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Original Research |
1 Department of Diagnostic Radiology and Organ Imaging, Prince of Wales Hospital, The Chinese University of Hong Kong, 30-32 Ngan Shing St., Shatin, Hong Kong, China.
Received April 6, 2004;
accepted after revision October 6, 2004.
Address correspondence to S. C. H. Yu
(simonyu{at}cuhk.edu.hk).
Abstract
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MATERIALS AND METHODS. An in vitro experiment was performed with the use of a model of a fluid collection containing floating sheets of gelatin sponge to mimic a complex body collection consisting of floating fibrinous strands. Five radiologists were asked to perform aspiration from two collections of normal saline and 5% methylcellulose of two different volumes using an ordinary aspiration needle and the drainage needle. The needle was evaluated in a prospective in vivo study of 30 postoperative abdominal collections in 29 consecutive patients that were drained by a single radiologist. Complete evacuation was attempted initially with a conventional aspiration needle. When there was sonographic evidence of residual fluid collection, a repeat aspiration using a drainage needle was performed during the same session.
RESULTS. In the in vitro experiment, the median percentage of fluid aspirated with the conventional needle from the 10- and 15-mL collections of saline was 10% and 15% and from the 10 mL and 15 mL of methylcellulose solution was 20% and 26.67%, respectively, whereas the drainage needle was able to remove 100% of fluid in all attempts. In the in vivo study, the conventional needle was able to remove all drainable fluid from the 12 simple collections. For the 18 complex collections, the drainage needle was always able to remove some residual fluid from the collection after aspiration with the conventional needle. The median percentage of fluid volume aspirated with the conventional needle was 55.6%, whereas that aspirated with both the conventional and drainage needles was 95.5%, with a significant difference by Wilcoxon's signed rank test (p < 0.001).
CONCLUSION. This drainage needle was effective in evacuating fluid from complex abdominal collections that could not be drained with conventional end-hole needles.
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An aspiration needle that is 18-gauge or larger is known to be efficient for aspiration of a simple fluid collection [2, 6, 7]. However, in cases of complex body collections that consist of internal solid components, including floating fibrinous strands and septa, the effectiveness of needle aspiration in removing such collections is limited. The free-floating mobile debris tends to float toward the end hole of aspiration needles because of the suction currents created during aspiration and to block the end hole of needles, preventing further removal of the collection, especially when the abscess is getting smaller and smaller. In this article, I describe a percutaneous drainage needle that is specially designed for effective drainage of complex abscess collections. The characteristic features of the needle and its performance in both in vitro and in vivo environments are discussed.
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In Vitro Experiment
A model of a fluid collection consisting of floating membranes was created
to mimic a body collection consisting of floating fibrinous strands. The model
was composed of a plastic cylindric container that was 4 cm in diameter and
contained 10 or 15 mL of normal saline or 5% methylcellulose solution and 40
pieces of sheets of gelatin sponge (Gelfoam, Upjohn). There were 10 pieces of
5 x 5 x 1 mm gelatin sponge sheets and five pieces of each of the
following six types of gelatin sponge sheets: 5 x 5 x 1 mm, 6
x 6 x 1 mm, 7 x 7 x 1 mm, 8 x 8 x 1 mm, 9
x 9 x 1 mm, and 10 x 10 x 1 mm. The gelatin sponge
sheets were pressed under water to expel air and left to soak with water for 4
hr before being immersed in the normal saline or 5% methylcellulose solution.
The reason for including two different kinds of fluid in the study was to
allow testing of the performance of the needle in two different fluid
viscosities.
Five radiologists were asked to perform needle aspiration of the collections with either a conventional aspiration needle or the drainage needle. The conventional aspiration needle was an 18-gauge thin-walled trocar needle that consisted of an outer cannula identical to that of the drainage needle with a single end hole (disposable trocar needle). The needles were connected to a 20-mL syringe for aspiration. Four collections were prepared for each doctor to aspirate with the conventional aspiration needle and four with the drainage needle; the collections consisted of 10 and 15 mL of normal saline and 10 and 15 mL of 5% methylcellulose solution (Table 1).
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The container of the collection was maintained at a 45° slanting position during the aspiration procedure so that the depth-to-width ratio of the collection was approximately 1. The reason for adopting such a design was to provide a collection with a constant 3D configuration throughout the aspiration procedure. With the tip of both the conventional needle and the drainage needle maintained at the center of the collection, aspiration was performed with care and slow suction to avoid creating a strong current that could bring a floating membrane to block the end hole. Repositioning the needle tip to avoid blockage of the needle tip by floating membranes was allowed. The needle was aggressively agitated to dislodge any blocking floating membrane.
A repeat aspiration was performed when the needle tip was blocked the first time. The volume of aspirate from each collection was recorded to the nearest milliliter when the needle became blocked by gelatin sponge sheets the second time. The volumes of aspirate obtained by the five doctors with the conventional needle and the drainage needle from the four types of collections are shown in Table 1. Wilcoxon's signed rank test was used to calculate the p value when the performance of the conventional needle and the drainage needle was compared.
In Vivo Study
The needle was put to trial in an in vivo study in which 30 abdominal
collections of 29 consecutive patients presenting with postoperative sepsis
were prospectively included. Informed consent was obtained from each patient.
The nature of the operation, the location and size of the collection, and the
features of the internal solid components of the collection as depicted on
sonography are specified in Table
2. Two collections (numbers 12 and 13) belonged to the same
patient. The needle aspiration procedures were performed under sonographic
guidance.
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For each of these collections, complete removal of the fluid component by needle aspiration was attempted initially with the conventional needle (disposable trocar needle). The needle tip was repositioned in a different part of the collection and in different locules of the fluid collection in cases of multiloculated collection until no more fluid could be aspirated. Power suctions with manual aspiration using 20-mL syringes were attempted. Maneuvers were used to prevent the needle's end hole from being blocked by the internal solid components within the collection, including needle withdrawal during aspiration and angling the needle. Aggressive repositioning and agitation of the needle were performed to dislodge blocking debris.
If the fluid collection as shown on sonography could not be completely removed during the initial aspiration, a repeat aspiration was performed during the same session with the drainage needle. The volume of fluid aspirated from the collection with the conventional needle and that aspirated with both the conventional and the drainage needle were recorded and also expressed as a percentage of the total volume of the collection. Wilcoxon's signed rank test was used to analyze the results obtained with the conventional needle alone and the results obtained with both kinds of needles with respect to the volume of the aspirate and the proportion of volume to the total volume of the collection.
The total volume of the fluid collection was taken as the sum of the fluid volume aspirated with both the conventional and the drainage needle plus the volume of residual collection as calculated with the measured dimensions of the residual fluid, rather than calculating from the preaspiration measured dimensions. It was believed that the total volume calculated with this method was likely to be more accurate than that estimated purely from the preaspiration measured dimensions of the collection because the error would likely be larger in a larger preaspiration collection; moreover, the shapes of the collections were usually pleomorphic and irregular and did not conform to a simple geometric configuration.
The volume of the residual collection was calculated with the following
formulas according to the morphologic configuration of the collection: For
spherical collections, volume was calculated as
, where
r is the average radius of the collection. For rectangular
collections, volume was calculated as h x l x
w, where h is the height of the collection, l is
the length of the collection, and w is the width of the collection.
For pyramidal collections, volume was equal to
, where
h is the height of the collection, l is the length of the
collection, and w is the width of the collection.
The patients were followed up with sonography at 2 weeks for evidence of possible abscess recurrence.
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In Vivo Study
Complex collections with internal solid components such as
multiloculations, fibrinous septa, or fibrinous strands as depicted on
sonography occurred in 18 (60%) of the 30 cases. Simple collections without
internal solid components occurred in the other 12 cases (40%), including one
with fine debris sediments seen on sonograms. The fluid collection could be
completely aspirated (100%) with the conventional needle from all 12 simple
collections (100%) that contained no internal solid components, as shown on
sonography. For these 12 collections, no further aspiration was attempted with
the drainage needle. In case 30 of Table
2, the patient had a simple collection with fine debris sediments;
in this case, the collection together with the debris could be completely
evacuated with the conventional needle.
For all 18 complex collections, the fluid component could not be completely evacuated with the conventional needle. A significant portion of residual collection (range, 14.3-74.1%; median, 44.4%; average, 42.54% ± 16.1% [SD]) remained after aspiration with the conventional needle in all 18 complex collections (100%). Although the proportion of residual fluid appeared to be higher in the six collections consisting of floating fibrinous strands (range, 37.5-74.1%; median, 48.7%; average, 50.7% ± 12.7%) than in those consisting only of combinations of multiloculations and septations (range, 14.3-66%; median, 38.2%; average, 38.5% ± 16.5%), analysis with the Mann-Whitney test did not show a significant difference (p =0.18).
In all 18 of these cases, a significant portion of the residual fluid could always be aspirated with the drainage needle from the residual collection that remained after aspiration with the conventional needle, although not all of the residual fluid was completely evacuated with the drainage needle in all cases. There was a significant difference in the volume of the aspirate obtained with the conventional needle alone and that obtained with both the conventional needle and the drainage needle (p < 0.001) (Table 3). There was also a significant difference in the percentage by volume of the collection aspirated with the conventional needle alone and that with both needles (p < 0.001) (Table 3). Apart from the fine debris sediments in the simple collection of case 30 in Table 2, the solid internal components of the complex collections could not be aspirated with either the conventional needle or the drainage needle.
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All five collections of bile-stained fluid containing no internal solid components were completely aspirated with the conventional needle. Otherwise, there was no definite association between the nature of the fluid and the presence of internal solid components. There was also no definite association between the fluid nature and the completeness of fluid aspiration with the conventional needle. Further intervention with catheter drainage was required for the five patients with posthepatectomy bile collection; the clinical condition of the remaining 24 patients who had postoperative sepsis improved significantly with resolution of sepsis after needle aspiration. Follow-up sonography over the subsequent 2 weeks showed no evidence of abscess recurrence.
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Infected intraperitoneal collection is a common cause of postoperative sepsis after abdominal surgery that can be effectively treated with percutaneous drainage. However, percutaneous drainage of complex abscesses and infected hematomas was reported to be associated with reduced success rates because of the presence of intervening internal solid components within these collections [9, 10]. Such internal solid components are common in intraperitoneal collections.
Except the five bile collections that were devoid of internal solid components and completely removable with needle aspiration, 18 (72%) of the other 25 collections in the present consecutive series of 30 collections contained internal solid components as shown on sonograms. In this study, such complex collections were always associated with incomplete evacuation on needle aspiration. Because only six of the 18 complex collections contained fibrinous strands, the presence of fibrinous strands was not the only cause of incomplete aspiration; the other internal solid components within a complex collection did play a part. Although fibrinous strands appeared to be more efficient in interfering with the aspiration process and to be associated with a greater proportion of residual fluid collection than loculations and septations alone, the difference in proportion of residual fluid was found to be not statistically significant in the six collections consisting of floating fibrinous strands as compared with the other 12 complex collections without floating fibrinous strands.
A number of devices have been designed for effective drainage of body collections; these include a host of drainage catheters with multiple side holes or multiple slits and sheathed needles that consist of a flexible sheath with multiple side holes such as the Yueh centesis needle [11-13]. These devices consist of multiple apertures devised to overcome the obstructive effects of various solid internal components. The drainage needle provides an additional choice to the list of drainage devices.
Compared with the use of drainage catheters in the percutaneous drainage of fluid collections, the use of aspiration needles is advantageous because they cost less and are easier to maneuver. The needle costs only US$10-15 (Global Product Management Office, Cook, personal communication). The metallic needle cannulas are more rigid and more steerable; therefore, they are more effective than catheters or flexible needle sheaths for crossing septations of multiloculated abscesses, obviating additional techniques such as using a guidewire to break septations to facilitate drainage. Although some drainage catheters or sheaths can be strengthened with the intraluminal introduction of a metallic trocar to facilitate crossing septations or locules, such maneuvers need to be performed carefully to avoid damage or perforation of the catheters or sheaths. For the treatment of multiple abscesses, needle aspiration alone made the drainage procedure simpler and more convenient than the placement of multiple catheters. Indwelling drainage catheters, especially when more than one, can be uncomfortable for some patients. Repositioning drainage catheters is often required for multiloculated abscesses.
The ability of the drainage needle to overcome the blocking effects of floating internal solid components during needle aspiration was shown in the in vitro experiment. The results of the in vivo study showed that the effectiveness of needle drainage for complex collections was improved with the use of the drainage needle. The results of the present study indicate that, first, internal solid components within a collection, especially fibrinous strands, tend to prevent complete evacuation of the fluid component of that collection; and, second, the performance of needles is not affected by the nature of the fluid. The performance of the needles is probably also not affected by the volume of the collection, although because of the small difference in volume between 10 and 15 mL, it is difficult to conclude definitely that the performance of the needles is not affected by the volume of the collection. Third, there is a significant difference in the ability of a conventional aspiration needle and the drainage needle in draining fluid collections that consist of internal solid components. Fourth, the drainage needle was highly effective in evacuating such collections in a variety of in vivo situations in the present study. However, the favorable results in the current simple experiment and small clinical series do not necessarily guarantee that the drainage needle would always be effective for all kinds of complex collections; therefore, further studies are advocated.
The main feature of the drainage needle is the design of multiple side holes near the stiff metallic cannula tip. The side holes in this needle do not make the needle less visible under CT; however, the side holes make the needle more visible and easier to recognize on sonography owing to the increase in reflective surface. The distal part of the needle is strong enough for it to be used independently within the collection without the trocar. Although some kind of aspiration needles may consist of a flexible plastic sheath or cannula that consists of multiple side holes that aim to enhance the effectiveness of fluid aspiration, such flexible cannulas or sheaths are not readily steerable and not rigid enough to cross septa or locules. Kinking may occur during such maneuvers. Moreover, reassembling the metallic trocar for repositioning the needle tip may result in perforation of the plastic sheath or cannula. Nevertheless, in this study, the drainage needle has not been shown to be better than such sheathed needles and a comparative clinical study is required.
A limitation of this study is that although the drainage needle has been proven to be highly effective in an in vitro model consisting of gelatin sponge sheets in two kinds of fluid in two volumes, the performance of the needle in other fluid volumes and fluid nature containing membranous materials of other consistencies and sizes is still unknown. It is also necessary to point out that if the collection requires catheter drainage, the drainage needle should not be used for the introduction of a curve-tip guidewire without fluoroscopy because it is possible that the guidewire may protrude from the side hole instead of the end hole and interfere with the Seldinger technique for catheter placement. Otherwise, the use of this needle does not differ from the conventional needle.
Intracavitary administration of fibrinolytic agents such as urokinase has been used as an adjunct to facilitate percutaneous drainage of multilocular abscesses and infected hematomas [14]; however, there are contraindications including coagulopathy, thrombocytopenia, pancreatic collection, history of bleeding or tumor in the central nervous system, hepatic failure, and hypersensitivity to urokinase. In addition, it cannot be used in a pregnant or lactating woman.
In conclusion, this drainage needle consists of features that combine the advantages of a simple aspiration needle and the effective drainage ability of a multi-side-hole drainage catheter. As indicated in the present study, the drainage needle is powerful in fluid evacuation from abdominal collections that are multiloculated and septate and that contain fibrous components.
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