different manufacturers; these groups were labeled as
A, B, C, D, and E.
The spinal needles were observed under SEM, magnified at
50⫻, 300⫻, 1,200⫻, and 2,000⫻. A significant number of
needles with damage at the tip was found. These samples
showed fissures at their tips or blunt tips. We also studied the
presence of metallic debris in excess of 10 ␮m adhered to the
spinal needle surface.
Catheters and Microcatheters
We observed under SEM 80 new catheters and microcatheters
for spinal and epidural blocks from different manufacturers
including A, 19G-catheter, with a single orifice, open distal end
and introducer; B, 20G-catheter, with 3 side orifices and closed
distal end; C, 28G-microcatheter with a single orifice, open end
and introducer; and D, 30G microcatheter with a single orifice
and open distal end. The distal end of our samples was cut,
measuring 10 mm in length. We handled the samples mechanically to avoid sample contamination; they were coated with a
gold microfilm and observed under SEM.
Epidural Filters
We observed 75 epidural filters with pores of sizes between 0.2
and 0.22 ␮m; these filters corresponded to 3 different makers
labeled as A, B, and C. We dismounted the filters, taking away
the outer plastic cover, avoiding manual handling of the filtering mesh to preserve it from external contamination. We iden-
TABLE 1. Percentage of Faulty Tips in New Spinal
Needles
Magnification
% Blunt Tips
% Fragmented Tips
50⫻
300⫻
1,200⫻
2,000⫻
8
12.5
20
23
8
37.5
42
45.5
Techniques in Regional Anesthesia and Pain Management, Vol 6, No 4 (October), 2002: pp 172-179
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TABLE 2. Percentage of Needles With Metallic
Fragments
Magnification
% Needles With
Metallic Fragments
50⫻
300⫻
1200⫻
2000⫻
14
20.5
27
27
tified a prefiltering and a postfiltering surface. The samples
were mounted over slides and coated with gold microfilm. We
used cryofracture technique to cut cleanly through the structure of the filtering layer. Cryofracture allows freeze fracturing
of samples; applying liquid nitrogen, the temperature of the
samples is lowered sharply and the elasticity of the treated
materials is significantly reduced. This process allows one to
make very precise cuts.
Fig 2. Spinal needles. Two Whitacre needles made by the
same company, with equal denomination. SEM, original
magnification 50ⴛ.
Results
Spinal Needles
Table 1 gives percentages of faulty spinal needles at different
degrees of magnification. Table 2 shows percentage of needles
with metallic fragments adhered to their surface (Figs 1-14).
Catheters and Microcatheters
Table 3 shows various aspects of these catheters and microcatheters.
Epidural Filters
Table 4 gives the average diameter of pores of the epidural
filters observed. We found that in the prefiltering surface, the
sizes of the pores varied (P ⬍ .01), being bigger than makers
had specified. Structural differences were found among the 3
types of filters studied. We could also see under SEM continuous filtering planes along the structure of the filters (Figs 15
and 16).
Fig 1. Spinal needles. Five Whitacre needles made by the
same company. SEM, original magnification 18ⴛ.
ELECTRON MICROSCOPY AND QUALITY CONTROL
Discussion
The type of spinal needle used to perform subarachnoid blocks
is relevant when evaluating the quality, safety, and complications derived from this technique.1 There have been several
improvements over the last years, and great efforts have been
made to design a safer spinal needle, modifying the design of
the tip and reducing the external diameter of the needle to
minimize the damage caused to the dural membrane.6,7 Studies
describing the dural membrane damage caused by Quincke
needles and pencil-point needles have shown that all spinal
needles produce tearing of fibers in their way through the dura.
Therefore, the concept of a nontraumatic needle is no longer
considered valid.8
The findings in our study show a number of spinal needles
with imperfections in their tips. The presence of such imperfections could increase the degree of damage to the dura when
used to perform subarachnoid blocks (Figs 4-12). Obviously,
when we use a bigger magnification, we can notice better the
Fig 3. Spinal needles. Three Whitacre needles made by the
same company, with equal denomination. SEM, original
magnification 40ⴛ.
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Fig 4. Spinal Whitacre needle with blunt tip. SEM, original
magnification 800ⴛ.
faults of the needles. When we watch a broken tip at 50⫻, the
fissure is at least 6 ␮m wide, and if we discover this fissure at
300⫻, this would be 1 ␮m wide (Figs 4-12). Therefore, when
the spinal needle punctures the dura mater, bundles of collagen
fibers could be pierced by these fissures. The collagen fibers
could then be dragged and possibly torn, giving place to a
bigger lesion than we could expect. These findings do not necessarily imply that all the needles observed were faulty or that
quality controls had been incorrect.
Fracture lines observed at 1,200⫻ or 2,000⫻ might not imply an increase in the lesion caused by the spinal needle because
their width is too small to allow the entrance of collagen fibers
inside them. We think that a needle is blunted when the tip
ends in a flat angle (Fig 4).
The tension caused in the dural membrane by a blunted tip
needle in its way through is bigger than if the needle had a
suitable point; this higher force of traction applied to the collagen fibers would also cause a bigger lesion. On the other hand,
the tent effect caused by the needle would be amplified, which
according to some researches could increase the number of
cases of paresthesias.
Metallic debris found on the surface of spinal needles or close
to the tip’s side orifice could act like minute blades, shearing
Fig 5. Spinal Whitacre needle with fragment tip. SEM, original magnification 250ⴛ.
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Fig 6. Spinal Whitacre needle with fragment tip. SEM, original magnification 30ⴛ.
collagen fibers when we introduce the needle (Figs 9-11). Occasionally, longitudinal fissures were also seen along spinal
needles; these fissures are generated during the making of spi-
Fig 7. Spinal Whitacre needle with fragment tip. SEM, original magnification 300ⴛ.
LOPEZ ET AL
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Fig 8. Spinal Whitacre needle with fragment tip. SEM, original magnification 300ⴛ.
Fig 10. Spinal Whitacre needle with imperfections in its lateral hole. SEM, original magnification 500ⴛ.
Fig 9. Spinal Whitacre needle with imperfections in its tip.
SEM, original magnification 300ⴛ.
ELECTRON MICROSCOPY AND QUALITY CONTROL
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Fig 11. Spinal Whitacre needle with metallic fragments on its surface. SEM, original magnification 300ⴛ.
Fig 12. Spinal Whitacre needle with longitudinal fissures.
SEM, original magnification 200ⴛ.
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Fig 13. Spinal Whitacre needle with foreign particles in its
lumen. SEM, original magnification 200ⴛ.
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TABLE 4. Average Diameter of Pores in Epidural Filters
Filter
Filter diameter (␮m)
Prefiltering Surface
Postfiltering Surface
A
B
C
0.70
0.26
0.45
0.26
2.07
0.46
TABLE 5. Filtering Membrane Thickness
Filter
A
B
C
Thickness (␮m)
Number of filtering planes
130
140
118
220
165
210
Fig 14. Spinal Whitacre needle. Detail of surface of its lumen.
SEM, original magnification 30ⴛ.
TABLE 3. Characteristics of Catheters and
Microcatheters
Catheters
A
B
C
D
Diameter
Orifices
Number
Location
Free particles
Number
Sizes (␮m)
Wall catheter
Thickness (␮m)
External
Diameter (␮m)
Orifices
Diameter (␮m)
19G
20G
28G
30G
Single
Distal
3
Side orifices
Single
Distal
Single
Side orifice
Scarce
2-10
Scarce
2-10
Scarce
2-10
Scarce
2-10
200
—
80
30
760
800
350
280
370
350
200
230
ELECTRON MICROSCOPY AND QUALITY CONTROL
Fig 15. Epidural filter. Detail of its pores. SEM, original magnification 20,000ⴛ. (Reprinted with permission.3)
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Fig 17. 20G-Epidural catheter. SEM, original magnification
100ⴛ.
Fig 16. Epidural filter. Detail of its pores. SEM, original magnification 10,000ⴛ. (Reprinted with permission.3)
is to stop the passage of particles. Staphylococcus and Escherichia coli measure about 0.5 to 1 ␮m. The size of pores is on
average over 0.2 ␮m, but the presence of several filtering planes
makes the passage of small particles very difficult. The tortuous
disposition of these filtering planes makes it more difficult to
block a catheter when particles become trapped because there
are numerous other ways left within the filter allowing the
passage of fluids (Figs 15 and 16).
SEM would be a useful tool in the evaluation of quality
controls and setting up of standards for different products used
in regional anesthesia; these techniques may help reducing the
presence of imperfections in these products, improving in this
way the safety and efficacy of regional anesthesia techniques.
nal needles in the polishing process, making the needle more
fragile (Fig 12).
Despite recent advances in spinal needle design and new data
brought about by electron microscopy, researchers do not seem
to agree with all the reasons given to explain post spinal dural
puncture headache and the factors influencing such complication. Even when studies performed by different authors used
the same type of spinal needle, the results were controversial.9
We think that there may be other factors to take in consideration. Electron microscopy shows how same type of spinal
needles and needles of the same make present minimal imperfections such as fissures, fractures, and debris. Also the damage
suffered by a needle, hitting bone while performing a spinal
block, may be of help in explaining different results between
similar studies.10-13
New research techniques such as SEM could be used to
improve quality controls and setting up standards to avoid the
presence of imperfections in spinal needles (Figs 13 and 14). In
relation to epidural catheters, we found differences in catheter
tips that could influence the degree of venous piercing or tip
migration (Figs 17 and 18). Multiple orifice catheters may
present bigger side holes than expected, making the catheter
wall weaker at this site and increasing the chance of placement
distortion and catheter obstruction. The aim of epidural filters
Fig 18. 30G-Microcatheter. SEM, original magnification
100ⴛ
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